Copyright © 2010 Pearson Education, Inc. Pharynx Oropharynx and laryngopharynx Allow passage of food, fluids, and air Skeletal muscle layers: inner longitudinal,

Copyright © 2010 Pearson Education, Inc.

Pharynx

• Oropharynx and laryngopharynx

• Allow passage of food, fluids, and air

• Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors


Esophagus

• Flat muscular tube from laryngopharynx to stomach

• Travels through the diaphragm via an opening called the esophageal hiatus

• Joins stomach at the cardiac orifice


Esophagus

• Esophageal glands secrete mucus to lubricate and aid in bolus movement

• Muscularis: consists of skeletal muscle superiorly; smooth muscle inferiorly

• Contains upper and lower esophageal sphincters: upper and lower that act as “gateways” for food

• Lower esophageal sphincter prevents backflow of stomach contents into the esophagus

Copyright © 2010 Pearson Education, Inc. Figure 23.12a

Mucosa(contains a stratifiedsquamous epithelium)

Submucosa (areolarconnective tissue)

LumenMuscularis externa

Adventitia (fibrousconnective tissue)

(a)

• Circular layer • Longitudinal layer


Digestive Processes: Mouth

• Ingestion

• Mechanical digestion

• Mastication is partly voluntary, partly reflexive

• Chemical digestion (salivary amylase and lingual lipase)

• Propulsion

• Deglutition (swallowing)


Deglutition – 2 major phases

• Involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups

• Buccal (oral) phase

• Voluntary contraction of the tongue

• Pharyngeal-esophageal phase

• Involuntary (sensory receptors initiate the swallowing reflex)

• Control center in the medulla and lower pons

Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 1

Tongue

Trachea

Pharynx

Epiglottis

Glottis

Bolus of food

Upper esophageal sphincter is contracted. Duringthe buccal phase, the tongue presses against the hardpalate, forcing the food bolus into the oropharynxwhere the involuntary phase begins.

1


Epiglottis

Esophagus

Uvula

Bolus

The uvula and larynx rise to prevent food fromentering respiratory passageways. The tongue blocksoff the mouth. The upper esophageal sphincterrelaxes, allowing food to enter the esophagus.

2


Bolus

The constrictor muscles of the pharynx contract,forcing food into the esophagus inferiorly. The upperesophageal sphincter contracts (closes) after entry.

3


Relaxed muscles

Bolus of food

Stomach

Circular musclescontract

Longitudinal musclescontract

Gastroesophagealsphincter closed

Food is moved throughthe esophagus to thestomach by peristalsis.

4


Relaxedmuscles

Gastroesophagealsphincter opens

The gastroesophagealsphincter opens, and foodenters the stomach.

5

Copyright © 2010 Pearson Education, Inc. Figure 23.13

Tongue

Trachea

Pharynx

Epiglottis

Glottis

Bolus of food

Epiglottis

Esophagus

Uvula

Bolus

Bolus

Relaxed muscles

Circular musclescontract

Bolus of food

Longitudinal musclescontract

Stomach

Relaxedmuscles

Gastroesophagealsphincter opens

Gastroesophagealsphincter closed

Upper esophageal sphincter iscontracted. During the buccal phase, thetongue presses against the hard palate,forcing the food bolus into the oropharynxwhere the involuntary phase begins.

Food is movedthrough the esophagusto the stomach byperistalsis.

The gastroesophagealsphincter opens, and foodenters the stomach.

The uvula and larynx rise to prevent foodfrom entering respiratory passageways. Thetongue blocks off the mouth. The upperesophageal sphincter relaxes, allowing foodto enter the esophagus.

The constrictor muscles of thepharynx contract, forcing foodinto the esophagus inferiorly. Theupper esophageal sphinctercontracts (closes) after entry.

1 2

4

3

5


The Stomach

Four Main Functions:

1. Temporary storage for ingested food

2. Mechanical breakdown of food

3. Chemical breakdown of food

4. Production of intrinsic factor, necessary for absorption of vitamin B12


Stomach: Gross Anatomy

• Cardiac region (cardia)

• Surrounds the cardiac orifice

• Fundus

• Dome-shaped region beneath the diaphragm

• Body

• Midportion



• Pyloric region: antrum, pyloric canal, and pylorus

• Pylorus is continuous with the duodenum through the pyloric valve (sphincter)

• Greater curvature

• Convex lateral surface

• Lesser curvature

• Concave medial surface


Cardia

Esophagus

Pyloric sphincter(valve) at pylorus

Pyloriccanal

Pyloricantrum

Rugae ofmucosa

Body

Lumen

Serosa

Fundus

Lessercurvature

Greatercurvature

Muscularisexterna • Longitudinal layer • Circular layer • Oblique layer

(a)

Duodenum



• Lesser omentum

• From the liver to the lesser curvature

• Greater omentum

• Drapes from greater curvature

• Anterior to the small intestine

• Protects abdominal viscera


Falciform ligament

Liver

Gallbladder

Spleen

Stomach

Ligamentum teres

Greater omentum

Small intestine

Cecum

(a)

Copyright © 2010 Pearson Education, Inc. Figure 23.30b

Liver

Lesser omentumGallbladder

StomachDuodenum

Transverse colon

Small intestine

Cecum

Urinary bladder(b)


Stomach: Microscopic Anatomy

• Still has four tunics

• Muscularis and mucosa are modified

• Muscularis externa

• Three layers of smooth muscle

• Inner oblique layer allows stomach to churn, mix, move, and physically break down food


3 muscular layers•Longitudinal•Circular•Oblique


Stomach: Microscopic Anatomy

• Mucosa

• Simple columnar epithelium composed of mucous cells

• Produce a layer of mucus that traps bicarbonate-rich fluid beneath it

• Protects the epithelial cells from acids, enzymes and abrasive materials

• Gastric pits lead into gastric glands


(b) Enlarged view of gastric pits and gastric glands

Mucous neck cells

Parietal cell

Surface epithelium(mucous cells)

Gastric pits

Chief cell

Enteroendocrine cell

Gastric pit

Gastric gland


Gastric Glands

• Cell types

• Mucous neck cells (secrete thin, acidic mucus)

• Parietal cells

• Chief cells

• Enteroendocrine cells

Copyright © 2010 Pearson Education, Inc. Figure 23.15c

(c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland

Pepsinogen

Mitochondria

PepsinHCl

Chief cell

Enteroendocrinecell

Parietal cell


Gastric Gland Secretions

• Glands in the fundus and body produce most of the gastric juice

Parietal cell secretions

• HCl

• pH 1.5–3.5 denatures protein in food, activates pepsin, and kills many bacteria

• Intrinsic factor

• Glycoprotein required for absorption of vitamin B12 in small intestine


Gastric Gland Secretions

• Chief cell secretions

• Inactive enzyme pepsinogen

• Converted to pepsin by HCl and by pepsin itself


Homeostatic Imbalance

• Gastritis: inflammation caused by anything that breaches the mucosal barrier

• Peptic or gastric ulcers: erosion of the stomach wall

• Most are caused by Helicobacter pylori bacteria

• Cause 80% of gastric ulcers

• Treated successfully with antibiotics


Bacteria

Mucosalayer ofstomach

(a) A gastric ulcer lesion (b) H. pylori bacteria


Digestive Processes in the Stomach

• Physical digestion

• Denaturation (breakdown) of proteins

• Enzymatic digestion of proteins by pepsin (and rennin in infants)

• Secretion of intrinsic factor required for absorption of vitamin B12

• Lack of intrinsic factor pernicious anemia

• Delivers chyme to the small intestine


Regulation of Gastric Secretion

• Regulated by CNS and hormonal mechanisms

• Events occur in three phases:

1. Cephalic (reflex) phase: few minutes before food entry:

• sight, smell, taste or thought of food initiates gastric secretion

• Prepares the stomach to receive food


Regulation of Gastric Secretion

2. Gastric phase: lasts for 3–4 hours after food enters the stomach (distending stomach)

• Stimulates stretch receptors

• Gastrin is released increasing gastric secretion production

• Distension and gastrin increase force of contraction

3. Intestinal phase: brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects to slow gastric activity down giving the intestine time to do its job


1 Propulsion: Peristaltic waves move from the fundus toward the pylorus.

2 3 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus.

Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach.

Pyloricvalveclosed

Pyloricvalveclosed

Pyloricvalveslightlyopened


Regulation of Gastric Emptying

• As chyme enters the duodenum in 3 ml spurts

• Receptors respond to stretch and chemical signals

• Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling

• Carbohydrate-rich chyme moves quickly through the duodenum

• Fatty chyme remains in the duodenum 6 hours or more


Small Intestine: Gross Anatomy

• Major organ of digestion and absorption

• 2–4 m (7-13 ft) long; from pyloric sphincter to ileocecal valve

• Three Subdivisions

1. Duodenum – contains the bile duct and main pancreatic duct

2. Jejunum

3. Ileum


Mouth (oral cavity)Tongue

Esophagus

LiverGallbladder

Anus

DuodenumJejunumIleum

Small intestine

Parotid glandSublingual glandSubmandibulargland

Salivaryglands

Pharynx

StomachPancreas(Spleen)

Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal

Largeintestine


Jejunum

Mucosawith folds

Cystic duct

DuodenumHepatopancreaticampulla and sphincter

Gallbladder

Right and lefthepatic ducts of liver

Bile duct and sphincter

Main pancreatic ductand sphincter

PancreasTail of pancreas

Head of pancreas

Common hepatic duct

Major duodenalpapilla

Accessory pancreatic duct


Structural Modifications

• Increase surface area of proximal part for nutrient absorption

• Circular folds (plicae circulares)

• Villi

• Microvilli

• Circular folds

• Permanent ridged

• Force chyme to slowly spiral through lumen


Vein carrying blood tohepatic portal vessel

MusclelayersCircularfoldsVilli

(a)

Lumen



• Villi

• Motile fingerlike extensions of the mucosa

• Villus epithelium

• Simple columnar absorptive cells (enterocytes)

• Goblet cells



• Microvilli

• Projections (brush border) of absorptive cells

• Contain brush border enzymes which complete carbohydrate and protein digestion in the small intestine


(b)

Absorptive cells

Lacteal

Intestinal crypt

Mucosaassociatedlymphoid tissue

MuscularismucosaeDuodenal gland Submucosa

EnteroendocrinecellsVenuleLymphatic vessel

Goblet cellBloodcapillaries

Vilus

Microvilli(brush border)


Intestinal Juice

• Secreted in response to distension or irritation of the mucosa

• Slightly alkaline and isotonic with blood plasma

• Largely water, enzyme-poor, but contains mucus

• Facilitates transport and absorption of nutrients


Liver

• Largest gland in the body

• Four lobes—right, left, caudate, and quadrate


Liver

• Falciform ligament

• Separates the (larger) right and (smaller) left lobes

• Suspends liver from the diaphragm and anterior abdominal wall

• Round ligament (ligamentum teres)

• Remnant of fetal umbilical vein along free edge of falciform ligament


SternumNipple

Liver

Right lobeof liver

Gallbladder

(a)

Bare area

Falciformligament

Left lobe of liver

Round ligament(ligamentum teres)


Lesser omentum(in fissure)

Left lobe of liver

(b)

Porta hepatiscontaining hepaticartery (left) andhepatic portal vein(right)

Quadrate lobeof liverLigamentum teres

Gallbladder

Hepatic vein (cut)

Sulcus forinferiorvena cava

Caudate lobeof liver

Bare area

Bile duct (cut)

Right lobe ofliver

Sternum

Nipple

Liver


Liver: Associated Structures

• Lesser omentum anchors liver to stomach

• Hepatic artery and hepatic portal vein

• Bile ducts

• Common hepatic duct leaves the liver

• Cystic duct connects to gallbladder

• Bile duct formed by the union of the above two ducts


Jejunum

Mucosawith folds

Cystic duct

DuodenumHepatopancreaticampulla and sphincter

Gallbladder

Right and lefthepatic ducts of liver

Bile duct and sphincter

Main pancreatic ductand sphincter

PancreasTail of pancreas

Head of pancreas

Common hepatic duct

Major duodenalpapilla

Accessory pancreatic duct


Liver: Microscopic Anatomy

• Liver lobules

• Hexagonal structural and functional units

• Filter and process blood

• Composed of hepatocytes (liver cells)

• Longitudinal central vein

Copyright © 2010 Pearson Education, Inc. Figure 23.25a, b

(a) (b)Lobule Central vein Connectivetissue septum



• Portal triad at each corner of lobule

• Bile duct receives bile from bile canaliculi

• Portal arteriole is a branch of the hepatic artery

• Hepatic venule is a branch of the hepatic portal vein

• Liver sinusoids are leaky capillaries between hepatic plates

• Kupffer cells (hepatic macrophages) in liver sinusoids

Copyright © 2010 Pearson Education, Inc. Figure 23.25c

(c)

Interlobular veins(to hepatic vein) Central vein

Sinusoids

Portal triad

Plates ofhepatocytes

Portal vein

Fenestratedlining (endothelial cells) of sinusoids

Bile duct (receivesbile from bile canaliculi)

Bile duct

Portal arteriolePortal venuleHepatic

macrophagesin sinusoid walls

Bile canaliculi



• Hepatocyte functions

• Process bloodborne nutrients

• Store fat-soluble vitamins

• Perform detoxification

• Produce ~900 ml bile per day


Bile

• Yellow-green, alkaline solution containing

• Bile salts: function in fat emulsification and absorption

• Bilirubin: pigment formed from heme

• Cholesterol, triglycerides, phospholipids, and electrolytes


Bile

• Enterohepatic circulation

• Recycles bile salts

• Bile salts duodenum reabsorbed from ileum hepatic portal blood liver secreted into bile


The Gallbladder

• Thin-walled muscular sac on the ventral surface of the liver

• Stores and concentrates bile by absorbing its water and ions

• Releases bile via the cystic duct, which flows into the bile duct

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Copyright © 2010 Pearson Education, Inc. Pharynx Oropharynx and laryngopharynx Allow passage of food, fluids, and air Skeletal muscle layers: inner longitudinal,