Chapter 25 the digestive system
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Chapter 25— The Digestive System. Ch. 25 Study Guide. Critically read 25.3 (stomach), 25.4 (liver, gallbladder, and pancreas), 25.5 (small intestine); pp. 977-995 Comprehend Terminology (those in bold)

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Ch 25 study guide
Ch. 25 Study Guide

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

Comprehend Terminology (those in bold)

Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions

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

I stomach 25 3 a introduction and gross anatomy

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

Introduction the stomach
§ Introduction-- the stomach

  • Location/size--

    • Upper left abdominal cavity—

    • Volume– 50 mL when empty and 1-2 L after a typical meal.

  • Functions–

    • Primarily as a food ____________ organ

    • Liquefies the food and begins the chemical digestion of proteins and fat

    • End result: Chyme–

Gross anatomy stomach
§ Gross Anatomy (stomach)

  • Lesser curvature—

  • Greater curvature—

    • Four regions— Fig. 25.12 a-b

    • Cardiac region (cardia)– inside the cardiac orifice

    • Fundic region (fundus)—

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

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

I stomach b cell types and their secretions

I. Stomach—B. Cell types and their secretions

The stomach wall
§ The stomach wall

  • Structures from the outermost layer:

    • Three muscle layers– muscularis externa

    • Gastric rugae– Wrinkles formed by mucosa and submucosa

    • 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

Cell types of the tubular glands
§ Cell types of the tubular glands

  • Mucous cells– secrete mucus, predominate in the cardiac and pyloric glands

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

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

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

  • Enteroendocrine cells– G cells included

Gastric secretions hcl
§ Gastric secretions--HCl

  • 2-3 L of gastric juice per day--mainly water, HCl, and pepsin

  • 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

  • Functions of HCl:

    • Activates enzymes—

    • Kills ingested bacteria

    • Converts Fe(3+) to Fe(2+)

Gastric secretions intrinsic factor
§ Gastric secretions—Intrinsic factor

  • Secretedby-- parietal cells

  • Chemistry--Glycoprotein

  • Function– essential to the absorption of ______________ by the small intestine

  • Disorder– pernicious anemia

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

Gastric secretions pepsin
§ Gastric secretions--Pepsin

  • Chief cells secrete a zymogens (inactive proteins) called pepsinogen

  • Pepsinogen  pepsin (by HCl)

  • Functions of the pepsin—

    • Digests proteins:

    • Autocatalytic effect of pepsin:

    • Once pepsin is formed, pepsin can converts pepsinogen into MORE pepsin.

      Fig. 25.15

Chapter 25 the digestive system

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

What are functions 1-3, respectively?

Gastric digestion and absorption
§ Gastric digestion and absorption function #3

  • Digestion—

    • Partially digest protein, starch, and fat

    • Most digestion and absorption occurs in the ________________

  • Absorption—

    • Not significant amount

    • Absorb aspirin, some lipid-soluble drugs, and little alcohol

I stomach c protection of the stomach

I. Stomach— function #3C. Protection of the stomach

Protection of the stomach
§ protection of the stomach function #3

  • 3 ways to protect against harsh acidic and enzymatic environment (Fig. x)

  • Mucous coat– thick, and alkaline mucus

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

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

Chapter 25 the digestive system

LUMEN function #3

Passage prevented

Mucus coating


to HCI



Cells lining gastric mucosa

(including those lining gastric pits and glands)


Peptic ulcer
§ peptic ulcer function #3

  • Definition– erosion in the wall of digestive tract caused by pepsin and HCl

  • Locations– duodenum most common, also in _______________________

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

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

    Fig. 25.16 a-b

Chapter 25 the digestive system

Normal function #3

Peptic ulcer

I stomach d regulation of the gastric function

I. Stomach— function #3D. Regulation of the gastric function

Regulation of gastric function
§ Regulation of Gastric function function #3

  • Three phases— overlap each other and all three can occur simultaneously

  • Cephalic phase– being controlled by the brain

  • Gastric phase– being controlled by the stomach

  • Intestinal phase– being controlled by the small intestine

Regulation of gastric function1
§ Regulation of Gastric function function #3

  • The cephalic phase– the stomach responds to sight, smell, taste, or thought of food.

  • Details–

    • mental inputs converge on the hypothalamus, to the medulla oblongata

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

  • Fig. 25.17

  • Regulation of gastric function2
    § Regulation of Gastric function function #3

    • The gastric phase– swallowed food activate gastric activity

      Details– Presence of food/proteins

      • Stretching– via a long vagovagal reflex and a short myenteric reflex

      • 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 25.18

    Chapter 25 the digestive system

    & function #3


    Regulation of gastric function3
    § Regulation of Gastric function function #3

    • The intestinal– duodenum responds to _______ and moderates gastric activity


    • 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

    Chapter 25 the digestive system

    _ function #3

    Ii 25 4 a the liver

    II. 25.4— function #3A. The liver

    Gross anatomy
    § Gross anatomy function #3

    • Location– inferior to the diaphragm …

    • The body’s largest organ—

    • Functions– Fig. x

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

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

      Fig. 25.19

    Chapter 25 the digestive system

    PROD. & function #3

    Chapter 25 the digestive system

    25- function #336

    Microscopic anatomy
    § Microscopic anatomy function #3

    • 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

    Chapter 25 the digestive system

    Fig. 25.20a-- function #3The hepatic lobules



    Central vein

    Hepatic triad:

    1-Branch of


    portal v.


    2-Branch of

    Hepatic a.

    3-Bile ductule


    Bile canaliculi



    Chapter 25 the digestive system

    Hepatic function #3








    Microscopic anatomy1
    § Microscopic anatomy function #3

    • 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

    Chapter 25 the digestive system
    § Bile function #3

    • Color– yellow-green fluid

    • Secreted by— the liver; @ 1 liter per day

      • 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

    Ii 25 4 b the gallbladder

    II. 25.4— function #3B. The gallbladder

    Gallbladder and bile flow
    § Gallbladder and bile flow function #3

    • 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

    Chapter 25 the digestive system

    1. Hepatic ducts function #3

    3. Cystic duct


    2. Common hepatic duct



    4. Bileduct


    Pancreatic duct


    pancreatic duct


    Minor duodenal



    6. Hepatopancreatic




    7. Major duodenal



    5. Hepatopancreatic



    Gallbladder and bile flow1
    § Gallbladder and bile flow function #3

    • 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

    Ii 25 4 c the pancreas

    II. 25.4— function #3C. The pancreas

    The pancreas
    § The pancreas function #3

    • Location– anterior/posterior (circle one) to the greater curvature of the stomach

    • Dimension– 12-15 cm long & 2.5 cm thick

    • 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

    The exocrine secretions of the pancreas
    § The exocrine secretions of the pancreas function #3

    • 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

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

      • What are they?

        Fig. 25.23

    Chapter 25 the digestive system

    25- function #349

    Regulation of pancreatic secretion
    § Regulation of pancreatic secretion function #3

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

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

      • Discharge of bile into the duodenum

      • the secretion of pancreatic enzymes

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