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34 Cards in this Set
- Front
- Back
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Where are most nutrients, electrolytes and H2O absorbed?
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The small intestine
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How many liters of fluid are received by the small intestine per day?
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9 L
(2L ingested, 1.5L saliva, 4.5L stomach/bile/pancreas, 1L intestine) |
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What percent of the fluid presented to the small intestine is conserved?
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98%
(61% duodenum/jejunum, 57% ileum) |
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In which part of the GI tract is the efficiency of absorption the greatest?
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Colon
(87%) |
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What are two types of ion transport in enterocytes?
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1. transcellular
2. paracellular (particularly for Na) |
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What are three types of transcellular transport?
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1. pumps
2. channels 3. carriers (transporters) |
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How do pumps work, and give two examples?
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Pumps use hydrolysis of ATP to move ions against their electrochemical gradient.
1. Na+/K+ ATPase (maintains low intracell [Na+]) 2. H+/K+ ATPase |
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What is a channel, and give two examples?
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Selective permeability of ions, dependent on electrochemical gradient.
1. Na+ 2. Cl- |
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What are carriers/transporters, and give three types?
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Proteins that depend on a favourable electrochemical gradient.
1. Uniport (1 substance) ex. GLUT2 2. Symport (2 substances, same dir'n) ex. Na+/Glucose 3. Antiport (2 substances, opposite dir'n) ex Na+/H+ |
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Give 4 methods of Na+ absorption:
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1. Coupled to organic solutes (proximal sm intestine)
2. Na+/H+ exchange (proximal sm intestine) 3. Neutral coupled NaCl absorption (ileum, colon) 4. Na+ channels (distal colon, rectum) |
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What is the most important means (quantitatively) of Na+ transport?
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Coupled transport
(to glucose - GLUT2, galactose, amino acids) |
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Where is the Na+/H+ exchanger most prominent?
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Apical membrane of proximal small intestine
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Where do the protons come from for the Na+/H+ exchanger?
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Cell metabolism
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Where is neutral coupled NaCl exchange the most prominent?
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Ileum, colon
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What are the two exchangers that make up neutral NaCl exchange?
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Na+/H+
Cl-/HCO3- |
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What hormone inhibits neutral NaCl absorption?
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Aldosterone
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Where are Na+ channels most prominent?
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distal colon, rectum
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What hormone enhances absorption by Na+ channels?
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Aldosterone
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What are the two ways that Cl- is absorbed?
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1. passive absorption
2. Cl-/HCO3- exchanger |
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What are the three pathways of water absorption?
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1. diffusion across lipid bilayer
2. through aquaporins (water filled pores) 3. via transporters (ie. glucose and amino acid transporters) |
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Why is water transport coupled with solute and ion transport?
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Water follows due to the osmotic imbalance created by the solute/ion.
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What are four functions of intestinal secretions?
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1. propel substances out of crypts
2. maintain fluidity of intraluminal contents 3. maintain osmotic equilibrium 4. dilute injurious substances |
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What does duodenal gland secretion consist of?
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isotonic electrolyte solution containing mucin
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What are the two pathological mechanisms for diarrhea?
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1. decreased absorption
2. increased secretion |
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What are three methods of decreased absorption for diarrhea?
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1. inhibited/defective enterocyte absorption of electrolytes & fluid
2. presence of osmoles in lumen 3. increased propulsive activity (less transit time) |
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What are two examples of inhibited enterocyte absorption, causing diarrhea?
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1. E. coli (heat stable enterotoxin)
2. congenital chloridorrhea |
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What are two examples of osmotically active agents in lumen causing diarrhea?
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1. lactose malabsorption
2. Mg hydroxide-containing antacids |
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What are two examples of increased propulsive activity causing diarrhea?
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1. Irritable bowel syndrome
2. Hyperthyroidism |
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What are three origins for secretory diarrhea?
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1. Bacterial infection
2. Neuro-endocrine tumours 3. Inflammation induced |
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What does high intracellular levels of cAMP, cGMP and Ca cause?
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Stimulates electrically neutral NaCl transport from serosa to mucosa.
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What bacteria cause net intestinal secretion?
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Vibrio cholera
heat stable enterotoxin (E. coli) heal labile enterotoxin (E. coli) |
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What is Verner-Morrison syndrome?
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aka VIPoma
non-islet cell pancreatic tumour that produces VIP (neuroendocrine tumour that causes secretory diarrhea) |
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What is Zollinger-Ellison syndrome?
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aka Gastrinoma
tumour in pancreas or duodenal mucosa that secretes gastrin |
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What happens to the intestinal mucosa in Celiac disease?
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villous atrophy
crypt hyperplasia mucosal inflammation |
