GI Anatomy

Question 1

GI system: Structure

Answer 1

• Structure:
  – Consists of the GI tract and the related solid organs of digestion
  – 7 continuous meters from mouth to anus
  – Begins to form as early as 4th week of gestation

Question 2

GI system: Function

Answer 2

• Functions
  – Provide nutrients for the body with propulsive and mixing movements
  – Secretion of digestive juices
  – Absorption of nutrients

Question 3

Esophagus: Structure

Answer 3

• Tube-shaped muscular conduit for food and fluids
• Connects the throat to the stomach
• Movement of food is facilitated by:
  – Secretion of mucus
  – Very strong muscle movement to propel food towards the stomach

Question 4

Esophagus: function

Answer 4

transports food

Question 5

Function of upper esophageal sphincter

Answer 5

• The upper esophageal sphincter prevents food and fluids from being aspirated into the lungs

Question 6

Function of lower esophageal sphincter

Answer 6

• The lower esophageal sphincter (LES)
  – AKA Cardiac Sphincter
  – Separates the esophagus from the stomach
  – Prevents acidic contents of the stomach from entering back into the esophagus

Question 7

Stomach: Structure

Answer 7

• Elastic reservoir for food, mixing, and initial digestion of proteins
• Normal capacity is 1000-1500 ml
• Lined with columnar epithelium containing
  millions of gastric glands
• These glands contain special cells that secrete HCl, intrinsic factor, and gastrin

Question 8

Stomach: functions

Answer 8

-Stores and chums food
-Pepsin digests protein
-HCL activates enzymes, breaks up food, kills germs
-Mucus protects stomach wall
-Limited absoprtion

Question 9

Layers of the Stomach

Answer 9

• Mucosa layer
  – Inner layer made up of special cells: G-cells, parietal, chief, and epithelial cells
  – Also contains blood vessels
• Two muscle layers
  – Help propel food from stomach to small intestine
• Serosa
  – Outer layer
  – Acts as covering for inner layers

Question 10

G-cells

Answer 10

– Produce gastrin, a hormone that facilitates production of HCL

Question 11

Parietal cells

Answer 11

– Produce Hydrochloric acid (HCl) to help break down food
– Produce Intrinsic factor (IF) to protect mucosa

Question 12

Chief cells

Answer 12

– Secrete pepsin

Question 13

Epithelial cells

Answer 13

– Secrete bicarbonate-rich solution to coat and protect mucosa

Question 14

Small Intestine: Structure

Answer 14

• Approximately 5-6 meters long
• Duodenum
  – First 22 cm
• Jejunum
  – Next 2 meters
• Ileum
  – Forms the remainder

Question 15

Small intestine: function

Answer 15

-Completes digestion
-Mucus protects gut wall
-Absorbs nutrients, most water
-Peptidase digests proteins
-Sucrase digests sugars
-Amylase digests polysaccharides

Question 16

The small intestine entire inner wall has circular folds of a mucous membrane called

Answer 16

plicae circulares

Question 17

The plicae circulares are permanent ridges that contain millions of fingerlike projections called

Answer 17

intestinal villi

Question 18

Each villus has its own microscopic projections called

Answer 18

microvilli

Question 19

The combined effect of circular folds, villi, and microvilli increases the surface area for digestion by

Answer 19

x600

Question 20

Crypts of Lieberkühn

Answer 20

– Intestinal glands that secrete about 2 L of fluid/day into lumen of intestine
– Fluid quickly reabsorbed by villi

Question 21

Goblet cells and Brunner glands

Answer 21

– Secrete large amounts of mucus to protect small intestine from damage of acidic gastric juices

Question 22

T/F small intestine cells have a slow turnover

Answer 22

False: Small intestine cells have a rapid turnover (48- 72 hours), one of the fastest turnover rates in the body

Question 23

The area where food passes from the small into the large intestine

Answer 23

ileocecal sphincter

Question 24

Distention of terminal ileum causes

Answer 24

relaxation to allow contents to enter large intestine

Question 25

Distention of cecum prevents

Answer 25

reflux back into ileum

Question 26

Large intestine: Structure

Answer 26

• 1.5 meters long; muscular tube that forms a frame around the small intestine
• 6.5 cm in diameter (greater than the diameter of the small intestine, hence its name)
• Includes the appendix, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum

Question 27

Large intestine: function

Answer 27

-Reabsorbs some water and ions
-Forms and stores feces

Question 28

Does the large intestine have villi or digestive enzymes?

Answer 28

The mucosa of the large intestine does not have villi and does not produce digestive enzymes

Question 29

Cells of the large intestine (3)

Answer 29

• Absorptive cells absorb water and electrolytes
• Goblet cells produce mucous
• Endocrine cells are present and produce hormones, but their function is not really understood
• The turnover of large intestine cells is 3-8 days

Question 30

Motility is due to:

Answer 30

contraction of 2 layers of smooth muscle (longitudinal and circular)

Question 31

Two types of GI motility:

Answer 31

– Propulsive (peristalsis)
– Mixing (segmental)

Question 32

GI motility is regulated by

Answer 32

the enteric nervous system, autonomic nervous system, and hormones

Question 33

Function of Rectum

Answer 33

Stores and expels feces