renal structure and function 2 Flashcards
define osmosis
the tendency of water to move from a more dilute solution to a more concentrated solution
define osmotic pressure
the tendency of a solution to take in water by osmosis
define osmol
the unit defining the osmotic strength of a solution
what is the osmolarity of the blood plasma?
300mOsm
how much of the blood is in the capillaries and veins?
65%
which sensors regulate blood volume?
volume sensors - neuronal and hormonal
sodium sensors
where are neuronal volume sensors found?
sensory fibres found mostly in RA as well as LA (less in LA)
how do neuronal volume sensors work?
act as stretch receptors - as venous return increases, they stretch more
signals volume of blood return to the heart/minute via the vagus
what are hormonal volume sensors and where are they found?
specialized muscle cells also found in the RA and IVC
what can cause increase stretching of hormonal volume sensors?
increased preload bc of increased blood volume
in response to stretch. what do hormonal volume sensors release?
atrial natriuretic peptide
explain how hormonal volume sensors help in restoring blood volume
release ANP –> decreases Na+ reabsorption in DCT –> increased water loss –> reduces blood volume –> brings it back to normal
what cells secrete BNP and when?
ventricular muscle cells when ventricles are overstretched e.g in heart failure
what do ANP and BNP do?
increase sodium excretion
how does the hypothalamus attach to the pituitary gland?
pituitary stalk
what sensors are found in the hypothalamus?
sensors that monitor osmotic strength of the blood
what is the hypothalamus?
a structure composed of tiny nuclei packed together
what are the two important nuclei involved in water balance?
the supraoptic and paraventricular nuclei.
how does the hypothalamus cause ADH secretion?
contains nuclei which contain receptors that measure osmotic pressure
also receive info from blood volume receptors via relays in the brainstem NTS
Send axons down pituitary stalk to end as secretory terminals on capillaries in the PPG axons secrete ADH
what is ADH?
antidiuretic hormone - peptide containing 9 amino acids
what stimulates ADH release?
high blood solute concentration
sympathetic arousal
which sensors detect blood sodium levels?
sodium detectors in the kidney
what sensors detect blood osmolarity?
osmoreceptors in the kidney
what condition must be met for concentrated urine to be formed?
if there is concentrated fluid in the extracellular space in the renal medulla
what is the vasa recta?
capillary network which surrounds the loops of Henle juxtamedullary nephrons
which is thinner - the descending or ascending loop of Henle?
Descending
what channels are found in the descending loop of Henle?
aquaporins
what happens to fluid as it goes down the descending loop of Henle?
gets more and more concentrated
what is the ascending loop of Henle impermeable to?
water
what mechanisms in the ascending loop of Henle causes ions to be pumped out into the ECF?
ROMK - renal outer medullary potassium channel
NKCC2 channels
Na+/K+ pump
where is ROMK found?
in the epithelial cells lining the cells of the ascending loops
what do ROMK do?
transport potassium out into the lumen, creating a positive voltage in the tubular lumen
where are NKCC2 channels found?
in the luminal walls of epithelial cells of the ascending loop of Henle
what does the NKCC2 channel do?
Pumps 1 sodium, 1 potassium and 2 chlorides into the ascending limb from the lumen
how are sodium and chlorine moved into the ECF from the ascending limb?
sodium is actively pumped out by a Na+/K+ pump
chloride moves out passively with sodium
how do loop diuretics work?
Block the transport of sodium and chloride out of the loop of Henle
what type of drug is furosemide and how does it work?
loop diuretic
block the transport of sodium and chloride out of the loop of Henle by inhibiting NKCC2 channels –> ons aren’t pumped into the ascending limb wall and therefore can’t be pumped into the ISF –> conc urine cant be formed
what is a risk of furosemide?
similar NKCC2 channel exists in the ear - too much furosemide can lead to irreversible hearing loss
what are side effects of furosemide?
low BP with standing, ringing in the ears and sensitivity to the sun.
what is the site of ADH action?
collecting duct
what happens to urine in the absence of ADH?
no reabsorption of water
dilute urine
what happens to urine in the presence of ADH?
reabsorption of water –> urine as concentrated as renal medullary fluid
what happens to urea in the kidneys?
actively pumped out of collecting duct into the ISF –> increases solute conc of renal medulla –> more concentrated urine
some urine passes into the ascending limb
some is lost in the urine
what is the countercurrent multiplier?
process of pumping salts into the extracellular fluid around the loop of Henle.
what is the countercurrent exchange?
provided by vasa recta which maintains concentration gradient. These prevent the wash out of blood as it follows the tubule in osmolarity
what is water diuresis and what does it lead to?
due to drinking too much water, blood becomes dilute. ADH release inhibited –> high volume of dilute urine –> called diabetes insipidus
what is osmotic diuresis and what does it lead to?
excess glucose in the blood, glucose isn’t totally reabsorbed in the PCT. Some glucose through the collecting duct provides an osmotic force –> water pulled into the urine –> high volume sugary urine –> called diabetes mellitus
