session 17 - Urinary system - glomerular filtration

Question 1

What are the 3 basic processes nephrons and collecting ducts perform?

Answer 1

•Glomerular filtration: Filtration of waste-laden blood in the glomerulus.

•Tubular reabsorption: The process of returning important substances from the filtrate back to the body.

•Tubular secretion: The movement of waste materials from the body to the filtrate.

Question 2

Define glomerular filtration

Answer 2

The formation of a protein-free filtrate (ultra filtrate) of plasma across the glomerular membrane.

Question 3

The filtration membrane consists of?

and the function of the filtration membrane?

Answer 3

Consists of..

Glomerular capillaries

The basal lamina

And the podocyte feet which form filtration slits

Function:

• Permits filtration of water and small solutes
• Prevents filtration of most plasma proteins, blood cells and platelets

Question 4

Glomerular filtration

What are the three filtration barriers?

and why does it have a large surface area?

Answer 4

oThree filtration barriers:

• Glomerular endothelial cells fenestrations
• Basal lamina between endothelium
• A filtration slit formed by a podocyte

o Volume of fluid filtered is large because of large surface area

Question 5

What is net filtration pressure?

And what determines it?

Answer 5

oNet Filtration Pressure (NFP): The total pressures that drive glomerular filtration

oPressures that determine NFP:

• Glomerular Blood Hydrostatic Pressure (GBHP): Promotes filtration.
• Capsular Hydrostatic Pressure (CHP): Opposes filtration.
• Blood Colloid Osmotic Pressure (BCOP): Opposes filtration.

Question 6

What is the Glomerular filtration rate (GFR)?

and what happens if it’s too high or too low?

Answer 6

oGlomerular Filtration Rate (GFR): The amount of filtrate formed in all the renal corpuscles of both kidneys each minute. Used tp assess kidney function and to determine kidney disease.

•average adult male rate is 125 mL / min

oHomeostasis of body fluids:requires constant GFR

•Too high: Useful substances are lost due to the speed of fluid passage through the nephron (we can’t reabsorb fast enough)

•Too low: Sufficient waste products may not be removed from the body

oDirectly related to NFP (net filtration pressure)

Question 7

What are the three prinicipal mechanisms to regulate Glomerular filteration rate (GFR)

Answer 7

•Renal autoregulation occurs when the kidneys themselves regulate GFR.

•Neural regulation occurs when the ANS regulates renal blood flow and GFR.

•Hormonal regulation involves angiotensin II and atrial natriuretic peptide (ANP).

Question 8

Explain renal autoregulation of GFR

(one of the principal mechanisms to regulate GFR)

Answer 8

oRenal autoregulation: Mechanisms that maintain a constant GFR despite changes in arterial BP

•Myogenic mechanism (myo - means muscle, muscle in your kidneys is in your arterioles)

– Increases in Systemic BP, stretches the afferent arterioles and increases GFR

In response..

–Smooth muscle contraction reduces the diameter of the arteriole returning the GFR to its previous level in seconds

Question 9

Renal autoregulation of GFR

Explain what the Tubuloglomerular feedback is

Answer 9

–Elevated systemic BP raises the GFR so that fluid flows too rapidly through the renal tubule and Na+, Cl-and water are not reabsorbed

–Macula densa detects that difference and releases a vasoconstrictor from the juxtaglomerular apparatus

–Afferent arterioles constrict and reduce GFR

Question 10

Explain the effect of Neural regulation of GFR

Answer 10

oAt rest, renal blood vessels are maximally dilated because sympathetic activity is minimal

•renal autoregulation prevails

oWith moderate sympathetic stimulation, both afferent and efferent arterioles constrict equally

•decreasing GFR equally

oWith extreme sympathetic stimulation (exercise or haemorrhage), vasoconstriction of afferent arterioles reduces GFR & reduced urine blood flow

•lowers urine output and permits blood flow to other tissues

Question 11

Which nervous system supplies the blood vessels in the kidneys ?

Answer 11

oSympathetic input: Blood vessels of the kidney are supplied by sympathetic fibers that release norepinephrine which cause vasoconstriction of afferent arterioles to decrease GFR

**sympathetic nervous system**

Question 12

Hormonal regulation of GFR

What are the two hormones that regulate GFR and their function?

Answer 12

oAtrial natriuretic peptide (ANP) increases GFR

•stretching of the atria that occurs with an increase in blood volume causes hormonal release

– Produced in the heart by the atria in response to being stretched due to increase in flow and is Released by the heart.

oAngiotensin II - reduces GFR

•potent vasoconstrictor that narrows both afferent and efferent arterioles reducing GFR

Question 13

Function of Neural regulation and sympathetic nervous system to change blood pressure

Answer 13

Baroreceptors stimulate sympathetic nervous system which cause vasoconstriction of systemic arterioles to increase blood pressure

Question 14

Renal autogregulation is to…

hormonal and neural regulation is to…

Answer 14

Renal autoregulation is to maintain constant GFR

hormonal and neural regulation is to change blood pressure to and regulate GFR