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Biology Y13 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is Homeostasis?

A

Homeostasis in mammals involves physiological control systems that maintain the internal environment within restricted limits.

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2
Q

Which two systems are the internal conditions regulated by?

A

endocrine and nervous system (but also behavioural patterns too)

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3
Q

what is the internal environment made up of?

A

tissue fluid

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4
Q

what is the role of tissue fluid?

A

tissue fluid surrounds our cells supplying nutrients and removing waste

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5
Q

why is it important to maintain tissue fluid?

A

maintaining the features of this fluid at the optimum levels protects the cells from changes in the internal environment, thereby giving the organism a degree of independence

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6
Q

why is it important to maintain your internal environment stable?

A

is vital for cells to function normally and to stop them being damaged despite external changes

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7
Q

are there any changes that occur to tissue fluid/blood during homeostasis?

A

yes, there are continuous fluctuations brought about by variations in internal and external conditions, such as changes in temperature, pH and water potential. These changes however, occur around the optimum point.

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8
Q

what needs to be maintained during homeostasis?

A

Body temp

Blood glucose conc.

Blood salt conc.

Water potential of blood

Blood pressure

Carbon dioxide conc.

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9
Q

why is the term stable/ constant slightly misleading?
What is the actual point in which homeostasis remains?

A

as our internal conditions are not kept absolutely constant but are kept within a narrow range. The values fluctuate within a range around an average referred to as the set point.

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10
Q

why is it important to maintain the right body temperature, and blood pH, water potential as well as blood glucose concentration? (why is homeostasis important?)

A
  • this is because temperature and pH affect enzyme activity, and enzymes control the rate of metabolic reactions (chemical reactions in living cells)
  • 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 leaving or entering by osmosis.
  • also important to maintain blood glucose conc. because cells need glucose for energy, so molecules move faster.
  • Independence from external conditions
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11
Q

explain the effect temperature has on metabolic reactions?

SO also explain the effect of high and low temperatures have on the rate of enzymes that control metabolic processes.

A

the rate of metabolic reactions increases when the temperature’s increased. More heat means more kinetic energy, so molecules move faster. this makes the substrate molecules more likely to collide with enzymes’ active sites. the energy of these collisions also increase, which means each collision is likely to result in a reaction

High temp
if temperature get’s too high (over 40°), the reaction eventually stops. the rise in temperature makes the enzymes’ molecules vibrate more. if temperature goes above a certain level, this vibration breaks some of the hydrogen bonds that hold the enzyme in it’s 3D shape. the active site changes shape and the enzyme and substrate no longer fit together. At this point, the enzyme is denatured - it no longer functions as a catalyst.

Low temperatures
if body temp is too low, enzyme activity is reduced, slowing the rate of metabolic processes. the highest rate of enzyme activity happens at their optimum temperature about 37 ° in humans

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12
Q

Explain the effect of pH of blood on enzymes controlling metabolic reactions?

What is usually optimum pH for enzymes?
which enzymes work best at lower pH’s

A

if blood pH is too high or too low (highly alkaline or acidic) enzymes become denatured. the ionic bonds and hydrogen bonds that hold them in their 3D shape are broken, so the shape of the enzymes active site is changed and it no longer works as a catalyst.

the highest rate of enzyme activity happens at their optimum pH, so this is when metabolic reacions are fastest. Optimum pH is usually around pH 7 (neutral), but some enzymes work best at other pHs e.g enzymes found in the stomach work best at low pHs

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13
Q

the greater the [H+], the lower the..?

A

pH ( and so more acidic environment)

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14
Q

How can we work out the pH of a solution?

A

pH = -log10 [H+]

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15
Q

why is a logarithmic scale used?

A

this is because concentration of [H+] can vary enormously and so it’s easier to compare values on a logarithmic scale.

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16
Q

Why is it also important to maintain the water potential of the blood?

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 leaving or entering by osmosis. In both instances the cells can not operate normally.

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17
Q

what is essential when maintaining a constant blood glucose concentration?

A

The maintenance of a constant blood glucose concentration is essential in ensuring a constant water potential. A constant blood glucose concentration also ensures a reliable source of glucose for respiration by cells

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18
Q

Why advantages do organisms gain from keeping their internal environment stable?

A

organism with the ability to maintain a constant internal environment are more independent of changes in the external environment. they may have a wider geographical range and therefore have a greater chance of finding food, shelter etc.

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19
Q

What are the control mechanisms of any self-regulating system, explain each of their roles?

A
  • the optimum point - the point at which the system best operates. this is monitored by a receptor
  • receptor - which detects any deviation from the optimum point (i.e a stimulus) and informs the coordinator
  • Coordinator - which coordinates information from receptors and sends instructions to an appropriate effector
  • Effector - often a muscle or a gland, which brings about change 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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20
Q

why do control systems have many receptors and effectors?

A

this allows them to have separate mechanisms that each produce a positive movement towards an optimum. this allows a greater degree of control of the particular factor

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21
Q

What are endotherms?

A

they derive most of their heat from metabolic activities that take place inside their bodies

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22
Q

How do endotherms keep warm?

A

vasoconstriction, shivering, raising of hair, increased metabolic rate, decrease in sweating, behavioural mechanisms such as sheltering from wind

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23
Q

How do endotherms keep cool?

A

vasodilation, increased sweating, behavioural mechanisms by avoiding the heat taking shelter

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24
Q

What are ectotherms?

A

obtain a proportion of their heat from outside of their bodies (so from environment)

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25
Q

How do ectotherms keep warm?

A
  • exposing themselves to the sun, taking shelter to prevent over-heating, gaining warmth from the ground
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26
Q

Negative Feedback and Positive feedback

A
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27
Q

What is negative feedback?

A

negative feedback occurs when the stimulus causes the corrective measure to be turned off. In doing so this tends to return the system to it’s original level. (and prevents and overshoot)
or
A series of changes that result in a substance being restored to its normal / optimum level.

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28
Q

what is the negative feedback pathway?

A

stimulus -> receptor –>coordinator –> effector –> response

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29
Q

what is an advantage of negative feedback?

A

A greater degree of control due to possession of separate mechanisms involving negative feedback, controls departures in different directions from the original state.

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30
Q

Give an example of negative feedback?

A

the control of blood glucose

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31
Q

What is Positive Feedback?

A

a deviation from normal conditions is detected and amplified, leading to a further deviation.

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32
Q

Give an example of positive feedback?

A

In early childbirth the release of the hormone oxytocin stimulates uterine contractions. The contractions trigger a positive feedback reaction. More oxytocin is released, initiating more contractions.

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33
Q

when is positive feedback more likely to occur?

A

occurs more often when there is a breakdown of control systems

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34
Q

give an example?

A

when you get hyperthermia, the body get’s too cold, the temperature control system tends to break down, leading to positive feedback resulting in the body temperature dropping even lower

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35
Q

Hormones and the regulation of blood glucose concentration

A
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36
Q

where are hormones produced?

A

hormones are produced in the endocrine glands, which secrete the hormone directly into the blood.

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37
Q

where are hormones carried in?

A

hormones are carried in the blood plasma to the cells on which they act - known as target cells

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38
Q

what do hormones bind to, how are they specific?

A

target cells - which have specific receptors on their cell-surface membranes that are complimentary to a specific hormone

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39
Q

hormones are effective in low or high concentrations?

A

hormones are effective in low concentrations, but often have widespread and long-lasting effects

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40
Q

How are hormones regulated?

A

Through negative feedback - regulation of blood glucose

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41
Q

what is glucose essential for?
What is the normal range for blood glucose?

A
  • respiration, they provide the source of energy for almost all organisms (thus need a relatively constant conc. )
  • Normal blood glucose concentration
    is 4 - 6 mmol dm-3.
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42
Q

what factors increases and decreases blood glucose?

A
  • blood glucose increases following digestion of food/drink containing carbohydrates
  • will decrease if you have not eaten, or exercised (E.g. muscle movement,
    increases respiration which uses glucose)
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43
Q

where is the pancreas located?

A

the pancreas is a large, pale coloured gland that is situated in the upper abdomen, behind the stomach

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44
Q

what is the role of the pancreas?

A

it produces enzymes for digestion and hormones for regulating blood glucose conc.

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45
Q

what is blood glucose concentration monitored by?

A

alpha (α) and beta (β) receptor cells. That are found in the islets of Langerhans, in the pancreas and release hormones insulin and glucagon to bring glucose levels back to normal

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46
Q

what is the difference between alpha (α) and beta (β) receptor cells?

A

alpha (α) receptor cells - are larger and produce hormone glucagon
beta (β) receptor cells - are smaller and produce Insulin

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47
Q

when is adrenaline released?

A

adrenaline is released by the adrenal glands when your body anticipates danger and this results in more glucose being released from stores of glycogen in the liver

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48
Q

Draw a diagram showing the negative feedback loop of blood glucose concentration

A
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49
Q

where is the liver located?
what is it made out of?

A

the liver is located in below the diaphragm and is made out of cells called hepatocytes.

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50
Q

what is the role of the liver in regulating blood glucose?

A

it serves a large variety of roles including regulation of blood glucose . the hormones insluin and glucagon are produced in the pancreas but in the liver is where they have their effects

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51
Q

What are three important processes that take place in the liver?

A
  • glycogenesis
  • glycogenolysis
  • gluconeogenesis
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52
Q

what is Glycogenesis?

A

the process of excess glucose being converted to glycogen when blood glucose is higher than normal. this occurs mainly in the liver

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53
Q

what is glycogenolysis?

A

the hydrolysis of glycogen back into glucose in the liver. this occurs when blood glucose levels are lower than normal

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54
Q

What is gluconeogenesis?

A

the process of creating glucose from a non-carbohydrate store in the liver. this occurs if all glycogen has been hydrolysed into glucose and your body still needs more glucose

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55
Q

whether these processes happen or not are controlled by?

A

the 3 hormones: insulin, glucagon and adrenaline

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56
Q

Describe the action of insulin in regulating blood glucose?

A
  • beta (β) receptor cells in the islets of Langerhans in the pancreas detect stimulus of when glucose levels are too high
  • and secrete insulin which increases the permeability of muscle and liver cells to glucose, so cells take up more glucose
  • Insulin will decrease blood glucose in the following ways
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57
Q

Describe how insulin decreases the blood glucose? (3 ways)

A
  1. attaches to glycoprotein receptors on the surface of target cells (body cells). this changes 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 (∴ removing excess glucose from the blood)
  2. attaches to glycoprotein receptors on the surface of target cells (body cells). there is an increase in protein carriers responsible for glucose transport in the cell surface membrane. 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 number of glucose transport channels, so that more glucose is absorbed from the blood into cells
  3. attaches to glycoprotein receptors on the surface of target cells (body cells). Activation of enzymes that convert glucose to glycogen and (fat). this results in glycogenesis in the liver.
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58
Q

which two hormones use the second messenger model mechanism?

A

Glucagon and Adrenaline

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59
Q

Describe the action of Glucagon in the regulation of blood glucose?v

A

alpha (α) receptor cells in the islets of Langerhans in the pancreas detect the stimulus when blood glucose is too low and will secrete glucagon into the blood plasma in response to this

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60
Q

Describe how glucagon causes the Blood glucose levels to increase? (3 ways)

A
  1. attaching to specific protein receptors on the cell-surface membrane of liver cells
  2. When glucagon binds to those receptors, it causes a protein to be activated into Adenylate Cyclase. This enzyme converts ATP into Cyclic AMP (cAMP). cAMP activates an enzyme, protein kinase, that can hydrolyse glycogen into glucose
  3. Activating enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis)
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61
Q

what is the overall effect?

A

to increase the concentration of glucose in the blood and return it to it’s optimum concentration. this raising of the blood glucose concentration cause alpha cells to reduce the secretion of glucagon = negative feedback

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62
Q

what other hormone increases the blood glucose concentration?

A

Adrenaline

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63
Q

what is the role of adrenaline?

A

at times of excitement, exercise, stress or to raise the blood glucose concentration adrenaline is released

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64
Q

where is adrenaline released from?

A

the adrenal glands

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65
Q

What is the second messenger model?

A

the binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane, which then produces a chemical known as a second messenger. the second messenger activates other enzymes in the cell to bring about a response.

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66
Q

Describe the role of Adrenaline in increasing the blood glucose concentration

A
  • adrenaline binds to a transmembrane protein receptor within the cell-surface membrane
  • 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 an enzyme called adenyl cyclase. the activated adenyl cyclase converts ATP to cyclic AMP (cAMP)
  • the cAMP acts as a second messenger that binds to protein kinase enzyme, changing it’s shape and therefore activating it
  • the active protein kinase enzyme activates a cascade (chain of reactions) that 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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67
Q

which two hormones act in opposite directions?

A

insulin and glucagon

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68
Q

explain how insulin and glucagon act in opposite directions?

A

insulin lowers the blood glucose concentration, whereas glucagon increases the blood glucose concentration. in this way the interaction these two hormes allows highly sensitive control of blood glucose concnetration

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69
Q

what is meant by the fact that these two hormones act antagonistically?

A

the two hormones are said to act antagonistically. the system is self-regulating through negative feedback in that it is the concentration of glucose in the blood that determines the quantity of insulin and glucagon produced.

in this way the interaction of these two hormones allows highly sensitive control of blood glucose concentration

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70
Q

why does blood glucose fluctuate?

A

this is because of the way negative feedbakc mechanisms work

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71
Q

Diabetes

A
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72
Q

what is diabetes?

A

diabetes is a disease in which a person is unable to metabolise carbohydrate, especially glucose, properly

73
Q

what is Diabetes mellitus?

A

‘sugar diabetes’ - a form of diabetes

74
Q

what are the two types of diabetes mellitus?

A
  • Type 1 and Type 2
75
Q

What are the typical symptoms of type 1 and type 2 diabetes?

A
  • feeling very thirsty
  • urinating very often
  • feeling more tired than usual
  • losing weight
76
Q

what is Type 1 diabetes?

A

the body is unable to produce insulin.

77
Q

How may this happen?

A

it may be the result of the body’s immune system attacking it’s own cells. in this case the B cells in the islet of Langerhans

78
Q

Why is type 1 diabetes deadly if left untreated?

A

After eating, the blood glucose level rises and stays high - this is called Hyperglycaemia and can result in death if untreated. the kidney’s can not reabsorb all the glucose, so some of its excreted out into urine.

79
Q

How is Type 1 diabetes treated?

A

insulin injections

80
Q

why can insulin not be taken through the mouth?

A

this cannot be taken through the mouth, being a protein, it would be digested through the alimentary canal.

81
Q

How many times a day can insulin be injected?

A

typically either two or 4 times a day

82
Q

why must the dose of insulin be exactly matched to glucose intake?

A

if a person with diabetes takes too much insulin, she will experience a low blood glucose (hypoglycaemia) that can result in unconsciousness

83
Q

to ensure, the correct dose, how is blood glucose monitored?

A

blood glucose concentration is monitored using biosensors.

84
Q

How can Type 1 diabetes be managed?

A
  • by injecting insulin, managing their carbohydrate intake and exercise
85
Q

No one really knows what causes the immune system to attack the B cells and cause Type 1 diabetes, but what are some explanations?

A
  • some people have a genetic predisposition to developing type 1 diabetes
  • may also be triggered by a viral infection
86
Q

What is Type 2 diabetes?

A

B cells don’t produce enough insulin or when the body cells to do not respond to insulin properly. cells don’t respond properly because the insulin receptors on their membranes don’t work properly.

glycoprotein receptors on body cells are being lost or losing their responsiveness to insulin. However may also be an inadequate supply of insulin from the pancreas

87
Q

What is type 2 diabetes linked to?

A

Obesity and poor diet

88
Q

When do people typically develop Type 2 diabetes?

A

around the age of 40

89
Q

How can Type 2 diabetes be treated?

A
  • health, balanced diet - regulating the intake of carbohydrate in the diet
  • losing weight (if necessary)
  • regular exercise
90
Q

Why is Type 2 diabetes becoming more common?

A

due to increasing levels of obesity, more unhealthy diets and low levels of physical activities

91
Q

What are the other additional health problems that type 2 diabetes can cause?

A
  • visual impairment
  • kidney failure
92
Q

How have health advisors improved the food industry?

A

they have challenged the food industry to reduce the advertising of junk food (particularly to children), to improve the nutritional value of their products, and to use clearer labelling products - allowing consumers to make healthier choices about what to buy

92
Q

explain the advantage of this?

A

so food companies have attempted to make their products more healthy. For example, by using sugar alternatives to sweeten food and drinks, also by reducing the fat, suagr and salt content of food

93
Q

But why do some food companies not want to do this?

A
  • because there is pressure on companies to increase profits
  • reluctant to spend money developing new healthier alternatives if unhealthy products are still popular and generate lots of profit
94
Q

The Kidneys

A
95
Q

what is the role of the liver?

A

Excess amino acids are broken down by the liver to produce a waste substance called urea, which is safe to transport to the kidneys.

96
Q

what is the role of the kidney’s?

A

The kidneys filter the blood, removing urea and excess water and salt, which forms urine. Urine is stored in the bladder before being excreted from the body.

97
Q

Describe the kidney’s production line?

A

All the blood in your body goes through
your kidneys every 5 minutes – that’s
around 1 litre of blood/minute!

About 180 litres of water are filtered out
of your blood/day

99% goes back to the blood – you make
around 1.8 litres of urine each day!

98
Q

What are the 4 main roles of the kidney’s?

A
  • Filter your blood.
  • Help with homeostasis.
  • Remove urea from your blood.
  • Remove excess water from your blood
  • Remove excess mineral ions from your
    blood.
99
Q

Where are your kidney’s located?

A

at the back of the abdominal cavity, one on each side of the spinal cord

100
Q

Draw a rough sketch of the kidney and label and state each part of the kidney?

A
  • fibrous capsule
  • cortex
  • medulla
  • renal pelvis
  • ureter
  • renal artery
  • renal vein
101
Q

what is the fibrous capsule?

A

an outer membrane that protects the kidney

102
Q

what is the cortex?

A

a lighter coloured outer region made up of renal (Bowman’s) capsules, convoluted tubules and blood vessels

103
Q

what is the Medulla?

A

a darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels

104
Q

what is the (renal) pelvis?

A

a funnel-shaped cavity that collects urine into the ureter

105
Q

what is the ureter?

A

a tube that carries urine to the bladder

106
Q

what is the renal artery?

A

supplies the kidney with blood from the heart via the aorta

107
Q

what is the renal vein?

A

returns blood to the heart via the vena cava

108
Q

where are nephrons found in the kidney?

A

found these extentions ranging from the cortex into the medulla

109
Q

what are the nephrons?

A

the nephron is the functional unit of the kidney . it is a narrow tube up to 14mm long.

110
Q

what are the structures within the nephron?

A
  • Renal (Bowman’s) capsule
  • Proximal convoluted tubule
  • loop of Henle
  • Distal convoluted tubule
  • collecting duct
111
Q

what is the renal capsule?

A

the closed end at the start of the nephron. it is cup-shaped and surrounds a mass of blood capillaries known as the glomerulus. the inner layer of the renal capsule is made up of specialised cells called podocytes

112
Q

what is the proximal convoluted tubule?

A

a series of loops surrounded by blood capillaries. its walls are made up of epithelial cells which have microvilli

113
Q

what is the loop of Henle?

A

a long, hairpin loop that extends from the cortex into the medulla of the kidney and back again. it is surrounded by blood capillaries

114
Q

what is the distal convoluted tubule?

A

a series of loops surrounded by blood capillaries, its walls are made up of epithelial cells , but is surrounded by fewer capillaries than the PCT

115
Q

What is the collecting duct?

A

a tube in 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

116
Q

what are the 4 different blood vessels associated with each nephron?

A
  • afferent arteriole
  • efferent arteriole
  • golmerulus
  • blood capillaries
117
Q

what is the afferent arteriole?

A

a tiny vessel that ultimately 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

118
Q

what is the glomerulus?

A

a many-branched knot of capillaries from which fluid is forced out of the blood. the glomerular cpillaries recombine to form the efferent arteriole

119
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 in the glomerulus. the efferent arteriole carries blood away from the renal capsule and later branches to form the blood capillaries

120
Q

what are the blood capillaries?

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

121
Q

Role of the nephron in osmoregulation

A
122
Q

what is he role of the kidney is osmoregulation?

A

one important function of the kidney is to maintain the water potential of the plasma and hence tissue fluid

123
Q

the nephron carries out osmoregulation in 4 steps what are they?

A
  • ultrafiltration (formation of glomerular filtrate)
  • Reabsorbtion of glucose + water by the proximal convoluted tubule
  • maintenance of the sodium ion gradient in the medulla by the loop of Henle
  • Reabsorbtion of water by the distal convoluted tubule
124
Q

Describe how Blood enters/ moves through the glomerulus?

A
  • blood enters the kidney via the renal artery, which branches frequently to give around a million tiny arterioles, each of which enters the renal (Bowman’s) capsule of a nephron
  • the afferent arteriole and it divides to give a complex of capillaries known as the glomerulus . the glomerulus capillaries then merge to give the efferent arteriole, which sub-divides again into capillaries, which wind their way up various tubules of nephrons before combining to form the renal vein
125
Q

Describe how ultrafiltration produces glomerular filtrate?

A
  • as the diameter of the afferent arteriole is greater than the efferent arteriole
  • there is a build up of hydrostatic pressure within the glomerulus
  • as a result, water glucose and mineral ions are squeezed out of the pores called podocytes in the capillary endothelium
  • through the basement membrane which acts as a filter
  • to form glomerular filtrate in the renal (Bowman’s) capsule
  • blood cells and proteins are too large to fit through the gaps in the capillary endothelium, so remain in the blood. this blood leaves via the efferent arteriole
126
Q

How are cells of bowman’s capsule adapted for ultrafiltration?

A
  • fenestrations between epithelial cells of capillaries
  • fluid can pass between and under folded membrane and podocytes
127
Q

What 3 layers do water, mineral ions, urea and glucose need to move through and how is the nephron specialised to assist this movement?

A
  • Capillary wall (endothelium) -Endothelium of capillaries of glomerulus have gaps
  • Basement membrane
  • Epithelium of Bowman’s capsule
  • Epithelium is made up of fenestrations, which have gaps between them
128
Q

what is the basement membrane?

A

a sheet of protein, continuous mesh and finest part of filter - blocks large molecules from entering

129
Q

what are the podocytes?

A

not tight together, form a network of slits over the capillary

130
Q

Selective reabsorption in the proximal convoluted tubule

A
131
Q

Approximately what percentage of glomerular filtrate is reabsorbed back into the blood?

A

85%

132
Q

what does ultrafiltration operate on?

A

operates on the size of the molecule - small ones are removed

133
Q

what is the importance of selective reabsorption?

A

Selective reabsorption occurs because during ultrafiltration, important components of the blood are filtered out (glucose, urea, etc) and they need to be reabsorbed into the body.

134
Q

which two biological molecules are all absorbed back into the blood?

A

all glucose and amino acids

135
Q

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

A
  • microvilli - increase the surface area to reabsorb substances from the filtrate
  • Many Carrier proteins for facilitated diffusion, active transport, Co-transport
  • a high density of mitochondria to provide energy for ATP for active transport
  • infoldings at their bases to give a large surface to transfer reabsorbed substances into blood capillaries
136
Q

explain the process of selective reabsorption?

A
  • sodium ions are actively transported out of the cells lining the proximal convoluted tubule into blood capillaries which carry them away
  • the sodium ion concentration of these cells is therefore lowered
  • sodium ions now diffuse down a concentration gradient from the lumen of the proximal convoluted tubule into the epithelial lining cells but only through special carrier proteins by facilitated diffusion
  • these carrier proteins are of specific types, each of which carries another molecule (glucose or amino acids) or chloride ions, etc) along with sodium ions. this is known as co-transport
  • the molecules which have been co-transported into the cells of the proximal convoluted tubule then diffuse into the blood.
  • As a result, all the glucose and most other valuable molecules are reabsorbed as well as water
137
Q

explain the movement of water in terms of water potential from the proximal convoluted tubule to the blood capillaries?

A

water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate. so water moves from epithelial cells (PCT) to the blood capillaries.

138
Q

How much water is reabsorbed by the proximal convoluted tubule into the blood?

A

85%

139
Q

where is the remainder of the water reabsorbed?

A

the remainder of the water is reabsorbed in the loop of Henle, the DCT and the collecting duct

140
Q

what happens to the filtrate which remains?

A

the filtrate which remains is passes along the ureter to the bladder and form urine

141
Q

what is urine?

A

urine is usually made up of excess water and dissolved salts, urea and other substances such as hormones and excess vitamins. urine doesn’t usually contain proteins as they are too large to be filtered out of the blood and usually doesn’t contain glucose either as it;’s all reabsorbed into the blood.

142
Q

What is the role of the loop of Henle?

A

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

143
Q

what is the concentration of urine produced directly related to?

A

the concentration of the urine produced is directly related to the length of the loop of Henle

144
Q

the longer the loop of Henle…?

A

The more concentrated the urine

145
Q

what are the two regions in the loop of Henle?

A
  • ascending limb
  • descending limb
146
Q

what is the descending limb?

A

the descending limb is narrow, with thin walls that are highly permeable to water (due to presence of aquaporins)

147
Q

what is the ascending limb?

A

the ascending limb is wider, with thick walls that are impermeable to water

148
Q

what does the loop of Henle act as?

A

a counter-current multiplier

149
Q

explain in detail how the loop of Henle acts as a counter-current multiplier?

A
  1. Mitochondria in the walls provide energy (ATP) to actively transport sodium ions out of the ascending limb of the loop of Henle
  2. this creates a low water potential (high ion concentration) in the region of the medulla between the two limbs (called the interstitial region) . In normal circumstances water would pass out of the ascending limb by osmosis . However, the thick walls are impermeable to to water, and so very little, if any escapes.
  3. The walls of the descending limb are very permeable to water and so water passes out the filtrate by osmosis into the interstitial space. the water enters the blood capillaries in this region by osmosis and is carried away.
  4. the filtrate progressively loses water this way as it moves down the descending limb lowering its water potential (High ion conc.). it reaches it’s 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 and therefore the filtrate develops a progressively higher water potential.

Absorption in the DCT and Collecting duct

  1. The filtrate moves into the Distal convoluted tubule. Here the filtrate has a low concentration of ions, so a high water potential compared to the an increasingly low water potential as we go down the medulla (interstitial space). Creating a water potential gradient.
  2. the collecting duct is permeable to water and so 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.
  3. 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.
150
Q

How does water move out of the collecting duct?

A

Aquaporins - channel proteins which are specific to water

151
Q

why can the hormone ADH control water loss?

A

as it can alter the number of aquaporin channels

152
Q

what is the role of the Distal convoluted tubule?

A

the main role of the distal convoluted tubule 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 absorb. To achieve this, the permeability of its walls become altered under the influence of various hormones

153
Q

explain how the distal convoluted tubule is adapted for its function?

A

the cells that make up the walls of the distal convoluted tubule have microvilli and many mitochondria that allow them to reabsorb material rapidly from the filtrate, by active transport.

154
Q

describe the role of the Collecting duct?

A
  • Reabsorption of water, controlled by
    hormones, Targeted by ADH
  • Through negative feedback: ADH causes more water reabsorption
155
Q

what is the counter-current multiplier?

A

the counter current flow means that the filtrate in the collecting duct with a lower water potential meets an interstitial fluid that has an even lower water potential. this means that although the water potential gradient between the collecting duct and interstitial fluid is small, it exits for the whole length of the collecting duct . there is therefore a steady flow of water into the interstitial fluid

156
Q

How much water enters the interstitial fluid?

A

around 80% of the water enters the interstitial fluid and hence the blood.

157
Q

what would happen if two flows were in the same direction?

A

less water would enter the blood

158
Q

why do desert animals have longer loops of Henle?

A

the longer the loop of Henle, the more sodium ions are actively transported out, and therefore an even more negative water potential is created. this results in more water being reabsorbed into the blood forming a very concentrated urine

159
Q

Osmoregulation

A
160
Q

what is osmoregulation?

A

Osmoregulation is the process by which organisms regulate the water content of the body.

161
Q

why is it important to regulate the water potential of the blood?

A
  • if blood is hypertonic (low water potential) - too much water will leave the cells and leave the blood by osmosis causing cells to shrivel/ shrink (crenation)
  • if blood is hypotonic (high water potential) - too much water from blood will move into cells by osmosis causing them to burst (lysis)
162
Q

why may the water potential of the blood be low (hypertonic)?

A
  • water is lost through sweating
  • no drinking enough water
  • lot’s of ions in the diet
163
Q

what is the corrective mechanism?

A

more water is reabsorbed by osmosis into the blood from the tubules of the nephrons. this means that the urine is more concentrated, as less water is lost in the urine.

164
Q

why may the water potential of the blood be too high (hypotonic)?

A
  • drinking too much water
  • not enough salt in diet
165
Q

what is the corrective mechanism?

A

less water is reabsorbed by osmosis into the blood from the tubules of the nephron. this means that the urine is more dilute and more water is lost in the urine.

166
Q

what is the role of the hypothalamus in osmoregulation?

A

changes in water potential are detected by the osmoreceptors located in the hypothalamus.

167
Q

where is ADH produced?

A

ADH is produced in the hypothalamus

168
Q

Explain what causes ADH hormone to be released, and what causes less ADH hormone to be released?

A
  • water entering or leaving osmoreceptors
169
Q

explain how osmoreceptors are involved in the release of ADH hormone when WP is too high or too low?

A
  • if the water potential of the blood is too low, water leaves the osmoreceptors by osmosis and they shrive.. this stimulates the hypothalamus to produce more of the hormone ADH
  • if the water potential is high, water enters the osmoreceptors by osmosis. This stimulates the hypothalamus to produce less ADH
170
Q

how is ADH released into the bloodstream?

A

Leaves the hypothalamus and makes it way to posterior pituatry gland, where it released into the blood stream

171
Q

what is the role of ADH in osmoregulation?

A

when ADH reaches the Kidney, it causes an increase in the permeability of the walls of the collecting duct and distal convoluted tubules to water. this means that more water can be reabsorbed into the blood. So urine is more concentrated

172
Q

What are Aquaporins?

A

aquaporins are protein channels for water to pass through them.

173
Q

describe the role of Aquaporins in osmoregulation?

A
  • ADH binds to receptors on the cell membrane of the DCT and collecting duct
  • when bound, it activates a phosphorylase enzyme in the cells
  • phosphorylase causes the vesicles containing aquaporins to fuse with the cell membrane and the aquaporins embed
  • with more aquaporins in the cell membrane, more water leaves the DCT and collecting duct and is reabsorbed by the blood.
174
Q

Draw a diagram to show the negative feedback cycle of osmoregulation

A
175
Q

describe how the water potential of the blood is returned back to normal when there is a fall in water potential?

A
  • osmoreceptors in the hypothalamus of the brain detect the fall in water potential
  • when the water potential of the blood is too low, water leaves the osmoreceptors by osmosis causing them to shrink
  • This stimulates the hypothalamus to produce more of the hormone ADH
  • ADH then passes to the posterior pituitary gland, where it is secreted from the capillaries, and travels in the blood.
  • ADH travels through the blood and into the kidney’s where it increases the permeability to water of the cell membrane of the DCT and the collecting duct
  • (specific protein) receptors on the cell membranes of the DCT and collecting duct bind to ADH
  • when bound, it activates a phosphorylase enzyme within the cell
  • phosphorylase causes vesicles within the cell to move to and duse with the cell membrane
  • these vesicles contain pieces of plasma membrane that have numerous water channels called aquaporins and so when they fuse with the membrane, the number of water channels is increased. (making cell-surface membrane much permeable to water)
  • ADH also increases the permeability to urea, which passes out and therefore further lowers the water potential of the fluid at the duct
    -more water leaves the DCT and collecting duct and is reabsorbed into the blood
176
Q

explain what the osmoreceptors do when the water potential slowly begins to increase?

A
  • the osmoreceptors will 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 detects the rise in water potential and sends fewer impulses to the pituitary gland
  • the pituitary gland reduces the release of ADH and the permeability of the collecting ducts to water and urea reverts to its former state
177
Q

describe how the water potential of the blood is returned back to normal when there is an increase in water potential?

A
  • the osmoreceptors in the hypothalamus detect the rise in water potential and increase the frequency of nerve impulses to the posterior pituitary gland to reduce it’s 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 to raise its ADH release back to normal level (negative feedback)
178
Q

FINISH

A

Biology Y13 (13 decks)

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