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Homeostasis > The Kidney > Flashcards

The Kidney Flashcards

1
Q

What is the Function of the Kidney?

A

Regulates water content of blood and filters blood

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2
Q

Where does Ultrafiltration occur?

A

Bowman’s Capsule

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3
Q

What happens during Ultrafiltration?

A

Small molecules including ( amino acids, glucose, urea and inorganic ions) are filtered out of the blood capillaries of the glomerulus to form the glomerular filtrate.

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4
Q

What are the two stages of Urine production in the kidneys?

A

1.Ultrafiltration
2.Selective reabsorption

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5
Q

What causes the small molecules in the blood capillaries of the glomerulus to be pushed out into the Bowman’s Capsule?

A

The afferent arteriole has a wider lumen than the efferent arteriole. This creates a high hydrostatic pressure as blood flows through the glomerular capillaries.
This increase in hydrostatic pressure causes small molecules to be pushed through the basement membrane.

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6
Q

The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule is separated by two cell layers with a basement membrane in between them.

What are these two cell layers and how do they allow small molecules to pass out?

A

The first Cell layer is the endothelium of the blood capillary. The endothelial cells have many pores to allow small molecules to pass out.

The second cell layer is the epithelium of the Bowman’s capsule- these epithelial cells have many tiny finger-like projections with gaps in between them and are known as podocytes which allows the filtrate to pass out.

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7
Q

What substances remain in the glomerular blood capillaries during Ultrafiltration and why?

A

Protein and red blood cells are too large to go through the endothelium so remain in the glomerular capillaries.

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8
Q

What is the Water potential of the blood plasma in the glomerular capillaries like compared to the water potential of the filtrate in the Bowman’s capsule? Why is this?

A

The solute concentration in the glomerular capillaries is greater than in the filtrate of the Bowman’s capsule.

This makes the water potential of the blood plasma in the glomerular capillaries lower than the filtrate in the Bowman’s capsule

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9
Q

The blood plasma in the glomerular capillaries has a lower water potential than the filtrate in the Bowman’s Capsule. What does this cause to happen?

A

Water moves down the water potential gradient from the Bowman’s Capsule into the blood plasma in the glomerular capillaries.

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10
Q

Where does Selective Reabsorption occur?

A

The Proximal Convoluted Tubule

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11
Q

What happens during Selective Reabsorption?

A

Useful molecules are reabsorbed from the filtrate and returned to the blood as the filtrate flows along the nephron.

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12
Q

How are the epithelial cells of the Proximal Convoluted Tubule adapted for Selective Reabsorption?

A

Many microvilli on the luminal membrane. ( the cell surface membrane that faces the lumen). This increases the surface area for reabsorption.

Many co-transporter proteins in the luminal membrane

Many Mitochondria. These provide energy for the sodium potassium pump proteins in the basal membranes of the cell.

Cells tightly packed together. These means that no fluid can pass between cells.

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13
Q

What are the basal membranes of the proximal convoluted tubule?

A

The basal membranes (of the proximal convoluted tubule epithelial cells) are the sections of the cell membrane that are closest to the blood capillaries.

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14
Q

Explain how selective reabsorption occurs

A

Sodium potassium pumps in the basal membrane pump sodium ions out of the epithelial cells into the blood.

This creates a concentration gradient as there is now a lower concentration of sodium ions inside the epithelial cell.
This causes sodium ions to move down the concentration gradient into the epithelial cell by facilitated diffusion. As the sodium ions flood in through this co-transporter protein they couple with with another solute such as glucose which is carried back into the cell with them.

Once inside the epithelial cells these solutes diffuse down their concentration gradients through specific carrier proteins in the basal membrane into the blood.

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15
Q

Why is no glucose present in Urine?

A

All glucose in the glomerular filtrate is reabsorbed into the blood.

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16
Q

What types of substances are reabsorbed from the glomerular filtrate?

A

Glucose, Amino acids, vitamins and inorganic ions.

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17
Q

Selective Reabsorption from the proximal convoluted tubule causes water to move into the blood. Why is this?

A

The movement of all these solutes from the proximal convoluted tubule into the capillaries increases the water potential of the filtrate and decreases the water potential of the blood in the capillaries.

This creates a steep water potential gradient and causes water to move into the blood by osmosis

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18
Q

What allows urea to be reabsorbed into the blood?

A

The concentration of urea in the filtrate is higher than in the capillaries, causing urea to diffuse from the filtrate back into the blood.

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18
Q

What part of the nephron is responsible for absorbing the remainder of the water?

A

The loop of Henle(the DCT) and the collecting duct

18
Q

Contrast the Descending and Ascending limbs of the loop of Henle.

A

The descending limb is narrower with thinner highly water permeable walls
It is impermeable to ions.

The ascending limb is wider with thick water impermeable walls.
It is permeable to ions.

19
Q

Explain how water is reabssorbed from the loop of henle and the collecting duct.

A

The ascending limb is permeable to ions (sodium) but impermeable to water.
Ions are pumped out of the limb into the interstitial space by active transport
This transport of ions occurs all the way up the ascending limb therefore the osmolarity of the urine decreases as it ascends.
The ions from the ascending limb create an area of high concentration around the loop of henle.This lowers the water potential of the interstitial space.
The descending limb is impermeable to ions but permeable to water. Water moves out of the DLdown the water potential gradient by osmosis due to a high concentration of ions in the surrounding tissue.
So the osmolarity of the urine increases as it descends the LoH
The concentration gradient of ions and water created by the LOH is maintained by a counter-current exchange mechanism.

19
Q

The concentration of urine is directly proportional to what?

A

The length of the loop of Henle

19
Q

Why is more water reabsorbed if the loop of henle is longer?

A

This increases the sodium ion concentration in the medulla, and the gradient is maintained for longer.
The water potential gradient is maintained for longer, so more water is reabsorbed from the loop and collecting duct by osmosis.

19
Q

What is Osmoregulation

A

the control of the water potential of the blood.

20
Q

What can cause the water potential of the blood to vary?

A

sweating
volume of water consumed
concentration of ions e.g. consumed or used

20
Q

What is the name of the receptors that the detect the rise or fall in water potential of the blood?

A

Osmoreceptors

20
Q

Where are Osmoreceptors located?

A

Hypothalamus

21
Q

What is ADH?

A

(Antidiuretic Hormone) is a hormone which causes the kidney to reabsorb more water.

21
Q

What does ADH reduce?

A

reduces the loss of water in the urine.

21
Q

When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why

A

When dehydrated the water potential of the blood is decreased.
Therefore water will move out of the osmoreceptor into the blood by osmosis.

21
Q

What part of the nephron does ADH effect?

A

the distal convoluted tubule and the collecting duct.

21
Q

Explain what happens when the water potential of the blood is too low.

A

fall is detected by osmoreceptors in the hypothalamus.

The posterior pituitary gland secretes more ADH.
ADH increases the permeability by fusing vesicles with aquaporins into the membrane in the DCT and the collecting duct.

More water is reabsorbed as more water leaves the nephron through the aquaporins into the blood capillary via the interstitial fluid down a water potential gradient by osmosis.

The water potential of the blood is increased.
There will be a smaller more concentrated urine.

21
Q

What happens when osmoreceptors detect a fall in blood water potential.

A

Impulses are sent to the posterior pituitary gland.
These nerve impulses stimulate the posterior pituitary gland to release antidiuretic hormone (ADH)

21
Q

What part of the brain releases ADH?

A

the posterior pituitary gland.

22
Q

How does ADH increase the permeability of the distal convoluted tubule and collecting duct?

A

Activates enzymes that cause vesicles containing aquaporins to fuse with the membrane- the more osmosis of water.

22
Q

Explain what happens when the water potential of the blood is too high.

A

Rise is detected by osmoreceptors in the hypothalamus

decrease in impulses sent to the posterior pituitary gland.

less ADH released causes decreased permeability in the membrane of the DCT and the collecting duct.

Less water is reabsorbed/ leaves the nephron through the aquaporins into the blood capillary via the interstitial fluid by osmosis down the water potential gradient.

There will be more volume of a less concentrated urine.
When the water potential returns to normal, this is detected and ADH returns to normal levels. ( negative feedback)

22
Q

Why is glucose found in the urine of someone with diabetes?

A

With diabetes there is a high concentration of glucose in the filtrate due to a lack of insulin production.
This means it cannot all be reabsorbed as the carrier proteins in the membrane of the PCT would be saturated.

23
Q

The kidney is surrounded by a tough outer layer. What is this called?

A

A fibrous capsule.

24
Q

What does the cortex of the kidney contain?

A

contains the glomerulus, as well as the Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule of the nephrons

25
Q

What does the medulla of the kidney contain?

A

contains the loop of Henle and collecting duct of the nephrons

26
Q

What is the Renal pelvis?

A

where the ureter joins the kidney

27
Q

Describe the network of blood capillaries in a nephron.

A

Each glomerulus is supplied with blood by an afferent arteriole (which carries blood from the renal artery)
The capillaries of the glomerulus rejoin to form an efferent arteriole.
Blood then flows from the efferent arteriole into a network of capillaries that run closely alongside the rest of the nephron.
Blood from these capillaries eventually flows into the renal vein

28
Q

What does the renal vein do?

A

carries deoxygenated blood away from the kidney.

29
Q

what does the renal artery do?

A

carries oxygenated blood to the kidneys.

30
Q

Explain the counter-current exchange mechanism in the nephron

A

Blood in the capillaries flows in the opposite direction to the urine in the loop of henle so doesnt wash away the osmotic gradient in the renal medulla.

31
Q

some mammals living in desert environments have been shown to secrete large amounts of ADH and have elongated loops. Explain how these features are adaptations to their habitat.

A

A longer loop of Henle allows more water to leave the filtrate in the descending limb;
[1 mark]
A longer loop of Henle allows more sodium/chloride ions to leave the filtrate in the ascending limb; [1 mark]
ADH acts on the collecting duct / distal convoluted tubule; [1 mark]
ADH makes cells more permeable OR ADH inserts aquaporins in plasma membranes; [1 mark]
So more water (from filtrate) is reabsorbed / returned to blood OR less water in urine;[1 mark]
By osmosis; [1 mark]
And urine is more concentrated; [1 mark]

32
Q
A

Homeostasis (2 decks)

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