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A Level Biology OCR > 5.2 Excretion > Flashcards

5.2 Excretion Flashcards

1
Q

What is excretion?

A

The removal of metabolic waste from the body

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2
Q

What is metabolic waste?

A

A chemical produced by the metabolic processes in the cells, and can be toxic

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3
Q

Why does waste need to be excreted?

A

At high concentrations, waste can:

  • Inhibit enzyme activity
  • Become toxic
  • Affect pH
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4
Q

Name 3 excretory products.

A
  • Carbon Dioxide
  • Nitrogenous waste e.g. urea
  • Other compounds such as bile pigments in faeces
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5
Q

What is egestion?

A

The elimination of faeces from the body.

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6
Q

What are the main excretory organs?

A
  • Lungs
  • Liver
  • Kidneys
  • Skin
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7
Q

What do the lungs excrete?

A

Carbon dioxide

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8
Q

What is bilirubin?

A

A bile pigment

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9
Q

How is urea transported?

A

Dssolved in blood plasma

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10
Q

What is the main role of the kidneys?

A

To remove urea from the blood and make urine

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11
Q

How is the skin involved in excretion?

A

Sweat released through the skin contains salts, urea, water, uric acid and ammonia, which are all excretory products.

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12
Q

In what form is carbon dioxide transported in the blood?

A

Hydrogen carbonate ions

HCO 3-

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13
Q

Which enzyme promotes carbonic acid dissociation?

A

Carbonic anhydrase

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14
Q

How is carbonic acid formed in erythrocytes?

A

Carbon dioxide + water > carbonic acid

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15
Q

Why is an acidic pH in red blood cells bad?

A

It changes the tertiary structure of haemoglobin, reducing its affinity for oxygen (haemoglobinic acid)

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16
Q

What happens to carbon dioxide that is not converted to hydrogencarbonate ions?

A

It combines directly with haemoglobin, forming carbaminohaemoglobin.

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17
Q

What happens if the blood pH drops a small amount?

A

Change is detected by the respiratory centre in medulla oblongata, which makes breathing rate increase to remove the excess carbon dioxide (CO2 causes more H+ to be produced)

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18
Q

What is respiratory acidosis?

A

When blood pH drops below 7.35 and can cause headaches, confusion etc.

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19
Q

Urea is less _____ and less ______ than ammonia

A

Toxic and soluble

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20
Q

Why does the body not excrete excess amino acids?

A

The body can’t store them, and it would be wasteful to excrete them without releasing their energy

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21
Q

What is a hepatocyte?

A

A specialised liver cell

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22
Q

What is the function of the hepatic artery?

A

To provide oxygenated blood for aerobic respiration in hepatocytes.

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23
Q

What is the function of the hepatic portal vein?

A

To take deoxygenated, digestive product rich blood from the digestive system into the liver.

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24
Q

What is bile?

A

Bile is a secretion from the liver which has functions in digestion (emulsifies lipids, neutralises stomach acid).

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25
Bile is made in the _____ and stored in the _____.
Made in liver, stored in gall bladder.
26
What is the function of the bile duct?
To carry bile from the liver to the gall bladder.
27
How are bile pigments made?
They are produced by the breakdown of red blood cells in the liver
28
Why do hepatocytes have loads of peroxisomes?
Peroxisomes contain powerful enzymes which breakdown toxins and poisons
29
Where is glycogen stored?
The liver
30
What does a Kuppfer cell do?
It’s a specialised macrophage which breaks down old red blood cells
31
What is the livers main roles?
Breakdown of excess amino acids and detoxification
32
Why must nitrogenous substances be removed from the body?
They can’t be stored, and in excess they can be damaging
33
What is deanimation?
The removal of the nitrogen containing amino group from an amino acid making ammonia and organic keto acid
34
What is the use of organic keto acid?
They can be respired to make ATP, or converted to carbohydrates and stored as glycogen
35
What is urea made of?
Ammonia + Carbon dioxide
36
What part of the ornithine cycle occurs in the mitochondria?
Ornithine> Citruline
37
Why can’t ammonia be excreted directly?
It’s too toxic and soluble
38
What is detoxification?
The breakdown of harmful substances into less harmful compounds that can be excreted
39
How is ethanol detoxified in the liver?
Ethanol> Ethanal> Acetic acid
40
What is liver cirrhosis?
Excess alcohol causes liver cells to die and scar tissue blocks blood flow
41
Why must paracetamol be broken down?
An excess amount in the blood can lead to liver and kidney failure
42
Why must excess insulin be broken down?
In excess it can cause problems with blood sugar
43
Where in the digestive system does the hepatic portal vein bring blood from?
Small intestine
44
What are liver lobules?
Cylindrical structures made of hepatocytes that are arranged in rows, radiating from the centre outwards.
45
What connects the hepatic artery and hepatic portal vein to the central vein?
Capillaries called sinusoids
46
How is the bile duct connected to the central vein?
Canalculi tubes
47
What is the main function of the kidney?
To excrete waste products from the body, e.g. urea
48
How does blood enter the kidney?
The renal artery
49
From outwards to inwards, what is the kidney structure?
Renal capsule, cortex, medulla, pelvis
50
What are nephrons?
Long tubules with a bundle of capillaries
51
Where does ultrafiltration take place?
Glomerulus and Bowmans capsule
52
What is the difference between the afferent and efferent arteriole?
Afferent- takes blood to the glomerulus | Efferent- takes blood away from glomerulus
53
Why does the efferent arteriole have a smaller diameter than the afferent arteriole?
To increase the pressure, which forces liquid and molecules out of the capillary and into the Bowmans capsule
54
What layers must a molecule pass through to get into Bowmans capsule?
The capillary endothelium, the basement membrane, and the podocyte/Bowmans capsule epithelium
55
Why is the proximal convoluted tubule convoluted?
To increase the surface area for diffusion
56
Where does selective reabsorption take place?
Proximal CT, Loop of Henle, Distal CT, collecting duct
57
What is completely selectively reabsorbed into the blood from the glomerular filtrate?
Glucose and amino acids
58
What is mostly reabsorbed (but dependant on conditions)?
Water and ions
59
What is reabsorbed in the Proximal convoluted tubule?
Most water, and all glucose and amino acids
60
How does selective reabsorption of glucose and amino acids work?
Na+ pumped out of cell, then diffuse back in with cotransport protein which brings back glucose and amino acids
61
What is the purpose of the loop of Henle?
To decrease the water potential of the tissue fluid in medulla, by removal of water and addition of ions
62
What happens in the descending limb of loop of Henle?
Water is removed by osmosis, and Na+ and Cl- diffuse in
63
What happens in the ascending limb of the loop of Henle?
Na+ and Cl- pumped out
64
What happens in the distal convoluted tubule?
K+ pumped in by active transport
65
What does ADH do?
Increase the collecting ducts permeability to water by aquaporins, so more water is reabsorbed.
66
What happens in the collecting duct?
Water gradually lost to decrease the water potential, but it remains above that of the surrounding tissue (allowing max water to be reabsorbed)
67
What is the equation for deamination?
Amino acid + Oxygen > Keto acid + Ammonia
68
What does the ornithine cycle require to start?
ATP and Carbon Dioxide
69
What is the equation for the formation of urea?
Ammonia + Carbon Dioxide > Urea + Water
70
What is the equation for the reaction that catalase catalyses?
Hydrogen peroxide > Water + Oxygen
71
Where does detoxification occur in hepatocytes?
The smooth endoplasmic reticulum
72
What enzyme catalyses ethanol > ethanal ?
Ethanol dehydrogenase
73
What enzyme catalyses ethanal > ethanoic acid?
Ethanal dehydrogenase
74
What are fenestrations?
Pores between capillary endothelium
75
What is osmoregulation?
The control of water potential in the body, by controlling salt and water levels
76
Where is ADH secreted from?
Posterior lobe of pituitary gland
77
Where are osmoreceptors found?
Hypothalamus
78
What is hypertension?
High blood pressure
79
What is acute kidney failure?
Fast development, short acting, easily treatable
80
What is chronic kidney failure?
Slow developing, long acting, hard to treat
81
What are the treatments for kidney failure?
Haemodialysis, peritoneal dialysis, kidney transplant
82
What is the peritoneum?
The layer of tissue lining the abdominal cavity
83
What do pregnancy tests test for?
HCG
84
Osmoregulation is an example of _________ feedback.
Negative
85
In haemodialysis, where is blood added back to the body?
Vein
86
Describe peritoneal dialysis.
- Dialysis fluid put into body through catheter and left in peritoneal cavity - Takes around an hour, happens multiple times a day
87
How do pregnancy tests work?
Monoclonal antibodies with blue bead test for HCG in urine
88
What 4 ways are the cells lining the proximal convoluted tubule specialised?
- Plasma membrane is highly folded to form microvilli - Cotransport proteins are in the plasma membrane - Membrane close to the capillary has microvilli and Na/K pumps - Many mitochondria
89
Which part of the nephron is impermeable to water?
Ascending loop of Henle
90
What mechanism does the loop of Henle create?
The countercurrent multiplier mechanism
91
What does the countercurrent multiplier mechanism do?
Helps to reabsorb water back into the blood
92
What are osmoreceptors?
Receptor cells in hypothalamus which monitor the water potential of the blood
93
What is water potential?
The tendency of water to move from one place to another.
94
What is the effector to control the body's water content?
The kidneys
95
What are aquaporins?
Vesicles containing water permeable channels
96
How does the cell membrane remove water permeable channels in the collecting duct?
It folds in on itself to create more new vesicles that remove water permeable channels.

A Level Biology OCR (28 decks)

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