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A level Biology > 5.2 Excretion as an example of homeostatic control > Flashcards

5.2 Excretion as an example of homeostatic control Flashcards

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1
Q

define excretion

A

the removal of metabollic waste from the body

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2
Q

Define metabolic waste

A

A substance that is produced in excess by the metabolic processes in the cells and it may become toxic

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3
Q

What must be excreted

A

carbon dioxide from respiration
nitrogen containing compounds such as urea
other compounds such as bile

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4
Q

what are the excretory organs

A

the lungs
the liver
the kidneys
the skin

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5
Q

what is excreted from the lungs

A

carbon dioxide

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6
Q

What is excreted from the liver

A

bilirubin - the bile pigment
converts excess amino acids into urea

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7
Q

What do the kidneys excrete

A

urea

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8
Q

What does the skin excrete

A

sweat which contains substances such as salts water uric acid and ammonia

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9
Q

Why is excretion important

A

The build up of some metabolic products could be fatal as they may interfere with cell processes by altering pH etc. other metabolic products may act as inhibitors and reduce enzyme activity

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10
Q

Why must carbon dioxide be excreted

A

It can react with water to form carbonic acid which can dissociate into H+ ions
These ions can affect the pH of red blood cell cytoplasm and the plasma which can alter the structure of proteins and affect their ability to perform their function

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11
Q

How is a drop in blood pH detected and counteracted

A

The extra H+ ions are detected by the respiratory centre in the medulla oblongata and cause an increase in breathing rate to help remove excess CO2

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12
Q

What can happen if blood pH drops below 7.35

A

It may cause headaches, drowsiness, restlessness, tremor and confusion

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13
Q

What can cause an increase in blood pH

A

Diseases or conditions which affect the lungs such as emphysema asthma or bronchitis

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14
Q

What is the condition when blood is acidic

A

respiratory acidosis

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15
Q

how do we excrete excess amino acids

A

The body cannot store excess amino acids so they are transported to the liver where the amino group is removed and initially the soluble and toxic compound ammonia is formed and then converted to the less toxic compound urea which can be transported to the kidneys for excretion

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16
Q

Why are excess amino acids not excreted but rather deaminated

A

They contain a similar amount of energy as carbohydrates so it would be wasteful to excrete them so they are deaminated and the keto acid can be used in respiration

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17
Q

Give the equation for the formation of urea from amino acids

A

amino acid + oxygen → keto acid+ ammonia
ammonia + carbon dioxide → urea + water

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18
Q

How does blood flow to the liver

A

The hepatic artery delivers oxygenated blood to the liver

the hepatic portal vein delivers deoxygenated blood from the digestive system to the liver which is rich in the products of digestion and may also contain toxic compounds which need their concentrations altered before it can continue to circulate around the body

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19
Q

How does bood leave the liver

A

Hepatic vein which then rejoins the vena cava

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20
Q

Why are the blood vessels and chambers in the liver arranged in the way that they are

A

To ensure greatest possible contact between the blood and liver cells

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21
Q

What is the liver split into

A

Lobes which are further split into lobules

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22
Q

What do the hepatic artery and hepatic portal vein split into

A

as they enter the liver they split into smaller and smaller vessels which run between and parallel to the lobules known as interlobular vessels

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23
Q

Describe the blood flow from the hepatic artery and hepatic portal vein

A

They split into smaller vessels running between and parallel the lobules as interlobular vessels.

At intervals they enter the lobule and the blood from the two vessels is mixed and passes along a special chamber called a sinusoid which is lined with liver cells which are able to remove substances from the blood and return other substances to the blood

At the end of the sinusoid the concentrations of many of its components have been altered and at the centre of each lobule is a branch of the hepatic vein known as an intralobular vessel which the sinusoids empty into

The branches of the hepatic vein from the different lobules join together to form the hepatic vein and blood is drained from the liver

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24
Q

Describe the contents of the sinusoids

A

lined with liver cells
contains macrophages called Kupffer cells

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25
Q

What is the primary function of the macrophages in the sinusoid

A

Their primary function appears to be breakdown and recycle of old red blood cells

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26
Q

What is the product of haemoglobin breakdown

A

bilirubin

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27
Q

Describe how bile is transported out of the liver

A

Bile is made in the liver cells and released into the bile canaliculi which join to form the bile duct and is transported to the gall bladder

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28
Q

Give the 11 components of the liver

A

Hepatic artery
hepatic portal vein
interlobular vessels
lobes
lobules
sinusoids
Kupffer cells
intralobular vessel
hepatic vein
bile canaliculi
bile duct

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29
Q

What are the metabolic functions of the liver

A

Control of blood glucose levels
synthesis of bile, plasma proteins and cholesterol
storage of glycogen
destruction of red blood cells
detoxification of alcohol and drugs
hormone breakdown

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30
Q

How does the liver detoxify hydrogen peroxide

A

catalase enzymes convert hydrogen peroxide to hydrogen and water

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31
Q

How does the liver detoxify drugs

A

Cytochrome p450 is a group of enzymes that can breakdown drugs including cocaine. They are also used in electron transport during respiration

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32
Q

Why do drugs have side effects

A

Cytochrome p450s role in metabolising drugs can interfere with other metabolic processes causing the unwanted side effects

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33
Q

How does the liver detoxify alcohol

A

it is broken down in the hepatocytes by ethanol dehydrogenase which produces ethanal

This is dehydrogenated further by ethanal dehydrogenase enzyme and the final compound is acetate

Acetate can enter respiration by combining with CoA to form acetyl CoA

The hydrogen atoms released from the dehydrogenation combine with NAD to form NADH

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34
Q

Explain why it would be wastefl to just excrete alcohol

A

Because it can be dehydrogenated to form acetate which can be used in respiration and it also forms 2NADH

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35
Q

Explain why someone that consumes a lot of alcohol may have fatty liver

A

NAD is also required to oxidise and breakdown fatty acids for use in respiration but if the liver has to detoxify too much alcohol it has insufficient NAD left to deal with the fatty acids so they are converted back to lipids and stored as fats in the hepatocytes

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36
Q

What 2 processes do amino acids undergo in the liver

A

deamination and the ornithine cycle

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37
Q

Describe deamination

A

It removes the amino group and produces ammonia which is very soluble and toxi and keto acid which can enter respiration

38
Q

Describe the ornithine cycle

A

Ammonia and CO2 combine with the amino acid citrulline and this is converted into arginine by addition of further ammonia
The arginine is then re-converted to ornithine by the removal of urea

39
Q

What is the equation for what occurs in the ornithine cycle

A

2NH3 + CO2 → CO(NH2)2 + H20

40
Q

What type of reactions occur in the ornithine cycle

A

condensation

41
Q

Define nephron

A

the functional unit of the kidney

42
Q

Define ultrafiltration

A

filtration of the blood at molecular level under pressure

43
Q

describe the structure of the kidneys

A

it has an outer region called the cortex
inner region called the medulla
the centre is the pelvis which leads to the ureter
It is lined with a capsule
blood flows through the renal artery and vein
Each kidney contains about one million nephrons which starts at the cortex

44
Q

What does the renal artery split into

A

many afferent arterioles which lead to a knot of capillaries in the glomerulus which then continues to the efferent arterioles

45
Q

How do the afferent and efferent arterioles differ

A

The afferent arteriole has a large diameter

46
Q

What parts of the nephron are in the cortex?

A

The glomerulus
proximal convoluted tubule
distal convoluted tubule
1/2 of collecting duct

47
Q

What parts of the nephron are located in the medulla

A

The loop of Henle
descending limb
ascending limb
1/2 of collecting duct

48
Q

what do the capillaries in the kidney go into

A

the glomerulus

49
Q

What are the filtering layers in ultrafiltration

A

The endothelium of the capillary
the basement membrane
the epithelial cells of the Bowmanns capsule

50
Q

Describe the endothelium of the capillary

A

There are narrow gaps between the cells of the endothelium wall as well as pores called fenestrations

the gaps allow blood plasma and substances dissolved in it to pass out of the capillary

51
Q

Describe the basement membrane

A

It consists of a mesh of collagen fibres and glycoproteins which acts as a filter to prevent the passage of molecules with a molecular mas greater than 69000 to pass through

52
Q

Describe the epithelial capillaries of the Bowmann’s capsule

A

They are cells called podocytes which have a specialised shape
They have projections called major processes and on each there are minor processes that hold the cells away from the endothelium of the capillary

These projections ensure there are gaps between the cells so that fluid can pass through them into the lumen of the Bowmann’s capsule

53
Q

Describe how hepatocytes are adapted

A

They have a very dense nucleus with specialised numbers of certain organelles

54
Q

Describe how pressure is maintained in the glomerulus

A

The afferent arteriole is wider than the efferent which tends to push blood into the Bowmann’s capsule that surrounds the glomerulus

55
Q

What is filtered out of the blood

A

water
amino acids
glucose
urea
inorganic mineral ions such as sodium

56
Q

What other pressure is acting on the capillary in the glomerulus

A

Hydrostatic and osmotic pressure

57
Q

Why is osmotic pressure beneficial in the glomerulus

A

This ensures that some of the fluid is retained in the blood due to the low water potential in the capillaries

58
Q

What is the funtcion of the nephrons

A

Ensures that urine has a low water potential and a high concentration of solutes that is found in the blood and tissue fluid - metabolic waste

59
Q

Describe how the plasma membrane of the proximal convoluted tubule closest to the tubule fluid is adapted

A

It is highly folded to form microvilli to increase the surface area for reabsorption

It also contains special cotransport proteins that transport glucose or amino acids in association with the sodium ions from the tubule into the cell

59
Q

Describe how the plasma membrane of the proximal convoluted tubule closest to the tubule fluid is adapted

A

It is highly folded to form microvilli to increase the surface area for reabsorption

It also contains special cotransport proteins that transport glucose or amino acids in association with the sodium ions from the tubule into the cell

60
Q

Describe how the plasma membrane closest to the tissue fluid in the proximal convoluted tubule is adapted

A

It is also folded to increase its surface area

It contains sodium/potassium pumps

61
Q

escribe how the cells lining the proximal convoluted tubule are adapted

A

They contain many mitochondira

62
Q

Describe the mechanism of reabsorption in the proximal convoluted tubule

A

1- Sodium ions are actively pumped out of the the cells lining the proximal convoluted tubule into the tissue fluid reducing their concentration in the cell

2- Sodium ions diffuse into the cell from the tubule fluid through a cotransport protein carrying a glucose or amino acid - secondary active transport

3-This decreases the water potential in the cell so water moves in by osmosis

4- glucose and amino acids diffuse out of the cell into the tissue fluid

repeat

63
Q

How are large molecules reabsorbed

A

endocytosis

64
Q

Why do mammals need to reabsorb water

A

The mammal would become dehydrated very quickly otherwise

65
Q

Why does urea concentration increase in the nephron past the loop of henle

A

Water is withdrawn from the tubule so the urea concentration increases

66
Q

Describe how water is reabsorbed in the loop of henle

A

1- There is active removal of odium and chlorine ions at the top of the ascending limb it is also impermeable to water

2-As mineral ions diffuse into the descending limb the concentration of the fluid rises so its water potential decreases

3- the fluid becomes increasing more concentrated deeper in the medulla

4- as the fluid rises up the medulla the mineral ions leave the fluid by diffusion

5- the effect of these ionic movements is to create a higher water potential in the fluid of the ascending limb and lower water potential in the tissue fluid of the medulla

6- as water flows down the collecting duct it passes through tissues with an ever-decreasing water potential gradinet so water moves out and into the tissue fluid via osmosis

67
Q

Describe the purpose of the distal convoluted tubule

A

active transport is used to adjust concentrations of various mineral ions

68
Q

Why does water potential of the tissue fluid in the medulla get more negative the lower down the medulla

A

This is because the tubule fluid has a very high concentration at the base of the ascending limb and mineral ions diffuse out making the tissue fluid have a very negative water potential compared to higher up

69
Q

What is the effect of alcohol on water absorption

A

It inhibits the release of ADH which can make you dehydrated

70
Q

What chain of events occurs when there is a very low water concentration in the blood

A

Osmoreceptors in the hypothalamus lose water by osmosis and shrink stimulating neurosecretory cells in the hypothalamus

This causes ADH to move down the axon body to the terminal bulb in the posterior pituitary gland where it is stored in vesicles

Action potentials cause the release of more ADH

The ADH is detected by cell surface receptors and a chain of enzyme controlled reactions occurs

Vesicles containing aquaporins move and fuse to the plasma membrane and this makes the plasma membrane more permeable to water

71
Q

What chain of vents occurs when water concentration in the blood is too high

A

Osmoreceptors in the hypothalamus swells and stimulates neurosecretory cells in the hypothalamus

ADH moves down the axon body to the terminal bulb in the posterior pituitary gland where it is stored in
vesicles

Action potentials stimulate the release of less ADH

The ADH is detected by cell surface receptors and a chain of enzyme controlled reactions occurs

The plasma membrane invaginates (folds inwards) to create new vesicles that remove aquaporins making the walls less permeable to water

72
Q

What happens to excess ADH in the body

A

Once the water potential of the blood rises again less ADH is released

Remaining ADH is broken down as it has a half life of 20 minutes

73
Q

Why must excess ADH get broken down

A

So that water potential of the blood doesnt get too high and cells do not undergo lysis

74
Q

Define hypertonic

A

High concentration of solutes

75
Q

Define hypotonic

A

Low concentration of solute

76
Q

Define kidney failure

A

If the kidneys fail completely they are unable to regulate the levels of water and electrolytes in the body or to remove waste products such as urea from the blood

77
Q

How can we assess kidney function

A

By estimating the glomerular filtration rate and by analysing urine for substances such as proteins

78
Q

Define glomerular filtration rate

A

it is a measure of how much fluid passes the nephrons per minute and a normal reading is 90-120 cm/min

79
Q

What are the causes of kidney failure

A

diabetes mellitus
heart disease
hypertension and infection

80
Q

What are the main treatments for kidney failure

A

renal dialysis and kidney transplant

81
Q

What are the 2 types of renal dialysis

A

haemodialysis

peritoneal dialysis

82
Q

Describe haemodialysis

A

Blood from an artery is passed into a machine that contains an artificial dialysis membrane shaped to form many artificial capillaries and increase surface area

the dialysis fluid contains the correct concentrations of mineral ions glucose urea and water and flows in a counter current to the blood

It is performed at a clinic 2-3 times a week for several hours a session

83
Q

What is added to the blood during haemodialysis

A

Heparin to prevent clotting and air bubbles are removed

84
Q

Describe peritoneal dialysis

A

The dialysis membrane is the body’s own abdominal membrane

First a surgeon implants a permanent tube in the abdomen. Dialysis solution is poured through the tube and fills the space between the abdominal wall and the organs and after several hours the solution is drained

This can be carried out at home or work

85
Q

What must be combined with peritoneal dialysis and why

A

A balanced diet and not to much protein as it turns into urea

86
Q

What are the advantages of a kidney transplant

A

Freedom from time-consuming dialysis

feeling physically fitter

better self image

improved quality of life

87
Q

What are the disadvantages of a kidney transplant

A

Need to take immunosuppressants and their side effects
need for major surgery
need regular check for rejection

88
Q

Describe urine analysis

A

Urine can be tested for molecules with an Mr less than 69000
such as glucose, alcohol, many recreational drugs, anabolic steroids

89
Q

Describe pregnancy testing

A

Urine is poured onto a test stick and hCG binds to the mobile antibodies attached to a blue bead

the mobile antibodies move down the test stick

If hCG is present it binds to fixed antibodies holding a bead in place and a blue line forms

Mobile antibodies with no hCG attached bind to another fixed site to show the test is working

90
Q

Describe testing for anabolic steroids

A

Anabolic steroids increase protein synthesis within cells which results in the build-up of cell tissue especially in the muscles.

anabolic steroids have a half life of 16 hours so the urine sample is analysed using gas chromatography

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