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Biology > Homeostasis - A2 > Flashcards

Homeostasis - A2 Flashcards

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1
Q

Define homeostasis.

A

The maintenance of a constant internal environment.

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2
Q

Why is homeostasis important in living things?

A

so internal cells maintain at optimum temperature to function normally (enzymes controlling biochemical reactions etc)

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3
Q

Why is it important to maintain a stable core temperature?

A
  • maintains stable rate of enzyme controlled reaction + prevent damage to membrane
  • if temps too low, enzymes won’t have sufficient kinetic energy
  • temps too high = denatured enzyme
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4
Q

Why is it important to maintain stable blood PH?

A
  • stable rate of enzyme controlled reaction (optimum conditions for proteins)
  • acid PH = H+ ions interact with H-bonds and ionic bonds, altering tertiary structure of protein. Active site shape changes = no enzyme substrate complexes.
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5
Q

Why is it important that blood glucose concentrations stay stable?

A
  • maintains constant blood water potential: prevents osmotic lysis.
  • maintains constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions
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6
Q

Outline the stages involved in negative feedback in homeostasis.

A

Receptors detect deviation - coordinator - corrective mechanism by effector - receptors detect that conditions have returned to normal

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7
Q

Suggest why coordinators may analyse inputs from several receptors before sending a signal?

A
  • receptors may send conflicting information
  • optimum response may require multiple types of effector
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8
Q

Why is there a lag time between hormone production and response by an effector?

A

Takes time to…
- produce hormone
- transport hormone to blood
- cause required change to the target protein

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9
Q

What factors affect blood glucose concentration?

A
  • amount of carbs digested from diet
  • rate of glycogenolysis
  • rate of gluconeogenesis
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10
Q

Define glycogenesis.

A

Liver converts glucose into the storage polymer glycogen.

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11
Q

Define glycogenolysis.

A

Liver hydrolyses glycogen into glucose which can diffuse into the blood.

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12
Q

Define gluconeogenesis.

A

Liver converts glycerol and amino acids into glucose.

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13
Q

Outline the role of glucagon when blood glucose concentration reduces.

A
  • ‘a’ cells in Islets of Langerhans in pancreas detect decrease and secrete glucagon into bloodstream
  • glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
  • glucose diffuses from liver into bloodstream
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14
Q

Outline the role of adrenaline when blood glucose concentration decreases.

A
  • adrenal glands produce adrenaline, it binds to surface receptors on liver cells and activates enzymes for glycogenolysis.
  • glucose diffuses from liver into bloodstream
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15
Q

Outline what happens when blood glucose concentration increases.

A
  • ‘b’ cells in Islets of Langerhans in pancreas detect increase and secrete insulin into bloodstream
  • insulin binds to surface receptors on target cells to…
  • increase cellular glucose uptake
  • activate enzymes for glycogenesis
  • stimulate adipose tissue to synthesis fat
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16
Q

Explain the action of glucagon.

A
  • works by activating enzymes
  • glycogen to glucose/glycogenolysis
  • gluconeogenesis
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17
Q

How does adrenaline inhibit glycogenesis?

A
  • adenylate cyclase activated
  • cAMP produced / second messenger produced
  • so gluconeogenesis occurs / glycogenesis inhibited
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18
Q

Describe how insulin leads to a decrease in blood glucose?

A
  • increases permeability of cells to glucose
  • increases glucose concentration gradient
  • triggers inhibition of enzymes for glycogenolysis
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19
Q

How does insulin increase permeability of cells to glucose?

A
  • increase number of glucose carrier proteins
  • triggers conformational change which opens glucose carrier proteins
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20
Q

How does insulin increase the glucose concentration gradient?

A
  • activates enzyme for glycogenesis in liver and muscles
  • stimulates fat synthesis in adipose tissue
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21
Q

Use the secondary messenger model to explain how glucagon and adrenaline work.

A
  • hormone receptor complexes form
  • conformational change to receptor activates G-protein
  • activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)
  • cAMP activates protein kinase A pathway
  • results in glycogenolysis
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22
Q

Explain the cause of type 1 diabetes and how it can be controlled.

A
  • body cannot produce insulin eg due to autoimmune response which attacks ‘b’ cells of Islets and Langerhans
  • treated by injecting insulin
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23
Q

Explain the causes of type 2 diabetes and how it can be controlled.

A
  • glycoprotein receptors are damaged or become less responsive to insulin
  • strong positive correlation with poor diet/obesity
  • treat by controlling diet and exercise regime
24
Q

Name some signs and symptoms of diabetes.

A
  • high blood glucose concentration
  • glucose in urine due to excess water in blood
  • polyuria
  • poor vision due to osmotic loss of water in eye lens
  • tiredness due to less uptake of glucose to muscle cells
  • sudden weight loss
25
Q

Suggest how a student could produce a required concentration of glucose from a stock solution.

A

volume of stock solution
=
required concentration x volume needed
÷
concentration of stock solution

26
Q

How would you work out the volume of distilled water in the glucose experiment?

A

final volume needed - how volume of stock solution

27
Q

Outline how colorimetry could be used to identify the glucose concentration in a sample.

A
  • benedict’s tests on solutions of known glucose concentration
  • use colorimeter to record absorbance
  • plot calibration curve: absorbance (y axis), glucose concentration (x axis)
  • benedict’s test on unknown sample. Use calibration curve to read glucose concentration and its absorbance value.
28
Q

Define osmoregulation.

A

Control of blood water potential via homeostatic mechanisms.

29
Q

Describe the gross structure of a kidney.
(7 marks)

A

Fibrous capsule - protects the kidney
Cortex - outer region consists of Bowman’s capsules, convoluted tubules, blood vessels
Medulla - inner region consists of collecting ducts, loops of Henle, blood vessels
Renal pelvis - cavity collects urine in ureter
Ureter - tube carrier urine into bladder
Renal artery - supplies kidney with oxygenated blood
Renal vein - returns deoxygenated blood from kidney to heart.

30
Q

Describe the structure of a nephron.
(5 marks)

A

Bowman’s capsule - at start of nephron, cup shaped, surrounds glomerulus, inner layer of podocytes
Proximal convoluted tubule (PCT) - series of loops surrounded by capillaries, walls made of epithelial cells with microvilli.
Loop of Henle - hairpin loop extends from cortex into medulla
Distal convoluted tubule - similar to PCT but fewer capillaries
Collecting duct - DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney.

31
Q

How is urea removed from the blood?

A
  • hydrostatic pressure
  • causes ultrafiltration at Bowman’s Capsule
  • through basement membrane/connective tissue
  • enables by small size of urea molecule
32
Q

Describe how ultrafiltration produces glomerular filtrate.

A
  • blood pressure / high hydrostatic pressure in glomerulus
  • forces small molecule out eg. glucose against osmotic gradient
  • pass through basement membrane / membrane acts as filter
  • protein too large to go through so stays behind
  • presence of pores in capillaries / presence of podocytes
33
Q

How are the Bowman’s capsule adapted for ultrafiltration?

A
  • fenestrations between epithelial cells of capillaries
  • fluid can pass between and under folded membrane of podocytes
34
Q

What happens during selective reabsorption and where does it occur?

A
  • useful molecules from glomerular filtrate eg. glucose are reabsorbed into the blood
  • occurs in proximal convoluted tubule
35
Q

Outline the transport processes in selective reabsorption.

A
  • Glucose from glomerular filtrate into cells lining proximal convoluted tube vie CO-TRANSPORT with Na+ ions.
  • Then from PCT to intercellular spaces via ACTIVE TRANSPORT.
  • From intercellular spaces to blood capillary lining tubule via DIFFUSION.
36
Q

How are cells in the PCT adapted for selective reabsorption?

A

Microvilli - higher surface area for co-transporter proteins
Many mitochondria - ATP for active transport of glucose into intercellular spaces
Folded basil membrane - larger surface area.

37
Q

What happens in the loop of Henle?

A
  • Active transport of Na+ and Cl- out of ascending limb
  • Water potential of interstitial fluid decreases
  • Osmosis of water out of descending limb (ascending limb is impermeable to water)
  • Water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of ascending limb. (results in mainly H2O)
  • enables good nutrients to re-enter blood.
38
Q

Explain the role of the distal convoluted tubule.

A

Reabsorption
- of water via osmosis
- of ions via active transport
Permeability of walls is determined by actions of hormones.

39
Q

Explain the role of the collecting duct.

A

Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaproins.

40
Q

Explain why it is important to maintain a Na+ gradient.

A

Counter-current multiplier: filtrate in collecting ducts is always beside an area of interstitial fluid that has lower water potential.
Maintains water potential gradient for maximum reabsorption of water.

41
Q

Explain the role of the hypothalamus in osmoregulation.

A
  • Osmosis of water out of osmoreceptors in hypothalamus cause them to shrink
  • This triggers hypothalamus to produce more antidiuretic hormone (ADH)
42
Q

Explain the role of the posterior pituitary gland in osmoregulation.

A

Stores and secretes the ADH produced by the hypothalamus.

43
Q

Explain the role of ADH in osmoregulation.

A

Make cells lining collecting duct more permeable to water:
- binds to receptors - activates phosphorylase causing vesicles with aquaporins on cell membrane to fuse with cell surface membrane
Makes cells lining collecting duct more permeable to urea:
- water potential in interstitial fluid decreases
- more water reabsorbed = more concentrated urine.

44
Q

Define endotherm.

A

Animals that regulate body temperatures from within the body (warm blooded)
- by both physiological and behavioural means.

45
Q

Define ectotherm.

A

Reptiles/animals that rely primarily on external environment to regulate body temperatures.
- by behavioural means only

46
Q

Name 4 ways we gain and lose heat.

A

CONDUCTION - heat transferred from hotter object to colder when in contact.
RADIATION - transfers from body to cooler object when not in contact
CONVECTION - warm air pockets replaces by cooler ones speed up heat loss by conduction and radiation
EVAPOURATION - change of liquid to vapour, removes heat from skin.

47
Q

Name and explain the 2 parts of the hypothalamus in the thermoregulatory centre in the brain.

A

Heat gain centre - activated by fall in blood temperature to increase blood temperature
Heat loss centre - activated by rise in blood temperature to decrease blood temperature.

48
Q

What do the thermoreceptors do?

A

Blood passes through the brain (core temperature) and skin (external temperature) and receptors pick up on temperature of blood.

49
Q

Regulation of temperature methods for conserving heat in a cold environement.

A

Vasoconstriction: reduced volume of blood to skin so less heat lost through radiation
Raising of hair: via erector muscles in skin, trapping layer of still air as insulator next to skin
Decrease sweating: reduces evaporation
Behavioural mechanisms: sheltering from wind, staying in sun, huddling

50
Q

Generating heat in cold environments.

A

Increased metabolic rates: respiration caused by adrenaline etc
Shivering: involuntary rhythmic muscle contractions that produce metabolic heat

51
Q

Losing heat in response to a warm environment.

A

Vasodilation: heat radiated from body via blood flow to skin surface
Increased sweating: evaporation of water from skin in form of heat (latent heat), reducing core temperature
Lowering of body hair - erector muscles relax in skin, reducing layer of insulation, more heat lost to environment
Behavioural mechanisms - avoiding heat of day, sheltering in burrows or shade to prevent heat from rising.

52
Q

Explain the effects of sweating or panting on temperature control?

A
  • evaporation of water from lining of mouth or skin
  • heat transferred from blood
53
Q

Describe the role of glycogen formation and its role in lowering blood glucose.

A
  • glucose concentration in liver/cell falls
  • below that in blood/ higher in blood
  • creates/maintains glucose concentration gradient
  • glucose enters cells/leaves blood via facilitated diffusion via carrier protein
54
Q

Describe how blood glucose levels can be increased using hormones.

A
  • release of glucagon
  • leads to formation of glucose in liver cells
  • from non-carbohydrates / amino acids / fatty acids
55
Q

Explain how urea is concentrated in the filtrate.

A
  • reabsorption of water by osmosis
  • at the PCT / descending LoH
  • at the DCT (distal convoluted tubule) / CD
  • active transport of ions / glucose creates gradient
56
Q

Explain how ADH causes movement of water from the lumen to collecting duct.

A
  • ADH causes vesicles containing aquaporins to be inserted into membrane
  • water enters cell via aquaporins
  • by osmosis / diffusion down water potential gradient
  • from cell to capillary
  • via interstitial fluid / tissue fluid
57
Q

Describe the secondary messenger
model.

A
  • Adenylate cyclase activated / cAMP produced / second messenger produced;
  • Activates enzyme(s) (in cell);
  • (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;

Biology (27 decks)

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