2.75 Urine

- The brain influences the functioning of the two kidneys
- The two kidneys are filtering our blood
- The molecules which are removed and come down the ureter collect in the bladder
- This forms urine
- Urine contains salts, water and urea
- Salt and water affect the composition of tissue fluid - osmoregulation
- Removal of urea is a part of the process of the excretion of metabolic waste
- The composition of urine varies and depends upon the conditions in which a person is operating

2.74 ADH.

- ADH (Anti-Diuretic Hormone)
- It is produced in a region of the brian known as the Hypothalamus. It flows through the blood stream and its target is the kidney
- The effect of ADH is to control and alter the composition of water which is in blood
- ADH has the ability to make the blood more or less concentrated
- It is important to have the tissue fluid isotonic to the cytoplasm of the cell
- ADH targets the collecting duct
- It allows more water to come out of the collecting duct
- The consequence of ADH secretion is that the urine coming from the nephron would be more concentrated and would have a lower volume

2.73 Glucose reabsorption

- "Selected reabsorption" means that glucose will go from the Glomerular filtrate back into the blood
- Water is moved back into the blood at the collecting duct
- Coming out of at the end of the nephron is urine, normally, it does not contain glucose
- Diabetes is when you test your urine and receive a positive test = there is glucose in your urine.
- In the PCT (proximal convoluted tubule) glucose is removed and is taken back into blood

2.72 Water re-absorption

- The dissolved contents of the blood are forced into the Bowman's Capusle and is known as the Glomerular filtrate (it contains glucose, water, salts and urea).
- When the filtration occurs, it will filter out too much water
- As the filtrate reaches the collecting duct and passes through it, water is removed from the filtrate and the water goes back into the blood vessels.
- The water has been selected and reabsorbed into the blood.
- Therefore, there is the word "selective reabsorption"
- "Selective reabsorption" occurs in the collecting duct.

2.71 Ultrafiltration

- The first process occurs at the Bowman's capsule - the filtration process begins.
- Blood arrives in the kidney in the afferent arteriole, a wide vessel (coming in - high pressure).
- The blood vessel coming out has a smaller diameter than the one coming in. This means that it develops a high pressure. The blood pressure increases in the glomerulus.
- The high pressure forces the liquid within blood, plasma (contains water, salts, amino acids, glucose and urea), out of the blood vessel and into the space = inside of the Bowman's capsule.
- When the plasma is forced into the Bowman's capsule, plasma --> "glomerular filtrate"

2.70 Nephron Structure

First Diagram:
- Nephron = The functional unit of the kidney, the part that does the filtration and controlling of the composition of blood
- Pelvic region - where the urine collects and drains down the Ureter
- There are different colours because the kidney is made up of millions of tubular structure
- The tube starts on the edge of the medulla and moves directly upwards and out into the cortex. It winds and then dips down into the medulla again and then up, there is another short twisted section and then a dead end.
- The dead end structure is known as the Bowman's capsule.

Second diagram:
- The tube is made up of twisted sections. Convoluted tubules.
- The tube at the bottom is known as the collecting duct.
- The dip is known as "the loop of Henle"
- The first twisted section = proximal (PCT)
- The second twisted section = distal (DCT)
- It is the arrangement of this nephron structure which gives the different coloured region in the kidney.