Digestive System Overview

A series of flashcards covering the anatomy and functions of the liver, small intestine, and large intestine, including digestion and absorption processes.

Blood supply of liver

• Hepatic artery

• Hepatic portal vein

• Hepatic veins

Hepatic artery

Blood vessel that supplies oxygenated blood to the liver.

Hepatic portal vein

Blood vessel that carries nutrient-rich blood from the gastrointestinal tract to the liver.

Hepatic veins

Blood vessels that drain deoxygenated blood from the liver into the inferior vena cava.

Bile salts

Compounds that emulsify fats, increasing surface area for lipase and essential for lipid digestion + absorption.

Functions of the liver

Produce bile, metabolize nutrients, detoxification, excretion of bilirubin and wastes, store nutrients, and make plasma proteins.

Anatomy of small intestine

segments: Duodenum,jejunum, ileum

includes circular folds, villa, microvilli that increase surface area for nutrient absorption.

Duodenum

First section of the small intestine that receives bile and pancreatic juice.

Jejunum

Middle section of the small intestine where most absorption occurs.

Ileum

Final section of the small intestine that ends at the ileocecal valve.

Histology of small intestine

• Villi w enterocytes + lacteal

• Goblet cells

• Intestinal crypts

• Microvilli w brush border enzymes

Villi

Small, finger-like projections in the small intestine that increase surface area for absorption.

Microvilli

Microscopic, hair-like projections on villi that increase surface area for absorption.

Goblet cells

Cells in the intestine that secrete mucus.

Intestinal crypts

Glandular structures in the small intestine that produce intestinal juices.

Absorption of nutrients in the small intestine

1. Carbohydrates- Enzymes: pancreatic amylase, brush-border enzymes

   • Absorption: monosaccharides enters blood.

2. Proteins- Enzymes: trypsin, chymotrypsin, carboxypeptidase, brush-border peptidases

   • Absorption: amino acids absorbed in blood.

3. Lipids- Emulsified by bile salts

   • Enzyme: pancreatic lipase \rightarrow fatty acids + monoglycerides

   • Absorption: into lacteals as chylomicrons.

Pancreatic amylase

Enzyme that breaks down carbohydrates into simple sugars.

Trypsin

Enzyme that digests proteins in the small intestine.

Pancreatic lipase

Enzyme that digests lipids into fatty acids and monoglycerides.

Anatomy of large intestine

Cecum \rightarrow ascending colon \rightarrow transverse \rightarrow descending \rightarrow sigmoid \rightarrow rectum \rightarrow anal canal. Includes haustra, taeniae coli, and epiploic appendages.

Cecum

First part of the large intestine.

Haustra

Pouches in the large intestine that allow for expansion.

Taeniae coli

Longitudinal bands of muscle in the large intestine that create haustra.

Stages of digestion

The process includes ingestion, secretion, propulsion, digestion (mechanical & chemical), absorption, and defecation.

Mechanical & chemical digestion in small intestine

Mechanical: segmentation + peristalsis
Chemical: pancreatic enzymes + brush-border enzymes digest carbs, proteins, lipids

Major functions of large intestine

1. Absorb water & electrolytes

2. Store feces

3. House gut bacteria

4. Secrete mucus

5. Propulsion & defecation

Histology & differences from small intestine (large intestine)

• No villi; smooth mucosa

• Many goblet cells

• Taeniae coli and haustra

• Less absorption of nutrients

Mechanical digestion in large intestine

• Haustral churning

• Mass peristalsis (3–4 times per day)

Defecation reflex

1. Distention of rectum \rightarrow stretch receptors

2. Parasympathetic reflex: contracts rectum & relaxes internal sphincter

3. Voluntary relaxation of external sphincter completes defecation

Ingestion

The process of taking food into the mouth.

Secretion

The release of water, acids, buffers, and enzymes into the lumen of the GI tract.

Propulsion

The movement of food through the digestive tract via swallowing and peristalsis.

Digestion

The breakdown of food into smaller molecules, involving both mechanical (physical breakdown) and chemical (enzymatic breakdown) processes.

Absorption

The passage of digested nutrients from the GI tract into the blood or lymph.

Defecation

The elimination of indigestible substances from the body as feces.