Lecture #13 - Digestive System

Question 1

What is the alimentary canal also known as?*

Answer 1

GI tract
(mouth to anus)

Question 2

The Peritoneal Cavity and Peritoneum

Define the peritoneum.

What are the different types of peritoneum? Define them.

What is the peritoneal cavity?

Answer 2

• peritoneum: a serous membrane
• visceral peritoneum: surrounds digestive organs
• parietal peritoneum: lines the body wall
• peritoneal cavity: slitlike space (in between visceral and parietal peritoneum)

Question 3

The Peritoneal Cavity and Peritoneum

What is the mesentery?

What are the functions of the mesentery?

Answer 3

• mesentery: a double layer of peritoneum
• holds organs in place
• sites of fat storage
• provides a route for circulatory vessels and nerves

Question 4

What is ingestion?

Answer 4

occurs in the mouth

Question 5

What is propulsion?

Answer 5

movement of food

Question 6

What is peristalsis?

Answer 6

• propulsion that moves food forward
• adjacent segments of the alimentary canal (GI tract) relax and contract

Question 7

What is mechanical breakdown?

Answer 7

prepares food for chemical digestion
(ex. chewing, churning food in stomach, segmentation)

Question 8

What is segmentation?

Answer 8

• is rhythmic local constrictions of intestine
• mixes food with digestive juices

Question 9

What is digestion?

Answer 9

complex molecules broken down to chemical components

Question 10

What is absorption?

Answer 10

transport of digested nutrients

Question 11

What is defecation?

Answer 11

elimination of indigestible substances as feces

Question 12

Histology of the Alimentary Canal Wall

What four layers make up the alimentary canal wall (esophagus to anus)? Describe their location and components.

Answer 12

• mucosa: innermost layer; consists of epithelium, lamina propria, musclaris mucosae
• submucosa: external to the mucosa; consists of blood and lymphatic vessels, nerve fibers
• muscularis layer: external to submucosa; contains two layers: circular muscularis (inner layer) and longitudinal muscularis (outer layer)
• serosa: outermost layer; is the visceral peritoneum

Question 13

Smooth Muscle

What is smooth muscles?

What sheets is it grouped into?

Answer 13

• primarily found in walls of viscera
• fibers elongated
• have one, central nucleus
• grouped into sheets:
  -> longitudinal layer: parallel to long axis of organ
  -> circular layer: deeper layer, fibers run around circumference of organ

Question 14

Nerve Plexuses

Describe myenteric nerve plexus and submucosal nerve plexus. Describe where they lie and what their function is.

Describe the innervation of these nerve plexuses

Answer 14

• myenteric nerve plexus: lies between circular and longitudinal mucularis; control peristalsis and segmentation
• submucosal nerve plexus: lies in submucosa; signals glands to secrete
• innervation: sympathetic and parasympathetic motor fibers; visceral sensory fibers

Question 15

Pharynx

What are the different parts of the pharynx?

Generally describe the pharynx.

Answer 15

• nasopharynx, oropharynx, laryngopharynx
  -> passage for air and food
  -> lined with stratified squamous epithelium

Question 16

Esophagus

Describe the esophagus.

Gross anatomy: Where does the esophagus begin and end?

Microscopic anatomy: Describe the epithelium of the esophagus.

Answer 16

• is a muscular tube

Gross Anatomy

• begins as a continuation of the pharynx
• joins the stomach inferior to the diaphragm
  -> cardiac sphincter: closes lumen to prevent stomach acid from entering esophagus

Microscopic Anatomy

• epithelium is nonkeratinized stratified squamous epithelium
• mucous glands: primarily compound tubuloalveolar glands

Question 17

Stomach

What happens in the stomach?

How long does food remain in the stomach for?

Answer 17

• site where food is churned into chyme
• secretion of pepsin begins protein digestion (function under acidic conditions)
• food remains in stomach for approx. 4 hours

Question 18

Microscopic Anatomy of the Stomach

Describe the microscopic anatomy of the stomach.

(What are the three layers of the stomach?

What type of epithelium is in the stomach?

Describe the mucosa of the stomach.)

Name the gastric glands of the stomachs fundus and body and describe what they secrete.

Answer 18

• circular, longitudinal, and oblique layer
• simple columnar epithelium
• mucosa is dotted with gastric pits and gastric glands
• mucous neck cells: secrete special mucus
• parietal cells: secrete hydrochloric acid and gastric intrinsic factor
• chief cells: secrete molecules that digest proteins

Question 19

The Small Intestine - Gross Anatomy

Describe the small intestine

What are the different subdivisions of the small intestine?

Describe the innervation of the small intestine

Answer 19

• longest portion of alimentary canal (GI tract)
• site of most enzymatic digestion and absorption
• three subdivisions: duodenum; jejunum; ileum
• innervation: parasympathetic fibers from vagus nerve; sympathetic from thoracic splanchnic nerve

Question 20

Small Intestine - The Duodenum

Describe the duodenum

Answer 20

• receives digestive enzymes and bile
• main pancreatic ducts and common bile duct enter duodenum
  -> Spincter control entry of bile and pancreatic juices

Question 21

The Small Intestine - Microscopic Anatomy

Describe the different modifications for absorption of the small intestine

Answer 21

• circular folds: transverse ridges of mucosa and submucosa
• villi: fingerlike projections of mucosa; covers with simple columnar epithelium
• microvilli: further increase surface area for absorption

Question 22

Histology of the Intestinal Wall

Describe the histology of the intestinal wall

Answer 22

AEIG

• absorptive enterocytes: uptake digested nutrients
• enteroendocrine cells: secrete hormones like cholecystokinin (CCK); CCK aids in fat digestion
• intestinal crypts: epithelial cells secrete intestinal juice; contain stem cells that renew intestinal epithelium
• goblet cells: secrete mucus that lubricate chyme; allows chyme to travel down GI tract

Question 23

The Large Intestine

What parts is the large intestine subdivided into?

Describe the large intestine

What are the special features of the large intestine

Answer 23

• cecum, appendix, colon, rectum, anal canal
• digested residue contains few nutrients; small amount of digestion by bacteria
• main function: absorb water and electrolytes
• peristalsis forces feces toward rectum

Special Features of Large Intestine

• tenia coli: thickening of longitudinal muscularis externa
• haustra: puckering created by teniae coli

Question 24

The Liver

Describe the liver and its functions

What cells are found here?

Answer 24

• largest organ in the body

MDSS

• makes blood (plasma) proteins
• detoxifies posions
• smooth ER produces bile
• stores sugar
• hepatocyte: functional cell of liver
• stellate macrophages: destroy bacteria

Question 25

The Gallbladder

Describe the gall bladder – what does it do?

Answer 25

• stores and concentrates bile
  -> bile emulsifies fats
• expels bile into duodenum
• cholecystokinin: released from enteroendocrine cells in response to fatty chyme to break down fats and proteins

Question 26

The Pancreas

Describe the the endocrine and exocrine function

Answer 26

Endocrine

• produces insulin and glucagon
• regulates blood sugar

Exocrine

• produces most enzymes that digest food in the small intestine
• acinar cells: make, store, and secrete pancreatic enzymes
• main pancreatic duct: extends the length of pancreas and joins bile duct to empty pancreatic juices into the duodenum