Overview of the Human Digestive System

Alimentary canal

The gastrointestinal tract that includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

Accessory organs

Tongue, teeth, salivary glands, gallbladder, liver, and pancreas.

Length of the alimentary canal

25-35 feet long.

Layers of the alimentary canal

Mucosa, submucosa, muscularis, and serosa.

Layers of the mucosa

Epithelium, lamina propria, and muscularis mucosa.

Function of the epithelium in the mucosa

Replenishes every 3-7 days, contains goblet cells for moisture and enteroendocrine cells for hormone release.

Contents of the lamina propria

Blood vessels, lymphatic vessels, and lymphocytes.

Function of the muscularis mucosa

Smooth muscle that increases surface area by staying in constant tension.

Contents of the submucosa

Connective tissue with blood vessels, lymphatic vessels, glands, and nerves.

Function of the muscularis layer

Promotes mechanical digestion, increases chemical exposure, and causes peristalsis.

Location of skeletal muscle in the alimentary canal

At both ends to control food intake and waste output.

Function of the serosa

Anchors the alimentary canal in place.

Control of myenteric and submucosal plexuses

Myenteric controls muscle contractions; submucosal regulates digestive secretions.

Hepatic portal system

It transports nutrient-rich blood from the small intestine to the liver for processing/storage.

Layers of the peritoneum

Parietal peritoneum lines the abdominal wall; visceral peritoneum covers organs.

Difference between propulsion and peristalsis

Propulsion is voluntary; peristalsis is automatic.

Mastication

The act of chewing.

Chyme

Partially digested food mixed with digestive juices in the gut.

Defecation

The elimination of undigested and unabsorbed food material.

Segmentation

Back-and-forth movement of food in the small intestine to enhance absorption.

Digestive nerves detection

Stretch, liquid amount, food quantity, and food type.

Hormones that regulate digestion

Gastrin, secretin, and cholecystokinin (CCK).

Function of the uvula

Prevents food from entering the nasopharynx.

Functions of the tongue

Ingestion, mechanical and chemical digestion, sensation, swallowing, vocalization, and food positioning.

Function of lingual lipase

Breaks down lipids once activated in the stomach.

Major salivary glands

Submandibular, sublingual, and parotid glands.

Enzyme that starts carbohydrate digestion in the mouth

Salivary amylase.

Antibody found in saliva

IgA, which provides antimicrobial protection.

Number of deciduous and permanent teeth

20 deciduous and 32 permanent teeth.

Types and numbers of human teeth

8 incisors, 4 cuspids, 8 pre-molars, 12 molars (including wisdom teeth).

Separation of the esophagus from the pharynx and stomach

The upper and lower esophageal sphincters.

Deglutition

Swallowing; 1 second for liquids and 4-8 seconds for solids.

Phases of swallowing

Voluntary, pharyngeal, and esophageal phases.

Parts of the stomach

Four parts.

Four parts of the stomach

Cardia, fundus, body, and pylorus.

Pyloric sphincter

Controls food movement from the stomach to the duodenum.

Rugae in the stomach

Folds that form when the stomach is empty.

Main stomach cells and their functions

Parietal: HCL & intrinsic factor; Chief: Pepsinogen; Mucus neck: Acidic mucus; Enteroendocrine: Hormones like gastrin.

pH of stomach acid

1.5 - 3.5.

Three phases of gastric secretion

Cephalic (thinking about food), gastric (eating), and intestinal (duodenum regulates).

Protection of stomach lining from acid

A bicarbonate-rich mucosal barrier.

Main function of the stomach

Releasing intrinsic factor for B12 absorption.

Order of macronutrient digestion speed in the stomach

Carbs fastest, then proteins, fats slowest (up to 6 hours).

Three sections of the small intestine

Duodenum, jejunum, and ileum.

Function of the hepatopancreatic ampulla and sphincter

Allows bile and pancreatic juice into the duodenum.

Increase of small intestine's surface area

Circular folds, villi, and microvilli.

Villi

Hair-like structures containing an arteriole, venule, and lacteal.

Microvilli

Digestive enzymes and enhance absorption.

Role of motilin in the small intestine

Stops segmentation and starts peristalsis.

Time for chyme to pass through the small intestine

3-5 hours.

Absorption of carbs, proteins, fats, and water

Carbs/proteins: into blood; Fats: into lacteals; Water: by osmosis.

Four sections of the large intestine

Cecum, colon, rectum, and anus.

Colon sections

Ascending, transverse, descending, sigmoid.

Function of the rectal valves

Separate gas from solid feces.

Control of defecation

Internal (involuntary) and external (voluntary) anal sphincters.

Species of bacteria in the gut

About 700 species; aid digestion, vitamin production, and immunity.

Role of dendritic cells in the large intestine

Present bacterial samples to T cells for immune surveillance.

Three types of mechanical digestion in the large intestine

Haustral contractions, peristalsis, and mass movements.

Valsalva maneuver

Forceful bearing down to defecate.

Effect of delayed defecation

Excess water absorption can cause constipation.

Largest gland in the body

Liver; hepatic artery (oxygen) and hepatic portal vein (nutrients).

Function of hepatocytes

Process nutrients, detoxify, and secrete bile.

Bile and emulsification

Bile breaks down lipids; emulsification is converting large fats into smaller ones.

Cause of white, fatty stool

Lack of bile secretion into intestines.

Pancreas secretion into the small intestine

Pancreatic juice (enzymes, water, salts, sodium bicarbonate).

Function of the gallbladder

Stores, concentrates, and releases bile.

Pancreatic amylase

Digests carbohydrates into monosaccharides like glucose.

Protein digestion

HCL and pepsin in the stomach; trypsin and chymotrypsin from the pancreas in the small intestine.

Lipid digestion

Occurs in the small intestine; bile and pancreatic lipase help.

Enzymes that digest DNA and RNA

Pancreatic nuclease, deoxyribonuclease (DNA), and ribonuclease (RNA).