OCR ALEVEL BIOLOGY - Kidney

Ultrafiltration

Blood enters the AFFERENT arteriole under high pressure (ARRIVING at the glomerulus). Afferent arteriole has a wider diameter, than the Efferent arteriole (EXITING the Glomerulus). the difference in diameter increases blood hydrostatic pressure in the glomerulus so fluid/filtrate is forced out into the Bowman's Capsule (which has low pressure).

Ultrafiltration Vs Tissue Fluid Formation Similarities

1. Both occur in the capillaries.
2. Large molecules (Proteins & Erythrocytes) remain in the blood.
3. Many molecules (Water, Sugar & Ions) are reabsorbed back into the capillaries.
4.Hydrostatic pressure greater than oncotic pressure.
5. Neutrophils can pass through in both.

Basement Membrane

A mass of collagen fibres and glycoprotein filters, which stops erythrocytes and large molecules (protein) passing through.

Gaps in Squamous Endothelial Cells of Capillaries

Allow small substances through but stop erythrocytes from passing through.

Podocytes

Epithelial cells in the Bowman's Capsule with extensions called PEDICELS, which ensure gaps to allow some substances through but not cells, platelets & large plasma proteins.

Ultrafiltration Vs Tissue Fluid Formation Differences

Ultrafiltration:
1.Filtrate enters BC then PCT.
2.Molecules that are not reabsorbed by capillaries from urine.
3.Blood filtered through 3 layers.
4.Knot of capillaries.

Tissue Fluid Formation:
1. Tissue Fluid enters intracellular space and bathes body tissues.
2. Molecules that are not reabsorbed by capillaries either enter cells or form lymph.
3. Blood filtered through 1 layer.
4. Network of capillaries.

Selective reabsorption

1. Na+ ions and glucose (as well as amino acids) enter the cells of the PCT through co-transport proteins.
2.Water potential of cell is lowered so water enters the cell by osmosis down a water potential gradient.
3. 3 Na+ ions are pumped out of the cell into the blood and 2 k+ ions go in (using ATP). Glucose goes into the blood capillary by facilitated diffusion, sometimes it can be actively transported into the blood.
4.Water potential of blood lowered so water enters blood down water potential gradient by osmosis.
5. Large molecules are removed by endocytosis.

Loop of Henle

The role of the loop of Henle is to establish a water potential gradient going down the medulla. This comes about because in the ascending limb there is active transport of sodium & chloride ions outwards. The walls of the descending limb are permeable to water, so water is removed from the descending limb. Also, water potential of tissues surrounding collecting ducts is lower than the fluid inside it, water is removed from the filtrate to form urine.

Osmoregulation

Maintaining a constant water potential of the blood, despite changes in the level of water and salt intake.

The role of the Hypothalamus in Osmoregulation

The hypothalamus contains osmoreceptors which signal to specialised neurosecretory cells. A fall in water potential causes the release of a hormone called ADH from the pituitary gland. ADH travels in the blood to the kidneys, attaching to ADH receptors, activating the intracellular enzyme phosphorylase. This causes vesicles containing aquaporins to fuse with the plasma membrane, reducing water loss by increasing the permeability of the collecting duct and DCT.

Pregnancy Tests

They work by detecting the hormone Human Chorionic Gonadotrophin (hCG) in urine. Coloured monoclonal antibodies complementary to hCG form a complex. Which moves up the strip & binds to immobilised antibodies complementary to hCG resulting in the presence of a coloured line, indicating pregnancy.

Aquaporins

They only allow passage of water NOT ions. Ions are too large to pass through the channel. The shape of the ion isn't complementary shaped to the aquaporin.

Measuring glomerular filtration rate

Kidney problems affect the rate at which blood is filtered. GFR is used as a measure to indicate kidney function.A blood test measures the level of creatinine in the blood. If the levels of creatinine in the blood increase it is a sign that the kidneys are not functioning properly. GFR reduces with age and men generally have more creatinine than women.

Renal/Haemodialysis Dialysis

Blood is taken from vessel and passes through a dialysis machine where it passes next to a partially permeable membrane. The other side has a fluid with the correct concentrations of substances so diffusion can occur. 3x a week for several hours.

peritoneal dialysis

This is where a fluid of the current concentrations is pumped into the abdomen wall between the wall and the peritoneum membrane. The peritoneum acts as a partially permeable membrane. Daily but can be done at home or work.

kidney transplant

Human tissue carries a special genetic 'marker' known as human leukocyte antigen (HLA). Ideally, you should receive your transplant from someone with an identical or very similar, HLA tissue type. Needs the same blood group as the recipient.

Advantages Vs Disadvantages Kidney Transplant

Advantages:
1. No time consuming dialysis.
2. Diet not as restricted.
3. Feel better.
4. Better life able to travel.
5. No longer chronically ill.

Disadvantages:
1. Immunosuppressant drugs for life,
2. Major surgery.
3. Risk of infection/MRSA.
4. Frequent rejection checks.
5. Side effects: the drugs can cause infection.

Monoclonal antibodies

Antibodies that are a single clone of cells that are produced to target particular cells or chemicals in the body.