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A LEVEL BIOLOGY > 5.1.2 Excretion > Flashcards

5.1.2 Excretion Flashcards

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1
Q

What is excretion?

A

-the removal of metabolic waste(i.e CO2, nitrogenous waste) that are toxic if allowed to build up
-excretion maintains homeostasis by helping to keep levels of certain substances in the blood roughly constant

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2
Q

Examples of substances that are excreted

A

-CO2= waste product of respiration that is excreted from the lungs
-bile= from breakdown of haemoglobin from old red blood cells in the liver, excreted from the liver into the small intestine via gall bladder + bile duct(colours the faeces)
-nitrogenous waste= formed from the breakdown of excess amino acids in the liver, excreted by kidneys in urine
-(mammals produce urine, birds produce uric acid + fish produce ammonia)

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3
Q

Structure of the liver: hepatocytes

A

-liver cells(can regenerate by mitosis)
-have large nucleus + golgi
-lots of mitochondria

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4
Q

Structure of the liver: hepatic artery

A

-supplies liver with oxygenated blood from the heart(liver has a good supply of oxygen for hepatocytes’ functions i.e mitosis)

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5
Q

Structure of the liver: hepatic portal vein

A

-brings blood from small intestine to the liver
-carries glucose, amino acids, CO2, ingested substances i.e drugs + alcohol)

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6
Q

Structure of the liver: hepatic vein

A

-carries deoxygenated blood away from the liver to the heart
-delivers excess amino acids which are converted into urea to the kidney

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7
Q

Structure of the liver: Bile duct

A

-carries bile(a substance produced by liver to emulsify lipids and neutralise stomach acids in small intestine) to the gall bladder to be stored

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8
Q

The histology/make up of the liver

A

-made up of liver lobules–} cylindrical structures made up of hepatocytes
-each lobule has a central vein that connects to the hepatic vein

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9
Q

Sinusoids

A

-hepatic artery + portal vein connect to central vein and mix in *capillaries called sinusoids
-act as canals carrying the blood
*single layer of cells that allows substances to diffuse into hepatocytes

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10
Q

Why is it important that blood mixes in sinusoids?

A

-it increases O2 concentration in the blood from the hepatic portal vein–} supplies hepatocytes with sufficient oxygen

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11
Q

Hepatocytes

A

-remove any harmful substances and oxygen from the blood in the sinusoids via diffusion
-substances are broken down by hepatocytes and less harmful substances re-enter the blood
-i.e excess amino acids are broken down into urea by hepatocytes

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12
Q

Central vein

A

-blood travels through sinusoids to central vein
-the central vein from all of the lobules connect up to form hepatic vein

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13
Q

Kupffer cells

A

-within the sinusoids
-act as resident macrophages of the liver–} phagocytosis for pathogens and ingested toxins

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14
Q

Bile canaliculi

A

-hepatocytes secrete bile from the breakdown of blood into this space
-bile can drain into the bile duct from here to be transported to gall bladder

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15
Q

Identifying histology of liver tissue

A

-hepatic portal vein has a larger lumen than the hepatic artery
-hepatic artery has narrow vessels + hepatic portal vein has branched vessels
-bile canaliculi is lined with hepatocytes(sweetcorn)

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16
Q

What are the 3 functions of the liver?

A

-storage of glycogen
-detoxification
-formation of urea

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17
Q

Storage of glycogen

A

-the liver responds to insulin and glucagon to control BGC levels
-when blood glucose levels rise, insulin levels increase —} cause hepatocytes to convert glucose into glycogen via glycogenesis
-glycogen is stored in the hepatocytes until glucose is released for energy
(glycogenolysis)
-amino acids + glycerol can be converted into glucose(gluconeogenesis)

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18
Q

Detoxification

A

-liver breaks down harmful substances like alcohol, drugs, unwanted hormones–} become less harmful compounds that can be excreted
-hydrogen peroxide(by product of metabolic process) is broken down by catalase into O2 + water
-alcohol= broken down by alcohol dehydrogenase into ethanal, then ethanoate(used for respiration or builds up fatty acids)
-drugs= i.e paracetamol are broken down(excess can lead to liver/kidney failure)
-excess hormones= i.e insulin is broken down(excess can lead to issues with BGC)

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19
Q

Why do excess amino acids need to be broken down?

A

-AA’s contain nitrogen in their amino groups
-nitrogenous substances cannot usually be stored in the body
-excess AA’s= excess nitrogenous substances

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20
Q

Deamination

A

-amine group is removed from amino acid as nitrogenous waste
-forms ammonia(NH3) and organic acids(can be respired to produce ATP/converted to carbohydrate + stored as glycogen)

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21
Q

The ornithine cycle

A

-ammonia is too toxic for mammals to excrete directly
-is combined with CO2 to produce water and urea(not toxic in small concentrations) which can be excreted
-require ATP

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22
Q

What are the kidneys made up of?

A

-millions of nephrons that act as filtering units

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23
Q

Explain the structure of the kidney?

A

-fibrous capsule= fairly tough outer layer
-cortex=dark outer layer where filtering takes place, has dense capillary network carrying blood from renal artery to nephrons
-medulla= (lighter colour) contains the tubules of nephrons that form the pyramids of the kidney + collecting ducts
-renal pelvis= central chamber where urine collects before passing out of ureters(tubes)

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24
Q

Explain the journey of blood into the liver

A

-blood leaves the liver via hepatic vein, feeds into vena cava and reaches renal artery
-renal artery splits into lots of arterioles + capillaries within cortex and medulla of the kidney
-nephrons are running alongside the capillaries–} substances can move between capillaries and nephron tubes during filtering process
-any substances left in capillary will flow out of kidney through renal vein
-any substances left in nephron tubules will enter pelvis and leave the body through the ureters as urine

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25
Q

What are nephrons?

A

-long nephron tubules alongside the bundle of capillaries where the blood is filtered
-around 1 million per kidney
-majority of filtered material is returned to the blood, removing nitrogenous waste + balancing water and mineral ions
-along the entire nephron it carries filtrate(yellow substance)

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26
Q

The structure of the nephron: Bowman’s capsule

A

-cup-shaped structure that contains glomerulus(bundle of capillaries)
-more blood goes into glomerulus than leaves it due to ultrafiltration

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27
Q

The structure of the nephron: Proximal convoluted tubule

A

-first coiled region after bowman’s capsule
-found in the cortex where many substances needed by the body are reabsorbed
-surrounded by capillaries

28
Q

The structure of the nephron: Loop of Henle

A

-long loop of tubule that drops from cortex into medulla
-creates a very high solute conc in the tissue fluid deep in medulla
-U shaped(travels back up through the medulla to cortex)

29
Q

The structure of the nephron: Distal convoluted tubule

A

-second coiled region where the permeability of its walls to water varies in response to ADH
-further regulation of ion balance and pH in blood takes place

30
Q

The structure of the nephron: collecting duct

A

-urine(containing excess filtrate + water) passes down the collecting duct through the medulla to pelvis
-more water balance takes place here
-walls are sensitive to ADH

31
Q

Nephron capillaries

A

-the network of capillaries around the nephron leads to venule, then the renal vein
-the blood that leaves the kidney has reduced levels of urea but levels of glucose, amino acids, mineral ions and other necessary substances are roughly the same

32
Q

Functions of the nephron: Ultrafiltration

A

-the glomerulus is supplied with blood from a short, wide afferent arteriole from the renal artery and the blood leaves through a narrower efferent arteriole–} creates a pressure gradient in the capillaries of glomerulus(hydrostatic pressure builds up in glomerulus)
-this forces blood out through capillary walls and it passes through 3 layers:
- a gap in the capillary wall/endothelium
- basement membrane(made up of network of collagen fibres + other proteins)–} contains pores which allows them to act as sieves so blood cells + most proteins retain in capillary as they are too big to pass through
-cells in the lining of these bowman’s capsule called podocytes(have ‘claw-clip’ extensions called pedicels) that wrap around membrane + form slits so cells, platelets + large plasma proteins that got through both layers don’t enter into tubule
-any molecule small enough(glucose, urea, water, ions) will pass into bowman’s capsule via gaps between the podocyte cells as glomerular filtrate

33
Q

How is selective reabsorption maintained throughout the nephron?

A

-through the loop of Henle, DCT + collecting duct, water is continuously reabsorbed via osmosis
-ion movement to help maintain steep water potential gradient–} remaining substances in filtrate i.e water, dissolved salts, urea, excess hormones + vitamins are excreted as urine
-urine doesn’t usually contain proteins or blood cells as they are too big to be filtered out

34
Q

Functions of the nephron: Selective reabsorption

A

-in the PCT, all of the glucose, amino acids, vitamins + hormones moved back from filtrate into blood
-sodium ions are moved by active transport from epithelial cell to capillary first to produce a conc gradient + then chloride ions follow via diffusion(Cl- to balance Na2+ charge)
-conc gradient allows sodium ions and useful substances like glucose, amino acids, vitamins, ions + some salts to move from the PCT lumen to the epithelial cell via facilitated diffusion and co-transport through transport proteins
-can diffuse down conc gradient into capillaries from the epithelial cells
-water will then follow via osmosis because water potential of the blood is lower then filtrate–} moves from PCT to capillaries down water potential gradient

35
Q

How is the PCT specialised for selective reabsorption?

A

-epithelial cell covered with microvilli which increases SA for substances for diffusion so more substances can be reabsorbed
-many mitochondria to provide ATP for active transport
-large no. of co-transport proteins
-substances only need to pass through a single epithelial cell—} short diffusion distance

36
Q

Regulating water potential

A

-the amount of water potential in the blood needs to be kept constant
–} is lost during excretion, sweating and is gained through eating and drinking
-changing the conc of urine helps maintain water potential

37
Q

Describe the negative feedback system to regulate water potential

A

-water potential is monitored by the osmoreceptors in the hypothalamus(sensitive to conc of ions)
-if water potential is too low, nerve impulses are sent to posterior pituitary gland–} ADH is released into bloodstream
-increases the permeability of the DCT and collecting duct to water–} can pass into the blood in surrounding capillaries
-if water potential is too high, it is picked up by osmoreceptors and nerve impulses are sent to posterior pituitary to inhibit ADH release(walls of collecting duct remain impermeable)

38
Q

Explain the mechanism of ADH

A

-to enter tubule cells, it binds to receptors on the cell membrane and triggers the formation of cyclic AMP(secondary messenger)–} leads to cascade of events:
-vesicles in the cell lining the collecting duct fuse with plasma membrane
-aquaporins(protein channels) are inserted into plasma membrane–} allow water to be passed into the membrane via osmosis, making DCT and the collecting duct more permeable to water
-more water is reabsorbed from these tubules into medulla + into blood via osmosis
-small amount of concentrated urine produced(some water lost from the body)

39
Q

How does ADH contribute to negative feedback?

A

-the more ADH that is released, the more water channels are inserted into plasma membrane
-makes it easier for water to leave tubules by diffusion
-when ADH levels fall, levels of cAMP fall so the water channels are removed from the tubule cell membranes and enclosed in vesicles + collecting duct remains impermeable to water

40
Q
A
41
Q

The loop of Henle

A

-enables mammals to produce urine that is more concentrated than their blood
-it is made up of two ‘limbs’
-the descending limb(cortex to medulla) is impermeable to ion movement + the ascending limb(medulla to cortex) is impermeable to water
-counter current multiplier mechanism= helps to reabsorb water back into blood via osmoregulation

42
Q

Counter current multiplier mechanism: ascending limb

A

-near the top of the ascending limb, Na+ and Cl- ions are actively transported into the medulla
-ascending limb is impermeable to water so the water stays inside the tubule
-high conc of ions in the tissue of the medulla creates a low water potential

43
Q

Counter current multiplier mechanism: descending limb

A

-due to low water potential in the medulla, water leaves the descending limb via osmosis
-this increases the conc of filtrate in the tubule as the descending limb is impermeable to ions
-the water in the medulla is reabsorbed into the blood via the capillary network
-the concentrated ions diffuse down the limb until they reach near the bottom of the ascending limb–} Na+ and Cl- ions diffuse* out into the medulla, lowering water potential
-this causes water to move out of the collecting duct via osmosis–} permeability of the collecting duct is controlled by the level of ADH
*diffuse as ions are concentrated enough to form gradient

44
Q

What impact does the length of the loop of Henle have on its function?

A

-the longer an animal’s loop of Henle, the more water they can reabsorb from filtrate
-longer ascending limb= lower water potential in the medulla, more water moves out of the nephron and collecting duct into the capillaries–} very concentrated urine
-animals who live in areas where there is little water usually have long loops to retain more water

45
Q

What is kidney failure and how is it detected?

A

-when the kidneys cannot carry out their usual function
-can be detected using glomerular filtration rate (GFR)–} a measure of the vol of blood flowing through kidney/rate of filtering
-measured indirectly by the level of creatinine in the blood(breakdown product of muscles)
-GFR(cm3/min) can be impacted by certain factors i.e age(lower), muscle mass(more= higher)

46
Q

Why can creatinine be used to determine GFR?

A

-it enters the bowman’s capsule and none of it gets reabsorbed into the nephron–} if there are higher levels in the blood it is a signal the kidneys aren’t working properly

47
Q

Common causes of kidney failure

A

-kidney infections(the structure of podocytes + tubules may be damaged due to swelling–} impacts filtering in the Bowman’s capsule + reabsorption)
-high BP(can damage the basement membrane + epithelial cells in Bowman and the capillaries within the glomeruli–} larger molecules i.e proteins and blood can get through capillary walls and into urine)
-genetic conditions(i.e polycystic kidney disease= healthy tissue replaced by fluid-filled cysts/damaged by pressure from cysts)

48
Q

Common effects of kidney failures

A

-loss of electrolyte balance= body cannot excrete sodium, potassium + chloride ions–} leads to osmotic imbalances in blood
-build-up of toxic urea in the blood= can poison cells
-high blood pressure= can cause heart problems, strokes
-weakened bones as the calcium/phosphorous balance in blood is lost
-anaemia= reduced production of red blood cells–} tiredness/lethargy

49
Q

How is kidney failure detected?

A

-normal GFR’s don’t fall below 70
-GFR of below 60 for more than 3 months may indicate severe chronic kidney disease—} little filtering of the blood in the kidney

50
Q

What is renal dialysis?

A

-when a patient’s blood is filtered artificially

51
Q

Haemodialysis

A

-the patient’s blood is passed through a dialysis machine—} blood flows from patient’s artery into machine on one side of a partially permeable membrane + dialysis fluid flows on the other side
-blood + dialysis fluid flow in opposite directions to maintain a steep conc gradient between the 2 fluids—} increases rate of diffusion(counter current exchange system)
-the membranes mimic the basement membrane of the bowman’s capsule–} waste products + excess water and ions are removed whereas blood cells and larger molecules i.e proteins remain in the blood

52
Q

Why is haemodialysis important?

A

-it is vital that patients lose the excess mineral ions + urea that have built up whilst maintaining levels of glucose and some ions
-dialysis fluid contains normal plasma levels of glucose to ensure no net movement of glucose out of the blood
-has normal plasma levels of mineral ions, so any excess ions in the blood move out by diffusion down a conc gradient
-fluid contains no urea= steep conc gradient, so urea moves from blood into fluid

53
Q

Disadvantages of haemodialysis

A

-patients may feel increasingly unwell between sessions because waste products + fluid start to build up in the blood
-each session takes around 3-5 hours and patients who rely on it have to remain attached to a dialysis machine several times a week
-must manage diets carefully i.e eat little protein + salts
-expensive

54
Q

Kidney transplants

A

-a new kidney is implanted into a patient’s body to replace a damaged one(blood vessels are joined and new ureter is inserted into bladder)
-must be from a person with the same blood and tissue type
-often donated from a living relative or an organ donor

55
Q

Advantages of kidney transplants

A

-a transplant is cheaper than long term dialysis
-more convenient and comfortable for a patient than constant dialysis sessions

56
Q

Disadvantages of kidney transplants

A

-major operation is risky
-risk of rejection–} antigens on the donor organ may differ from antigens of the patient, which will be rejected by the immune system and may lead to destruction of the kidney
-transplants don’t last forever(average of around 10 years)–} must return to dialysis or wait for another donor

57
Q

Dialysis vs Transplant

A

-dialysis is more readily available than donors
-patients have to monitor diet and have regular sessions on dialysis whereas a transplant frees them from this
-long term dialysis is more expensive than a transplant and can eventually cause damage to the body

58
Q

How is urine a diagnostic tool?

A

-urine contains water, urea, mineral salts as well as breakdown products
-when affected by a disease, new substances will appear in the urine i.e presence of glucose= diabetes/large amounts of creatinine= muscle damage

59
Q

What is hCG?

A

-a hormone only found in the urine of pregnant women
-pregnancy tests detect this

60
Q

How do pregnancy tests work?

A

-when urine is applied to the wick, any hCG will bind to the antibody on mobile monoclonal antibodies that have small coloured beads attached to them–} form hCG-antibody complex
-urine moves up the test strip carrying the beads with it
-it reaches a window where there are immobilised monoclonal antibodies that only bind to hCG
-if a woman is pregnant, the hCG turns the strip blue/forms a line because the immobilised antibodies binds to the complex which has small coloured beads attached
-if no hCG is present the beads will pass through the test area without binding to anything
(regardless of hCG presence or not, urine moves to a second window where the immobilised antibodies bind to mobile antibodies to form a coloured line–} must be 2 lines to indicate pregancy)

61
Q

Monoclonal antibodies

A

-antibodies from a single clone of cells that are produced to target particular cells/chemicals in the body

62
Q

How are monoclonal antibodies made for pregnancy tests?

A
  • a mouse is injected with hCG which then secretes B cells
    -the cells are removed from the mouse and fused with a myeloma(fast dividing cancer cell)–} forms a hybridoma
    -each hybridoma reproduces rapidly to produce clones of the desired antibody and these monoclonal antibodies are collected and purified for usage
63
Q

Anabolic steroids

A

-drugs that build up muscle tissue i.e testosterone and Nandrolone
-athletes are banned from using these steroids= increases performance i.e strength + power BUT has dangerous side-effects i.e liver damage
-they are excreted in the urine which can be used to test for the presence of them via gas chromatography/mass spectrometry(GC/MS)

64
Q

How does GC/MS work?

A

-urine sample is vaporised with a known solvent and passed through a column containing a polymer
-different substances move through the column at different speeds so the substances in the urine separate
- a mass spectrometer converts them into ions and separates them depending on mass + charge
-results are analysed and compared to the results of known substances to decipher which substances were in the urine sample

65
Q

Testing for drugs

A

-urine is used for the testing of many recreational drugs as well as alcohol
-it is possible to find drug traces in the urine as it is filtered through the kidneys and stored in the bladder
-drug testing is usually a two step process:
1) urine sample is applied to the test strip and with the presence of a drug, a colour change occurs to indicate a positive result
2) a sample is usually run through a GC/MS to confirm the presence of a drug

A LEVEL BIOLOGY (21 decks)

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