Anatomy and Physiology Chapter 26 - End of Renal Corpuscle Exchange

3 ways the GFR is regulated

1. juxtaglomerular complex

   1. macula densa

   2. granular cells

   3. myogenic mechanism: intrinsic mechanism

2. hormonal regulation

   1. renin

   2. natriuretic peptides

3. tubuloglomerular feedback: intrinsic mechanism

macula densa

cells are chemoreceptors and sense NaCl levels in the tubular fluid in the ascending limb of the nephron

granular cells

cells are mechanoreceptors and sense blood pressure in the afferent arteriole; produce and store renin

myogenic mechanism = intrinsic mechanism

• mesangial cells control arteriole diameter

• low BP = afferent arteriole vasodilates; more liquid and increase in hydrostatic and net infiltration

• high BP = afferent arteriole vasoconstrict; less liquid and decrease hydrostatic and net filtration

3 things about renin

• restricts water and salt loss by stimulating absorption

• juxtaglomerular complex triggers:

  • low BP at glomerulus

  • JCG cells sympathetically innervated

  • lower osmotic concentration in tubular fluid at macula densa

• released by JGC

6 steps after the triggering of renin

1. renin is released from the kidney and enter the bloodstream

2. angiotensinogen (inactive plasma protein) is cut by renin to make angiotensin I

3. angiotensin I (inactive) is converted in the lungs

4. ACE converts angiotensin I to angiotensin II which acts as a nephron

5. vasoconstriction occurs

6. increase BP

3 things about natriuretic peptides

• reverse of renin

• if blood volume increases, GFR increases to promote fluid loss

• if blood volume increase is severe, heart releases natriuretic peptides

  • due to stretching of heart wall = ANP for atrial stretch and BNP for ventricles stretched

  • afferent glomerular pressure - increase GFR via vasodilation

  • decrease Na+ absorption for increased urine production

tubuloglomerular feedback: intrinsic mechanism

• macula densa cells sense high NaCl = release vasoconstrictors to stimulate smooth muscle around afferent arteriole to decrease BP

• macula densa cells sense low NaCl = vasoconstrictor release inhibited; renin released from granular cells to increase BP

5 types of mechanism transports

1. facilitated diffusion

2. osmosis

3. active transport

4. cotransport: moves 2+ molecules in the same direction

5. counter-transport: moves 1 molecule in, while another moves out

3 things about dilute urine formation

• occurs at the collecting system

• regulating urine volume by establishing a concentration gradient

• forming concentrated or dilute urine via hormones

  • ADH increases permeability of the collecting duct to water

    • stimulates aquaporin synthesis for water to pass out easily

4 things about ADH

• from supraoptic neurons of hypothalamus

• released in response to:

  • increase osmotic pressure (increase solute = decrease water) detected in hypothalamus

  • decrease BP and/or volume detected in heart (osmoreceptors)

  • angiotensin II

• functions to increase reabsorption of water in DCT and CD

• ethanol prevents release of ADH

3 things about aldosterone

• from adrenal cortex

• released in response to:

  • decrease in Na+, blood volume or pressure, or increase in K+

  • direct effect

  • angiotensin II

• functions to keep Na+ (and therefore water) and get rid of K+

  • increase synthesis of Na+/K+ countertransporter in DCT and CD

3 things about countercurrent multiplication

• establish and maintain increasing osmotic gradient from renal cortex to medulla

• reabsorb solutes and water before DCT and CD

• establish concentration gradient in peritubular fluid for passive water absorption

5 things about countercurrent multiplier

• filtrate flow in nephron loop

• exchange of substances between ascending and descending limbs

• Na/Cl pump at TAL increases peritubular osmotic concentration

• provides higher osmotic concentration around DTL

• a feedback loop multiplying concentration differences between hypotonic TAL (less solute) and hypertonic medulla (more solute)

4 things about medullary osmotic gradient

• Na+-K+/2 Cl- transporter

• K+ returned back to fluid via Na/K pump

• almost 2/3 of Na and Cl entering TAL pumped out before they get to DCT

• pump out faster at base of TAL (and medulla osmolarity higher)

3 things about the role of urea

• nephron loop, DCT, and CD impermeable to urea

• concentration gets really high

• papillary duct permeable so 1/3 of solutes in deepest medulla = urea (cause base of medulla to be higher)