Lecture #13 - Digestive System Flashcards
What is the alimentary canal also known as?*
GI tract
(mouth to anus)
The Peritoneal Cavity and Peritoneum
Define the peritoneum.
What are the different types of peritoneum? Define them.
What is the peritoneal cavity?
- 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)
The Peritoneal Cavity and Peritoneum
What is the mesentery?
What are the functions of the mesentery?
- mesentery: a double layer of peritoneum
- holds organs in place
- sites of fat storage
- provides a route for circulatory vessels and nerves
What is ingestion?
occurs in the mouth
What is propulsion?
movement of food
What is peristalsis?
- propulsion that moves food forward
- adjacent segments of the alimentary canal (GI tract) relax and contract
What is mechanical breakdown?
prepares food for chemical digestion
(ex. chewing, churning food in stomach, segmentation)
What is segmentation?
- is rhythmic local constrictions of intestine
- mixes food with digestive juices
What is digestion?
complex molecules broken down to chemical components
What is absorption?
transport of digested nutrients
What is defecation?
elimination of indigestible substances as feces
Histology of the Alimentary Canal Wall
What four layers make up the alimentary canal wall (esophagus to anus)? Describe their location and components.
- 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
Smooth Muscle
What is smooth muscles?
What sheets is it grouped into?
- 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
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
- 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
Pharynx
What are the different parts of the pharynx?
Generally describe the pharynx.
- nasopharynx, oropharynx, laryngopharynx
-> passage for air and food
-> lined with stratified squamous epithelium
Esophagus
Describe the esophagus.
Gross anatomy: Where does the esophagus begin and end?
Microscopic anatomy: Describe the epithelium of the esophagus.
- 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
Stomach
What happens in the stomach?
How long does food remain in the stomach for?
- 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
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.
- 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
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
- 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
Small Intestine - The Duodenum
Describe the duodenum
- receives digestive enzymes and bile
- main pancreatic ducts and common bile duct enter duodenum
-> Spincter control entry of bile and pancreatic juices
The Small Intestine - Microscopic Anatomy
Describe the different modifications for absorption of the small intestine
- 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
Histology of the Intestinal Wall
Describe the histology of the intestinal wall
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
The Large Intestine
What parts is the large intestine subdivided into?
Describe the large intestine
What are the special features of the large intestine
- 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
The Liver
Describe the liver and its functions
What cells are found here?
- 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
The Gallbladder
Describe the gall bladder – what does it do?
- 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
The Pancreas
Describe the the endocrine and exocrine function
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
