Renal - Function 2/2

Question 1

In the kidney, what is the excretion equation? Where do they occur?

Answer 1

filtration (kidneys) + secretion (capillary to renal tubule) - reabsorption (renal tubule to capillary)

Question 2

During renal filtration, what is a substance which is totally reabsorbed and totally excreted?

Answer 2

Glucose is totally reabsorbed (i.e. all that is filtered is reabsorbed)

Creatinine is totally excreted (i.e. all that is filtered is excreted)

Question 3

What does the glomerulus do?

Answer 3

It filters out the large particles in blood (i.e. large proteins, cells)

Question 4

In the start of the proximal tube (just after the glomerulus), what is the concentration of the solutes compared to blood?

Answer 4

For all the small particles (that pass through the podocytes) the concentration is exactly the same but for the large particles they are not present

Question 5

How does glomerular filtration rate vary with renal blood pressure? Why is this the case?

Answer 5

From ~80mmHg up the GFR remains constant. This is because the blood flow to the kidney is tight regulated

Question 6

How can the blood flow to glomerulus be tightly regulated?

Answer 6

The glomerular capillaries have two arterioles (afferent and efferent arteriole) which have a large proportion of smooth muscle so can greatly control the blood flow

Question 7

Label the diagram

Answer 7

Question 8

How does construction of the afferent and efferent arteriole affect the blood pressure in the glomerulus?

Answer 8

Constriction of the afferent arteriole causes decreased glomerulus pressure (efferent remains the same, afferent decreases and glomerulus is the average of the two so decreases)

Constriction of the efferent arteriole causes increased glomerulus pressure (afferent remains the same, efferent increases and glomerulus is the average of the two so increases)

Question 9

What is glomerular filtration dependent on?

Answer 9

The concentration gradient within the glomerulus, i.e. the net filtration pressure

Question 10

What is the net filtration pressure equation for the kidney? What is the source of each pressure and what is the approximate value?

Answer 10

Net filtration pressure = GBHP - CHP - BCOP

Glomerular blood hydrostatic pressure - The pressure exerted by the afferent and efferent arterioles (~50mmHg)

Capsular hydrostatic pressure - the pressure exerted against the GBHP by the elastic recoil of the glomerular capsule (~15mmHg)

Blood colloid osmotic pressure - The osmotic pressure going back into the glomerulus cased by the large proteins filtered out in the glomerulus (~25mmHg)

Question 11

What is the factor that needs to change to regulate the glomerular filtration rate?

Answer 11

Net filtration pressure

Question 12

How is glomerular filtration rate regulated? What is their relative affect on the body over time?

Answer 12

Autoregulation (rapid), neural and hormonal (long term)

Question 13

What are the types of auto regulation of the GFR? Explain how they work and their impact on GFR

Answer 13

Myogenic mechanism - as the smooth muscle of the arterioles is stretched (by increasing blood pressure), they react by contracting therefore reducing blood flow

Tubuloglomerular feedback - The ascending loop of Henle is very close to the afferent and efferent tubule and if there is increased GFR this means that there is less time for Na+ and Cl- to be re-absorbed resulting in higher amounts (not concentrations). This creates a signal to the afferent arteriole to vasoconstrict reducing GFR

Question 14

What neural pathway controls GFR? Explain how it works and its impact on GFR

Answer 14

Renal sympathetic nerves release norepinephrine which causes constriction of the afferent arteriole (therefore decrease blood flow) by activating the α1 receptors and increasing the release of renin (an enzyme that produces angiotensin that leads to increased blood pressure)

Question 15

What are the hormonal controls of the GFR? Explain when these are stimulated and their impact on GFR

Answer 15

Angiotensin II is produced when there is decreased blood volume or pressure causing constriction of the afferent and efferent arterioles leading to decreased GFR

Atrial natriuretic peptide (ANP) is stimulated by the stretching of the atria. This causes relation of cells in the glomerulus resulting in increased capillary surface area for increased GFR

Question 16

What does the juxtaglomerular apparatus consist of?

Answer 16

It is formed by the ascending loop of Henle and the afferent and efferent arterioles

Question 17

What are the two types of nephrons? What is their difference in function and structures?

Answer 17

Cortical and juxtamedullary nephrons

Cortical nephron has a shorter Loop of Henle and dilutes urin

Juxtamedullary nephron has a longer Loop of Henle and is important int eh production of concentrated urine

Question 18

What is the pathway for filtration in the renal system?

Answer 18

Proximal tubule, descending Loop of Henle, ascending Loop of Henle, Late distal tube and collecting duct

Question 19

What is the function of the proximal tubule?

Answer 19

This is where the largest amount of solute and water is reabsorbed from filtered fluid occurs (i.e. glomerular filtrate, salt, water, glucose, amino acids etc.)

Question 20

What is the function of the descending Loop of Henle?

Answer 20

Mainly water reabsorption

Question 21

What is the function of the ascending Loop of Henle?

Answer 21

Ions (i.e. Na+, K+ and Cl-) are actively reabsorbed (mainly in the thick segment) and no water

Question 22

What is the function of the late distal tube and collecting duct?

Answer 22

More Na+ and Cl- reabsorption and has variable water reabsorption (depend on the presence of ADH, more = more water reabsorption)

Question 23

What is the make up of solution in the proximal tubule? Explain how it became like this

Answer 23

It is pretty much just plasma without the large proteins

After the glomerulus only water and the smallest particles can get through to the proximal tubule

Question 24

How is sodium removed in the proximal convoluted tubules?

Answer 24

Na+ moves down it concentration gradient via a symporter with glucose (1 glucose for 2 Na+ FYI) and antiporter (1 Na+ for 1 H+) into the proximal convoluted tubules cells. It is then actively pumped out into the peritubular capillaries by a NaK ATPase pump

Question 25

What other things are able to move due to the movement of Na+ out of the proximal convoluted tubule?

Answer 25

Water (maintain osmolarity) and glucose (symporter)

Question 26

What happens to the volume and concentration of water and salt ions in the fluid after the proximal convoluted tubule?

Answer 26

The volume decreases because for every Na+ that is removed, an H2O is also removed

The concentration won’t change because the same ration of water and Na+ will leave

Question 27

What is the descending loop of Henle permeable to? What is it not permeable to?

Answer 27

Highly permeable to water but not ions and urea

Question 28

How does water get reabsorbed in the descending loop of Henle?

Answer 28

As the loop of Henle descends it goes deeper into the medulla which is has a high tonicity (i.e. has lots of ions). This causes water to move into peritubular capillaries

Question 29

What is the ascending loop of Henle permeable to? What is it not permeable to?

Answer 29

It is permeable to ions (Na+, K+, Cl-) and impermeable to water

Question 30

How do the ascending and descending loops of Henle interact with the peritubular capillaries each other to filter out the ions and water? Explain

Answer 30

There is a counter current mechanism which means that the blood is moving in the opposite direction to the flow of fluid. This causes lots of ions to be removed into the capillaries as it passes the ascending loop of Henle first making it very concentrated which then passes the descending loop of Henle and due to its high ion concentration causes water to move into it

Question 31

What is the water permeability of the distal convoluted tubule and collecting duct dependent on?

Answer 31

The presence of ADH makes the urine more concentrated by making the more permeable to water, absence of ADH makes urine more dilute by making them less permeable to water (i.e. no more water can be removed)