Chapter 25— The Digestive System

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Ch. 25 Study Guide

1. Critically read 25.3 (stomach), 25.4 (liver, gallbladder, and pancreas), 25.5 (small intestine); pp. 977-995

2. Comprehend Terminology (those in bold)3. Study-- Figure questions, Think About It

questions, and Before You Go On (section-ending) questions

4. Do end-of-chapter questions:– Testing Your Recall— 1-4, 6, 9, 10, 15-17– True or False– 1, 3-10– Testing Your Comprehension– 2, 5

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I. Stomach (25.3)—A. Introduction and gross

anatomy

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§ Introduction-- the stomach1. Location/size--

– Upper left abdominal cavity—– Volume– 50 mL when empty and 1-2 L after a

typical meal.

2. Functions– – Primarily as a food ____________ organ– Liquefies the food and begins the chemical

digestion of proteins and fat– End result: Chyme–

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§ Gross Anatomy (stomach)1. Lesser curvature—

2. Greater curvature—

3. Four regions— Fig. 25.12 a-bA. Cardiac region (cardia)– inside the cardiac

orifice

B. Fundic region (fundus)—

C. Body (corpus)– inferior to the cardiac orifice; greatest part of the organ

D. Pyroric region– narrower pouch at the inferior; subdivided into antrum and pyloric canal

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Figure 25.12b

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I. Stomach—B. Cell types and their

secretions

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§ The stomach wall• Structures from the outermost layer:

1. Three muscle layers– muscularis externa

2. Gastric rugae– Wrinkles formed by mucosa and submucosa

3. Gastric pits– depressions in mucosa• Lined with ____________ epithelium• Tubular glands (cardiac, pyloric, and gastric

glands) open into the pits• Cell types– Addressed shortly . . .

• Fig. 25.13 a-b 25-9

Gastric/pyloric glands of the gastric pits (next slide)

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Tubular glands differ depending on areas.

§ Cell types of the tubular glands1. Mucous cells– secrete mucus, predominate in

the cardiac and pyloric glands

2. Regenerative (stem) cells– in the base of the pit and neck of the gland; function—

3. Parietal cells– mostly in the upper half of the gastric gland; secrete hydrochloric acid and intrinsic factor

4. Chief cells– most numerous and only in gastric glands; secrete chymosin and lipase in infancy; _________________ later on

5. Enteroendocrine cells– G cells included 25-12

§ Gastric secretions--HCl• 2-3 L of gastric juice per day--mainly water,

HCl, and pepsin

1. HCl – by parietal cells: Fig. 25.14

– CO2 + water (CAH) H2CO3 HCO3

- + H+

– Chloride shift--HCO3

- exchanges for chloride

ions (Cl-) from the blood plasma– Alkaline tide– during digestion, high-pH blood

2. Functions of HCl:– Activates enzymes—– Kills ingested bacteria– Converts Fe(3+) to Fe(2+)

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CAH

Chloride shift

§ Gastric secretions—Intrinsic factor

1. Secreted by-- parietal cells

2. Chemistry--Glycoprotein

3. Function– essential to the absorption of ______________ by the small intestine

4. Disorder– pernicious anemia

5. Treatment– injection of vitamin B12 or take vitamin B12 and intrinsic factor orally

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§ Gastric secretions--Pepsin1. Chief cells secrete a zymogens (inactive

proteins) called pepsinogen

2. Pepsinogen pepsin (by HCl)

3. Functions of the pepsin—A. Digests proteins:

B. Autocatalytic effect of pepsin:– Once pepsin is formed, pepsin can converts

pepsinogen into MORE pepsin.

Fig. 25.1525-16

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Pepsin has two functions #1 and #2 below (as shown); HCl has function #3

What are functions 1-3, respectively?

§ Gastric digestion and absorption1. Digestion—

– Partially digest protein, starch, and fat– Most digestion and absorption occurs in the

________________

2. Absorption—– Not significant amount– Absorb aspirin, some lipid-soluble drugs, and

little alcohol

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I. Stomach—C. Protection of the

stomach

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§ protection of the stomach• 3 ways to protect against harsh acidic and

enzymatic environment (Fig. x)

1. Mucous coat– thick, and alkaline mucus

2. Epithelial cell replacement– cells live 3-6 days; replaced by new cells in the gastric pits

3. ____________ — prevents gastric juice from seeping between them to damage CT of the lamina propria or beyond

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LUMEN Mucus coating

Impermeableto HCI

Cells lining gastric mucosa(including those lining gastric pits and glands)

Submucosa

Tightjunction

Passage prevented

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§ peptic ulcer1. Definition– erosion in the wall of digestive tract

caused by pepsin and HCl

2. Locations– duodenum most common, also in _______________________

3. Causes– mucosal defense is compromised; hypersecretion of acid/pepsin, Helicobacter pylori (bacterium), smoking, use of aspirin

4. Treatments-- Cimetidine (H2 blocker on parietal cells); antibiotics against Helicobacter (better)

Fig. 25.16 a-b25-22

Normal Peptic ulcer25-23

I. Stomach—D. Regulation of the gastric

function

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§ Regulation of Gastric function• Three phases— overlap each other and all

three can occur simultaneously

1. Cephalic phase– being controlled by the brain

2. Gastric phase– being controlled by the stomach

3. Intestinal phase– being controlled by the small intestine

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§ Regulation of Gastric function• The cephalic phase– the stomach

responds to sight, smell, taste, or thought of food.

• Details– A. mental inputs converge on the

hypothalamus, to the medulla oblongata

B. vagus nerve fibers from medulla innervate the stomach to stimulate gastric activity.

• Fig. 25.17

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§ Regulation of Gastric function• The gastric phase– swallowed food

activate gastric activity

Details– Presence of food/proteins A. Stretching– via a long vagovagal reflex and a short

myenteric reflex

B. Through chemicals—Ach, gastrin, histamin– On parietal cells (by Ach, gastrin, histamin)- to

secrete HCl– On chief cells (by Ach and gastrin)– pepsinogen– Digested protein: stimulates the G cells secrete even

more gastrin

Fig. 25.17 b and 25.1825-28

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Ach&

Fig. 25.18– Feedback control of gastric secretion.

(+ feedback)

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§ Regulation of Gastric function• The intestinal– duodenum responds to

_______ and moderates gastric activity

Details– • Initially enhances gastric secretion• Soon, acid and semidigested fats trigger the

enterogastric reflex– to: – Inhibit vagal nuclei– Stimulate sympathetic neurons– Secretin and cholecystokinin inhibit gastric

activity

Fig. 25.17c 25-31

_

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II. 25.4—A. The liver

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§ Gross anatomy

1. Location– inferior to the diaphragm …

2. The body’s largest organ—

3. Functions– Fig. x

4. Four lobes— right, left, quadrate, and caudate lobes

5. Other important terminology– falciform ligament, round ligament; bare area, porta hepatis

Fig. 25.19

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PROD. &

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§ Microscopic anatomy1. Lots tiny cylinders– hepatic lobules

(each 2mm x 1mm)– Each hepatic lobule– central vein +

radiating hepatic sinusoids + sheets of hepatocytes

– Functions of hepatocytes and hepatic macrophages--

Fig. 25.20 a, c

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Stroma

3-Bile ductule (a)

Hepatocytes

Hepatic triad:

Central vein

1-Branch ofhepaticportal v.

2-Branch ofHepatic a.

Bile canaliculi

Hepaticsinusoid

Fig. 25.20a--The hepatic lobules

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Hepatocyte

Sinusoid

Fenestration

Hepaticmacrophage

Endothelialcells

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§ Microscopic anatomy2. Stroma (C.T.)-- Among hepatic lobules

– Hepatic triad– two blood vessels and a bile ductule

– Blood circulation in the liver– blood vessels of a triad to the sinusoids, to the central vein, to right and left hepatic veins and to the _____________ before going back to the heart

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§ Bile1. Color– yellow-green fluid

2. Secreted by— the liver; @ 1 liter per day

3. Components— bile acids, cholesterol, phospholipids (lecithin), neutral fats, minerals, bile pigments (major pigment is bilirubin)

– Bile acids (steroids) and lecithin aid in fat digestion and absorption

– _____% of bile acids are reabsorbed in the ileum and reused (called enterohepatic circulation)

– All others are wastes, destined in the feces– Waste products too concentrated-- gallstones

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II. 25.4—B. The gallbladder

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§ Gallbladder and bile flow1. Gallbladder– (Fig. 25.21)

– Location– on the underside of the liver– Dimension– 10 cm long– Pathway-- Its neck (cervix) leads into the

________ duct, which then joins the bile duct– Function– store and concentrate bile

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1. Hepatic ducts

2. Common hepatic duct

3. Cystic duct

4. Bile duct

Gallbladder: Neck

Body

HeadPancreatic duct

Jejunum

Duodenum

Pancreas

Minor duodenalpapilla

6. Hepatopancreaticsphincter

7. Major duodenalpapilla

5. Hepatopancreaticampulla

Accessorypancreatic duct

Duodenojejunalflexure

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§ Gallbladder and bile flow3. Bile’s pathway– (see also Fig. 25.21)

– Bile canaliculi (between layers of hepatocytes)– Small bile ductules of the triads

– Right and left hepatic ducts, converge to form– The common hepatic duct– Joins the cystic duct (of the gallbladder)– Forms the bile duct– Joins the pancreatic duct to become the

hepatopancreatic ampulla– Terminates at the major duodenal papilla

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II. 25.4—C. The pancreas

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§ The pancreas1. Location– anterior/posterior (circle one) to the

greater curvature of the stomach

2. Dimension– 12-15 cm long & 2.5 cm thick

3. Functions– both endocrine (1%; insulin + glucagon) and exocrine gland (99%; secretes pancreatic juice)

– Pancreatic juice: alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, ions

– Path of pancreatic juice: through either main or accessory pancreatic ducts

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§ The exocrine secretions of the pancreas

1. Zymogens– trypsinogen, chymotrypsinogen, and procarboxypeptidase (all digest proteins)

– Trypsinogen becomes ________ by enterokinase (from small intestine); an autocatalytic reac.

– Trypsin also convert the other two zymogens into active forms

2. Other enzymes-- become fully active upon exposure to bile or ions in the intestines

– What are they?

Fig. 25.23

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§ Regulation of pancreatic secretion

1. Acetylcholine– (from vagus and enteric nerves in response to gastric phases); stimulates enzymes secretion and release

2. Cholecystokinin– (from duodenum and jejunum in response to fats); stimulates—

– Discharge of bile into the duodenum– the secretion of pancreatic enzymes

3. Secretin– (same as #2; in response to acidity of chyme); stimulates the secretion of sodium bicarbonate from _____

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