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OCR AS/A Level Biology Context > 5.1.2: excretion > Flashcards

5.1.2: excretion Flashcards

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1
Q

define excretion

A

the removal of metabolic waste from the body

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2
Q

give 2 examples of excretion in the body

A
  • the lungs excrete CO2
  • kidneys produce urine which contains urea
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3
Q

give examples of metabolic waste in the body

A
  • CO2
  • nitrogenous waste eg ammonia, urea
  • bile pigments
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4
Q

why is it dangerous to allow products such as CO2 and urea to accumulate in the body

A
  • change the cytoplasm and body fluid pH
  • causes enzymes to work less efficiently
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5
Q

hat is the effect of an accumulation of CO2 on the body

A

blood pH falls, acidosis

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6
Q

what is the effect if ammonia accumulates in the body

A
  • increase in cytoplasm pH
  • interferes with metabolic processes eg respiration
  • interferes with receptors for neurotransmitters in the brain
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7
Q

what is the effect if urea accumulates in the body

A
  • diffuses into cells and decreases their water potential
  • causes more water to be absorbed by osmosis until it bursts
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8
Q

what is the effect if uric acid accumulates in the body

A
  • forms crystals in joints
  • causing gout
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9
Q

what is the effect if bile pigments build up in the body

A
  • turns skin yellow (jaundice)
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10
Q

which blood vessel does the liver receive oxygenated blood from

A

hepatic artery

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11
Q

where does the liver receive deoxygenated blood from

A

digestive system via hepatic portal vein

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12
Q

why des the liver receive blood from the digestive system

A

allows liver to absorb and metabolise many of the nutrients absorbed into the blood in the small intestine

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13
Q

which blood vessel does deoxygenated blood leave through

A

hepatic vein

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14
Q

what structure connects the liver and gall bladder

A

bile duct

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15
Q

what are liver cells called

A

hepatocytes

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16
Q

what is a sinusoid?

A

wide capillaries that carry blood from branches of the hepatic artery and hepatic portal vein

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17
Q

what type of cells line sinusoids

A

endothelial cells

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18
Q

why do hepatocytes have large surface areas

A

to maximise the exchange of substances

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19
Q

what are the 3 main functions of the liver

A
  • storage of glycogen
  • formation of urea
  • detoxification
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20
Q

describe how the liver stores glycogen

A
  • plays a vital role in glycogenesis
  • helps regulate blood gluc conc
  • insulin triggers the process after it detects an inc. blood-gluc conc
  • synthesis of glycogen removes glucose molecules from the bloodstream
  • glycogen acts as a a compact and efficient carbohydrate storage molecule
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21
Q

what happens to excess amino acids instead of being excreted

A

they are deaminated

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22
Q

describe the process of deamination

A
  • NH2 group is removed with an extra H
  • combines to form NH3 which forms NH4+ in the cytoplasm
  • remaining keto acid enters the krebs cycle to be respired, converted to glucose or converted to glycogen or fat for storage
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23
Q

how is ammonia made less toxic and less soluble

A

converted to urea

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24
Q

what combines with ammonia to form urea

A

CO2

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25
Q

describe respiratory acidosis

A
  • H ions lower blood pH
  • detected by respiratory centre
  • located in medulla oblongata
  • nerve impulses sent to SAN
  • nerve impulse sent to diaphragm and external intercostal muscles
  • increase in HR and BR
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26
Q

what process converts ammonia to urea

A

ornithine cycle

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27
Q

describe the ornithine cycle

A
  • ammonia combines w CO2 to give H2O and citrulline
  • citrulline combines w NH3 to give H2O and arginine
  • arginine combines w H2O to give urea and ornithine
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28
Q

detoxification meaning

A

the breakdown by the liver of substances not needed or are toxic

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29
Q

what substances are usually detoxified

A
  • lactate
  • alcohol
  • hormones
  • medicinal drugs
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30
Q

what happens to excess lactate in the body

A

absorbed by hepatocytes and metabolised

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31
Q

what happens to lactate in the liver

A

converted to pyruvate

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32
Q

describe the detoxification of alcohol in the liver

A

ethanol -> ethanol (via ethanol dehydrogenase)
ethanal -> ethanoic acid (ethanal dehydrogenase)
ethanoic acid -> ethanoate (acetate) (add coenzyme A)
ethanoate/acetate -> acetyl coenzyme A

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33
Q

why does excessive alcohol consumption lead to fatty liver

A
  • available NAD used for detox. of alcohol so not available for other aspects of metabolism including oxidation of fatty acids
  • fatty acids then accumulate
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34
Q

why is fatty liver a problem

A

this stored fat reduces the ability of the hepatocytes to carry out their many functions

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35
Q

give an example of a condition caused by fatty liver

A

cirrhosis

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36
Q

the fat that accumulates in fatty liver is stored in the hepatocytes. what effect may this have on hepatocyte function

A
  • fat stored in droplets
  • cells swollen
  • disrupts normal cell function
  • particularly intracellular transport
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37
Q

how are hormones metabolised

A

protein hormones and peptide hormones are hydrolysed into amino acids and then converted to urea

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38
Q

where is the central vein located in a lobule

A

in the centre

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39
Q

where is the portal area located in a lobule

A

edges of lobule in connective tissue

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40
Q

what are the kidneys responsible for

A
  • osmoregulation
  • excretion of waste substances
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41
Q

name 3 substances the human kidney removes from the blood

A
  • urea
  • salts
  • water
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42
Q

function of renal artery

A

carries oxygenated blood from the body containing waste to the kidneys

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43
Q

function of renal vein

A

carries deoxygenated blood that is filtered back to the body from the kidneys

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44
Q

function of the kidney

A

regulates water content of blood and filters blood

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45
Q

what is the function of the ureter

A

carries urine from kidneys to bladder

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46
Q

what is the function of the bladder

A

stores urine temporarily

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47
Q

what is the function of the urethra

A

releases urine outside of the body

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48
Q

what layer surrounds the kidneys itself

A

fibrous capsule

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49
Q

the kidneys are a part of a system in the body. name the system

A

excretory

50
Q

give a difference, similarity, and example of products of excretion and secretion

A
  • difference: excretion is removal of waste but secretion is useful products
  • similarity: requires ATP
  • excretion product: urea
  • secretion product: hormones
51
Q

what are the 3 main areas of the kidney

A
  • cortex
  • medulla
  • renal pelvis
52
Q

what nephron structures does the cortex contain

A
  • glomerulus
  • bowmans capsule
  • PCT
  • DCT
53
Q

what nephron structures does the medulla contain

A
  • loop of henle
  • collecting duct
54
Q

what structure does the renal pelvis contain

A

where the ureter joins the kidney

55
Q

what is a nephron

A

a functional unit of the kidney which forms urine

56
Q

does the afferent arteriole carry oxygenated or deoxygenated blood

A

oxygenated

57
Q

does the efferent arteriole carry oxygenated or deoxygenated blood

A

deoxygenated

58
Q

what are the 2 stages of urine formation in the nephron

A
  • ultrafiltration
  • selective reabsorption
59
Q

where does ultrafiltration occur

A

Bowman’s capsule

60
Q

describe how the afferent arteriole is adapted to its function

A
  • larger lumen
  • meaning it is easier for the blood to flow towards the glomerulus than it is to flow away
  • results in high hydrostatic pressure
61
Q

why is a high hydrostatic pressure needed in the glomerulus

A
  • creates a pressure difference between glomerulus and the bowmans capsule
  • small molecules forced out of capillaries into the bowman’s capsule resulting in glomerular filtrate
62
Q

what is the glomerular filtrate composed of

A
  • glucose
  • urea
  • water
  • amino acids
  • mineral ions
  • vitamins
  • hormones
63
Q

why can plasma proteins not pass through into filtrate

A

they are too large and cannot pass through the capsule

64
Q

explain why the blood pressure in the glomerulus is considerably higher than in other capillaries

A
  • wide afferent arteriole
  • narrow efferent arteriole
  • builds up pressure
  • to achieve filtration
65
Q

what is the purpose of the basement membrane

A

size-selective and restricts the passage of blood cells and large proteins from entering the nephron

66
Q

what is a useful adaptation of the endothelium of the glomerular capillaries

A

it is fenestrated

67
Q

what is the name of the cells that form the inner surface of the bowmans capsule

A

podocytes

68
Q

what is the main adaptation of podocytes

A
  • have cellular extensions called paedicels that wrap around blood vessels of the glonerulus
  • produce slits/pores for fluid to move freely into the nephron and form filtrate
69
Q

describe how ultrafiltration occurs in the glomerulus

A
  • high hydrostatic pressure
  • allows substances such as water, glucose, urea to pass through
  • small gaps/pores in capillary endothelium
  • and through capillary basement membrane
70
Q

if a person has a disease that affects their glomeruli, suggest why high quantities of protein is found in their urine

A
  • affects basement membrane
  • proteins pass into glomerular filtrate
71
Q

describe the function of epithelial cells lining the proximal convulated tubule

A
  • selectively reabsorbs solutes from the glomerular filtrate
  • by secondary active transport
72
Q

what is reabsorbed by the PCT

A
  • all glucose and vitamins
  • all amino acids and hormones
  • some cl- and na+
  • some water
73
Q

describe the process of selective reabsorption in the PCT

A
  • actively transporting Na+ out of the epithelial cells lining the PCT into blood capillaries and carrying them away
  • the movement of Na+ lowers conc in ep. cells
  • Na+ ions go down their conc grad from lumen to ep. cells via carrier protein
  • carries glucose and aa via cotransport
  • once in ep. cells, ions and glucose/aa diffuse itno blood via conc grad
74
Q

describe how the PCT brings about changes in conc of filtrate

A
  • selective reabsorption
  • of glucose and amino acids
  • co-transport using na+
  • water follows by osmosis so conc of ions/urea increases
75
Q

why is there less glucose overall re absorbed back

A

although much of the glucose is reabsorbed in the PCT some will be used in respiration to produce ATP for AT

76
Q

osmoregulation meaning

A

the control of the water potential of the body

77
Q

what detects changes in the water potential of the body and where is it located

A
  • osmoreceptors
  • hypothalamus
78
Q

where does reabsorption of water occur

A

loop of henle

79
Q

describe the reabsorption of water in the loop of henle

A
  • osmosis of water out of filtrate due to low water potential in surrounding tissues
  • na+ and cl- diffuse out of filtrate into surrounding tissue down concentration gradients
  • na+ and cl- pumped out by active transport out of filtrate
80
Q

explain the trends in the loop of henle of concentration of filtrate

A
  • conc rises in descending limb because sodium ions enter and water is lost
  • conc falls in ascending limb because sodium and chloride ions actively removed
  • but water remains in ascending limb as its walls are impermeable to water
81
Q

what is the response of osmoreceptors to a low water potential of the blood

A

secretion of ADH from posterior pituitary gland

82
Q

describe how osmoregulation occurs in the collecting duct

A
  • osmoreceptors in the hypothalamus detect the decrease in water potential in the blood
  • the pituitary gland releases the hormone ADH
  • ADH travels in the blood to the kidney
  • ADH increases the permeability of the collecting duct cells
  • more water is reabsorbed from the urine into the lood
  • the water potential of blood increases so no more ADH is made
83
Q

describe how ADH stimulates the collecting ducts cells to become more permeable to water

A
  • ADH binds to receptors in the membrane of collecting duct cells
  • causes cAMP to form
  • stimulates vesicles containing aquaporins to fuse w the CSM
  • allows more osmosis of filtrate down water potential gradient
84
Q

what is the function of the counter current principle in the loop of henle

A
  • maintains a high salt concentration in the medulla
  • enables water reabsorption from the collecting ducts when ADH is present
85
Q

what effect does a longer loop of henle have on water reabsorption

A
  • less water loss/more water reabsorbed
86
Q

why is more water reabsorbed if the loop of henle is longer

A
  • more sodium and chloride ions pumps out of ascending limb
  • which causes water potential of the medulla to become more negative
  • increasing steepness of the water potential gradient so more water is reabsorbed
87
Q

explain the relationship between the length of the loop of henle and the water potential of the urine each mammal produces

A
  • the longer the loop of henle the lower the water potential of urine
  • ions pass out from ascending limb into medulla
  • creating lower water potential in medulla
  • water reabsorbed from collecting duct in medulla
  • by osmosis
88
Q

what is the typical role of the loop of henle

A
  • causes a decrease in water potential to establish a water potential gradient in the medulla
  • in asc. limb AT outwards of solutes
  • descending limb permeable to water
  • water potential of tissues surrounding collecting duct is lower than fluid inside
  • water removed from filtrate
89
Q

what is the role of diuretics

A
  • reduces the amount of Na+ that is reabsorbed by the nephron
90
Q

what is the effect of less sodium ions being reabsorbed by the nephron

A
  • less ADH reabsorbed
  • means more water removed from the body in the urine lower water content of blood
  • therefore reduces blood volume and blood pressure
91
Q

coffee contains caffeine which inhibits the release of ADH. describe and explain the effect of drinking coffee on the volume and concentration of urine released

A
  • volume increases
  • concentration decreases
  • wall of collecting duct is impermeable to water
  • fewer water channels
  • in membrane of epithelial cells
  • less water reabsorbed
  • by osmosis
  • drinking increases liquid intake and therefore liquid loss
92
Q

state one function of the DCT

A

reabsorption of ions eg Cl-

93
Q

why can kidney failure occur

A
  • blood loss in an accident
  • high blood pressure
  • diabetes
  • overuse of drugs
  • certain infections
94
Q

what is a consequence of kidney failure

A
  • urea, water, salts and various toxins are retained and not excreted
  • less blood if filtered by the glomerulus causing the GFR to decrease
  • leads to build up of toxins in the blood
  • electrolyte balance in the blood is disrupted
95
Q

what are the 2 treatments available for kidney failure

A
  • renal dialysis
  • kidney transplant
96
Q

what are the 2 forms of renal dialysis

A
  • haemodialysis
  • peritoneal dialysis
97
Q

what is a dialysate

A

a solution containing substances needed in the blood eg glucose in the right concentrations

98
Q

describe briefly how haemodialysis occurs

A
  • in the dialysis machine a partially permeable dialysis membrane sparates blood and dialysate
  • the blood is passed through tubes of dialysis membrane which are surrounded by dialysate
  • dialysate is constantly refreshed so conc grad is maintained between dialysis fluids and blood
99
Q

why is there no urea in the dialystae

A

to ensure all urea diffuses down its conc grad out of the blood

100
Q

what type of flow is used in a haemodialyser

A

counter current

101
Q

why does a haemodialyser use a counter current flow

A
  • creates a steep conc grad along the length of the dialyser
  • ensures all waste eg urea diffuses out the blood
102
Q

what drug is added to the blood and why

A
  • anticoagulent
  • prevents blood clots forming
103
Q

how does peritoneal dialysis work

A
  • dialysis is introduced to the abdominal cavity through a catheter
  • urea, other metabolic waste products and excess substances diffuse across the abdominal lining into the dialysate
  • the dialysate is then removed and replaced with more
104
Q

disadvantages of dialysis

A
  • heavy restrictions on patients
  • controlled diet
  • regular hospital trips
  • long treatments
105
Q

disadvantages of kidney transplant

A
  • risk of immune response due to foreign antigens
  • risk of rejection
  • have to take immunosuppresants which have long term side effects
  • leaves patients vulnerable
  • not enough donors to cope with demands
106
Q

what are the benefits of a kidney transplant over dialysis

A
  • patient has more freedom
  • diets less restrictive
  • dialysis is expensive
  • dialysis only works for a limited amount of time
107
Q

what is the most common urine test used to test for

A

sugar/glucose

108
Q

why can you easily test for glucose in urine

A
  • all glucose in filtrate should be reabsorbed by the PCT
  • no glucose should be present in urine
109
Q

what can glucose in urine tell us about a patient

A
  • there is something wrong with a perosns homeostatic control of glucose
110
Q

what other substances can urine be used to test for apart from glucose

A
  • ketones produced by people with diabetes
  • proteins, indicates issue with blood filration mechanism
  • nitrate ions indicate a bacterial infection in urinary tract
111
Q

define monoclonal antibody

A

antibodies produced by single clones of cells

112
Q

what hormone is present in pregnant woman

A

hCG

113
Q

describe how a pregnancy test works

A
  • hCG binds to mobile monoclonal antibodies in sample pad
  • monoclonal antibodies move down test pad
  • result window/first zone is where the monoclonal antibodies that have combined with hCG bind to first layer of antibodies which give coloured dye indicating hCG is present and the woman is pregnant
  • second zone/control window have ntibodies not bound to hCG which shows a coloured like that the antibodies are mobile and the test works
114
Q

what other substance can urine test for

A

anabolic steroids

115
Q

what test can be done to test for anabolic steroids

A

gas chromatography and mass chromatography

116
Q

give 3 features of an efficient selective reabsorption surface

A
  • surface is one cell thick to reduce diffusion distance
  • microvilli increases the surface area for diffusion
  • cells may contain many mitochondria to release energy for sodium-potassium pumps
117
Q

give 3 problems which can occur as a result of kidney failure

A
  • GFR decreases
  • ion balance not maintained
  • risk of arrhythmia and cardiac arrest as K+ imbalance affects frequency of nerve impulses from the SAN
118
Q

suggest why a high intake of protein in the diet will be likely to result in a high conc of urea in urine

A
  • high intake of proteins leads to a large amount of aa
  • excess aa cannot be stored
  • aa deaminated
  • large amount of protein enters the orthinine cycle
  • increased conc of urea
119
Q

suggest the effects of complete kidney failure on the composition of the blood

A
  • contains high conc of ions eg cl-
  • high water potential
  • high urea conc
120
Q

nephritis is a condition where the tissue of the glomerulus and PCT is inflamed and damaged. suggest 2 differences in the composition of a person with nephritis compared with a healthy person

A
  • urine contains more aa
  • blood cells present
  • glucose present
  • more water present
121
Q

suggest 2 ways in which the structure of an aquaproin prevents the passage of ions

A
  • shape of channel is complementary only to water molecules
  • positive charge repels positive charge
  • ions are too large
122
Q

suggest where ADH is removed from the blood and describe what happens to the ADH molecule

A
  • NH2 removed during deamination
  • enters ornthine cycle
  • ultrafiltered form blood
  • not all urea is reabsorbed
  • which is then excreted

OCR AS/A Level Biology Context (24 decks)

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