Homeostasis Flashcards
1
Q
Homeostasis
A
maintenance of a constant internal environment within restricted limits
2
Q
Give reasons why homeostasis is important for organisms
A
- limit impact of changes in temperature/pH on enzyme activity that control metabolic processes
- ensure stable glucose concentration so it available as a respiratory substrate and to maintain water potential
- allow organisms to be independent of external environment so have a wider geographical range and greater chance of finding food/shelter
3
Q
Negative Feedback
A
- deviation from norm
- initiates corrective mechanism
- reverse change to restore normal conditions
4
Q
Positive Feedback
A
mechanism whereby deviation from norm is detected and results in a change that causes greater deviation from norm
5
Q
Suggest an advantage of positive feedback
A
small stimulus results in large and rapid response
6
Q
Suggest why it is advantageous to have separate mechanisms involving negative feedback to maintain homeostasis
A
- each mechanism controls departures in different directions from original state
- positive movement towards norm (optimum)
- greater degree of homeostatic control
7
Q
Describe how body temperature is regulated
A
- temperature is detected by thermoreceptors in hypothalamus
- impulses are sent to heat-promoting/loss centre of hypothalamus
- impulses are sent via SNS to sweat glands (sweat), skeletal muscle (shivering) and skin arterioles (vasodilation/vasoconstriction)
8
Q
Suggest advantages of endotherms over ectotherms
A
- enzymes at optimum conditions
- ability to survive better in a wider range of habitats so greater chance of finding food/shelter
- active at all times
9
Q
Suggest disadvantages of endotherms over ectotherms
A
- higher respiratory rate
- require higher food intake
10
Q
Give characteristic features of hormones
A
- produced in endocrine glands
- carried to target cells in blood plasma
- bind to specific receptors of cell-surface membrane
- effective in low concentrations
- widespread and long last effects
11
Q
Describe what is meant by the second messenger model in hormone action
A
hormone outside cell causes a new chemical pathway to be activated by second messenger within cell
12
Q
State hormones involved in second messenger mechanism of blood glucose regulation
A
- adrenaline (under stress/exercise)
- glucagon (normal physiological conditions)
13
Q
Explain the process by which adrenaline raises blood glucose concentration
A
- adrenaline binds to transmembrane receptor protein on cell-surface membrane of target cell
- hormone-receptor complex activates adenyl cyclase
- catalyses formation of cAMP from ATP
- second messenger cAMP activates protein kinase
- catalyses glycogenolysis so glucose concentration increases
14
Q
Describe where in the pancreas hormones involved in blood glucose regulation are found
A
- islets of Langerhans
- larger α cells produce glucagon
- smaller β cells produce insulin
15
Q
Give ways in which blood glucose concentration is increased
A
glycogenolysis - glycogen to glucose
gluconeogenesis - amino acids/ glycerol to glucose
16
Q
Give ways in which blood glucose concentration is decreased
A
glycolysis - glucose to ATP
glycogenesis - glucose to glycogen stored in liver/muscle
lipogenesis - glucose to lipids/fatty acids stored as adipose tissue
17
Q
Explain how the body responds to a rise in blood glucose concentration
A
- β cells produce insulin when receptors on cell-surface membrane detect high glucose concentration
- insulin changes tertiary structure of glucose carrier proteins
- insulin causes vesicles containing glucose carrier protein to fuse with cell-surface membrane
- increase in facilitated diffusion of glucose into cells so respiration rate increases
- insulin activated enzymes which catalyse glycogenesis and lipogenesis
- negative feedback reduces secretion of insulin to maintain optimal blood glucose concentration
18
Q
Explain how the body responds to a fall in blood glucose concentration
A
- α cells produce glucagon when receptors on cell-surface membrane detect low glucose concentration
- glucagon binds to receptors hepatocytes
- activate enzymes which catalyse glycogenolysis and gluconeogenesis
- negative feedback reduces secretion of glucagon to maintain optimal blood glucose concentration
19
Q
Suggest the difference between Type I and Type II diabetes
A
- Type I is when body is unable to produce insulin (autoimmune response attacks β cells)
- Type II is when body lacks glycoprotein receptors/ unresponsive to insulin and/or insufficient supply of insulin
20
Q
Suggest why insulin shots could be used to treat Type II diabetes even though the body produces insulin
A
- inadequate supply of insulin
- high requirement of insulin than normal due to lack of responsiveness of glycoprotein receptors on cells
21
Q
Suggest why on some occasions our blood glucose concentration is above the normal amount
A
- eaten a meal containing carbohydrates
- not enough insulin produced in time
- glucose cannot enter cells so remains in blood
22
Q
Suggest why a urine test is an unreliable measure of blood glucose concentration
A
- not directly related to blood glucose concentration since there is variation amongst individuals
- coloured scale is subjective
- range of urine glucose concentrations for each colour so imprecise
23
Q
Explain why oxygen consumption of an organism increases as their body temperature increases
A
- enzymes have more kinetic energy so higher activity
- respiration rate increases so higher oxygen requirement
- more energy/ATP
24
Q
Explain how panting helps reduce body temperature of an organism
A
- evaporation of water in mouth
- heat transferred from blood
25
Suggest benefits of gene therapy to treat diabetes compared to insulin shots
- avoid injection
- not need to monitor blood glucose concentration as often
- diet not restricted
- long lasting
26
Explain how people with Type II diabetes have reduced ability to regulate blood glucose concentration
- abnormal/fewer receptors for insulin
- fewer glucose transport proteins (vesicles do not fuse)
- less glucose enters cells for respiration/converted to glycogen
- blood glucose concentration is above normal
27
Suggest why doctors want to lower upper value for blood glucose concentration that identifies prediabetic
- some prediabetics will be identified diabetics
- detection leads to treatment sooner which is more likely successful
- diabetes is life-threatening
28
Osmoregulation
homeostatic control of water potential of blood
29
Nephron
functional unit through which glomerular filtrate passes before emerging as urine
30
Give all the stages of osmoregulation that occurs in nephron
- ultrafiltration to form glomerular filtrate
- reabsorption of glucose and water in proximal convoluted tubule
- maintenance of gradient of sodium in medulla by loop of Henle
- reabsorption of water in distal convoluted tubule and collecting duct
31
Explain the process of ultrafiltration in nephron
- diameter of efferent arteriole is smaller than afferent
- build up of hydrostatic pressure within glomerulus
- fluid containing water, mineral ions and glucose forced out of glomerular capillaries to form filtrate
32
Explain adaptations of nephron to ensure only select components of blood plasma enter renal capsule to form filtrate
- pores of glomerular endothelial cells prevent filtration of blood cells and large proteins but allows components of blood plasma to pass through
- slit pores between podocytes (lining renal capsule)prevents filtration of medium-sized proteins
- only water, mineral ions, glucose and amino acids allowed passage to form filtrate
33
Explain the process by which reabsorption takes place in proximal convoluted tubule of nephron
- sodium ions are actively transported out of epithelial cells lining proximal convoluted tubule into blood capillaries
- sodium ion concentration of cells is lowered so sodium ions diffuse down concentration gradient from lumen by facilitated diffusion
- co-transported with glucose and amino acids which diffuse down concentration gradient into blood capillaries
34
Explain how epithelial cells lining proximal convoluted tubule are adapted for reabsorption of filtrate
- microvilli providing large surface area for faster reabsorption of filtrate from lumen
- infoldings at their bases to give a large surface area for faster transfer of substances into capillaries
- high density of mitochondria to provide ATP for active transport of sodium
35
Explain the role of the loop of Henle in reabsorption of water from collecting ducts
- counter current multiplication
- sodium ions are actively transported out of ascending limb which impermeable to water
- lowers water potential of medullary interstitial space
- water moves out of descending limb which is water permeable by osmosis and enters capillaries
- as filtrate moves up ascending limb towards collecting duct it develops a progressively higher water potential
- water potential gradient set up between filtrate in collecting duct and interstitial space
- water withdrawn out of aquaporins along length of collecting duct and enters blood capillaries
36
Describe what is meant by counter current multiplication in nephron
- filtrate flows in opposite directions in descending and ascending loop of Henle
- sodium ions are reabsorbed in ascending limb while water is not
- lowers water potential in medullary interstitial space so water is reabsorbed passively in descending limb by osmosis
37
Describe the role of distal convoluted tubules in nephron
- selective reabsorption of water and ions
- by active transport
- permeability of walls is controlled by hormones
38
Explain why a longer ascending loop of Henle allows marine mammals to remove all excess salt from their bodies
- forms counter current multiplier
- longer loop results in higher concentration of sodium in medulla which lowers water potential
- hence more water reabsorbed from collecting ducts
- so urine more concentrated than sea water
39
Explain how the body responds to a fall in water potential
- osmoreceptors cells in hypothalamus detect fall in water potential by shrinking due to osmotic loss
- change in shape of osmoreceptor causes hypothalamus to produce ADH
- ADH passes through posterior pituitary gland where it is secreted into blood capillaries
- ADH binds to protein receptors on cells of distal convoluted tubule and collecting duct
- causes vesicles containing aquaporins to fuse with cell-surface membrane
- membrane is more permeable to water and urea (lowers water potential of interstitial space further so more water is reabsorbed)
- negative feedback to reduce release of ADH when water potential returns to normal
40
Explain how the body responds to a rise in water potential
- osmoreceptors cells in hypothalamus detect rise in water potential by expanding due to osmotic gain
- nerve impulses sent to pituitary gland to reduce release of ADH
- decrease in permeability of collecting duct to water and urea
- less water reabsorbed from collecting duct
- negative feedback to raise ADH levels when water potential returns to normal
41
Suggest why concentration of urea in glomerular filtrate is higher for a protein-rich diet compared to carbohydrate rich
- urea formed from surplus of protein
| - when deaminated
42
Explain how a small amount of glucagon causes a rapid increase in blood glucose concentration
- cascade effect
- glucagon activates adenyl cyclase
- many cAMP produced from ATP
- activation of many protein kinase enzymes
- glycogen = polymer so hydrolysis releases many glucose molecule molecules into blood
43
Explain how glucagon increase blood glucose concentration
- binds to receptors in hepatocytes
- glycogenolysis via enzyme action
- gluconeogensis
44
Name organ in the body that has glucagon receptors
Liver
45
Explain the difference between the blood glucose concentration in heptic vein compared to hepatic portal vein
- lower blood glucose concentration
| - glucose converted to glycogen so removed from blood
46
Explain why a person who has fasted for several days will still maintain a relatively constant blood glucose concentration
gluconeogenesis
47
Which organ produces hormones involved in glucose control
pancreas
48
Suggest and explain how glycogen breakdown in liver and muscle cells in increased when an animal runs from a predator
- adrenaline released when animal sense danger
- adrenaline binds to complementary receptors on muscle cells
- causing increased protein kinase activity
- more glucose for respiration due to glycogenolysis
- lower blood glucose levels since glucose used by cells
- glucagon released and binds to complementary receptors on liver cells
- causes further glycogenolysis
49
Suggest and explain when insulin concentration is highest in blood
- when glucose concentration is highest (ignore time lag)
| - insulin stimulates uptake of glucose/ high concentration of glucose results in release of glucose
50
Describe what would happen if humans drank sea water
more water lost in urine than drank so will dehydrate
51
Explain why human kidneys only produce urine with a lower salt concentration than sea water
- lowers water potential of blood so water moves out of cells by osmosis
- humans do not have a long enough loop of Henle so not enough water reabsorbed to concentrate urine
- hence urine has lower salt concentration than seawater
52
Suggest why podocytes cannot undergo mitosis
- already specialised
- irregular structure
- spindle fibres cannot form
- mitosis would alter size of gaps / change rate of ultrafiltration
53
Compare transport in PCT to DCT
- both active transport
- both selective reabsorption
- both involve sodium
- DCT cotransports ions only where PCT involves glucose and amino avoids as well
