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biology paper 2 > 3.6.4 homeostasis > Flashcards

3.6.4 homeostasis Flashcards

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1
Q

what is homeostasis?

A

maintenance of a stable internal environment

keeps the environment stable inside the body in which cells and enzymes function (blood and tissue fluid)

maintains the environment through different processes within acceptable limits around norms, optimum/set points

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2
Q

what is the importance of homeostasis?

A

temperature and pH = changes here can impair the ability of the enzyme and distort structures/active site

major changes to the water potential of blood and tissue fluid can cause cells to burst or crenate as a result of osmosis

a reasonably constant blood glucose concentration is necessary for cellular respiration

allows for greater autonomy as organisms are more independent of the external environment

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3
Q

what is the relationship between homeostasis and feedback mechanisms?

A

optimum point = desired level

receptor = detects deviation/stimulus

coordinator = coordinates the information from various sources

effector = brings about the response and restores the optimum

feedback mechanism = by which a receptor detects a stimulus and effector brings about the appropriate response to reduce the stimulus

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4
Q

what is the relationship between negative feedback and homeostasis?

A

series of changes that results in a system being restored to it’s original store

deviation from norms that set the corrective response that reduces the stimulus eg temperature

most homeostatic mechanisms operate via negative feedback

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5
Q

how can negative feedback be fine-tuned?

A

the possession of separate mechanisms involving negative feedback, controls departures in different directions from the original state

gives a greater degree of control

eg insulin and glucagon

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6
Q

what is the relationship between positive feedback and homeostasis?

A

positive feedback is a series of changes that result in a system deviating further from it’s original state

deviation from norm that creates a response that causes further deviation from the norm

eg oxytocin

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7
Q

what are hormones?

A

hormones carry information from one part of a mammals body to another part

produced by endocrine glands, contain secretory cells which secrete hormones directly into the blood

carried by blood plasma

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8
Q

how do hormones work?

A

small molecules, can be polypeptides or steroids

concentration in blood are always very small

short life in body and broken down by enzymes or lost in urine

affect particular cells called target cells which contain receptors that are complimentary to the hormone

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9
Q

what is the role of the pancreas in regulating blood glucose?

A

unusual gland as it has both an endocrine function and exocrine function

endocrine: secretes hormone insulin and glucagon

controls blood glucose levels, produced by cells
ISLETS OF LANGERHANS

a cells are larger and secrete glucagon

b cells are smaller and secrete insulin

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10
Q

what factors influence blood concentration?

A

healthy human: 100cm3 of blood contains between 80-120mg of glucose

  1. directly from diet - from breakdown of other carbs such as starch, maltose and sucrose
  2. from the breakdown of glycogen (glycogenolysis) - stored in the liver and muscle cells
  3. from gluconeogenesis - production of new glucose from sources other than carbohydrates
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11
Q

what is the issue with low concentration blood glucose?

A

hypoglycaemia

not enough for cellular respiration

problematic for cells that only respire glucose

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12
Q

what is the issue with high concentration blood glucose?

A

hyperglycaemia

disrupts the normal functioning of cells

affects the water potential and osmosis

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13
Q

what three hormones maintain a constant blood glucose level?

A

insulin
glucagon
adrenaline

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14
Q

what happens after a meal containing carbohydrates, how is glucose absorbed into the blood?

A

B cells in the islets of Langerhans have receptors that detect the raised glucose levels

B cells respond by secreting insulin into the blood plasma

almost all body cells have glycoproteins on their CSM that bind with insulin

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15
Q

how does insulin affect the target cells?

A

binds to receptors and causes the tertiary structure of glucose channel proteins to change shape and open

allows more glucose in from the blood

increases the number of channel proteins in the membrane

activates enzymes that convert glucose to glycogen and fat

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16
Q

summarise the regulation of blood glucose concentration

A

increasing absorption of glucose from the blood into the cells by increasing the number of glucose channel proteins in the CSM of target cells

increasing the respiratory rate of the cells which uses up more glucose

activating enzymes that glucose into glycogen

activating enzymes that glucose into fats

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17
Q

what are the effects of glucagon?

A

a cell that detects a fall in the blood glucose and responds by secreting the hormone glycogen into blood plasma
this attaches to specific protein receptors on CSM

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18
Q

how does glycogen increase blood glucose concentration?

A

activating enzymes that convert glycogen to glucose

activating enzymes that lead to the production of glucose from other compounds such as amino acids and glycerol (gluconeogenis)

so blood glucose rises and cells reduce in secretion of glucagon

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19
Q

describe the second messenger model

A
  1. glucagon or adrenaline (first messenger) attaches to a transmembrane protein receptor on the CSM of a liver
  2. protein changes shape and activates an enzyme in the inside of the plasma membrane adenyl cyclase
  3. enzyme converts ATP to cAMP (cyclic adenosine monophosphate)
  4. the cAMP acts as a second messenger that activates other enzymes that carry out the breakdown of glycogen to glucose eg protein kinase
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20
Q

describe the hormone interaction in regulating blood glucose

A

insulin and glucagon are said to be antagonistic

system is self-regulating, blood sugar concentration determines the quality produced
never remains constant

negative feedback = glucose levels fall below the set point and glucagon leads a rise

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21
Q

what is diabetes?

A

one of the most common metabolic diseases in humans

over 6% may be living with diabetes that is not diagnosed

3.2 million diagnosed in the UK

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22
Q

what are the two types of diabetes?

A
  1. Juvenile-onset diabetes: Type 1
  2. Non-insulin dependant diabetes: Type 2
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23
Q

what is Type 1 diabetes?

A

pancreas is incapable of secreting sufficient insulin

often a auto-immune condition T cells attack and destroy B cells in the islets of langerhans

may be due to a deficiency in the gene that codes for insulin

24
Q

what is Type 2 diabetes?

A

usually the pancreas does secrete insulin but liver and muscle cells do not respond properly because glycoprotein receptors on body cells have lost responsiveness to insulin

frequently begins later in life - 40+

increasingly associated with poor diet and obesity

90% of cases in the UK are type 2

symptoms usually develop and are less severe

25
Q

what are the signs and symptoms of symptoms?

A

blood glucose above normal

glucose in urine

excessive urination

thrush/genital itching

weight loss or increased thirst and hunger

tiredness

26
Q

how is Type 1 diabetes controlled?

A

insulin injections (not tablets as would be digested in stomach)

dose must be matched to glucose intake to prevent hypo/hyperglucaemia

blood glucose can be maintained using biosensors to calculate dose

management of exercise and carbohydrate intake is important

pancreatic cell transplants are being trialled

27
Q

how is Type 2 diabetes controlled?

A

mainly carefully managed by the balance of diet and exercise

some patients may benefit from insulin injections or drugs that stimulate insulin production

other drugs can slow down the rate at which glucose is absorbed from the intestine

28
Q

where is the location of the kidney and what is it’s role?

A

excretion of nitrogenous waste (urea) and other toxic substances

osmoregulation = the homeostatic control of the water potential of the blood

located high in the rear of the abnormal cavity

brain shaped organs

29
Q

describe the kidney’s structure

A
  1. renal cortex = a lighter coloured outer region made up of Bowman’s capsules, convoluted tubules and blood vessels
  2. nephron
  3. rental pelvis = a funnel shaped cavity that collects urine into the ureter
  4. renal artery = supplies the kidney with blood from the heart via the aorta
  5. renal vein = returns blood to the heart via the vena cava
  6. ureter = a tube that carriers urine to the bladder
  7. renal capsule = an outer membrane that protects the kidney
  8. renal pyramids
  9. renal columns
  10. renal medulla = a dark coloured inner region made up of loops of hence, collecting ducts and blood vessels
30
Q

what are nephrons?

A

each kidney contains about a million coiled tubular structures = nephrons

found in:
renal (bowman) capsule
proximal convoluted tubule (PCT)
loop of henle
distal convoluted tubule (OCT)
collecting duct

31
Q

what is the role of the nephron in excretion and osmoregulation?

A

glomerular filtration and ultrafiltration

selective reabsorption of water and glucose in the PCT

maintenance of a sodium ion gradient in the medulla by the loop of henle

reabsorption of water by the PCT and collect dusts

32
Q

describe the renal (bowman’s capsule)

A

the closed end at the start of the nephron

cup-shaped and surrounds a knot of blood vessels called the glomerulus

inner layer of the renal capsule is made up of specialised cells called podocytes

each renal capsule is supplied with blood by the afferent arteriole
this splits into a tangle of capillaries called the glomerulus

capillaries of the glomerulus then re-join to form an efferent arteriole
then leads off to form a network of capillaries that run alongside the rest of the nephron

33
Q

what is ultrafiltration?

A

the endothelium of glomerular capillaries has many gaps up to 100nm wide

inner layer if the renal capsule is made up of podocytes (many projections with gaps in-between that filtrate pass through)

basement membrane allows small molecules but stop protein molecules passing through

all act as a filter: no plasma proteins or RBC’s or WVC’s pass through

34
Q

describe the formation of glomerular filtrate by ultrafiltration

A

diameter of the afferent arteriole is greater than that of the efferent arteriole. there is a build up of hydrostatic pressure within the glomerulus

species within the endothelium wall and between the podocytes have hydrostatic pressure that is sufficient to over come resistance and filtrate is forced from the blood into the renal capsule

blood cells and plasma proteins are too large to pass through

filtrate contains all molecules below a certain size which needs to be reabsorbed

35
Q

describe selective reabsorption by the proximal convoluted tubules

A

fluid that filters through into the renal capsule is virtually identical to blood plasma proteins

many of the substances in the filtrate needs to be kept in the body

selective reabsorption takes place in the PCT whereby 85% of the filtrate is reabsorbed back into the blood

36
Q

what function do PCTs have to enable selective reabsorption?

A

PCT cells have microvilli that increase SA for reabsorption of solutes

many mitochondria to provide ATP for active transport

infolding at their bases to give a large SA to reabsorb substances into blood capillaries

37
Q

describe the reabsorption in the proximal convoluted tubule

A
  1. Na+ and K+ pump in proximal tubule cell membrane uses ATP made by numerous mitochondria. The membrane is folded to increase SA, this lowers the concentration of Na+ in the cell
  2. Very close nearby the blood plasma rapidly removes absorbed Na+, CL and amino acids. This helps further uptake from the lumen of the tubule
  3. Microvilli increase SA, helping uptake of solutes. Na+ moves passively into the cell down its concentration gradient. It moves in using protein transporter molecules in the membrane, which bring in glucose and amino acids at the same time
38
Q

what is the role of the loop of heale?

A

mammals are able to form urine which is much more concentrated then blood plasma (hypertonic)
this has enabled them to colonise to very dry habitats

concentrate salts in the medulla, the further into the medulla, the lower the water potential of the interstitial fluid
allows water to be reabsorbed (osmosis) from the collecting duct, throughout it’s whole length as filtrate passes down through the medulla to the pelvis

39
Q

what is the concentration of a mammals urine dependant on?

A

the concentration of a mammals urine is related to the length of the loop of henle

the longer the hairpin, the more concentrated the urine

40
Q

describe the counter-current mechanism in the loop of henle

A
  • sodium ions are actively transported out of the ascending limb (cannot follow by osmosis as the walls are impermeable to water)
  • sodium ions create a low water pressure in the interstitial (tissue fluid) between the two limbs and descending limb
  • water passes out from the filtrate in the descending limb by osmosis. this continues as the filtrate passes down to hairpin and the filtrate develops a progressively lower water potential
  • water passes out by osmosis and enters the blood capillaries
  • at the base of the ascending limb, the water potential is low, sodium ions can diffuse out initially
  • filtrate leaving the ascending limb is slightly hypotonic to blood plasma - concentrated urine is completed in the PCT
    always meet interstitial fluid with a lower water potenital
41
Q

what hormone controls osmoregulation?

A

homeostatic control of osmoregulation is achieved by a hormone that acts on the PCT and collecting duct

ANTIDIURETIC HORMONE (ADH)

42
Q

explain the role of the loop of henle in the absorption of water from the filtrate

A
  1. in the ascending limb sodium ions are actively removed
  2. ascending limb is impermeable to water
  3. in the descending limb sodium ions diffuse in
  4. descending limb water moves out by osmosis
  5. lower water potential so high concentration of ions in the medulla
  6. the longer the loop of henle the lower the water potential in the medulla
  7. water leaves collecting duct by osmosis (down water potential gradient)
43
Q

describe the distal convoluted tubule

A

from the top of the ascending limb, the tubule fluid passes through the distal convoluted tubule

here active transport is used to make final adjustments to the concentration of various salts in the tubule and water by osmosis

pH is controlled by selecting which ions to absorb

44
Q

what is osmoregulation?

A

control of water potential in the bodies fluids

the water potential of the blood depends on the concentration of solutes eg glucose

the kidneys act as an effector to help control water potential in the blood and tissue fluid

cool day and water = large volume of dilute urine
hot day and water = small volume of concentration of urine

45
Q

how is water lost/gained in the body?

A

water is gained from food, drink and metabolism

water is lost in urine, sweat, faeces and water vapour in exhaled air

levels of water gain and loss varies

46
Q

how does osmoregulation occur?

A

ADH + PCT + collecting duct

the walls of the collecting duct and the PCT can be made less permeable to water according to needs of the body
allows more or less water to be reabsorbed back into the blood

the permeability of the PCT and collecting duct is controlled by ADH in the blood

cells lining the wall have membrane bound receptors for ADH
released if water potential is too low

ADH binds to these receptors and causes an activation of enzyme phosphorylase

Phosphorylase causes vesicles contain water permeable channels (aquaporins) to fuse with the CSM
makes walls more permeable to water

more ADH in the blood means more aquaporins are inserted allowing more water to be reabsorbed and more concentrated urine is produced with a lower water potential

ADH also increases the permeability of the collecting duct to urea, some passes out, lowering water potential

47
Q

what if water potentials are too high?

A

less ADH is released and less water is reabsorbed

CSM folds inwards to create new vesicles that remove the aquaporins from the membrane

wall is less permeable and water remains in collecting duct = more dilute urine

48
Q

how is the release of ADH controlled?

A
  1. hypothalamus detects too little water in the blood
  2. pituitary gland releases ADH
  3. kidney maintain blood water level
  4. less water is lost in urine (urine more concentrated)
  5. Blood water level returns to normal
49
Q

what is the role of the hypothalamus and posterior pituitary gland?

A

osmoreceptors in the hypothalamus monitor the blood’s water potential

when the water potential is too low, the cells lose water by osmosis + shrink
this generates electrical impulses that cause ADH to pass to the posterior pituitary gland&raquo_space;> blood

osmoreceptors also send nerve impulses to the thirst centre

when water potential rises, osmoreceptors detect the rise and send fewer impulses to the PPG + less ADH released

50
Q

what is required practical 11?

A

measuring the concentration of glucose using a calibration curve

51
Q

How can Benedict’s solution be used to measure the concentration of glucose in a solution?

A

Use a colorimeter to measure the absorbance of a series of solutions of known concentrations to create a calibration curve. Compare the absorbance of an unknown sample to the calibration curve.

52
Q

what is a serial dilution?

A

a dilution where successive concentration increase/decrease in a logarithmic fashion

53
Q

outline the procedure of this practical

A
  1. Make a serial dilution of glucose, ranging from 0 to 10 mmol dm-3
  2. Place 2 cm’ of each of the unknown samples in separate boiling tubes.
  3. Add 2 cm’ of Benedict’s solution to all boiling tubes.
  4. Place boiling tubes in a water bath at 90°C for four minutes.
  5. Zero the colorimeter using a cuvette with distilled water and set to red filter.
  6. Place known samples into cuvette and measure the absorbance of each
    using the colorimeter.
  7. Make a calibration curve.
  8. Measure the absorbance of the unknown samples using the colorimeter. Use the calibration curve to determine glucose concentrations.
54
Q

what are the axes in a calibration curve?

A

absorbance against glucose concentration

55
Q

what would a high glucose concentration in urine suggest?

A

It may suggest diabetes. Lack of insulin leads to high blood glucose concentration, hence high concentration in the glomerular filtrate, so not all glucose can be reabsorbed in the proximal convoluted tubule.

56
Q

state the hazards and precautions of this practical

A

Benedict’s solution is an irritant, wear eye protection and avoid contact with skin

Handle the hot water bath with care

57
Q

how can you increase the accuracy of the estimate of the unknown glucose solution?

A

Increase the number of concentrations (at smaller intervals) for the calibration curve within the range of concentrations that the unknown solution belongs in.

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