Pathophysiology and physiology of GI tract Flashcards
The GI tract has three main functions. Name these.
- Digestion (large insoluble food molecules -> small water-soluble food molecules).
- Absorption (products of digestion and other small molecules are transported into the epithelial cells that line the GI tract).
- Elimination
Name characteristics of carbohydrates.
- Polymer, made from monosaccharides
- Monosaccharides are linked together to form di- or polysaccharides.
Name characteristics of proteins.
- Consists of one or more polypeptides (i.e. chain of amino acids).
- Unique shape enables proteins to perform various tasks in the body.
- Essential amino acids -> must be consumed through food.
Name characteristics of fat.
- Class of nutrients known as lipids (triglycerides, phospholipids, sterol).
- Energy sources and stored for energy
- Essential fatty acids: linolenic acid (omega-3) and linoleic acid (omega-6).
Name organs of the GI tract.
- Mouth
- Esophagus
- Stomach
- Pancreas
- Liver
- Bile tract
- Small intestine
- Colon
Name characteristics of the mouth/oropharynx
- Chewing and mixing food with saliva.
- Salivary glands (parotid, submandibular, and sublingual glands) that produce saliva.
- Saliva function: dilute, taste, protection.
- Tongue function: swallow bolus
What is peristalsis and what are sphincter contractions?
- Peristalsis is when circular and longitudinal muscles contract to transport the bolus from the esophagus to the stomach.
- Sphincter contractions is the contraction of muscles that are located in the esophagus, pylorus (stomach), ileocecal valve, rectal muscle that regulate how much food is directed through.
In the esophagus, the bolus (i.e. food) is transported to the stomach via peristalsis of the muscles of the esophagus. These muscles consist of circular and longitudinal muscles. Choose whether these muscles are located in the inner- or outer layer of the esophagus.
- Inner layer -> circular muscles
- Outer layer -> longitudinal muscles
The stomach consists of four parts. Name these and think of what function is associated with these parts.
- Fundus (upper part), corpus (middle part), antrum (lower part), pylorus (connection between duodenum and stomach).
- The upper(/proximal) part is important for storage.
- The lower(/distal) part is important for grinding and mixing of the good.
- The pylorus is responsible for the gradual release of food via the pylorus to the small intestine.
The stomach contains gastric juices with molecules and hormones that are important for digestion. Name these.
- Gastrin: stimulates secretion of gastric acid (HCl).
- Gastric acid: inactivates amylase (from saliva) and kills bacteria.
- Pepsinogen: important for protein digestion.
- Intrinsic Factor (IF): produced by parietal cells, absorption of B12 only possible after interaction with IF.
- Ghrelin, leptin: regulation of appetite.
Describe the negative feedback loop of the stomach when food enters the stomach.
- Food in the stomach causes the cells of the stomach wall to release gastrin.
- Gastrin stimulates the production of gastric acid.
- Stomach pH drops down to 1.5 pH.
- Acidity in the stomach causes the cells of the stomach wall to stop releasing gastrin.
What cells in the small intestine are responsible for absorption?
Villi and micro villi
The small intestine consists of the duodenum, jejunum and ileum. Name characteristics of these parts of the small intestine.
- Duodenum: smallest (25-30cm), contains bile duct and pancreatic duct, absorption of minerals (Na, K, Fe, Ca, Mg, Zn, PO4 3-, etc.)
- Jejunum: 2-2.5 m, absorption of proteins, fats, carbohydrates, vit. C, vit. ADEK,, vit. B.
- Ileum: 3-3.5m, (re)absorption fluids, absorption B12, bile salts, other nutrients left.
Name characteristics of the pancreas.
- Contains head, body, tail.
- Positioned behind the stomach and part of the duodenum.
- Contains endocrine (secretion into blood) and exocrine tissue (secretion through ducts).
Name functions/characteristics of the endocrine and exocrine tissues of the pancreas.
Endocrine tissue:
* Islets of Langerhans
* Production of glucagon, insulin and somatostatin, responsible for glucose regulation.
Exocrine tissue:
* Production of pancreatic juice (enzymes such as trypsinogen, elastase, lipase, amylase, carboxypeptidase)
* Production/secretion of bicarbonate ions that neutralize stomach acid, in turn activating enzymes
Name the four functions of the liver.
- Metabolism, synthesis of amino acids and proteins, production of triglycerides and LDL and HDL.
- Detoxification, breakdown of red blood cells and medications.
- Generation and secretion of e.g. clotting factor, bile, enzymes.
- Storage of vitamins, zinc, copper, glycogen, blood.
Bile:
* What does it contain?
* Where is it stored?
* How is it regulated/activated?
- It contains: bile salts, cholesterol, phospholipids, waste products
- Stored in the gallbladder
- Taste and smell activate CCK, which stimulates the gallbladder to contract and release bile. But also when fatty foods enter the duodenum.
Why can bile salts act as an emulsifier?
Bile salts act as an emulsifier because they have a hydrophilic head that is attracted to water molecules and a hydrophobic tail that is attracted to lipid molecules.
What is meant with enterohepatic circulation?
Enterohepatic circulation refers to the circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver.
