GI Tract Circulation and Histology

Study Notes

The abdomen is part of the trunk, bordered by the diaphragm, musculo-aponeurotic walls, pelvic inlet, and vertebrae.
The abdominal cavity contains the alimentary canal and accessory organs.

Alimentary Canal: Lower esophageal sphincter, stomach, small intestine (duodenum, jejunum, ileum), and large intestine (cecum, ascending colon, transverse colon, descending colon).
Accessory Organs: Liver, gallbladder, pancreas, spleen, kidneys, and peritoneal structures including vessels and nerves.

Peritoneum: A transparent, thin membrane lining the abdominopelvic cavity, continuous with serosa of organs.
Parietal Peritoneum: Lines body walls, well-localized pain, sensitive to various stimuli.
Visceral Peritoneum: Covers visceral organs, less localized pain, important in sensing ischemia and inflammation.
Major folds include mesenteries and omenta, aiding in positioning and vascularity of abdominal structures.

Greater Omentum: A large apron-like fold extending from the stomach to the abdominal wall, rich in fat and lymph nodes, mobilizes to wrap around inflamed organs.
Lesser Omentum: Connects the liver to the stomach and duodenum; contains important vascular structures like the hepatic artery, bile duct, and portal vein.
Mesentery: Connects the small intestine to the posterior abdominal wall, housing vessels and nerves.
Mesocolon: Similar function for the large intestine.

Retroperitoneal structures: Parts of the duodenum, pancreas, kidneys, adrenal glands, and major blood vessels are not fully surrounded by peritoneum.
Clinical relevance of peritoneal sacs: The omental bursa is a common area for surgical access.

Celiac Trunk: Supplies the foregut (liver, stomach, pancreas, and spleen).
Superior Mesenteric Artery: Supplies midgut structures, including the small intestine and parts of the large intestine.
Inferior Mesenteric Artery: Supplies hindgut structures and the superior anus.

Portal circulation carries nutrient-rich blood from the digestive organs to the liver.
Hepatic portal vein formed by the splenic and superior mesenteric veins, important for detoxifying blood.

Four main layers:
- Mucosa: Involved in absorption and secretion; lined with epithelial cells.
- Submucosa: Contains blood vessels and nerves.
- Muscularis: Smooth muscle for propulsion and movement.
- Serosa/Adventitia: Connective tissue providing structure.

Esophagus: Non-keratinized stratified squamous epithelium, with areas of mucous-secreting glands and muscular transitions.
Stomach: Simple columnar epithelium with glands for acid secretion, featuring a unique three-layer muscularis.
Small Intestine: Highly folded mucosa (plicae circulares, villi, microvilli) optimized for absorption, with Peyer's patches in the ileum.
Large Intestine: Simple columnar epithelium, with a greater number of goblet cells and unique teniae coli, reflecting its function in water absorption and defecation.

Found throughout the GI tract, particularly in the stomach and small intestine, these cells produce hormones crucial for digestion and regulatory functions.
Types of hormones produced include gastrin, CCK, secretin, and others, each with specific stimuli and functions related to digestion and metabolism.

The peritoneal membrane covers a surface area similar to skin but contains minimal peritoneal fluid, facilitating absorption through venous pores and lymphatic capillaries.
Ascites refers to the abnormal accumulation of fluid in the peritoneal cavity, often due to inflammation or disease.

Understanding the morphological and functional aspects of the GI tract and its supporting structures is crucial for clinical applications, especially in surgery and digestive health.