2.76

2.76 Understand that organisms are able to respond to changes in their environment.

• S for MRS GREN stands for sensitivity
• Types of changes in the environment include light, temperature, pressure and chemical
• Organisms are required to have receptors in order to detect changes in environment
• And in order to respond to changes in environment organisms must have effectors
• Its the response that ensures organisms are able to survive the changes of environment

2.75 Urine

• Urine contains water, salts and urea.

2.74 ADH

• ADH stands for Anti-diuretic hormone.
• ADH is produced in the region of the brain known as the Hypothalamus.
• It flows through the blood stream and its target is the kidney.
• The effect of ADH is to control or alter the quantity or composition of water in blood.
• ADH has the ability to make the blood more or less concentrated.
• ADH targets the collecting duct.
• ADH is responsible for increasing the amount of water added to the blood.
• The urine becomes more concentrated and the volume decreases.

2.73 Glucose Reabsorption

• The glomerula filtrate contains glucose.
• Normally urine does not contain glucose unless this person has diabetes.
• In the proximal convoluted tubule glucose is removed.
• Glucose is then taken back into blood.
• Glucose is selectively reabsorbed into blood in the proximal convoluted tubule.
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2.72 Water re-absorption

• When the filtration occurs it will filter out too much water.
• As the filtrate passes through the structure to the collecting duct, water is removed from the filtrate.
• The water is then returned back into the blood vessels.
• The water will go back into the blood stream.
• The water has been selected and been reabsorbed into the blood.
• Then we get the phrase selected reabsorption.

2.71 Ultrafiltration

• Nephron is the structure which carries out the filtration of our blood.
• The filtration of blood begins with the arrival of blood in the afferent arteriole.
• The blood is under high pressure.
• The blood vessel starts to branch and become much smaller. This coiled structure is known as the glomerulus.
• The blood vessel coming out of the Bowman's capsule has a smaller diameter than the blood vessel going in.
• The blood pressure increases in the glomerulus.
• The high pressure forces the liquid within blood (plasma) out of the blood vessel.
• Plasma contains water, salts, amino acids, glucose and urea.
• The plasma is then referred to as the glomerula filtrate.

2.70 Nephron Structure

• The dead-end, cup shaped structure is known as the Bowman's capsule.
• The Nephron structure is made up of twisted structures known as the convoluted tubules.
• The tube that begins from the medulla to the cortex is known as the collecting duct.
• The dip down from the cortex to the medulla then back to the cortex is called the loop of Henle.
• The tight knot of blood vessels in the Bowman's capsule is known as the glomerulus.
• The first twisted section is known as the proximal convoluted tubules (PCT) and the second twisted section is known as the distal convoluted tubules (DCT).
• There are millions of these Nephrons in a single kidney.