Chp 25 cont’d

The small intestine is divided into three parts:

The small intestine maximizes surface area for digestion and absorption through several structural adaptations:

Epithelium: Features simple columnar cells with microvilli.
Microvilli: Tiny cellular extensions that increase surface area; collectively referred to as the brush border.
- Brush border enzymes are present, aiding in enzymatic digestion.
Villi and Crypts: Folds in the intestinal lining.
- Villi are finger-like projections that increase surface area.
- Crypts are invaginations between villi that contain stem cells and glands.
Plica Circulars (Circular Folds): Large folds visible to the naked eye, similar to rugae in the stomach.

Chyme: The acidic, nutrient-rich mixture entering the duodenum from the stomach.
Brunner's Glands: Found in the submucosa of the duodenum; secrete a high-pH alkaline solution to protect against acidic chyme.
Pancreatic Secretions: The pancreas secretes a high-pH bicarbonate solution to neutralize chyme.

Duodenum: Contains Brunner's glands in the submucosa.
Jejunum: Characterized by very large villi and an absence of glands in the submucosa.
Ileum: Contains Peyer's patches (aggregates of lymphatic tissue) in the submucosa for protection against waste material.

Duodenum: Villi and crypts present with epithelial tissue (Brunner's glands) in the submucosa.
Jejunum: Villi and crypts present with connective tissue in the submucosa; villi are much larger.
Ileum: Villi and crypts present with lymphatic tissue (Peyer's patches) in the submucosa.

Ileocecal Valve: A one-way valve that prevents fecal matter from backing up into the ileum.

Cecum: The pouch-like beginning of the large intestine.
- Appendix: Attached to the cecum; harbors beneficial bacteria and has some lymphatic roles.
Ascending Colon, Transverse Colon, Descending Colon, Sigmoid Colon, Rectum, and Anus

Absorption: Primarily absorbs water and electrolytes; less surface area is needed compared to the small intestine.
Epithelium: Simple columnar epithelium with crypts and numerous goblet cells (no villi).
Goblet Cells: Secrete mucus to lubricate the intestinal lining and reduce friction, especially as fecal matter hardens.
Gut Bacteria: Produce vitamins that are reclaimed by the large intestine.

Transition to Stratified Squamous Epithelium: Occurs as the canal approaches the anus.
Internal Anal Sphincter: Involuntary smooth muscle that keeps the anus closed.
External Anal Sphincter: Voluntary skeletal muscle that allows for voluntary release of fecal matter.

Location: Retroperitoneal, below the stomach.
Endocrine Function: Secretes hormones into the bloodstream for blood sugar homeostasis.
- Insulin: Lowers blood sugar by facilitating glucose uptake by cells.
- Glucagon: Raises blood sugar by stimulating the breakdown of glycogen in the liver.
  $Type II Diabetes:$
- Type II diabetes is developed due to hormone receptors not liking to be bothered too much. If receptors are constantly stimulated from excess sugar it becomes desensitized and removed, which leads to insulin resistance.
Exocrine Function: Secretes digestive enzymes and a high-pH bicarbonate buffer into the duodenum.
- Acinar Cells: Cells that secrete digestive enzymes.
- Pancreatic Duct: Transports secretions directly into the duodenum.

Liver Functions: Over 200 known functions, including:
- Lymphatic role: Blood recycling and surveillance for pathogens.
- Blood storage: Can store blood in case of shock.
- Nutrient regulation: Regulates nutrients from blood.
- Bile production: Bile is injected into the duodenum.
Hepatic Portal System: Transports blood from the stomach, small and large intestines, pancreas, and spleen to the liver.
Liver Lobule: The functional unit of the liver, with a hexagonal structure.
- Central Vein: Located in the center of the lobule.
- Portal Triad: Located at each corner of the lobule; consists of a branch of the hepatic artery, a branch of the hepatic portal vein, and a bile duct branch.
- Hepatocytes: Cells within the liver lobule that perform liver functions.
- Liver Sinusoids: Sinusoidal capillaries that allow for massive fluid and cell exchange.
Hepatic Vein: Drains blood from the central veins into the inferior vena cava.

Bile: Produced by the liver; stored in the gallbladder.
- Function: Aids in the digestion and absorption of fats, excretes waste products.
Gallbladder: Stores and concentrates bile.
- Cystic Duct: Connects the gallbladder to the common bile duct.
Common Bile Duct: Carries bile to the duodenum.
Hepatopancreatic Sphincter (Sphincter of Oddi): Controls the secretion of pancreatic juices and bile into the duodenum.