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Flashcards in Excretion Deck (16):

What is excretion?

The removal of waste products (products that are not needed by cells e.g. Carbon dioxide, water, urea etc) made from the metabolic reactions of the body.


How do waste products leave the body?
(Organs of excretion)

- The lungs excrete carbon dioxide and water.
- The skin excretes water, (urea) and excess mineral ions (e.g. Sodium ions).
- The kidneys excrete water, urea, mineral ions and other substances.


What are the two roles of the kidneys?

- Excretion (removal of waste products such as urea etc.).
- Osmoregulation (keeping the water content of the blood constant).


How does the kidney carry out it’s role of excretion?

The kidney is made up of millions of nephrons. These structures are involved in filtering he blood, releasing substances back into the blood (reabsorption), and producing urine. The urine from each nephron is funnelled into the centre of the kidney. It then moves through the ureter to be stored in the bladder.


What is the human excretory system made up of?

Vena cava, aorta, renal artery, renal vein, kidney, ureter, bladder, urethra.


Name, in order, the nephron processes.

Ultrafiltration, reabsorption of substances in the proximal convoluted tubule, reabsorption of substances in the loop of Henlé, reabsorption of substances in the distal convoluted tubule, osmoregulation in the collecting duct.


What are nephrons made up of?

Glomerulus, bowman’s capsule, proximal convoluted tubule, loop of Henlé, distal convoluted tubule, collecting duct.


What is ultrafiltration?

Ultrafiltration occurs between the glomerulus (bundle of capillaries) and the bowman’s capsule, producing the glomerular filtrate.
The vessel leaving the glomerulus has a smaller diameter than the vessel entering, causing a high blood pressure in the glomerulus.
The high pressure forces water, glucose, mineral ions and urea (the glomerular filtrate) out, whilst larger components (e.g. Red blood cells and proteins) remain in the blood.


What is reabsorbed from the glomerular filtrate into the blood in the...?

- Proximal convoluted tubule:
100% glucose (actively transported). Some mineral ions.

- Loop of Henlé:
Some water.

- Distal convoluted tubule:
More water and mineral ions.

- Collecting duct:
Even more water.


What does urine contain?

Water, mineral ions, urea


What is osmoregulation?

The control of water and salt concentration in the body fluids. This is a homeostatic mechanism.


What is the collecting duct, and what does it do?

The collecting duct is shared with many other nephrons.
Even more water is reabsorbed back into the blood from here.
ADH is a hormone that causes even more water absorption (osmoregulation).
The resultant urine passes to the centre of the kidney.


How are water levels in the blood regulated?

If the water content in the blood falls below normal, receptors in the brain (hypothalamus) detect this and stimulate the release of ADH from the pituitary gland. ADH causes more water to be reabsorbed from the collecting duct of the nephron (as it increases the permeability of the collecting duct, so more water can be reabsorbed back into the blood capillaries), resulting in the kidneys producing less urine that is more concentrated. This causes the water content of the blood to be restored back to normal.
On the other hand, if the water content is above normal, less ADH is released, causing the kidneys to produce more urine that is less concentrated.


Why does a person with diabetes have glucose in their urine?

People who are diabetic have a very high blood glucose level.
All of it goes into the glomerular filtrate, but not all of it can be reabsorbed.


How does the structure of the blood vessels entering and leaving the glomerulus help to move glucose into the bowman’s capsule?

The blood vessel entering the glomerulus has a larger diameter than the one exiting. This causes a high blood pressure in the glomerulus, forcing small substances out of the blood (e.g. Glucose, water, urea etc.) whilst bigger cells remain in the blood (e.g. red blood cells, proteins etc). This is known as ultrafiltration.


How and why is glucose reabsorbed from the proximal convoluted back into the blood capillaries?

All of the glucose from the glomerular filtrate is actively transported form an area of low concentration to an area of high concentration against a concentration gradient. It is easily reabsorbed by the network of thin-walled capillaries closely surrounding the proximal convoluted tubule. In this process, energy is used up in the form of ATP.
This is because the glucose is needed for respiration and, therefore, the production of energy to survive.