Topic 8: Kidney

Question 1

Describe some functions of the kidneys

Answer 1

Kidneys are removers of waste and maintainers of balanced blood component.
- Maintain extracellular fluid composition & volume
- Maintain mass balance
- Filtration followed by reabsorption
- Secretion of some waste products
- Produce some hormones

Question 2

Where are the kidneys located?

Answer 2

• Near the abdomen and at the bottom of the rib cage
• Left kidney is higher than right one
• More to the back, near the spine

Question 3

Name the connection pathways around kidneys

Answer 3

• Renal arteries: bring oxygenated and nutritious blood from heart –> aorta –> kidnets
• Renal veins: take blood from kidneys –> vena cava –> heart
• Ureters: bring urine from kidneys –. urinary bladder

Question 4

Describe the internal anatomy of kidneys

Answer 4

Kidneys are bean-shaped organs
- Renal pelvis: collects all the urine from kidneys –> ureters
- Renal pyramid: are bundles of tubules (nephrons) producing urine
- Nephrons: micro functional units of kidneys
- Renal cortex: refers to the outer most part of the internal structure
- Renal medulla: refers to the inner part of the internal structure

Question 5

Describe the anatomy of nephrons and the general functions of each section

Answer 5

Nephrons are the units of kidneys, which take form as small tubules.
Nephrons include the renal corpuscle (blood filtration); proximal convoluted tubule (main reabsorption site); loop of henle; distal convoluted; collecting duct (fine-tuning of the urin’s composition.

Question 6

Describe the structure of the renal corpuscle

Answer 6

Renal corpuscle is made up of:
- Glomerulus: a tangle of porous capillaries. The porosity allows substances to leave the bloodstream and enter nephrons.
- Bowman’s capsule: surrounds the glomerulus to which the substances from glomerulus go into.

Question 7

Explain the ultrafiltration

Answer 7

Vessel at which the blood flows into the glomerulus is larger than the one blood goes out which creates a water pressure inside the glomerlus, forcing substances out of blood into Bowman’s capscule.

Question 8

Desccribe the glomerular filter

Answer 8

Glomerular filter has 3 layers.
- Wall of the capillary (endolethium): has fenestrae which are holes allowing substances to move through.
- Glumaerular basement membrane
- Podocytes: cells covering the outer surfaces/wraps around glomerular capillaries. There are gaps between these cells, allowing small substances to pass through to Bowman space.

Question 9

What substances can and cannot go through glomerular filter?

Answer 9

• Can go through: small molecules like H2O, glucose, amino acids, small ions like Na+, K+, urea
• Cannot go through: large proteins, blood cells

Question 10

Describe the structure and functions of the proximal convoluted tubule

Answer 10

Proximal convoluted tubule is lined with cells covered in microvilli which helps to increase surface area –> increase reabsorption rate.
This is the main reabsorption site of most solutes (glucose, Na+, amino acids, vitamins, bicarbonate).

Question 11

Describe the mechanism of reabsorping glucose

Answer 11

On the outer membrane of the proximal convoluted tubule, there are SGLT transporters actively pumping Na+ out of nephrons back into bloodstream. Glucose are also pumped together with Na+ and the active transport ensures maximum reabsorption of glucose.

Question 12

Describe the structure and function of loop of Henle

Answer 12

Loop of Henle is comprised of thin, descending limb and thick, ascending limb. Urine descends towards the medulla, then ascends back towards the cortex.

This assists in decreasing the water content of urine (prevent dehydration).

Question 13

Describe the mechanism by which loop of Henle helps maintain water balance.

Answer 13

As the urine descends towards the medulla, the osmolarity outside increases –> water from inside the nephrons diffuses out.

As the urine ascends back towards the cortex, the think wall of the ascending limb prevents water from going back out.

To stabilize the composition inside and outside the nephrons, solutes including Na+ and Cl- are actively pumped out.

Question 14

Describe the structure and functions of distal convoluted tubule

Answer 14

Distal convoluted tubule is similar to proximal one, but shorter and less microvilli.

Excess K+ and H+ are actively pumped into here to be removed in the urine.

Control the concentration of H+ helps maintain the blood pH

Question 15

Describe the functions of collecting duct

Answer 15

Collecting ducts helps collect all urine produced across many nephrons and delivers to the renal pelvis.
This duct is involved in maintaining water balance:
- Is permeable to water
- Reabsorbs water under the influence of Vasopressin
- Vasopressin increase the permeability of the collecting duct to water

Question 16

Name hormones involved in the functions of kidneys

Answer 16

• Aldosterone: produced by the adrenal gland
  + response to low blood pressure/blood volume
  + increase the absorption of excess K+ at distal convoluted tubule to remove in the urine
  + increase the reabsorption of Na+ at distal convoluted tubule
  –> increase blood volume because water follows passively
  –> increase blood pressure
• Vasopressin (ADH): produced by the hypothalamus
  + response to high blood osmolarity
  + increase the reabsorption of H2O in collecting duct by inserting more aquaporins
  –> increase blood volume, decrease osmolarity

Question 17

Explain renal threshold

Answer 17

Renal threshold the level of blood component above which the kidneys will remove it in the urine.

Question 18

Describe the composition of urine

Answer 18

• 95% water
• more than 2.5% urea (byproduct of protein metabolism)
• Na+
• urochrome: byproduct of haemoglobin breakdown, makes urine yellow