urinary systems part 2 1051-Gametogenesis and Fertilisation

what occurs within the glomerulus?

-everything except blood and proteins enter Bowmans capsule lumen (if<1.8nm allowed, if >3.6nm not allowed)

-glom also has charge selectivity-negative cannot pass

-15-25% water and solutes are removed from the plasma

has epithelial cells, basement membrane, has podocytes

-afferent arteriole→ network of capillaries→ efferent arteriole

-certain molecules secreted from interstitial fluid into proximal tubules

how do hydrostatic and oncotic pressures affect glomerular filtration?

-hydrostatic pressure-pressure from fluid on the walls: pushes fluid into lumen of Bowmans capsule

-oncotic- by plasma protein on walls : pulls fluid back into capillary

balance between the two forced impacts rate and direction of fluid movement

what is GFR and clearance?

GFR is 120ml/min

clearance- the amount of fluid cleared completely of a certain substance

how do you calculate net filtration pressure?

glom capillary pressure- intracapsular pressure

then -colloid osmotic pressure

what are some features of the juxtaglomerular apparatus

-is where afferent arterioles come into contact w the distal tubule

-JG cell sense blood pressure

-macular densa cells (at the point of contact w the distal tubule) sense Na+ conc of intertubular fluid

e.g. if bp decreases→ decreased stretch of JG cells→ renin release→ bp back to norm

e.g. filtrate decreased flow rate→ macula densa cells sense→ vasodilation of afferent arteriole & renin secretion by JG cells→ return flowrate back to normal

what do tubule epithelial cells do? how are they specialised to do this?

-have unique transport mechanisms on either side of cell to regulate ion movement

-have tight junctions to prevent paracellular transport, have certain polarity to allow some things through

PT epithelia have lots microvilli, mitochondria & large SA cause it reclaims 80% filtered fluid, (transport of Na+, Cl- out, and H+, K+ and toxins and drugs in)(e.g. cotransport of Na+ and Glucose)

Loop of henle- water conservation- reclaims 5-10% filtrate, big difference in descending and ascending limb- as diff roles

what are some differences between the ascending and descending limb of the loop of henle?

-DL is very permeable to water- no tight junctions, have no AT of ions, v. permeable to urea and ion

-AL impermeable to water, thick segment has AT of ions, impermeable to urea, permeable to ions

how does the collecting duct control base-acid balance?

-in mammal blood plasma/ primary urine: high bicarbonate ion conc. low proton conc.

-reabsorption of bicarbonate ions 80% in PT

-acidification of intertubule fluid

-alpha intercalated cells (acid secreting) and beta intercalated cells (base secreting) sense bicarbonate, CO2/ proton conc.

-depending on what is sensed- modulate expression, abundance in pm/ activity of transporters, pumps and channes

-also under hormonal control (aldosterone, angiotensin II)

describe the process of counter current multiplication?

-isosmotic fluid in PT enters DL (300mOsm)

-since Na+ conc. is high in IF, water moves out (meaning Na+ conc. in DL increases)

-AL is initially low in Na+ conc. due to AT out into IF, when high conc. Na+ from DL arrives in AL, it is AT out

-there is always a difference of 200mOsm

describe countercurrent multiplication (shitty)

-Na+ AT out of AL means IF now has is 400mOsm, and AL has 200mOsm

-now the DL is 300mOsm and the IF is 400mOsm and water moves out passively until equilibrates (so bottom part is isosmotic)

-water leaving doesn’t affect IF osmolarity but does Inc conc. of DL→ goes into AL where AT of Na+ out

-osmolarity increases the deeper you move into the medulla

-osmotic pressure increases as depth increases

-also means more conc. Na+ around CD

describe the way renin works?

renin→ angiotensinogen (liver)→ angiotensin I →Angiotensin converting enzyme→ angiotensin II→ adrenal cortex→ aldosterone→ increased Na+ reabsorption

how do the descending and ascending vasa recta differ?

-descending: increased osmolarity IF, Na+ diffuse in, lose water

-ascending: lose Na+ to more dilutes IF, gain water

how is the CD specialised?

transport proteins UT-A1 and UT-A3 aid in tranport of urea from CD to IF

-vasopressin (ADH) upregulates expression UT-A1 and UT-A3)

how does ADH work?

increased osmolarity detected by osmoreceptors/ angiotensin II detected/ baroreceptors in heart sense change in blood pressure in hypothalamus

→ posterior pituary gland releases ADH

→ upregulates translocation of AQP-2 on apical side of pm in CD (dorsolateral side always has AQP3 &4)

→more water reabsorption in IF