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BIOLOGY PAPER 2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Internal environment is made up of tissue fluids that bathe each cell, supplying nutrients and remove wastes. what does maintaining these features at optimum level enable

A

-maintaining features of this fluid at the optimum level protects the cells from changes in the external environment
-giving organism a degree of independence

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2
Q

define homeostasis

A

maintenance of internal environment within restricted limits

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3
Q

what does homeostasis maintain

A

chemical make-up, volume and other features of blood and tissue fluid within restricted limits

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4
Q

what does homeostasis ensure

A

-cells of the body to experience constant conditions and function optimally
-cells are surrounded with tissue fluid which is regulated to maintain an environment that fluctuates around the optimum point for factors like water potential, temperature and pH

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5
Q

Explain how control mechanisms are coordinated

A
  • Positive feedback - deviation from optimum causes changes that result in further deviation from optimum. Small stimulus leads to large response.

Negative feedback - the change produced by the control system leads to a change that turns the system off and reduces deviation from the optimum

Control systems have many receptors and effectors. They often have two separate mechanisms for causing movement towards the optimum from different directions. This allows greater control. The coordinator analyses information from all receptors before taking action to ensure appropriate measures are taken.”

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6
Q

Compare thermoregulation in ectotherms and endotherms

A
  • ectotherms > gain heat from environment so their body temp fluctuates with that of environment > so they control their body temp by adapting their bhvr to external temp changes eg reptiles
  • endotherm > gain most of their heat from internal metabolic activities > body temp remains relatively constant despite external temp fluctuations. use bhvr to maintain constant body temp als use wide range of physiological mechanisms to regulate their temp
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7
Q

importance of homeostasis to temperature and blood pH

A

-enzymes and proteins (channel proteins) are sensitive to changes in pH and temp
-change to these factors reduce ROR of enzymes OR even denature them in sub-optimal conditions
-can prevent them to carry their roles effectively
-so maintaining a constant pH and temp = reactions take place at a suitable rate

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8
Q

Define negative feedback

A

Negative feedback occurs when the stimulus turns off the corrective measures and returns system to optimum level (avoiding overshoots)

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9
Q

Explain how negative feedback helps to control homeostatic processes

A

-Negative feedback has two separate mechanisms to regulate deviation from the optimum (one in each direction).
-Receptor detects deviation from optimum , information from receptors is coordinated and intruction given to an effector to bring about a response to return to optimum, negative feedback mechanism detects this change and brings about appropriate response

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10
Q

Explain how negative feedback mechanisms give a greater degree of control

A

The separate mechanisms to regulate deviation in either direction allow greater control because they are positive actions in both directions (rather than just allowing something to naturally return to normal)

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11
Q

Distinguish between negative feedback and positive feedback

A

Negative feedback causes corrective measures to be switched off when optimum has been restored whereas in positive feedback the corrective mechanism remains turned on and further deviation from optimum occurs.

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12
Q

what does changes in water potential of blood and tissue cause

A

-cells to shrink and expand (could even burst) due to water leaving entering via osmosis
-cells cannot operate normally

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13
Q

what does a constant blood glucose conc ensure

A

-constant water potential
-reliable source of glucose for respiration by cells

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14
Q

organisms with ability to maintain a constant internal environment are more likely what

A

-independent of changes in the external environment
-eg wider geographical range > greater chance of finding food, shelter etc

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15
Q

explain how control mechanisms work

A

-optimum point = point at which system works best. monitored by ….
-receptor = detects deviation from optimum point ( ie stimulus) and informs the ….
-coordinator = coordinates info from receptors and send info to…
-effector = muscle/gland that brings about changes to return system to optimum point. return to normality creates a ….
-feedback mechanism = receptors responds to stimulus created by change to system brought about by receptor

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16
Q

Describe how hormones work

A
  • produced in endocrine glands and secreted directly into the blood
  • carried in blood plasma to the target cells on which they act. Target cells have specific receptors complementary to the specific hormone
  • effective in low concentrations but have long lasting, widespread effects”
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17
Q

where are hormones produced

A

-produced in glands that directly secrete hormone into blood (endocrine glands)

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18
Q

where are hormones carried at

A

-blood plasma to target cells that have specific receptors on cell surface membrane complementary to specific hormone

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19
Q

effects of hormones

A

-effective in low conc
-widespread and long-lasting effects

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20
Q

which 2 hormones uses the second messenger model

A

-adrenaline
-glucagon

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21
Q

Describe the process that results in the hydrolysis of glycogen when
adrenaline is released.

(Explain the second messenger model of hormone action)

A

“Second messenger model is used for non lipid soluble hormones in order to get their ‘message’ into the cell.
e.g.adrenaline in regulation of blood glucose concentration.
- adrenaline binds to complementary protein receptor spanning cell surface membrane of liver cell
- causes protein to change shape on inside of membrane
- change in protein shape leads to activation of enzyme adenyl cyclase
- activated adenyl cyclase converts ATP to cyclic AMP (cAMP)
- cAMP acts as second messenger binding to, changing the shape of and therefore activating protein kinase (a-kinase)
- a-kinase hydrolyses glycogen to glucose which moves from the liver cell to the blood by facilitated diffusion”

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22
Q

what are islets of Langerhans

A

groups of hormone-producing cells

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23
Q

what cells are the liver made up of

A

hepatocytes

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24
Q

whats glycogenesis

A

glucose converted into glycogen

25
Q

whats glycogenolysis

A

breakdown of glycogen into gluclose

26
Q

whats gluconeogenesis

A

production of glucose from other sources eg carbohydrates

27
Q

what happens if conc of blood glucose rises too high

A

-lowers water potential of blood
creating osmotic problems

28
Q

factors that affect blood glucose conc

A

-diet > form of glucose absorbed following hydrolysis of other carbohydrates eg starch, maltose, lactose, sucrose
-Glycogenolysis
-Gluconeogenesis

29
Q

Most body cells have glycoprotein receptors on their cell-surface
membrane. Describe the results of insulin binding to these
receptors.

A

-Tertiary structure of the glucose carrier proteins changes and
causes them to open.
-more glucose move into cell via facilitated diffusion
-increase in no. of carrier proteins for glucose transport in cell surface membrane
-at low insulin conc, protein of which channel is made is part of membrane of vesicle
-rise in insulin conc, vesicle fuses with cell surface membrane, increasing the no. of glucose transport channels
-activation of enzyme for convert glucose into glycogen and fat

30
Q

how is blood glucose conc lowered in many ways

A

-increasing rate of absorption of glucose into cells,esp muscle
-increasing respiratory rate of cells > use up more glucose > increasing uptake of glucose from blood
-increasing rate of conversion of glucose into glycogen in cells of liver/muscle
-increasing rate of conversion of glucose to fat

31
Q

effect of blood glucose conc being lowered in many ways

A

-lowering of blood glucose conc causes B cells to reduce their secretion of insulin
-causing negative feedback

32
Q

glucagon and alpha cells of pancreas

A

-attaching to specific protein receptors on cell surface membrane of liver cells
-activating enzyme that converts glycogen to glucose
-activating enzymes involved in conversion of a.a and glycerol not glucose (gluconeogenesis)

33
Q

overall effect of glucagon and alpha cells on the pancreas

A

-increase conc of glucose in blood and return to optimum conc
-raising of blood glucose conc causes alpha cells to reduce secretion of glucagon
- = negative feedback

34
Q

Explain the role of the pancreas and liver in regulating blood glucose

A

Pancreas produces insulin (from beta cells in the Islets of Langerhans) and glucagon (from the alpha cells of the Islets of Langerhans)
- Glycogenesis - glucose –> glycogen. High blood glucose concentration, glucose taken into hepatocytes and converted to glycogen
- Glycogenolysis - glycogen –> glucose. Low blood glucose concentration, glycogen hydrolysed to glucose and diffuses back into blood
- Gluconeogenesis - production of glucose from sources other than carbohydrate. Glycerol and amino acids used to produce glucose when glycogen supply is exhausted”

35
Q

Describe the factors that influence blood glucose concentration

A
  • Diet: glucose from the hydrolysis of other carbohydrates
  • Glycogenolysis
  • Gluconeogenesis”
36
Q

role of adrenaline in regulating the blood glucose level

A

-produced in adrenal glands in tims o excitement / stress
-attaching to protein receptors on cell surface membrane of target cells
-activating enzymes that causes hydrolysis of glycogen to glucose in liver (glycogenolysis)

37
Q

Explain the role of insulin in regulating blood glucose concentration

A

-Insulin binds to complementary receptor on carrier protein
-Change in tertiary structure and therefore shape of carrier protein allowing glucose to pass through
-Vesicles containing glucose carrier proteins fuse with membrane and increase the number of carriers
-Activation of enzymes that convert glucose to glycogen and fat
This causes blood glucose concentration to decrease due to:
- Increased glucose into cells
-Increased rate of respiration
-Increased glycogenesis
-Increased conversion of glucose to fat”

38
Q

whats diabetes

A

metabolic disorder caused by inability to control blood glucose conc due to lack of insulin or loss of responsiveness to insulin

39
Q

2 forms of diabetes

A

-type I
-type II

40
Q

whats type I diabetes

A

-insulin dependent
-body unable to produce insulin
-may be due to result of an autoimmune response whereby body’s immune system attacks its own cells )B cells of the islets of Langerhans)
-develops quickly
-obvious signs and symptoms

41
Q

Whats type II diabetes

A

-insulin independent
-due to glycoprotein receptors on body cells being lost / losing their responsiveness to insulin
-can also be due to inadequate supply of insulin from pancreas
-usually develops with people + 40 yrs
-obesity and poor diet = risk factor
-less serve + unnoticeable symptoms

42
Q

control of type I diabetes

A

-insulin injections

43
Q

why cant insulin injections be taken by mouth

A

-its a protein
-so will be digested in alimentary canal

44
Q

why must dose of insulin must be matched exactly to glucose intake

A

-if person with diabetes take too much then they will experience a low blood glucose conc that can result in un consciousness

45
Q

how do you ensure correct dose of blood glucose conc is given

A

monitored using biosensors

46
Q

whats a biosensor

A

A device that uses biological molecules to measure the level of
certain chemicals

47
Q

how is type II diabetes controlled

A

-regulating intake of carbohydrate in diet and matching this to the amount of exercise
-some cases, may be supplemented by injections of insulin or by use of drugs to stimulate insulin production
-other drugs can slow down the rate at which body absorbs glucose from the intestine

48
Q

Describe the two types of diabetes and explain how they differ

A

Type 1 diabetes: pancreas does not produce insulin
Type 2 diabetes: Less glycoprotein receptors on cells or they lose their responsiveness to insulin, sometimes an inadequate supply of insulin

49
Q

Outline the sources of water and salt, loss and gain in a human

A

-Sources of water: diet, metabolism (repsiration)
-Loss of water: urine, expired air, evaporation from skin, faeces, sweat
-Sources of salt: diet
-Loss of salt: urine, faeces, sweat”

50
Q

structure of Mammalia kidney

A

-fibrous capsule - outer membrane that protects kidney
-cortex - lighter coloured outer region made up of renal capsules, convoluted tubules and blood vessels
-medulla - darker coloured inner region made up of loops of Henle, collecting ducts an blood vessels
-renal pelvis - funnel-shaped cavity that collects urine into ureter
-ureter - tub that carries urine to bladder
-renal artery - supplies kidney with blood from heart via aorta
-renal vein - returns blood to heat via vena cava

51
Q

Describe ultrafiltration and the production of glomerular filtrate

A

-Afferent arteriole larger than efferent arteriole causing high hydrostatic pressure in the glomerulus
-Water, glucose, urea, mineral ions (glomerular filtrate) forced out of the capillary into the renal capsule
-Blood cells and proteins too large to pass through
-Movement of filtrate out of the glomerulus is resisted by capillary endothelial cells, epithelial cells of renal capsule, hydrostatic pressure of fluid in renal capsule, low water potential in the blood”

52
Q

Explain how the structure of a nephron enhances ultrafiltration

A

-Podocytes in renal capsule: have spaces between them to allow filtrate to pass round them not through them
-Endothelium of glomerular capillaries has spaces between the cells allowing fluid to pass round not through the cells”

53
Q

Explain how water and glucose are reabsorbed by the proximal convoluted tubule

A

-Na+ actively transported out of epithelial cells by sodium potassium pump (carrier protein) into the blood
-This maintains a higher concentration of Na+ in the lumen of the PCT compared with the inside of the epithelial cells
-Na+ diffuse into the epithelial cell through a co-transport protein (carrier protein)
The movement of Na+ carries glucose/amino acids throught the same protein into the epithelial cell
Glucose/amino acids move into the blood by facilitated diffusion (through another carrier protein)
Epithelial cells of PCT are adapted by having microvilli and infoldings for large surface area, and lots of mitochondria”

54
Q

Explain how a gradient of sodium ions in the medulla is maintained by the loop of Henle

A

-Na+ actively transported out of ascending limb into the medulla
-This lowers water potential in the interstitial region (area between the limbs of the loop of Henle). The impermeable walls of the ascending limb prevent water moving out
-Water passes out of the filtrate in the descending limb into the interstitial region, enter blood capillaries and moves away
-Water potential of filtrate decreases, becoming lowest at the hairpin
-Na+ diffuse out of the filtrate down a concentration gradient at the base of the ascending limb and further up are actively transported out (point 1)
-The water potential in the interstitial space between the ascending limb and the collecting duct is a gradient from highest water potential in the cortex to the lowest water potential in the medulla (highest ion concentration)
-Water leaves the collecting duct by osmosis down it’s concentration gradient and is carried away by blood vessels”

55
Q

Explain how the loop of Henle acts a counter current multiplier

A

The water potential of the filtrate in the collecting duct reduces as it moves down, meeting interstitial fluid with an even lower water potential. This ensures a small but constant water potential gradient along the whole length of the collecting duct.

56
Q

Explain the role of the distal convoluted tubule and collecting duct in reabsorbing water

A

-DCT has microvilli on its epithelial cells and many mitochondria, increasing reabsorption from the filtrate by active transport.
-DCT makes final adjustments to water and salts that are reabsorbed and controls blood pH by selecting which ions to reabsorb
-Water moved by osmosis from the collecting duct into the interstitial fluid and then into the blood”

57
Q

Define osmoregulation

A

Maintenance of water potential of the blood plasma and therefore tissue fluid

58
Q

Explain how the water potential of the blood is regulated

A

-Water potential of the blood depends on the solutes and well as volume of water.
-Water potential of the blood is detected, the hormone ADH is either secreted or stopped, the permeability of the collecting ducts to water is altered and more or less water is absorbed

59
Q

Describe the roles of hypothalamus, posterior pituitary and antidiuretic hormone in osmoregulation

A

-Osmoreceptors in the hypothalamus detect a fall in the water potential of the blood (water is lost by osmosis from these cells and they shrink)
-This causes the hypothalamus to produce antidiuretic hormone (ADH)
-ADH passes to the posterior pituitary gland and is secreted into the capillaries
-ADH travels in the blood to the kidneys and increases the permeability of the DCT and collecting duct to water
-Specific protein receptors in the membranes of the cells making up the walls of the DCT and collecting duct bind to ADH and cause activation of phosphorylase enzymes in the cell
-Phosphorylase causes vesicles in the cell containing aquaporins to move to and fuse with the cell membrane
-ADH also increases permeability to urea which passes out further lowering water around the collecting duct
-More water leaves the collecting duct and is reabsorbed into the blood
-When the above and drinking restore water potential of blood the osmoreceptors detect this and the process is reversed

BIOLOGY PAPER 2 (15 decks)

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