2.75 Urine

2.75 recall that urine contains water, urea and salts

Urine consists of Salts, Water and Urea.

The Salts and Water are removed as part of the Osmoregulation process to maintain a isotonic tissue fluid with the cells in the body, and the removal of Urea is part of the excretion of metabolic waste.

The composition of Urine varies, depending on the conditions of the person.

2.74 ADH

2.74 Describe the role of AGH in regulating the water content of the blood.

Anti-Diuretic hormone – produced in a region of the brain known as the hypothalamus, like all hormones it flows through the blood stream to its target; the kidney. It’s job is to control and alter the quantity of water in the blood such that the tissue fluid is isotonic with the cells

ADH targets the collecting duct in the kidney nephron; applying the hormone increases the amount of water reabsorbed from the collecting duct. It makes the collecting duct walls more porous.

2.73 Glucose reabsorption

2.73 Understand that selective reabsorption of glucose occurs at the proximal convoluted tubule.

Selected reabsorption – a molecule is selected, and then reabsorbed into the blood; we have removed a molecule from the blood, and we want to put it back.

Urine does not normally have glucose in it, but it is found in the Glomerular filtrate. Note: If a positive test for glucose is found in the urine, it could suggest that the individual has Diabetes.

In the first convoluted tubule (the Proximal CT) glucose is removed and reabsorbed into the blood.

2.72 Water re-absorption

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

When ultrafiltration occurs, too much water is displaced from the blood, so it must be returned into the blood stream, this happens in the Collecting duct.

Water is removed from the filtrate as it travels down the duct to the Pelvic region; the water is then recalculated back into the blood through blood vessels. This is known as Selective reabsorption.

2.71 Ultrafiltration

2.71 describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate.

The filtration of our blood takes place in the Nephron, resulting with two products: the filtered blood and Urine (waste).

The Urine (composed of water, salts and Urea) drains out of the Collecting duct into the pelvic region, and then drains into the bladder.

1. Blood arrives into the kidney under high pressure through the Afferent Arteriole
2. The Arteriole begins to branch off and create a twisted knot-like structure called the Glomerulus; the Efferent arteriole has a smaller diameter resulting in a pressure increase in the glomerulus.
3. The high pressure forces plasma (contains water, salts, amino acids, glucose, urea) out of the blood vessel into the inside of the Bowman’s capsule, The plasma is called Glomerular filtrate

2.70 Nephron Structure

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

Nephron = the functioning unit of the kidney, the part that does the filtration and the controlling of the composition of blood

The image below shows the structure of the kidney and the position of the nephrons, NB: There are millions of nephrons in each kidney for simplicity, only one has been drawn in the diagram

The image below outlines all the relevant sections of the nephron, and just below that I have briefly explained what they are/do.

Glomerulus – The knot of blood vessels where the blood is filtered from

Bowman’s Capsule – the “Dead End” to the Nephron, Ultrafiltraion happens here [see 2.71]

Proximal Convoluted tubule – The first twisted section

Loop of Henlé - The Nephron dips into the Medulla

Distal Convoluted tubule – The second twisted section, back in the Cortex

Collecting duct – The final tube where the urine travels to the Pelvic region.