5.3 HOMEOSTASIS Flashcards

Question

What are the advantages of endotherms?

Answer 1

Advantages of endotherms: - can live in colder habitats - core body temp kept constant - can be active at all times of day/year

Answer 2

Disadvantages of endotherms: - huge proportion of energy intake used on temp regulation - less energy from food is used for growth - more food must be eaten per day - may hibernate if food is scarce

Answer 3

Advantages of ecotherms: - less food is needed per day - more energy from food is used for growth - can survive longer without eating - rate of respiration slower

Answer 4

Disadvantages of ectotherms: - less active in cold temperatures - must have sufficient energy stores to survive cold weather - puts them at risk of predation - may need to be inactive and hibernate in cold weather

Answer 5

Introduction to the liver: - largest internal organ in a mammals body -makes up 5% body mass - involved in many metabolic processes - receives oxygenated blood from the hepatic artery (off aorta)(25% blood supply) - receives deoxygenated from the hepatic portal vein (75%)(vein coming from gut)

Answer 6

Hepatocytes (liver cells): - arranged in single rows along the sinusoids - as blood flows through each sinusoid to the central branch of the hepatic vein the hepatocytes add materials to the blood- products manufactured by liver e.g plasma proteins - they also remove materials from blood (oxygen, food substances, toxins e.g alcohol, metabolites) needed by theses cells or produced by other body cells - levels of cholesterol vitamins A and D and iron are absorbed then stored and released from the liver as necessary - the cells are identical and contains numerous mitochondria, lysosomes, glycogen granules and fat droplets - have prominent golgi - cell membrane facing sinusoids has microvilli

Answer 7

Sinusoids: - open channels through which blood flows in direct contact with hepatocytes - are different to normal capillaries in that they are wider and the walls are more porous - blood in sinusoids comes from 2 sources- hepatic portal vein (from small intestine) and hepatic artery - blood flows to central branch of hepatic vein- blood to 'hub' - lined with kupffer cells which move within sinusoid and are involved in defence

Answer 8

Kupffer cells: - move about the sinusoid and are part of the body's defence mechanism - they are phagocytes (macrophages) and ingest matter and are responsible for breakdown of hb in rbc producing bile pigments (billirubin/billiverdin)

Answer 9

Bile canaliculi: - also found in lobules - each canaliculus is a blind-ended tube between two rows of liver cells - hepatocytes secrete bile into the canaliculi - canaliculi merge to form bile ducts in which bile is drained from the liver - movement is in opposite direction to the flow of blood in sinusoids i.e away from centre

Answer 10

Functions of the liver: - disposes of worn out rbc (reusing them in masking bile) - involved in carbohydrate metabolism and regulates blood sugar levels - removes excess amino acids in the blood, breaking them down into ammonia then urea - controls the level of fats in the blood by making cholesterol - helps the body to destroy poisons such as alcohol, and to get rid of other unwanted substances e.g hormones - makes and regulates many hormones, including sex hormones

Answer 11

To help with the regulation of blood sugar, the liver can store 100g of glycogen. Insulin stimulates hepatocytes to convert glucose to glycogen. Glucagon stimulates hepatocytes to convert glycogen to glucose.

Answer 12

Urea is formed as the human body is unable to store excess dietary protein and hepatocytes firstly deanimate the amino acids = the amino group is removed and ammonia is formed. Ammonia is then converted to urea as it is toxic and excreted via the kidneys. The rest of the amino acid (keto acids) are either converted to lipids and cholesterol or enter the krebs cycle.

Answer 13

Ornithine cycle: - because ammonia is so toxic and soluble it cannot remain in the body and must be converted to a less toxic substance - the ornithine cycle is the metabolic pathway which combines ammonia with co2 to form urea (CO(NH2)2) - uses ATP

Answer 14

Detoxification occurs in the SER of hepatocytes.

Answer 15

Broken down: hydrogen peroxide - produced by many metabolic reactions, broken down by catalase alcohol - toxic, small molecule and lipid soluble so can cross phospholipid bilayer easily hormones - removed so effects do not continue but not toxic e.g thyroxine, oestrogen and testosterone medicines - e,.g paracetamol and antibiotics

Answer 16

Detoxification of alcohol: - ethanol converted first to ethanal by ethanol dehydrogenase - ethanal then converted to ethanoate by ethanal dehydrogenase - ethanoate combines with COA (to form acetylCOA) and can then enter the krebs cycle in the mitochondria and be used to produce ATP or can be used to build up fatty acids

Answer 17

Fatty liver: - when a lot of alcohol is drunk then a lot of oxidised NAD is used during the detoxification process - oxidised NAD is also needed to oxidise fatty acids in the hepatocytes - the fatty acids are therefore deposited in the liver cells which reduces their ability to function effectively

Answer 18

Cirrhosis: - alcohol damages the hepatocytes and damaged cells are replaced by fibrous tissue and the structure of the blood supply is lost such that blood does not enter the sinusoids and is not 'processed' by liver cells - the combined effects of fatty liver and damage to hepatocytes results in cirrhosis - a person with liver cirrhosis cannot convert ammonia to urea as well which can result in damage to the nervous system and occasionally a coma

Answer 19

The renal artery brings blood containing urea and other substances in solution to the kidney

Answer 20

The renal vein carries blood away from the kidney, after urea and other substances have been removed from the blood by the kidney

Answer 21

The ureter is a tube through which urine passes from the kidney to the bladder

Answer 22

The urethra is the tube through which urine passes to the outside of the body

Answer 23

Role of the kidney: - two important homeostatic roles in the body - filtering nitrogenous waste products out of the blood (especially urea) - maintenance of water balance and pH of the blood

Answer 24

Kidney structure: capsule - thin membranus sheath that covers the outer surface of each kidney. protects the vital tissue from injury pelvis - the central chamber where urine collects before passing out down the ureter cortex - darker, outer layer where the filtering of the blood takes place. has a very dense network of capillaries carrying blood from the renal artery to the nephrons medulla - lighter in colour, contains the tubules of the nephrons that form the pyramids of the kidney and collecting ducts

Answer 25

The nephron: - nephrons are the functional units of the kidneys - each nephron is 3cm long - 1.5 million nephrons in each kidney - blood is filtered in the nephrons and the majority of filtered material is returned to the blood removing nitrogenous waste and balancing mineral ions and water

Answer 26

Function of the nephron: - ultrafiltration - absorption - osmoregulation - excretion

Answer 27

Ultrafiltration is the process of filtering blood plasma through the Bowmans capsule under pressure

Answer 28

Ultrafiltration works: - the difference in diameter between the afferent and efferent arterioles ensures high pressure in the glomerulus so substances are pushed out of the plasma into the nephron - water, amino acids, glucose, urea and inorganic ions form the glomerular filtrate - anything with a molecular mass >69000 is not able to filter out (e.g proteins and blood cells)- this allows blood to maintain a lower water potential for the process of water reabsorption that happens later

Answer 29

Rate of filtration: - water potential affects the rate of filtration, but it is affected by highs and solute concentration - overall, the effect of pressure outweighs the effect of solute conc, so the movement is from the glomerulus into the Bowman's capsule

Answer 30

Structure of Bowman's capsule: capillary endothelium - very thin - perforated with thousands of pores about 10nm in diameter - provides a barrier to cells but not plasma membranes basement membrane - meshwork of collagen and glycoprotein fibres - water and small molecules can pass through - proteins are too large and are repelled by negative charges on fibres podocytes - epithelial cells that make up the lining of the Bowmans capsule - also have extensions called pedicels that wrap around the capillaries, forming slits that ensure that any larger substances such as blood cells, platelets or proteins that may have made it through in the capsule lumen

Answer 31

False colour SEM micrograph: - podocytes are the blue cells - capillaries of the glomerulus are purple

Answer 32

Convoluted tubules: proximal convoluted tubule - lots of infoldings - lots of microvilli - lots of mitochondria - active reabsorption of solutes distal convoluted tubule - columnar epithelium - no infoldings - few mitochondria - some ion transport and water reabsorption

Answer 33

Reabsorption happens in the proximated convoluted tubule, reabsorption of ions, water and valuable nutrients such as glucose and amino acids 1. Na+ actively transported out into the blood by Na+/K+ pump , this requires ATP 2. Na+ levels inside the epithelial cell falls 3. Na+ is then able to diffuse into the cell from the lumen of the proximal convoluted tubule through a co-transport protein bringing glucose and amino acids with it 4. glucose, amino acids and Na+ diffuse into the blood from cells 5. water moves down the wp gradients and Cl- ions move down their electrochemical gradient into the blood 6. blood plasma rapidly removes glucose, amino acids, water, Na and Cl ions along to allow further uptake

Answer 34

Success of reabsorption: - 80% of glomerular filtrate is reabsorbed at this stage - most urea is also reabsorbed here as it is small and has moved down its conc gradient - by the end of the proximal tubule, glomerular filtrate is isotonic to tissue fluid and blood

Answer 35

Diabetes and glucose: - normally, all glucose is reabsorbed in selective reabsorption - however, if there is too much glucose then there will not be enough co-transporter proteins - if there is still glucose left in urine - suggestive of diabates

Answer 36

Water reabsorption - loop of Henle: - the loop of Henle is able to create a very high concentration or salts in the tissue fluid, so water can be reabsorbed from the loop and collecting duct. this allows urine to be more concentrated than blood - descending loop → permeable to water and ions - ascending loop → permeable to sodium ions

Answer 37

descending loop: - water enters the descending limb from the proximal convoluted tubules - upper part or descending loop is impermeable to water - lower part or descending loop is permeable to water - not permeable to Na or Cl ions - water moves out of limb by osmosis down water potential gradient into tissue fluid (due to an increasingly concentrated medulla tissue fluid) then into blood capillaries

Answer 38

ascending loop of Henle: - impermeable to water - first (thin) section allows Na and Cl ions to diffuse out - second (thick) section actively pumps out ions - this increases the number of ions in the tissue fluid. therefore, lowering the water potential

Answer 39

Water reabsorption results: - having two limbs working in the opposite direction, enables a maximum concentration to build up outside the loop-this is called the counter current multiplier

Answer 40

distal convoluted tubule: - permeability or the walls varies depending on the levels of ADH - if the body lacks salt, Na+ actively pumped out or tubule and Cl- follows - water can also leave depending on ADH levels

Answer 41

Collecting duct: - when water reaches the cd, water also leaves due to the high solute conc in the medulla - water moves from the cd by osmosis until the water potential of the urine is equal to the water potential, of the tissue fluid - ADH controls the permeability of the collecting duct walls

Answer 42

Osmoregulation is the balancing and control of the water potential in the blood - kidneys are the main organ responsible for osmoregulation

Answer 43

ADH- Anti Diuretic Hormone: - a homone that increases the permeability of the distal convouted tubule and collecting duct to water -a protein hormone made of 9 amino acids.

Answer 44

ADH release: - osmoreceptor cells in the hypothalamus monitor the water potential in the blood - when water potential falls, osmoreceptor cells trigger neurosecretory cells in hypothalamus - ADH released from nerve endings in the prosteror pituitary gland - ADH released into the blood and travels to the kidneys

Answer 45

ADH action: -low water potential= more ADH released, high water potential= ADH release inhibited 1. ADH acts on cells in the collecting duct and distal convoluted tubule 2. ADH binds to membrane-bound receptors on the plasma membrane - starting a cascade or events 3. binding triggers formation or cyclic AMP (secondary messenger) 4. phosphorylase enzyme is activated 5. vesicles (containing aquaporins in their membrane) fuse with cell surface membrane on the side of the cell in contact with medulla tissue fluid 6. aquaporins make cell membrane more permeable to water - therefore more ADH means more water channels 7. water moves into the medulla through aquaporins and is reabsorbed into capillaries by osmosis.

Answer 46

Affects of ADH : - more ADH • more reabsorption or water into blood • decrease volume of water in urine • more concentrated urine. - less ADH • less reabsorption or water into blood • increased volume or water in urine • more dilute urine

Answer 47

Currently tested for via urine: - diabetes (glucose or ketones will be present) - nephritis (proteins and bloud cells will be present, also more solutes than normal) - bacterial infection (leukocytes will be present) - muscle dumage (creatine will be present) - pregnancy (HCG hormone - drug taking (eg steroids, cannabis)

Answer 48

Pregnancy testing: - modern pregnancy tests test for HCG (human chorionic gonadotrophin hormone) in the urine - they rely on the use of monoclonal antibodies (an antibody produced by a single clone of cells or cell line and consisting or identical antibody molecules)

Answer 49

Production of monoclonal antibodies: 1. a mouse is injected with HCG so it produces the appropriate antibody 2. B-cells that make the antibody are removed from the spleen 3. the antibodies are fused with a mycloma - a type of cancer cell which divides very rapidly 4. new fused cell is known as a hybridoma s. each hybidama reproduces rapidly 6. monoclonal antibodies are collected - complementary to HCG

Answer 50

If pregnant: • monoclonal antibodies with small coloured beads attached • immobilised monoclonal antibodies bind to form HCG-antibody complex so coloured line shows - binds to just antibody (doesn’t require HCG) so gets a coloured line

Answer 51

If not pregnant: • no hcG to bind • no hcG so cannot bind • binds to just antibody (doesn't require HCG) so gets a coloured line

Answer 52

Urine testing and anabolic steroids: •anabolic steroids are drugs that mimic the action of testosterone and stimulate the growth of muscles - they are extracted in the urine • urine can be tested using gas chromatography and mass spectrometry • urine sample is vapourised with a known solvent and passed along a tube. the lining of the tube then absorbs the gases and the resulting chromatogram can be analysed

Answer 53

Causes of kidney failure: - kidney infections - the structure of podocytes and tubules themselves may be damaged or destroyed - raised blood pressure - can damage the structure or 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

Answer 54

Effects of kidney failure: - if kidneys are infected or affected by high blood pressure • protein in the urine - if the basement membrane or podocytes of the Bowman's capsule are damaged, they no longer act as filters and large plasma proteins can pass into the filtrate and are passed out in the urine • blood in the urine - another symptom the filtering process is no longer working - if kidneys fail completely, the concentrations or urea and mineral ions build up in the body • loss of electrolyte balance - if the kidneys fail, the body cannot excrete excess sodium, potassium and chloride ions. this causes osmotic imbalances in the tissues and eventual death • build up of toxic urea in the blood- if the kidneys fail, the body cannot get rid of urea and it can poison the cells • high blood pressure-the kidneys play an important role in controlling the blood pressure by maintaining the water balance of the blood. if the kidneys fail, the blood pressure increases and this can cause a range of health issues including heart problems and strokes • weakened bones -the calcium/phosphorus balance in the blood is lost • pain and stiffness in joints - abnormal proteins build up in blood • anaemia - the kidneys are involved in the production ot a hormone called erythropoietin that stimulates the formation of red blood cells causing tiredness and lethargy

Answer 55

Measuring glomerular filtration rate: • kidney problems almost always affect the rate at which blood is filtered in the Bowman's capsule or the nephrons • glomerular filtration rate (GFR) is widely used as a measure to indicate kidney disease • rate or filtration is not measured directly - a simple blood test measures the levels of creatine in the blood • creatine is a breakdown product of muscles and is usel to give an estimate GR (eGER) units in cm3/min • if the levels of creatine in the blood go up, it is a signal that the kidneys are not working properly • certain factors need to be taken into account to in the calculations to work out the GER e.g GER decreases steadily with age even it you are healthy, and men usually have more muscle mass and therefore more creatine than women

Answer 56

Treating kidney failure with dialysis: • normal GERs do not fall below 70 even in very old people • a GER below 60 for more than a 3 months is taken to indicate moderate to severe chronic kidney disease- and if it falls below 15, that is kidney fullure, as the kidneys are filtering so little blood they are basically ineffective - two main ways kidney failure is treated • renal dialysis where the function of the kidnays is carried out artificially • transplant where a new, healthy kidney is put into the body to replace the failed kidneys - two main types of dialysis- haemodialysis and perinatal dialysis

Answer 57

Haemodialysis: • involves the use of a dialysis machine so usually carried out in hospital • blood leaves the patients body from an artery and flows into the dialysis machine, where it flows between partially permeabie dialysis membranes • these membranes mimic the basement of the Bowman's capsule -on the other side of the membranes is the dialysis fluid •during dialysis it is vital that patients lose the excess urea and mineral ions that have built up in the blood • it is equally important they do not lose substances such as glucose and mineral ions •the loss of these substances is prevented by careful control or the dialysis fluid • it contains normal plasma levels of glucose to ensure there is no net movement of glucose out of the blood • the dialysis fluid also contains normal plasma levels or mineral ions, so any excess mineral ion in the blood move out by diffusion down a concentration gradient into fluid, thus restoring the correct electrolyte balance of the blood. • dialysis fluid contains no urea so steep conc gradient between fluid and blood and urea leaves blood • blood and dialysis fluid flow in opposite directions to maintain a countercurrent exchange system and maximise exchange • takes about 8 hours and has to be repeated regularly - several times a week • diets managed carefully - reactively little protein and salt and monitoring fluid intake at beginning or dialysis process can eat what they like.

Answer 58

Perineal dialysis : • done inside the body -makes use of natural dialysis membranes formed by the lining or the abdomen (Perionum). • usually done at home, patient can carry on with normal life • dialysis fluid introduced to abdomen using a catheter • left for several hours for dialysis to take place and across perineal membranes, so urea and excess mineral ions pass out of blood capillaries into tissue fluid and out across mumbrane into dialylis fluid • fluid then drained and discarded

Answer 59

Transplant: - long term dialysis can have side effects, best solution is transplant • single healthy kidney from donor placed within body, blood vessels are joined and the ureter of new kidney is inserted in bladder. • if sucessful, new kidney will function for many years •main problem is risk of rejection - antigens on donated organ differ from antigens on cells of recipient and immune system is likely to recognise - antigen matching (close as possible) - tissue type similar (people from same blood group) - drugs to suppress immune response for rest of life, however prevent patients from responding to infectious disease • transplant organs dont last forever kidney usually last 9-10 years however some have lasted for around 50.

Answer 60

Structure of nephron: . bowman's capsule - cup shaped structure that contains the glomerulus (a tangle of capillaries). more blood goes into the glomerulus than leaves it due to the ultrafiltration processes that take place . proximal convoluted tubule - the first, coiled region of the tubule after the bowman's capsule, found in the cortex of the kidney. this is where many of the substances needed by the body are reabsorbed into the blood . loop of henle - a long loop of tubule that creates a region with a very high solute concentration in the tissue fluid deep in the kidney medulla. the descending loop runs down from the cortex through the medulla to a hairpin bend at the bottom of the loop. the ascending limb travels back up through the medulla to the cortex . distal convoluted tubule - a second twisted tubule where the fine tuning of water balance of the body takes place. the permeability of the walls to water varies in response to the levels of ADH in the blood. further regulation of the ion balance and pH of the blood also takes place in this tubule . collecting duct - the urine passes down the collecting duct through the medulla to the pelvis more fine tuning of the water balance takes place, the walls of this part of the tubule are also sensitive to ADH - the nephron has a network of capillaries around it which finally lead to a venule and then to the renal vein. the blood that leaves the kidney has greatly reduced levels of urea, but the levels of glucose and other substances such as amino acids are needed by the body are almost the same as when the blood entered the kidneys (may be slightly less as some glucose will have been used for selective reabsorption). the mineral ion concentration in the blood has also been restored to ideal levels

Answer 61

Process of ultrafiltration: 1. high hydrostatic pressure in capillaries of glomerulus forces small molecules such as urea, glucose, amino acids, ions and water into the bowman's capsule 2. small molecules forced through pores/gaps/fenestrations in the endothelium of the capillaries in the glomerulus 3. small molecules forced through the basement membrane 4. basement membrane acts as a secondary sieve, blood cells and many proteins are too big to leave so are retained in the capillary due to size 5. podocytes in walls of bowman's capsule act as an additional filter to wrap around capillaries and form slits to ensure any cells, platelets or large plasma proteins do not enter the tubule itself 6. the filtrate that enters the capsule contains glucose, salt, urea and many other substances in the same concentrations of blood plasma

Answer 62

Mechanism of ADH action: 1. ADH binds to receptors on the cells membrane of tubule cells and triggers the formation of cAMP, which causes a cascade of events 2. vesicles in the cells lining of the collecting duct fuse with the cell surface membranes on the side of the cell in contact with the tissue fluid of the medulla 3. the membranes of these vesicles contain protein based water channels (aquaporins) and when they are inserted into the cell surface membrane, they make it permeable to water 4. this provides a route for water to move out of the tubule cells into the tissue fluids of the medulla and the blood capillaries by osmosis 5. the more ADH released the more water channels are inserted into the membranes of the tubule cells. this makes it easy for more water to leave the tubules by diffusion, resulting in the formation of a small amount of very concentrated urine. 6. water is returned to the capillaries, maintaining the water potential of the blood and therefore the tissue fluid of the body 7. when ADH levels fall, the reverse happens. levels of cAMP falls then the water tubules are removed from the tubule cell membranes and enclosed in vesicles again. the collecting duct duct becomes impermeable to water once more, so no water can leave. this results in the production of large amounts of very dilute urine, and maintains the water potential of the blood and the tissue fluid.

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5.3 HOMEOSTASIS Flashcards

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