excretion Flashcards
excretion definition
the process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body
- it is a key part of homeostasis
outline the importance of excretion
metabolic waste products can have serious negative impacts on the body if left to accumulate
mammals are very large + active + endotherms - this means they have high metabolic rates and so produce lots of metabolic waste
give 5 examples of metabolic waste substances
CO2
nitrogenous waste - ammonia, urea, uric acid
bile pigments
how is CO2 produced and why does it need to be excreted
produced during decarboxylation of respiratory substrates
high levels cause cell damage as blood ph falls below normal range - acidosis
how is CO2 excreted
breathed out from lungs
how is ammonia produced and why does it need to be excreted
produced during deamination of excess amino acids
high levels increase the ph of cytoplasm and interferes with metabolic processes e.g. respiration and receptors for neurotransmitters in the brain
how is urea produces and why does it need to be excreted
produced in the orthonine cycle in liver cells
it can readily diffuse into cells, so high levels will decreases cell water potentials causing increased water uptake by osmosis, causing them to eventually burst
how is uric acid produced and why does it need to be excreted
produced in adenine + guanine (purine) break down in liver
high levels can result in uric acid forming crystals in joints causing gout (a form of arthritis)
how are nitrogenous compounds excreted
in urine - after some processing/detoxifying
how are bile pigments produced and why do they need to be excreted
produced during breakdown of haemoglobin - specifically haem groups
high levels accumulate in skin and turn it yellow - jaundice
how are bile pigments excreted
in faeces
another toxic byproduct is H2O2 - how does the body remove this
it is broken down by catalase into H2 and O2
outline 3 functions of the liver
- detoxification + breakdown of toxic substances
- producing excretory waste (urea)
- glycogen storage
outline the blood vessels that run through the liver
hepatic artery - brings liver oxy blood from the heart
hepatic vein - takes deoxy blood form liver back to heart
hepatic portal vein - brings deoxy blood from gut to liver
what is the function of the hepatic portal vein
it allows the liver to metabolise the nutrients absorbed into blood in small intestine
what is good about the many blood vessels that pass through the liver
liver requires a constant blood supply to carry out processes
what is the function of the gall bladder
to store bile salts and bile pigments
what are bile salts
found in gall bladder, these help to digest fat
how are the liver and the gall bladder connected
via the bile duct
bile canaliculi definition
small vessels that drain bile from hepatocyles to bile duct
hepatocyte definition
liver cells specialised to carry out necessary functions
what do hepatocytes do
- synthesise proteins
- transform and store carbs
- synthesise cholesterol and bile salts
- form bile and secrete into bile duct + canaliculi
- absorb substances from blood
- secrete hormones
hepatic lobule definition
small divisions of the liver made of hepatocytes, shaped like irregular polygons, consisting of a portal triad and a central hepatic vein, as well as sinusoid vessels - basic functional units of the liver
these are separated from each other by connective tissue consisting of cells that secretes an extra cellular matrix
sinusoid vessels definition
these are vessels adapted for the exchange of materials between blood and hepatocytes
they have very thin walls made of one layer of thin cells and are wide so have slower blood flow
they also contain kupffer cells - a type of phagocyte
what 3 vessels are in a portal triad
bile duct
hepatic artery
hepatic portal vein
what is orthonine
an amino acid
give the equation for deamination
amino acid + O2»_space;> keto acid + NH3
what is a keto acid
an acid with a carboxylic group and a ketone group
give 2 uses for keto acids
these can be used in the krebs cycle or they can be converted into cholesterol/lipids
outline the orthonine cycle
goes from orthonine»_space;> citrulline»_space;> argenine»_space;> back to orthonine
orthonine + NH3 + CO2 + ATP - H2O = citrulline
citrulline + NH3 + ATP - H2O = argenine
argenine + H2O = urea CO(NH2)2
overall equation:
2NH3 + CO2»_space;> CO(NH2)2 + H2O
what is the point of the orthonine cycle
to remove excess ammonia by converting it into urea
outline the process of alcohol detoxification
ethanol is oxidised by NAD and the enzyme ethanol dehydrogenase - this forms ethanal
ethanal is oxidised by NAD and the enzyme ethanal dehydrogenase - this forms ethanoate/acetate
this is added to coenzyme A - this forms acetyl coA
when NAD is used in oxidation, it gains a H to become reduced - NADH
why can excessive drinking cause fat gain and liver disease
excessive drinking means there is a lot of NAD used up in alcohol detoxification
NAD is also needed for the liver to break down fat, so less NAD = less fat breakdown = more fat being deposited
over time this can lead to liver disease
what happens to acetyl coA after alcohol detoxification
it can be used in respiration
if acetyl coA can be used in respiration why doesn’t drinking alcohol cause an increase in energy
theoretically this would be true, however alcohol is also a depressant, as it blocks nervous receptors
what are 2 important functions of kidneys
osmoregulation - regulation of water content of the blood - this is essential for maintaining healthy blood pressures
excretion - kidneys excrete the toxic waste products of metabolism e.g. urea, as well as substances in excess of requirement e.g. salts
what is the fibrous capsule of the kidney
the tough outer layer - capsule
what are the cortex and medulla of the kidney
these are regions within the kidney
cortex is the outer part, the medulla is the central part
what blood vessels run through the kidneys
the renal vein - carries filtered + deoxy blood away from the kidneys to heart
the renal artery - carries unfiltered + oxy blood to the kidneys to be filtered
these branch off into smaller vessels within the kidneys
ureter definition
a vessel that carries urine from the kidney to the bladder where it is temporarily stored
urethra definition
the vessel that carries urine form the bladder to outside the body to be excreted
what is the renal pelvis
where the kidney joins the ureter
nephron definition
the functional units of the kidney, made up of tiny tubes, where urine is formed and blood is filtered
how many nephrons are in 1 kidney
thousands
outline the passage of substances from blood through a nephron
- glomerulus where substances get filtered out of blood
- bowmans capsule where the substances get filtered into
- travels through proximal convoluted tubule
- travels through the loop of henle
- travels through distal convoluted tubule
- travels through collecting duct to renal pelvis
describe the passage of blood through the glomerulus
each glomerulus is supplied with blood from the afferent arteriole - which carries oxy + unfiltered blood from renal artery - and oxy + filtered blood leaves from the efferent arteriole
the afferent arteriole has a larger lumen, whereas the efferent arteriole has a thinner lumen, so in the glomerulus blood pressure increases
why is the blood pressure high in the glomerulus
it is necessary for ultrafiltration
outline the process of ultrafiltration
blood in the glomerulus is at high hydrostatic pressures, and so it is pushed out of fenestrations in the capillary endothelium
hydrostatic pressure»_space; solute potential (some stuff wants to go back in) so mostly stuff comes out
it can then enter the bowmans capsule, through pores in the membrane, and continue along the nephron
ultrafiltration occurs in the space between membranes - this is where the basement membrane is located
only molecules with a RMW relative molecular weight or under 69,000 can pass through the 3 part membrane
outline the structure + function of the basement membrane
it is part of a 3 part membrane - capillary endothelium, basement membrane, bowmans capsule podocytes
it is made of collagen and glycoprotein fibres, and provides as extra layer of sieving, ensuring large molecules cannot pass out
it has a slight negative charge meaning it can repel substances back into blood
what kind of molecules cannot leave the blood in ultrafiltration
cells, proteins, ions, and other large molecules with RMW of over 69,000
what molecules are in the glomerular filtrate
glucose, amino acids, ions, urea, water
what kind of molecules do urine tests test for
molecules with a RMW of under 69,000
what is the glomerulus
a tangle of capillary blood vessels
where does selective reabsorption take place
proximal convoluted tubule
what is the structure of the proximal convoluted tubule
filterate flows through the lumen
it is lined with epithelial cells with brush borders which increases the SA:V, and many mitochondria to produce energy for active transport
pumps in membrane to transport ions + other substances
there is a capillary network running alongside the PCT, but slightly separated by tissue fluid
outline the process of selective reabsorption of ions and useful substances
- in PCT there is a high conc of ions e.g. Na+ as they get filtered
- specific cotransport proteins in epithelial cells carry glucose and amino acids back with Na+ - amino acids/glucose can diffuse out into the tissue fluid and capillaries
- Na+ is actively pumped out by a Na+/K+ pump - creating a conc gradient to move Na+ into the blood
selective reabsorption of water
- PCT has a high conc of water and urea
- capillaries have a low water potential and urea conc after being filtered
-water moves into blood passively via osmosis - some urea also passes back as it can fit through phospholipid bilayer but this level is non toxic
selective reabsorption of drugs + hormones
these don’t get reabsorbed as there are no specific proteins to transport them back across
how does the Na+/K+ pump work
3 Na+ out
2 K+ in
where does water reabsorption take place
loop of henle
outline the process of water reabsorption in the loop of henle
- at the start of the ascending limb salts move out passively due to steep conc gradient
- salts e.g. NaCl are actively pumped out of the ascending limb as conc gradient isn’t steep enough
- this causes water potential to increase in the ascending limb and water potential to decrease outside the loop of henle
- water moves out of the descending limb by osmosis, as the ascending limb is impermeable to water + descending limb is impermeable to salts
- water potential decreases in the ascending limb
- solute concentration is greatest at the base of the loop of henle, as all water has moved out but salts are still inside
what is the process in the loop of henle called and why
counter current multiplication - because it multiplies the effect of the gradient
loop of henle memorising trick
w n i U i n w
water not ions not
ions water
U = loop of henle
how might the loop of henle be different in certain animals
animals in desert climates often have a much longer loop of henle as more water needs to be reabsorbed
what happens to the efferent arteriole after ultrafiltration
it branches off into a network of capillaries that runs closely to the nephron tubules, allowing for lots of exchange/diffusion of substances in and out of the nephron
these capillaries are also the site of selective reabsorption
capillaries then join together and deoxy + filtered blood rejoins renal vein
what does the distal convoluted tubule do
reabsorbs water and ions
give 5 reasons that could cause kidney failure
- blood loss in an accident
- diabetes
- high blood pressure
- overuse of certain drugs
- infections
kidney failure can be fatal after a short time, or it can exist as a long term condition
what does kidney failure mean
this is when kidneys are not functioning properly, meaning
- urea + salt + water + some toxins are not excreted
- less blood is filtered by glomerulus (low GFR) leading to a build up of toxins and abnormal proteins in blood
- electrolyte balance in blood is disrupted, which can be very harmful
- high blood pressure
- weakened bones
- anaemia
- pain and stiff joints as a result of abnormal proteins in blood
remember humans can survive with just 1 kidney
what are some impacts of poor blood electrolyte balance
excess K+ = abdominal cramps, tiredness, muscle weakness, paralysis, cardiac arrest or arrhythmia (as it disrupts impulses from SAN)
excess Na+ = disorientation, muscle spasms and weakness, increased blood pressure
what are two treatment options for kidney failure
dialysis
transplants
why are kidney transplants hard to get
although only one kdiney is needed for a transplant, a donor with a compatible blood group must be found
what are disadvantages of kidney transplants
- patient must take immunosuppressants for the rest of their lives to prevent the transplant from being rejected, as they are often still different tissue types
- immunosuppressants can cause side effects
- they also leave the patient vulnerable to infection
what are advantages of kidney transplants
- freedom unlike dialysis
- less diet restriction
- less expensive than dialysis
- long term solution
what are the 2 types of dialysis
haemodialysis
peritoneal dialysis
how does haemodialysis work
patient requires regular treatment in hospital using a haemodialyser - this acts like an artificial kidney
dialysate contains concs of necessary substances similar to ideal blood concs - these then pass into blood if there is an imbalance - dialysate contains no urea, so conc gradient allows for excretion
partially permeable membrane separates patient blood from dialysate, which flpw in opposite directions to maintain conc gradient across length of machine
dialysate must be refreshed to maintain conc gradient
each session is approx 3 hours
the drug herapin - a blood thinner - is added to blood to prevent clotting
patient diet must be very controlled to restrict salt intake and minimise urea production
how does peritoneal dialysis work
patient requires regular treatment, done at home
dialysate contains concs of necessary substances similar to ideal blood concs - these then pass into blood if there is an imbalance - dialysate contains no urea, so conc gradient allows for excretion
dialysate is introduced into abdominal cavity through a catheter, and exchange occurs across abdominal lining (peritoneum)
dialysate must be refreshed to maintain conc gradient
MEDICAL DIAGNOSIS FROM EXCRETORY PRODUCTS - theory of urine sugar tests
- all glucose in filtrate should be reabsorbed in PCT, so no glucose in urine
- if urine contains glucose, something is likley wrong with persons glucose control - this means the cotransporter proteins are too saturated and cannot reabsorb all glucose
- suggests diabetes - poor insulin function
MEDICAL DIAGNOSIS FROM EXCRETORY PRODUCTS - theory of urine ketone tests
e.g. acetone, acetoacetate
- both of these are produced in the metabolism of diabetics
- if ketones are present in urine or blood its suggests diabetes
MEDICAL DIAGNOSIS FROM EXCRETORY PRODUCTS - theory of urine protein tests
- proteins are generally too large to pass through 3 part membrane
- if present suggests high blood pressure or kidney infection or faulty blood filtration mechanism
MEDICAL DIAGNOSIS FROM EXCRETORY PRODUCTS - theory of urine ion tests
- if urine contains nitrate ions NO3- this may indicate a bacterial infection in urinary tract
MEDICAL DIAGNOSIS FROM EXCRETORY PRODUCTS - theory of anabolic steroid tests
- can be used in sports to rabidly build muscle mass as it stimulates protein synthesis
- detected in blood or urine via gas chromatography / mass spec
MEDICAL DIAGNOSIS FROM EXCRETORY PRODUCTS - theory of pregnancy tests
- pregnancy tests contain monoclonal antibodies specific to hCG - a hormone produced by pregnant people, prevents uterus lining from shedding, therefore being excreted in their urine
- this hormone is secreted by early embryo after it has implanted in the uterus
- antibodies in testing sticks all originate from a clone of B-cells that produce an antibody specific to hCG
- minimal chance of false positives
- control line where excess mobile monoclonal antibodies will attach shows if test is working
- those lines appear because of high concentration of monoclonal antibodies with dye attached, allows dye to be seen
what does a GFR < 60 mean
chronic kidney disease
what does a GFR < 15 mean
kidney failure
how can GFR be estimated
using creatinine levels in urine
however this can also be affected by diet, exercise levels, ethnicity, genes, gender
outline the negative feedback cycle that occurs when water content of blood is high
- low blood osmolarity detected by osmoreceptors in hypothalamus
- less signals sent to posterior pituitary
- brain produces less ADH
- less aquaporins inserted into cell surface membrane of cells lining collecting ducts so less permeable to water
- low volume of water reabsorbed
- urine is more dilute
- water content of blood normal
outline the negative feedback cycle that occurs when water content of blood is low
- high blood osmolarity detected by osmoreceptors in hypothalamus
- more signals sent to posterior pituitary
- brain produces more ADH and activates thirst centre
- more aquaporins inserted into cell surface membrane of o cell surface membrane of cells lining collecting ducts so more permeable to water
- high volume of water reabsorbed
- urine is more concentrated
- water content of blood is normal
what are osmoreceptors and how do they work
osmoreceptors are cells which detect changes in water potential of blood, located in hypothalamus
this occurs as chanes in blood water potential cause water to move in and out of cells which causes osmoreceptor cells to burst or shrink
osmolarity definition
solute concentration
so low omsolarity = high water potential
aquaporins definition
water transport protein channels
- not necessary for water to travel across membranes but it increases movement
what does ADH actually do
ADH binds to receptors on cells lining the collecting duct and DCT
this causes vesicles containing aquaporins to travel to the membrane, allowing aquaporins to fuse to membrane
this increases water permeability, also increases urea permeability
kidney dissection
cut kidney in half lengthways
cortex is lighter than medulla
