Excretion Flashcards
(25 cards)
What is excretion?
Removal of waste products of metabolic
Excretion of carbon dioxide
Waste product from aerobic respiration, transported in blood stream to lungs, excreted in exhalation
Urea excretion:
It is produced in liver in breakdown of excess amino acids, enters blood stream and passes through kidneys where urea is removed from the blood and excreted via urine
It is a nitrogenous waste product
What do fish and insects / birds excrete as a nitrogenous waste product?
Fish - ammonia
Insects / birds - Uric acid
How are bile pigments excreted?
They are found in haemoglobin, haemoglobin is broken down when end of life and converted to other molecules which are removed from the bloodstream from the liver and excreted into bile
Thee are bile pigments
Bile is stored in the gall bladder and released into small intestine they leave body in faeces
What is the livers role in excretion?
Production of urea and excretion of bile pigments
What are the blood vessels involved in the liver?
Hepatic portal vein carries deoxygenated blood from intestines that is rich with nutrients
Hepatic artery carries oxygenated blood from lungs
Hepatic vein carries deoxygenated blood away from liver and to lung
What are hepatocytes?
Liver cells
They synthesis and secret a range of molecules including proteins
Mitochondria to generate ATP
If liver is damaged, hepatocuytes go under mitosis to replace lost tissue
How are hepatocytes arranged in the liver ?
How do they interact with blood
They form cavities called sinusoids this is where oxyugened and deoxygenated blood from the hepatic artery Arterioles and hepatic portal vein venue join and mix.
As blood travels down sinusoid, oxygen diffuses from blood to hepatocytes. Other molecules will travel between hepatocytes and blood.
Hepatocytes form urea in the ornithine cycle
Urea diffused from hepatocytes into blood in the sinusoid cavaity
What is a kuppfer cell?
Is a macrophage, form part of the immune system
Kuppfer cells ingest foreign material including pathogens such as bacteria or virus that may have entered through hepatic portal vein
How does liver form bile?
When RBC are broken down haemoglobin is converted into bile pigments which is secreted in bile which is formed in hepatocytes.
It is secreted into spaces called canaliculi
Bile is drained from canaliculi into bile ductule, many of these forms bile duct. Bile is transferred to gall bladder where it is stored until it is passed to the digestive system.
Function of hepatocytes in response to insulin:
Can absorb excess glucose from blood and convert it into glycogen
In response to glucagon it can hydrolyse glycogen back into glucose and release into blood
What is detoxification in liver?
Neutralisation and breakdown of unwanted chemicals such as alcohol, drugs, hormones and toxins produced in chemical reactions
Liver contains enzymes to break down toxins into non toxic substances
What does the ornithine cycle do in the liver?
It forms urea from reacting ammonia
Excess proteins cannot be stored so they go to liver to be delaminated which is when amine group is removed from amino acids —- makes it ammonia
Ammonia is toxic which is why it has to be converted to urea
What is the kidney responsible for?
Excretion of urea produced in liver and osmoregulation (the process of controlling the water potential of blood)
What is the structure of the kidney?
Renal artery supplies blood to be filtered, renal vein carries filtered blood away
Kidneys are made up of cortex, medulla and pelvis
Cortex contains many capillary networks that carry blood from the renal reveries to nephrons
Medulla contains nephrons
Pelvis is where urine is collected before leaving the kidney and going to ureter
Structure of nephrons:
Millions of nephrons in the medulla of a kidney
This is where blood is filtered and useful substances are re absorbed into blood
What does the nephron consist of?
Bownmans capsule - where ultra filtration occurs from glomerulus
Proximal convoluted tubule - glucose is re absorbed
Loop of Henle - sodium ions are actively transported out of the ascending limb into the medulla to create a low water potential
Water moves out of the ascending limb and out of the distal convoluted tubule and collecting duct by osmosis due to the water potential gradient. Liquid remaining in teh collecting duct forms urine. It contains water, dissolved salts, urea and other substances e.g hormones
What is ultrafiltration?
Blood enters through afferent Arterioles, enters glomerulus in high hydrostatic pressure because glomerulus is lots of smaller capillaries. Water and small molecules diffuse out of capillaries into bowman’s capsule.
Filtrate goes through capillary walls, basement membrane and bowman’s capsule wall which has podocytes that act as an additional filter, large proteins and blood cells dont fit so this blood leaves in efferent Arterioles.
What is selective re absorption? How?
Filtrate enters proximal convoluted tubule
Concentration of sodium ions is decreased because sodium ions are actively pumped out of ascending limb into medulla to lower w.p of medulla so water diffuses out of ascending limb and return to blood.
Glucose moves with sodium ions - cotransport so reternters blood vessels and re absorbed
About 80% of water in PCT moves back to capillaries at this stage due to gradient of w.p
What happens in loop of Henle?
Filtrate enters descending limb. Sodium and chloride ions gradient enable re absorption
At bottom of loop, some sodium and chloride ions are transported out by diffusion becasue there is a dilute solute due to all the water that has moved out.
Mitochondria in walls of cells provide energy to actively transport sodium and chloride ions out of ascending limb. Lowers w.p of medulla compared to filtrate so water moves out of descending limb into medulla by osmosis. (Descending limb is permeable to water becsue of aquaporins)
Re absorption of water at DCT and collecting duct:
All sodium ions being actively transported out of loop of Henle so when it reaches DCT it is very dilute
The section of medulla near DCT and collecting duct is very concentrated
Even more water diffused out of DCT and collecting duct, what remains forms urine
What is the role of hypothalamus and pituitary gland in water regulation?
Hypothalamus - has osmoreceptors that detect changes in the water potential of the blood. This involves neg feedback and brain
If the w.p is too low, water moves out of osmorecptors by osmosis and they shrivel. This stimulates the hypothalamus to produce ADH
If it is high, water enters osmoreceptors, hypothalamus I stimulated to produce lead ADH
It imoves to posterior pitutitary gland which si where it is released to L blood. Travels to kidney
What does ADH do?
Makes urine more concentrated
Bind to complimentary receptors located on target cells in DCT and collecting duct.
When it binds, adenyl cyclase is activated to make cAMP. This activates an enzyme which causes vesicles containing aquaporins to fuse with the membrane. They are channel proteins that allow water to be transported from collecting duct to medulla. Membrane is more permeable to water and more water leaves to be re absorbed into blood
