Anatomy and Histology

1. Rectum: short, dilated, terminal portion of the large intestine.

2. Very rich in goblet cells

3. Anal canal: stratified squamous epithelium. 2‐3cm. Surrounded by voluntary muscle (anal sphincter). Stratified squamous epithelium transitions to skin containing sebaceous glands and large apocrine sweat glands 

Wikipedia:

Rectum:
Der Mastdarm, eingedeutscht Rektum, Adjektiv rektal) ist ein Teil des Enddarms und damit des Dickdarms und dient der Zwischenspeicherung des Kots, d. h. der unverdaulichen und unverträglichen Nahrungsreste.

1. Retroperitoneal

2. Anal canal is inferior to the rectum

3. Transition from mucosal epithelium to stratified squamous non‐keratinized epithelium

4. Blood vessels in the lamina propria and submucosa may become distended = haemorrhoids 

1. Development: glandular outgrowth of the primitive foregut

2. Location: Upper right quadrant (right hypochondrium, and epigastric)

3. Form: largest visceral organ (~1.4kg), two surfaces

4. Diaphragmatic surface = anterior, posterior, superior

5. Visceral surface = inferior, covered by visceral peritoneum 

• Essential for survival
• Supports all other organs
• Only organ that can regenerate (Prometheus)
• Multifunctional, giant gland 
• Fat Metabolism -> oxidising triglycerides, synthesis of plasma lipoproteins, synthesis of cholesterol and phospholipid
• Carbohydrate Metabolism -> Conversion of carbohydrates into fatty acids and triglycerides, regulation of blood glucose by glycogenesis, glycogenolysis, glyconeogenesis
• Protein Metabolism -> synthesis of plasma proteins (albumin, coagulants), synthesis of non-essential amino acids, detoxification or metabolic waste (ammonia)
• Storage -> glycogen, vitamins A, D, K, B12, iron, copper
• Intermediary metabolism -> detoxification of drugs and toxins (e.g. alcohol, pharmaceuticals, industrial chemicals)
• Secretion -> bile for lipid emulsification and digestion, hormones (IGF, thrombopoietin, angiotensin) 

•  Acinus: berry-shaped unity of the liver parenchyma centred on a portal tract. Lies between two or more terminal hepatic venules and blood flows from the portal tract through the sinusoids to the venules.

•  Three zones:

  •  Zone 1: periportal, i.e. closest to portal triad, well oxygenated, oxidative enzymes, gluconeogenesis, fatty acid oxidation, cholesterol synthesis

  •  Zone 2: transition

  •  Zone 3: centrilobular i.e. closest to centrilobular venule, poorly oxygenated, reductive enzymes, e.g. glycolysis, lipolysis, cytochrome P450. least oxygenated. 

Bilirubin from hemoglobin metabolism ‐> excess = jaundice (yellow discoloration of the tissues due to increased levels of bilirubin and associated deposition of bile pigments) 

1. Function: receives, concentrates and stores bile produced by the liver

2. Bile, or gall aids lipid digestion

3. 92% water, 6% bile salts, 0.3% bilirubin, 0.9- 2.4% fats

4. Excreted from hepatocytes into bile canaliculi, a network of canals between hepatocytes in the liver

5. Drain into interlobular bile ducts (bile ductules) -> hepatic duct -> common bile duct 

1. Small organ where the bile produced by the liver is stored and concentrated before its release into the small intestine.

2. Location: visceral surface of the right lobe of the liver, in a fossa between the right and quadrate lobes

3. Form: muscular pear‐shaped sack with three parts, fundus (rounded end), body, neck

4. 70‐100 mL volume

5. Feed by a branch of the right hepatic artery

6. Cystic duct branches off the common duct to the gallbladder for storage

7. Ducts lined with cuboid/columnar epithelium

8. Hollow organ 

1. Histologically similar to the rest of the GIT, except NO submucosal muscle

2. Muscular sac lined by simple columnar epithelium with mucous glands in the neck submucosa

3. Microvilli increase surface area for water reabsorption, and thus concentration of bile

4. Lamina propria + epithelium = mucosa

5. Submucosa is a thin layer of loose elastic connective tissue with smaller blood vessels, lymphatics. In the neck of the gallbladder mucus secreting glands

6. Muscular layer: Muscle fibers lie in longitudinal, oblique and transverse directions, NOT arranged in separate layers

7. Serosa is dense irregular connective tissue, continuous with the peritoneum 

Gallengangöffnung

1. Combines with the major pancreatic duct, feeding into the duodenum

2. Thus, bile and lipases are combined before injection into the small intestine

3. Sphincter oddi 

die Bauchspeicheldrüse

1. Pancreas: lobulated gland covered by a thin collagenous capsule which extends as a delicate septa between the lobules.

2. Location: posterior to the stomach, sits in the duodenal curvature, (secondary) retroperitoneal

3. Form: elongated, slender, pink, lumpy, with a head (sits in the duodenal curvature), neck, body and tail, ca. 80g, 20‐25 cm in length

4. Tail, body, neck, and head

5. Function: exocrine and endocrine gland 

Eine exokrine Drüse (exokrin „nach außen abgebend“) ist eine Drüse, die ihr Sekret an eine innere oder äußere Körperoberfläche abgibt.

1. Tubuloacinar Exocrine gland makes up the bulk (ca. 99%) of the organ

2. Acinus made up of an irregular cluster of pyramid‐shaped secretory cells.

3. Adjacent acini separated by supporting tissue with numerous capillaries.

4. Secretes 1.5‐2 L d‐1 of an enzyme‐rich alkaline “digestive juice” into the duodenum

5. High HCO3‐ neutralises acid

6. Luminal digestion = pancreatic enzymes breakdown proteins, carbohydrates, lipids and nucleic acids

7. Duodenal neuroendocrine cells release secretin which stimulates pancreatic secretions

8. Pancreas also richly innervated by ANS 

1. Endocrine gland constitutes ca. 1‐2%

2. Endocrine cells are found in scattered groups, islets of Langerhans

3. Ca. 1‐2 million islets

4. Islets are well vascularised (fenestrated capillaries) for delivery of hormones into blood

5. Primarily four cell types α‐, β‐, δ‐, and F or PP‐cells

6. α‐cells secrete glucagon, increasing glycogen breakdown and liver glucose release, raising blood sugar

7. β‐cells secrete insulin, increasing glucose uptake and utilization, lowering blood glucose

8. δ‐cells secrete somatostatin, inhibits glucagon and insulin, slowing food absorption

9. F or PP‐cells secrete pancreatic polypeptide, inhibiting gallbladder and some

   pancreatic enzyme production, controlling nutrient absorption