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A-level Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis

A

Maintaining a constant internal environment despite external changes

Controlling temperature
Controlling blood glucose concentration

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2
Q

What is a negative feedback loop?

A

A system which brings a change back to the neutral or normal state( often optimum)

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3
Q

What is a positive feedback loop?

A

When a system moves away from the optimum and keeps moving away (exaggerating the problem)

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4
Q

Why is homeostasis important?

A

Ensures cells are at suitable conditions to function metabolic processes properly

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5
Q

Why is it important to maintain pH and temperature in the body?

A

So proteins and enzymes can function properly

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6
Q

Why is it important to maintain water potential in the body?

A

Do cells do not shrivel or burst due to fluctuations in the water potential

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7
Q

Explain what happens when the bodies core temperature increases

A
  1. Thermoregulatory centre in the hypothalamus of the brain detect the rise in temperature using thermoreceptors.
  2. Blood vessels then dilate and sweat glands activate as capillaries move close to the surface of the skin.
  3. Body temperature decrease as sweat evaporates and the cooling mechanism is halted as the body returns to its original temperature.
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8
Q

Explain what happens when the bodies core temperature decreases.

A
  1. Thermoreceptors in the thermoregulatory centre in the brains hypothalamus detects the fall in temperature.
  2. Blood vessels constrict and skeletal muscles activated to begin shivering.
  3. The body temperature increases back to the original core temperature and the warming mechanism is halted.
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9
Q

What are endocrine glands?

A

They secrete hormones directly into the blood

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10
Q

What are exocrine glands?

A

Glands that secrete substances into an epithelial surface

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11
Q

Why is the pancreas special in terms of exo and endocrine glands?

A

Can act as both an exocrine gland by decreasing pancreatic juices for digestion
Or as an endocrine gland by secreting hormones form the islets of langerhans

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12
Q

What are the islets of langerhans?

A

Group of cells in the pancreas:

Large alpha cells- produce glucagon

Small beta cells- produce insulin

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13
Q

What is insulin?

A

A hormone that is produced by the beta cells of the islets of langerhans which decreases the blood glucose concentration by increasing the rate of conversion of glucose to glycogen

A quaternary protein made from 2x polypeptide chains and 51 amino acids

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14
Q

How does insulin lower blood glucose concentration?

A
  1. Binds to complementary receptors which change the shape of glucose channel proteins
  2. So more glucose can diffuse from the blood into the cells
  3. This glucose can then be used in respiration(glycolysis)
    Or
    Converted into glycogen
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15
Q

What is glycogenesis?

A

The conversion of glucose to glycogen

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16
Q

What is glycogenolysis?

A

The breakdown of glycogen to glucose

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17
Q

What is gluconeogenesis?

A

Synthesis of glucose from non carbohydrate sources

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18
Q

What factors affect blood glucose concentration?

A 
Liver metabolism 
Glycogenolysis 
Glycogenesis 
Gluconeogenesis 
Glucose from the diet
Exercise
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19
Q

What is caused by having to little glucose in the blood?

A

Hypoglycaemia

Therefore release glucagon

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20
Q

What is caused by having too much glucose in the blood?

A

Hyperglycaemia

Therefore release insulin

21
Q

What happens when blood glucose concentrations rise too high?

A
  1. Beta cells of the islets of langerhans detect the rise in blood glucose concentration.
  2. They secrete insulin and release this into the blood.
  3. Insulin binds to receptors on targeted cells and starts glycogenesis
  4. There is increased respiration of glucose in glycolysis
  5. This is also a change in the tertiary structure of the glucose channel proteins enabling more glucose to diffuse out of the blood
  6. Glucose concentration in the blood falls.
22
Q

What happens when blood glucose concentration falls too low?

A
  1. The alpha cells of the islets of langerhans detect the fall in blood glucose concentration
  2. They secrete glucagon and release it into the blood
  3. Glucagon binds to specific targeted cells activating enzymes
  4. These enzymes converts ATM to cAMP (via the secondary messenger model) which activated other enzymes
  5. These enzymes then start glycogenolysis and gluconeogenesis
  6. Increases glucose in cells which then diffuses into the blood
  7. Glucose concentration in the blood rises
23
Q

What is the secondary messenger model during glucose regulation?

A

Role of adrenaline binding to an enzyme (adenyl cyclase) which converts ATP to cAMP
cAMP activate the enzyme protein kinase which catalysed the conversion of glycogen to glucose

24
Q

What is diabetes?

A

Condition in which the body is no longer able to produce sufficient insulin to control its blood glucose concentration

This results in a person being unable to metabolise carbohydrates and glucose properly

25
Q

What is type 1 diabetes?

A

Insulin dependent
Possibly genetic
When the body cannot synthesis enough insulin (as beta cells are destroyed)
Cannot store glucose as glycogen

Controlled by insulin injections.

26
Q

What is type 2 diabetes?

A

Insulin independent
Influenced by environmental factors such as diet and exercise

Insulin is produced however glycoproteins are unresponsive ( built up tolerance)

Controlled by management of diet and exercise

27
Q

How is insulin produce externally from the body?

A

Used to be extracted from pigs

Produced from GM ecoli

28
Q

Why is insulin from GM ecoli better than insulin from pigs?

A

Exact copies of insulin therefore faster acting

Less chance of tolerance development

Less chance of rejection

Low risk of infection

Cheap to manufacture

Fewer ethical or moral objections

29
Q

What is the function of the kidney?

A

Osmoregulation and excretion

30
Q

What is excretion

A

The removal of metabolic toxic waste

31
Q

What are the functions of these structural components of the kidney?

Fibrous capsule

Cortex

Medulla

Renal pelvis

Ureter

Renal artery

Renal vein

A

Fibrous capsule- outer membrane than protects the kidney

Cortex- outer region made up of renal bowmans capsules

Medulla- inner region made up of loops of Henle

Renal pelvis- collects urine into the ureter

Ureter- tube that carries urine to the bladder

Renal artery- supplies the kidney with blood from the heart

Renal vein- returns blood to the heart from the kidney

32
Q

What are the functions for these structural components of the nephron?

Renal corpuscle

Renal capsule

Glomerulus

Proximal convoluted tubule

Loop of Henle

Distal convoluted tubule

Collecting duct

A

Renal corpuscle- consists of the renal capsule and the glomerulus

Renal bowmans capsule- cup shaped surround in mass of capillaries (glomerulus)

Glomerulus- creates the glomerulus filtrate

Proximal convoluted tubule - where reabsorption of glucose takes place

Loop of Henle- maintenance of gradient of sodium ions in the medulla

Distal convoluted tubule- reabsorption of water

Collecting duct- collection of urine and moves it into the ureter

33
Q

What are the stages in the formation of urine in the kidney?

A
  1. Ultrafiltration
  2. Selective reabsorption
  3. Maintenance of sodium ion gradient
  4. Osmoregulation
34
Q

What happens in ultrafiltration in the kidney?

A

Hydrostatic pressure forces fluid of of the blood and into the limen of the renal capsule.
This is the glomerular filtrate

Blood is left with a lower water potential, red blood cells, proteins as these are too large to be pushed through the gaps between the squamous cells

35
Q

What is contained in the glomerular filtrate?

A 
Water 
Amino acids
Glucose
Urea
Inorganic ions
36
Q

What is the process of selective reabsorption?

A
  1. Sodium ions are actively pumped out of the cells lining the PCT (proximal convoluted tubule) into the nephron fluid
  2. Concentration of sodium ions in the cell falls creating a concentration gradient.
  3. Sodium diffused back in through co-transport proteins along with glucose or amino acids into capillaries
  4. Water follows by osmosis as the water potential is now lowered
  5. Glucose and amino acids diffuse into the blood
37
Q

What components of the glomerular filter are re absorbed?

A

All sugars
All amino acids
Some water
Some ions

38
Q

What is the function of the loop of Henle?

A

To reduce the volume of urine without changing the concentration

Uses a hairpin counter current multiplier system

39
Q

Explain how the loop of Henle reduces the volume and not the concentration of urine?

A
  1. Sodium and chloride ions are actively pumped out of the ascending limb (relatively impermeable to water) of the loop of Henle.
  2. The water potential in the medulla is lowered
  3. Water moves out of the descending limb (permeable to water) via osmosis
  4. This concentrates the fluid in the loop of Henle and the water enters the blood capillaries.
  5. filtrate progressively loses water as it moves down the descending limb, and therefore has the lowest water potential at the bottom of the hair pin loop.
  6. At the base of the ascending limb, sodium and chloride ions diffuse out of the filtrate which is gaining a higher water potential.
  7. There is a constant water potential gradient down the length of the collecting duct.
  8. the collecting duct is permeable to water (controlled by ADH adding aquaporins to the membrane) and therefore water moves out of the filtrate via osmosis and into the blood vessels that occupy this space.
  9. As water diffuses out of the collecting duct the urine loses volume
40
Q

What is osmoregulation?

A

The control of water potential in the body

41
Q

What are osmoreceptors?

A

Receptors that detect changes in water potential

42
Q

What is ADH?

A

Anti Diuretic Hormone

This prevents the production of urine.

43
Q

Explain how water potential is regulated on a hot day?

A
  1. Osmoreceptors in the hypothalamus detect a fall in the water potential (in the blood) as they shrink and shrivel
  2. Cells in the hypothalamus produce ADH and store it in the post posterior pituitary gland (PPG) to be released when water potential drops below normal.
  3. The PPG relaxes ADH into the blood plasma at the kidneys and increases the frequency of impulses to the osmoreceptors to make us thirsty.
  4. ADH binds to protein receptors in epithelial cells of the collecting duct.
  5. The binding of ADH causes vesicles containing aquaporins to move to the lumen side of the epithelial cells.
  6. The vesicles executors the aquaporins which get added to the collecting duct membranes as the vesicles and membranes merge.
  7. Water moves from the filtrate in collecting duct and into the cells and blood within the capillaries
  8. Urines water potential decreases and becomes hypertonic to the blood plasma
  9. Blood water potential rises and is detected by osmoreceptors, therefore sending fewer impulses to the PPG.
  10. Less ADH is release and less aquaporins are added to the membranes
44
Q

Briefly explain the osmoregulation negative feedback loop when water potential increases

A
  1. Detected by osmoreceptors in the hypothalamus
  2. Less ADH is released
  3. Collecting duct is less permeable to water
  4. Less water is reabsorbed
  5. Water potential decreases back to optimum
45
Q

Briefly explain the osmoregulation negative feedback loop when water potential decreases

A
  1. Detected by osmoreceptors in the hypothalamus
  2. More ADH is released
  3. Collecting duct is more permeable to water
  4. More water is reabsorbed
  5. Water potential increases back to optimum
46
Q

What is the counter current multiplier?

A

Fluid in the ascending limb of the loop of henle is flowing in the opposite direction to the filtrate in the collecting duct. This means that the filtrate in the collecting duct with a lower water potential meets the interstitial fluid with an even lower water potential and therefore there is a constant gradient down the whole length of the collecting duct.

47
Q

What are podocytes?

A

Cells found in the inner layer of the renal capsule which have spaces between the cells allowing filtrate to pass beneath them and through gaps.

48
Q

How are the proximal and distal convoluted tubule adapted for their function?

A
  • Microvilli provide large SA for re absorbance of substances from filtrate
  • Infoldings at the bases to give a large SA to transport reabsorbed substances into the blood capillairies
  • High density of mitochondria for active transport

A-level Biology (23 decks)

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