2.76 understand that urine contains water, urea and salts

In the beginning of the ultrafiltration/reabsorption process water, urea, salts and glucose are 'squeezed' our of the blood due to high pressure. However, during reabsorption all of the glucose (and a little bit of water and salts) is reabsorbed. Everything that remains in the glomerulus filtrate (water, urea and salts) is combined to form urine.

2.75 describe the role of ADH in regulating the water content of the blood

Osmoregulation determines how much water is reabsorbed into the blood at nephrons. The amount of water reabsorbed is controlled by ADH (anti-diuretic hormone). ADH makes the nephrons more/less permeable to allow more/less water to be reabsorbed back into the blood. This occurs like this...

- The brain is constantly monitoring the level of water in the blood
- The brain instructs the pituitary gland to release ADH into the blood (according to how much water needs to be reabsorbed)

NOTE: the process of osmoregulation is controlled by a mechanism called 'negative feedback'. This basically means if the water gets too high/low a mechanism will be triggered that brings the level down/up (back to normal)

2.74 understand that selective reabsorption of glucose occurs at the proximal convoluted tubule

ONLY glucose is absorbed at the first (proximal) convoluted tubule, this makes for selective reabsorption as only a certain substance(s) (in this case, glucose) can be absorbed, not everything is absorbed.

2.73 understand that water is reabsorbed into the blood from the collecting duct

If you don't know what happens regarding the water leaving the blood, it may be a good idea to go to one of these posts... 2.69 2.71 2.72. If you don't know what a nephron is or how it works, i would recommend checking out 2.71.

The glomerulus filtrate will flow along the nephron (next to the capillary). All the useful stuff (such as the glucose, some of the salt, and some of the water (depending on osmoregulation) will be reabsorbed (by active transport) back into the blood. The glucose is reabsorbed at the first (proximal) collecting tubule, the water is reabsorbed from the collecting duct, sufficient salt is kind of just absorbed throughout.

2.72 describe ultrafiltration in the Bowman's capsule and the composition of the glomerular filtrate

I have kind of answered this in 2.69 and 2.71 but here it is again just for bants

The renal artery will take oxygenated blood from the heart into the glomerulus (this is part of a nephron, in a kidney, go to 2.71 if you are unsure what a nephron is/how it work). This blood will build up in pressure as it is 'squashed' up. Due to the high pressure, all small molecules (such as glucose, water, urea and salts) will pass through a membrane inbetween the glomerulus and the Bowman's capsule, (all the bigger molecules will stay in the blood). The filtered liquid (the small molecules, e.g. water, glucose, urea and salts) is known as the glomerular filtrate.

2.71 describe the structure of a nephron, to include Bowman's capsule and glomerulus, convoluted tubules, loop of Henlé and collecting duct

Each of your two kidneys contains thousands of nephrons to help with osmoregulation and removal of urea (basically, they filter the blood). This is what they look like...

Inbetween the glomerulus and bowman capsule is a membrane that allows small molecules (such as water, glucose, urea and salts) to travel through, this is known as the filtrate and travels along through the orangey tube. As it travels, useful substances (such as glucose, some salt and a certain amount of water (depending on osmoregulation)) will be reabsorbed into the bloodstream (the red tube). All the unwanted stuff (like

urea, water and salt) is collected at the collecting duct. Here it all combines together to make urine which travels down the ureter, into the bladder where it is stored.

image credit: BBC

2.70 describe the structure of the urinary system, including the kidneys, ureters, bladder and urethra

Lets start with a diagram...

- The aorta takes oxygenated blood to the kidney (as the renal artery) and the vena cava takes deoxygenated blood away from the kidney (as the renal vein)

- The kidney is where the urea is turned into urine, there the blood is filtered (and the waste parts are taken out) and where osmoregulation occurs

- The urine travels down the ureter into the bladder

- Urine is stored in the bladder

- The urine travels down the urethra and out of the body

2.69 understand how the kidney carries out its roles of excretion and osmoregulation

Excretion
The kidneys remove urea from the blood. This is done in the nephron....

- Blood (from the renal artery) flows through the glomerulus, increasing pressure as it 'bunches up'.
- This high pressure causes small molecules (water, urea, glucose and salts) too squeeze through the membrane in-between the blood vessels (in the glomerulus) and the Bowman's capsule.
- This membrane acts as a filter so the bigger molecules (proteins and blood cells) do not leave the blood.
- As the filtrate (the small molecules that have been filtered out) flows through the nephron, the useful stuff (such as glucose) is selectively reabsorbed back into the bloodstream.
- The remaining substances are waste as they are of no use to the body, these substances include water, salts and urea.
- These remaining substances combine to form urine, which flows out of the nephron, through the ureter and down to the bladder where it is stored.

Osmoregulation
Osmoregulation is the adjustment of water content of the blood (it is a form of homeostasis). Basically, the kidney makes sure the blood has the right level of water in it. To do this, it has to constantly balance the amount of water that enters and leaves the blood. This is done by adjusting the amount of water the blood reabsorbed when flowing through the nephron. If the person is dehydrates (or very sweaty) the kidneys will reabsorb lots of water (this means less water is lost in urine). Similarly, if someone is very hydrated, the kidney can lower the level of water reabsorbed into the bloodstream, this means the person will lose more water through urine (this is why you wee loads if you drink loads). This is controlled by ADH (produced in the pituitary gland) which changes the permeability of the kidney tubules accordingly (to allow more/less water to be reabsorbed).

There is a little more on how osmoregulation takes place in post 2.75

2.68 recall that the lungs, kidneys and skin are organs of excretion

Excretion (removal of waste products) is carried out by the skin, the lungs and the kidneys.

The skin excretes waste salt etc as sweat (perspiration), the lungs excrete carbon dioxide, the kidneys excrete urea (urea is produces from excess amino acid in the liver).

2.67 understand the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf

During photosynthesis, plants use light energy (from the sun) to combine carbon dioxide and water. This produces glucose and oxygen. The plant can use glucose (in respiration) but cannot use oxygen, therefore, oxygen is a waste product.

During respiration, plants use oxygen and produce carbon dioxide (this time, the oxygen is useful and carbon dioxide is a waste product.

Gases diffuse in and out of a leaf via the stomata when they are open (during daytime/light/when photosynthesis is occurring)...