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Year 2 Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What does the term homeostasis mean?

A

Maintenance (controlling) of a constant internal environment

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2
Q

What conditions need to be kept within strict internal limits?

A
  • temperature
  • blood glucose levels
  • water and ion content
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3
Q

Why is maintaining a constant internal environment important in mammals?

A

Regulate enzyme activity (prevent denaturing of enzymes)

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4
Q

Why is maintaining blood glucose levels important?

A
  • glucose essential for respiration (respiratory substrate)
  • prolonged high levels leads to diabetes
  • affects water potential of blood- if conc raises too high, it lowers the water potential of the blood and creates osmotic problems
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5
Q

Why is maintaining water potential of the blood and tissue fluid important?

A
  • changes to the water potential of the blood and tissue fluid may cause cells to shrink and expand (even to bursting point) as a result of water entering or leaving by osmosis = both instances cells can not operate properly
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6
Q

The control of any self-regulating system involves a series of stages that feature:

A
  • optimum point = point at which system operates best- this is monitored by a…
  • receptor = which detects any deviation from the optimum point (I.e. a stimulus) and informs the…
  • coordinator= which coordinates information from receptors and sends instructions to an appropriate…
  • effector= often a muscle or gland which brings about the changes needed to return the system to the optimum point- this return to normality creates a…
  • feedback mechanism = by which a receptor responds to a stimulus created by the change to the system brought about by the effector
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7
Q

Most systems, including biological ones, use negative feedback- what is negative feedback?

A

change produced by the control system triggers a response that reduces effect of change e.g. blood glucose concentration regulation

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8
Q

What is positive feedback?

A

Occurs when a deviation from the optimum causes changes that result in an even greater deviation from the normal e.g. oxytocin (causes contraction of the uterus at child birth and positive feedback means contractions get stronger and more frequent over time leading to birth of baby) and in neurones where a stimulus leads to a small influx of sodium ions- this influx increases the permeability of the neurone membrane to sodium ions, more ions enter, causing a further increase in permeability and even more rapid entry of ions (in this way, a small stimulus can bring about a large and rapid response)

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9
Q

Explain why negative feedback is important in maintaining a system at a set point

A

If the information is not fed back once an effector has corrected any deviation and returned the system to a set point, the receptor will continue to stimulate the effector and an over-correction will lead to a deviation in the opposite direction from the original one

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10
Q

Explain the advantage of having separate negative feedback mechanisms to control deviations away from normal

A

It gives a greater degree of homeostatic control

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11
Q

Describe what happens if thermoreceptors detect a rise in temperature

A
  • normal core body temperature
  • thermoreceptors (in hypothalamus) detect temperature rise
  • hypothalamus heat loss centre
  • impulses to skin (effector organ): vasodilation, sweating, piloerector muscles relax
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12
Q

Describe what happens if the thermoreceptors detect a fall in temperature?

A
  • normal core body temperature
  • thermoreceptors (in hypothalamus) detect drop in temperature
  • hypothalamus heat gain centre
  • impulses to skin (effector organ): vasoconstriction, piloerector muscles contract, shivering
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13
Q

The regulation of blood glucose is an example of how different hormones interact in achieving

A

Homeostasis

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14
Q

Hormones differ from one another chemically but they all have certain characteristics in common:

A
  • produced in glands (endocrine glands), which secrete the hormone directly into the blood
  • carried in the blood plasma to the cells on which they act (target cells) which have specific receptors on their cell-surface membrane that are complementary to a specific hormone
  • effective in very low concentrations, but often have widespread and long-lasting effects
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15
Q

One mechanism of hormone action is known as the second messenger model- what is this?

A

This mechanism is used by adrenaline and glucagon in the regulation of blood glucose concentration

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16
Q

Describe the second messenger model regarding role of 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 on the inside of the membrane
  • this change of protein shape leads to the activation of an enzyme called adenyl cyclase- activated adenyl cyclase converts ATP to cyclic AMP (cAMP)
  • the cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and therefore activating it
  • the active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell via facilitated diffusion and into the blood through channel proteins
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17
Q

Discuss role of pancreas

A
  • large pale-coloured gland situated in the upper abdomen, behind the stomach
  • it produces enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose concentration
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18
Q

When examined microscopically, the pancreas is made up largely of cells that produce its digestive enzymes. Scattered throughout these cells are groups of hormone-producing cells known as

A

islets of Langerhans

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19
Q

The cells of the islets of Langerhans include:

A
  • alpha cells, which are large and produce the hormone glucagon
  • beta cells, which are smaller and produce the hormone insulin
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20
Q

Discuss role of liver

A
  • liver located immediately below the diaphragm and made up of cells called hepatocytes
  • liver serves variety of roles including regulating blood glucose concentration
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21
Q

While the pancreas produces the hormones insulin and glucagon it is in the _____ where they have their effects

A

Liver

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22
Q

What are the 3 important processes associated with regulating blood glucose which take place in the liver?

A
  • glycogenesis
  • glycogenolysis
  • gluconeogenesis
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23
Q

What is glycogenesis?

A

conversion of glucose to glycogen

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24
Q

When does glycogenesis occur?

A

When blood glucose concentration is higher than normal, the liver removes glucose from the blood and converts it to glycogen

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25
Q

What is glycogenolysis?

A

Breakdown of glycogen to glucose

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26
Q

When does glycogenolysis occur?

A

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

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27
Q

What is gluconeogenesis?

A

Production of glucose from sources other than carbohydrate- when its supply of glycogen is exhausted, the liver can produce glucose from non-carbohydrate sources such as glycerol and amino acids

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28
Q

What are factors that influence blood glucose concentration?

A
  • directly from the diet (form off glucose absorbed following hydrolysis of other carbohydrates such as starch, maltose, lactose and sucrose)
  • glycogenolysis
  • gluconeogenesis
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29
Q

As animals do not eat continuously, and their diet varies, their intake of glucose fluctuates. Likewise, glucose is used during respiration at different rates depending on the level of mental and physical activity. It is against these changes in supply and demand that the 3 main hormones operate to maintain a constant blood glucose concentration:

A
  • insulin
  • glucagon
  • adrenaline
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30
Q

The beta cells of the islets of Langerhans in the pancreas have receptors that detect the stimulus of a rise in blood glucose concentration and respond by secreting the hormone

A

insulin directly into the blood plasma

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31
Q

Almost all body cells (except red blood cells) have glycoprotein receptors on their cell-surface membrane that bind specifically with insulin molecules. When it combines with the receptors, insulin brings about:

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 by facilitated diffusion
  • an increase in the number of the carrier proteins responsible for glucose transportation in the cell-surface membrane. At low insulin concentrations, the protein from which these channels are made is part of the membrane of the vesicles. A rise in insulin concentrations results in these vesicles fusing with the cell-surface membrane, so increasing the number of glucose transport channels
  • activation of the enzyme that converts glucose to glycogen and fat
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32
Q

As a result of the effects insulin brings about (when it binds to cell-surface glycoprotein receptors)the blood glucose concentration is lowered in one more ways:

A
  • increasing the rate of absorption of glucose into the cells, especially in muscle cells
  • by increasing the respiratory rate of the cells, which therefore use up more glucose, thus increasing their uptake of glucose from the blood
  • increasing rate of conversion of glucose into glycogen (glycogenesis) in the cells of the liver and muscles

Effects= remove glucose from the blood so return its concentration to the optimum- this lowering of the blood glucose concentration causes the beta cells to reduce their secretion of insulin = negative feedback

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33
Q

The alpha cells of the islets of Langerhans detect a fall in blood glucose concentration and respond by secreting the hormone

A

Glucagon directly into the blood plasma

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34
Q

Glucagon’s actions include:

A
  • attaching to specific protein receptors on the cell-surface membrane of liver cells
  • activating enzymes that convert glycogen to glucose
  • activating enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis)

Effects= overall effect is to increase the concentration of glucose in the blood and return it to its optimum concentration- this raising of blood glucose concentration causes the alpha cells to reduce the secretion of glucagon = negative feedback

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35
Q

There are at least 4 other hormones than glucagon that can raise blood glucose concentration and best know one of these is

A

Adrenaline

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36
Q

Adrenaline is produced by

A

The adrenal glands that lie above the kidneys at times of excitement or stress

37
Q

In a nutshell, adrenaline raises blood glucose concentration by:

A
  • 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
38
Q

The two hormones glucagon and insulin work in opposite directions so they’re said to work

A

Antagonistically

39
Q

What is diabetes?

A

Metabolic disorder caused by an inability to control blood glucose concentration due to a lack of the hormone insulin, or a loss of responsiveness to insulin

40
Q

What are the 2 forms of diabetes?

A
  • type I (insulin dependent)

- type II (insulin independent)

41
Q

Explain type I diabetes (insulin dependent)

A
  • due to body not being able to produce insulin
  • normally begins in childhood
  • may be result of autoimmune response whereby the body’s immune system attacks its own cells (in this case, the beta cells of the islets of Langerhans)
  • type I generally develops over a few weeks and symptoms are often obvious e.g. fatigue, extreme thirst
42
Q

Explain type 2 diabetes (insulin independent)

A
  • normally due to glycoprotein receptors on the body cells being lost or losing their responsiveness (however may also be due to an inadequate supply of insulin from the pancreas
  • type II generally develops in people over age of 40
    (but there is an increasing number of cases of obesity and poor die leading to type II in adolescents
  • type II develops slowly and symptoms normally less severe and go unnoticed
    -people who are overweight are particularly likely to develop type II
  • about 90% of people with diabetes have type II
43
Q

Although diabetes can not be cured, recent trials in ____________________ have shown promise

A

Insulin-producing cells

44
Q

Diabetes can be successfully treated and treatments vary depending on

A

Diabetes type

45
Q

Explain how type I diabetes is treated?

A
  • controlled by insulin injections (cannot be taken orally as, being a protein, insulin would be digested)
  • injected typically 2-4 times a day
  • dose of insulin must be matched exactly to the glucose intake- if a person with diabetes takes too much insulin, they will experience a low blood glucose concentration that will result in unconsciousness = to ensure correct dose, blood glucose concentration is monitored using biosensors
46
Q

How is type II diabetes usually controlled?

A
  • by regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken - in some cases this may be supplemented by injections of insulin or by the use of drugs that stimulate insulin production. Other drugs can slow down the rate at which the body absorbs glucose from the intestine
47
Q

Suggest an explanation as to why tiredness is a symptom of diabetes?

A

If the level of blood glucose concentration is below normal, there may be insufficient glucose for the release of energy by cells during respiration. Muscle and brain cells in particular may therefore be less active,leading to tiredness

48
Q

Suggest what lifestyle advice you would give in order to help someone prevent developing diabetes type II

A
  • match your carbohydrate intake to the amount of exercise that you take
  • avoid becoming overweight by not consuming excessive quantities of carbohydrate and by taking regular exercise
49
Q

In the blood, an optimum concentration of water and salts is maintained to ensure

A

A fairly constant water potential of blood plasma and tissue fluid- homeostatic control of water potential of blood=osmoregulation

50
Q

A section through the kidney shows it is made up of the:

Only nephrons examined but to show bugger picture

A
  • fibrous capsule (outer membrane that protects the kidney)
  • cortex (lighter-coloured outer region made up of renal (Bowman’s) capsules, convoluted tubules and blood vessels
  • medulla (darker-coloured inner region made up of loops of Henle, collecting ducts and blood vessels)
  • renal pelvis (funnel-shaped cavity that collects urine into the ureter)
  • ureter (tube that carries urine to the bladder)
  • renal artery (supplies the kidney with blood from from the heart via the aorta)
  • renal vein (returns blood to heart via vena cava)
51
Q

A microscopic examination of the cortex and medulla reveals around one million tiny tubular structures in each kidney- these are the basic structural and functional units of the kidney:

A

The nephrons

52
Q

The nephron is the functional unit of the kidney- it is a narrow tube up to 14mm long closed at one end, with two twisted regions separated by a long hairpin loop. Each nephronis made up of:

A
  • renal (Bowman’s) capsule= closed end at start of nephron- it is cup-shaped and surrounds a mass of blood capillaries known as the glomerulus. Inner layer of renal capsule is made up of specialised cells called podocytes
  • proximal convoluted tubule= series of loops surrounded by blood capillaries- its walls are made of epithelial cells which have microvilli
  • loop of Henle= a long, hairpin loop that extends from the cortex into the medulla of the kidney and back again- it is surrounded by blood capillaries
  • distal convoluted tubule= series of loops surrounded by blood capillaries- its walls are made of epithelial cells but it is surrounded by fewer capillaries than the proximal tubule
  • collecting duct= a tube into which a number of distal convoluted tubules from a number of nephrons empty- it is lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of the kidney
53
Q

Each nephron is an individual unit for

A

Filtering the blood

54
Q

Associated with each nephron are a number of blood vessels:

A
  • afferent arteriole
  • glomerulus
  • efferent arteriole
  • blood capillaries
55
Q

What is the afferent arteriole?

A

A tiny vessel that arises from the renal artery and supplies the nephron with blood. The afferent arteriole enters the Bowman’s capsule of the nephron where it forms the glomerulus

56
Q

What is the glomerulus?

A

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

57
Q

What is the efferent arteriole?

A

A tiny vessel that leaves the Bowman’s capsule and has a smaller diameter than 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

58
Q

What are the blood capillaries branched from the efferent arteriole?

A

A concentrated network of capillaries that surrounds the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule and from where they reabsorb mineral salts, glucose and water- these capillaries merge together into venules (tiny veins) that in turn merge together to form the renal vein

59
Q

One important function of the kidney is to maintain the water potential of plasma and hence tissue fluid (osmoregulation)- the nephron carries out its role in osmoregulation in a series of stages:

A

1- formation of glomerular filtrate by ultrafiltration
2- selective reabsorption of glucose and water by the proximal convoluted tubule
3- maintenance of a gradient of sodium ions in the medulla by the loop of Henle
4- reabsorption of water by the distal convoluted tubule and collecting ducts

60
Q

Function of kidneys:

A

Kidney is an organ of excretion and osmoregulation
•Excretion is the removal of toxic or excess waste products of metabolism from the body
•Osmoregulation is the regulation of the water potential of the blood and body fluids

61
Q

Excretion of urea, excess water and excess solutes from the blood, in urine occurs in a two-stage process:

A
  • Ultrafiltration is the filtering of small molecules, including urea, out of the blood and into the Bowman’s capsule
  • Selective reabsorption of useful molecules e.g. glucose and some water back into the blood
  • Most selective reabsorption takes place in proximal convoluted tubule (PCT)
62
Q

Explain the process of ultrafiltration

A
  • water, glucose and minerals ions are filtered out of the blood in the capillaries of the glomerulus to form the glomerular filtrate
  • Into the lumen of the Bowman’s capsule
  • Under high hydrostatic pressure (as diameter of afferent arteriole is greater than that of the efferent arteriole= build up of hydrostatic pressure in glomerulus
  • Large proteins ,erythrocytes and leucocytes remain in blood
63
Q

The movement of the glomerular filtrate out of the glomerulus is resisted by the:

A
  • capillary epithelial cells
  • epithelial cells of renal capsule
  • hydrostatic pressure of the fluid in renal capsule space
  • low water potential of the blood in the glomerulus
64
Q

Even though the movement of the glomerular filtrate out of the glomerulus is resisted, this total resistance would be sufficient to prevent filtrate leaving the glomerular capillaries, but there are some modifications to reduce this barrier to the flow of filtrate:

A
  • inner layer of renal capsule is made up of specialised cells called podocytes; these cells have spaces between them, allowing filtrate to pass beneath them and through gaps between their branches =filtrate passes between these cells rather than through them
  • endothelium of glomerular capillaries have spaces up to 100nm wide between its cells = again, fluid can therefore pass between ,rather than through, these cells
  • as a result, hydrostatic pressure of blood in the glomerulus is sufficient to overcome the resistance and so filtrate passes from the blood into the renal capsule
65
Q

What is present in the glomerular filtrate?

A
  • Glucose
  • Amino acids
  • Small proteins
  • Water
  • Inorganic ions (e.g. Na+, Cl-)
  • Urea
  • Uric acid
66
Q

Many of the substances in the filtrate passing out of the blood each minute are extremely important and useful to the body so are

A

Reabsorbed

67
Q

Explain how the structure of the Bowman’s capsule is related to its function of ultrafiltration

A
  • Basement membrane acts as the actual filter
  • Excludes molecules with Mr greater than 69 000
  • Capillary endothelium contains fenestrations (gaps) that allow molecules through
  • Podocytes contain many finger-like projections (allow some molecules to pass through gaps)
  • Increase area of contact with capillaries
  • Flattened cells to provide short diffusion distance
68
Q

Which substances are reabsorbed from glomerular filtrate?

A
  • Glucose
  • Amino acids
  • Small proteins
69
Q

The proximal convoluted tubules are adapted to reabsorb substances into the blood by having epithelial cells that have:

A
  • microvilli to provide a large surface area fo reabsorb substances from the filtrate
  • infoldings at their bases to give a large surface area to transfer reabsorbed substances into blood capillaries
  • high density of mitochondria to provide ATP for active transport e.g Sodium potassium pump
70
Q

Explain the process of reabsorption of glucose and water by the proximal convoluted tubule

A

1- sodium ions actively transported out of the cells lining the proximal convoluted tubule into blood capillaries which carry them away =sodium ion concentration of these cells is therefore lowered

2- sodium ions now diffuse down a diffusion gradient from the lumen of the proximal convoluted tubule into the epithelial lining cells (but only through special carrier proteins by facilitated diffusion)

3- these carrier proteins are of specific types, each of which carries another molecule (glucose or amino acids etc) along with the sodium ions = co-transport

4- the molecules which have been co-transported into the cells of the proximal convoluted tubule then diffuse into the blood = all the glucose and most other valuable molecules are reabsorbed as well as water

71
Q

What is the role of the loop of Henle?

A

To establish a lower water potential in the tissue fluid of the medulla than the water potential of the fluid in the collecting duct
•This allows water to be reabsorbed from the fluid in the collecting duct by osmosis down a water potential gradient
•The water potential becomes increasingly lower (more negative) deeper in the medulla to maintain this water potential gradient

72
Q

The loop of Henle has 2 regions:

A
  • descending limb= narrow with thin walls that are highly permeable to water
  • ascending limb= thicker and impermeable to water
73
Q

Explain how the loop of Henle is responsible for water absorption and ensures the urine has a lower water potential than the blood

A

1- sodium ions actively transported out of ascending limb using ATP provided by the many mitochondria in the cells of its walls

2-this creates a low water potential (high ion concentration) in the region of the medulla between between the two limbs. In normal circumstances water would pass out of the ascending limb by osmosis. However, the thick walls are almost impermeable to water and so very little, if any, escapes

3- the walls of the descending limb are however very permeable to water and so it passes out the filtrate by osmosis into the region of the medulla between the two limbs

4- the filtrate progressively loses water in this way as it moves down the descending limb lowering its water potential; it reaches its lowest water potential at the tip of the hairpin

5- at the base of the ascending limb, sodium ions diffuse out of the filtrate and as it moves up the ascending limb these ions are also actively pumped out (step 1) and therefore the filtrate develops a progressively higher water potential

6- in the interstitial space between the ascending limb and the collecting duct there is a gradient of water potential with the highest water potential (lowest concentration of ions) in the cortex and and increasingly lower water potential (higher concentration of ions) the further into the medulla one goes

7- the collecting duct is permeable to water and so as the filtrate moves down it, water passes out of it by osmosis. This water passes by osmosis into the blood vessels that occupy this space and is carried away

8- as water passes out of the filtrate its water potential is lowered. However, the water potential is also lowered in the interstitial space and so water continues to move out by osmosis down the whole length of the collecting duct- the counter-current multiplier ensures that there is always a water potential gradient drawing water out of the tubule

74
Q

What supplies kidneys with blood?

A

Renal arteries

75
Q

The water that passes out the collecting duct by osmosis does so through channel proteins that are specific to water (aquaporins). What hormone can alter the number of these channels and so control water loss?

A

ADH

76
Q

By the time the filtrate, now urine, leaves the collecting duct on its way to the bladder, it has lost most of its water and so

A

It has a lower water potential (is more concentrated) than the blood

77
Q

The cells that make up the walls of the DCT have microvilli and many mitochondria that allow them to reabsorb material rapidly from the filtrate by active transport. The main role of the DCT however is

A

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- to achieve this, the permeability of its walls becomes altered under the influence of various hormones

78
Q

Explain Hairpin Countercurrent Multiplier:

A
  • Hairpin arrangement of tubule
  • Countercurrent since filtrate flows in opposite directions in the two limbs of the loop
  • Multiplier increases the efficiency of transfer of (sodium and chloride) ions out of the ascending limb into the medulla to create a higher salt concentration (lower water potential) at the base of the loop
79
Q

Name the structure in the nephron where the majority of water is reabsorbed

A

Proximal convoluted tubule

80
Q

Some desert mammals have long loops of Henle. How is this feature an adaption to living in desert conditions?

A
  • longer the loop of Henle, the more concentrated (lower water potential) the tissue fluid in the medulla becomes
  • causes more water to be reabsorbed from fluid in collecting duct
  • so less water lost in urine
81
Q

The homeostatic control of osmoregulation (regulation of water potential in the blood) is achieved by a hormone that acts on the

A

Distal convoluted tubule and collecting duct

82
Q

The water potential of the blood depends on

A

The concentration of solutes like glucose, proteins, sodium chloride, and other mineral ions as well as the volume of water in the body

83
Q

A rise in solute concentration lowers its water potential (of blood); this may be caused by:

A
  • too little water being consumed
  • much sweating occurring
  • large amounts of ions, for example sodium chloride, being taken in
84
Q

Explain how the body responds to a fall in water potential of the blood:

A
  • cells called osmoreceptors in the hypothalamus detect the fall in water potential
  • it is thought that when the water potential of the blood is low, water is lost from osmoreceptors through osmosis
  • due to the water loss, the osmoreceptor cells shrink, a change that causes the hypothalamus to produce a hormone called ADH
  • ADH passes to the posterior pituitary gland, from where it is secreted into the capillaries
  • ADH passes into the blood of the kidneys, where it increases the permeability to water of the cell-surface membrane of the cells that make up the walls of the distal convoluted tubule and the collecting duct
  • specific protein receptors on the cell-surface membrane of these cells bind to ADH molecules, leading to activation of an enzyme called phosphorylase within the cell
  • activation of phosphorylase causes vesicles within the cell to move to, and fuse with its-cell surface membrane
  • these vesicles contain pieces of plasma membrane that have numerous aquaporins, and so when they fuse with the membrane, the number of water channels is significantly increased, making the cell-surface membrane much more permeable to water
  • ADH increases the permeability of the collecting duct to urea, which therefore passes out, further lowering the water potential of the fluid around the duct
  • the combined effect is that more water leaves the collecting duct by osmosis, down a water potential gradient and re-enters the blood
  • as the reabsorbed water came from the blood in the first place, this will not in itself, increase the water potential of the blood, but merely prevent it getting lower- osmoreceptors also send nerve impulses to the thirst centre of the brain, to encourage the individual to seek out and drink more water
  • the osmoreceptors in the hypothalamus detect the rise in water potential and send fewer impulses to the pituitary gland
  • the pituitary gland reduces the release of ADH and the permeability of collecting ducts to water and urea reverts it to its former state. = negative feedback
85
Q

A fall in the solute concentration of the blood increases the water potential this may be caused by:

A
  • large volumes of water being consumed

- salts used in metabolism or excreted are nit being replaced in the diet

86
Q

Explain how the body responds to a rise in water potential of the blood

A
  • osmoreceptors in hypothalamus detect the rise in water potential and increase the frequency of nerve impulses to the pituitary gland to reduce its release of ADH
  • less ADH, via the blood, leads to a decrease in the permeability of the collecting ducts to water and urea
  • less water is reabsorbed into the blood from the collecting duct
  • more dilute urine is produced and the water potential of the blood falls
  • when the water potential of the blood has returned to normal, the osmoreceptors in the hypothalamus cause the pituitary gland to raise its ADH release back to normal levels= negative feedback
87
Q

Like other mammals, seals produce urine which is more concentrated than their blood plasma. Explain the role of the loop of Henle in producing concentrated urine

A
  1. salt/(sodium) ions diffuse into descending limb;
  2. water moves out of descending limb;
  3. salt/(sodium) ions actively removed from ascending limb;
  4. ascending limb impermeable to water;
  5. low water potential/ high concentration of ions in medulla/tissue fluid; 6. water leaves collecting duct / distal tubule;
  6. due to difference in water potential / by osmosis;
88
Q

How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency?

A
  1. Body temp./37 °C is optimum temp for enzymes;
  2. excess heat denatures enzymes/alters tertiary structure/
    alters shape of active site/enzyme;
  3. substrate cannot bind/eq,;
  4. reactions cease/slowed;
  5. too little reduces kinetic energy of molecules / molecules
    move more slowly;
  6. fewer collisions/fewer ES complexes formed’

Year 2 Biology (4 decks)

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