Chapter 24: system - deanza.edu DigestSys1.pdf · The human digestive system consists of:

Welcome to Bio40C

Dr. Ann Reisenauer“Dr. R”

Bio40C – Human A&P Class schedule Text: Principles of Anatomy and Physiology, 12th edition My faculty website

http://www.deanza.edu/faculty/reisenauerann/ Lecture outlines, lab assignments, presentations, extra credit

How to contact me: Email: [email protected] Office hours: TuTh 12-12:30 pm in SC2106 or by appt

Copyright 2009, John Wiley &Sons, Inc.

Chapter 24:The Digestive System


Overview of the digestivesystem

Digestive organs & accessory organsLayers of the GI tract

Upper GI tract


2 groups of organs composethe digestive system

The human digestivesystem consists of: A digestive tube–the

alimentary canal or GItract

Accessory organs thatsecrete digestiveenzymes


2 groups of organs composethe digestive system

Alimentary canal orGastrointestinal (GI) tract mouth, most of pharynx,

esophagus, stomach, smallintestine, and large intestine

Accessory digestive organs teeth, tongue, salivary

glands, liver, gallbladder, andpancreas


Digestion includes 6 basicprocesses1. Ingestion2. Secretion of water, acid, buffers, and

enzymes into lumen3. Mixing and propulsion4. Digestion

Mechanical digestion – churns food Chemical digestion – breaks it down

5. Absorption of nutrients into blood or lymph6. Defecation – elimination of feces


Layers of the GI TractCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lumen

veinartery

Mucosa

Submucosa

Muscularis

Serosa

lymphvessel

nervesupply

Wall of GI tractfrom loweresophagus toanal canal hasthe same 4basic layers


Layers of the GI Tract Wall Mucosa:

Innermost layer of cells produces

mucus that protects thelining

digestive enzymes

Submucosa: layer of loose connective

tissue that contains bloodvessels, lymphaticvessels and nerves.


Layers of the GI Tract Wall

Muscularis: made of 2 layers of smooth

muscle that move food alongthe GI tract

inner – circular outer – longitudinal

Serosa: Outer lining that is part of the

peritoneum muscularis

serosa


Mixing and propulsion: peristalsis vs segmentation

Peristalsis Coordinated waves

of contractions of thecircular andlongitudinal layers ofthe muscularis

Push bolus forward Segmental

contractions Mixing movements


Neural regulation of theGI tract

Enteric nervous system (ENS) Intrinsic set of nerves - “brain of

gut” Neurons extend from esophagus to

anus Neurons of ENS are arranged in 2

plexuses Myenteric plexus – located between

smooth muscle layers of themuscularis

Controls GI tract motility Submucosal plexus

controls secretions


ENS regulation of the GI tract Motor neurons supply the

longitudinal and circularsmooth muscles of themuscularis

Sensory neurons supplythe mucosal epithelium

Functions Chemoreceptors – activated

by chemicals in food Stretch receptors – activated

when food distends the wallof GI tract


ANS regulation of the GI tractAutonomic nervous system

regulates the ENS Vagus (X) nerves supply

parasympathetic fibers to mostof GI tract Increase GI secretion and

motility by stimulating the ENS Sympathetic nerves decrease

GI secretions and motility byinhibiting the ENS Emotions (anger, anxiety) slow

digestion because theystimulate the sympatheticnerves that supply the GI tract


Both the enteric nervous systemand ANS regulate the GI tract


Peritoneum Largest serous membrane

of the body Divided into

Parietal peritoneum – lineswall of cavity

Visceral peritoneum – coverssome organs and is theirserosa

Space between is peritonealcavity


Peritoneal Folds Peritoneal folds weave

between the viscera andbind the organs togetherand to walls of abdominalcavity

5 major peritoneal folds: Greater omentum falciform ligament lesser omentum mesentery mesocolon


Peritoneal Folds

‘fatty apron’


Mouth Oral cavity Formed by cheeks,

hard and soft palates,and tongue

Oral cavity properextends from gums andteeth to the fauces(opening between oralcavity and pharynx orthroat )

epiglottis

hard palate nasopharynx

softpalate


The salivary glands Secrete saliva Saliva

functions to keep mucusmembranes of mouthand throat moist

lubricates and dissolvesfoods

begins digestion ofcarbohydrates

3 major salivary glands Parotid Submandibular Sublingual


Saliva Saliva

Mostly water 99.5% 0.5% solutes – mucus, immunoglobulin A, lysozyme

(bactericidal), and salivary amylase (enzyme thatdigests starch), ions, dissolved gases, urea, uric acid

Not all salivary glands produce the same saliva Salivation is entirely under nervous control

Controlled by ANS Parasympathetic stimulation promotes secretion of saliva Sympathetic stimulation decreases salivation


Mumps An inflammation and

enlargement of theparotid salivaryglands caused byinfection with themumps virus(myxovirus).

Vaccine developedin 1967


Tongue Tongue

Accessory digestive organ Skeletal muscle covered by

mucous membrane Functions

Maneuvers food for chewingand swallowing

Speech Lingual glands secrete

salivary lipase

epiglottis

hard palate nasopharynx

softpalate


Teeth Accessory digestive organ

adapted for mechanicaldigestion

3 major regions – crown, neck,and root

Composition primarily made up of dentin, a

calcified connective tissue Enamel - protective Cementum - attaches root to

periodontol ligament Pulp - connective tissue

containing blood vessels,nerves, lymphatic vessels


Teeth –adapted for mechanical digestion

Incisors Adapted for cutting into

food Cuspids

Used to tear and shredfood

Premolars and molars Crush and grind food


Digestion in the mouth Mechanical digestion

Chewing or mastication Food manipulated by tongue, ground by teeth, and mixed

with saliva Forms bolus

Chemical digestion Salivary amylase – converts starches to disaccharides

Acts in the mouth; inactivated by stomach acid Lingual lipase – breaks down triglycerides

Secreted by lingual glands of tongue Becomes activated in acidic environment of stomach


Pharynx (throat) Extends from the internal

nares to the esophagus 3 parts

Nasopharynx Functions only in respiration

Oropharynx Digestive and respiratory

functions Laryngopharynx

Digestive and respiratoryfunctions


Esophagus Muscular tube that connects the

pharynx to the stomach Functions

Secretes mucous Transports food No enzymes produced, no

absorption Contains an upper and a lower

esophageal sphincter


Esophagus - anatomy Histology (4 layers)

Mucosa – protects against wear and tear from food particles Submucosa Muscularis

Superior 1/3 is skeletal muscle Middle 1/3 is skeletal and smooth muscle Inferior 1/3 is smooth muscle

2 sphincters upper esophageal sphincter (UES) regulates movement of food

into esophagus lower esophageal sphincter (LES) regulates movement of food

into stomach Superficial layer is adventitia – rather than serosa

attaches esophagus to surrounding structuresCopyright 2009, John Wiley &

Sons, Inc.

Swallowing (deglutition) Facilitated by saliva and mucus Involves mouth, pharynx, and esophagus 3 stages

Voluntary – bolus passed to oropharynx Pharyngeal – involuntary passage through

pharynx into esophagus Esophageal – involuntary passage through

esophagus to stomach Peristalsis pushes bolus forward


Swallowing (deglutition)3 stages Voluntary – bolus

passed to oropharynx Pharyngeal – the

tongue rises against thepalate, the epiglottisseals off the entrance tothe trachea

Esophageal – foodmoves to stomach byperistalsis

Swallowinghttp://www.youtube.com/watch?v=08VyJOEcDos


Anatomy of the Stomach 4 main regions

Cardia, fundus, body, pylorus Lesser and greater curvatures Same 4 layers

Mucosa Exocrine and endocrine cells Large folds called rugae

Submucosa Muscularis – additional 3rd layer

of smooth muscle Inner oblique layer

Serosa – part of visceralperitoneum


Anatomy of the stomach Muscularis

3 layers of muscle 2 sphincters

Mucosa Rugae Gastric pits

Secretions from severalgastric glands flow intoeach gastric pit and theninto the stomach

Exocrine gland cells –secrete gastric juice

2-3 L per day Endocrine cells

esophagus

gastroesophagealsphincter

pyloricsphincter

gastric pit

gastric gland

a. Stomach

cells thatsecretegastricjuice

muscularis layer has three layersof musclemucosa layerhas rugae

LES


Functions of the Stomach Mixes saliva, food and gastric

juice to form chyme Stomach controls movement

of chyme into the smallintestine

Serves as mixing chamberand holding area for food Most expandable part of GI

tract Secretes gastric juice

HCl, digestive enzymes Secretes gastrin into blood


Gastric secretions

Chief cells → pepsinogen and gastric lipase

Parietal cells → HCl and intrinsic factor

Mucous neck cells → mucous

G cells → gastrin, stimulates gastric activity

3 types of exocrine gland cells

Endocrine cells


Gastric secretions Mucous cells

Mucus protects themucosal cells lining thestomach

Parietal cells Secrete HCl → acidifies the

stomach contents (pH of 2) Kills microorganisms

found in food Denatures proteins Activates pepsinogen

Secrete intrinsic factor Facilitates absorption of

vitamin B12 in the ileum

gastric pitSEM 3,260×


Gastric secretions Chief cells

Secrete an inactiveproenzyme, pepsinogen

Protein digestion Rennin is secreted in

infants Coagulates proteins in

milk aids in milk digestion

Gastric lipase fat digestion


Gastric secretionsEndocrine function G cells secrete gastrin

Released when foodenters the stomach

Stimulates secretion ofgastric acid (HCl) by theparietal cells and aids ingastric motility


Recap:Digestion by the stomach Mechanical digestion

Mixing waves – gentle, rippling peristaltic movements –creates chyme

Chemical digestion Carbohydrate Digestion

Salivary amylase breaks down carbs to disaccharides until itsinactivated by acidic gastric juice

Lipid digestion Lingual lipase is activated by acidic gastric juice Gastric lipase Digest triglycerides into fatty acids and mono- or diglycerides


Digestion by the stomach Protein digestion

Parietal cells secrete H+ and Cl- separatelybut net effect is HCl

Kills many microbes Acidic pH denatures proteins

Pepsin breaks down proteins into smallerpeptides

Enzyme is secreted as inactive precursor,pepsinogen


Protein digestion – Pepsin

Pepsin is an enzyme that degrades food proteins into peptides secreted by the chief cells

The inactive pro-form, pepsinogen, is activated by HCl HCl allows pepsinogen to unfold and cleave itself into the active

enzyme, pepsin

Pepsinogen (inactive) Pepsin

HCl


Nutrient absorption in stomach Small amount of nutrient absorption

Some water, ions, short chain fatty acids,certain drugs (aspirin) and alcohol

Digestive sys - swallowing and stomach 1:48http://www.youtube.com/watch?v=Q-n_Q0qKXzg&feature=fvw


Stomach Ailments Peptic ulcers

open sores that develop in areasexposed to acidic gastric juice

the lining of the stomach, uppersmall intestine or esophagus.

Causes Infection with the bacterium

Helicobacter pylori Aspirin and other nonsteroidal anti-

inflammatory drugs Hypersecretion of HCl But NOT stress or diet


Peptic ulcer disease Helicobacter pylori is the

most frequent cause of PUD. This bacterium lives in the

mucus and can causegastric ulcers.

H. pylori is especially well-adapted for survival in thestomach. It produces an enzyme that,

through a series ofbiochemical reactions,shields the bacterium fromthe acidity of the stomach



Gastroesophageal refluxdisease (heartburn)

The lower esophagealsphincter fails to closeadequately after food entersthe stomach

The stomach contents refluxinto the inferior portion of theesophagus.

HCl from the stomach contentsirritates the esophageal wallresulting in heartburn.

Documents

Chapter 24: system - deanza.edu DigestSys1.pdf · The human digestive system consists of: