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What is excretion?

The removal of metabolic waste from the body.


What is metabolic waste?

Waste substances that may be toxic or are produced in excess by the reactions inside cells.


What is deamination?

The removal of the amine group from an amino acid to produce ammonia.


Why are the two main products that must be excreted?

Carbon dioxide from respiration in every cell.
Urea is produced in the liver from excess amino acids.


How are the two main substances excreted from the body?

CO2 is passed into the bloodstream, and transported in the blood as HCO3- ion to the lungs.
In the lungs the CO2 diffuses into the alveoli to be breathed out.

Urea is passed into the bloodstream to the kidneys, dissolved in plasma.
Becomes part of urine which is stored in the bladder and exerted via the urethra.


Why must CO2 be removed?

CO2 form hydrogen carbonate ions in the blood plasma. The H+ ions combine with haemoglobin, and compete with oxygen for space on it. Less oxygen is transported.

The CO2 can also directly combine with haemoglobin to form carbaminohaemoglobin. This has a lower affinity for O2 than normal haemoglobin.

Excess CO2 can causes respiratory acidosis. The H+ ions lower the pH of the blood, which is detected in the medulla oblongata and increases breathing rate and changes blood pressure.


Why must nitrogenous compounds be removed?

Body cannot store amino acids, but it would be wasteful to excrete them.
The toxic amino group is removed by deamination.
The amino group initially forms ammonia, which is converted to urea.
Remaining keto acid used in respiration or converted to carb for storage.


What is the equation for deamination and the ornithine cycle.

Amino acid + oxygen ---> keto acid + ammonia

Ammonia + CO2 ---> urea + water.


What is the hepatic portal vein?

An unusual blood vessel that has capillaries at both ends.
It carries blood from the digestive system to the liver.


Describe the blood flow to and from the liver.

Oxygenated blood from the heart. From the aorta via the hepatic artery into the liver.
Aerobic respiration.

Deoxygenated blood from the digestive system rich in products of digestion. Enters the liver via the hepatic portal vein.

Deoxygenated Blood leaves the liver via the hepatic vein, rejoining the vena carva and the blood returns to normal circulation.

A bile duct is also connected to the liver. It carries bile from the liver to the gall bladder.


Describe the structure of the liver.

Made up of cylindrical lobules made of hepatocytes.

Each lobule has a central vein in the middle that connects to the hepatic vein.

Hepatic artery and hepatic portal vein are connected to the central vein by capillaries called sinusoids.

The sinusoids are lined by liver cells.
Blood runs through the sinusoids, past the hepatocytes that remove harmful substances and oxygen from the blood.

Inter lobular celled occur as the HA and HPV split into smaller and smaller vessels, they run between and parallel to the lobules.

Bile duct connects to the central vein by tubes called canaliculi.


What are kupffer cells?

Specialised macrophages, they move about within the sinusoids an breakdown an recycle RBCs.
One product of this is billirubin.


What is a waste product from the breakdown of haemoglobin?

Billirubin. Excreted as part of the bike and in faeces.
Brown pigment.


What is urea?

An excretory product formed from the breakdown of excess amino acids.


Give some functions of the liver.

Formation of urea.
Breakdown of hormones.
Breakdown of RBCs.
Detoxification of alcohol.


What I the ornithine cycle?

The process in which ammonia is converted to urea.
Occurs partly in the cytosol and partly in mitochondria.
ATP is used.


What is detoxification?

The conversion of toxic molecule to less toxic molecules.
Eg hydrogen peroxide produced in the body, or drugs externally taken.

Catalase converts hydrogen peroxide to oxygen and water.


Describe the detoxification of alcohol.

Broken down in the hepatocytes by ethanol dehydrogenase, and creates ethanal.
This is further dehydrogenated by ethanal dehydrogenase.
Ethanoic acid is the final product.

Ethanol --> ethanal --> ethanoic acid
At each stage 2H join NAD to make red NAD.

Ethanoic acid + coenzyme A --> acetyl coenzyme A.


What is the nephron?

The functional unit of the kidney.
It is a microscopic tubule that receives from the blood capillaries in the cortex and converts it to urine, which drains into the ureter.


What is the glomerulus?

A fine network of capillaries that increases the local bold pressure to squeeze fluid out of the blood.
It is surrounded by a cup or funnel shaped capsule which collects the fluid and leads into the nephron.


What are the roles of the kidneys?

Remove waste products from the blood and produce urine.


Describe the supply to and from the kidneys.

Renal artery supplies blood.
Renal vein takes blood away.
Urine passes out of the kidney down the ureter to the bladder.


What are the regions of the kidney?

Outer region: cortex
Inner region: medulla
Centre: pelvis which leads to the ureter.



What is selective reabsorption and where does it occur?

When useful substances are reabsorbed from the nephron into the bloodstream while other excretory substances remain in the nephron.



How does the composition of the fluid change in the bowmans capsule during selective reabsorption?

In the descending limb of the loop of henle the water potential decreases by the addition of salts and removal of water.

In the ascending limb the water potential increases as salts are removed by AT.

In the collecting duct the water potential is decreased again by the removal of water, ensuring urine has a low potential and high conc of solutes.


Label the structure of kidney and stuff

Efferent/Afferent arteriole
Bowmans capsule
Proximal convoluted tubule
Distal convoluted tubule
Descending limb
Ascending limb
Loop of henle
Collecting duct

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What are Afferent and efferent vessels?

Afferent bring blood to the organ.
Efferent carry blood away.


Describe the Afferent and efferent arterioles in the kidneys.

Blood flows into the glomerulus from the Afferent arteriole, and is wider than the efferent.
This ensures the blood in the capillaries of the glomerulus is under increased pressure.
This pressure in the glomerulus is higher than in the bowmans capsule and pushes fluid from the blood into the bowmans capsule.


What is ultrafiltration?

Filtration at a molecular level.
As in the glomerulus where large molecules and cells are left in the blood and smaller molecules pass into the bowmans capsule.

Blood from the renal artery enters smaller arterioles in the cortex.

The efferent arteriole is smaller in diameter than the Afferent arteriole, so the blood in the glomerulus is under high pressure.

The high pressure forces liquid and small molecules in the blood out of the glomerulus and into the bowmans capsule.

Has to pass through 3 layers to get into the bowmans capsule.

The filtrate (useful substances and small molecules) now passes along the rest of the nephron reabsorbing useful substances along the way.

The filtrate flows through the collecting duct and passes out the kidney along the ureter.


What are podocytes?

Specialised cells that make up the lining of the bowmans capsule.

They have projections called major processes, these ensure gaps between the cells.
Fluid from the blood in the glomerulus can pass between these cells into the lumen of the bowmans capsule.