Homeostasis - A2 Flashcards
1
Q
Define homeostasis.
A
The maintenance of a constant internal environment.
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)
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
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.
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
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
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
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
9
Q
What factors affect blood glucose concentration?
A
- amount of carbs digested from diet
- rate of glycogenolysis
- rate of gluconeogenesis
10
Q
Define glycogenesis.
A
Liver converts glucose into the storage polymer glycogen.
11
Q
Define glycogenolysis.
A
Liver hydrolyses glycogen into glucose which can diffuse into the blood.
12
Q
Define gluconeogenesis.
A
Liver converts glycerol and amino acids into glucose.
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
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
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
16
Q
Explain the action of glucagon.
A
- works by activating enzymes
- glycogen to glucose/glycogenolysis
- gluconeogenesis
17
Q
How does adrenaline inhibit glycogenesis?
A
- adenylate cyclase activated
- cAMP produced / second messenger produced
- so gluconeogenesis occurs / glycogenesis inhibited
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
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
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
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
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
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
Suggest how a student could produce a required concentration of glucose from a stock solution.
volume of stock solution
=
required concentration x volume needed
÷
concentration of stock solution
26
How would you work out the volume of distilled water in the glucose experiment?
final volume needed - how volume of stock solution
27
Outline how colorimetry could be used to identify the glucose concentration in a sample.
- 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
Define osmoregulation.
Control of blood water potential via homeostatic mechanisms.
29
Describe the gross structure of a kidney.
(7 marks)
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
Describe the structure of a nephron.
(5 marks)
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
How is urea removed from the blood?
- hydrostatic pressure
- causes ultrafiltration at Bowman's Capsule
- through basement membrane/connective tissue
- enables by small size of urea molecule
32
Describe how ultrafiltration produces glomerular filtrate.
- 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
How are the Bowman's capsule adapted for ultrafiltration?
- fenestrations between epithelial cells of capillaries
- fluid can pass between and under folded membrane of podocytes
34
What happens during selective reabsorption and where does it occur?
- useful molecules from glomerular filtrate eg. glucose are reabsorbed into the blood
- occurs in proximal convoluted tubule
35
Outline the transport processes in selective reabsorption.
- 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
How are cells in the PCT adapted for selective reabsorption?
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
What happens in the loop of Henle?
- 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
Explain the role of the distal convoluted tubule.
Reabsorption
- of water via osmosis
- of ions via active transport
Permeability of walls is determined by actions of hormones.
39
Explain the role of the collecting duct.
Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaproins.
40
Explain why it is important to maintain a Na+ gradient.
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
Explain the role of the hypothalamus in osmoregulation.
- Osmosis of water out of osmoreceptors in hypothalamus cause them to shrink
- This triggers hypothalamus to produce more antidiuretic hormone (ADH)
42
Explain the role of the posterior pituitary gland in osmoregulation.
Stores and secretes the ADH produced by the hypothalamus.
43
Explain the role of ADH in osmoregulation.
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
Define endotherm.
Animals that regulate body temperatures from within the body (warm blooded)
- by both physiological and behavioural means.
45
Define ectotherm.
Reptiles/animals that rely primarily on external environment to regulate body temperatures.
- by behavioural means only
46
Name 4 ways we gain and lose heat.
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
Name and explain the 2 parts of the hypothalamus in the thermoregulatory centre in the brain.
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
What do the thermoreceptors do?
Blood passes through the brain (core temperature) and skin (external temperature) and receptors pick up on temperature of blood.
49
Regulation of temperature methods for conserving heat in a cold environement.
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
Generating heat in cold environments.
Increased metabolic rates: respiration caused by adrenaline etc
Shivering: involuntary rhythmic muscle contractions that produce metabolic heat
51
Losing heat in response to a warm environment.
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
Explain the effects of sweating or panting on temperature control?
- evaporation of water from lining of mouth or skin
- heat transferred from blood
53
Describe the role of glycogen formation and its role in lowering blood glucose.
- 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
Describe how blood glucose levels can be increased using hormones.
- release of glucagon
- leads to formation of glucose in liver cells
- from non-carbohydrates / amino acids / fatty acids
55
Explain how urea is concentrated in the filtrate.
- 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
Explain how ADH causes movement of water from the lumen to collecting duct.
- 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
Describe the secondary messenger
model.
- Adenylate cyclase activated / cAMP produced / second messenger produced;
- Activates enzyme(s) (in cell);
- (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;
