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OCR A-level Biology > Excretion > Flashcards

Excretion Flashcards

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1
Q

Why do we need excretion?

A

To remove harmful metabolic waste products

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2
Q

What are the 3 main waste products that need excreting?

A

CO2 from respiration

Nitrogenous waste (e.g urea)

Other compounds like bile pigments (found in faeces)

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3
Q

What are the 4 main excretory organs?

A

Lungs
Liver
Kidneys
Skin

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4
Q

What may occur if CO2 isn’t excreted properly?

A

Build up of CO2

Dissolves into blood plasma forming H2CO2 (carbonic acid)

Dissociates to form H+ which changes the pH of blood

This can change the shape of haemoglobin reducing the affinity of erythrocytes to O2

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5
Q

How does the body ensure that CO2 doesn’t build up

A

High CO2 concentrations detected by the medulla oblongata

Increases breathing rate to remove the CO2

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6
Q

What is the pH threshold of the blood and what does it cause if the pH drops below this value?

A

pH 7.35

Respiratory Acidosis

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7
Q

Why does the body not excrete excess amino acids?

A

They contain lots of energy that can be used in respiration

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8
Q

What is the name of the process where the harmful amino group is removed?

A

Deamination

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9
Q

Where does deamination occur?

A

Liver

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10
Q

What is the equation for deamination?

A

amino acid + oxygen = keto acid + ammonia

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11
Q

What is ammonia converted to after deamination?

A

Urea

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12
Q

What is the equation for the formation of Urea?

A

ammonia + carbon dioxide = urea + water

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13
Q

What is the name of liver cells?

A

Hepatocyes

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14
Q

Why must the liver have a good blood supply?

A

it is involved in many metabolic processes so requires O2 for respiration

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15
Q

What are the 2 sources of blood supply TO the liver?

A

Hepatic artery

Hepatic portal vein

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16
Q

What blood is found in the Hepatic Artery?

A

Oxygenated blood from the heart

provides oxygen for aerobic respiration of the hepatocytes

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17
Q

What blood is found in the Hepatic Portal Vein?

A

Deoxygenated blood from the digestive system

Rich in the products of digestion

any toxic compounds that have been absorbed must be removed

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18
Q

What blood vessel does blood leave the Liver by?

A

Hepatic Vein

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19
Q

What is the fourth vessel that is connected to the liver?

A

Bile duct

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20
Q

What is the function of Bile in the liver?

A

aid digestion of fats

Contains pigments (bilirubin) that must be excreted

Created by liver cells as a result of haemoglobin breakdown.

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21
Q

Describe the histology of the liver

A

Divided into lobes and then further into lobules

Inter lobular vessels (branches of the hepatic artery and hepatic portal vein) deliver their fluids into a sinusoid

It then reaches the intra lobular vessel in the centre where it leaves the liver via the Hepatic vein

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22
Q

What is a sinusoid?

A

A cavity surrounded by hepatocytes where blood flows through as toxins are removed

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23
Q

What is a bile canaliculus?

A

A cavity where bile flows into as it is produced by the hepatocytes

Flows into bile duct were bile is transported to gall bladder

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24
Q

What is the function of Kupffer cells?

A

Specialised macrophages that breakdown old erythrocytes

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25
Q

How might hepatocytes be specialised to carry out metabolic reactions?

A

Dense cytoplasm

High numbers of specific organelles

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26
Q

What are the metabolic functions of the liver?

A

control of blood glucose, amino acid and lipid levels

synthesis of bile, plasma and cholesterol

synthesis of RBC’s

storage of vitamins (A, D, B12)

Detoxification of drugs and alcohol

breakdown of hormones

breakdown of RBC’s

Storage of glycogen

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27
Q

In what form does the liver store glycogen?

A

Granules in the cytoplasm of hepatocytes

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28
Q

Describe 2 enzymes the liver uses to detoxify compounds?

A

Catalase - converts H2O2 to H2O

Cytochrome P450 - Break down drugs such as cocaine and various medicinal drugs. Can interfere with other metabolic functions giving the side affects of drugs

Ethanol dehydrogenase - turn ethanol to acetate and H+ which are used used in respiration

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29
Q

Why does alcohol lead to hepatitis or liver cirrhosis?

A

Too much NAD is used to remove H+ produced when alcohol is broken down

Not enough NAD available for fatty acid breakdown

fat builds up on liver causing hepatitis or cirrhosis

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30
Q

What is the ornithine cycle?

A

Conversion of ammonia (NH3) to urea (CO(NH2)2)

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31
Q

Why must ammonia be converted immediately after it is formed in deamination?

A

it is highly soluble and highly toxic

32
Q

Where does urea go after it is created?

A

to the kidneys

it is then filtered out of the blood

excreted in the urine

33
Q

What are the two main blood vessels connected to the kidneys?

A

Renal Vein

Renal Artery

34
Q

What is the other vessel connected to the kidneys and what is its function?

A

Ureter

transport urine from kidneys to the bladder

35
Q

What are the 3 main sections of the kidneys?

A

Cortex - outer region
Medulla - inner region
Pelvis - centre connected to the pelvis

36
Q

What is the name of the tine tubules that make up the kidneys?

A

Nephrons

37
Q

What is the name of the structure at the start of a nephron?

A

Bowman’s capsule

38
Q

What is the name of the knot of capillaries in the Bowman’s Capsule?

A

Glomerulus

39
Q

what is the name of the process where blood is pushed into the Bowman’s capsule?

A

Ultrafiltration

40
Q

How is the Bowman’s capsule specialised to carry out ultrafiltration?

A

The endothelium of capillary - small gap between capillary and endothelium, also contains fenestrations which allow substances through

Basement membrane - a fine mesh of collagen and glycoproteins between capillary and endothelium, keep RBC’s in the capillary

Epithelia of Bowman’s capsule (Podocytes) - Have projections that make gaps between cells so fluid can pass into the lumen of the Bowman’s capsule

41
Q

What the the 4 parts of a nephron tubule called?

A

Bowman’s capsule
Proximal convoluted tubule
loop of Henle
Distal convoluted tubule

42
Q

What is filtered out of the blood in the kidneys?

A 
Water
Amino acids
Glucose
Urea
Inorganic mineral ions (Na+, Cl-, K+)
43
Q

What is the function of the nephron after ultra filtration?

A

selective reabsorption

44
Q

What is reabsorbed into the blood in the proximal convoluted tubule?

A

Sugars, Mineral ions and some water

45
Q

What happens in the descending limb of the loop of Henle?

A

mineral ions added back
water removed
water potential decreased

46
Q

What happens in the ascending limb of loop of Henle?

A

mineral ions removed by active transport

water potential increased

47
Q

What happens in the collecting duct?

A

Water removed

water potential decreased

48
Q

What is the final product left in the collecting duct?

A

Urine

49
Q

How are the cells lining the proximal convoluted tubule specialised to perform selective reabsorption?

A

surface membrane folded to form microvilli

surface membrane contains cotransporter proteins for moving glucose or amino acids into the cells

has lots of mitochondria to produce lots of ATP for active transport

50
Q

Explain the role of Na+ in selective reabsorbtion

A

Na+ is actively transported out of the cell

It then diffuses back into the cell and acts as a cotransporter by bringing glucose or amino acids in against their concentration gradient

Known as secondary active transport

51
Q

What are the two main parts of the loop of Henle?

A

Descending limb

Ascending limb

52
Q

What is the function of the loop of Henle?

A

To reabsorb water from the filtrate

53
Q

How does the loop of Henle regulate ion concentrations in the filtrate?

A

Filtrate entering decending limb is of high water potential

Water moves out down its osmotic gradient

Filtrate at the highest concentration at the bottom of the loop

Na+ and CL- are actively transported out of the ascending limb and water moves in

Filtrate is at its most dilute at the top of the ascending limb

54
Q

Why must osmoregulation occur?

A

Too much or too little water could cause cell lysis or crenation

55
Q

What hormone controls permeability of the collecting duct?

A

Antidiuretic Hormone (ADH)

56
Q

What binds to cell surface or collecting duct cells in order to increase permeability?

A

Vesicles containing aquaporins

57
Q

What happens when ADH concentration is high?

A

More aquaporins bind to cells in collecting duct

Increased permeability

more reabsorption of water

Urine becomes more concetrated

58
Q

What happens when ADH concentrations fall?

A

Membrane invaginates to re-form vesicles

membrane permeability is reduced

less reabsorption of water

urine is more dilute

59
Q

Where in the brain detects changes in water potential in the blood?

A

Osmoreceptors in the Hypothalamus

60
Q

Where is ADH stored and released from?

A

posterior pituitary gland

61
Q

By what process of movement is ADH released?

A

Exocytosis

62
Q

What is the measure of Kidney function?

A

Glomerular filtration rate (GFR)

63
Q

How do you measure GFR?

A

Analysis of urine for certain protiens

64
Q

What is normal GFR, and what values would indicate issues?

A

Healthy = 90-120 cm3/min
Chronic kidney disease = <60 cm3/min
Kidney failure = <15 cm3/min

65
Q

What are common causes of Kidney faliure?

A

Diabetes mellitus
Heart disease
hypertension
infection

66
Q

What are the 2 main treatments for Kidney failure?

A

Renal Dialysis

Kidney transplant

67
Q

What are the 2 types of renal dialysis?

A 
Haemodialysis
Peritoneal dialysis (PD)
68
Q

describe the process of haemodialysis

A

Blood is passed into the machine containing the dialysis membrane

anti-clotting agent is added

Dialysis fluid flows in countercurrent direction to improve the efficiency of exchange

69
Q

How often does haemodialysis need to be performed?

A

2-3 times /week at a clinic

70
Q

Describe peritoneal dialysis?

A

The membrane is implanted in the bodys own abdominal membrane (peritoneum)

Dialysis fluid is poured into the abdomen via a tube and then must be drained after a few hours

71
Q

What are the advantages of a Kidney transplant?

A

No need for time consuming dialysis

Feeling physically fitter

Ability to travel

Don’t feel chronically ill

72
Q

What the disadvantages of a Kidney transplant?

A

Requires major surgery

Must take immunosuppressant drugs that can cause hypertension and make infections more common

Possibility for rejection

Organ waiting list is long so may take years to get a match

73
Q

Give example of molecules that can be detected in urine analysis and where they are used in the world

A

Glucose in diabetes diagnosis

Alcohol to determine if drivers are drunk

Recreational drugs, tests done by police or employers

human chronic gonadotrophin (hCG) in pregnancy tests

anabolic steroids, in sporting competitions

74
Q

What is used in pregnancy tests to test for hCG?

A

monoclonal antibodies

75
Q

What process is used to test for anabolic steroids after a urine sample has been taken?

A

Gas Chromatography

OCR A-level Biology (24 decks)

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