2.75 Urine

1. The urine contains water, urea and salts.
2. Salts and water affects the composition of tissue fluid., known as osmoregulation.
3. Urea is a form of metabolic waste.
4. The composition of urine: salts, water, and urea varies and depends upon the conditions which a person is operating.

2.74 ADH

1. ADH-Anti diretic hormone
2. This hormone is produced in a section of the brain known as the hypothelamis

1. Like all hormones it flows through the bloodstream
2. Its target is the kidney.
3. The effect of this hormone is to control the quantity of water in blood as it is important that the tissue fuid is isotonic in every cell.
4. ADH actually targets the collecting duct. The effect of this is that it allows more water to come out of the collecting duct.
5. It is possible to increase the amount of water going into the blood through the collecting duct by applying ADH. It makes the collecting duct wall more porus therefore more water can escape from the collecting duct and flow into the bloodstream.
6. The consequences of this ADH excretion is that the urine would be more concentrated and it would have a lower volume.

2.73 Glucose reabsorption

1. Urine that emerges from the collecting duct does not contain glucose
2. However, if urine is tested for glucose and receives a positive response, the condition is known as diabetes.
3. Glucose is in the fluid within the bowman's capsule.
4. The reason for this is that proximal convoluted tubule, glucose is removed and is taken back into the blood.

5. Glucose is selectively reabsorbed into the blood in the proximal convoluted tubule.

2.72 Water re-absorption

1. We have blood coming into the kidney. It is placed under high pressure.
2. The dissolved contents in the blood are forced into the bowman's capule's tube, and would become known as the glomerula filtrate.
3. This glomerula filtrate contained salts, water, glucose and urea.
4. When the filtration occurs, it filters out too much water.
5. The filtrate passes along the tube and once it reaches the collecting duct, water is removed from the filtrate.
6. that water is returned back to blood vessels therefore the water has been selected and has been reabsorped into the blood. We get the word, selective reabsorption.
7. Selective reabsorption takes place in the collecting duct.

2.71 Ultrafiltration

• Nephron is the tubular structure in the kidney. This is the structure which carries out the filtration of our blood and ultimately results in two things
• Filtered blood
• Urine
• Thr urine that comes out of the plevic region is composed largely of water, salts, and molecule known as urea (nitrogen waste).
• The process of filtration, known as ultra filtration, filtration of molecules, starts in the bowman's capsule.

• FIltration of blood begins when the blood arrives in the kidney, in the nephron, in the vessel known as the aferet arteriole. The blood here is under high pressure
• The blood vessel coming out of the bowman's capsule is known as the efferent arteriole. The diameter of this blood vessel is much smaller than the afferent arteriole.
• The blood develops a high pressure as it flows from a wide blood vessel (afferent arteriole) to a narrow blood vessel (efferent arteriole), the blood pressure increasing in the glomerulis.
• The high pressure forces the liquid within the blood (plasma) and is forced into the space within the insidde of the bowman's capsule.

• The plasma then becomes known as the glumerula filtrate.

2.70 Nephron structure

1. The branch of the aorta taking blood into the kidney is known as the renal artery
2. Th kidney filters the blood and the contents which are removed and excreted from the blood are called urine, which comes down the structure known as the ureter, and is then collected in the bladder for release.
3. The filtered blood exits through the renal vein and would return to the vena cava .
4. If we slice through the kidney to show the internal structure, we see different colored regions
5. The outer lighter region is known as the cortex, and the inner darker region is known as the medulla and the innermost lightest region is known as the pelvic region.
6. The urine is collected in the pelvic region from where it drains down the ureter.

1. The reason for these different colors is because the kidney is made up of various tubular structures.
2. The tubular structure can be shown in here:

1. The tube structure is known as the nephron.
2. The first twisted section is known as the proximal convoluted tubule section.
3. The second twisted section is known as the distal convoluted tubule section.

4. There are millions of these nephrons (tubular structure) in the kidney.

2.69 urtinary system

1. In the urinary system we have: 
• two kidneys- a left one and a right one, each with its own blood supply, carrying out the process of excretion, filtration, and osmoregulation. From each kidney there is a tube that leads to the bladder, which is called a ureter. 
• ureter-carries urine from the kidney to the bladder. 
• Bladder- the urine is conducted to the outside of the body to be excreted down a structure called the urethra, which either travels down through the vagina or the penis. 

2.68b osmoregulation

1. osmo-osmosis
2. regulation-to control 
3. We have cells in the body and ideally if the tissue fluid that surround these cells look like the ones in he diagram, this must be isotonic with the cytoplasm of these cells. 
4. This means that the amount of water going outside and inside of the cell is equal which further means that the cell will maintain its shape, size and function. 
5. The danger to the tissue is that the blood circulating to the tissue would be concentrated causing a hypertonic tissue fluid or it may be dilute causing a hypotonic tissue fluid. 
6. Hypertonic would remove too much water and hypotonic would add too much water to the cell. 
7. We want to keep the tissue fluid isotonic to the cell's cytoplasm. 
8. This achieved by controlling the composition of blood. 
9. Blood forms the tissue fluid. It is the role of the kidney to control the composition of blood 
10. Blood which circulates through our kidney, excess water, excess salts can be removed and excreted through the uretus.
11. If the kidney can control the content of water and salts in the blood, the kidney can keep the blood and therefore the tissue fluid isotonic with the cell's cytoplasm, maintaining the function of the cell

2.68a excretion

1. The kidneys excrete a molecule known as uria which contains nitrogen, which is toxic to the body and therefore cannot be stored. 
2. The original form of nitrogen circulating in our blood stream which is potentially toxic are the amino acids. 
3. Amino acids are used for growth, however, amino acids which are in excess must be removed because they're toxic. 
4. Blood circulates to the liver and the amino acids are broken down into the molecule called urea. 
5. The urea re enters the blood stream and to be removed by the body it circulates to the kidney. 
6. the kidneys filter the urea from the blood and the urea will be added to water to form urine. 
7. This urine drains down the uritus to collect in the bladder. 
8. The filtered blood, removed of the toxic amino acids, returns into the body through veins. 
9. This is called excretion 

2.67b Human organs of Excretion

1. Main organs of excretion: 
• Lungs- excretes Carbon dioxide 
• kidneys- responsible for the excretion of excess water, molecule uria (nitrogen waste from amino acids), and salts.
• skin- excretes water and salts, a little bit of uria. 

2.67a Excretion in plants

1. photosynthesis-involves the leaf absorbing sunlight and while doing so it combines carbon dioxide and water to produce glucose and oxygen, a gas which is given off. 
2. In this case, the gas which is given off, oxygen, is an example of excretion as its a waste molecule.
3. Excretion- the release of metabolic waste. 
4. Respiration-glucose and oxygen are used, and through a series of enzyme reactions, the glucose molecules break down and the energy is used to form ATP, water, and carbon dioxide. In this process, the waste product is carbon dioxide and water. However, like the oxygen in the reaction above, Carbon dioxide is also given off, its a metabolic waste therefore its excretion. 
5. Plants excrete oxygen when they photosynthesize and they excrete Carbon dioxide when they go through the process of respiration.