Ganong 24e chapter 25 - Overview of GIT (1) Flashcards
Is saliva more alkaline or more acidic than plasma? Why is this useful?
Saliva is more alkaline than plasma. This helps to neutralize any gastric acid reflux in the oesophagus.
Name 4 components of saliva and briefly explain their usefulness.
Amylase - digests starch.
IgA and lysozyme - kills bacteria
Mucin - lubricates the bolus
Name two secretory cells of the gastric wall glands, and state what they secrete.
Chief cells - Pepsinogen and Gastric lipase
Parietal cells - Hydrochloric acid and Intrinsic Factor
What is Gastrin? Where does it come from?
Gastrin is a hormone produced by G cells in the antrum of the stomach. Gastrin stimulates Parietal cells to secrete their secretions (intrinsic factor and HCl). Gastrin also stimulates other cells of the stomach, and stimulates growth of the mucosa of the stomach and intestines.
Name three ways that Parietal cells can be stimulated to start secreting.
Gastrin (from G-cells), Histamine (from neighbouring enterochromaffin-like cells), and ACh (from enteric nerve endings and the Vagus nerve). All three bind to specific receptors on the basolateral membrane of the Parietal cell.
Name three different cell types of the pancreas and explain what they secrete.
Exocrine cells - secrete zymogens.
Endocrine cells - secete insulin + glucagon.
Duct cells - secrete bicarbonate.
What is the approximate pH of the stomach? What is the approximate pH of the jejunum?
Stomach - approx 2-3.
Jejunum - approx 6-7.
Name the principle function of secretin.
Stimulates pancreatic duct cells to secrete bicarbonate.
What is in bile?
Bile salts, Bile pigments, Cholesterol, Inorganic salts, Fatty acids. But 97% of bile is just water.
What is the relationship between the terms “bile salts” and “bile acids” ?
Bile acids are conjugated to glycine or taurine in the liver to form bile salts.
What does it mean when you say that bile salts are “amphipathic”?
This means that they have both hydrophilic and hydrophobic domains, and they form micelles.
Is bile acidic or alkaline?
Alkaline
How much fluid is produced by gastric secretions per day?
2.5L
How much fluid is produced by endogenous secretions of the entire GIT per day?
About 7L. Pretty much entirely reabsorbed.
How does the colon promote water reabsorption?
It pumps sodium across the apical membrane into the epithelial cells, using a transporter called ENaC (epithelial sodium channel), and water follows by osmosis.
Name three principle actions of Cholecystokinin (think about its name!)
- Stimulates pancreatic enzyme secretion.
- Stimulates contraction of the gall bladder.
- Stimulates relaxation of the sphincter of Oddi, to allow bile and pancreatic juice to flow into the duodenum.
How do the products of digestion affect CCK?
CCK secretion is increased by the presence of the products of digestion in the small intestine. As the products move away, and as the CCK-releasing peptides are degraded, CCK secretion decreases.
Which cells secrete CCK?
I cells in the upper small intestine.
Which cells secrete Secretin?
S cells in the upper small intestine.
What is Somatostatin? What does it do?
Somatostatin inhibits many features of digestion. It is released in response to gastric acid, and it inhibits the secretion of gastrin, insulin, pancreatic enzymes, and also inhibits motility and absorption.
How much blood does the liver receive from the Portal Vein in the fasting state?
1300mL/min
Name the essential amino acids.
Private Tim Hall: Phenylalanine Valine Threonine Tryptophan Isoleucine Methionine Histidine Arginine Leucine Lysine
