Physio 6 Flashcards
How does the Atrial Natriuretic Hormone affect the fluid volume in the body?
Decreases it by decreasing Na reabsorption
Function of Parathyroid hormone
Increases calcium ion reabsorption
decreases Phosphate ion reabsorption
The distal tubule has a low permeability to which ions?
Water and urea
What tranporter is present in the ealry distal tubule?
triple co-transporter protein - drives the reabsorption of the salt in the early distal tubule
What transporter is present in the later part of the distal tubule?
Na ion reabsorption and secretion of K ion
Aldosterone mediated
Pearmeability of the early collecting duct similar to what
similar to late part of the distal tubu
later parts of the distal tubule
more influencd by the icrculating levels of ADH
Features of ADH secretion:
neuroprotein
secreted by the Hypothalamus(cell body here) and secreted into the posterior pituitary gland
stored in the vesicles within the nerve terminals
when they are stimulated it causes the release of it into the blood vessels –> calcium dependent exocytosis
basolateral membrane in the distal tubule cells with the Type 2 ADH receptor –> ADH binds to it –> increases the concentration of cAMP in the cells –> increases the insertion of aquaporins into the apical membrane of the tubular cell –> increased pathway for water movemebt into the cell and thus into the blood
What type of hormone is ADH?
peptide hormone –> short half life
What happens when the levels of ADH go down?
aquaporins get internalised within the cytoplasm within intracellular vesicles and moves away from the apical membrane
What is the main function of circulating levels of ADH?
changes the expression of the aquaporins - water reabsorption
What stimulates the secretion of ADH/ vasopressin?
- dehydrated –> increased osmolarity of plasma
- decrease in ECF volume –> if we lose a lot of blood (haemorrhage) - *only if large
activation of the stretch receptors within the atria of the heart –>changes occur only if the blood volume levels is extremely low
- GI - fluid causes stretch in the upper part of the GI tract –> exacts feed forward inhibition of ADH
- Nicotine stimulates ADH release
- Alcohol inhibitis the ADH release
overhydrated
reduced the secretion of ADH from post.pituitary –> reduced the permeability of tubular cells for the reabsorption of water –> decreased water
dehyrdated
increase plasma osmolarity –> increased ADH secretion from the posterior pituitary
cortical interstitial fluid –> 300
osmotic gradient btw the tubular fluid (100) and the interstitial fluid. because of ADH the cells in the distal tubule express aquaporins. water leavs the tubular fluid down the osmotic gradient and loses it, and we’ve concentrated the tubular fluid and has increased to 300.
then it flows down to the collecting duct (cortex before going down to medulla and pelvis). in the collecting duct it is exposed to the. 600 outside, 300 inside. then the water moves from the tubule to the interstitial fluid and hence becomes more concentrated to about 1200 mosmol/l. small volume of very concentrated urine
overhydrated
minimal ADH secretion –> hence the cells of the distal tubule of the collecting duct are impermeable to water. tubular fluid leaves ascending with 100. pot gradient of about 300 -> 100. but no pathway for water to move. in then enters the collecting duct. pot gradient again but becuase no ADH no aquaporins –> hence no modification in terms of water content as it passes through distal collecting tubule and collecting duct
If we increase the ADH level what happens to the salt levels?
No change as it affects only water reabsporption
Increase in plasma osmolarity –> stimulates what
Hypothalamus stimulated and nincreases ADH secretion and increases thirst –> to decrease plasma osmolarity
What are the two types of diabetes insipidus?
central
nephrogenic
Central insipidus
the individual unable to secrete ADH
Nephrogenic
defect in the expression of the Type 2 vasopressin receptor
or defect in the cell response when the hormone binds to the cell
(production is normal but it isnt acting on the ADH cells)
What are the symptoms of diabetes insipidus?
Large columes of dilute urine (upto 20 l/ day)
constant thirst - as ADH produced continuously
Treatment for central diabetes insuipidus
ADH replacement
Treatment for nephrogenic diabetes insuipidus
medicines
What is the major site of reabsorption of salt?
proximal tubule - salt and water
What happens to the GFR as it makes its way through the proximal tubule?
125 –> 45 as it enters loop of henle
What is aldosterone?
steroid hormone secreted by the adrenal cortex
longer half life –> 2-3 weeks
What stimulates the secretion of the Aldosterone?
increase in palsma concentration of K ion - direct secretion from the adrenal cortex
Decrease in the plasma concentration of Na ions - RAAS secretion mediated indirect secretion of Na
What does aldosterone do?
Stimulates Na+ reabsorption and K+ secretion
Na+ retention contributes to an increased blood volume(as water follows sodium) & pressure
What would happen if we have no aldosterone?
Progressively excrete salt from the body and it would in turn have an impact on the blood volume
Where are the effects of aldosterone seen?
distal tubule and collecting duct
Where is the majority of K reabsorbed in the nephron?
Proximal tubule
What are the 3 main ways in the which renin can be stimulated and secreted?
- Reduced pressure in afferent arteriole
(pressure sensitive - barosensitive cells) - Macula densa cells if the NaCl levels in the blood is less
- Increases sympathetic nerve activity as a reult of reduced arterial blood pressure (as the grsnular cells are under direct control of the sympathetic system)
Actions of aldosterone
increases expression of apical sodium channels -> increases the pathway for sodium to move from the tubular fluid to the cell
- Increases the number and activity of the Na/K transporters on the basolateral membrane
Control of renin release
Reduced pressure in afferent arteriole
More renin released, more Na+ reabsorbed, blood vol. increased, blood pressure restored.
Macula densa cells sense the amount of NaCl in the distal tubule
If NaCl reduced, more renin released, more Na+ reabsorbed
Increased sympathetic activity as a result of reduced arterial blood pressure
Granular (renin-secreting) cells directly innervated by sympathetic nervous system, causes renin release.
What are the conditions that can be caused by abnormal increases in the RAA system?
- hypertension
- fluid retention (decreased CO, decreased BP, increased renin secretion –> aldosterone secretion –> increased fluid and salt retention
What do diuretics do?
Block the triple co-transporters
ANP hormone
released from the wall of the atria of the heart –> when they are mechanically stretched
promotes excretion of Na, diuresis and decreases the plasma volume and decreases BP
ANP hormone
released from the wall of the atria of the heart –> when they are mechanically stretched
promotes excretion of Na, diuresis and decreases the plasma volume and decreases BP
smooth muscle vasodilation in the arterioles, increase in GFR,
What is timulated when the bladder starts to get filled?
Micturition reflex
can be voluntarily controlled by the external urethral sphincter and pelvic diaphragm
