Ch18

What is peristalsis and what is its function?

Wave-like contractions that push food forward in one direction; function

→ propulsion.

What is segmentation and what is its function?

Back-and-forth churning contractions that mix chyme with enzymes; function

→ mixing, no forward movement.

What is deglutition?

Swallowing (voluntary + involuntary phases).

What is digestion?

Mechanical + chemical breakdown of food into small molecules.

What is absorption?

Movement of nutrients from GI tract into blood or lymph.

What is the mucosa and what does it do?

Innermost layer responsible for secretion and absorption.

What is the submucosa and what does it do?

Vascular layer that transports absorbed nutrients and contains nerves.

What is the muscularis and what does it do?

Smooth muscle layer responsible for peristalsis and segmentation.

What is the serosa and what does it do?

Outer protective covering of the GI tract.

What is GERD and what causes it?

Acid reflux into esophagus due to a weak lower esophageal sphincter.

What are the functions of the stomach?

Stores food, mixes with gastric juices, begins protein digestion, kills bacteria, slowly empties chyme into duodenum.

What do mucous neck cells secrete and why?

Mucus

→ protects stomach lining.

What do parietal cells secrete and why?

HCl (kills microbes, activates pepsin) + intrinsic factor (B12 absorption).

What do chief cells secrete?

Pepsinogen (inactive

→ pepsin for protein digestion).

What do G cells secrete?

Gastrin

→ stimulates HCl and pepsinogen release.

How is HCl produced in the stomach?

Parietal cells pump H⁺ out via the H⁺/K⁺ ATPase exchangers; H⁺ + Cl⁻

→ HCl in lumen.

Main causes of peptic ulcers?

H. pylori, NSAIDs, excess HCl.

Treatments for peptic ulcers?

Antibiotics, H₂ blockers, PPIs.

What do Paneth cells do?

Secrete lysozyme + defensins for immune protection.

What generates intestinal slow waves?

Interstitial Cells of Cajal (pacemaker cells).

What is enterokinase and what does it do?

Brush border enzyme that activates trypsinogen

→ trypsin (activates all pancreatic enzymes).

What are bile pigments and where do they come from?

Bilirubin from breakdown of heme (old RBCs).

What are bile salts made from?

Cholesterol in the liver

What is enterohepatic circulation?

Recycling of bile salts: liver

→ intestine

→ ileum absorption

→ portal vein

→ liver.

Main functions of the liver?

Detoxification, metabolism, plasma protein synthesis, bile production, storage (glycogen).

How does the liver detoxify blood?

Kupffer cells, cytochrome P450 enzymes, excretion in bile, conversion (ammonia

→urea), conjugation.

What is physiological jaundice of the newborn?

Immature liver can’t conjugate bilirubin; treated with blue light.

Define zymogen + example.

Inactive enzyme precursor; ex: pepsinogen, trypsinogen.

What produces pancreatic enzymes?

Acinar cells.

What produces pancreatic bicarbonate?

Ductal cells

What does secretin do?

Stimulates pancreatic bicarbonate and water; helps CCK.

What does CCK do?

Contracts gallbladder, releases bile, increases pancreatic enzymes, inhibits stomach.

What does GIP do?

Inhibits stomach; stimulates insulin release.

What does GLP-1 do?

Stimulates insulin; inhibits stomach.

What does guanylin do?

Increases Cl⁻ + water secretion

→ diarrhea when overstimulated (traveler’s diarrhea).

What does gastrin do?

Stimulates HCl, pepsinogen, maintains gastric mucosa.

What does somatostatin do?

Inhibits gastrin.

What does ghrelin do?

Hunger hormone.

Key events in cephalic phase?

Vagus nerve stimulates HCl before food arrives.

Key events in gastric phase?

Food stretches stomach; proteins stimulate gastrin

→ HCl + pepsinogen.

Key events in intestinal phase?

SI releases CCK, secretin, GIP

→ slows stomach.

Major HCl stimulus in cephalic phase?

Vagus nerve.

What is the gastroileal reflex?

Increased stomach activity

→ ileum movement

→ opens ileocecal valve.

What is the ileogastric reflex?

Distended ileum

→ slows stomach motility.

What is the intestino-intestinal reflex?

Over-distension in one area

→ relaxation in other areas.

Mechanism of E. coli traveler’s diarrhea?

Enterotoxin overstimulates guanylin

→ excess Cl⁻ + water

→ diarrhea.

What is enterogastrone?

Any SI hormone that inhibits stomach (CCK, secretin, GIP, GLP-1).

What are chylomicrons and where made?

Made in intestine; lipoproteins that transport dietary fats

→ lymph.

What is VLDL and source?

Made in liver; carries triglycerides.

What is LDL and its function?

Formed in blood; delivers cholesterol to tissues (“bad”).

What is HDL and its role?

Made in liver/intestine; removes cholesterol

→ protects against atherosclerosis.

Where does carbohydrate digestion occur?

Mouth + small intestine.

Where does protein digestion occur?

Stomach + small intestine.

Where does fat digestion occur?

Small intestine only.

How are proteins digested and absorbed?

Stomach (pepsin), SI (pancreatic enzymes + brush border); amino acids

→ blood via cotransport with sodium.

How are fats digested and absorbed?

Bile emulsifies; lipase breaks down; absorbed

→ triglycerides

→ chylomicrons

→ lymph.

What are brush border enzymes and examples?

Enzymes on microvilli for final digestion: lactase, sucrase, maltase, aminopeptidase.

Primary functions of the digestive system?

Ingestion, digestion, absorption, excretion.

Sections of the small intestine?

Duodenum (shortest), jejunum, ileum (longest).

Functions of the large intestine?

Water absorption, feces formation, feces storage.

Role of intestinal microbiota?

Produce vitamins, digest food, protect from pathogens.

What does the enteric nervous system do?

Regulates GI motility, secretions, and reflexes.