Homeostasis and the Kidneys

Question 1

What is homeostasis?

Answer 1

It is the maintenance of a constant environment.

Question 2

What is a negative feedback mechanism?

Answer 2

A change in a system produces a second change, which reverses the first change.

Question 3

What is excretion?

Answer 3

It’s the removal of wastes made by the body

Question 4

What are the 2 main functions of the kidneys?

Answer 4

Excretion, removal of nitrogenous metabolic waste.

Osmoregulation, control of the water potential of the body’s fluids by regulating the water content and the solute concentration.

Question 5

Where and why is urea made?

Answer 5

Its made in the liver after excess amino acids are deaminated. Other nitrogen-containing waste products can also be converted to urea.

Question 6

What are the 3 main regions of the kidney?

Answer 6

Outer cortex.
Inner medulla.
Renal pelvis.

Question 7

Where does the kidney receive blood from?

Answer 7

Receives it from a renal artery and returns blood to the general circulation in a renal vein.

Question 8

Where does ultrafiltration occur?

Answer 8

At the Bowman’s capsule.

Question 9

What is the capillary network surrounding the loop of henle called?

Answer 9

Vasa recta.

Question 10

Why is there a high pressure in the glomerulus?

Answer 10

The hearts contraction increases the pressure of arterial blood.
The afferent arteriole has a wider diameter than the efferent arteriole.

Question 11

What is the selective barrier that acts like a sieve during ultrafiltration?

Answer 11

The basement membrane of the podocytes.

Question 12

What is within the glomerular filtrate?

Answer 12

Water.
Glucose.
Salts.
Urea.
Amino acids.

Question 13

What is too large to pass through the basement membrane?

Answer 13

Red blood cells.
Large plasma proteins.

Question 14

What is selective reabsorption?

Answer 14

The uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream.

Question 15

Where does selective reabsorption take place?

Answer 15

Takes place in the proximal convoluted tubule (PCT).

Question 16

What features of the PCT make it suitable for selective reabsorption?

Answer 16

Large S.A.
Cubioidal epithelial cells in its walls with a S.A. increased by microvilli.
Many mitochondria providing the ATP for active transport.
A close association with capillaries.
Tight junctions between the cells of PCT epithelium.

Question 17

How does selective reabsorption reabsorb the glucose and amino acids?

Answer 17

By co-transport. Na+ is actively transported out of the epithelial cells decreasing the concentration gradient. A glucose molecule and 2 Na+ ions bind to a transporter protein in a cuboidal epithelium cell membrane and are carried into the cell by facilitated diffusion. Sodium diffuses into the capillary down its concentration gradient providing the energy for the secondary active transport of glucose into the blood, against its concentration gradient.

Question 18

How and Where is most of the water reabsorbed from the glomerular filtrate?

Answer 18

About 90% is reabsorbed in the PCT by osmosis. This happens because the reabsorbed ions lower the water potential of the blood.

Question 19

What condition may cause glucose to be lost in the urine?

Answer 19

Diabetes, Type 1 and 2.

Question 20

How does the loop of henle reabsorb some of the water from the glomerular filtrate?

Answer 20

The ascending limb (impermeable) actively transport sodium and chloride ions out of the filtrate into the tissue fluid which makes the medulla have a lower water potential. The walls of the descending limb are permeable to water so water diffuses out by osmosis down a water potential gradient into the vasa recta (capillaries).

Question 21

What is the hormone that causes the DCT and the collecting duct to become permeable to water?

Answer 21

ADH (Antidiuretic hormone).

Question 22

Where is Antidiuretic hormone produced and what effect does it have?

Answer 22

It is produced in the hypothalamus and secreted by the posterior pituitary gland. It increases permeability of the cells of the distal convoluted tubule and collecting duct by causing aqua porins to fuse with the membrane, increasing water reabsorption.

Question 23

How does osmoregulation work?

Answer 23

-Osmoreceptors in the hypothalamus detect a reduced water potential.
-ADH is released, increasing the permeability of the walls of the DCT and collecting duct to water.
-More water is reabsorbed into the region of high solute concentration.
-More water is reabsorbed from the medulla into the vasa recta.
-Water potential of blood is restored to normal.
The opposite occurs if the water potential of the blood decreases.

Question 24

What are the commonest causes of kidney failure?

Answer 24

Diabetes.
High blood pressure (Prevents ultrafiltration).
Auto-immune disease.
Infection.
Crushing injuries.

Question 25

What treatments are used to reduce the concentration of waste products and control the volume of body fluids if the kidneys are damaged?

Answer 25

Reducing intake of certain nutrients.
Using drugs to reduce blood pressure.
Regulating the concentration of dissolved potassium and calcium.
Dialysis.
Kidney transplant.

Question 26

What are the 2 forms of dialysis?

Answer 26

Haemodialysis.
CAPD (Continuous ambulatory peritoneal dialysis).

Question 27

How does Haemodialysis work?

Answer 27

Blood is taken from and artery and run through long, narrow fibres made of selectively permeable dialysis tubing which are surrounded by the dialysis fluid. The pores in the tubing let molecules out into the dialysis fluid.

Question 28

How does CAPD work?

Answer 28

The patient drains a bag of dialysis fluid through a catheter in the abdomen, into the body cavity. The peritoneum is the membrane lining the body cavity and it has a rich supply of capillaries so it acts as the dialysis membrane. The fluid is then drained from the abdomen.

Question 29

Why must the recipient of a donated organ take immunosuppressant’s?

Answer 29

To prevent the body attacking the donated organ but because it suppresses the immune system, the patients are more susceptible to infection.

Question 30

Where is the transplanted kidney placed?

Answer 30

In the lower abdomen, attached to the iliac artery and vein.

Question 31

What are the 3 forms that ammonia can be excreted as and which organisms excrete which?

Answer 31

Ammonia, most aquatic organisms.

Uric acid, birds reptiles and insects (very little water is needed for its excretion).

Urea, mammals.

Question 32

What are the 2 types of nephron and what are their differences?

Answer 32

Cortical nephrons, short loop of henle.
Juxtamedullary nephrons, long loop of henle.

Question 33

What is metabolic water?

Answer 33

Water produced from the oxidation of food reserves.