LECTURE 25 - THE DIGESTIVE SYSTEM

what are the 4 tunics of the small intestine? know the histology of each tunic.

-tunica mucosa

• simple columnar epithelium —→ lines the lumen for absorption and mucous secretion

• lamina propria —→ underlying CT with blood capillaries and lacteals for absorption and nutrition

• muscularis mucosa —→ smooth muscle for movement within the mucosa

-tunica submucosa

• areolar tissue with elastin fibers —→ allows for expansion

• contains blood vessels, nerves, and lymphatics

-tunica muscularis

• smooth muscle layer for GI peristalsis

-tunica serous

• simple squamous epithelium (called mesothelium) and areolar CT

what are the 4 specialized substructures that we see within the small intestine? what are their functions?

-plicae: circular folds that increase surface area

-villi: fingerlike projections from tunica mucosa

-intestinal glands: secrete digestive enzymes/hormones

-goblet cells: secrete mucus to protect epithelial cells from being digested

what are the main functions of the large intestine?

function: site for absorption of water, vitamins and minerals; compacts wastes into feces

what materials are absorbed in the large intestine?

water, vitamins, and minerals

what sub-region of the large intestine is responsible for collecting and compacting material arriving from the ileum?

• what valve separates this structure from the ileum?

• what organ is attached to this region?

-The Cecum

-ileocecal valve

-appendix

what is the taenia coil? what pouch-like structure does the taenia coil help form?

• what is the histology of the taenia coil?

taenia coli = external strips of longitudinal smooth muscle forming pouches called haustra

-histology: smooth muscle

where is the liver located? what ligaments are associated with the liver?

-location: right side, superior portion of the abdominal cavity

-associated ligaments:

• falciform ligament: anchors liver to diaphragm

• round ligament: former umbilical vein; extends from liver to navel

be able to identify the lobes of the liver, the bile ducts, and the gall bladder. 

• where is each bile duct carrying bile to/from

-lobes of the liver:

• right (largest)

• left

• cuadate

• quadrate

-the bile ducts

• cystic duct

• hepatic duct

• common bile duct

-gall bladder

• receives bile via hepatic and cystic ducts

• reservoir for bile produced in in liver

• drains via the cystic and common bile ducts into duodenum

what are the functions of the liver? what does the liver produce? what is the function of this secretion?

-functions:

• bile production for fat digestion

• storage of some fat, fat-soluable vitamins, and iron

• removal and storage of glucose received via portal circulation

• conversion of carbohydrates to fat

what is the function of the gall bladder?

to store the bile produced by the liver

know the pathway of bile from the liver and gallbladder to the duodenum.

• produced by the liver —→

• hepatic duct —→

• cystic duct —→

• gall bladder (for storage)* —→

• cystic duct* —→

• common bile duct —→

• duodenum

* = when bile is being stored

what are the digestive functions of the pancreas? what hormones does the pancreas secrete?

-functions:

• digestive functions:

  • exocrine secretion of digestive enzymes

• endocrine functions:

  • produces and secretes the hormones insulin, somatostatin, gastrin, and glucagon

where is the pancreas located in the body

location: attached to inner curvature of the duodenum; retroperitoneal

what are the 5 digestive processes? be able to define each. 

• where are carbs, fats, proteins, digested? where are they absorbed?

1. ingestion

2. mastication

   • mechanical breakdown by teeth and tongue

3. digestion

   • molecular breakdown of carbs and proteins

     • by enzymes from salivary glands, stomach, pancreas, and duodenum

   • molecular breakdown of fats

     • by enzymes from pancreas and bile from liver

4. absorption

   • transported into the capillaries of the small intestine

     • sugars from carbohydrates

     • amino acids from proteins

   • transported into the lacteals of the small intestine

     • fatty products

5. egestion

   • elimination of fiber, non-digestible foodstuffs, sloughed intestinal cells, and bacteria