Kidney

Question 1

Descending Loop of Henle: (3)

Answer 1

As filtrate moves down the descending Loop of Henle, concentration of solutes increases in the surrounding
ISF around the nephron tubule.

This portion is permeable to water, so water leads osmosis, and is reabsorbed into the bloodstream.

Filtrate is left concentrated.

Question 2

Ascending Loop of Henle: (3)

Answer 2

Surrounding fluid becomes dilute

This portion is impermeable to water but permeable to sodium chloride, which diffuses out and is reabsorbed
into the bloodstream, lowering the solute concentration of the filtrate

Filtrate is then diluted

Question 3

Distal Convoluted Tubule: (2)

Answer 3

Sodium chloride are reabsorbed, and bicarbonate ions are reabsorbed into the blood to balance the pH levels

Drugs and poisons are secreted into the filtrate to be removed from the body

Question 4

Collecting Duct: (4)

Answer 4

Filtrate enters collecting duct

As it moves down, it passes a region where surrounding fluid has higher solute concentration allowing for
water to leave collecting duct via osmosis.

Urine is now concentrated

Urea also diffuses out of the lower portion of the duct adding to the increase in solute concentration in ISF,
allowing for more water to be reabsorbed

Question 5

Urine =

Answer 5

water + urea + sodium chloride + hydrogen ions + drugs + poison

Question 6

Nephron =

Answer 6

Renal Corpuscle + Proximal Tubule + Loop of Henle + Distal Tubule

Question 7

Counter current System in the kidney and its role in maintaining a medullary osmotic gradient.

Medullary osmotic gradient – counter current multiplier:

Answer 7

• The primary cause of the medullary osmotic gradient is the active transport of solutes
• In the ascending limb of the loop, active transport of Na+ ions drives passive transport of Cl- ions
• Addition of these ions to the ISF of the medulla increases its osmolarity
• Squamous epithelial cells of the descending limb of the loop are permeable to water but
  impermeable to most solutes
• Water leaves the filtrate in the descending limb of the loop, but the solutes cannot enter, thus
  increasing filtrate osmolarity
• Due to water movement, new filtrate entering the descending limb becomes more and more
  concentrated as it flows to the bottom of the loop
• Cuboidal epithelial cells of the ascending limb provide for active reabsorption of Na+ and Cl- ions, but are impermeable to water
• Due to the active reabsorption of solutes along the ascending limb, the filtrate being concentrated in
  the loop bottom becomes more and more diluted towards the distal convoluted tubule
• The limbs of the loop are close enough that each influences the processes occurring in the other
• Water moves out of the descending limb and produces saltier filtrate toward the loop bottom
• In the ascending limb, the solutes pumped out of the concentrated filtrate increase the medullary
  osmotic gradient
• More solutes leaving the ascending limb cause more water to leave the descending limb and vice versa
• These processes multiply each other until the dynamic equilibrium is achieved between osmolarity of
  fluids in the different limbs of the Loop of Henle and the surrounding medullar space
• This mechanism that constantly establishes the osmolarity gradient throughout the renal medulla is
  called the counter current multiplier

Question 8

Medullary osmotic gradient – urea recycling: (6)

Answer 8

• The effect of urea recycling greatly increases the medullary osmotic gradient values to their final
  amounts
• When filtrate enters the medullary part of the collecting duct, most water has been reabsorbed, leaving
  urea relatively concentrated
• Collecting duct cells are highly permeable to urea, so urea diffuses into the medulla, this increasing
  the interstitial osmolarity
• The effect of urea recycling greatly increases the medullary osmotic gradient values to their final
  amounts
• The rest of the nephron tubules are poorly permeable to urea; therefore, urea is recycled back to the
  collecting duct in the medulla
• Along with sodium chloride, urea provides a great deal of the solute load in the medulla, producing
  much of the medullary osmotic gradient

Question 9

Medullary osmotic gradient – vasa recta counter current exchange:

Answer 9

• An ordinary capillary carrying blood from the cortex, and through the medulla, would remove the
  solutes necessary to generate the medullary osmotic gradient
• The shape of the vasa recta follows the limbs of the loop, providing a mechanism to maintain the
  gradient
• Blood enters the medulla of the kidney with normal osmolarity
• As blood moves into the medulla, highly permeable vasa recta capillaries exchange solutes with ISF
• Blood osmolarity increases
• As the blood moves out of the medulla, up to the cortex, it loses solutes
• Blood osmolarity decreases nearly to the normal value
• The small increase of osmolarity in the blood leaving the vasa recta:
  Is the result of the blood colloid osmolarity
  Indicates that some water is lost from the body
• Tissues are provided with nutrients and oxygen, but solutes that maintain the medulla osmotic
  gradient are not transported away from the nephron

Question 10

Kidneys control blood volume and pressure buy changing water level (removing more or less water)
Hormones involved in kidneys: (4)

Answer 10

Vasopressin
Aldosterone
Renin
Atrial natriuretic peptide

Question 11

Vasopressin: (4)

Answer 11

• Antidiuretic hormone
• Released in response to low blood volume or high plasma osmolarity
• Cause kidneys to retain water by increasing water permeability of collecting duct
• Increase blood pressure

Question 12

Aldosterone:

Answer 12

• Causes sodium retention and water retention

Question 13

Renin: (2)

Answer 13

• Is released in response to low blood pressure
• Releases Angiotensin II which causes:
  Vasoconstriction
  Releases Vasopressin/Aldosterone
  Causes thirst which increases water intake

Question 14

Atrial natriuretic peptide: (2)

Answer 14

• Decreases blood pressure c
• Causes:
  Vasodilation
  Increases glomerular filtration
  Inhibits release of Renin and Aldosterone
  Inhibits sodium reabsorption → Less Na+ back in blood → Less water back in blood

Question 15

Control blood pH
Bicarbonate ions released in filtrate
Reabsorbed back into blood stream based on pH of blood
- If blood is too ______ more bicarbonate ions reabsorbed
- If blood is too _______ less bicarbonate ions reabsorbed
Collecting ducts also secrete bicarbonate into acidic bloc

Answer 15

acidic
alkaline

Question 16

RBC formation homeostasis:

Answer 16

• Kidneys secrets erythropoietin (EPO) → a stimulating factor for RBC formation
• When RBC count drops, resulting oxygen deficiency state is detected by kidneys which causes kidneys to
  increase EPO production

Question 17

Calcium homeostasis:

Answer 17

• Low blood calcium causes release of parathyroid hormone (PTH) → also causes kidneys to retain calcium
• This causes kidneys to release calcitriol (active vitamin D)
• Calcitriol promotes absorption of calcium in small intestine and increases reabsorption of calcium in nephrons

Question 18

How are water levels maintained?

Answer 18

Hypothalamus + Posterior pituitary gland + kidneys maintain water balance in body

Osmoreceptors in hypothalamus monitor water levels

Neurosecretory cells in hypothalamus secrete ADH if
osmoreceptors detect low levels of water/increase in blood osmolarity (more solutes in blood)

The ADH travels down axons and is stored in posterior pituitary until needed

ADH targets kidney’s collecting
ducts to conserve water

Question 19

How ADH works on collecting duct cells:

Answer 19

Collecting duct cells have ADH receptor proteins on the cell membrane.

When ADH binds to receptor, this stimulates the attachment of aquaporin proteins to the cell membrane, facilitating movement of water from lumen of collecting ducts to the blood stream (reabsorption)

An ADH receptor will receive the ADH hormone, a secondary messenger and protein kinase within the cells activate vesicles containing aquaporin proteins to move to the cell surface and allow for exocytosis to include the aquaporins on the membrane on cell. More aquaporins means that osmosis can take place more readily and more efficiently, thus the amount of water reabsorbed from the collecting ducts increases.

Question 20

Effect of ADH on balancing of Blood Osmolarity:

Answer 20

Question 21

Diuretics –. Enhances urine output + increases urine formation: (4)

Answer 21

1. Alcohol – ADH inhibitor leading to dehydration (leads to hangover) (this is why the longstanding presence of alcohol in the system can cause a person to suffer a hangover)
2. Drugs for hypertension or oedema (e.g.: furosemide or Lasix); Na+ reabsorption inhibitors (and resultant H2O reabsorption)
3. Loop diuretics inhibit the medullary gradient formation (make the loop of Henle and the vasa recta inefficient) → kidney will not be able to release concentrated urine but rather diluted urine
4. Osmotic diuretics: Substances that are not reabsorbed and this water will remain within the filtrate
   (for e.g., high glucose of a diabetic patient)

Question 22

Antidiuretic hormone disorders: (2)

Answer 22

1. Mutation in ADH production or lack of receptors for ADH
   - Causes severe dehydration and solute imbalance
   - Diabetes insipidus
2. Hypersecretion of ADH
   - Syndrome of inappropriate ADH secretion (SIADH)
   - This will cause the body to retain far too much water and as a result the individual will be too hydrated.

Question 23

Polyuria vs Oliguria vs Anuria

Answer 23

Question 24

How do kidneys maintain homeostasis?

Answer 24

Aldosterone, renin, ANP (atrial natriuretic peptide) help maintain salt balance in order to control blood volume

Aldosterone: adrenal hormone that regulates sodium excretion
➔ Mechanism used to regulate sodium excretion → increases Na+ reabsorption from distal tubule and
collecting duct

Aldosterone secretion is controlled by the RAAS (renin-angiotensin-aldosterone system)

Question 25

Juxtaglomerular apparatus (JGA)=

Answer 25

= afferent arteriole + efferent arteriole + distal tubule

Question 26

What is juxtaglomerular apparatus?

Answer 26

It is a specialised structure made from the afferent arteriole and the convoluted distal tubule. It is located near the vascular pole of the Bowman’s capsule and its main function is to correct changes in blood pressure within the nephrons of the kidneys.

Question 27

Mechanism of RAAS system to balance blood pressure and blood volume: (7)

Answer 27

1. Blood pressure or blood volume drops 2. Sensors in the JGA in the afferent arteriole detect the decrease 3. This stimulates renin-secreting cells in afferent arteriole to secrete renin 4. Renin causes angiotensinogen (liver) to convert into Angiotensin I 5. ACE (angiotensin converting enzyme produced in lungs) converts Angiotensin I to Angiotensin II 6. This causes adrenal gland to secrete aldosterone and causes arterioles to constrict causing blood pressure to increase 7. Aldosterone increases reabsorption of sodium and hence water, increasing blood volume + blood pressure

Question 28

Clinical Application: Renin-Angiotensin System controls blood volume and blood pressure ACE inhibitors: (2)

Answer 28

- Medication for blood pressure - These inhibit angiotensin converting enzyme in the lungs (ACE) Block normal production of Angiotensin II Aldosterone concentration will decrease Sodium + water excretion will increase Blood volume will be slightly reduced Blood vessels will dilate → lowering blood pressure

Question 29

Coordinated Regulation of Salt and Water Balance ADH (triggered by change in blood osmolarity) and RAAS (triggered by change in blood volume or blood pressure) both increase water reabsorption, but only _____ maintains body fluid _______ (leads to sodium reabsorption by release of aldosterone) by stimulating Na+ ________.

Answer 29

RAAS osmolarity reabsorption

Question 30

Atrial natriuretic peptide(ANP), opposes the RAAS - Secreted by atrial _________ of the heart - Released in response to an increase in blood volume and ______ - inhibits the release of ______...aldosterone... (NaCl reabsorption) ---ADH secretion - lowers blood pressure and volume

Answer 30

myocardium pressure renin

Question 31

_____, ADH, and the RAAS - checks and balances to control blood osmolarity, salt concentration, volume, and pressure

Answer 31

ANP

Question 32

Kidney disorders If kidneys malfunction: (4)

Answer 32

- high blood pressure - anaemia (too few RBCs) - vitamin D deficiency - dangerous fluctuations in blood pH

Question 33

Disorders of the urinary system: Causes of renal dysfunction → (3)

Answer 33

obstruction + infection + inflammation

Question 34

What are the 3 types of kidney disease?

Answer 34