Module 5 Section 2: Excretion Flashcards
Different vessels connected to the liver
Hepatic artery
Hepatic vein
Hepatic portal vein
Bile duct
Function of hepatic artery
Hepatic artery supplies the liver with oxygenated blood from the heart
Liver has a good supply of oxygen for respiration to provide lots of energy
Function of hepatic vein
Hepatic vein takes deoxygenated blood away from the liver
Function of hepatic portal vein
Hepatic portal vein brings blood from the duodenum and ileum (part of small intestine)
Rich in products of digestion
This means any harmful substances are filtered out and broken down straight away
Always shown as branched vessels leading into cells
Function of bile duct
The bile duct takes bile to the gall bladder to be stored
Bile then released into duodenum via bile duct
Bile is produced by the liver to emulsify fats
Structure of liver
Liver made up of liver lobules
These are cylindrical structures made of cells called hepatocytes
These are arranged in rows radiating out from the centre
Structure of lobules
Each lobule has a central vein in the middle which connects to the hepatic vein
Many branches of the hepatic artery, hepatic portal vein and bile duct are also found surrounding and connecting to each lobule to supply them with blood
Lobules are separated by connective tissue made up of extracellular matrix
Structure of hepatocytes
Large nuclei
Prominent golgi apparatus
Lots of mitochondria
Function of sinusoids
Exchange materials directly with hepatocytes
Contain kupffer cells which act as the macrophages of the liver
Kupffer cells are attached to the walls of the sinusoids and remove bacteria and break down old red blood cells
The harmful substances are removed along with oxygen and broken down by hepatocytes into less harmful substances that then re-enter the blood and drain into a central vein
Lined with incomplete layer of endothelial cells to allow blood to reach hepatocytes for substance exchange
How are the hepatic artery and hepatic portal vein connect to the central vein
Hepatic artery and hepatic portal vein are connected to the central vein by capillaries called sinusoids
How is bile made in the liver
Heptacytes produce bile and secrete it into tubes called bile canaculi
These tubes drain into the bile ducts
The bile ducts from all the lobules eventually connect up and leave the liver
How is the hepatic vein formed in the liver from sinusoids
Blood runs to the central vein in each sinusoid
The central veins from all sinusoids in all lobules connect up to form the hepatic vein
What is excretion
This is the removal of the waste products of metabolism from the body
How does excretion help metabolism
Metabolism is all the chemical reaction that happen in the cells
Produces carbon dioxide and nitrogenous waste which aren’t needed by the body
If they were to build up in the body then they would cause damage
Excretion removes these
How is carbon dioxide a waste product and how is it removed
CO2 is a waste product of respiration
Too much in the blood is toxic so it’s removed through the lungs or gills
Lungs and gills act as excretory organs
What does excreting waste products in the blood do for the body
Excreting waste products from the body maintains normal metabolism
Also maintains homeostasis by helping to keep the levels of certain substances in the blood roughly constant
Why are amino acids broken down by the liver
Amino acids from the diet contain nitrogen in their amino groups
Nitrogenous substances can’t usually be stored by the body
Means that excess amino acids can be damaging to the body
This means they must be used by the body (e.g. to make proteins) or be broken down and excreted
How are excess amino acids broken down by the liver
The amino groups (NH2) are removed from excess amino acids forming ammonia and organic acids (this is deamination)
Organic acids can be respired to give ATP or converted to glycogen and stored
Ammonia is too toxic to be directly excreted
It’s combined with CO2 in the orthinine cycle to make urea
The urea is released from the liver into the blood
The kidneys then filter the blood and remove the urea as urine which is excreted from the body
What can the liver break down
Excess amino acids
Alcohol
Drugs
Unwanted hormones
What is detoxification
Where harmful substances (e.g. alcohol, drugs, hormones, amino acids) are broken down into less harmful compounds
These are then excreted from the body
How does the liver break down alcohol
Ethanol is a toxic substance that can damage cells
It’s broken down by the liver into ethanal and then into less harmful acetic acid (using ethanol hydrogenase and ethanal dehydrogenase)
Excess alcohol over a long period of can lead to cirrhosis of the liver which is where liver cells die and scar tissue blocks blood flow
Example of the liver breaking down drugs
Paracetamol is broken down by the liver
Excess of this can lead to liver and kidney failure
Why does the liver need to break down hormones
E.g. insulin
This is a hormone that controls blood glucose concentration
Insulin is broken down by liver as in excess is can cause problems with blood sugar levels
Excess hormones in the blood can cause too much of a response from cells which could be problematic for conditions inside body
How and why does the liver store glycogen
The body needs glucose for energy
Liver converts excess glucose in the blood to glycogen (glycogenesis) and stores it as granules in the cytoplasm of its cells until glucose is needed for energy
How is lactate detoxified
Lactate is the end product of anaerobic respiration
It is an energy rich compound which is absorbed by hepatocytes and metabolised into pyruvate
This pyruvate enters mitochondria and is respired to produce energy to convert the rest of the lactate into glucose
How to notice liver on microscope
Deamination
Excess amino acids cannot be stored by the body.
So they are broken down (deamination) and excreted.
Deamination is the removal of the amine group (oxidation)
Occurs in the mitochondria and cytoplasm of the hepatocytes
This forms ammonia and carbon dioxide
Steps of excretion of urea
Deamination
Ornithine cycle
Label diagram
Process of the ornithine cycle
The ammonia and carbon dioxide are combined with ornithine to make citrulline
Citrulline leaves mitochondria by facilitated diffusion into the cytoplasm of the liver cell
Citrulline gets converted to argino-succinic acid by adding ATP (forms AMP) - 2 phosphate bonds are broken.
More nitrogen is added as NH2 and water is released.
Argino-succinic acid is converted to the intermediate compound arginine.
Water is added, ornithine and urea is released - into the bloodstream where it is removed by the kidneys
Function of kidney
Excretes waste products e.g. urea from liver
Regulate water potential of the blood
Label diagram
Function of renal pelvis
Central chamber where urine collects before passing out down ureter
Function of renal medulla
Contains tubules of the nephrons that form pyramids of the kidney and collecting ducts
Function of renal cortex
Outer layer where filtering of blood takes place
Dense capillary network carrying blood from renal artery to nephrons
Function of ureter
Where waste travels out of kidney to form urine in bladder
Function of renal vein
Delivers deoxygenated blood out of kidney after filtration
Function of renal artery
Delivers oxygenated blood to kidney to be filtered
Label nephron
Overview of process of how blood is filtered in nephrons
Blood from renal artery enters smaller arterioles in the cortex
Each arteriole splits into a structure called glomerulus inside the Bowman’s capsule
Ultrafiltration takes place
Efferent arteriole is smaller in diameter than afferent arteriole so blood in glomerulus is under high pressure
High pressure forces liquid and small molecules in the blood out of capillary into Bowman’s capsule
Liquid and small molecules pass along rest of nephron and useful substances are reabsorbed
Filtrate then flows through collecting duct and passes out of kidneys along ureter
Process of ultrafiltration
Liquid and small molecules pass through 3 layers to get to Bowman’s capsule and enter nephron tubule
Capillary wall, basement membrane and epithelium of Bowman’s capsule
Larger molecules like proteins and blood cells can’t pass through and stay in blood
Process of selective reabsorption
Na+ actively transported out of cells (across basal membrane)
Therefore the Na+ concentration inside the cell drops below the Na+ concentration in the lumen of the PCT
Creates a concentration gradient from the filtrate in lumen of PCT down to cytoplasm of cells lining PCT
Therefore Na+ diffuses from the lumen into the cell via co-transporter protein
This allows amino acids and glucose to be transported in simultaneously which increases their concentration inside the cell
They can then diffuse down a concentration gradient through cell into blood
From the influx of solutes to the cells of the PCT, water potential in those cells decreases
Water moves down the water potential gradient from the nephron to the blood
Urea is absorbed by diffusion due to its small size
Process of producing urine in loop of Henle (long one)
Near the top of the ASCENDING limb, Na+ and Cl - ions are actively pumped out into medulla
The ASCENDING limb is impermeable to water, so the water stays inside the tubule.
This creates a low water potential in the medulla, because there’s a high concentration of ions.
Because there’s a lower water potential in the medulla than in the DESCENDING limb, water moves out of the DESCENDING limb into the medulla by osmosis (fluid was isotonic when entering loop of Henle)
This makes the filtrate more concentrated (hypertonic) as the ions can’t simply diffuse out because the DESCENDING limb isn’t permeable to them).
The water in the medulla is reabsorbed into the blood through the capillary network (vasa recta)
Near the bottom of the ASCENDING limb Na+ and CI-ions diffuse out into the medulla, further lowering the water potential in the medulla.
(The ASCENDING limb is impermeable to water, so it stays in the tubule.)
When fluid reaches top of ascending limb it is hypotonic (lower conc of solute) to the blood again and enters DCT and collecting duct
The first three stages massively increase the ion concentration in the medulla, which lowers the water potential.
This causes water to move out of the collecting duct by osmosis.
As before, the water in the medulla is reabsorbed into the blood through the capillary network.
Process of haemodialysis
Patient’s blood passed through dialysis machine
Blood flows on one side of partially permeable membrane (mimicking basement membrane) and dialysis fluid flows on other side
Waste products and excess water and ions diffuse across the membrane into dialysis fluid and are removed from blood
Process of peritoneal dialysis
Dialysis fluid is put through a tube that passes from the outside of a patient’s abdomen into their abdominal cavity.
Waste products diffuse out of patient’s blood into the dialysis fluid across the peritoneum (the membrane the lines the abdominal cavity).
After some time, the fluid is drained out via the tube.
What is a kidney transplant
A kidney transplant is where a new kidney is implanted into a patient’s body to replace a damaged kidney.
What happens in the negative feedback loop when water is in short supply
Concentration of inorganic ions in the blood rises and the water potential of the blood and tissue fluid becomes more negative.
Detected by the osmoreceptors in the hypothalamus.
They send nerve impulses to the posterior pituitary which releases stored ADH into the blood.
ADH is picked up by receptors in the cells of the collecting duct and increases the permeability of the tubules to water by increasing amount of aquaporins in membrane
Water leaves the filtrate in the tubules and passes into the blood in the surrounding capillary network.
A small volume of concentrated urine is produced
What happens in the negative feedback loop when water is in excess
Blood becomes more dilute and its water potential becomes less negative.
Change detected by the osmoreceptors of the hypothalamus
Nerve impulses to the posterior pituitary are reduced or stopped so the release of ADH by the pituitary is inhibited.
Very little reabsorption of water can take place because the walls of the collecting duct remain impermeable to water as less aquaporins inserted into membrane
In this way the concentration of the blood is maintained
Large amounts of dilute urine are produced
