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AQA A Level Biology > 6-16 Homeostasis > Flashcards

6-16 Homeostasis Flashcards

1
Q

What is homeostasis?

A

The maintenance of internal conditions

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2
Q

What is negative feedback?

A

A change from the optimum causes a response which moves towards the optimum

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3
Q

What does ectothermic mean?

A

Where an organism gains heat from their environment so their body temperature fluctuates with the environment
Adapt their behaviour to suit the conditions

Expose themself to the sun
Reptiles and amphibians

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4
Q

What does endothermic mean?

A

Metabollic activities take place inside their bodies which provides the heat needed

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5
Q

What is the difference in speed between the nervous and hormonal system?

A

The nervous system is faster than the hormonal system

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6
Q

What are the characteristics of hormones?

A

Produced in the glands
Carried in the blood plasma to the cells on which they act (target cells)
Are effective in low concentrations but have long lasting effects

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7
Q

What is the mechanism involving adrenaline?

A

Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of a liver cell
The binding of adrenaline causes the protein to change shape

The change of protein shape leads to the activation of an enzyme called adenyl cyclase. The activated adenyl cyclase converts ATP to cyclic AMP (cAMP)
The cAMP in turn changes the shape and activates protein kinase enzyme
The active protein kinase enzyme catalyses the conversion of glycogen to glucose

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8
Q

What are the groups of hormone producing cells known as?

A

Islets of Langerhans

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9
Q

What are the two types of cells in the islets of langerhans?

A

Alpha: larger and produces the hormone glucagon
Beta: smaller and produces the hormone insulin

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10
Q

What are the three process in the regulation of blood sugar?

A

Glycogenesis
Glycogenolysis

Gluconeogenesis

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11
Q

What is glycogenesis?

A

The conversion of glucose into glycogen
When blood glucose concentration is higher than normal the liver removes glucose from the blood and converts it to glycogen

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12
Q

What is glycogenolysis?

A

The breakdown of glycogen to glucose
When blood glucose concentration is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose concentration

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13
Q

What is gluconeogenesis?

A

The production of glucose from sources other than carbohydrate
When its supply of oxygen is exhausted, the liver can produce glucose from non-carbohydrate sources such as glycerol and amino acids

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14
Q

Why do hormones only affect target cells?

A

Because only target cells have the specific protein receptors that are complementary to the shape of that specific hormone

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15
Q

What occurs if the blood glucose concentration is too high?

A

It lowers the water potential of the blood and causes dehydration

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16
Q

What occurs if the blood glucose concentration is too low?

A

Cells will be deprived of energy and die

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17
Q

What are the factors which increase glucose concentration?

A

Your diet where glucose is absorbed via the absorption of carbohydrates
From the hydrolysis in the small intestine of glycogen (glycogenolysis)

From gluconeogenesis

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18
Q

What are the three main hormones involved in the regulation of blood glucose concentration?

A

Insulin, glucagon and adrenaline

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19
Q

What do B cells of the pancreas do?

A

They have receptors which detect the stimulus of a rise in blood glucose concentration
Then they respond by secreting the hormone insulin directly into the blood plasma

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20
Q

What type of molecule is insulin?

A

A globular protein

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21
Q

What does insulin bind to?

A

Insulin bind specifically to glycoprotein molecules on the cell surface membranes of body cells

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22
Q

What does insulin cause when it binds to receptors on body cells?

A

A change in the tertiary structure of the glucose transport carrier proteins, causing them to change shape and open, allowing more glucose into the cells via facilitated diffusion
An increase in the number of carrier proteins responsible for glucose transport. At low insulin concentrations, the protein from which these channels are made is part of the membrane of vesicles. A rise in insulin concentration results in these vesicles fusing with the cell-surface membrane so increasing the number of glucose transport channels

Activation of the enzymes that convert glucose to glycogen and fat

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23
Q

How does the lowering of blood glucose affect B cells?

A

Their secretion of insulin reduces

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24
Q

What is the function of the alpha cells of the islets of Langerhans?

A

They detect a fall in blood glucose concentration and respond by secreting the hormone glucagon directly into blood plasma

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25
Q

What are the effects of glucagon in the blood?

A

It attaches to specific protein receptors on the cell surface membrane of liver cells
It activates enzymes that convert glycogen to glucose

Activates enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis)

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26
Q

How does the raising of blood glucose affect alpha cells?

A

It causes the alpha cells to reduce the secretion of glucagon

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27
Q

What is the role of adrenaline in regulating the blood glucose level?

A

Adrenaline increases the blood glucose concentration
It does this by:

Attaching to protein receptors on the cell-surface membrane of target cells
Activating enzymes that causes the breakdown of glycogen to glucose in the liver

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28
Q

What is diabetes?

A

A disease in where a person is unable to metabolise carbohydrate, especially glucose, properly

29
Q

What is type I diabetes?

A

Insulin dependent

Due to the body being unable to produce insulin

30
Q

What is type II diabetes?

A

Insulin independent
Normally due to glycoprotein receptors on body cell being lost or losing their responsiveness to insulin

It may also be due to an inadequate supply of insulin from the pancreas

31
Q

What are the treatment options for type I diabetes?

A

Controlled by injections of insulin
The dose of insulin must be matched exactly to the glucose intake

To ensure the correct dose, blood glucose concentration is monitored using biosensors

32
Q

What are the treatment options for type II diabetes?

A

By regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken
And in some cases, injecting insulin and using drugs to slow down the rate at which glucose is absorbed

33
Q

What are the two stages of the control of blood glucose concentration?

A

Low blood sugar: glucagon, hydrolyses glycogen bonds, glycogenolysis
High blood sugar: insulin, adds glucose to glycogen, creates glycosidic bonds, glucogenesis

34
Q

What is osmoregulation?

A

The homeostatic control of the water potential of the blood

35
Q

What carries out osmoregulation?

A

The kidney and in particular, the nephron

36
Q

What is the shape of the nephron?

A

A narrow tube closed at one end with two twisted regions separated by a long paperclip loop

37
Q

What is the structure of the nephron?

A

Renal capsule
Proximal convoluted tubule

Loop of Henle
Distal convoluted tubule
Collecting duct

38
Q

What is the renal capsule?

A

The closed end at the start of the nephron
It surrounds a mass of blood capillaries known as the glomerulus

The inner layer is made of specialised cells called podocytes

39
Q

What is the proximal convoluted tubule?

A

A series of loops surrounded by blood capillaries

It’s walls are made of epithelial cells and microvilli

40
Q

What is the loop of Henle?

A

A long hairpin loop which extends from the cortex into the medulla of the kidney (further towards the centre) and back again
It is surrounded by blood capillaries

41
Q

What is the distal convoluted tubule?

A

A series of loops surrounded by blood capillaries
Its walls are made of epithelial cells

Surrounded by fewer capillaries than the proximal tubule

42
Q

What is the collecting duct?

A

A tube into which a number of distal convoluted tubules from a number of nephrons empty
Lined with epithelial cells and becomes increasingly wide as it empties

43
Q

What are the four blood vessels in the nephron?

A

Afferent arteriole
Glomerulus

Efferent arteriole
Blood capillaries

44
Q

What is the afferent arteriole?

A

A tiny vessel which arises from the renal artery and supplies the nephron with blood
The afferent arteriole enters the renal capsule of the nephron where it forms the glomerulus

45
Q

What is the glomerulus?

A

A many branched knot of capillaries from which the fluid is forced out of the blood
The glomerulus capillaries recombine to form the efferent arteriole

46
Q

What is the efferent arteriole?

A

A tiny vessel that leaves the renal capsule
It has a smaller diameter than the afferent arteriole and so causes an increase in blood pressure within the glomerulus

The efferent arteriole carries blood away from the renal capsule and later branches to form the blood capillaries

47
Q

What are the blood capillaries in the nephron?

A

A concentrated network of capillaries that surrounds the proximal convoluted tubule and forms where they reabsorb mineral salts, glucose and water
The capillaries merge together into venules, tiny veins that in turn merge into the renal vein

48
Q

What are the stages of osmoregulation of the nephron?

A

The formation of glomerular filtrate by ultrafiltration
Reabsorption of glucose and water by the proximal convoluted tubule

Maintenance of a gradient of sodium ions in the medulla by the loop of Henle
Reabsorption of water by the distal convoluted tubule and collecting ducts

49
Q

What is the process of the formation of glomerular filtrate by ultrafiltration?

A

The walls of the glomerulus capillaries are made up of epithelial cells with pores between them
As the diameter of the afferent arteriole is greater than that of the efferent arteriole, there is a build up of hydrostatic pressure

Therefore water, glucose and mineral ions are squeezed out of the capillary to form the glomerular filtrate
Blood cells and proteins do not pass through as they are too large

50
Q

What is the movement of filtrate out of the glomerulus resisted by?

A

Connective tissue and epithelial cells
Hydrostatic pressure of the fluid in the renal capsule space

The low water potential of the blood

51
Q

What modifications cause filtrate to move out of the glomerulus?

A

The inner layer called podocytes have spaces between them which allows filtrate to pass between these cells rather than through them
The endothelium has spaces between its cells to allow the movement of fluid

52
Q

During ultrafiltration of the glomerulus, where does filtrate move between?

A

Filtrate passes from the blood into the renal capsule

Useful substances are small so are reabsorbed

53
Q

How are the epithelial cells in proximal convoluted tubules adapted to reabsorb substances into the blood?

A

They have microvili to provide a large surface area
They have infoldings at their bases to to give a larger surface area to transfer reabsorbed substances into blood capillaries

They have a high density of mitochondria to provide ATP for active transport

54
Q

What is the process for the reabsorption of glucose and water by the proximal convoluted tubule?

A

Sodium ions are actively transported out of the proximal convoluted tubule cells into blood capillaries which lowers the sodium ion concentration
Sodium ions diffuse down a concentration gradient from the lumen of the proximal convoluted tubule into the epithelial lining cells through carrier proteins via facilitated diffusion

These carrier proteins are of specific types, each of which carries another molecule along with the sodium ions
The molecules which have co-transported into the cells of the proximal convoluted tubule diffuse into the blood. This causes most valuable molecules to be absorbed

55
Q

What is the purpose of the loop of Henle?

A

It is responsible for water being reabsorbed from the collecting duct, thereby concentrating the urine so that it has a lower water potential than the blood

56
Q

What are the two regions of the loop of Henle?

A

Descending limb: narrow, thin walls which are highly permeable to water
Ascending limb: wider, thick walls which are impermeable to water

57
Q

What is the process of the loops of Henle?

A

Sodium ions actively transported out of the ascending limb using ATP provided by mitochondria
This causes a low water potential in the medulla region between the two limbs. No water moves into this region as the walls are impermeable

In the descending limb where the walls are permeable, water enters the interstatial space which then enters blood capillaries by osmosis and is carried away
The filtrate progressively loses water as it moves down the descending limb, reaching its lowest water potential at the tip
At the base of the ascending limb, sodium ions diffuse out of the filtrate and as it moves up they are also actively pumped out which raises the water potential
In the interstatial space between the ascending limb and the collecting duct, there is a water potential gradient with the lowest potential reaching into the medulla
The collecting duct is permeable to water and so as the filtrate moves down it, water passes out. This water passes by osmosis into the blood vessels that occupy this space, and is carried away
As water passes out of the filtrate, its water potential is lowered. However water is lowered in the intestinal space so water continues to move out by osmosis down the whole length of the collecting duct. The counter current multiplier ensures there is always a water potential gradient drawing water out of the tubule

58
Q

What is the structure of the loop of Henle?

A

Filtrate from the proximal convoluted tubule goes into the start of the loop, moving from the cortex into the medulla
Descending limb with walls permeable to water

Filtrate then moves into the ascending limb which is impermeable to water
Then the filtrate moves into the distal convoluted tubule
Then filtrate moves into the collecting duct with walls that vary in their permeability to water

59
Q

What allows water to move in the collecting duct?

A

Water moves out of the collecting duct through channel proteins that are specific to water

60
Q

How does ADH affect osmosis in the collecting duct?

A

Antidiuretic hormone can alter the number of these channels and so control water loss
By the time the filtrate, now called urine, leaves the collecting duct on its way to the bladder, it has lost most of its water and so has a lower water potential than the blood

61
Q

What is the distal convoluted tubule? What is its role?

A

The cells making up the distal convoluted tubule have microvilli and many mitochnodria that allow them to reabsorb material rapidly from the filtrate by active transport
The main role is to make final adjustments to the water and salts that are reabsorbed and to control the pH of the blood by selecting which ions to reabsorb

The wall therefore changes in permeability under the influence of various hormones

62
Q

Why is the loop of Henle called a counter-current multiplier?

A

The filtrate in the collecting duct with a lower water potential meets interstatial fluid that has a lower water potential
Therefore there is a constant flow of water into the interstatial fluid and then into the blood

63
Q

What causes a low water potential in the blood?

A

Too little water being consumed
Large amounts of sweating

Large amounts of ions being taken in e.g. sodium chloride

64
Q

What is the process for the body’s response to a fall in water potential?

A

Osmoreceptors in the hypothalamus detect the fall in water potential
When water potential is low, water is lost from these receptors which causes them to shrink

This change causes the hypothalamus to produce ADH
ADH passes into the pituitary gland then into the capillaries
ADH passes into the kidney through the blood where it increases the permeability to water of the cell-surface membranes of the collecting duct and distal convoluted tubule
Protein receptors on the cell surface membrane of the distal convoluted tubule and collecting duct bind to ADH, leading to the activation of an enzyme phosphorylase
The activation of phosphorylase causes vesicles to fuse with the cell-surface membrane
These vesicles contain pieces of plasma membrane that have numerous water channel proteins so fusing increases the number of water channels and increases the permeability

65
Q

What is the cortex?

A

An outer region of the kidney make up of renal capsules, convoluted tubules and blood vessels

66
Q

What is the medulla?

A

The inner region of the kidney made of loops of Henle, collecting ducts and blood vessels

67
Q

What is the simplified process of the loop of Henle?

A

Sodium moves out of the ascending limb
Low water potential in the region between the limbs

The walls are impermeable
In the descending limb, the walls are permeable so water moves into the interstitial space
The filtrate loses water as it moves down the descending limb
At the start of the ascending limb, sodium diffuses and, further up, is actively transported out
In the interstitial space, the lowest water potential reaches into the medulla
Collecting duct = permeable to water so water passes out of the filtrate going down the collecting duct and into the blood where it is carried away
The water potential of the filtrate is lowered but water is lowered in the interstitial space so the water potential gradient still causes movement. This is a countercurrent multiplier

68
Q

What is another name for the renal capsule?

A

The Bowman’s capsule

AQA A Level Biology (19 decks)

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