Kidney

Question 1

What does renal mean

Answer 1

Something related to the kidney

Question 2

What are the main functions of the kidney

Answer 2

Maintain extracellular fluid composition and volume

Maintain mass balance/clearance

Filtration followed by reabsorption

Secretion of some waste product

Produces some hormones (erythropoietin)

Question 3

what are the main components of a nephron

Answer 3

Renal corpuscle

Proximal convoluted tubule

Loop of Henle

Distal convoluted tubule

Collecting duct

Question 4

Where is majjority of the volume reabsorbed?

Answer 4

70% almost immediately reabsorbed in the proximal convoluted tubule

Fine tunin in the remaining sections

Question 5

Describe the general anatomy of the renal corpuscle

Answer 5

Has Bowman’s capsule surrounding the glomerulus.

The glomerular filter is formed of 3 layers; endothelium, glomerular basement membrane and podocytes

Question 6

What is the glomerulus

Answer 6

It is like a ball of wool and a tangle of porous capillaries, whos function is to allow for material to leave the blood stream into the bowmans capsule

Question 7

What is the bowmans capsule

Answer 7

Surrounds the glomerulus, and absorbs filtrate from glomerulus

Question 8

What is the function of podocytes

Answer 8

They form a filtration barrier which is wrapped around glomerular capillaries to ensure large proteins dont leave the capillary

Question 9

What goes through the renal corpuscle

Answer 9

Small molecules (<3 nm)

water, glucose, amino acids

urea, small ions like Na+, K+

Question 10

What doesn’t go through the renal corpuscle?.

Answer 10

Large proteins

Blood cells (red and white)

Question 11

What are some common tests to measure glomerular filtration

Answer 11

Inulin and Creatinine. These substances aren’t reabsorbed by the kidney. Thus, we see the concentration of the substance in urine x urine flow rate, divided by concentration of substance in blood, to give us to glomerular filtration rate. It shows how much has been absorbed into the kidney through the glomerulus

Question 11

Function of the proximal convoluted tubule

Answer 11

It is lined with cells covered in microvilli, and is the main site of reabsorption of most solutes (glucose, Na+, amino acids, vitamins and bicarbonate) (70% of solutes reabsorbed). Also allows for reabsorption of water

Main part is seen in ability for reabsorption of glucose into the bloodstream

Active transport ensures maximum reabsorption of glucose

Question 12

What is the loop of henle

Answer 12

It has a thin descending limb and a thick ascending limb. It assists in decreasing the water content of urine by reabsorbing water and electrolytes, thereby regulating concentration of urine

It is split into the descending and ascending limb

Question 13

Explain the descending limb and its function

Answer 13

Descending limb is permeable to water but not to ions like Na+ and Cl-. As filtrate flows down the limb, water moves out of the tubule into interstitial fluid through osmosis. The movement of water concentrates the filtrate, increasing its solute concentration as it descends deeper.

Question 14

Explain the ascending limb and its function

Answer 14

The ascending limb is impermeable to water. Instead it actively transports ions, particularly Na+ and Cl- ions into surrounding interstitial fluid. Active transport through specialised ion channels and co transporters.

Active transport creates concentration gradient in interstitial fluid, with higher concentrations of ions deeper in the medulla

This active transport is important as high difference in solute concentration will put walls under stress

Question 15

Explain the interstitial osmolarity as we go down the loop of henle

Answer 15

As we go down the loop of henle, the interstitial osmolarity increases. This is because descending is permeable to water –> initial water in interstitial fluid increases, thus osmolarity is low, however as water keeps getting out, it reaches a point where water can’t go out anymore and due to active transport of ions out of the ascending limb, there is increased osmolarity but no water –> interstiail fluid decreases. Increased osmolarity going down the loop of henle

Question 16

What is the role of the kidney in hormonal control

Answer 16

It produces aldosterone, which is in response to low blood pressure, ultimately increasing the retention of Na+ in the distal convoluted tubule and collecting duct

It also responds to the hormone Anti-diuretic hormone (ADH) which is produced by hypothallamus in response to high solute concentration in blood. This increases reabsoroption of water in nephron collecting duct by increasing insertion of aquaporins into collecting duct walls

Question 17

What is the role of the distal convoluted tubule

Answer 17

Similar to proximal convoluted tubule but shorter with fewer microvilli. Excess K+ is actively secreted into nephron here, under control of aldosterone. Excess H+ secreted here to maintain pH. Mainly less permeable to water compared to proximal, and mainly regulates reabsorption of specific ions such as Na+, Ca2+, Cl- etc.

Question 18

What is the function of collecting ducts?

Answer 18

Collects urine produced by nephrons and delivers it to the renal pelvis

Involved in water balance, as it is permeable to water. It reabsorbs water under influence of ADH. ADH increases permeability of collecting duct to water via aquaporins

Question 19

How are solutes moved from nephrons

Answer 19

Nephrons are surrounded by capillaries. Substances leaving nephron are reabsorbed into bloodstream straight away due to capillaries surrounding the nephron

Question 20

What is the renal threshold

Answer 20

Concentration of a substance in blood, above which the kidney removes it in the urine

Question 21

What is the renal threshold of glucose

Answer 21

10mmols/L

Question 22

What is the main composition of urine

Answer 22

95% water, 2.5% urea, Na+ largest component after urea, and urachrome

Question 23

Describe the mechanism of reabsorption of glucose

Answer 23

Na+ is actively pumped out of the tubule, glucose is then co transported with Na+ via a transmembrane protein. This is active transport and ensures maximum reabsorption of glucose