excretion Flashcards
define excretion
is the removal of metabolic waste from the body ,this means the removal from the body of the unwanted products of cell metabolism
what products must be excreted
- carbon dioxide from
- nitrogen containing compounds such as urea
- other compounds such as bile pigments found in faeces
name the excretory organs
- lungs
- liver
- the skin
- kidneys
describe the lungs as an excretory organs
every living cell in the body produces carbon dioxide as a result of respiration, carbon dioxide is passed from the cells of respiring tissues into the bloodstream, where it is transported to the lungs . in the lungs the carbon dioxide diffuse into the alveoli to be excreted as you breathe out
describe the kidneys as an excretory organ
the urea is passed into the bloodstream to be transported to the kidneys. urea is transported in solution - dissolved in the plasma. in the kidneys the urea is removed from the blood to become a part of the urine. urine is stored in the bladder before being excreted from the body via the urethra
describe the liver as a excretory organ
the liver directly involved in excretion . it has many metabolic roles and some of the substances produced will be passed into the bile for excretion with the faeces , for example the pigment bilirubin
the liver is also involved in converting excess amino acids to urea. amino acids are broken by the process of deaminatiom . the nitrogen containing part of the molecule is then combined with carbon dioxide to mla eurea
describe the skin as an excretory organ
the skin is also involved in excretion , but excretion is not the primary function of the skin. sweat contains a range of substances including salts, urea, water, uric acid and ammonia. urea, uric acid and ammonia are all excretory products. the loss of water and salts may be important part of homeostasis - maintaining the body temperature and the water potential of the blood
describe the importance of excretion
allowing the products of metabolism to build up could be fatal, some metabolic products such as carbon dioxide and ammonia are toxic. they interfere with cell processes by altering the PH , so that normal metabolism is prevented. other metabolic products may act as inhibitors and reduce the activity of essential enzymes .
the aorta splits into this so carries oxygen to the liver
hepatic artery
this comes from the digestive system so bring glucose to the liver
hepatic portal vein `
takes blood away from the liver to join the vena cava
hepatic vein
carries bile from the liver to the gall bladder
bile duct
what is the liver divided into and then what is it further divided into
lobes
lobules
what is the hepatic artery and hepatioc portal #vein split into
interlobular vessels
what are the special chambers in the liver called
sinusoid
what goes on to from the hepatic veins
intralobular vessels
what are the liver cells with many microvilli
hepatocytes
what are the specialised macrophages called in the liver
kupffer cells
what does heamoglobin break down form in the liver
bilirubin
where is the bile released into initially prior to the bile duct
bile canaliculi
where is bile stored
gall bladder
what are the two sources of blood suppiled to the liver
the hepatic artery
the hepatic portal vein
describe the hepatic artery
oxygenated blood from the heart travels from the aorta via the hepatic artery to the liver . this supplied the oxygen that is essential for aerobic respiration
describe the hepatic portal vein
deoxygenated blood from the digestive system enters the liver via the hepatic portal vein . the blood is rich in the products of digestion . the blood may also contain toxic compounds that have been absorbed from the intestines
what are the functions of the liver
- control of blood , glucose levels, amino acids, lipid levels
- synthesis of bile, plasma proteins , cholesterol
- synthesis of red blood cells in the fetus
- storage of vitamins A, B, B12, iron and glucose
- detoxification of alcohol and drugs
- breakdown of hormones
- destruction of red blood cells
describe detoxification
toxins need to be rendered harmless by oxidation , reduction , methylation or by combination with another molecule
describe catalase
converts hygrogen peroxide to oxygen and water . catalase has a particularly high turnover number of five million
describe cytochrome p4500
which is a group of enzymes used to break down drugs including cocaine . the cytochromes are also use din other metabolic reactions such as electron transport during respiration . their role in metabolising drugs can interfere with other metabolic roles and causes the unwanted side effects of some medicinal drugs
what are the two types of enzymes involved in detoxification
catalase
cytochrome p4500
alcohol or ethanol is a drug that …..
alcohol or ethanol is a drug that depresses nerve activity . in addition alcohol contains chemical potential energy which can be used for respiration
describe detoxification of alcohol
alcohol is broken own in the hepatocytes by the action of the enzyme ethanol dehydrogenase . the resulting compound is ethanal . this is dehydrogenated further by the enzyme ethanal dehydrogenase . the final compound produced is ethanoate . this joins with co-enzyme A to form acetyl co-enzyme A , which enters the process of aerobic respiration . the hydrogen atoms release from alcohol are combined with another co-enzyme called NAD, to form reduced NAD
NAD is also required to oxidise and breakdown fatty acids for use in respiration.
what happens if the liver has to detoxify too much alcohol
it uses up its store of NAD and has insufficient left to deal with the fatty acids . these fatty acids are then converted back to lipids and stored as fat in the hepatocytes , causing the liver to become enlarged. this is a condition known as fatty liver which can lead to alcohol related hepatitis or to cirrhosis
describe the formation of urea
everyday we need 40-60g of protein . however most people in developed countries eat far more than this. excess amino acids cannot be stored, because the amino group make them toxic. however the amino acid molecule contains a lot of energy so it would be wasteful to excrete the whole molecule . therefore excess amino acids undergo treatment in the liver to remove and excrete the amino component . this treatment consists of two processes , deamination and ornithine cycle
describe deamination
the process of deamination removes the amino group and produces ammonia. ammonia is very soluble and highly toxic . therefore ammonia must not be allowed to accumulate . deamination also produces an organic compound , a keto acid, which can enter respiration directly to release its energy
describe the ornithine cycle an it stages
forms urea
the ammonia and carbon dioxide combine with the amino acid ornithine produce citrulline . this is converted to arginine by addition of further ammonia. the arginine is then reconverted to ornithine by the removal of urea
why does ammonia have to be converted
because its soluble and toxic so needs to be converted to a less toxic from very quickly
what is the equation for the orthinine cycle
ammonia + carbon dioxide = urea + water
why is it better to have urea instead of ammonia
urea is both less soulble and toxic than ammonia . it can be passed back into the blood and transported around the body to the kidneys. in the kidneys the urea is filtered out of the blood and concentrated in urine , urine can be stored safely in the bladder until it is released
define nephron
the functional unit of the kidney
define ultrafiltration
filtration of the blood at a molecular level under pressure
where is the kidney positioned
on each side of the spine , just below the lowest rib
each kidney is supplied with blood from the ………..
and is drained from the ……
renal artery
renal vein
in a longitude section of the kidney , what are the three regions it consists of
- the outer region is called the cortex
- the inner region is called the medulla
- the center is the pelvis, which leads into the ureter
the bulk of each kidney consists of tiny tubules called
nephrons
each nephron starts in the ……..
at a cup shaped structure called the …….
the remainder of the nephron is coiled tubule that passes through the ……
to form a loop down into the …..
and back into ……
before joining a …..
cortex bowman's capsule cortex medulla the cortex collecting duct that passes back down into the medulla
the renal artery splits to from many ….
which each lead to a ….
afferent arterioles
a knot of capillaries called the glomerulus
each glomerulus is surrounded by the
bowmans capsule
the filter is the barrier between the blood in the capillaries and the lumen of the bowman’s capsule. this barrier consists of three layers, which are adapted to ultrafiltration , what are these
- the endothelium of the capillary
- the basement membrane
- the epithelial cells of the bowman’s capsule
describe the endothelium of the capillary
there are now narrow gaps between the cells of the endothelium of the capillary wall. the cells of the endothelium also contain pores, called fenestrations . the gaps allow blood plasma and the substances dissolved in to pass out of the capillary
describe the basement membrane
this membrane consists of a fine mesh of collagen fibres and glycoproteins . this mesh acts as a filter to prevent the passage of molecules with a relative molecular mass of greater than 69000. this mean that most proteins are held in the capillaries of the glomerulus
describe the epithelial cells in the bowmans capsule
these cells, called podocytes have a specialized shape , they have many finger like projections , called major processes . on each major process are minor processes or foot processes that hold the cells away from the endothelium of the capillary . these projections ensure that there are gaps between the cells. fluid from the blood in the glomerulus can pass between these cells into the lumen of the bowmans capsule
the bowmans capsule leads into the rest of the tubule, which has three parts
- proximal convoluted tubule
-loop of henle
distal convoluted tubule
describe ultrafiltration
- is the filtering of blood at the molecular level. blood flow into the glomerulus through the afferent arteriole , which is wider than the efferent arteriole that carries blood away from the glomerulus
- the difference in diameters ensures that the blood in the capillaries of the glomerulus maintains a pressure higher than the pressure in the bowman’s capsule . this pressure difference tends to push fluid from the blood into the bowmans capsule that surrounds the glomerulus
the blood plasma contains what substances
- water
- amino acids
- glucose
- urea
- inorganic mineral ions
what is the functions of the nephrons
as the fluid from the bowmans capsule passes along the nephron tubule, its composition is altered by selective reabsorption , substances are absorbed back into the tissue fluid and blood capillaries surrounding the nephron
- in proximal convoluted tubule, the fluid is altered by the reabsorption of all the sugars , most mineral ions and some water
- in the descending limb of the loop of henle, the water potential of the fluid is decreased by the addition of mineral ions and the removal of water
- in the ascending limb of the loop of henle , the water potential is increased as minerals ions are removed by active transport
- in the collecting duct , the water potential is decreased again by the removal of water. the final product In the collecting duct is urine
describe selective reabsorption
reabsorption involves active transport and cotransport . the cells lining the proximal convoluted tubule are specialised to achieve this reabsorption
- the cell surface membrane is contact with the tubule fluid is highly folded to form microvilli . the microvilli increases the surface area for reabsorption
- the cell surface membrane also contains special cotransporter proteins that transports glucose or amino acids, in association with sodium ions, from the tubule into the cell
- the opposite membrane of the cell, close to the tissue fluid and blood capillaries , is also folded to increase its surface area. this membrane contains sodium/ potassium pumps that pump sodium ions out of the cell and potassium ions into the cell
- the cell cytoplasm has many mitochondria , this indicates that an active, or energy requiring , process is involved, because many mitochondria will produce a lot of ATP
describe the mechanism of selective reabsorption
1- sodium ions are actively pumped out of the cells lining the tubule
2-concentrations of sodium ions in cell cytoplasm decreases , creating a concentration gradient
3-sodium ions diffuse into the cell through a cotransport protein, carrying glucose or an amino acid at the same time
4- water moved into the cell by osmosis
5- glucose / amino acids diffuse into the blood
describe the reabsorption of water
each minute about 125 cm3 of fluid is filtered from the blood and enters the nephrons . after selective reabsorption in the proximal convoluted tubule, about 45 cm3 of fluid is left. by the time this fluid reaches the bladder, the volume has dropped to about 1.5 cm3
describe the loop of henle
- diffusion of sodium and chloride ions into the descending limb
- water moves out of descending limb by osmosis and enters capillaries
- sodium and chloride ions diffuse out of the lower part of ascending limb
- active removal of sodium and chloride ions from the ascending limb
- water move out of the collecting ducts by osmosis and enters the capillaries
- urine passes down collecting duct to pelvis
describe the collecting duct
from the top of the ascending limb the tubule fluid passes along a short distal convoluted tubule where active transport is used to adjust the concentrations of various mineral ions. from here the fluid flows into the collecting duct . at this stage the tubule fluid still contains lot of water- it has a high water potential.. the collecting duct carries the fluid back down through the medulla to the pelvis. as the tubule fluid passes down the collecting duct , water moves by osmosis from the tubule fluid into the surrounding tissue. it then enters the blood capillaries by osmosis and is carried away
describe the concentration changes in the tubule fluid
1- glucose decreases in concentration as it is selectively reabsorbed from the proximal tubule
2-sodium ions diffuse into the descending limb of the loop of henle, causing the concentration to rise. they are then pumped out of the ascending limb so the concentrations falls
3- the urea concentration rises as water is withdrawn from the tubule. urea is also actively moved into the tubule
4- sodium ions are removed from the tubule, but their concentrations rise as water is removed from the tubule, and potassium ions increase in concentrations as water is removed . potassium ions are also actively transported into the tubule to be removed in urine
what is an osmoreceptor
a sensory receptor that detects changes in water potential
what is osmoregulation
is the control of the water potential in the body, controls both water and salt levels in the body . the correct water balance between cells and the surrounding fluids must be maintained to prevent water entering cells and causing lysis or leaving cells and causing crenation
these gains or losses of water must be balanced , the kidneys act as an effector to control the water content of the body and the salt concentrations in the body fluid.
describe the mechanism of osmoregulation
the kidneys alter the volume of urine produced by altering the permeability of the collecting ducts , the walls of then collecting ducts can be made more or less permeable according to the needs of the body
1- if you need to conserve less water, (on a cool day or when you have drunk a lot of fluid ) , the walls of the collecting ducts become less permeable . this means that less water is reabsorbed and a greater volume of urine will be produced
2- if you need to conserve more water, ( on a hot day or when you have drunk very little ) , the collecting duct walls are made more permeable so that more water can be absorbed into the blood. you will produce a smaller volume of urine
describe what happens when water potential of the blood is high
- detected by osmoreceptors in hypothalamus
- sends action potentials into vesicles down the neurosecretory cells
- less ADH is released from the posterior pituitary into the blood
- bind to the receptors on the target cells. the collecting duct walls become less permeable
- aquaporins are removed as membrane is folded
- less water reabsorbed into blood and more urine is produced
- decreased water potential in blood
describe what happens when water potential of the blood is low
- osmoreceptor cells lose water by osmosis and shrink as a result they stimulate neurosecretory cells in the hypothalamus
- the neurosecretory cells are specialised neurones that produce and release ADH
- the ADH is produced and manufactured in the cell body which lies in the hypothalamus
- ADH moves down the axon to the terminal bulb In the posterior pituitary gland , where it is stored in vesicles
- when neurosecretory cells are stimulated by osmoreceptors they carry action potentials down their axon and cause the release of ADH by exocytosis
- ADH enters the blood capillaries running through the posterior pituitary gland. it is transported around the body and acts on the cells of the collecting duct ( makes walls more permeable )
- once the water potential of the blood rises again , less ADH is released. ADH is slowly broken down
define ADH
a hormone that control the permeability of the collecting duct walls
what is kidney failure
if the kidney fails to completely they are unable to regulate the levels of water and electrolytes in the body or to remove waste products such as urea from the blood, this will rapidly lead to death
how do you asses kidney failure
-kidney function can be assessed by estimating the glomerular filtration rate (GRF) and by analysing the urine for substances such as protein . proteins in the urine indicate the filtration mechanism has been damaged.
what are the causes of kidney failure
diabetes mellitus ( both type 1+ 2 diabetes ) , heart disease, hypertension , infection
what are the treatments of kidney failure
renal dialysis
kidney transplant
describe renal dialysis
is the most common treatment for kidney failure . waste products , excess fluid and mineral ions are removed from the blood by passing it over a partially permeable dialysis membrane that allows the exchange of substances between the blood and dialysis fluid . the dialysis fluid contains the correct concentrations of mineral ions, urea, water and other substances found in the blood plasma.
any substances in excess in the blood diffuse across the membrane into the dialysis fluid. any substances that are too low in concentrations will diffuse into the blood from the dialysis plasma
what are the two types of renal dialysis
- haemodialysis
- peritoneal dialysis
describe haemodialysis
blood from the artery or vein is passed into a machine that contains an artificial membrane shaped to form many artificial capillaries, which increase the surface area for exchange. heparin in added to avoid clotting. the artificial capillaries are surrounded by dialysis fluid , which flows in the opposite direction to the blood. this improves the efficiency of exchange . any bubbles are removed before the blood is returned to the body via a vein
-haemodialysis is usually performed at a clinic two or three times a week for several hours at each session. some patient learn to carry it out at home
describe peritoneal dialysis
the dialysis membrane is the body’s own abdominal membrane. first a surgeon implants a permanent tube in the abdomen . dialysis solution is poured through the tube and fills spaces between the abdominal wall and organs , after several hours the used solution is drained from the abdomen
- it can be carried out at home or work. because the patient can walk around while having dialysis
- must be combined with a carefully monitored diet
describe kidney transplants
is the best life extending treatment for kidney failure , this involves major surgery . while the patients is under anaesthesia , the surgeon implants the new organ into the lower abdomen and attaches it to the blood supply and the bladder. patients are given immunosuppressant drugs to help prevent their immune system recognising the new organ as a foreign object and rejecting it.
- many patients feel much better immediately after the transport
-
advantages of kidney transplants
- freedom from time consuming renal dialysis
- feeling physically fitter
- improved quality of life , able to travel
- improved self image, no longer have a feeling of being chronically ill
disadvantages of kidney transplant
- need to take immunosuppressant drugs , as more prone to infection
- need for major surgery under general anaesthetics , risk
- need for regular check for signs of rejection
- side effects of immunosuppressant drugs, fluid retention , high blood pressure, susceptibility to infections
describe urine analysis
molecules with a relative molecular mass of less than 69000 can enter the nephron. any metabolic product or other substances in the blood can therefore be passed into the urine if it is small enough. if these substances are not reabsorbed further down the nephron they can be detected in urine
what can urine be tested for
- glucose in the diagnosis of diabetes
- alcohol to determine blood alcohol levels in drivers
- many recreational drugs
- human chorionic gonadotrophin (hCG) in pregnancy testing
- anabolic steroids , to detect improper use in sporting events
describe how pregnancy testing works
1- urine is poured onto the test stick
2- hCG binds to mobile antibodies attached to a blue bead
3-mobile antibodies move down test stick
4-if hCG is present , it binds to fixed antibodies holding bead in place , a blue line forms
5- mobile antibodies with no hCG attached bind to another fixed site to show the test is working
describe anabolic steroids and how you can test for them
anabolic steroids increase protein synthesis within cells, which results in the build up of cell tissue , especially in the muscles. non medical uses for anabolic steroids are controversial , because they can give advantages in competitive sports and they have dangerous side effects
- all major sporting bodies ban the use of anabolic steroids. anabolic steroids have a half life of about 16 hours and remain in the blood for many days . they are relatively small molecules and can enter the nephron easily.
- testing for anabolic steroids involves analysing a urine sample in a laboratory using gas chromatography
what is the glomerulus filtration rate and what is the normal reading
the rate at which fluid enters the nephrons
- in the range of 90-120 cm3 min-1
how is water gained and lost from the body
gained
- food, drink and metabolism
lost
-urine, sweat, water vapour, faeces
