Lecture 17 Flashcards
What is the space in between the cells?
Lateral intercellular (paracellular) space, only permeable via tight junctions for small uncharged molecules
What are the two types of cell transport?
Transcellular and paracellular transport
How can you calculate electrical resistance of an epithelial tissue?
Ohms law
What does it mean for the number of tight junctions when theres a high electrical resistance?
Theres a high number of tight junction strands
What are the classifications of epithelium?
Leaky epithelium, paracellular transport dominates AND tight epithelium, transcellular transport dominates
What are the features the transport which occurs at the proximal end?
More leaky epithelium, this means lower electrical resistance and number of strands, more bulk transport, duodenum/proximal tubule
What are the features of transport that occur at the distal end?
More tight epithelium, which means higher number of electrical resistance, higher number of strands and more hormonally controlled (transcellular), colon/collect duct
What is special about the transport in the distal section of GI tract and kidney?
This last section is what your body can up or down regulate depending on what your body needs
What is absorption
From lumen to blood, first entry step via the apical membrane
what is secretion?
Blood to lumen, first entry step via the basolateral membrane
What is needed in terms of the electrochemical gradient in transepithelial transport?
A gradient is needed, and this can be either passive or established actively
What is needed in terms of electroneutrality for transepithelial transport?
A movement of an ion will cause an ion of the opposite charge to move along with it so that charge of the cell is maintained.
What happens in terms of osmolarity in transepithelial transport?
the movement of ions will cause differences in osmolarity that causes water to move by osmosis
What can be said about the speed of water transport?
Very fast, so fast that you can not measure an osmotic gradient
What does the sodium glucose symporter do?
It uses energy of a Na gradient to actively accumulate glucose above its concentration gradient
What is the function of GLUT
Mediates glucose exit across the basolateral membrane via passive diffusion
What happens in glucose-galactose malabsorption syndrome?
A mutation to the glucose symporter in the small intestine means that sugar is retained in the intestine lumen, increasing the osmolarity , inducing water reflux and causing diarrhea.
What is a treatment for glucose galactose malabsorption?
Removing glucose and galactose from the diet. Using fructose as a source of carbohydrates. (GLUT5 and GLUT2)
What happens in the kidney?
It filters glucose in the plasma, needs to be reabsorbed.
What does the NaK2Cl symporter do?
It uses the energy of the Na gradient to actively accumulate chloride above its electrochemical gradient
What is the rate determining step of chloride secretion?
The Cl- channel (CFTR) which is strictly regulated
What is secretory diarrhoea?
When there is excessive stimulation of secretory cells in the crypts of the small intestine and colon
What causes this stimulation?
Abnormally high concentration of endogenous secretagogues produced by tumours or inflammation, or secretion of eneterotoxins from bacteria such as cholerae
What is the function of enterotoxins?
They irreversibly activate adenylate cyclase causing maximal stimulation of the CFTR leading to a secretion that overwhelms the absorptive capacity of the colon.
What is the life cycle of the small intestine cells
crypt cells (secretion of chloride ) are always undergoing renewal, then they get pushed to the villus (absorption of glucose ) then get lost into the lumen.
How can secretory diarrhoea be treated?
Upregulate absorption by oral rehydration therapy, this will eventually cause patients to cure themselves as the lifecycle of infection takes 5 days.
What organs do cystic fibrosis affect
Airways (clogging of bronchial passages), liver (clogs bile ducts), pancreas (damage to ducts, no secretion of pancreatic enzymes), small intestine (blocked colon), male reproductive tract (no ejaculation fluid) skin (salty sweat)
What is a common theme in cystic fibrosis?
Involvement of epithelial tissues, usually die due to respiratory disease
What are clinical managements of cystic fibrosis
Chest percussion to improve clearance, antibiotics, pancreatic enzyme replacement, attention to nutritional status, median survival is 38 years
What is interesting about the chloride ion channel?
Secretagogue activates cAMP which activates protein kinase A which phosphorylates the R domain which sits in the pore of the channel. Only when phosphorylated, the channel can bind ATP which is used to open the channel.
What is the pathology of cystic fibrosis for lungs?
The lung surface is dry due to enhanced Na+ absorption, isotonic fluid secretion is prevented
Describe cystic fibrosis and sweat formation
Epithelial cells in the ducts of sweat glands don’t reabsorb NaCl causing salty sweat
What is the pathology behind salty sweat in cystic fibrosis
As the membrane potential is depolarized, Cl- wants to go down its electrochemical gradient but cannot so it accumulates in the duct lumen
