Wjec Biology // By4 // 4.6 // Homeostasis And Kidney Function

Front 1

Homeostasis and Kidney Function

Back 1

Kidney

Front 2

Homeostasis
1. Definition: Homeostasis
2. Process of Negative Feedback

Back 2

1. The maintenance of a constant internal environment via the process of negative feed back.
2. Receptor detects deviation from a point.
- Sends instructions to co-ordinator.
- Co-ordinator communicates with effector, to carry out corrective procedures.
- Once correction is made, instructions sent to receptor, which then switches off.
- Co-ordinator is no longer alerted to the deviation from normal.

Front 3

Kidney
1. Two Kidney Functions
2. Describe production of Urea
3. How is urea removed?
4. Why does urea need to be removed?

Back 3

1. Removal of nitrogenous metabolic waste and osmoregulation.
2. Excess proteins need to be broken down. The amino acids are deaminated in the liver, producing ammonia which is quickly converted to urea.
3. It is released in to the blood and then removed by the kidneys.
4. It is poisonous.

Front 4

Structure of the Kidney
1. What is the kidney made out of?
2. Describe the structure of a nephron
3. What are other two capillary structures?

Back 4

1. Consist of millions of uriniferous tubules or nephrons.
2. Within a Bowmans capsule there is a knot of capillaries known as glomerulus.
- Blood supply to nephron begins at afferent arteriole, which connects to glomerulus.
- From glomerulus blood is carried out by efferent arterioles to two other capillary networks.
3. Serving the proximal and distal convoluted tubules.
- Other serves the loop of henle and is known as the vasa recta.

Front 5

Ultrafiltration
1. What is ultrafiltration?
2. Describe the process of ultrafiltration
3. Name the structure within the glomerulus and describe its function

Back 5

1. Filtration under pressure separating small soluble molecules from the blood plasma.
2. Small molecules such as glucose, water, urea and salts are filtered from the capillaries, from the glomerulus to the bowmans capsule. blood entering glomerulus is separated from space inside the BC by two cell layers and basement membrane.
3. Basement membrane of capillary forms a selective barrier, between blood and nephron. Molecular Sieve.
- First cell layer - wall of capillary - contains many small gaps
- Basement membrane between the two acts as filter during ultrafiltrtion.
- Second layer - wall of BC - epithelial cells called podocytes.

Front 6

Ultrafiltration continued..
4. What does the sieve action do?
5. How does the glomerulus maintain its pressure?

Back 6

4. Allows smaller molecules to pass through, retaining blood proteins and cells.
5. Most of the pressure comes the hydrostatic pressure of the blood.
- Further amplified by narrow efferent arterioles and the water potential in blood produced by colloidal plasma proteins.
- Can be altered by changing diameter of arterioles.

Front 7

Selective Reabsorption
1. What is selective reabsorption?
2. Where are glucose, water and salts absorbed at?
3. How is glucose and salts reabsorbed?
4. What is the function of the loop of henle?

Back 7

1. Selective reabsorption is the process of reabsorbing glucose and salts back into the blood as filtrate flows along nephron.
2. All the glucose, most of the water and salts = proximal convoluted tubule.
- Small amounts of water and salts in the distal tubule.
- Remaining water absorbed by collecting duct.
3. They are reabsorbed by active transport.
4. Collectively concentrate salts in tissue fluid of the kidney.

Front 8

Selective Reabsorption continued..
5. What is the function of concentrating the salts and what is the principle of the loop of henle?
6. Process that occurs in ascending limb
7. Process that occurs in descending limb
8. What is the effect of concentrations in the loop of henle?
9. How are the cell walls adapted in the PCT

Back 8

5. It causes osmotic flow of water out of collecting ducts concentrating urine, making it hypertonic to blood. Counter Current multiplier.
6. Fluid flows up and NA+ and CL- are A.T out and into the tissue fluid, creating a low WP.
Ascending limb is relatively impermeable to water whilst descending is permeable.
7. Water leaves filtrate of descending limb via osmosis, carried away by blood in vasa recta.
8. Filtrate becomes more conc as it reaches hairpin.
- Becomes more dilute as it travels up ascending limb.
- Osmotic Gradient is maintained throughout, down the descending limb as surrounding fluid becomes more conc.
-Effect is multiplied by length of loop of henle.
- This results in osmotic extraction of water from adjacent permeable collecting ducts.
9. Microvilli for large SA for absorption.
Numerous mitochondria providing ATP for AT.

Front 9

Osmoregulation
1. Process of negative feedback for osmoregulation
2. What controls the permeability of collecting duct?
3. Draw the process of negative feedback for osmoregulation.

Back 9

1. Receptors in hypothalamus detect change, pituitary gland acts as co-ordinator and collecting duct acts as effector.
2. Hormone, ADH. Making the walls of the collecting duct more permeable, concentrating urine.

Front 10

Adaptations to different environments
1. Adaptations of nitrogenous waste for Aquatic animals, Birds and Mammals
2. Adaptation of loop of henle in desert conditions
3. What is the other process to obtain water?
4. How can they conserve water?

Back 10

1. Aquatic = ammonia, highly toxic, extremely soluble in water, diffuses out of gills, and diluted.
Birds = uric acid, insoluble and non toxic, large energy cost but little water, allowing them to live in dry environments.
Mammals = urea, requires less energy, not as toxic so can tolerate high concs for short periods of time.
2. Longer loop of henle allowing for greater solute concentration.
3. Metabolic water, break down of food reserves during respiration.
4. Remain underground in cool and humid environments minimising evaporation.