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Y13 Biology > Topic 6 C: Homeostasis > Flashcards

Topic 6 C: Homeostasis Flashcards

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1
Q

Homeostasis definition and what does it ensure?

A

Maintenance of a stable internal environment, it is the ability to return to optimum point.
- ensures optimal conditions for enzyme action and cell function

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2
Q

Homeostasis affecting enzyme action?

A
  • enzymes control rate of metabolic reactions in cells
  • temperature and pH affect enzyme activity
  • small fluctuations can impair role of different enzymes
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3
Q

Homeostasis changing water potential?

A
  • cause cells to shrink and expand due to osmosis
  • constant blood glucose levels ensure constant water potential
  • constant blood glucose crucial for respiration
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4
Q

Water potential definition?

A

Likelihood of water molecules to diffuse in / out solution.

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5
Q

Negative feedback and increased body temperature?

A
  • increased body temp = more frequent e-s complexes
  • molecules move faster due to more KE
  • substrates more likely to collide with active site
  • energy of collisions also increase - increased chance of reaction
  • increased rate of reaction
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6
Q

Why does the active site change shape when denatured?

A
  • enzyme molecules vibrate more, breaking hydrogen bonds holding the 3D tertiary structure.
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7
Q

Negative feedback and decreased body temperature?

A
  • less frequent e-s complexes
  • molecules move slower due to less KE
  • substrate and enzyme collide with less energy
  • less likely for bonds to be formed / broken - less successful collisions
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8
Q

Negative feedback and pH?

A
  • different enzymes work best at different pH
  • hydrogen and ionic bonds hold tertiary structure
  • excess H+ (acid) or OH- (alkali) ions break these bonds
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9
Q

How is pH calculated?

A
  • based on H+ ion concentration

pH = - log 10 (H+)

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10
Q

Why is pH calculated how it is?

A
  • easier to compare results
  • can plot small and large numbers
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11
Q

Exam question: How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency? (5)

A
  • optimum temp = body temp / 37
  • if too high, enzyme active site denatures due to hydrogen and ionic bonds breaking
  • reduces rate of reaction (if too low)
  • reduced kinetic energy of molecules (if too low)
  • fewer collisions / fewer e-s complexes formed (if too low)
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12
Q

What are negative feedback loops functions?

A

Reduce the initial effect of the stimulus to help maintain a normal range or balance within an organism

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13
Q

What is a corrective measure in negative feedback loop?

A

Two mechanisms - factors that become too high or too low. it may involve the nervous system or the endocrine system

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14
Q

What is a feedback mechanism in the negative feedback loop?

A

A receptor detects a stimulus created by the change to the system and the effector brings about the appropriate response

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15
Q

Explain the negative feedback loop when there is an increase.

A
  1. start off with factor within normal range
  2. factor increases above normal range
  3. receptors detect change (stimulus) which triggers corrective mechanism A
  4. factor returns to within normal range (optimum)
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16
Q

Explain negative feedback loop when there is a decrease.

A
  1. start off with factor within normal range
  2. factor decreases above normal range
  3. receptors detect change (stimulus) which triggers corrective mechanism B
  4. factor returns to within normal range (optimum)
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17
Q

What are the dangers of the negative feedback loop?

A

Over-correction - when the effector has corrected the deviation it is important that information is fed back to the receptor. If this doesnt happen, receptor will continue to over-stimulate the effector.

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18
Q

What is the function of the positive feedback loop?

A

Amplifies the effect of the original stimulus so that the response causes the factor to deviate more from the normal range.

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19
Q

Explain the positive feedback loop and broken bones.

A
  • the repair of broken bones involves special cells called osteoblasts and osteoclasts. They secrete hormone osteocalcin (protein).
    1.osteoblast released - possesses an insulin receptor which when stimulated, causes them to release more inactive osteocalcin. Insulin effect enhanced.
    2. osteoclasts secrete acid which lowers pH and causes the inactive form of the protein to change into the active form - it changes shape / tertiary structure. Hydrogen and ionic bonds broken.
    3. active osteocalcin binds to receptors on B cells in the pancreas to stimulate the release of insulin
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20
Q

Conclusion of positive feedback loop and broken bones?

A
  • osteocalcin causes more insulin released
  • more insulin causes more inactive osteocalcin release
  • change in pH breaks ionic and hydrogen bonds
  • change to tertiary structure
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21
Q

Hormone definition?

A

Chemical messengers secreted by glands to target cells

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22
Q

How do hormones work?

A
  • glands secrete them directly into blood
  • target cells with specific receptors
  • receptors complementary
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23
Q

Role of pancreas?

A
  • detects changes in blood glucose
  • contains clusters of endocrine cells called islets of langerhans
  • cells contain alpha and beta cells
  • beta cells act as receptor to secrete insulin
  • alpha cells act as a receptor to secrete glucagon
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24
Q

Examples of effectors involved with blood glucose?

A

liver
muscle
fat cells

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25
Q

What happens when blood glucose concentration is too high?

A
  1. receptors = A and B cells in pancreas detect increase
  2. less glucagon (A) and more insulin (B) secreted
  3. effectors = insulin binds to specific receptors on cell membranes of muscle and liver cells making their muscle cell membrane more permeable to glucose. take up more glucose by carrier proteins and absorbed by facilitated diffusion
    (carrier protein = GLUT4 protein - insulin sensitive)
  4. insulin also activates enzymes in muscle and liver cells that convert glucose into glycogen = glycogenesis
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26
Q

What happens when blood glucose is too low?

A
  1. receptors = A and B cells in pancreas detect increase
  2. more glucagon (A) secreted and less insulin (B) secreted
  3. effectors = glucagon binds to specific receptors on cell membranes of liver cells
  4. binding activates enzymes involved in the breakdown of glycogen into glucose = glycogenolysis
  5. glucagon also activates enzymes involved in the formation of glucose from glycerol and amino acids (non-carbohydrate) = gluconeogenesis. It occurs if all glycogen has been hydrolysed into glucose is still needed.
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27
Q

Exam question: Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours. (3)

A
  • glucagon released
  • glycogen converted into glucose from the liver
  • also get glucose from non-carbohydrates - glycerol and amino acids
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28
Q

Where does glucose come from?

A
  • diet
  • hydrolysis of glycogen
  • non-carb sources
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29
Q

What do alpha and beta cells have that help to detect blood glucose concentration?

A

Have receptors.

30
Q

Insulin and beta cells - the effects?

A
  1. increases rate of facilitated diffusion
    - changes tertiary structure of glucose transport proteins (GLUT4)
    - allows more glucose to pass into cells to FD
    - increases number of protein carriers within cell membrane
    - increases the SA for FD
  2. activating enzymes converting glucose to glycogen
    - results in glycogenesis in the liver
31
Q

Glucagon and alpha - the effects?

A
  1. activating enzymes converting glycogen to glucose
    1. glucagon binds to receptors and activates a protein
    2. protein activates into an enzyme - adenylyl cyclase
    3. ATP converted cyclic AMP (cAMP)
    4. activates enzyme protein kinase
    5. glycogen hydrolysed into glucose
  2. activating enzymes converting glycerol into glucose
    - results in gluconeogenesis in liver
32
Q

Exam Question: Explain how insulin lowers the concentration of blood glucose (3)

A
  • insulin will bind to receptor on membrane of muscles
  • facilitated diffusion occurs, with help of carrier protein
  • glucose diffuses into the muscle
  • excess is stored as glycogen
33
Q

Purpose of adrenaline in second messenger model?

A
  1. activates glycogenolysis and inhibits glycogenesis
  2. activates glucagon secretion and inhibits insulin secretion
34
Q

Second messenger model process?

A
  1. BIND - glucagon (first messenger) binds to liver cell membrane receptor and changes receptor proteins shape - activating a G protein
  2. ACTIVATE - G protein activates into an enzyme called adenylate cyclase
  3. 2ND MOLECULE - adenylyl cyclase converts ATP to cAMP (cyclic amp) -
  4. BIND & ACTIVATE - cAMP activates protein kinase and creates an enzyme cascade (chain reaction) - cAMP is the second messenger as its the second molecule to cause activation
  5. Glycogen now hydrolysed into glucose (glycogenolysis)
35
Q

Exam question: Explain how insulin lowers the concentration of blood glucose? (3)

A
  • binds to receptors on target cell
  • causes more transport / carrier proteins to become active
  • glucose diffuses into cells and lowers blood glucose
  • enzymes in cells convert glucose into glycogen
  • stimulates fatty acids / lipids / fat formation
  • raises rate of respiration in cells, using more glucose
36
Q

Adrenaline messenger model?

A
  1. adrenaline (first messenger), binds to adrenaline receptors of liver cells, which are our target cells in this case. this changes the shape of the receptor protein
  2. first enzyme activated - this change of shape activates a protein, which activates adenylyl cyclase
  3. second messenger - adenylyl cyclase catalyses the conversion of ATP to the second messenger cyclic cAMP
  4. positive feedback - effect of adrenaline is amplified so each molecule can stimulate many molecules of cAMP, which in turn activates many enzyme molecules
37
Q

Cause of type 1 diabetes and definition?

A

Pancreas fails to produce sufficient insulin to control glucose
- normally begins in childhood due to auto-immune response
-immune system attacks beta cells - cant secrete insulin
- affects glycogen stores - individual feels fatigued
- blood glucose levels will rise and stay high = hyperglycaemia

38
Q

Type 1 diabetes treatment?

A

insulin injections and carbohydrate-controlled diet
- therapy has to be carefully controlled - too much causes drop in blood glucose levels making you hypoglycaemic

39
Q

What the link between high blood glucose and kidneys?

A
  • kidneys are unable to filter out excess glucose in blood so it often appears in urine
  • kidneys produce large amounts of urine which dehydrates the individual: they feel thirsty all day
40
Q

Type 2 diabetes definition and cause?

A

Receptors have reduced in number / no longer respond to insulin
- reduced sensitivity occurs in liver and fat storage cells
- beta cells produce larger amounts of insulin that damages them
- lack of response means reduced glucose uptake by muscles
- risk factors include obesity, poor diet, and lack of exercise

41
Q

Type 2 diabetes treatment?

A

carbohydrate-controlled diet and regular exercise
- people should eat diet low in fat, sugar and salt with plenty of whole grains, fruits and vegetables

42
Q

Osmoregulation definition?

A

the homeostatic control of the water potential of blood

43
Q

2 main functions of kidneys?

A
  1. osmoregulatory organ = regulates water content of the blood which is vital for maintaining blood pressure
  2. excretory organ = excrete toxic waste products of metabolism (e.g., urea) and excretes substances in excess (e.g., salts)
44
Q

What is kidney surrounded by?

A

tough outer layer known as fibrous capsule

45
Q

Nephron definition?

A

Functioning tubule unit responsible for formation of urine.

46
Q

Nephron structure?

A
  1. bowmans capsule
    - closed end at start of nephron that surrounds mass of blood capillaries (glomerulus). Also contains specialised cells called podocytes
  2. Proximal and Distal convoluted tubules - series of loops surrounded by blood capillaries, walls are made from epithelial cells containing microvilli. distal surrounded by fewer capillaries
  3. loop of henle - hair-pin loop that extends from cortex to medulla and back, surrounded by many blood capillaries
  4. collecting ducts - tube where many DCTs empty, becomes increasingly wide as it empies into renal pelvis
47
Q

Exam question: Some people who have diabetes dont secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who doesnt secrete insulin. (4)

A
  • high conc of glucose in blood
  • high conc in tubule
  • reabsorbed by faciliated diffusion / active transport
  • requires carrier proteins
  • these are working at maximum rate
  • not all glucose is reabsrobed / some lost in urine
48
Q

Role of different blood vessels associated with nephron?

A
  1. bowmans capsule - contains glomerulus (bundle of capillaries) where ultrafiltration occurs
  2. afferent arteriole - supplies blood to glomerulus and carries blood from renal artery to nephron
  3. efferent arteriole - capillaries of glomerulus rejoin to form this = tiny vessel that filters blood away from the glomerulus, has smaller diameter than afferent arteriole so blood is at high pressure within glomerulus
  4. network of capillaries - blood flows into these from efferent arteriole and eventually flows into renal vein
49
Q

Two stages in formation of urine?

A
  1. ultrafiltration
  2. selective reabsorption
50
Q

Summary of ultrafiltration and selective absorption?

A
  1. ultrafiltration - bowmans capsule - small molecules (e.g., amino acids, water, glucose, urea & inorganic ions) filtered out of blood capillary of glomerulus and into bowmans capsule to form filtrate = glomerular filtrate
  2. selective reabsorption - PCT - useful molecules reabsorbed from filtrate and returned to blood as the filtrate flows along the nephron
51
Q

What does urine contain?

A
  • excess water, dissolved salts and urea
  • small substances e.g., hormones
  • doesnt contain proteins / blood cells - too big to be filtered
  • all glucose reabsorbed by active transport
52
Q

Four main stages of osmoregulation?

A
  1. formation of glomerular filtrate
  2. reabsorption of glucose (PCT)
  3. maintenance of sodium ion gradient (Loop of Henle)
  4. reabsorption of water (DCT)
53
Q
  1. Formation of glomerular filtrate process?
A
  1. blood enters via afferent arteriole at high pressure as coming from renal artery.
  2. capillaries (glomerulus) get narrower, increasing hydrostatic pressure of blood moving through, this causes smaller molecules within blood to be forced out into bowmans capsule
  3. end result = smaller molecules forced out to make filtrate
    - the liquid and small molecules have to pass through three layers to get into bowmans capsule and into nephron tubules (capillary endothelium, basement membrane, and epithelial cells (podocytes)) and blood leaves via efferent arteriole
    - holes in capillary endothelium and gaps between podocytes allows dissolved substances in blood plasma to pass into BC
54
Q

Exam question: Describe how ultrafiltration occurs in glomerulus? (5)

A
  • blood / hydrostatic pressure
  • small molecules
  • pass through basement membrane
  • protein too large to go through / stays behind
  • presence of pores in capillary endothelium / presence of podocytes
55
Q
  1. reabsorption of glucose process?
A
  1. sodium and potassium pumps use ATP from mitochondria to actively transport sodium ions out of PCT cells into bloodstream (adaptation - mitochondria)
  2. PCT epithelial cells have low conc of sodium ions now compared to filtrate flowing through. sodium ions from filtrate move into PCT by facilitated diffusion using a co-transporter protein - both sodium and glucose attaches and goes into PCT. (adaptation -microvilli)
  3. now high conc of glucose in PCT and now diffused into blood - reabsorbed
56
Q

Exam question: Explain how activity of kidneys result in clearance value for glucose? (3)

A
  • filtration out of blood plasma
  • hydrostatic pressure
  • PCT
  • all reabsorbed
  • active transport
57
Q
  1. maintenance of sodium ion gradient process?
A
  1. mitochondria in ascending limb provides energy for active transport of sodium ions into interstitial space
  2. lowers water potential in interstitial space, water cannot move into space by ascending limb as walls are thick and impermeable to water
  3. water from descending limb able to move by osmosis into interstitial space, then is reabsorbed into the blood
  4. filtrate is progressively losing water as it moves down descending limb, reaches lowest WP at base of loop.
58
Q
  1. reabsorption of water process?
A
  1. as solution in interstitial space is very dilute, some sodium ions move out of filtrate by diffusion
  2. due to sodium ions being actively transported out of PCT, when filtrate reaches the top of the PCT, it is very dilute / high wp
  3. dilute liquid goes through DCT and collecting duct, the section of the medulla that surrounds these two parts is very concentrated. this means even more water will move out filtrate by osmosis
  4. end result = remaining fluid in collecting duct will form urine
59
Q

Exam question: Suggest how the length of the loop of henle will differ for a desert animal compared to a human, explain. (4)

A
  • desert animals will have longer loop of henle
  • more sodium ions actively tranported out
  • more water reabsorbed - urine will be more concentrated
  • longer loop of henle creates larger sa for active transport
60
Q

Exam question: Name body part that releases antiduiretic hormone ADH into blood.

A

Posterior pituitary

61
Q

Effects of hypertonic blood conditions?

A
  • blood has too low wp and lots of ions
  • too much water will leave cells by osmosis
  • cell will shrivel (crenation)
  • causes = too much sweating / not drinking enough / high ion or salt diet
  • result = more water reabsorbed and urine more concentrated
62
Q

Effects of hypotonic blood conditions?

A
  • blood has too high wp with few ions
  • lots of water will move into cells by osmosis
  • cells will burst (lysis)
  • causes = drinking too much water / not enough salt in diet
  • result = less water reabsorbed and urine more dilute
63
Q

What detects hypertonic and hypotonic blood conditions?

A
  • hypothalamus
  • posterior pituitary gland
  • antidiuretic hormone
64
Q

what are osmoreceptors

A
  • receptors that monitor water potential of blood
  • specialised sensory neurones - nerve cells
  • found in hypothalamus within brain
65
Q

What happens if levels of wp decrease?

A
  1. hypothalamus detects change
  2. water move out of osmoreceptors by osmosis - cells decrease in vol
  3. nerve impulses travel along sensory neurones to posterior pituitary gland
  4. pituitary gland releases ADH
  5. ADH molecules enter the blood and travel through whole body
  6. kidneys reabsorb more water - reduces loss of water in urine
66
Q

Exam question: Explain role of loop of henle in absoprtion of water from filtrate. (6)

A
  1. in ascending limb sodium ions actively removed
  2. ascending limb impermeable to water
  3. in descending limb, sodium ions diffuse in
  4. descending limb, water moves out
  5. low wp in medulla / tissue fluid
  6. longer the loop of henle, the lower the wp
    7 . water leaves collecting duct / DCT
  7. by osmosis
67
Q

How ADH regulates water potential within blood process?

A
  1. ADH released from pituitary gland and binds to receptor proteins in cell surface membrane of DCT and collecting duct cells of kidney
  2. once bound, activates enzyme phosphorylase, this causes vesicles containing channel proteins - aquaporins - to move towards cell membrane and fuse
  3. aquaporins are channel proteins which allow water to move through by osmosis, phosphorylase increases number of channel proteins, which means more water leaves DCT and collecting ducts
  4. end result = when ADH reaches kidney, it causes wall of collecting duct and DCT to become more permeable to water, more water will leave nephron and be reabsorbed into bloodstream
68
Q

Exam question: Explain how ADH is involved in the control of the volume of urine produced. (4)

A
  • if wp of blood falls, detected by receptors in hypothalamus
  • leads to ADH released from pituitary gland
  • ADH makes cells of collecting duct / DCT permeable to water
  • water leaves filtrate by osmosis
  • smaller volume of urine produced
69
Q

What happens if levels of wp increase?

A
  1. hypothalamus detects change
  2. osmoreceptors not stimulated within hypothalamus
  3. no nerve impulses sent to the posterior pituitary gland
  4. no ADH secreted or less is secreted if stimulation has taken place
  5. large amount of dilute urine is produced and more water is lost
70
Q

Effect of wp increase on aquaporins?

A
  • aquaporins moved out of luminal membranes of collecting duct cells they are no longer permeable to water
  • the filtrate flows along the collecting duct but loses no water and is very dilute, this flows from the kidneys through the ureters and into the bladder

Y13 Biology (11 decks)

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