GI and Hepatics Flashcards
Retroperitoneal Organs (GI Tract)
Esophagus Some of the duodenum Ascending and descending colon, Pancreas (except for tail end) Rectum
Histological organization of the digestive tract
Mucosa
Submucosa
Muscularis externa
Serosa
Mucosa of digestive tract
- Stratisfied squamous (oral cavity, pharynx, esophagus, anal canal)
- Areolar connective tissue
- Muscularis mucosae (internal circular and external longitudinal smooth muscles)
Submucosa of digestive tract
Dense, irregular connective tissue with many blood and lymph vessels; some with submucosal glands
Muscularis externa of digestive tract
Layer of smooth muscles; circular on the inside and longitudinal on the outside.
Myenteric plexus lies between to too smooth muscle layers.
Serosa of digestive tract
Loose connective tissue with blood and lymphatic vessels. Adventitia connects digestive tract to surrounding structrues.
Movement of digestive materials through GI tract
- Peristalsis (contractions of circular smooth muscle layer followed by contractions of longitudinal smooth muscle layer)
- Segmentation (churning and fragmentation to mix bolus with intestinal secretion)
Histology of the Esophagus
Nonkeratinized, stratisfied squamous epithelium
Upper 1/3 is skeletal, middle 1/3 is skeletal and smooth, lower 1/3 is smooth muscle.
Histology and anatomy of the Stomach
Simple columnar epithelium
Rugae - folds within to allow for expansion
Gastric pits and glands (mucus and gastrin production)
Histology of Small Intestines
Simple columnar epithelium
Circular folds with microvilli increases surface area for 90% of reabsorption of nutrients (brush borders)
Lacteals absorbs materials not able to enter capillaries
Anatomy of Large Intestines
Large diameter but thinner walls than small intestines.
Abundant in goblet cells to produce mucus which houses intestinal bacteria.
Gastric glands and their secretions
- Parietal cells (intrinsic factor and H+/Cl- via ATPase and alkaline tide respectively)
- G-cells (gastrin; stimulates parietal and chief cell secretion, and motility)
- Chief cells (pepsinogen which is converted to the enzyme pepsin for protein digestion)
- D cells (somatostatin; opposes gastrin)
- P/D1 cells (ghrelin - inducing hunger; antagonist to leptin)
Sections of the small intestines
Duodenum, jejunum and ileum
Function of the Duodenum
Receives chyme and neutralizes acids
Absorption of nutrients
Receives secretion from gallbladder and pancreas
Produce hormones
Hormones secreted in the duodenum
- Gastrin - G cells (increase gastric motility and acids/enzymes)
- Secretin - cells in small intestines (increase buffer secretion by pancreas and bile from by liver; reduces motility and secretory rates)
- Cholecystokinin - cells in the duodenum and jejunum (stimulates gallbladder contraction to release bile and pancreatic enzymes)
- Gastric inhibitory peptide
- Vasoactive intestinal peptide (stimulates secretion of intestinal glands, dilates regional capillaries, inhibits gastric acid production)
- Enterocrinin (alkaline mucus production)
Function of the Jejunum
Majority of absorption is in the duodenum and jejunum
Function of the Ileum
Absorbs bile salt and vitamin B12
Ileocecal valve controls chyme entering the cecum / large intestines
Anatomy and division of Large Intestines
- Cecum (begin compaction of chyme)
- Ascending, transverse, descending, sigmoid (H20 reabsorption, propelling chyme through to anus and producing Vitamin K and B5 and biotin)
- Rectum (stores feces, stretch receptors stimulation induces defecation)
Function of the Pancreas
- Endocrine - pancreatic acini; simple cuboidal
- – secretes H20, bicarbonate and phosphate buffer to neutralize acidic chyme (stimulated by secretin)
- – secretes digestive enzymes (stimulated by cholecystokinin) - Exocrine - islet of Langerhans
- – alpha cells - glucagon (breakdown of glycogen)
- – beta cells - insulin (build glycogen, metabolize glucose into fat storage or ATP synthesis)
Anatomy of Liver
Upper right quadrant
Right and left lobe separated by falciform ligament
Blood supply of Liver
Portal vein and hepatic artery enters the portal triad.
Histology of Liver
Consist of hepatic lobules (basic functional unit)
Hepatocytes line the lobules like spokes on a wheel
Sinusoids runs between lines of hepatocytes to central vein.
Role of Liver
- Metabolic regulation: carbohydrates, lipid, amino acid, waste removal, vitamin storage (A, D, E, K, B12), mineral storage, drug inactivation)
- Hematologic regulation: phagocytosis and antigen presentation, synthesis of plasma proteins (albumin), removal of circulating hormones, antibodies and toxins
- Bile production: by hepatic cells into bile salts via cholesterol, digests lipids
Biliary system and its digestive function
Helps in lipid digestion through emulsification or breakdown of fat droplets by bile salts which then promotes lipid absorption through the intestinal epithelium.
Bile / bile salts are produced in the liver and stored in the gallbladder.
