Excretion Flashcards
What are the 2 roles of the kidneys?
Filter nitrogenous waste products (urea) out of the blood
Maintain water potential of the blood/tissue fluid (osmoregulation)
How much blood passes through the kidneys per minute?
90-120cm cubed
How much urine do people produce per day?
1-2 dm cubed
What are the regions of the kidneys?
Capsule Cortex Medulla Pelvis Ureter
What blood vessel transports blood to the kidneys?
Renal artery
What blood vessel transports blood away from the kidneys?
Renal vein
What is the medulla of the kidneys made of?
Renal pyramids
Where does each nephron start?
In the Cortex of the kidney
What is vasa recta?
The blood that enters in the artery, branches to become the capillary network around the nephron
Compare the blood in the renal vein and renal artery?
Renal vein has much reduced urea concentration
Renal vein has almost the same concentration of glucose and amino acids
The renal vein has a restored ion balance (back to ideal levels)
Why is there slightly less glucose in the renal vein than the renal artery?
Some of the kidney cells will use the glucose in respiration
What parts of a nephron are in the cortex?
Afferent arteriole Efferent arteriole Glomerulus Bowman's capsule Proximal convoluted tubule Distal convoluted tubule
What parts of a nephron are in the medulla?
Descending limb
Loop of Henle
Ascending limb
What is ultrafiltration?
The filtering of substances out of the blood at the molecular level
Why is the blood pressure in the glomerulus high?
Due to the decrease in diameter from afferent arteriole to efferent arteriole
Why is there a lower water potential in the blood compared to the fluid in the Bowman’s capsule?
Blood contains plasma proteins that are too large to be filtered so stay in the blood and lower water potential
Why does the fluid enter the Bowman’s capsule?
The hydrostatic pressure is greater than the force of osmosis so the fluid is forced out of the blood
What is the fluid in the Bowman’s capsule called?
Filtrate (it has been filtered)
What are the 3 layers that molecules have to pass through to move from the blood to the renal filtrate?
The endothelium of the capillary
Basement membrane of capillary
Special cells called podocytes
What about the endothelium of the capillary allows molecules to pass into the Bowman’s capsule
There are small gaps so only small molecules like glucose can get through while large molecules like red blood cells can’t
What is the basement membrane of the Bowman’s capsule made of?
It is like a fine mesh made of collagen and glycoproteins
What does the basement membrane of the Bowman’s capsule do?
It acts as a filter and prevents the passage of molecules with a relative molecular mass greater than 69000. Most proteins and all blood cells are too large to leave the glomerulus
What do podocytes do?
They are an additional filter, they have extensions called pedicels that wrap around the capillaries forming slits. Fluid from the blood in the glomerulus can pass between these cells into the lumen of the Bowman’s capsule.
What is the glomerular filtration rate (GFR)?
The volume of blood filtered through the kidneys in a given time
What does the glomerular filtration rate (GFR) give us an idea of?
How well the kidneys are working
What happens to the useful substances that were filtered into the Bowman’s capsule?
Selective reabsorption
Where does most selective reabsorption occur?
85% occurs in the proximal convoluted tubule
How are the cells lining the proximal convoluted tubule adapted for selective reabsorption.
Microvilli - increase SA, more reabsorption
Gaps between microvilli - useful substances absorbed into cell easily - small diffusion pathway
Mitochondria - provide energy for active transport
Capillary close by to take away substances that are reabsorbed.
How does glucose/amino acids get reabsorbed?
Na+ - K+ pump removed Na+ from the cells lining the proximal convoluted tubule.
This lowers the [Na+] in the cell so they transported into the cell with glucose/amino acids by facilitated diffusion.
[Glucose/amino acids] increases in the cell so they diffuse into the tissue fluid.
What extra thing can aid the reabsorption of glucose/amino acids?
Active transport into the cell (alongside the facilitated diffusion)
How is water reabsorbed in the proximal convoluted tubule?
Glucose/amino acids moving into the cell by facilitated diffusion lowers the water potential of the cell so water moves in by osmosis and then gets reabsorbed into the blood.
Why isn’t all glucose reabsorbed when there is a high concentration?
All glucose carriers will become saturated so excess glucose is excreted
What is the role of the loop of Henle?
Create a low water potential in the tissue fluid around the nephron.
What happens to ions in the descending limb?
They do not leave as it is impermeable to ions. However, Na+ and Cl- ions diffuse into it.
What happens to water at the descending limb?
Moves out by osmosis and moves into the capillaries
What happens at the lower part of the ascending limb?
It is permeable to ions but not to water so Na+ and Cl- ions diffuse out but the water remains in
What happens in the upper part of the ascending limb?
Active removal of Na+ and Cl- ions creates a low water potential in surrounding tissue
What does the low water potential in the tissue around the ascending limb cause?
Water to move out of the collecting duct by osmosis and enter the capillary. Any water that stays in the collecting duct passes to pelvis as urine.
How does the collecting duct change the concentration of urine?
It’s permeability to water can change. Lower water potential in blood, more permeable, more water reabsorbed into the blood.
Higher water potential in blood is opposite
How do the 2 limbs of the loop of Henle act as a counter current multiplier?
The ascending limb uses ATP to create the concentration gradient needed for water to be removed from the descending limb - moving back into the blood
Definition of counter-current system?
This is where fluid flows in opposite directions in two vessels close to one another
Why is a counter-current system important for the two limbs of the loop of Henle?
It maximises the concentration gradient that can be built up between the two, all the way along the length
What hormone mediates Na+ ions?
Aldosterone
What mediates Calcium ions?
PTH
After the ascending limb where does further balancing of water and salt content occur?
Distal convoluted tubule
What do the cells of the distal convoluted tubule have to maximise the effectiveness of transporting ions?
Microvilli - large SA
Lots of mitochondria for active transport
If the body lacks salt what occurs at the distal convoluted tubule?
Sodium ions are actively pumped out, then chloride ions follow because of the electrochemical gradient and move back into the blood
What is the distal convoluted tubule also permeable to apart from ions?
Water
What hormone does the distal convoluted tubule and the collecting ducts respond to in order to save more water?
ADH (Anti-diuretic hormone)
Where is the final volume and concentration of urine determined?
Collecting ducts
What does osmoregulation mean?
Maintenance of water potential in the blood
Why is osmoregulation important?
Affects osmosis into cells
Too high in blood, cells burst
Too low in blood, cells shrivel, dehydrate, low metabolism
How does the body gain water?
Food, drink, metabolism
How does the body lose water?
Breathing, sweat, urine
Where is ADH made?
Hypothalamus
Where is ADH stored/secreted?
Posterior pituitary gland
What monitors the water potential of the blood flowing through the brain?
Osmoreceptors
What type of hormone is ADH?
Peptide/protein
When is ADH released into the bloodstream?
When the water potential of the blood falls
What part of the nephron does ADH act on?
The cells of the collecting duct (and DCT)
Have specific receptors that are a complementary shape to ADH
What cells produce ADH?
ADH-synthesising nerve cells
Neurosecretory cells
What happens when the water potential of the blood decreases?
Detected by osmoreceptors in hypothalamus
Posterior pituitary gland stimulated to release more ADH into the blood
ADH increases permeability of DCT and collecting duct so more water is reabsorbed into blood
A small amount of highly concentrated urine is produced and less water is lost
What happens when the water potential of the blood increases?
Detected by osmoreceptors in hypothalamus
Posterior pituitary gland releases less ADH into blood
Less ADH so permeability of DCT and collecting duct decreases so less water is reabsorbed into blood
A large amount of dilute urine is produce and more water is lost
How does ADH increase the water reabsorbed at the DCT and the collecting duct?
ADH attaches to receptors on the cell surface membrane of cells lining it
Triggers cAMP - causes cascade of enzymes
Vesicles containing aquaporin fuse with cell surface membrane membrane
Increases cells permeability to water
More water moves out of them into tissue fluid around nephron then back to capillaries by osmosis
Why must ADH be broken down?
Otherwise permeability would remain high and water would continue to enter the blood leading to the blood having a too high water potential
Where is ADH broken down?
Kidneys
What is another name for the Bowman’s capsule?
Capsule lumen
What can cause kidney failure?
Kidney infections High blood pressure Diabetes mellitus Heart disease Blood loss in an accident Overuse of some drugs
What problems can kidney failure cause?
Waste products aren’t removed
Fluid starts to accumulate
Ion unbalance
Anaemia
How do you measure glomerular filtration rate?
Not directly, a blood test measures the concentration of creatinine in the blood.
Creatinine levels in blood and urine is used to calculate the creatine clearance which reflects GFR
Why is creatinine used to measure ultrafiltration rate?
It is a breakdown product of creatine phosphate in muscle cells and is usually filtered out by the kidneys.
What are the units for GFR?
cm³min⁻¹
What is the normal GFR?
90-120cm³min⁻¹ (down to about 75 in old age)
What are the 3 ways to treat kidney failure?
Haemodialysis
Peritoneal dialysis
Transplant
What are the 2 types of dialysis?
Haemodialysis
Peritoneal dialysis
How does haemodialysis work?
Arterial blood leaves the arms and is pumped around the machine.
Blood thinners are added to prevent clotting
Blood enters the dialysis machine that contains dialysis fluid. Dialysis fluid flows in a counter-current system to blood and contains no urea and the correct concentration of sugar and mineral ions.
Dialysis fluid with waste products is removed
Clean blood leaves dialysis machine and goes through bubble trap and return to a vein in the arm
What is another name for dialysis fluid?
Dialysate
What is the main process used in haemodialysis?
Diffusion!!!!!
Where does peritoneal dialysis occur?
Inside the body using the peritoneum membrane which forms the lining of the abdomen
How do you do peritoneal dialysis?
Dialysis fluid is introduced into the abdomen using a catheter and is left for several hours, allowing dialysis to occur across the peritoneal membrane. Urea, excess salt and water diffuse out of surrounding blood capillaries, into the tissue fluid, across the peritoneum, into the dialysis fluid.
After several hours, the dialysis fluid is drained off and discarded and replaced.
What is the disadvantage of haemodialysis?
It takes 8 hours, 2-3 times a week
What is the advantage of haemodialysis?
Removes urea for the patient
What is the advantage of peritoneal dialysis?
Removes urea for the patient
Done at home
Live a fairly normal life
When a kidney is transplanted what happens to the old kidneys?
They are left in the body
How is a kidney transplanted?
The blood vessels are joined to the ureter of the new kidney and is inserted into the bladder.
Why would someone need immunosuppressant drugs after a transplant?
Help prevent their immune system recognising the new organ as foreign and rejecting it
What are the advantages of a kidney transplant?
Freedom from time-consuming renal dialysis
Feeling physically fitter
Improved quality of life - able to travel
Improved self image - no longer have the feeling of being chronically ill
What are the disadvantages of a kidney transplant?
Need to take immunosuppressant drugs
Side effects - fluid retention, high blood pressure, susceptible to infections
Need major surgery under general anaesthetic
Need regular checks for signs of rejection
Ethical objections
What are ethical issues with kidney transplants?
Can be from deceased or living donors
3 year wait for a deceased donor kidney
Kidneys from living donors carry risk to that donor
Demand for kidneys is rising
Number of kidneys available in UK hasn’t really changed
People have to opt in to donate, more would be available if it was ‘presumed consent’
Could legalise buying kidneys
What substances can be detected in urine?
Molecules with a molecular mass of less than 69000 (can enter nephron) that are nor reabsorbed.
What can urine be tested for?
Glucose in diagnosis of diabetes Alcohol Recreational drugs hCG in pregnancy tests Anabolic steroids - cheating in sport Protein - bP too high/kidney infection Nitrate - bacterial infection in urinary tract
What are monoclonal antibodies?
Clones of 1 specific antibody
How are monoclonal antibodies made?
Mice are injected with hCG and they produce the antibodies which are then removed
Why will 1 coloured line always show up on a pregnancy test?
Control line - always made as mobile hCG antibodies with coloured beads will always attach to the anti antibodies at the end making one line
How do pregnancy tests detect pregnancy?
Urine passes along the strip, contains hCG.
hCG attaches to mobile monoclonal antibodies with coloured beads.
These then move/attach to immobile monoclonal antibodies which order the beads in a line
The excess monoclonal antibodies (without hCG) moves/attach to anti antibodies at the end which recognise antibodies and order the beads in a line (control line)
What is the definition of excretion?
The process by which an organism gets rid of waste metabolic products.
What are examples of things that are excreted?
Nitrogenous waste from amino acid metabolism and carbon dioxide from respiration
Why are things excreted?
The waste products are toxic or harmful and could damage the cells if allowed to accumulate
What are the 3 ways carbon dioxide is transported in the blood?
HCO3
In blood plasma as CO2 (5%)
Carbaminohaemoglobin (10%)
What is produced when carbon dioxide reacts reversibly with water?
Carbonic acid
How does carbonic acid go to HCO3- ions?
Carbonic acid dissociates to give H+ ions and HCO3- ions
What happens to the H+ ions that dissociate from carbonic acid?
Combines with oxyhaemoglobin to form haemoglobinic acid
What do H+ ions make haemoglobin do?
Give up it’s oxygen to allow the H+ ions to join
What would happen if H+ ions weren’t removed?
Become too acidic and denature enzymes
How is carbon dioxide excreted?
Via the lungs
What detects a small change in pH?
Respiratory centre in the medulla oblongata
When there is extra H+ ions, what does the respiratory centre in the medulla oblongata do?
Increase breathing rate in order to remove excess carbon dioxide.
H+ ions can also be removed by the kidneys
What is it called when the pH in the body drops below 7.35
Respiratory acidosis
What does sweat contain?
Salts, urea, water, uric acid, ammonia
How does the skin act as an excretory organ?
Urea, uric acid and ammonia are excretory products that are removed by the skin
How does the skin act as an organ of homeostasis?
Loss of water/salts are important parts of homeostasis
What is the problem with nitrogenous compounds?
The body can’t store them
Why are nitrogenous compounds important?
They release as much energy as carbohydrates
What does the body do with nitrogenous compounds?
Transport to liver. Amino acid group removed (deamination). Amino group forms ammonia. Ammonia converted to urea, transported to kidneys and excreted. Remaining keto acids used in respiration/stored.
What are liver cells called?
Hepatocytes
Why is a good blood supply to the liver important?
The liver is the largest organ in the body.
Liver cells carry out hundreds of metabolic processes and has an important role in homeostasis.
What 2 blood vessels supply blood to the liver?
Hepatic artery
Hepatic portal vein
What vessel does blood leave the liver in?
Hepatic vein
Where does the hepatic vein rejoin?
Vena cava
What vessel is connected to the liver but does not supply blood?
Bile duct
What does the bile duct do?
Carries bile from the liver to the gall bladder
Why does the liver have 2 different supplies of blood?
Hepatic artery - Supplies oxygenated blood, oxygen needed for respiration, lots of energy.
Hepatic portal vein - Blood from intestines, rich in digestion products. If ingested harmful substances, filtered and broken down straight away.
How is the liver divided?
2 lobes (left and right) Each lobe separated into many lobules
What are liver lobules?
Make up lobes of the liver.
Cylindrical structures made of hepatocyte cells that are arranged in rows radiating from a central vein.
How do you know which vessel is the hepatic portal vein?
The widest/biggest one
How do you know which vessel is the bile duct?
Smallest one and its on it’s own
Which way does the bile flow compared to the blood?
Opposite direction, away from the centre
What is another name for the central vein?
Intralobular vein
What is the chamber called where the hepatic artery and hepatic portal vein join?
Sinusoid
What do the cells that line the sinusoid do?
Add to/remove substances from the blood
What is the chamber called that lead to the bile duct?
Bile canaliculus
What are the 2 functions of bile?
Excretory - contains bilirubin
Digestive - emulsifies fat
What are kupffer cells?
Phagocytic cells in the sinusoid that ingest debris, bacteria and break down old red blood cells
What is the product of breaking down red blood cells that is excreted as part of bile?
Bilirubin
What are sinusoids adapted for?
Exchange of materials between blood and hepatocytes
How are sinusoids adapted for exchange of materials between blood and hepatocytes?
Microvilli on hepatocytes that border the sinusoid - increased SA
Porous - close contact between blood and hepatocytes
Wide - slow blood flow
How are sinusoids different to capillaries?
More porous
Wider
Why do hepatocytes have a very large nucleus, several golgi apparatus, rough ER, smooth ER and lots of mitochondria?
Make lots of proteins - like enzymes
Require energy - maybe for active transport
Make lots of lipids
What are the functions of the liver?
Control of: blood glucose, amino acid and lipid levels
Synthesis of: RBCs in fetus, bile, plasma proteins and cholesterol
Storage of vitamins, iron and glycogen
Detoxification of: Alcohol/drugs
Breakdown of hormones/RBCs
How can toxins be made harmless?
Oxidation, reduction, methylation and joining it with another molecule
What enzyme is used by hepatocytes to break down alcohol?
Ethanol dehydrogenase
What does breaking down ethanol form?
Ethanal
What enzyme is used to dehydrogenate ethanal?
Ethanal dehydrogenase
What is formed from the dehydrogenation of ethanal?
Acetate/ethanoate which combines with CoA to form Acetyl CoA which then enters aerobic respiration
What happens to the hydrogen that is released from the dehydrogenation of ethanol/ethanal?
They are combined with NAD to form NADH
What happens if the liver has to detoxify too much alcohol?
NAD is used to breakdown fatty acids for use in respiration, If too much detoxification occurs it has insufficient NAD as it gets reduced.
What happens to the fatty acids in the liver if they are not broken down?
They are converted back to lipids which are stored in the hepatocytes causing the liver to become enlarged.
What are the 2 steps in the formation of urea from excess amino acids?
Deamination
Ornithine cycle
What does deamination produce?
Ammonia and a keto acid
What is the problem with ammonia?
It is toxic and very soluble (more water would be needed to excrete it)
What is deamination?
Removing NH3 from an amino acid
What is Ornithine joined with in order to form citrulline in the ornithine cycle?
NH3 + CO2
water is produced
What is citrulline joined with to form arginine in the ornithine cycle?
NH3
water is produced
What joins with arginine to produce urea and ornithine in the ornithine cycle?
Water
What is the whole ornithine cycle?
Ornithine + NH3 + CO2 = H2O + citrulline
Citrulline + NH3 = H2O + Arginine
Arginine + H2O = Urea + Ornithine
What is the basic equation for the ornithine cycle?
2NH3 + CO2 = CO(NH2)2 + H2O
What is the definition of detoxification?
The conversion of toxic molecules to less toxic/non toxic molecules
