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A-Level Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis?

A

Maintaining a constant internal environment

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2
Q

What does homeostasis control?

A 
Water levels (osmoregulation)
Tissue fluid
O2 levels
Blood sugar levels
Composition of blood
Temperature (thermoregulation)
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3
Q

Explain why the control + maintenance of internal conditions are important for an organism

A

Temperature = stops proteins denaturing = enzymes needed for reactions = eg. respiration
In/decrease rate of diffusion
Sugar levels = water potential = lysis of cells
Respiration
O2 levels = respiration

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4
Q

What is thermoregulation?

A

The control of internal body temperature

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5
Q

What is an ectotherm?

A

Maintain a proportion of their heat from outside sources

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6
Q

What is an example of an ectotherm?

A

Lizard + snakes

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7
Q

What is an endotherm?

A

Derive heat from source of metabolic activities inside their body

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8
Q

What is an example of an exotherm?

A

Mammals + birds

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9
Q

What is the hypothalamus?

A

Control unit for most responses

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10
Q

What does the hypothalamus link?

A

N.S to endocrine system via pituitary gland

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11
Q

What is the response to a decrease in temperature?

A

Vasoconstriction of arterioles
Shivering
Piloerection
+ metabolism

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12
Q

What is the response to an increase in temperature?

A

Vasodilation
Sweating
Pilorelaxation
- metabolism

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13
Q

What is a negative feedback loop?

A

Initiating corrective mechanisms whenever the internal environment deviates from its normal or acceptable levels

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14
Q

What is a positive feedback loop?

A

Deviation from normal conditions is amplified, leading to further deviation

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15
Q

What are examples of negative feedback mechanisms in the body?

A

Temperature control
Blood sugar levels control
Changes in heart rate

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16
Q

What are examples of positive feedback mechanisms in the body?

A

Blood clotting
Oxytocin causes more contractions
Adrenaline - HR increases till stimuli removed
Disease - increases temperature

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17
Q

What is osmoregulation?

A

The homeostasis control of water potential in the blood

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18
Q

What is the role of the kidney?

A

Control the vol of water in the body
Clean the blood
Remove any unwanted water, waste or toxins

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19
Q

What is the nephron?

A

The filtering unit of the kidney, which performs the jobs of filtering + fluid balance

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20
Q

What are the processes of osmoregulation?

A

Ultrafiltration
Selective reabsorption
Counter current multiplier
Reabsorption

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21
Q

Where does ultrafiltration happen?

A

Glomerulus

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22
Q

What is ultrafiltration as a result of?

A

Hydrostatic pressure

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23
Q

Which is bigger the efferent or afferent arteriole?

A

Afferent

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24
Q

What does the capillaries merge to form?

A

Efferent arteriole

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25
Q

Describe ultrafiltration

A

Afferent arteriole is wider than efferent
Hydrostatic pressure builds
Causes ultrafiltration through pores of membrane

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26
Q

What moves out for ultrafiltration?

A

H2O
C6H12O6
Urea
Mineral ions

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27
Q

What remains in for ultrafiltration?

A

RBCs

Proteins

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28
Q

What is the movement of filtrate restricted in the glomerulus by?

A 
Capillary epithelial cells
Connective tissues
Epithelial cells of renal capsule
Low hydrostatic pressure
Low water potential of blood
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29
Q

What are the main adaptions of Bowman’s capsule to combat barriers of filtrate movement in glomerulus?

A

Podocytes (specialised cells)

Gaps in epithelial cells

30
Q

What is the importance of podocytes?

A

Attach to capillaries to form gaps = shorter diffusion pathway

31
Q

What is the importance of gaps in epithelial cells?

A

Easy to pass through = shorter diffusion pathway

32
Q

What is selective reabsorption?

A

Reabsorption of certain molecules back into the blood?

33
Q

How does selective reabsorption happen?

A

Co-transport

34
Q

Where does co-transport happen in reabsorption?

A

Proximal convoluted tubule

35
Q

Where does counter current mechanism happen in reabsorption?

A

Loop of Henle

36
Q

Where does anti diuretic hormone happen in reabsorption?

A

Collecting duct

37
Q

Describe co-transport

A

Na+ actively pumped out of cell to lumen from NaK pump
Higher conc inside lumen so lower conc inside cell
Na+ facilitatedly diffuses back in via another carrier protein
Coupled movement with glucose/amino acid
Molecule conc increases
Molecules diffuse into blood alongside some water

38
Q

Describe the medulla

A

Inner region made up of loops of Henle, collecting ducts + blood vessels

39
Q

Describe convoluted tubule

A

Series of loops surrounded by blood capillaries

Walls made up of epithelial cells with microvilli

40
Q

Describe ureter

A

Tube that carries urine to the bladder

41
Q

Describe glomerulus

A

Many branched knot of capillaries from which fluid is forced out of the blood

42
Q

Describe renal vein

A

Returns blood to heart via vena cava

43
Q

Describe cortex

A

Outer region made up of renal capsules (Bowman’s capsule), convoluted tubules + blood vessels

44
Q

Describe Loop of Henle

A

Long hairpin loop extending from cortex + into medulla

45
Q

Describe Bowman’s capsule

A

Cup shaped structure at the start of nephron, surrounding a mass of blood capillaries (glomerulus)

46
Q

Describe renal artery

A

Supplies kidney with blood from heart via aorta

47
Q

Describe collecting duct

A

Tube with several distal convoluted tubules from several nephrons empty
Increases width as it empties into the pelvis of the kidney

48
Q

How many regions does the loop of Henle of have?

A

2

49
Q

What are the 2 regions of the loop of Henle called?

A

Descending limb

Ascending limb

50
Q

What does the 2 regions of the loop of Henle allow?

A

Allows salts to be transferred from descending to ascending limb

51
Q

What is the arrangement called that is involved in the reabsorption of water?

A

Counter-current multiplies system

52
Q

Describe the descending limb

A

Into the medulla
Narrow
Thin walls
Highly permeable to H2O

53
Q

Describe the ascending limb

A

Back to cortex
Wider
Thicker
Impermeable to H2O

54
Q

What happens at the descending limb?

A

H2O leaves via osmosis

+ enters the blood

55
Q

What helps H2O to leave from the descending limb?

A

Low H2O potential surrounding it

56
Q

What is happening at the same time in the loop of Henle, whilst the descending limb happens?

A

Na+ is actively transported out of the ascending limb into the interstitial region

57
Q

What happens at the ascending limb?

A

Ascending = impermeable = H2O cannot leave

58
Q

Why is there a high H2O potential in the distal convoluted tubule?

A

To form H2O potential gradient = H20 can move out of collecting duct + into the blood

59
Q

Why can H2O move out of the collecting duct?

A

As its walls vary in permeability

60
Q

Where does ultrafiltration happen?

A

Glomerulus

61
Q

Where does selective reabsorption happen?

A

Proximal convoluted tubule

62
Q

Where does the counter current multiplier happen?

A

Loop of Henle

63
Q

Where does reabsorption into the blood happen?

A

Distal convoluted tubule

Collecting duct

64
Q

Explain why your water levels vary

A 
External temperature
Exercise
Fluid intake
Salt intake
Diet Drug intake 
Medication
65
Q

Which hormone controls H2O?

A

ADH

66
Q

Where is ADH secreted from?

A

Posterior pituitary gland

67
Q

What does ADH do?

A

Increase permeability of DCT + CD

= concentrates the urine

68
Q

What happens when you are dehydrated?

A

Decrease ψ of blood
Osmoreceptor cells in hypothalamus detect change
Cells lose water = shrivel
Stimulate neurosecretory cells in hypothalamus
Increased AP’s to posterior pituitary gland
ADH secreted into blood
Travels in blood to DCT + CD
Permeability increases
More H2O reabsorbed into blood

69
Q

What when you have too much water?

A 
Increase ψ of blood
Osmoreceptors detect change
Gain H2O = swell
Doesn't stimulate neurosecretory cells
Decreased AP's to posterior pituitary gland
ADH not secreted 
Permeability decreases at DCT + CD
Less water reabsorbed
70
Q

How does ADH actually work?

A 
Binds to complementary receptors on DCT + CD
Activates enzyme phosphorylase 
Aquaporin fuses with membrane
Increases permeability
Water leaves CD
Increases ψ gradient
Concentrated urine

A-Level Biology (21 decks)

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