PHSC1122 Physio II - Chapter 26 Renal System (26.4)

Glomerular filtration

driven by hydrostatic pressure and involves passage across a filtration membrane

Hydrostatic pressure

fluid pressure that drives glomerular filtration

Colloid osmotic pressure

pressure of materials in solution on each side of capillary walls

Hydrostatic and colloid osmotic pressures

Glomerular filtration is governed by a balance between what pressures?

Glomerular hydrostatic pressure (GHP)

blood pressure in glomerular capillaries, usually higher than in peripheral capillaries

Into the efferent arteriole

Where does blood leaving glomerular capillaries flow?

Glomerular capillaries

Is hydrostatic pressure higher in the glomerular capillaries or the peripheral capillaries?

Out of bloodstream and into filtrate

Where does glomerular pressure tend to push water and solutes?

Capsular hydrostatic pressure (CsHP)

blood pressure that opposes glomerular hydrostatic pressure and pushes water and solutes out of filtrate and into bloodstream; results from resistance to flow along nephron and conducting system

Out of filtrate and into bloodstream

Where does capsular hydrostatic pressure tend to push water and solutes?

Resistance to flow along nephron and conducting system

What does capsular hydrostatic pressure (CsHP) result from?

Net hydrostatic pressure (NHP)

difference between glomerular hydrostatic pressure and capsular hydrostatic pressure

Glomerular hydrostatic pressure (GHP) - capsule hydrostatic pressure (CsHP)

How is net hydrostatic pressure calculated?

35 mmHg

What would the net hydrostatic pressure (NHP) be if the GHP was 50 mmHg and the CsHP was 15 mmHg?

Colloid osmotic pressure

pressure due to materials in solution

Blood colloid osmotic pressure (BCOP)

osmotic pressure resulting from suspended proteins in blood

Suspended proteins in blood

What does blood colloid osmotic pressure result from?

Net filtration pressure (NFP)

average pressure forcing water and dissolved substances out of glomerular capillaries and into capsular spaces; difference between net hydrostatic pressure and blood colloid osmotic pressure in the glomerulus

Out of glomerular capillaries into capsular spaces

Net filtration pressure (NFP) is the average pressure forcing water and dissolved substances where?

Net hydrostatic pressure (NHP) - blood colloid osmotic pressure (BCOP)

How is net filtration pressure (NFP) calculated?

15 mmHg

What would the net filtration pressure (NFP) be if GHP were 50 mmHg, CsHP were 25 mmHg, and BCOP were 10 mmHg?

Glomerular filtration rate (GFR)

amount of filtrate kidneys produce each minute

125 mL/min

average glomerular filtration rate (GFR)

Leaves bloodstream and enters capsular spaces

What happens to about 10 percent of fluid delivered to kidneys?

180 L

About how much filtrate do glomeruli generate per day? (approx. 70x total plasma volume)

Net filtration pressure

determines GFR

Autoregulation, hormonal regulation, autonomic regulation

three interacting levels of control or regulation of GFR

Autoregulation of GFR

maintains adequate GFR despite changes in local blood pressure and blood flow; involves changing luminal diameters of afferent arterioles, efferent arterioles, and glomerular capillaries

Luminal diameters of afferent arterioles, efferent arterioles, and glomerular capillaries

What does autoregulation of GFR involve changing?

Kidneys

initiate the hormonal regulation of GFR

Renin-angiotensin-aldosterone system (RAAS) and natriuretic peptides

two parts of the hormonal regulation of GFR

Renin-angiotensin-aldosterone system (RAAS)

system where the juxtaglomerular complex (JGC) releases renin which converts angiotensinogen to inactive angiotensin I, which is converted to angiotensin II by angiotensin-converting enzyme (ACE)

Decrease in blood or systemic pressures, blockage in renal artery or branches; stimulation by sympathetic innervation; and decrease in osmotic concentration of tubular fluid at macula densa

3 stimuli that cause the juxtaglomerular complex (JGC) to release renin

Renin

converts inactive angiotensinogen to inactive angiotensin I

Angiotensin-converting enzyme (ACE)

converts inactive angiotensin I to angiotensin II; primarily in lung capillaries

(1) Contraction of vascular smooth muscle in peripheral capillary beds (2) Increased aldosterone secretion by adrenal glands, which increases Na+ retention (3) Increased arterial pressures (4) Stimulation of thirst centers (5) Increased production of ADH

5 effects of angiotensin II

Increase in systemic blood pressure, blood volume, and restoration of normal GFR

overall effect of angiotensin II

Increase GFR to promote fluid loss

Increase in blood volume causes hormonal regulation to try to do what?

Natriuretic peptides

released by heart in response to stretched walls due to increased blood volume or pressure; trigger dilation of afferent glomerular arterioles and constriction of efferent glomerular arterioles to increase glomerular pressures and GFR

Atrial natriuretic peptide (ANP)

released by atria; also decreases sodium reabsorption

Heart

What organ releases natriuretic peptides?

Stretched walls due to increased blood volume or pressure

What does the heart release natriuretic peptides in response to?

Dilation of afferent glomerular arterioles and constriction of efferent glomerular arterioles to increase glomerular pressures and GFR

What do natriuretic peptides trigger?

Glomerular pressure, GFR, and urine production

What do natriuretic peptides increase?

Increased urine production and decreased blood volume and pressure

Net result of natriuretic peptides

ANS sympathetic activation

What causes autonomic regulation of GFR?

Constricts afferent glomerular arterioles, decreases GFR, slows filtrate production

3 functions of sympathetic activation in autonomic regulation of GFR

Sympathetic activation

responsible for autonomic regulation of GFR and can override local regulatory mechanisms that act to stabilize GFR