Excretion Flashcards
Define excretion
the removal of metabolic waste from the body
Define metabolic waste
toxic waste substances + substances produced in excess by the reactions inside cells
Why can’t we store amino acids?
The amine group makes them toxic
What does the deamination of amino acids produce?
Ammonia and Keto acid
How is urea formed from ammonia?
Through the ornithine cycle
What is urea?
the major end product of nitrogen metabolism in animals
Why does the ornithine cycle occur?
Because urea is less toxic than ammonia:
ammonia is more soluble in water, so large volumes of water would be required to excrete it, causing dehydration.
Where does the ornithine cycle occur and where does the urea formed go?
The ornithine cycle occurs in the liver. The urea is then transported to the kidneys where it is filtered out of the blood and stored in the bladder.
How does oxygenated blood enter the liver?
Blood from the heart travels through the aorta and enters the liver through the hepatic artery. The oxygen is required by hepatocytes for aerobic respiration.
How does deoxygenated blood enter the liver?
Blood comes from the digestive system via the hepatic portal vein. It is rich with digested products (and potentially toxic compounds) absorbed by the small intestine.
How does blood leave the liver?
Via the hepatic vein which rejoins normal blood circulation at the vena cava.
What are some of the roles of hepatocytes?
Detoxification.
Homeostatic control of blood glucose.
Deamination of excess amino acids in the ornithine cycle.
Secrete bile stored in the gall bladder.
What are Kupffer cells and their role in the liver?
They are macrophages, playing an important role in homeostasis and ingesting old RBC’s and foreign particles.
What are sinusoids in the liver?
low pressure vascular channels, receiving blood from the hepatic artery and portal vein at the periphery of lobules and delivering it to the central veins. They are lined with endothelial cells and flanked by plates of hepatocytes and occasional kuppfer cells.
Outline how alcohol is detoxified in the liver.
Ethanol is oxidised to ethanal by the enzyme ethanol dehydrogenase (reducing NAD). Ethanal is then oxidised by NAD (forming reduced NAD) forming acetyl coenzyme A which is used in respiration.
What happens if there is too much alcohol in the liver?
There is insufficient NAD to detoxify it, so fatty acids are converted to lipids and stored in hepatocytes (resulting in an enlarged liver which can lead to cirrhosis).
What are the three sections of the kidney, from the centre out?
Pelvis, Medulla, Cortex (surrounded by the capsule)
Describe the structure of the nephron, in the order that blood/filtrate flows through it.
Afferent arteriole, glomerulus, bowman’s capsule, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct.
What is the nephron?
Where the blood is filtered and reabsorbed in the kidney.
What is the glomerulus?
A dense capillary network where ultrafiltration occurs due to blood being at such high pressure.
Why is the blood under high pressure in the glomerulus?
The lumen of the efferent arteriole is narrower than that of the afferent arteriole.
What is the proximal convoluted tubule?
First, coiled region of the tubule after the bowman’s capsule, found in the cortex of the kidney, where substances are reabsorbed into the blood via capillaries running anti-parallel.
What is the loop of henle?
Long loop which passes through areas of very high solute concentration in the medulla with the purpose of producing more concentrated urine. (reducing water loss)
