Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Chapter 16The Digestive System

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Topics (1 of 2)IntroductionAn Overview of the Digestive TractThe Oral CavityThe PharynxThe EsophagusThe StomachThe Small Intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Topics (2 of 2)The PancreasThe LiverThe Gall bladderThe Large IntestineDigestion and AbsorptionAging and the Digestive SystemIntegration with Other Systems

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Introduction

Provides the fuel to keep all cells functioning

Provides the building blocks for cell growth and repair

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Introduction

Components– Digestive tract

Muscular tube

– Accessory organsSalivary glands

Gallbladder

Liver

Pancreas

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Introduction

Functions involve 6 related processes– Ingestion– Mechanical processing– Digestion– Secretion– Absorption– Excretion

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Introduction

Ingestion– Food enters digestive tract through the

mouth

Mechanical processing– Physical manipulation of solid foods

Tongue and teeth

Swirling and mixing motions of the digestive tract

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Introduction

Digestion– Chemical breakdown of food for

absorption

Secretion– Release of water, acids, enzymes, and

buffers

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Introduction

Absorption– Movement of substances across

digestive epithelium into interstitial fluid of digestive tract

Excretion– Removal of waste products from body

fluids through defecation

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Introduction

Defensive roles of the digestive tract– Protects surrounding tissues against

corrosive effects of digestive acids and enzymes

– Protects against bacteria using nonspecific defenses

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An Overview ofthe Digestive Tract

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

An Overview of the Digestive Tract

Begins at the oral cavity

Continues through the pharynx, esophagus, stomach, and small and large intestines

Ends at the rectum

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An Overview of the Digestive Tract

Each subdivision– Functions overlap– Each has its own specialization

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An Overview of the Digestive Tract

Histological organization– 4 major layers

Mucosa

Submucosa

Muscularis externa

Serosa

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An Overview of the Digestive Tract

The mucosa– Inner lining of the

digestive tract– Consists of

Mucosal epitheliumMoistened by glandular secretions

Lamina propriaUnderlying layer of loose connective tissue

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An Overview of the Digestive TractThe mucosa– Formed into folds

Folds increase surface area for absorption

Folds permit expansion after a large meal

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An Overview of the Digestive Tract

The mucosa– Features in the

small intestineForm fingerlike projections

Called villi

Further increase the area for absorption

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An Overview of the Digestive Tract

The mucosa– Stratified squamous epithelium

Allows for most severe mechanical stresses

Found in the oral cavity, pharynx, esophagus, and anus

– Simple columnar epitheliumLines the rest of the digestive tract

Contains various types of secretory cells

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An Overview of the Digestive TractThe mucosa– Ducts open onto epithelial surfaces

Carry secretions of glands

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An Overview of the Digestive Tract

The mucosa– Muscularis mucosae

Narrow band of smooth muscle and elastic fibers

Located in most regions of the digestive tract

Move the mucosal folds and villi

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An Overview of the Digestive Tract

The submucosa– Second layer of

loose connective tissue

– Immediately deep to the muscularis mucosae

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An Overview of the Digestive Tract

The submucosa– Contains

Large blood vessels

Lymphatic vessels

Network of nerve fibers

Sensory neurons

Parasympathetic motor neurons

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An Overview of the Digestive Tract

The submucosa– Submucosal plexus

Neural tissue

Controls and coordinates contractions of the smooth muscle layers

Regulates secretion of digestive glands

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An Overview of the Digestive Tract

The muscularis externa– Band of smooth

muscle cellsInner circular layer

Outer longitudinal layer

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An Overview of the Digestive Tract

The muscularis externa– Muscle contractions

Autonomic reflexes

Agitate materials

Propel material along the digestive tract

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An Overview of the Digestive Tract

The muscularis externa– Myenteric plexus

Nerve network

Located between the smooth muscle layers

Controls autonomic reflexes

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An Overview of the Digestive Tract

The muscularis externa– Autonomic control

Parasympathetic stimulationIncreases muscle tone and activity

Sympathetic stimulationPromotes muscle inhibition and relaxation

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An Overview of the Digestive Tract

The serosa– Serous membrane– Covers the muscularis

externa within the peritoneal cavity

– Visceral peritoneum is continuous with the parietal peritoneum

– Parietal peritoneum lines the inner surface of the body wall

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An Overview of the Digestive Tract

The serosa– Mesenteries

Suspend portions of the digestive tract within the peritoneal cavity

Stabilize the positions of attached organs

Prevent entanglement of the intestines

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An Overview of the Digestive Tract

The serosa– Mesenteries

Double sheets of serous membraneComposed of the visceral and parietal peritoneum

Loose connective tissue between epithelial surfaces

Pathway for blood vessels, nerves, and lymphatic vessels

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An Overview of the Digestive Tract

The serosa– Not found in the oral cavity, pharynx,

esophagus, and rectum

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An Overview of the Digestive Tract

Adventitia– Dense network of collagen fibers– Surrounds are the muscularis mucosae

in the absence of serosa– Firmly attaches components of the

digestive system to adjacent structures

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An Overview of the Digestive Tract

The movement of digestive materials– Pacesetter cells

Found in the smooth muscle of the digestive tract

Trigger waves of contractionResults in rhythmic cycles of activity

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An Overview of the Digestive Tract

The movement of digestive materials– Coordinated contractions important for 2

processesPeristalsis

The movement of material along the tract

SegmentationThe mechanical mixing of material

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An Overview of the Digestive Tract

Peristalsis– Waves of muscular contractions of the

muscularis externa– Propels food through the digestive tract

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An Overview of the Digestive Tract

Peristalsis– Circular muscles contract behind

contents– Longitudinal muscles contract

Contraction shortens adjacent segments of the tract

– Wave of contraction of the circular muscles

Forces material in the desired direction

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An Overview of the Digestive Tract

Peristalsis

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An Overview of the Digestive Tract

Segmentation– Movements that churn and fragment

digestive materials– Results in a thorough mixing of contents

with intestinal secretions– Does not propel material in any direction

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The Oral Cavity

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The Oral Cavity

The first part of the digestive tract to receive food

Lined by a mucous membrane of stratified squamous epithelium

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The Oral Cavity

Senses and analyzes materials before swallowing

Mechanically processes material with the tongue and teeth

Lubricates material with mucous and salivary secretions

Begins digestion of carbohydrates and lipids with enzymes

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The Oral Cavity

Also referred to as the buccal cavity– Cheeks form the

lateral wallsAnteriorly

Continuous with the lips or labia

VestibuleSpace between the cheeks or lips and teeth

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The Oral Cavity

Gums or gingivae– Pink ridges that

surround the base of the teeth

– Cover tooth-bearing surfaces of the upper and lower jaws

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The Oral Cavity

Hard and soft palates– Form the roof of the oral cavity

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The Oral Cavity Tongue– Dominates the floor of the oral cavity– Free anterior portion connected to underlying

epitheliumThin fold of mucous membrane

Called the lingual frenulum

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The Oral Cavity Division between the oral cavity and oropharynx– Base of the tongue– Uvula

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The Oral Cavity

The tongue– Manipulates materials inside the mouth– Brings food into the oral cavity

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The Oral Cavity

The tongue– Primary functions

Mechanical processing through compression, abrasion, and distortion

Manipulating to assist in chewing

Preparing materials for swallowing

Performing sensory analysis by touch, temperature, and taste receptors

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The Oral Cavity The tongue– Lies mostly within the oral cavity– Base extends into the oropharynx

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The Oral Cavity The tongue– Lingual tonsils

Prominent lateral swellings at the base of the tongue

Lymphoid nodules that help resist infection

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The Oral Cavity

Salivary glands– 3 pairs– Secrete into the

oral cavityParotid salivary glands

Sublingual salivary glands

Submandibular salivary glands

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The Oral Cavity

Parotid salivary glands– Lie under the skin– Located in the

lateral and posterior surfaces of the mandible

– Parotid ductEmpties into the vestibule at the level of the second molar

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The Oral Cavity

Sublingual salivary glands– Located beneath

the mucus membrane

On the floor of the mouth

– Sublingual ductsNumerous ductsOpen along either side of the lingual frenulum

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The Oral Cavity

Submandibular salivary glands– Located in the floor

of the mouth– Along the inner

surfaces of the mandible

– DuctsOpen into the mouth behind the teethOn either side of the lingual frenulum

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The Oral Cavity

Salivary glands– Produce 1–1.5 liters of saliva per day

99.4% water

Also contains mucins, ions, buffers, waste products, metabolites, and enzymes

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The Oral Cavity

Salivary glands– Mucins

Absorb water

Form mucus

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The Oral Cavity

Salivary glands– Saliva

Produced in large quantities at mealtimes

Lubricates the mouth

Dissolves chemicals that stimulate the taste buds

Reduces friction with food, enabling swallowing

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The Oral Cavity

Salivary glands– Saliva

Flushes and cleans oral surfaces

Contains IgA antibodies and lysozymesControl oral bacteria

Leads to recurring infections

Causes progressive erosion of the teeth and gums

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The Oral Cavity

Salivary secretions– Different kinds produced by different

glandsParotid glands

Secretion rich in salivary amylase

Breaks down starches into smaller molecules

Allows absorption in the digestive tract

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The Oral Cavity

Salivary secretions– Submandibular and sublingual gland

secretionsContain fewer enzymes

Contain more buffers and mucus

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The Oral Cavity

Salivary secretions– During meals

Submandibular glandsProduce 70% of secretions

pH rises from acidic to basic

Secretions controlled by autonomic nervous system

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The Oral Cavity

Teeth– Perform chewing or mastication

Breaks down tough connective tissues in meat

Breaks down plant fibers in vegetables

Helps saturate materials with salivary secretions

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The Oral Cavity Parts of the tooth– Neck

Marks the boundary between the root and the crown

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The Oral Cavity

Parts of the tooth– Enamel

Covers the crownContains a crystalline form of calcium phosphate

Hardest biologically manufactured substance

Requires adequate amounts of calcium, phosphates, and vitamin D3 during childhood

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The Oral Cavity

Parts of the tooth– Dentin

Mineralized matrix similar to that of bone

Does not contain cells

Makes up the bulk of each tooth

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The Oral Cavity

Parts of the tooth– Pulp cavity

Contains cytoplasmic processes cells

Extend into the dentin

Receives blood vessels and nerves through the root canal

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The Oral Cavity

Parts of the tooth– Root

Base of the tooth

Sits within a bony socket

Called an alveolus

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The Oral Cavity

Parts of the tooth– Periodontal

ligamentCollagen fibers

Extends from the dentin of the root to surrounding bone

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The Oral Cavity

Parts of the tooth– Cementum

Layer that covers the dentin of the root

Provides protection and firmly anchors the periodontal ligament

Similar in structure to bone

Softer

Does not undergo remodeling

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The Oral Cavity

Parts of the tooth– Penetration of the gum surface

Epithelial cells form tight attachments to the tooth

Prevent bacterial access to the cementum or the root

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The Oral Cavity

4 types of teeth– Incisors– Cuspids or canines– Bicuspids or premolars– Molars

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The Oral Cavity

Functions of teeth– Incisors

Blade-shaped teeth

Found at the front of the mouth

Used for clipping or cutting

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The Oral Cavity

Functions of teeth– Cuspids

ConicalSharp ridgeline and a pointed tip

Used for tearing or slashing

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The Oral Cavity

Functions of teeth– Bicuspids and

molarsFlattened crowns with prominent ridges

Used for crushing, mashing, and grinding

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The Oral Cavity

Dental succession– 2 sets form during

developmentDeciduous teeth

First to appear

Also referred to as primary teeth, milk teeth, or baby teeth

Full set is 20

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The Oral Cavity

Dental succession– Secondary dentition

Also referred to as permanent dentition

Permits processing of a wider variety of foods

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The Oral Cavity

Dental succession– Periodontal ligaments and roots of

deciduous teeth erode– Deciduous teeth fall out or are pushed

aside– Secondary teeth erupt – Full set of 32 teeth

3 new teeth appear on each side of the upper and lower jaws

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The Oral Cavity

Dental succession– Wisdom teeth

Third molars

Become impacted if eruption is not permittedMay form abscess

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The Pharynx

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The Pharynx

Common passageway– Allows for passage of solid food, liquids,

and air– 3 major subdivisions– Regions composed of stratified

squamous epithelium– Lamina propria

Contains mucous glands and tonsils

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The Pharynx

Pharyngeal muscles– Initiate swallowing process

Cooperate with muscles of the oral cavity and esophagus

– Force food into the esophagus

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The Esophagus

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The Esophagus

Muscular tube

25 cm long

2 cm in diameter

Conveys solid food and liquids to the stomach

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The Esophagus

Begins at the pharynx

Runs posterior to the trachea

Passes through the mediastinum

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The Esophagus

Enters the peritoneal cavity– Through the esophageal hiatus

Opening in the diaphragm

Empties into the stomach

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The Esophagus

Lined with stratified squamous epithelium– Resists abrasion– Resists hot or cold temperatures– Resists chemical attack

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The Esophagus

Epithelial surface lubricated by mucous gland secretions– Prevent materials from sticking to the

esophagus during swallowing

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The Esophagus

Muscularis externa– Upper third contains skeletal muscle– Middle third contains skeletal and

smooth muscle– Lower third contains smooth muscle

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The Esophagus

Esophageal sphincter– Circular muscle– Located in the superior and inferior ends

Inferior sphincter normally in active contraction

Prevents backflow of material from the stomach

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The Esophagus

Swallowing– Deglutition– Complex process– Can be initiated voluntarily

Proceeds automatically

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The Esophagus

Swallowing– Before swallowing

Food must have the proper consistency and texture

Tongue compacts debris into a small massReferred to as a bolus

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The Esophagus

Process of swallowing– Oral phase– Pharyngeal phase– Esophageal phase

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The Esophagus Oral phase of swallowing– Begins with the

compression of the bolus against the hard palate

– Tongue retracts– Bolus forced into the

pharynxElevates the soft palate to prevent entrance into the nasopharynx

– Only phase that can be consciously controlled

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The Esophagus

Pharyngeal phase of swallowing– Bolus contacts

sensory receptorsLocated around the pharynx and pharyngeal wall

Initiates the involuntary swallowing reflex

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The Esophagus

Swallowing reflex– Larynx elevates– Epiglottis folds to protect the glottis

Directs food past the closed glottis

– Pharyngeal muscles contract– Bolus forced through the esophageal

entranceGuarded by the upper esophageal sphincter

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The Esophagus

Esophageal phase of swallowing– Begins when the bolus enters

the esophagus– Peristaltic contractions push

the bolus toward the stomach– Bolus triggers the opening of

the lower esophageal sphincter

– Bolus enters the stomach

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The Esophagus

Swallowing– Typically takes about 9 seconds– Fluids move faster

Do not require peristaltic contractions

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The Stomach

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The Stomach

Located in the left upper quadrant of the abdominopelvic cavity

Receives food from the esophagus

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The Stomach

4 primary functions– Temporary storage of ingested food– Mechanical breakdown of ingested food– Breakdown of chemical bonds in foods

Through actions of acids and enzymes

– Production of intrinsic factorNecessary for the absorption of B12

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The Stomach

Chyme– Mixture of ingested material and

secretions from stomach glands– Viscous– Highly acidic

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The Stomach

Muscular, J-shaped organ

4 main regions– Cardia– Fundus– Body– Pylorus

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The Stomach Cardia– Smallest part of the stomach– Connects with the esophagus

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The Stomach Fundus– Superior bulge of the stomach– Extends above the cardia

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The Stomach Body– Large area– Located between the fundus and the

curve of the J

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The Stomach Pylorus– Distal part of the J– Connects the stomach with the small

intestine

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The Stomach

Pyloric sphincter– Regulates flow of chyme between the

stomach and small intestine

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The Stomach

Rugae– Prominent ridges and

folds of mucosa– Visible when the stomach

is emptyStomach resembles a muscular tube with a narrow lumen

– Flatten out as the stomach expands

Stomach can hold 1–1.5 liters of material when fully expanded

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Muscularis externa– 3 layers

Extra layer adds strength and assists in movement necessary to form chymeLongitudinal layerCircular layerInner oblique layer

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Visceral peritoneum– Covers the outer surface of the stomach– Is continuous with a pair of mesenteries

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Mesenteries– Greater omentum

Extends below the greater curvatureForms an enormous pouch

Hangs over and protects the abdominal viscera

– Lesser omentumExtends from the lesser curvature to the liver

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

The gastric wall– Lined by simple columnar epithelium

Dominated by mucous cellsProduces an alkaline mucus

Protects cells from acids, enzymes, and abrasive materials

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach The gastric wall– Gastric pits

Shallow depressions

Open onto the gastric surface

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach The gastric wall– Mucous cells located at the base, or neck, or

the gastric pitsActively divide

Replace superficial cells of the mucous epitheliumCells are shed into the chyme

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

The gastric wall– Fundus

Gastric pits communicate with gastric glandsGlands extend deep into lamina propria

Glands secrete 1.5 liters of gastric juice per day

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach The gastric wall– Gastric juice

Components produced by parietal cells and chief cells

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

The gastric wall– Pylorus

Gastric glands also contain endocrine cells

These walls regulate gastric activity

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach Parietal cells– Secrete intrinsic factor

Facilitates absorption of B12 across intestinal lining

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Parietal cells– Secrete hydrochloric acid

Lowers the pH of gastric juicepH of 1.5–2

Kills microorganisms

Breaks down plant cell walls

Breaks down connective tissues in meat

Activates enzyme secretions of chief cells

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach Chief cells– Secrete pepsinogen into the stomach lining

Protein that converts to pepsin on contact with hydrochloric acid

A proteolytic enzyme

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Chief cells– In newborns

Produce reninCoagulates milk

Slows passage through the stomach

Allows more time for digestion

Produce gastric lipaseInitiates the digestion of milk fats

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

The regulation of gastric activity– Central nervous system controls acid

and enzyme productionRegulated by

Reflexes within the walls of the digestive tract

Hormones of the digestive tract

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

The regulation of gastric activity– 3 overlapping phases

Named according to the location of the control center

Cephalic phase

Gastric phase

Intestinal phase

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Cephalic phase of gastric regulation– Initiated by the smell,

sight, taste, or thought of food

– Directed by the CNS– Prepares the

stomach to receive food

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Cephalic phase of gastric regulation– Parasympathetic fibers innervate

mucous cells, parietal cells, chief cells, and endocrine cells

Fibers found in the submucosal plexus

Controlled by the vagus nerves

– Phase last only a few minutes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Gastric phase of gastric regulation– Begins with the

arrival of food in the stomach

– StimulatesStretch receptors in the stomach wallChemoreceptors in the mucosa

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Gastric phase of gastric regulation– Receptor stimulation triggers local

reflexes Reflexes controlled by submucosal and myenteric plexuses

Myenteric plexus stimulates mixing waves in stomach wall

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Gastric phase of gastric regulation– Submucosal plexus

Stimulates parietal cells and chief cells

Stimulates endocrine cellsRelease gastrin into circulatory system

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Gastric phase of gastric regulation– Gastrin

Stimulates parietal and chief cellsAccelerates secretory activities

Effect on parietal cells most pronounced

Drops the pH of gastric juice

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Gastric phase of gastric regulation– Phase continues for several hours– Gastrin stimulates stomach contractions

Swirl and churn gastric contents

Mix materials to form chyme

Contractions move chyme through the stomach

Pylorus contracts, pushing chyme through pyloric sphincter

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Begins when chyme

starts to enter the small intestine

– Regulatory controls are primarily inhibitory

Control the rate of gastric emptyingEnsure efficiency of small intestine

Secretory, digestive, and absorptive functions

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Movement of chyme

Reduces stimulation of stretch receptors in the stomach

Increases stimulation of stretch receptors in the small intestine

Produces enterogastric reflex

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Enterogastric reflex

Inhibits neural stimulation Reduces gastrin production

Reduces gastric motility

Reduces further movement of chyme

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Chyme enters small intestine

Stimulates the release of intestinal hormones

Secretin

Cholecystokinin (CCK)

Gastric inhibitory peptide (GIP)

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Stimulation of inhibitory reflexes that

depress gastric activityOccurs when the proximal portion of the small intestine

Becomes too full

Becomes too acidic

Is excessively irritated by chyme

Is filled with partially digested proteins, carbohydrates, or fats

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Rate of chyme movement

Highest with a distended stomach and little protein

Alcohol and caffeine stimulate gastric secretion and motility

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Digestion in the stomach– Pepsin performs the preliminary

digestion of proteins– Salivary amylase continues carbohydrate

digestionRemains active until pH falls below 4.5

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Digestion in the stomach– Pepsin

Becomes more active as contents become fluid and pH drops to 2.0

Begins protein disassemblyNot completed in the stomach

Breaks complex proteins into small peptide and polypeptide chains

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Stomach

Intestinal phase of gastric regulation– Nutrients not absorbed in stomach

Epithelial cells covered by alkaline mucusNot directly exposed to chyme

Epithelial cells lack specialized transport mechanisms

Gastric lining is impermeable to water

Digestion is incomplete when chyme exits the stomach

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Responsible for 90% of nutrient absorption

Approximately 20 feet long

Diameter of 4 cm at the stomach– Reduces to 2.5 cm at the large intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Contains 3 segments– Duodenum– Jejunum– Ileum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Duodenum– 25 cm long– Closest

segment to the stomach

– Curves in a C-shape

Encloses the pancreas

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Duodenum– Receives chyme from the stomach– Receives digestive secretions from the

pancreas and liver– Lies outside the peritoneal cavity

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Jejunum– Connects to the

duodenum at a sharp bend

– 8 feet long– Supported by a sheet

of mesentery– Responsible for the

bulk of chemical digestion and nutrient absorption

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Ileum– Averages 12

feet in length– Ends at the

ileocecal valveSphincter

Controls material flow from the ileum to the cecum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Fills much of the peritoneal cavity

Stabilized by mesentery attached to dorsal body wall

Connective tissue in mesentery contains blood vessels, lymphatic vessels, and nerves

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Plicae

Also referred to as plicae circulares

Series of transverse folds in the intestinal wall

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Villi

Fingerlike projections on the intestinal liningCovered by simple columnar epithelium with microvilli

Resemble the bristles on a brushReferred to as a brush border

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Epithelium contains several plicae– Each plica contains many villi– Each villus covered by epithelium

blanketed in microvilli– Absorptive area roughly 2,200 ft²

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Villus

Contains a capillary network

Transports respiratory gases

Transports absorbed nutrients to hepatic portal circulation

Contains nerve endings

Contains a lymphatic capillary

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Lymphatic capillary

Called a lacteal

Transports materials that cannot enter blood capillaries

Example: protein-lipid packages of absorbed fatty acids

Called a chylomicron

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Intestinal glands

Entrances located at the base of the villi

Contain stem cells that divide continuously

Replenish intestinal epithelium

Contain endocrine cells that produce intestinal hormones

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

The intestinal wall– Duodenum

Contains duodenal glandsSubmucosal glands

Secrete alkaline mucus

Buffers the acids in chyme

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal movements– Chyme enters the small intestine– Segmentation contractions mix chyme,

mucous secretions, and enzymes– Weak peristaltic contractions slowly

move material

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal movements– Peristaltic contractions

Allow increased time for digestion and absorption

Local reflexes not under CNS controlLimited to a few centimeters from the stimulus site

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal movements– Stomach distention initiates the

gastroenteric reflexAccelerates glandular secretion and peristalsis

– Increased peristalsis moves material through the small intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal movements– Food entering the stomach triggers

gastrin release– Gastrin responsible for the gastroileal

reflexRelaxes the ileocecal valve

Allows food to enter the large intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal secretions– Intestinal juice

Arrives through osmosis

Secreted by intestinal glandsStimulated by touch and stretch receptors in the intestinal walls

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal secretions– Intestinal juice

Moistens intestinal contents

Helps buffer acids

Keeps digestive enzymes and products of digestion in solution

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal secretions– Regulated by hormonal and CNS

controls– Focused in the duodenum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Functions of intestinal secretions– Acid content of chyme must be

neutralized– Appropriate enzymes must be added

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal secretions– Duodenal glands

Protect the duodenal epithelium from gastric acids and enzymes

Increase secretions stimulated byLocal reflexes

Parasympathetic stimulation through the vagus nerve

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal secretions– Parasympathetic stimulation

Duodenal glands begin secreting during cephalic stage of gastric secretion

Before chyme reaches the pyloric sphincter

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal secretions– Sympathetic stimulation

Inhibits the activation of the duodenal glands

Duodenal lining unprepared for the acid chyme

Stress may result in duodenal ulcers

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Various peptide hormones produced by

duodenal endocrine cells– Coordinate the stomach, duodenum,

pancreas, and liver

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Gastrin– Secretin– Cholecystokinin (CCK)– Gastric inhibitory peptide (GIP)

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Gastrin

Secreted by duodenal cellsIn response to large quantities of incompletely digested proteins

Increases stomach motility

Stimulates production of acids and enzymes

Also secreted in the distal portion of the stomach

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Secretin

Released as pH of the duodenum fallsOccurs when acidic chyme arrives from the stomach

Increases the secretion of bile and buffersFrom the liver and pancreas

High concentration reduces gastric motility and secretion

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Cholecystokinin (CCK)

Secreted when chyme arrives in the duodenum

Especially with the presence of lipids and partially digested proteins

Also targets the pancreas and gall bladder

High concentration reduces gastric motility and secretion

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Cholecystokinin

PancreasAccelerates the production and secretion of all types of digestive enzymes

GallbladderCauses the ejection of bile into the duodenum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones– Gastric inhibitory peptide (GIP)

Released by the presence of fats and carbohydrates in the small intestine

Inhibits gastric activity

Causes insulin release from the pancreatic islets

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Intestinal hormones

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Digestion in the small intestine– Location of most of the important

components of digestionFinal products of digestion are absorbed

Simple sugars, fatty acids, and amino acids

Most of the water content is absorbed

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Small Intestine

Digestion in the small intestine– Enzymes and buffers for digestion

Only a few produced in the small intestine

Most are contributed by the liver and pancreas

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Lies behind the stomach

Extends from the duodenum toward the spleen

Roughly 6 inches long

Located retroperitoneal

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Surface– Pinkish-gray organ– Lumpy texture– Tissue is soft and

easily torn– Only anterior

surface covered by peritoneum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Histological organization– Pancreatic islets

Endocrine cells

Secrete insulin and glucagon

1% of the cellular population of the pancreas

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas Histological organization– Exocrine cells and ducts make up most

of the pancreasProduce pancreatic juice

Mixture of digestive enzymes and buffers

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas Histological organization– Exocrine ducts

Branch throughout the pancreas

End at the pancreatic aciniSaclike pouches

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Histological organization– Acinar cells

Located in the pancreatic acini

Secrete enzymes and buffersMix with enzymes and buffers produced by epithelial cells in the ducts

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Histological organization– Pancreatic duct

Collects secretions from all ducts in the pancreas

Carries secretions to the duodenum

Penetrates duodenal wall with the common bile duct

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

Histological organization– Pancreatic enzymes

Responsible for most of the digestion in the small intestine

Classified according to intended targetsCarbohydrases digest sugars and starches

Lipases break down lipids

Nucleases break down nucleic acids

Proteases break proteins apart

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Pancreas

The control of pancreatic secretion– 1000 ml of pancreatic juice produced

daily– Secretion controlled mainly by duodenal

hormonesSecretin released in duodenum

Triggers pancreas to secrete watery, alkaline fluid

pH between 7.5–8.8

Contains buffers, primarily sodium bicarbonate

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Largest visceral organ

Firm, reddish-brown

Roughly 2.5% of total body weight

Lies in the right hypochondriac and epigastric regions

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Anatomy of the liver– Wrapped in a tough fibrous capsule– Covered by a layer of visceral peritoneum– Divided into 4 unequal lobes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Anatomy of the liver– Left and right lobes

Larger

– Caudate lobe– Quadrate lobe

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Anatomy of the liver– Falciform ligament

Tough connective tissue fold

Marks the division between the left and right lobes

Thickened posterior margin Referred to as the round ligament

Fibrous remnant of the umbilical vein

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Anatomy of the liver– Gallbladder

Located in a recess under the right lobe

Muscular sac

Stores and concentrates bile

Excretes bile into the small intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Histological organization of the liver– Lobes divided by connective tissue

Tissue forms 100,000 liver lobulesBasic functional unit of the liver

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Liver lobules

Contain hepatocytesLiver cells

Arranged into irregular plates

Resemble the spokes of a wheel

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Plates

Only 1 cell thick

Covered with microvilli where exposed

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Sinusoids

Specialized and highly permeable capillaries

Form passageways between adjacent plates

Empty into the central vein

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Kupffer cells

Phagocytic cells

Located in the sinusoidal lining

Part of the monocyte-macrophage system

Engulf pathogens, cell debris, and damaged blood cells

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Blood flow

Enters sinusoids From branches of the hepatic portal vein and hepatic artery

Forms the hepatic triad

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Histological organization of the liver– Blood flow

Hepatic triadPortal area

Includes a small branch of the bile duct, the hepatic portal vein, and the hepatic artery

Located at the 6 corners of each lobule

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Blood flow

Blood continues through the sinusoids

Hepatocytes absorb solutes from the plasmaSecrete plasma proteins

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Blood flow

Blood leaves the sinusoids

Enters the central vein of the lobule

Central veins of each lobule mergeForm the hepatic veins

Empty into the inferior vena cava

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Hepatocytes

Secrete bileReleased into bile canaliculi

Network of narrow channels

Located between adjacent liver cells

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Histological organization of the liver– Bile canaliculi

Extend outward from the central vein

Carry bile to increasingly larger bile ductsBile eventually leaves through the common hepatic duct

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Histological organization of the liver– Common hepatic duct

Flows into the common bile ductEmpties into the duodenum

Flows into the cystic ductLeads to the gallbladder

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Liver functions– 3 general roles

Metabolic regulation

Hematological regulation

Bile production

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Metabolic regulation– Primary organ that regulates the

composition of circulating blood– Exposed to all blood that leaves

absorptive areas of the digestive tractBefore blood reaches general circulation

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Metabolic regulation– Hepatocytes

Extract absorbed nutrients or toxins from the blood

Monitor and adjust circulating levels of organic nutrients

Remove and store excess

Correct deficiencies

Mobilize reserves or synthesize compounds

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Hematological regulation– Largest blood reservoir in the body– Receives 25% of cardiac output– Kupffer cells remove aged or damaged

red blood cellsAlso remove debris and pathogens

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver Hematological regulation– Kupffer cells

Antigen-presenting cells

Can stimulate an immune response

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

Hematological regulation– Hepatocytes

Synthesize plasma proteinsDetermine the osmotic concentration of blood

Transport nutrients

Make up the clotting and complement systems

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

The production and role of bile– Synthesized in the liver– Excreted into the lumen of the duodenum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

The production and role of bile– Consists of

Water

Ions

Bilirubin

Cholesterol

Bile salts

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

The production and role of bile– Bile salts

Assortment of lipids

Synthesized from cholesterol

Required for the normal digestion and absorption of fats

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

The production and role of bile– Dietary lipids are not water soluble– Mechanical processing in the stomach

produces large droplets– Pancreatic lipase only interacts with the

surfaceNot lipid soluble

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

The production and role of bile– Lipids

The larger the droplet, the more lipids present

Remain isolated and protected from digestive enzymes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Liver

The production and role of bile– Bile salts

Break lipid droplets apartProcess called emulsification

Creates tiny droplets

Increases surface area for enzyme attack

Superficial coating of bile salts

Facilitates interaction with enzymes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Gallbladder

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Gallbladder

Hollow, muscular, pear-shaped organ

Stores and concentrates bile prior to excretion

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The GallbladderCystic duct– Extends from the gallbladder– Joins with the common hepatic duct

Forms the common bile duct

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The GallbladderCommon bile duct– Joins the pancreatic duct– Enters the duodenum at the duodenal papilla

Entrance surrounded by the hepatopancreatic sphincter

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Gallbladder

Bile storage– Bile secreted continuously

Approximately 1 liter per day

– Released into duodenum only when stimulated by CCK

– Hepatopancreatic sphincter remains closed without CCK

CCK forces bile to enter the cystic duct

CCK stored in the gallbladder

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Gallbladder

Bile release– Chyme enters duodenum– CCK released

Secretion increases with the fat content of chyme

– Hepatopancreatic sphincter relaxes– Wall of gallbladder stimulated to contract– Bile released

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Gallbladder

Bile modification– Gallbladder holds 40–70 ml of bile when

full– Composition of bile changes while inside

the gallbladderWater absorbed

Increased concentration of bile salts and other components

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Gallbladder

Gallstones– Precipitation of bile salts

Results when bile salts become too concentrated

– Cause a variety of clinical problems

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Horseshoe-shaped

Begins at the end of the ileum

Ends at the anus

Lies below the stomach and liver

Frames the small intestine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Main functions– Reabsorption of water and compaction of

intestinal contents into feces– Absorption of important vitamins freed by

bacterial action– Storage of fecal material prior to

defecation

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Also referred to as the large bowel

Approximately 5 feet long

Width of 3 inches

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

3 divisions– Cecum

Pouchlike

– ColonLargest portion

– RectumFinal 6 inches

End of the digestive tract

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The cecum– Expanded pouch– Receives material

from the ileumEntrance guarded by the ileocecal valve

– Begins compaction

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The cecum– Appendix

Also referred to as the vermiform appendix

Slender and hollow

Attaches to the posterior medial side of the cecum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The cecum– Appendix

Approximately 3.5 inches long

Shape is variable

Lymphoid nodules dominate the walls

Functions primarily as a lymphatic organ

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The colon– Larger diameter

and thinner wall than the small intestine

– HaustraExternal pouches

Permit distention and elongation

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The colon– Taeniae coli

3 longitudinal bands of smooth muscle

Run along the outer surface of the colon

Just beneath the serosa

Muscle tone creates the haustra

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The colon– Divided into 4

segmentsAscending colon

Transverse colon

Descending colon

Sigmoid colon

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Ascending colon– Begins at the ileocecal valve– Ascends along the right side of the

peritoneal cavity– Reaches the inferior margin of the liver– Turns horizontally

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Transverse colon– Continues toward the left side of the

body– Passes below the stomach– Follows the curve of the body wall– Turns inferiorly near the spleen

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Descending colon– Continues along

the left side of the body

– Curves to form the sigmoid

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Sigmoid colon– S-shaped section– Empties into the

rectum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The rectum– Forms the end of the digestive tract– Expanded organ for the temporary

storage of feces– Last portion called the anal canal

Contains longitudinal foldsCalled anal columns

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The rectum– Anal columns

Distal margins joined by transverse folds

Transverse folds mark the boundary between columnar epithelium of the rectum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The rectum– Epidermis becomes keratinized

Occurs close to the anus

Identical to the epidermis on the skin surface

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

The functions of the large intestine– Absorption– Preparation of the fecal material for

elimination

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Absorption in the large intestine– Reabsorption of water

1500 ml of material enter daily

200 ml of feces ejected

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Absorption in the large intestine– Composition of feces

75% water

5% bacteria

Remaining contentsIndigestible materials

Inorganic materials

Remains of epithelial cells

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Absorption in the large intestine– Other absorbed substances

Bile salts and vitamins

Organic waste compoundsExample: bilirubin

Toxins generated by bacterial actions

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Bile salts– Most bile salts that remain in the cecum

are reabsorbed– Transported to the liver for secretion in

bile

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Vitamins– Organic molecules– Related to lipids and carbohydrates– Essential for many metabolic reactions

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Vitamins– Enzymes require binding of an additional

molecule before binding to substratesReferred to as a cofactor

CoenzymesNonprotein molecules that function as cofactors

Many vitamins are coenzymes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Vitamins– Bacteria in colon generate 3 vitamins

Vitamin K

Biotin

Vitamin B3

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Vitamins– Vitamin K

Fat-soluble

Needed in the liverAllows the synthesis of 4 clotting factors

Includes prothrombin

Half of daily requirement produced by intestinal bacteria

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Vitamins– Biotin

Water-soluble

Important in glucose metabolism

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Vitamins– Vitamin B3

Pantothenic acid

Water-soluble

Required to manufacture steroid hormones and some neurotransmitters

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Organic wastes– Bacteria convert bilirubin into other

productsSome absorbed in bloodstream

Excreted in the urineProduce the yellow color

Others remain in the colonFurther modified after exposure to oxygen

Produce pigments that give feces its color

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Toxins– Bacterial action breaks down peptides,

generatingAmmonia

Nitrogen-containing compounds

Hydrogen sulfide

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Toxins– Hydrogen sulfide and nitrogen-containing

compoundsResponsible for odor in feces

– Ammonia and other toxinsAbsorbed into hepatic portal system

Removed by the liver for excretion in urine

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Absorption in the large intestine– Indigestible carbohydrates

Not altered by intestinal enzymes

Arrive in the colon intact

Provide nutrient source for resident bacteria

Metabolic activities responsible for intestinal gas

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Movements of the large intestine– Caused by the gastroileal and

gastroenteric reflexesMovement through the cecum to the transverse colon

Very slow

Takes hours to allow for reabsorption of water

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Movements of the large intestine– From the transverse colon through the

rest of the large intestineMass movements

Powerful peristaltic contractions

Occur a few times per day

Stimulated by distention of the stomach and duodenum

Force material into the rectum for defecation

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Rectum remains empty– Powerful peristalsis forces material out of

the sigmoid colon– Rectal wall becomes distended– Defecation reflex triggered

Involves 2 positive feedback loops

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Shorter positive feedback loop

Stretch receptors in rectal wall activated

Receptors stimulate series of increased local peristaltic contractions

Confined to the sigmoid colon and rectum

Contractions move feces toward the anusIncrease the distention of the rectum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Longer positive feedback loop

Stretch receptors in rectal wall activated

Stimulate parasympathetic motor neuronsLocated in the sacral spinal cord

Stimulate increased mass movements in descending and sigmoid colons

Push feces toward the rectumFurther increases distention

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Passage of feces through the anal canal

Requires relaxation of the internal anal sphincter

External anal sphincter automatically closes

Must be opened through voluntary control

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Voluntary control

If not receivedPeristaltic contractions cease

Additional rectal expansion triggers the defecation reflex again

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Other consciously directed activities

Tensing of the abdominal muscles

Exhaling while closing the glottis

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

The Large Intestine

Defecation– Responses of consciously directed

activitiesElevates intra-abdominal pressure

Helps force material out of the rectum

Forces blood into veins in the anal canalCauses them to stretch

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Components broken down differently– Large organic molecules

Broken down before absorption

– Water, electrolytes, and vitaminsAbsorbed before processing

May require special transport mechanisms

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

The processing and absorption of nutrients– Digestive system breaks down physical

structure– Disassembles component molecules into

smaller fragmentsProduces small organic molecules

Can be released into the bloodstream

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

The processing and absorption of nutrients– Small organic molecules

Absorbed by cells

Used to generate ATP; synthesize carbohydrates, proteins, and lipids

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

The processing and absorption of nutrients– Foods

Complex chains of simpler moleculesCarbohydrates composed of simple sugars

Proteins composed of amino acids

Lipids are fatty acids

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

The processing and absorption of nutrients– Hydrolysis

Component molecule bonds broken by digestive enzymes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

The processing and absorption of nutrients– Digestive enzymes have specific targets

Carbohydrases break up sugars

Lipases separate fatty acids from glycerides

Proteases break amino acid bonds

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Carbohydrate digestion and absorption– Begins in the mouth

Salivary amylaseBreaks down complex carbohydrates

Produces a mixture of disaccharides and trisaccharides

Continues to digest starches and glycogen

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Carbohydrate digestion and absorption– Pancreatic amylase

Breaks down remaining complex carbohydrates

Occurs in the duodenum

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Carbohydrate digestion and absorption– Disaccharides and trisaccharides

Fragmented by brush border enzymesFound on the surfaces of intestinal microvilli

Produce simple sugars

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Carbohydrate digestion and absorption– Monosaccharides

Absorbed by intestinal epithelium

Require carrier-mediated transport mechanisms

Facilitated diffusion or cotransport

For example, glucose uptake requires cotransport with sodium ions

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Carbohydrate digestion and absorption– Simple sugars in intestinal cells

Diffuse through the cytoplasm

Cross the basement membrane through facilitated diffusion

Enter interstitial fluid

Delivered to the hepatic portal vein and liver

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Triglycerides

3 fatty acids connected to a glycerol molecule

Unaffected by conditions in the stomach

Form large lipid droplets

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Bile salts in duodenum

Emulsify large lipid drops into tiny droplets

Can be attacked by pancreatic lipase

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Pancreatic lipase

Enzyme that breaks triglycerides apart

Creates a mixture of fatty acids and monoglycerides

Mix with bile salts

Form micellesLipid-bile salt complex

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Micelles

Contact the intestinal epithelium

Triglyceride products diffuse across the cell membrane

Enter the cytoplasm

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Intestinal cells

Use the fatty acids and monoglycerides

Manufacture new triglyceridesCoated with proteins

Creates a soluble complex

Referred to as a chylomicron

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Chylomicrons (1 of 2)

Secreted by exocytosis into interstitial fluids

Pass through large gaps between adjacent endothelial cells

Enter intestinal lacteals

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Lipid digestion and absorption– Chylomicrons (2 of 2)

Proceed along lymphatic vessels

Travel through the thoracic duct

Enter the bloodstream at the left subclavian vein

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Protein digestion and absorption– Complex structure– Digestion complex and time-consuming

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Protein digestion and absorption– Structure of food disrupted

Proteolytic enzymes attack individual protein molecules

Involves mechanical processing through mastication

Chemical processing with hydrochloric acid

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Protein digestion and absorption– Acidic contents of the stomach

Provides the proper environment for pepsinProteolytic enzyme

Secreted by chief cells of the stomach

Reduce large proteins into polypeptide segments

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Protein digestion and absorption– Pancreatic proteolytic enzymes

Begin when chyme enters the duodenum

Trypsin, chymotrypsin, and carboxypeptidase

Break peptide bonds in different amino acids

Complete disassembly of polypeptide fragments

Create short peptide chains and amino acids

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Protein digestion and absorption– Peptidases

Enzymes on the surface of the intestinal microvilli

Complete the breakdown of peptide chains into amino acids

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Protein digestion and absorption– Amino acids absorbed into intestinal

epithelial cellsRequires facilitated diffusion and cotransport

– Carrier proteins release absorbed amino acids into interstitial fluid

– Most diffuse into intestinal capillaries

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Water and electrolyte absorption– Water conservation

Roughly 9000 ml of water enter the digestive tract daily

150 ml lost through fecal wastes

Occurs passively, following osmotic gradients

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Water and electrolyte absorption– Dissolved nutrients and ions

Continually absorbed by intestinal epithelial cells

Gradually lower solute concentration of intestinal contents

Forces water to move into surrounding tissues

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

Water and electrolyte absorption– Calcium absorption

Occurs under hormonal control

Requires the presence of parathyroid hormone and calcitrol

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

The absorption of vitamins– Essential organic compounds– Required in very small quantities– 2 major groups

Fat-soluble vitamins

Water-soluble vitamins

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

4 fat-soluble vitamins– A, D, E, and K– Enter the duodenum in fat droplets

Mixed with dietary lipids

– Remain associated with lipids with micelle formation

– Absorbed from micelles with the products of lipid digestion

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Digestion and Absorption

9 water-soluble vitamins– B vitamins common in milk and meats

B12 not easily absorbed by digestive epithelium

Must bind with intrinsic factor first

– Vitamin C found in citrus

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

Digestion and absorption remain essentially normal

Changes in the digestive system parallel changes in other systems

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

The division rate of epithelial stem cells declines– Digestive epithelium becomes more

susceptible to damageAbrasion, acids, or enzymes

Peptic ulcers more likely

– Stratified epithelium becomes thinner and more fragile

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

Smooth muscle tone decreases– General motility decreases– Peristaltic contractions are weaker

Slows intestinal movement and promotes constipation

– Sagging and inflammation of the haustra– Weakened muscular sphincters lead to

reflux

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

The effects of cumulative damage become apparent– Gradual loss of teeth

Dental caries or cavities

Gingivitis or inflammation of the gums

– Chronic exposure to toxins and chemicals

Leads to liver diseases

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

Cancer rates increase– Most common in organs with stem cell

division to maintain epithelium

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Aging and the Digestive System

Changes in other systems have direct or indirect effects on the digestive system– Reduction in bone mass and calcium

content in the skeletonLeads to erosion of the tooth sockets

– Decline in smell and taste sensitivityLeads to dietary changes

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Integration with Other Systems

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Integration with Other Systems

Bledsoe et al., Anatomy & Physiology for Emergency Care, 2nd Ed.© 2008 by Pearson Education, Inc. Upper Saddle River, NJ

Summary

Identify the organs of the digestive system and describe their functionsDescribe the histology of the digestive system componentsDescribe the process of digestion and how the parts of the digestive tract interactDescribe the functions of the accessory organs of digestionUnderstand how materials are digested and absorbed