2.75 Urine

2.75 Recall that urine contains water, urea and salts.

2.74 ADH

2.74 Describe the role of ADH in regulating the water content of blood,

- ADH = Anti-Diuretic Hormone. Is produced in a region of the brain called the Hypothalamus, and its target is the kidney.

- The affect of ADH is to control and alter the composition or quantity of water in blood.

- So ADH has the ability to make the blood more or less concentrated. And we previously established that it is very important for the tissue fluid to be isotonic with the cytoplasm of the cells. This is the role of ADH

- ADH targets the collecting duct. The affect of ADH is that it allows more water to go into the collecting duct increasing the amount of water in the blood. So we have already learned that the collecting duct is where water is selectively reabsorbed into the blood. So applying more of the hormone ADH would make the collecting duct walls more porous so more water can escape from the glomerule filtrate into the collecting duct.

- The consequences of ADH secretion is that the urine coming from the bladder would be more concentrated and have a lower volume. So with ADH secretion more water goes back into the blood, the urine becomes more concentrated, and the volume decreases.

- Our brain releases different amount of the hormone ADH depending on things like the weather - hot or cold day? so that our blood has enough water in it to keep us hydrated.

2.73 Glucose reabsorption

2.73 Understand that selective reabsorbtion of glucose occurs at the proximal convoluted tubule (PCT)

- Selective reabsorbtion means that a molecule is selected to be reabsorbed. This means it will go from the glomerule filtrate and back into the blood. This may seem strange because it has been removed from the blood and now going to be put back into the blood.

- The glucose is removed before the end of the Nephron Tubule because no glucose is found in the Urine (unless you are diabetic). So normally there would be no glucose in the urine. So the glucose has to be returned to the blood stream between the Bowman's capsule (where it is present in the plasma which become the glomerule filtrate) and the pelvic region.

- The answer is that the glucose re-enters the bloodstream at the proximal convuluted tubule which is the section just before the Loop of Henle.

2.72 Water re-absorption

2.72 Understand that water is reabsorbed into the blood from the collecting duct.

- When the plasma is filtered from the blood in the Bowman's capsule, too much water is taken with the plasma from the blood.

- So as the filtrate passes along the Nephron Tube, when it reaches the collecting duct the water is removed from the filtrate and returned back to the blood vessels and back into the blood stream.

- This water has been selected and is reabsorbed by the blood into the blood stream. Because of this is is called Selective Reabsorbtion

- Loop of Henle also collects water but it is the collecting duct that does the controlling of water content of urine and therefore blood.

2.71 Ultrafiltration

2.71 Describe ultrafiltration in the Bowman's capsule and the composition of the glomerular filtrate.

- The same diagram here is being shown. It is the Nephron which carries out the filtration of our blood, which results in filtered blood with the waste products removed, and the waste known as urine.

Looking at how the urine is actually formed:

- Begins in the Bowman's capsule and is known as ultrafiltration - the filtration of mollecules. Explained using the larger diagram.

- Filtration of blood begins with blood arriving in the Kidney, in the Nephron in the Afferent Arteriole. This blood is under high pressure and as it comes in, and it starts to branch and become much much smaller. This twisted smaller structure is known as the glomerulas.

- The next part to notice is the blood coming out of the Bowman's capsule by the Efferent Arteriole. We should notice that the diameter of this blood vessel in which the blood leaves the Bowman's capsule, is much smaller than the Afferent Arteriole which leads the blood into the Bowman's capsule. Because of the smaller tube, this means the blood pressure increases, and it has a very high pressure. So the glomerulas function is to increase the pressure of the blood. So while the blood is in the glomerulas it is of a very high pressure.

- The consequence of this is that the high pressured blood forces the liquid within blood (plasma - contains components dissolved in blood (salts, water, amino acids, glucose and urea) which forces them out of the blood vessel.

- The high pressure of blood in these twisted tubes, forces the plasma into the space surrounding the glomerulas which is the inside of the Bowman's capsule. When this happens we call this Glomerula filtrate.

- So the blood has been filtered by pressure, due to the restricted space in the blood vessel at the twisted point, which forces the plasma into the Bowman's capsule. The cleaner blood then continues on to do it's job and the plasma travels down the Bowman's capsule and begins it's journey till excretion (See first diagram to understand).

2.70 Nephron Structure

2.70 Describe the structure of a nephron, to include Browman's capsule and glomerulus, convoluted tubules, loop of Henle and collecting duct.

- The Nephron is the functional unit of the kidney which does the filtering and the controlling of the composition of blood.

- Blood in the Aorta goes into the kidney via the Renal Artery, and the waste to be excreted is sent down the Ureter and the clean; now filtered blood, goes back to the bloodstream via the Renal Vein which then leads it to the Vena Carva.

- If we slice through the kidney we see different coloured regions. The outer lighter region is the Cortex. The inner darker region is the Medulla. And the very inside lighter coloured space; which is a space, and is known as the pelvic region. This is where the urine collects and drains down the Ureter.

- The reason for the different colours is because the kidney is made up of millions of tubes. This can be seen in the diagram.

- The dead end of the tube which dips in and out of the Cortex and Medulla is called the Bowman's Capsule. This tube is called the Nephron, which we will now look at in more detail.

- The diagram shows the Nephron close up. The part above the dotted line is the Cortex, and below the dotted line is the Medulla

- At the end of the tube in the diagram is in fact the pelvic region, the end of this tube is where the urine emerges.

- The tube is made up of twisted sections, these parts which are in the Cortex are known as the Convoluted Tubules. And the long tube heading towards the pelvic region in the Medulla is called the Collecting Duct (A Duct is a tube).

- The dip inbetween the two Convoluted Tubules which is in the Medulla part of the Kidney is called the Loop of Henle.

- And then the dead end structure is called the Bowman's Capsule. In the diagram you can see the blood vessels tightly noting around it. These are called the Glomerulus.

The Whole structure starts at the Bowman's capsule ---> Proximal Convoluted Tubules (PCT) ---> Loop of Henle --->  Distal Convoluted Tubules (DCT) ---> Collecting Duct ---> Pelvic Region.

- It is the arrangement of this Nephron Structure which gives the Kidney the different colours on the cross section diagram.

2.69 Urinary system

2.69 Understand the structure of the urinary system, including the kidneys, ureters, bladder and urethra.

Most people have two Kidneys – Each with its own separate blood supply, carrying out the process of excretion, filtration and osmoregulation.

From each kidney there is a tube which leads to the bladder. This is called the ureter.

The ureter carries urine from the kidney to the bladder. And then the urine travels through the urethra to exit the body. The urethra is present in both the vagina and the penis so it depends on your sex.