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A-level Biology > 5.15 - Homeostasis > Flashcards

5.15 - Homeostasis Flashcards

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1
Q

function of the kidney

A
  • Excretion - filter nitrogenous waste out of the blood, especially urea
  • Osmoregulation - help maintain water balance and pH of the blood and hence the tissue fluid
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2
Q

the nephron - Bowman’s capsule

A
  • cup-shaped structure that contains the glomerulus, a tangle of capillaries
  • more blood goes into it than leaves due to ultrafiltration
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3
Q

renal artery

A

carries oxygenated blood to the kidneys

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4
Q

renal vein

A

carries deoxygenated blood that has had urea and excess salt removed away from the kidneys

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5
Q

renal cortex

A
  • the dark outer layer of the kidney
  • where the filtering of the blood takes place
  • has a very dense capillary network carrying blood from the renal artery to the nephrons
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6
Q

renal medulla

A
  • the inner part of the kidney that is lighter in colour
  • contains tubules of the nephrons that form the pyramids of the kidney and the collecting ducts
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7
Q

renal capsule

A

the very outer layer of the kidney for protection

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8
Q

ureter

A

takes urine from the kidneys into the bladder

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9
Q

nephron- proximal convoluted tubule

A
  • found in the cortex of the kidney
  • where most substances needed by the body are reabsorbed back into the blood
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10
Q

nephron - loop of Henle

A
  • in the medulla
  • a long loop of tubule that creates a region with very high solute concentration in the tissue fluid
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11
Q

nephron - Distal convoluted tubule

A
  • in the cortex
  • where the fine tuning of the water balance of the body takes place
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12
Q

nephron - collecting duct

A
  • the urine passes through the collecting duct through the medulla into the pelvis
  • more fine tuning of the water balance takes place
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13
Q

osmoregulation - the action of ADH

A
  • specialised sensory neurones called osmoreceptors in the hypothalamus monitor blood water potential
  • if there is a decrease in water potential, nerve impulses are sent along sensory neurones to the posterior pituitary gland
  • the posterior pituitary gland excretes ADH into the blood
  • ADH binds to receptors on the plasma membrane of the collecting ducts
  • causes aquaporins to move from the cytoplasm to protein receptors
  • the proteins receptors open, making the membranes more permeable to water
  • water is reabsorbed into the collecting ducts from the urine
  • the urine volume becomes less and it is more concentrated as more water is reabsorbed by the blood
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14
Q

nephron -ultrafiltration

A
  • the blood enters the glomerulus through the afferent arteriole with a wider diameter
  • the blood exits the glomerulus through an efferent arteriole with a smaller diameter
  • creates hydrostatic pressure in the glomerulus which forces the blood through the capillary wall
  • podocytes in the walls of the bowman’s capsule act as an additional filter
    -the filtrate that enters the capsule contains plasma and micromolecules such as salt, glucose and urea.
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15
Q

nephron - selective reabsorption in the PCT

A
  • reabsorption of essential substances
  • The basal membranes (of the proximal convoluted tubule epithelial cells) are the sections of the cell membrane that are closest to the blood capillaries
  • Sodium-potassium pumps in these basal membranes move sodium ions out of the epithelial cells and into the blood, where they are carried away
  • This lowers the concentration of sodium ions inside the epithelial cells, causing sodium ions in the filtrate to diffuse down their concentration gradient through the luminal membranes (of the epithelial cells)
  • These sodium ions do not diffuse freely through the luminal membranes, they must pass through co-transporter proteins in the membrane
  • There are several types of these co-transporter proteins – each type transports a sodium ion and another solute from the filtrate (eg. glucose or a particular amino acid)
  • Once inside the epithelial cells these solutes diffuse down their concentration gradients, passing through transport proteins in the basal membranes (of the epithelial cells) into the blood
  • All glucose in the glomerular filtrate is reabsorbed into the blood
  • This means no glucose should be present in the urine
  • Amino acids, vitamins and inorganic ions are reabsorbed
  • The movement of all these solutes from the proximal convoluted tubule into the capillaries increases the water potential of the filtrate and decreases the water potential of the blood in the capillaries
  • This creates a steep water potential gradient and causes water to move into the blood by osmosis
  • A significant amount of urea is reabsorbed too
  • The concentration of urea in the filtrate is higher than in the capillaries, causing urea to diffuse from the filtrate back into the blood
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16
Q

nephron - selective reabsorption in the loop of Henle

A
  • the descending loop of Henle in permeable to water so water leaves via osmosis and is reabsorbed back into the blood due to a lower water potential in the surrounding tissue fluid, increasing solute potential in the tubule
  • the ascending loop of Henle is impermeable to water
  • ## active transport of sodium and chlorine ions out of nephron into the tissue fluid, decreasing the water potential outside of the limb (so water can be reabsorbed at descending limb) and increasing it inside the limb
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17
Q

nephron - function of distal convoluted tubule

A
  • reabsorb mineral ions
  • sodium ions in, potassium ions out of tubule and into blood through active transport
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18
Q

the renal pelvis

A

The central chamber where the urine collects before passing down the ureter

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19
Q

examples of positive feedback systems

A
  • the blood clotting cascade, where platelets stick to a damaged blood vessel ad release factors than initiate clotting and attract more platelets
  • oxytocin in childbirth, where the head of the baby pressing against the cervix stimulates oxytocin, which stimulates the uterus to contract, pushing the head of the baby even harder against the cervix which triggers the release of more oxytocin until the baby is born
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20
Q

thermoregulation

A

the maintenance of relatively constant core body temperature to maintain optimum enzyme activity

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21
Q

ectotherms

A
  • animals that use their surroundings to warm their bodies
  • core body temperature is heavily dependent of surroundings
  • include all invertebrates, fish, amphibians and reptiles
  • many ectotherms living in water do not need to thermoregulate due to the high heat capacity of water meaning the temperature of their environment doesn’t change much
  • ectotherms on land need to regulate their temperature as the temperature of the air can change dramatically both between seasons and within a 24-hour period
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22
Q

endotherms

A
  • animals that rely on their metabolic processes to warm up
  • usually maintain a very stable core body temperature regardless of the temperature of the environment
  • have adaptations which enable them to maintain body temperature and to take advantage of warmth from the environment
  • endotherms survive in a wide range of environments
  • as keeping warm and keeping cool are both active processes, the metabolic rate of endotherms is much larger than ectotherms, so they need to consume more food
  • mammals and birds are endotherms
23
Q

temperature regulation in ectotherms - behavioural responses

A

Increase body temperature by:
- basking in the sun, orientating their bodies so maximum surface area is exposed to the sun or stretching out to increase surface area exposed to the sun
- pressing against the warm ground to gain body temperature by conduction
- increasing ectothermic metabolic reactions by contracting muscles or vibrating
Decrease body temperature by:
- sheltering from the sun by seeking shade
- pressing bodies against cool earth, stones, water or mud
- orientating body so minimum surface area is exposed to the sun
- minimise movements to reduce metabolic heat generated

24
Q

temperature regulation in ectotherms - physiological responses to warming

A
  • dark colours tend to absorb more radiation than light colours, so lizards living in colder climates tend to be darker coloured
  • some alter their heart rate to increase or decrease metabolic rate to affect the warming or cooling across body surfaces
25
Q

How endotherms detect temperature changes

A
  • peripheral temperature receptors in the skin detect changes in surface temperature
  • temperature receptors in the hypothalamus detect the temperature of the blood
  • temperature of the skin is much more likely to be affected by external conditions than the hypothalamus
  • combination of the two allows the body to respond to actual changes in blood temperature and pre-empt possible problems that might be caused by changes in the external environment
  • maintains the core body temperature in a dynamic equilibrium within about 1°C of 37°C
26
Q

how endotherms cool down

A
  • vasodilation, the arterioles near the surface of the skin dilate and the vessels that connect arterioles and venules (arteriovenous shunt vessels) constrict. This forced blood through the capillary networks close to the surface of the skin, losing heat to the environment as a result of increased radiation or conduction from pressing against cool surfaces
  • increased sweating, as the sweat evaporates from the surface of the skin heat is lost, cooling the blood below the surface. Animals that do not have sweat glands all over their body may pant, losing heat through evaporation of saliva
  • reducing the insulating effect of hair or feathers, the erector pili muscles (hair erector muscles) relax, so the hair or feathers of an animal lie close to the skin, avoiding trapping an insulating layer of air
27
Q

how endotherms warm up

A
  • vasoconstriction, the arterioles near the surface of the skin contract and the vessels connecting arterioles and venules (arteriovenous shunt vessels) dilate. The warm blood is kept well below the surface to keep vital organs warm and not lose heat to the atmosphere
  • decreased sweating to reduce cooling by evaporation of water from the surface of the skin
  • raising the body hair or feathers by contracting the erector pili muscles in the skin traps an insulating layer of air and so reduces cooling through the skin
  • shivering, where the large voluntary muscles of the body involuntarily and rapidly contract and relax. The metabolic heat from the exothermic reactions warm up the body
28
Q

adaptations of endotherms that live in hot climates

A
  • relatively large surface area to volume ratio to maximise cooling e.g. wrinkly skin or large ears
  • pale fur or feathers to reflect radiation
29
Q

adaptations of exotherms that live in cold climates

A
  • relatively small surface area to volume ratio to reduce cooling e.g. small ears
  • a thick layer of insulating fat underneath the skin e.g. blubber in whales and seals
  • hibernation (building up fat stores, build a well insulated shelter and lowering metabolic rate to pass most of the winter in a deep sleep-like state)
30
Q

how are polar bears adapted to live in a cold climate

A
  • small ears to reduce SA:V
  • fur on their feet to insulate them from the ice
  • hollow hairs to trap a permanent layer of insulating air
  • black skin to absorb more radiation
  • thick layer of fat underneath the skin
31
Q

controlling thermoregulation in endotherms

A
  • the heat loss centre, activated when the temperature of the blood flowing through the hypothalamus increases. Sends impulses through autonomic motor neurones to effectors in the skin and muscles, triggering responses that act to lower the core body temperature
  • the heat gain centre, where the temperature of the blood flowing through the hypothalamus decreases. Sends impulses through the autonomic nervous system to effectors in the skin and the muscles, triggering responses to raise the core body temperature
32
Q

main metabolic waste products in mammals

A
  • carbon dioxide, one of the waste products of respiration, excreted from the lungs
  • bile pigments, formed from the breakdown of haemoglobin from old red blood cells in the liver. Excreted in the bile duct from the liver and into the small intestine via the gall bladder and bile duct. Colours the faeces
  • nitrogenous waste products (urea), formed from the breakdown of excess amino acids by the liver. Excreted by the kidneys in the urine
33
Q

external structure of the liver

A
  • receives oxygenated blood from the heart via the hepatic artery
  • receives deoxygenated blood from the digestive system via the hepatic portal vein. This allows the liver to absorb and metabolise many of the nutrients that are absorbed into the blood in the small intestine
  • deoxygenated blood then leaves the liver in the hepatic vein and flows back to the heart
  • The liver is also connected directly to the gall bladder, where the bile is drained into from the bile ductules in the liver, which is then released into the duodenum via the bile duct
34
Q

internal structure of the liver

A
  • mainly made out of hepatocyte cells which have large nuclei, prominent Golgi apparatus and lots of mitochondria (as are metabolically active)
  • the blood from the hepatic artery and hepatic portal vein mix in spaces called sinusoids which are surrounded by hepatocytes
  • increases oxygen content of blood from the hepatic portal vein so the hepatocytes have enough oxygen for their needs
  • sinusoids contain Kupffer cells, which act as the resident macrophages of the liver, ingesting foreign particles and helping to protect against disease
  • the hepatocytes secrete bile from the breakdown of blood into spaces called canaliculi
  • the bile then drains into the bile ductules, which takes it into the gall bladder
35
Q

functions of the liver

A
  • carbohydrate metabolism
  • deamination of excess amino acids
  • detoxification
36
Q

carbohydrate metabolism in the liver

A
  • hepatocytes are closely involved in the homeostatic control of glucose concentration in the blood
  • when blood glucose levels rise, insulin levels rise which stimulates the hepatocytes to convert glucose to the storage carbohydrate glycogen
  • when blood glucose levels fall, the hepatocytes are stimulated by the hormone glucagon to convert glycogen back into glucose
37
Q

deamination of excess amino acids in the liver

A
  • hepatocytes synthesise most of the plasma proteins and also convert amino acids into other amino acids (transamination) which is important because the diet does not always include the required balance of amino acids
  • deamination = the removal of an amine group from a molecule
  • the body cannot store proteins or amino acids, so the hepatocytes deaminate the amino acids and convert the amine group into ammonia which is very toxic and then to urea
  • the remainder of the amino acid can then be fed into cellular respiration or converted into lipids for storage
  • urea is excreted by the kidneys
38
Q

detoxification in the liver

A
  • the liver is the site where most toxic substances that are either produced by metabolic pathways or taken in (e.g. alcohol) are detoxified and made harmless
  • the liver breaks down hydrogen peroxide, which is a by-product of various metabolic pathways. Hepatocytes contain the enzyme catalase that splits hydrogen peroxide into oxygen and water
  • the liver also breaks down ethanol. Hepatocytes contain the enzyme alcohol dehydrogenase that converts ethanol into ethanal, which is then converted to ethanoate which may be used to build up fatty acids or used in cellular respiration
39
Q

osmoregulation when there is an excess of water

A
  • when large amounts of liquid are taken in, the blood becomes more dilute and the water potential becomes less negative
  • the change is detected by osmoreceptors in the hypothalamus
  • nerve impulses to the posterior pituitary are reduced or stopped
  • 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
  • the concentration of the blood is maintained an large amounts of dilute urine is produced
40
Q

urine and pregnancy testing

A
  • the human embryo implants in the uterus around 6 days after conception
  • the site of the developing placenta begins to produce a chemical called human chorionic gonadotrophin (hCG)
  • some of this hormone is found in the blood and the urine of the mother
  • until the 1960s, the most readily available pregnancy test was injecting the urine of a pregnant woman into an African clawed toad
  • if the woman was pregnant, the hCG triggered egg production in the toad within 8-12 hours of the injection
  • now modern pregnancy tests test for hCG in the urine using monoclonal antibodies
41
Q

making monoclonal antibodies for a pregnancy test

A
  • monoclonal antibodies are antibodies from a single clone of cells that are produced to target particular cells or chemicals in the body
  • a mouse is injected with hCG so it makes the appropriate antibody
  • B-cells that make the required antibody are removed from the spleen of the mouse and fused with a myeloma (a type of cancer cell which divides rapidly), resulting in a clone of millions of ‘living factories’ that make the desired antibody
  • the antibodies are collected and purified to be used in pregnancy tests
42
Q

main stages in a pregnancy test

A
  • the wick is soaked in the first urine passed in the morning, which will have the highest levels of hCG
  • the test contains mobile monoclonal antibodies that have very small coloured beads attached to them
  • the antibodies will only bind to hCG
  • if the woman is pregnant, the hCG in her urine binds to the mobile monoclonal antibodies and forms a hCG/antibody complex with coloured beads
  • the urine carries along the test structure until it reaches a window
  • in the window there are immobilised monoclonal antibodies arranged in a line or a pattern such as a plus sign that only bind to the hCG/antibody complex
  • if the woman is pregnant, a coloured line or pattern appears in the first window
  • the urine continues up through the test to the second window
  • in the second window there is usually a line of immobilised antibodies that bind to the mobile antibodies regardless of whether they have bound to hCG or not
  • the coloured line is formed regardless of whether the woman is pregnant or not because it just indicates if the test is working
43
Q

urine testing and anabolic steroids

A
  • athletes and body builders may try to cheat in competitions by using anabolic steroid, which mimic the action of testosterone and stimulate the growth of muscles
  • they are excreted by the urine
  • by testing the urine using gas chromatography and mass spectrometry, scientists can determine whether an individual has been using these drugs, which are banned in all sports
  • the urine sample is vapourised with a known solvent and passed along a tube
  • the lining of the tube absorbs the gases and is analysed to give a chromatogram that can be read to show the presence of drugs
44
Q

urine and drug testing

A
  • urine is tested for the presence of many different drugs because drugs or metabolites are filtered through the kidneys and stored in the bladder so it is possible to find drug traces in the urine some time after a drug has been used
  • if someone is suspected of having taken an illegal drug, they may be asked to provide a urine sample
  • this sample will be divided into two
  • the first sample will be tested by an immunoassay using monoclonal antibodies to bind to the drug or its breakdown product
  • if this shows positive, the second sample may be run through a gas chromatograph/mass spectrometer to confirm the presence of a drug
  • ethanol/alcohol persists in the urine for 6-24hrs, amphetamines persist form 1-3 days, cocaine persists for 2-5 days, cannabis persists for 22hrs-30 days depending on use
45
Q

causes of kidney failure

A
  • kidney infections, where the structure of podocytes and the tubules themselves may be damaged or destroyed
  • raised blood pressure that can damage the structure of the epithelial cells and basement membrane of the Bowman’s capsule
  • genetic conditions such as polycystic kidney disease where the healthy kidney tissue is replaced by fluid-filled cysts or damaged by pressure from cysts
46
Q

signs of infected kidneys or kidneys affected by high blood pressure

A
  • protein in the urine, if the basement membrane or podocytes of the Bowman’s capsule is damaged, they no longer act as filters and the large plasma proteins can pass into the filtrate and out through the urine
  • blood in the urine, showing that the filtering process is not working properly
47
Q

effects of kidney failure

A

Concentrations of urea and mineral ions build up in the body causing:
- loss of electrolyte balance as the body cannot excrete excess sodium, potassium and chlorine ions, causing osmotic imbalance in the tissues and eventual death
- build up of toxic urea in the blood which can poison the cells
- high blood pressure which can cause a range of problems such as heart problems and strokes
- weakened bones as the calcium/phosphorous balance in the blood is lost
- pain and stiffness in joints as abnormal proteins build up in the body
- anaemia, as the kidneys are involved in the production of a hormone that stimulates the formation of red blood cells. When kidneys fail it can reduce the production of red blood cells, causing tiredness and lethargy

48
Q

measuring glomerular filtration rate

A
  • GFR is widely used as a measure to indicate kidney disease as kidney problems almost always affect the rate at which blood is filtered in the Bowman’s capsule
  • rate of filtration is not measured directly
  • a blood test measures the amount of creatinine in the blood
  • creatinine is a breakdown product of muscles as is used to give an estimated glomerular filtration rate (eGFR, cm³/min)
  • if the levels of creatinine in the blood go up it is a signal that the kidneys are not working properly
  • certain factors need to be taken into account such as GFR decreases steadily with age and men usually have more creatinine than women because they usually have more muscle mass
49
Q

haemodialysis

A
  • involves the use of a dialysis machine
  • usually carried out in hospital
  • blood leaves the patient’s body from an artery and flows into the dialysis machine where it flows between partially permeable dialysis membranes
  • these membranes mimic the basement membranes of the Bowman’s capsule
  • the dialysis fluid on the other side of the membranes contains the normal plasma levels of glucose to ensure there is o net movement of glucose out of the blood and normal levels of mineral ions so any excess mineral ions in the blood move out by diffusion, restoring the correct electrolyte balance of the blood
  • the dialysis fluid contains no urea so there is a very steep concentration gradient and much of the urea leaves the blood
  • the blood and dialysis fluid move in opposite directions to maintain a countercurrent system that maximises the exchange taking place
50
Q

peritoneal dialysis

A
  • performed inside of the body
  • makes use of the natural dialysis membranes formed by the peritoneum (lining of the abdomen)
  • usually done at home and the patient can carry on their normal life while it takes place
  • dialysis is introduced into the abdomen using a catheter
  • left for several hours for dialysis to take place across the peritoneal membranes
  • urea and excess mineral ions pass out the blood capillaries, into the tissue fluid and across the peritoneal membrane into the dialysis fluid
  • the fluid is drained off and discarded, leaving the blood contents balanced
51
Q

negatives of haemodialysis

A
  • takes about eight hours and has to be repeated regularly
  • patients with kidney failure have to be attached to a dialysis machine several times a week for many hours
  • they need to manage their diets carefully, eating relatively little protein and salt and monitoring their fluid intake to keep their blood chemistry as stable as possible between dialysis treatments
52
Q

treating kidney failure by transplant

A
  • long term dialysis has serious side effects, so the best solution for a patient is a kidney transplant
  • a single healthy kidney from a donor is placed within the body, the blood vessels are joined and the ureter of the new kidney is inserted into the bladder
  • if the transplant is successful, the kidney will function normally for many years
53
Q

problems with treating kidney failure by transplant

A
  • the risk of rejection
  • the antigens of the donor organ differ from the antigens on the cells of the recipient and the immune system is likely to recognise this
  • this can result in rejection and the destruction of the new kidney
  • immunosuppressants given to reduce the risk of rejection prevent the patients from responding effectively to infectious diseases
  • transplanted organs don’t last forever, the average transplanted kidney lasts around 10 years. Once the organ starts to fail, the patient has to return to dialysis and wait for another suitable kidney is found
54
Q

ways of reducing the risk of rejection of a transplanted kidney

A
  • match between the antigens of the donor and the recipient is made as close as possible (a ‘tissue type’ very similar)
  • the recipient is given drugs to suppress their immune response (immunosuppressant drugs) for the rest of their lives, which helps to prevent rejection

A-level Biology (24 decks)

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