GI Anatomy Flashcards
GI system: Structure
- 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
GI system: Function
- Functions
– Provide nutrients for the body with propulsive and mixing movements
– Secretion of digestive juices
– Absorption of nutrients
Esophagus: Structure
- 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
Esophagus: function
transports food
Function of upper esophageal sphincter
- The upper esophageal sphincter prevents food and fluids from being aspirated into the lungs
Function of lower esophageal sphincter
- 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
Stomach: Structure
- 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
Stomach: functions
-Stores and chums food
-Pepsin digests protein
-HCL activates enzymes, breaks up food, kills germs
-Mucus protects stomach wall
-Limited absoprtion
Layers of the Stomach
- 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
G-cells
– Produce gastrin, a hormone that facilitates production of HCL
Parietal cells
– Produce Hydrochloric acid (HCl) to help break down food
– Produce Intrinsic factor (IF) to protect mucosa
Chief cells
– Secrete pepsin
Epithelial cells
– Secrete bicarbonate-rich solution to coat and protect mucosa
Small Intestine: Structure
- Approximately 5-6 meters long
- Duodenum
– First 22 cm - Jejunum
– Next 2 meters - Ileum
– Forms the remainder
Small intestine: function
-Completes digestion
-Mucus protects gut wall
-Absorbs nutrients, most water
-Peptidase digests proteins
-Sucrase digests sugars
-Amylase digests polysaccharides
The small intestine entire inner wall has circular folds of a mucous membrane called
plicae circulares
The plicae circulares are permanent ridges that contain millions of fingerlike projections called
intestinal villi
Each villus has its own microscopic projections called
microvilli
The combined effect of circular folds, villi, and microvilli increases the surface area for digestion by
x600
Crypts of Lieberkühn
– Intestinal glands that secrete about 2 L of fluid/day into lumen of intestine
– Fluid quickly reabsorbed by villi
Goblet cells and Brunner glands
– Secrete large amounts of mucus to protect small intestine from damage of acidic gastric juices
T/F small intestine cells have a slow turnover
False: Small intestine cells have a rapid turnover (48- 72 hours), one of the fastest turnover rates in the body
The area where food passes from the small into the large intestine
ileocecal sphincter
Distention of terminal ileum causes
relaxation to allow contents to enter large intestine
Distention of cecum prevents
reflux back into ileum
Large intestine: Structure
- 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
Large intestine: function
-Reabsorbs some water and ions
-Forms and stores feces
Does the large intestine have villi or digestive enzymes?
The mucosa of the large intestine does not have villi and does not produce digestive enzymes
Cells of the large intestine (3)
- 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
Motility is due to:
contraction of 2 layers of smooth muscle (longitudinal and circular)
Two types of GI motility:
– Propulsive (peristalsis)
– Mixing (segmental)
GI motility is regulated by
the enteric nervous system, autonomic nervous system, and hormones
Function of Rectum
Stores and expels feces
