Excretion

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Define excretin
Excretion is the removal of metabolic waster from the body.
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What is metabolic waste?
Metabolic waste consists of waster substances that may be toxic or are produced in excess by the reactions inside cells.
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Define deamination
The removal of an amine group from an amino acid to produce ammonia.
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What 3 main effects does a high level of carbon dioxide have?
1.Carbon dioxide combines directly with haemoglobin to form carbaminohaemoglobin which has a lower affinity for oxygen. 2.Reduces oxygen transport due to hydrogen ions competing with oxygen. 3.Respiratory acidosis - carbon dioxide dissolves in the
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Outline the removal or nitrogenous compound.
They are transported to the liver where deamination occurs which converts the ammonia to urea which can be transported to the kidney for excretion. The remaining keto acid can be used directly in resporation to release energy or converted for storage
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What two sources supply the liver with blood?
1.Oxygenated blood from the heart tavels from the aorta via the hepatic artery into the liver. This supplies oxygen that is essential for aerobic respiration. 2.Deoxygenated blood from the digestive system enters the liver via the hepatic portal vein
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How does blood leave the liver?
Blood leaves the liver via the hepatic vein. This rejoins the vena cava and the blood returns to normal circulation.
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What vessel other than the hepatic artery, hepatic portal vein and the hepatic vein is connected to the liver and what is its function?
The bile duct which carries bile from the liver to the gall bladder where it is stored until required to aid in the digestion of fats in the small intestine.
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Describe the arrangement of cells inside the liver.
The liver is divided into lobes which are further divided into lobules. As the hepatic artery and the hepatic portal vein enter the liver they split into small vessels which run parallel to inter-lobular vessels, as intervals branches from
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What are Kupffer cells.
Specialised macrophages that move within the sinusoids and are involved in the breakdown and recycling of old red blood cells.
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What is bilirubin?
One of the waste products from the breakdown of haemoglobin. It is excreted as part of the bile and is the brown pigment in faeces.
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List 6 functions of the liver.
1.Control of: blood glucose levels, amino acid levels and lipid levels. 2.Synthesis of: red blood cells in the fetus, bile, plasma proteins and cholesterol. 3.Detoxification of: alcohol, drugs. 4.Breakdown of hormones.
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What is urea?
An excretory product formed from the breakdown of excess amino acids.
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What is the ornithine cycle?
The process in which ammonia is converted to urea. It occurs partly in the cytosol and partly in mitochondira, as ATP is used.
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Outline the ornithine cycle.
Ammonia is combined with carbon dioxide to form citrulline, water is produced. Ammonia then combines with the citrulline to form arginine, water is produced. Water then combines with arginine to form ornithine, urea is produced.
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Define detoxification.
Detoxification is the conversion of toxic molecules to less toxic or non-toxic molecules.
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Outline the process of detoxification of alcohol.
Ethanol is broken down in the hepatocytes by ethanol dehydrogenase to form ethanal. This is dehydrogenated further by ethanal dehydrogenase. The final compound is ethanoate which is combine with coenzyme A which enters the process of respiration.
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What happens when the liver has to detoxify too much alcohol?
There is insufficient NAD to deal with oxidising and breaking down fatty acids, which are converted back into lipids and stored into the hepatocytes which can cause 'fatty liver'.
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What is the nephron?
The nephron is the functional unit of the kidney. It is microscopic tubule that receives fluid from the blood capillaries in the cortex and converts this to urine which drains into the ureter.
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What is the glomerulus?
The glomerulus is a fine network of capillaries that increases the local blood pressure to squeeze fluid out of the blood. It is surrounded by a capsule which collects the fluid and leads into the nephron.
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What is selective reabsorption?
In selective reabsorption useful substances are reabsorbed from the nephron into the bloodstream.
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How does the composition of the fluid in the nephron change?
In the proximal convoluted tubule the fluid is altered by reabsorption of all sugars, most salts and some water. The the descending limb of the loop of Henle the water potential of fluid is decreased by the addition of salts and removal of water. In
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What does the afferent arteriole do?
Carries blood into the glomerulus.
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What does the efferent arteriole do?
Carries blood away from the glomerulus.
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How does the difference in diameter between the afferent and efferent arterioles push fluid from the blood into the Bowman's capsule?
The afferent arteriole is wider than the efferent arteriole, this ensures that the blood in the glomerulus is under increased pressure. The pressure in the glomerulus is higher than the pressure in the Bowman's capsule this pushes fluid from the
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How is the endothelium of the capillaries adapted for ultrafiltration?
Has narrow gaps between its cells that blood plasma and the substances dissolved in it can pass through.
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How is the basement membrane adapted for ultrafiltration?
Consists of a fine mesh of collagen fibres and glycoproteins that act as a filter to prevent the passge of molecules with a relative molecular mass greater than 69000 (blood cells and most proteins) these remain in the capillaries of the glomerulus.
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How are the epithelial cells of the Bowman's capsule adapted for ultrafiltration?
Podocytes have many finger-like projections call major processes, these ensure that there are gaps between the cells. Fluid from the blood in the glomerulus can pass between these cells and into the lumen of the Bowman's capsule.
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What 5 things are filtered out of the blood?
Water, amino acids, glucose, urea and inorganic ions (sodium, calcium, potassium).
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How are the cells lining the proximal convoluted tubule specialised to achieve reabsorption?
1.The cell surface membrane in contact with the tubule fluid form microvilli this increases the surface area for reabsorption. 2.This membrane also contains co-transport proteins that transport glucose or amino acids in association with sodium ions,
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How does reabsorption occur?
The sodium-potassium pumps remove sodium ions from the cells lining the proximal convoluted tubule, reducing the concentration of sodium ions in the cell cytoplasm. Sodium ions are transported into cell along with glucose or amino acids via
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What is the role of the loop of Henle?
To create a low water potential in the tissue of the medulla, this ensures that more water can be reabsorbed from the fluid in the collecting duct.
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As the fluid descends deeper into the medulla via the descending limb why does it water potential become lower?
1.Loss of water by osmosis to the surrounding tissue. 2.Diffusion of sodium and chloride ions into the tubule from the surrounding tissue fluid.
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As fluid ascends back up towards the cortex via the ascending limb why does its water potential become higher?
1.At the base of the tubule, sodium and chloride ions diffuse out of the tubule into the tissue fluid. 2.Higher up the tubule, sodium and chloride ions are actively transported out into the tissue fluid. 2.The wall of the ascending limb is
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What is the arrangement of the loop of Henle known as?
A hairpin countercurrent multiplier.
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What is the overall effect if a hairpin countercurrent multiplier system?
Increases the efficiency of salt transfer from the ascending limb to the descending limb, this causes a build-up of salt concentration in the surrounding tissue fluid causing a low water potential.
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What is osmoregulation?
The control and regulation of the water potential of the blood and body fluids. In humans the kidneys control the water potential of the blood.
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In the distal convoluted tubule what is used to adjust the concentrations of various salts?
Active transport.
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What happens in the collecting duct?
As the tubule fluid flows into the collecting duct it has a high water potential. As the tuble fluid passes down the collecting duct water moves by osmosis from the tubule fluid into the surrounding tissue, it then enters the blood capillaries by
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Card 2

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What is metabolic waste?

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Metabolic waste consists of waster substances that may be toxic or are produced in excess by the reactions inside cells.

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Define deamination

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Card 4

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What 3 main effects does a high level of carbon dioxide have?

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Card 5

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Outline the removal or nitrogenous compound.

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