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A LEVEL BIOLOGY > Homeostatis > Flashcards

Homeostatis Flashcards

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1
Q

What is homeostasis?

A

the maintenance of a constant internal environment

- it involves trying to maintain the chemical make-up, volume and other features of blood and tissue fluid

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2
Q

At optimum point of homeostasis, what changes occur?

A 
changes in:
- temperature
- pH
- water potential 
> Homeostasis has the ability to return to that optimum point so organisms maintain a balanced equilibrium
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3
Q

Importance of homeostasis

A
  • the enzymes that control biological reactions and other protein such as channel proteins are sensitive to changes in pH and temperature, denaturing them
  • changes to the water potential of the blood and tissue fluids may cause to shrink and expand as a result of water leaving or entering by osmosis. The maintenance of a constant blood glucose concentration is essential in ensuring a constant water potential
  • organisms with the ability to maintain a constant internal environment are more independent of changes in external environment
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4
Q

Control mechanisms

A
  • optimum point: the point at which the system operates best and is monitored by a receptor
  • receptor which detects any deviation from the optimum point and informs the coordinator
  • coordinator which coordinates information from receptors and sends instructions to an appropriate effector
  • effector which is 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
  • 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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5
Q

Coordination of control mechanisms: Negative Feedback

A
  • negative feedback: when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
    > An example of this is the regulation of blood glucose
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6
Q

Coordination of control mechanisms: Positive Feedback

A
  • this occurs when a deviation from optimum causes changes that result in neurones where a stimulus leads to a small influx of sodium ions
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7
Q

Features of control systems

A
  • they have many receptors and effectors which allows them to have separate mechanisms that each produce a positive movement towards optimum
  • has separate mechanisms that controls departures in different directions from an original state
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8
Q

Vasoconstriction

A

narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels

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9
Q

Vasodilation

A

dilation of blood vessels which decrease blood pressure

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10
Q

Animals two principal coordinating systems:

A
  • The nervous system: which communicates rapidly
  • the hormonal system, which usually communicates more slowly
    > They both interact in order to maintain the constancy of the internal environment
    > both systems also use chemical messengers
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11
Q

Conserving and gaining heat in response

A
  • Shivering: muscles undergo involuntary rhythmic contractions that produce metabolic heat
  • Raising of hair: This enables a thicker layer of still air which is a good insulator to be trapped next to the skin, insulation and conserving heat in mammals with thick fur
  • decrease in sweating: sweating is reduced
  • increased metabolic rate:: metabolic activity including respiration is increased so more heat is generated
  • behavioural mechanisms:
    sheltering from the wind, basking in the sun and huddling together all help animals to maintain their core body temp
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12
Q

Losing heat in response to a warm environment

A
  • vasodilation: diameter of arterioles near the surface of the skin becomes larger and this allows warm blood to pass close to the surface of the skin
  • increased sweating: evaporate water from the skin surface requires energy in the form of heat
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13
Q

Hormones and their mode of action

A

Hormones are:

  • produced in glands which secrete the hormone directly into the blood
  • carried in the blood plasma where they act as target cells– they have specific recpetors on their cell surface membrane
  • are effective in very low concentrations but often have long-lasted effects
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14
Q

Mechanism of hormone action is know as:

A

the second messenger model

which is used by two hormones involved in the regulation of blood glucose concentration, namely adrenaline and glucagon

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15
Q

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 on the inside of the membrane
  • The change of protein shape leads to the activation of the enzyme of adenyl cyclease which converts ATP to cyclic AMP (cAMP)
  • The cAMP acts as a second messenger that binds to protein kinase enzyme changing its shape and activating it
  • the enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins
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16
Q

The role of the pancreas in regulating blood glucose

A
  • the pancreas produces enzymes such as protease, amylase and lipase for digestion
  • produces hormones such as insulin and glucagon for regulating blood glucose concentration
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17
Q

cells of the islets of Langerhans include:

A
  • a cells which are the larger and produce the hormone glucagon
  • B cells which are smaller and produce insulin
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18
Q

Endotherms

A
  • endo means inside
    Temperature regulation:
  • all mammals generate heat within their bodies – endothermic
  • due to exergonic reactions like respiration in the liver
  • physiological regulation mechanisms involve sweat glands, skeletal muscle movements
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19
Q

role of receptors

A

they recognise changes in the surroundings (stimuli) and send impulses to the control centre

20
Q

role of control centre

A

Make a decision about the appropriate actions and send an electrical impulse to the effectors

21
Q

role of effectors

A

A muscle or a gland that carries out the response to make the change

22
Q

What is osmoregulation?

A

Homeostatic control of the water potential of the blood

23
Q

Liver undergoes 3 stages to regulate blood sugar levels

A
  • glycogenesis
  • Glycogenolysis
  • Gluconeogenesis
24
Q

What is gylcogenesis

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

25
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

26
Q

What is Gluconeogenesis

A

What is the 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

27
Q

Regulation of blood glucose concentration

A
  • Glucose is a substrate for respiration, providing the source of energy
  • it is essential that the blood of the mammals contains a relatively constant concentration of glucose for respiration
  • if the concentration falls too low, the cells will be deprived of energy and die, brain cells are especially sensitive because they can only respire glucose
  • if concentration rises too high, it lowers water potential of the blood and creates osmotic problems that can cause dehydration
    HOMEOSTATIC CONTROL OF BLOOD GLUCOSE IS THEREFORE ESSENTIAL
28
Q

Factors that influence blood glucose concentration

A

The normal concentration of blood glucose is 5mmoldm-3. Blood glucose comes from 3 sources:
- directly from the diet in the form of glucose absorbed following hydrolysis of carbs such as starch, maltose, lactose and sucrose
- from the hydrolysis in the small intestine of glycogen = glycogenolysis stored in the liver and muscle cells
- from gluconeogenesis which is the production of glucose from other sources other than carbohydrate
ANIMALS DON’T EAT SO GLUCOSE LEVELS FLUCTUATE AND THEY NEED INSULIN, GLUCAGON AND ADRENALINE TO MAINTAIN A CONSTANT GLUCOSE CONCENTRATION

29
Q

Insulin and B cells of the pancreas

A

b cells of the islets of Langerhans in the pancreas have receptors that detect the stimulus of a rise in blood glucose and respond by secreting insulin
INSULIN IS A GLOBULAR PROTEIN MADE UP OF 51 AMINO ACIDS

30
Q

Insulin brings about

A
  • change in teritary structure of the glucose transport carrier proteins causing them to change shape and open allowing more glucose into cells by facilitated diffusion.
    increase in number of carrier proteins responsible for glucose transport in the cell surface membrane
  • activation of the enzymes that convert glucose to glycogen and fat
31
Q

Blood glucose concentration is lowered in one or more of the following ways

A
  • increasing the rate of absorption of glucose in the cells, especially in muscle cells
  • by increasing the respiratory rate of the cells which use up more glucose, thus increasing their uptake of glucose from the blood
  • by increasing the rate of conversation of glucose into glycogen in the cells of the liver and muscles
  • by increasing the rate of conversion of glucose to fat
    THE LOWERING OF GLUCOSE CONCENTRATION CAUSES THE B CELLS TO REDUCE THEIR SECRETION OF INSULIN = negative feedback
32
Q

Glucagon and the a cells of the pancreas

A

a cells of the islets of Langerhans detect a fall in blood glucose concentration and respond by secreting the hormone glucagon into the blood plasma
Glucagon action:
- 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 in to glucose (gluconeogenisis)

33
Q

Role of adrenaline in regulating the blood glucose level

A

Adrenaline rises the blood glucose concentration by:

  • attaching to protein receptors on the cell-surface membrane of target cells
  • activating enzymes involved in the conversion of amino acids and glycerol into glucose in the liver
34
Q

Hormone interaction in regulating blood glucose

A

the two hormones insulin and glucagon act in opposite directions

  • insulin lowers the blood glucose concentration whereas glucagon increase s it
  • the two hormones act antagonistically
35
Q

What is diabetes

A

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

36
Q

Type 1 diabetes (insulin dependent)

A
  • type 1 is caused by the body being unable to produce insulin
  • it may be a result of an autoimmune response whereby the body’s immune system attacks its own cells
  • so b cells of the islets of Langerhans.
37
Q

Type 2 diabetes (insulin independent)

A
  • due to glycoprotein receptors on body cells being lost or lose their responsiveness to insulin
  • it could also be due to an inadequate supply of insulin from the pancreas
  • it usually occurs in people of age of 40
  • there is a increasing number of cases of obesity and poor diet leading to type 2 diabetes
  • it happens gradually and symptoms are usually less severe and may go unnoticed
38
Q

How to control type 1 diabetes

A
  • controlled by injections of isulin
  • it can’t be taken by mouth because its a protein and it would be digested in the alimentary canal
  • so its injected two or four times a day
  • dose of insulin must match intake glucose
  • if a person takes too much insulin they will experience a low blood concentration and result in unconsciousness
  • to ensure the correct dose, blood glucose concentration is monitored using biosensors
  • by injecting insulin, managing their carbohydrate intake and exercise carefully, people with diabetes can lead normal lives
39
Q

Type 2 diabetes

A
  • usually controlled by regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken
  • maybe the use of drugs that stimulate insulin production
  • or other drugs can slow down the rate at which the body absorbs glucose from the intestine
40
Q

structure of the mammalian kidney

A
  • fibrous capsule: an outer membrane that protects the kidney
  • cortex: a lighter coloured outer region made up of renal (bowmans) capsule, convoluted tubules and blood vessels
  • medulla: dark coloured inner region made up of loops of Henle, collecting ducts and blood vessels
  • renal pelvis: funnel shaped cavity that collects urine into ureter
  • ureter: a tube that carries urine to the bladder
  • renal artery: supplies the kidney with blood from the heart via the aorta
  • renal vein: returns blood to the heart via the vena cava
41
Q

Structure of the nephron

A
  • glomerulus: mass of blood capillaries
  • bowmans capsule: cup shaped and surrounds the glomerulus. the inner layer of the bowmans capsule is made up specialised cells called podocytes
  • promiximal convoluted tubule: loops surrounding by blood capillaries. its walls are made of epithelial cells that have microvilli
  • loop of henle: a long loop that extends from cortex into medulla of kidney and back (ascending and descending)
  • Distal convoluted tubule: series of loops surrounded by blood capillaries. its walls are made of epithelial cells but its surrounded by less capillaries than proximal tubule
  • collecting duct: a tube from which distal convoluted tubule empty in, lines by epithelial cells and becomes wide as it empties into the pelvis of kidney
42
Q

Nephron has blood vessels

A
  • afferent arteriole: tiny vessel that arises from renal artery and supplies nephron with blood. The affarent enters the bowmans capsule of nephron to form…
  • glomerulus: branched knot of capillaries from which fluid is forced out of blood. glomerular capillaries recombine to form…
  • efferent arteriole: tiny vessels that leaves the bowmans capsule. has a smaller diameter than the affarent. affarent carries blood away from bowmans capsule and branches to form…
  • blood capillaries: capillaries that surround the PCT , the loop of Henle and DCT and from where they reabsorb mineral salts, glucose and water. These capillaries merge together into venules that merge to form the renal vein
43
Q

Osmoregulation in stages

A

1) formation of glomerular filtrate by ultrafiltration
2) reabsorption of glucose and water by PCT
3) maintenance of a gradient of sodium ions in the medulla by the loop of Henle
4) reabsorption of water by the DCT and collecting ducts

44
Q

Regulation of the water potential of the blood

A

The water potential of the blood depends on the concentration of solutes like glucose, proteins, sodium chloride and other mineral ions
A rise is solutes concentration lowers its water potential. This may be caused by:
- too little water being consumed
- much sweating occurs
- large amounts of irons e.g sodium chloride being take in

45
Q

The body responds to this fall in water potential as follows:

A
  • Osmorecetors in the hypothalamus of the brain detect the water fall in water potential
  • if the water potential is lower, water is lost from osmoreceptor cells by osmosis
  • osmoreceptors in the cells shrink, a change causes the hypothalamus called ADH
  • ADH is passed to the posterior pituitary gland from where its secreted into capillaries
  • ADH passes in the blood increasing the permeability to water of the cell surface membrane of the cells that make up walls of DCT and the collecting duct
  • protein receptors on the cell surface membrane of these cells bind to ADH leading to activation of phophorylase
  • Phosphorylase causes vesicles within the cell to move and fuse with its cell surface
  • vesicles contain pieces of plasma membrane that have aquaporins and when they fuse with the membrane, the number of water channels increase making the cell surface membrane more permeable to water
  • ADH increases the permeability of collecting duct to urea which passes out, lowering the water potential of the fluid around the duct
  • the more water that leaves the collecting duct by osmosis goes down a WP gradient and re enters the blood
  • re absorbed water came from the blood and this will increase the WP of the blood and prevent it getting lower,
    osmoreceptors send nerve impulses to the thirst centre of the brain to encourage individual to drink more water
  • osmoreceptors in the hypothalamus detect the rise in water potential and send fewer impulses to the pituitary gland
  • pituitary gland reduces the release of ADH and the permeability of the collecting ducts to water and urea reverts to its former state
    THIS IS AN EXAMPLE OF HOMEOSTASIS AND NEGATIVE FEEDBACK
46
Q

A fall in the solute concentration of the blood raises its water potential. This may be caused by:

A
  • large volumes of water being consumed

- salts used in metabolism or excreted not being replaced in the diet

47
Q

The body responds to this rise in water potential as follows:

A
  • osmoreceptors in the hypothalamus detect the rise in the 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 WP of the blood falls
  • When the water potential of the blood has returned to normal the osmorecetors in the hypothalamus cause the pituitary to raise its ADH release back to normal levels
    THIS IS NEGATIVE FEEDBACK

A LEVEL BIOLOGY (7 decks)

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