Renal system

Question 1

Where are the kidneys located?

Answer 1

Posterior abdominal wall

Question 2

What are the functions of the kidney?

Answer 2

• Excretion of waste products & toxins
• Maintenance of homeostasis and formation of urine
• Regulation of electrolyte balance
• Regulation of fluid balance
• Regulation of acid: base balance
• Produce renin- control Bp
• Control erythropoietin
• Metabolism of vitamin D

Question 3

Nephron=

Answer 3

Microscopic funcitonal unit of the kidney.
Approximately 1 million per kidney.
It consists of:
- Glomerulus
- Bowmans capsule
- Proximal convoluted tubule (PCT)
- Nephron loop/ loop of henle
- Distal convoluted tubule (DCT)
- Collecting duct (CD)
Glomerulus (network of capillaries) sits inside glomerular capsule

Question 4

What is the formation of urine?

Answer 4

1- (glomerular) filtration
2- (tubular) reabsorption
3- (tubular) secretion

Question 5

Glomerulus=

Answer 5

network of small capillaries

Question 6

Bowmans capsule/ glomerular capsule=

Answer 6

is a cup-like sac at the beginning of the tubular component of a nephron in the that performs the first step in the filtration.
There are two arterioles within: Afferent & efferent. Plasma travels through afferent arterioles to be filtered by glomerulus and then leaves through efferent.

Question 7

Explain stage one: filtration

Answer 7

-Movement of H20 & solutes from blood into filtrate under pressure.
- The rate at which kidney/ nephron filters blood is known as glomerular filtration rate (GFR)
(The net filtration out is known as hydrostatic pressure.
The net filtration in is known as the pressure in capsular space)
- The filtrate passing into the proximal convoluted tubule contains everything in the blood except red and white blood cells, platelets and large proteins e.g., albumin
- Filtrate contains: glucose, amino acids, wastes, vitamins, electrolytes, nutrients, water i.e., basically plasma minus proteins

Question 8

Explain stage two: reabsorption

Answer 8

The return of useful substances & water from filtrate into blood. Is a selective process.
The proximal convoluted tubule is the mains site of reabsorption.
Reabsorption continues throughout tubules by active and passive means and the influence of hormones.
Aldosterone influences reabsorption in distal convoluted tubule.
ADH affects permeability of collecting duct to H2O.

Question 9

Explain stage three: secretion

Answer 9

Is the active removal of unwanted substances/ wastes from blood into filtrate.
It occurs all along the tubule
It is important for regulating k+ and pH.

Question 10

Auto-regulation=

Answer 10

If pressure is high, afferent arteriole constricts to reduce pressure entering glomerulus. If pressure is low, efferent arteriole constricts to increase pressure in glomerulus.
Low pressure in afferent arteriole also stimulate release of renin.

Question 11

Juxtamedullary nephrons=

Answer 11

Play a role in kidneys ability to concentrate urine. They are characterised by their long nephron loops (loops of Henle) that extend into the medulla. They are divided into two main segments:
1- Descending limb= permeable to water allowing water to leave the tubule.
2- Ascending limb= impermeable to water but actively transports sodium, chloride and potassium ions out of the tubule and into surrounding medullary interstitium.

Question 12

Role of ADH and the kidney=

Answer 12

• ADH secretion is increased/ decreased in response to osmotality
• Increase in ADH leads to greater reabsorption so a loss of urine.
• Decrease in ADH leads to loss of reabsorption so more urine.

Question 13

What are the mechanisms to maintain acid base balance?

Answer 13

• Buffers e.g., bicarbonate and proteins. Acts as sponges and soaks up excess H+ or OH- ions
• Respiratory system/ lungs: detects changes in H+ concentration. If H+ increases this causes the respiratory rate to increase which results in excess H+ breathed out as CO2.
• Renal system/ kidneys: If pH falls (i.e. acidosis) this results in secretion of H+ into urine (and bicarbonate tops up the buffers).
  In the tubules H+ combines with a buffer and is excreted in the urine (e.g ammonia)
  Opposite if alkalotic

Question 14

Explain the production of erythropoietin

Answer 14

-Produced in kidney
- Stimulates bone marrow to produce red blood cells
- Is stimulated by hypoxaemia

Question 15

What promotes filtration?

Answer 15

• The arterial blood pressure
• Net filtration pressure: sum of forces

Question 16

Explain the regulation of glomerular filtration rate in the kidneys

Answer 16

Myogenic mechanism:
- Afferent arteriole constricts/ dilates to reduce or increase blood flow to the glomerulus and maintain GFR

Tubuloglomerular feedback:
- Involves juxtaglomerular apparatus which includes macula densa cells of the distal tube.
- Macula densa cells sense sodium chloride (NaCl concentration in the filtrate.
- High NaCl cause afferentt arteriole constriction, low NaCl causes dilation of the afferent arteriole.

Hormonal regulation
- Renin is released by the JGA when blood pressure of NaCl is low
- Renin is converted into angiotensin II which constricts efferent arterioles which increases pressure in the glomerulus to m maintain GFR.

Neural regulation
- Sympathetic nervous system causes vasoconstriction of both afferent and efferent arterioles, reducing blood flow and GFR.
- This prioritises blood flow to vital organs

Question 17

Urine chemical composition=

Answer 17

Urine= 95% water, 5% solutes
It has:
- water
- urea
- sodium, potassium, phosphate, sulphate
- creatinine
- uric acid

Question 18

Vasa recta=

Answer 18

The vasa recta capillaries are long, hairpin-shaped blood vessels that run parallel to the loops of Henle. The hairpin turns slow the rate of blood flow, which helps maintain the osmotic gradient required for water reabsorption.

Question 19

Renin- angiotensin- aldosterone mechanism

Answer 19

Sodium and water movement = blood pressure control
- Renin released from junta-glomerular apparatus in response to low pressure
- Renin converts circulating angiotensinogen into angiotensin I
- Angiotensin I is converted into angiotensin II by angiotensin converting enzyme from lungs
Angiotensin II causes:
- Vasoconstriction of systemic blood vessels
- Release of aldosterone from adrenal cortex causing reabsorption of Na+ and H2O in renal tubules, also influences ADH release

Question 20

Calcium and phosphate regulation

Answer 20

• Main hormonal control of calcium homeostasis is through release of parathyroid hormone
• Kidneys role in Ca2+ homeostasis is through reabsorption of Ca2+ and metabolism of vitamin D into an active form
• Ca2+ is reabsorbed as phosphate is excreted