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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

What is the metabolic function of the liver?

A
  • controls blood glucose, amino acids and lipid levels
  • synthesis of bile, plasma proteins and cholesterol
  • synthesis of red blood cells within a fetus
  • storage of vitamins A,D and B12
  • storage of iron and glycogen
  • detoxification of drugs and alcohol
  • breakdown of hormones
  • destruction of red blood cells
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2
Q

What are destroyed red blood cells turned into?

A

forms bilirubin which creates bile

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3
Q

How is hydrogen peroxide detoxified?

A
  • done by the enzyme catalase
  • is converted to oxygen and water
  • turnover of 5 million per second
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4
Q

How are drugs detoxified?

A
  • done by the enzyme cytochrome p450
  • breakdown of recreational drugs e.g. cocaine
  • cytochrome p450 is also used in other metabolic reactions e.g. electron transport during respiration
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5
Q

How is alcohol detoxified?

A

ethanol —> ethanal —> ethanoate acid —> acetyl CoA (for respiration)

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6
Q

How is ethanol turned into ethanal?

A
  • by ethanol dehydrogenase
  • removes 2 hydrogen ions which then creates reduced NAD
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7
Q

How is ethanal turned into ethanoate acid?

A
  • ethanal dehydrogenase
  • removes 2 hydrogen ions which then creates reduced NAD
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8
Q

What does the detoxification of alcohol mean?

A
  • Due to the removal of hydrogen ions from ethanol and ethanal, the krebs cycle cannot take place
  • Fatty acids within the krebs cycle are converted back to lipids and stored in the hepatocytes
  • causes an enlarged liver and conditions such as cirrhosis
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9
Q

How is urea formed?

A

amino acids —> ammonia and keto acid —> urea

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10
Q

How are amino acids turned into ammonia and keto acid?

A
  • addition of oxygen
  • deamination
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11
Q

Describe deamination

A
  • removes amino acids by adding oxygen
  • creates ammonia and keto acid
  • keto acid is converted into pyruvate and enters the link reaction or enters directly at the krebs cycle
  • ammonia is immediately converted into urea as it is very soluble and highly toxic
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12
Q

Describe the 2 problems with ammonia

A
  • very soluble
  • toxic
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13
Q

Why is ammonia being highly soluble an issue?

A

Interferes with osmosis

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14
Q

Describe the ornithine cycle

A
  • ammonia is combine with CO2 to produce urea
  • ammonia and CO2 combine with the amino acid ornithine to produce citrulline
  • citrulline is converted to arginine by more addition of ammonia
  • arginine is then re-converted to ornithine by the removal of urea
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15
Q

What is the outer region of the kidney called?

A

The cortex

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16
Q

What is the inner region of the kidney called?

A

The medulla

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17
Q

What is the centre of the kidney called?

A

The pelvis

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18
Q

What is the role of the kidney?

A

Remove waste products from the blood and produce urine

19
Q

Where does the urine go after it has been produced in the Kidney?

A

Passes out of the kidney through the ureter and is stored in the bladder

20
Q

What are the majority of tubules called in kidneys?

A

Nephrons

21
Q

How many nephrons are there in each kidney?

A

1 million

22
Q

Describe the journey/shape of nephrons

A
  • starts in the cortex at the bowman’s capsule
  • remainder of nephron coiled in a tubule that passes through the cortex forming a loop down into the medulla and back into the cortex
  • then joins the collecting duct which passes back down into the medulla
23
Q

What is the bowman’s capsule?

A

A cup-shaped structure where selective reabsorption takes place

24
Q

What are the three layers of the barrier within the bowman’s capsule?

A
  • The endothelium of the capillary
  • The basement membrane
  • The epithelial cells of the bowman’s capsule
25
Q

Describe the endothelium of the capillary

A
  • Has narrow gaps between the cells
  • cells also contain pores (fenestrations)
26
Q

What is the purpose of the gaps between cells within the endothelium of the capillary?

A

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

27
Q

Describe the basement membrane

A
  • fine mesh of collagen fibres and glycoproteins
    -acts as filter to prevent the passage of molecules with a relative molecular mass greater than 69,000
  • means most proteins are held in the capillaries of the glomerulus
28
Q

Describe the epithelial cells of the Bowman’s capsule

A
  • called podocytes
  • have a specialised shapes
  • many finger like projections (called major processes)
  • major processes there are minor processes - hold the cells away from the endothelium of the capillary
  • ensures gaps between the cells
  • fluid from the blood can pass between the gaps into the lumen of the bowman’s capsule
29
Q

Why is there a high hydrostatic pressure within the glomerulus?

A

The afferent arterioles have a larger diameter than efferent arteriole meaning there is more blood flowing into the glomerulus than out

30
Q

What does the high hydrostatic pressure within the glomerulus cause?

A

Causes small parts of the blood to be passes out of the glomerulus e.g. water, amino acids, glucose, urea and inorganic mineral ions

31
Q

What happens to the small parts of the blood passed into the glomerulus?

A

They are passed into the lumen after going through the three different membranes within the glomerulus - the endothelium of the capillary, the basement membrane and the epithelial of the bowman’s capsule

32
Q

Why does some water move back into the blood during ultrafiltration?

A

There is a low oncotic pressure - the high water potential in the bowman’s capsule and low water potential in the glomerulus causes the water to move by osmosis back into the glomerulus

33
Q

Describe the process of selective reabsorption

A
  • sodium is moved out of the cells lining the tubule by active transport via a sodium potassium ion pump
  • Concentration of sodium ions in the cytoplasm decreases creating a concentration gradient with the tubule fluid
  • Sodium ions co-transport amino acids or glucose as they diffuse into a cell via a co-transport protein within the plasma membrane
  • water moves into the cell by osmosis
34
Q

How do substances from the blood move to the tissue fluid and blood?

A

They move by facilitated diffusion however if there is an equilibrium then they will be moved by active transport - this causes water to follow by osmosis

35
Q

How are small proteins reabsorbed into the blood?

A

Endocytosis

36
Q

What are the adaptations of the proximal convoluted tubule for selective reabsorption?

A
  • folded to create microvilli and increase surface area for reabsorption (closer to the tubule fluid)
  • special co-transport proteins in the membrane to transport glucose and amino acids
  • the membrane is in contact with tissue fluid for small diffusion distances
  • cytoplasm of the cells have many mitochondria as ATP is needed for active transport of sodium ions
37
Q

Describe what happens within the loop of henle

A
  • sodium and chloride ions move out of the ascending limb by active transport
  • this lowers the water potential in surrounding tissue fluid
  • this means water will leave the descending limb by osmosis
  • Sodium and chloride ions diffuse out the descending limb by facilitated diffusion
  • This is then repeated lower down the descending limb
  • By the bottom of the descending limb, the tubule fluid is extremely concentrated (lower water potential)
  • This means that at the bottom of the ascending limb, sodium and chloride ions are moved out by facilitated diffusion
  • Once equilibrium is reached, more chloride ions are moved out by active transport (process is repeated)
38
Q

What does a longer loop of henle mean?

A

More sodium and chloride ions are pumped out of the ascending limb into the medulla meaning a build up of a concentration gradient

39
Q

What is active transport used for in the loop of henle?

A

Used at the distal convoluted tubule to adjust concentrations of various mineral ions

40
Q

Define osmoregulation

A

Control of water potential in the body

41
Q

Why is it important to control water balance?

A

Prevents water entering and leaving cells and causing lysis or crenation

42
Q

When does the body conserve more water?

A

on a hot day

43
Q

When does the body conserve less water?

A

On a cold day

A-level Biology (23 decks)

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