A2 - Unit 1 - Excretion Flashcards
What is excretion?
The removal of metabolic waste from the body
What is metabolic waste?
Consists of 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
What are the main two products in large amounts in the body?
Carbon dioxide from respiration
Nitrogen-containing compounds such as urea
Where is carbon dioxide produced in the body?
In every living cell as a result of respiration
Where is urea produced in the body?
In the liver from excess amino acids
Where is carbon dioxide excreted from the body?
Passed from the cells of respiring tissues into the bloodstream.
It is transported in the blood (mostly in the form of hydrogencarbonate ions) to the lungs.
In the lungs the carbon dioxide diffuses into the alveoli to be excreted as we breathe out
Where is urea excreted from the body?
Produced by breaking down excess amino acids in the liver. This process is called deamination. The urea is then passed into the bloodstream to be transported to the kidneys the urea is removed from the blood to become a part of urine
Urine is stored in the bladder before being excreted via the urethra
Why must carbon dioxide be removed from the body?
Excess CO2 in the body produces hydrogencarbonate ions with also formed hydrogen ions. The hydrogen ions compete with oxygen for space on the haemoglobin and reduces oxygen transport
CO2 also combines with haemoglobin to produce carbaminohaemoglobin. This molecule has a lower affinity for oxygen than normal haemoglobin
Excess CO2 can cause respiratory acidosis, CO2 dissolves in the blood plasma to produce carbonic acid, acid dissociates to release hydrogen ions and lowers the pH of the blood
Why must nitrogenous compounds be removed from the body?
Body cannot store proteins or amino acids
Contain almost as much energy as carbohydrates
Transported to liver
Potentially toxic amino group removed (deamination)
Initially forms ammonia, which is transported to less soluble and less toxic compound urea
Remaining keto acid can be used directly in respiration to release its energy or it may be converted to a carbohydrate or fat for storage
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
What two sources of blood is the liver supplied with?
Oxygenated blood from the hear
Deoxygenated blood from the digestive system
Why is oxygenated blood from the heart supplied to the liver?
Blood travels from the aorta, via the hepatic artery into the liver. Supplied the oxygen which is essential for aerobic respiration.
Liver cells are very active as they carry out many metabolic processes, requiring ATP for energy
Why is deoxygenated blood from the digestive system supplied to the liver?
Enters liver via hepatic portal vein. This blood is rich in the products of digestion.
Conc of various compounds will be uncontrolled, blood may contain toxic compounds that have been absorbed in the intestine
How does blood leave the liver?
Via the hepatic vein. Rejoins the vena cava and the blood returns to normal circulation
What does the bile duct do?
Carries bile from the liver to the gall bladder where it is stored until required to aid the digestion of fats in the small intestines
How are cells arranged inside the liver?
Liver divided into lobes, further divided into lobules
Hepatic artery and hepatic portal vein run between, and parallel to the lobules
Blood from both vessels mixed and passes along a special chamber called a sinusoid
Hepatic vein drains blood from the liver
Blood that flows along the sinusoid is in very close contact with liver cells, able to remove molecules from the blood and pass molecules into the blood
Give 4 metabolic functions of the liver cells
Protein synthesis
Transformation and storage of carbohydrates
synthesis of cholesterol and bile salts
detoxification
What are Kupffer cells?
Specialised macrophages
Move about within the sinusoids and are involved in the breakdown and recycling of old red blood cells
What is the primary function of Kupffer cells?
Appears to be the breakdown and recycling of old red blood cells
What is bilirubin?
One of the waste products from the breakdown of haemoglobin
What is urea?
An excretory product formed from the breakdown of excess amino acids
What is the ornithine cycle?
The process in which ammonia is converted to urea. It occurs partly in the cytosol and partly in mitochondria, as ATP is used
What 6 functions does the liver have?
Control of blood glucose levels, amino acid levels, lipid levels
Synthesis of red blood cells in the fetus, bile, plasma proteins, cholesterol
Storage of Vitamins A, D and B12, iron, glycogen
Detoxification of alcohol, drugs
Breakdown of hormones
Destruction of red blood cells
How is urea formed from amino acids?
Amino acid ——–> ammonia ———> urea
^ ^
deamination ornithine cycle
What equation can the ornithine cycle be summarised as?
Ammonia + carbon dioxide —> urea + water
What is detoxification?
The conversion of toxic molecules to less toxic or non-toxic molecules
How is ethanol detoxified in the body?
Ethanol -> ethanol -> ethanoic acid -> acetyl coenzyme A
And acetyl coenzyme A is used in respiration
What is produced in the detoxification of alcohol?
NAD is converted into reduced NAD
What happens if you consume too much alcohol?
If the liver has to detoxify too much alcohol it has insufficient NAD to deal with the fatty acids
These fatty acids are then converted back to lipids and are stored in hepatocytes, causing the liver to become enlarged
What is a nephron?
The functional unit of the kidney
A microscopic tubule that receives fluid from the blood capillaries in the cortex and converts this to urine which drains into the ureter
What is the glomerulus?
A fine network of capillaries that increases the local blood pressure that increases the local blood pressure to squeeze fluid out of the blood
Surrounded by a cup or funnel-shaped capsule which collects the fluid and leads into the nephron
Explain the structure of the kidney
Outer region called the cortex
Inner region is called medulla
Centre called the pelvis which leads into the ureter
What four things is the nephron divided into?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
What is selective reabsorption?
Useful substances are reabsorbed from the nephron into the bloodstream while other excretory substances remain in the nephron
How does the composition of fluid change in the nephron?
PCT fluid is altered by the reabsorbed of all the sugars, most salts and some water
85% of the fluid reabsorbed here
Descending limb of the loop of Henle, water potential of the fluid is decreased by addition of salts and removal of water
Ascending limb, water potential increased as salts are removed by active transport
Collecting duct, water potential is decreased again by the removal of water
Ensures the final product has low water potential
What are afferent vessels?
Bring blood into the organ
What are efferent vessels?
Vessels carry blood away from the organ
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 Bowman’s capsule
What are podocytes?
Specialised cells that make up the lining of the Bowman’s capsule
Why are the afferent arteriole and the efferent arteriole different diameters?
to put the blood in the capillaries under increased pressure
The pressure difference tends to push fluid from the blood into the Bowman’s capsule that surrounds the glomerulus
What does the lumen of the Bowman’s capsule consist of?
Endothelium of the capillary
Basement membrane
Epithelial cells of the Bowman’s capsule