Renal Blood Supply and Regulation of Renal Blood Flow

- Concept of renal blood supply - Understand renal blood flow (RBF) - Regulation of renal blood flow by intrinsic mechanisms - Regulation of renal blood flow by extrinsic mechanisms

with blood flow at rest, ? of the CO goes to the kidney

20-25%

what vessels supply the kidney

renal aa

what vessels return “clean” blood to the caudal vena cava from the kidney

renal vv

blood enters the kidney through the renal artery and flows into smaller and smaller arteries, eventually forming the tiniest of arteriole called the ? to enter the nephron

afferent arteriole

describe the blood flow through the kidney

- Renal a.
- Segmental a.
- Interlobar a.
- Arcuate a.
- Interlobular a.
- Afferent arteriole
- Glomerulus**
- Efferent arteriole
- Peritubular capillary
- Vasa recta
- Interlobular v.
- Arcuate v.
- Interlobar v.
- Segmental v.
- Renal v.

what is the amount of blood filtered by the kidney’s glomeruli per unit of time

glomerular filtration rate (GFR)

what are the two main factors affecting renal blood flow

• blood pressure gradient between renal artery and renal vein

• renal vascular resistance (RVR) - resistance to blood flow caused by renal blood vessels

what determines the renal blood pressure gradient

renal artery BP - renal vein BP

what happens if the renal blood pressure gradient is increased or an increase in blood pressure

increased renal blood flow

what happens if there is a decrease in blood pressure

decreased renal blood flow

what factors affect renal vascular resistance

blood viscosity

renal blood vessel length

renal blood vessel diameter

restrictions in the blood vessels including fats, cholesterol, and plaques

higher renal vascular resistance = ? RBF

lower

what are the results of vasodilation in renal blood flow

reduce renal vascular resistance

increase blood flow

decrease blood pressure inside vessel

what are the effects of vasoconstriction in renal blood flow

increased renal vascular resistance

decreased blood flow

increased blood pressure inside vessel

? is responsible for vasodilation and vasoconstriction controlled by signals and hormones

smooth muscle (tunica media)

maintaining a certain blood flow is ? for renal function and urine production

essential

too low or too high blood flow can cause damage to kidneys because nephron tubule wall is very ? (some only one cell layer) and can damage renal capillaries

thin

the purpose of regulation of RBF is to maintain the RBF and GRF at a certain level aka ?

homeostasis

what cells in the nephron help regulate renal blood flow and where are they located?

• juxtaglomerular cells (afferent arteriole)

  • Macula densa cells (DCT)

macula densa cells physically contract the ? arteriole where the JG cells are (touch each other)

afferent

what are the two types of mechanisims used to regulate renal blood flow

intrinsic mechanisms (without outside assistance

extrinsic mechanisms with assistance of other organs

what are the two intrinsic mechanisms for regulating RBF

myogenic mechanism

tubular glomerular feedback mechanism

what are the three extrinsic mechanisms for regulating RBF

SNS mechanism

renin angiotensin aldosterone system (RAAS)

atrial natriuretic peptide (ANP)

what extrinsic mechanism acts to decrease BP and RBF

atrial natriuretic peptide (ANP)

which organ is involved with intrinsic mechanisms

kidney only

which organs are involved in extrinsic mechanisms?

kidney, liver, lung, brain, adrenal gland, heart

what are the steps of the myogenic mechanism in high BP

• when BP is increased, smooth muscle cells of the afferent arteriole are stretched

• activated stretch sensitive Na+ channels open, so Na+ rushes in

• Na+ causes CA++ release from SR

• Increases muscle contration and thus vasoconstriction of afferent arteriole

  • decreases RBF and GFR

What are the steps in the myogenic mechanisms in case of low BP

• when blood pressure is low, smooth muscle cells are less stressed

• stretch sensitive Na+ channels close so No Na+ moves in

• No Na+ means No Ca++ release

• increases relaxation of smooth muscle

• vasodilation of afferent arteriole

• increases RBF and GFR

most sodium chloride (NaCl) in the filtrate are reabsorbed back to the blood at ? but some NaCl travels along tubules and reach DCT

PCT

? cells in the DCT (near the interface of DCT and ascending limb of Loop of Henle) are NaCl sensory cells that are very sensitive to abnormal NaCl concentrations

Macula Densa

what do MD cells do then they sense high concentrations of NaCl

release adenosine, causing vasoconstriction of the afferent arteriole (remember that MD cells physically contact the afferent arteriole)

what do MD cells do when they sense low concentrations of NaCl

release prostacyclin (PGI2) and nitric oxide (NO) , causing vasodilation of afferent arteriole

what steps occur with the tubular glomerular feedback mechanism in cases of high BP

- RBF and GFR are increased,
- Filtrate contains extra Na+ and Cl- ions,
- Macula densa cells (NaCl sensory cells) in DCT sense high concentrations of Na+ & Cl- and release adenosine.
- Adenosine causes vasoconstriction of afferent arteriole (smooth muscle) to decrease RBF and GFR.

What steps occur with the tubular glomerular feedback mechanism in cases of low BP?

- RBF and GFR are decreased,
- Filtrate contains low amount of Na+ and Cl- ions,
- Macula densa cells (NaCl sensory cells) in DCT detect low concentrations of Na+ & Cl- and produce PGI2 and N.O.
- PGI2 and N.O cause vasodilation of afferent arteriole to increase RBF and GFP.
- PGI2 and N.O. stimulate J.G. cells to release renin to increase BP and then increase RBF and GFR. (stimulates RAAS as well as vasodilation)

When systemic blood pressure (BP) is very low, blood volume is also low. RBF and GFR are low. Intrinsic mechanism alone is not sufficient to correct the issues = ________________ nervous system will kick in

sympathetic

What are the steps in activation of the SNS to regulate renal blood flow?

- Heart sends low BP and signals brain
- SNS activated
- Triggers adrenals to produce epi and norepi
- Epi/Norepi are transported to afferent arterioles to activate JG cells
- JG cells release renin
- RAAS increases BP, RBF, GFR

What are the steps in RAAS after the JG cells have been stimulated?

- JG cells release renin
- Renin converts angiotensinogen to angiotensin I
- ACE converts angiotensin I to angiotensin II

What are the effects of angiotensin II?

- Activates pituitary gland
- Activates osmoreceptors
- Activates adrenal gland
- Regulates nephron
- Regulates systemic BP

What does RAAS stimulate the pituitary to secrete?

ADH - Anti-Diuretic Hormone

What does ADH do?

- ADH acts on collecting duct,

- Making the collecting duct water permeable by adding aquaporins.

- More water is reabsorbed back to blood.

What are the net effects of ADH action on the collecting ducts?

- Increase blood volume

- Increase blood pressure

- Increase renal blood flow (RBF)

- Increase GFR

Angiotensin II activates osmoreceptors in the hypothalamus causing the sensation of _________.

thirst

What are the effects of increased water consumption after the stimulation of thirst?

- Increase blood volume

- Increase blood pressure

- Increase renal blood flow (RBF)

- Increase GFR

What effects does aldosterone have on the DCT of the nephrons?

- Increase sodium reabsorption from DCT back to blood.

- More water moves back to blood (Water follows salt)

What hormones is secreted from the adrenal gland in response to angiotensin II?

Aldosterone

What are the net effects of aldosterones action on the DCTs?

- Increase blood volume

- Increase blood pressure

- Increase renal blood flow (RBF)

- Increase GFR

What are the effects of angiotensin II on the PCT?

- Increases sodium permeability of PCT.

- More sodium are reabsorbed back to blood.

- More water moves back to blood.

What are the net effects of angiotensin II's action on the PCT?

- Increase blood volume

- Increase blood pressure

- Increase renal blood flow (RBF)

- Increase GFR

How does angiotensin II control systemic blood pressure?

Angiotensin II binds to its receptors on systemic artery (smooth muscle cells) causing vasoconstriction of artery

What are the net effects of angiotensin II's actions on systemic BP?

- Increase systemic blood pressure
- Increase renal blood flow (RBF)
- Increase GFR

When Blood Pressure and RBF are too high, the heart releases __________ __________ _____________ to correct the issues.

Atrial natriuretic peptide (ANP)

What are the effects of ANP on RBF?

- Acts on arteries to reduce BP
- Acts on Afferent arteriole to increase urine production
- Acts on PCT to increase urine production

NET EFFECT: Reduce RBF & GFR

What are the effects of epi and norepi on the heart?

- Increase Heart rate
- Increase Contraction
- Increase Blood pressure