Chapter 15 The Kidney

Question 1

What is the structure of the kidney?

Answer 1

A pair of reddish broke organs covered into a thick layer of fat/connective tissue
Blood enters via the renal artery and leaves via the renal vein
Nephrons as the functional unit
Outer= Cortex
Middle= Medulla, with renal pyramids
Renal Pelvis at the centre
Ureter removing urine

Question 2

What are the main roles of the kidney?

Answer 2

Excretion
Osmoregulation

Question 3

What is the path the blood in the kidney?

Answer 3

Renal artery
Wide afferent arteriole
Glomerulus
Thin efferent arteriole
Renal vein

Pressure difference enables formation of filtrate

Question 4

What is the path of the filtrate within the kidney?

Answer 4

Formed in the glomerulus, moves into the Bowman’s capsule
PCT- selective reabsorption of glucose
Loop of Henlé- concentrated medulla
DCT
Collecting Duct - osmoregulation
Ureter - Bladder - Ureter

Water to surrounding capillaries also

Question 5

What is the process of ultrafiltration?

Answer 5

3 part filter:
1. Fenestrations within the blood capillary. The formation of tissue fluid due to the high hydrostatic force, smaller than 1 micrometer pass through
2. Basement membrane, collagen type 4, charged so will deflect charged molecules. 0.25 micrometers
3. Podocytes, lining the bowman’s capsule, less than 4nm gap

Question 6

What is the process of selective reabsorption, including the process of facilitated diffusion?

Answer 6

Using the sodium potassium pump, 3Na+ will be pumped from the PCT cell into the blood, and 2K+ into the cell
This creates an electrochemical gradient between the cell and the lumen of the PCT
Na+ will diffuse through its co transport protein with glucose, from the filtrate/lumen into the cell
Glucose will then diffuse into the blood via a channel protein

Question 7

How are podocytes adapted to their function?

Answer 7

Wrap around capillaries, leaving slits between the pedicels so only molecules less than 4nm in size can pass through

Question 8

How are PCT cells adapted for selective reabsorption?

Answer 8

Cells covered in microvilli to increase the surface area for diffusion
Many mitochondria for active transport
Brush border

Question 9

What is the function of the loop of Henlé?

Answer 9

Enables mammals to produce urine more concentrated than blood, by increasing the concentration of ions down the medulla

Question 10

What happens to the filtrate in the loop of Henlé?

Answer 10

IONS SPECIFY CHLORIDE and NA+ IONS

Counter current multiplier: nothing, water, passive, active
The first section of the descending limb is impermeable to water and ions
The next region of the descending limb is permeable to water, and so water water moves out via osmosis into the capillaries surrounding the nephron. This produced concentrated urine.
The first section of the ascending limb is permeable to ion movement and so they diffuse into the medulla
The next region actively transports ions out of the filtrate, producing dilute urine and a concentrated medulla.

Question 11

Why is it important that the concentration of ions in the medulla is high?

Answer 11

Enables control of urea concentration, osmoregulation
Permeability of collecting ducts changed via ADH, however, this only works if the surroundings are very concentrated, creating a water potential gradient with the medulla, for water to osmose out

Question 12

What is the glomerular filtration rate?

Answer 12

Volume of blood through the kidneys in a given time

Question 13

What do DCT cells look like?

Answer 13

Cuboidal
Without microvilli

Question 14

Histology!

Answer 14

To include glomerulus, loop of Henlé, pct, DCT, collecting duct…

Question 15

What is osmoregulation and why is it important?

Answer 15

Controlling water potential inspire of external changes
Cytolysis or crenation of cells if the blood water potential alters too much

Question 16

How is ADH secreted?

Answer 16

ADH is made in the hypothalamus but stored in the posterior pituitary
When osmoreceptors in the hypothalamus detect a low blood water potential, they stimulate the release of ADH from the posterior pituitary into the blood via nerve impulses

Question 17

What is the action of ADH? What does it actually do?

Answer 17

Target cells in the collecting duct
Causes vesicles in the cells to fuse with the cell surface membrane, inserting water based channels called aqua porins
As the surroundings are very concentrated, this causes water to osmose into the medulla and then blood capillaries
The results in concentrated urine

Question 18

In what conditions is ADH secreted? What happens when ADH is no longer being secreted?

Answer 18

Secreted when the blood water potential is too low
Stopped when the blood water potential is high
This reduces the amount of cAMP present, and so the aqua porins are removed from the cell surface membranes, and packaged back into vesicles

Question 19

What are the mechanisms elicited by the hormone ADH to stimulate a response?

Answer 19

ADH binds to its complimentary g-protein coupled glycoprotein receptor
This causes a conformational change to the receptor, which promotes the conversion of GTP to GDP
The GDP binds the coupled G-protein, causing a conformational change which results in the disassociation of its subunits
The subunits will interact with molecules such as adenyl cyclase, which promotes the conversion of ATP to cAMP, which act as secondary messengers
The cAMP will activate protein kinase A, which goes on to phosphorylate enzymes which move aqua porins to the cell surface membrane

Question 20

What are uses of urine in testing?

Answer 20

HCG for pregnancy
Glucose for kidney failure or diabetes
Testing for drugs

Question 21

How do you make monoclonal antibodies?

Answer 21

Insert a desired antigen into a mouse e.g hCG
The mouse will go on to produce antibodies with receptors compliments to the antigen
B cells are extracted and fused with myeloma cells to produce hybridomas
They hybridomas are screened to ensure they produce the correct antibodies
It proliferates, and the antibodies are harvested and purified

Question 22

How does a pregnancy test work?

Answer 22

The wick is soaked with urine, in the morning as this is when hCG is the highest
Contain mobile antibodies with attached coloured beads
These mobile antibodies bind with hCG to form a hormone-antibody complex
There are immobilised antibodies in the first and second window.
One window is a control, they will bind to the mobilised antibodies regardless
The other contains immobilised antibodies which will only bind is the hormone-receptor complex is present
Two lines indicate a positive test.

Question 23

How can urine be tested for traces of drugs?

Answer 23

Gas chromatography
Immunoassay and monoclonal antibodies

Question 24

Why might the kidneys fail?

Answer 24

Kidney infections- podocytes and tubules destroyed
Raised blood pressure- damage to cells, podocytes
Genetic conditions

Question 25

What are some common symptoms of kidney failure and what do they mean?

Answer 25

Protein in the urine- passes through the basement membrane, filter broken, possibly due to high pressure
Blood in urine- as above
Build up of urea and loss of electrolyte balance
Weakened bones, pain, and stiffness

Question 26

What is the GFR? What are some common comparisons?

Answer 26

Glomerulus filtration rate, used to measure kidney diseases
Measures amount of creative, higher level, not function properly
Chronic kidney disease: GFR<60 for 3 months
Kidney failure GFR<15

Question 27

How does haemodialysis work?

Answer 27

Uses a dialysis machine, which contains membranes that mimic the basement membranes
Normal level of glucose and proteins
Needs steep concentration gradients as its reliant on purely diffusion
Counter current to maximise diffusion, and needs a controlled diet
Several hospital visits a week, long periods of time

Question 28

How does peritoneal dialysis work?

Answer 28

Dextrose fluid placed into the peritoneal cavity, in the abdomen
As a lower water potential, causes water and dissolved substances (urea, salts) to move into the fluid with it
Mimics the function of the kidney, and can use active transport as living cells
Fluid drained and process repeated

Question 29

What are the advantages and disadvantages of kidney transplants?

Answer 29

No need to dialysis machines, less hospital visits

However risk of rejection, may be mitigated by tissue types
Immunosuppressants but increases the severity of disease
May only last 10 years, then back to dialysis
Demand much higher than availability

Question 30

Compare peritoneal and haemodialysis?

Answer 30

Peritoneal needs to be carried out several times a day whilst Haemo once or twice a week
This is because it is less efficient, as the conc gradient decreases over time, the fluid is not replenished constantly, only between dialysis
And not counter current so must be more frequent

Question 31

What happens at the DCT?

Answer 31

Fine tuning of the chloride and sodium ions in the blood and K+
So balancing of ions