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a-level biology a2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What change the concentration of glucose in your blood?

A

Eating

Exercise

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2
Q

Why does the blood glucose concentration need to be carefully controlled?

A

Because all cells need a constant supply to work.

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3
Q

What is the concentration of glucose in the blood normally?

A

90g per 100cm3.

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4
Q

What monitors the concentration of glucose?

A

Pancreas

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5
Q

When does the blood glucose rise?

A

After eating food containing carbs

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6
Q

When does the blood glucose fall?

A

After exercise as more glucose used in respiration to release energy.

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7
Q

What controls the blood glucose concentration?

A

The hormonal system using two hormones:

Insulin

Glucagon

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8
Q

How and where do hormones travel to?

A

travel in the blood to their target cells (effectors).

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9
Q

What are insulin and glucagon secreted by?

A

clusters of cells in the pancreas called islets of Langerhans

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10
Q

What cells secrete insulin?

A

Beta cells

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11
Q

What cells secrete glucagon?

A

Alpha cells

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12
Q

What does insulin do?

A

Lowers blood glucose concentraion when it’s too high

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13
Q

How does insulin lower the blood glucose concentration when it’s too high?

A
  1. Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.
  2. It increases the permeability of muscle cell membrane to glucose which increases the glucose uptake and increases number of channel proteins.
  3. Insulin activates enzymes in liver and muscle cells that convert glucose into glycogen.
  4. The cells are able to store glycogen in their cytoplasm as an energy source.
  5. The process of forming glycogen from glucose is called glycogensis.
  6. Insulin also increases the rate of respiration of glucose especially in muscle cells.
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14
Q

What process is involved in insulin lowering blood gluc. conc

A

Glycogensis

Glucose into glycogen

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15
Q

How does glucagon raise the blood glucose concentraion when its too low?

A
  1. Glucagon binds to specific receptors on the cell membranes of liver cells.
  2. Glucagon activates enzymes in liver cells that break down glycogen into glucose.
  3. The process of breaking down glycogen is called glycogenolysis.
  4. Glucagon also activates enzymes that are involved that are involved in the formation of glucose from glycerol and amino acids.
  5. The process of forming glucose from non-carbs is called gluconeogenesis.
  6. Glucagon decreases the rate of respirstion of glucose in cells.
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16
Q

What processes are involved in glucagon to raise the blood gluc. conc.

A

Glycogenolysis - glycogen broken down into glucose

Gluconeogenesis - forming glucose from non-carbohydrates

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17
Q

Why do hormones have a slower response than nerve impulses?

A

Because they travel in the blood to their target cells.

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18
Q

Why are hormones long lasting compared to nerve impulses?

A

They aren’t broken down as quickly as neurotransmitters so last longer.

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19
Q

What does negative feedback mechanisms do?

A

Keep blood glucose concentration normal

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20
Q

What makes glucose transporters available for facilitated diffusion

A

insulin

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21
Q

What contain a channel protein?

A

Skeletal and cardiac muscle cels

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22
Q

What is GLUT4?

A

A channel protein

It is a glucose transporter

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23
Q

Where is GLUT4 stored in when the insulin levels are low?

A

Vesicles in the cytoplasn of cells.

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24
Q

What triggers the movement of GLUT4 to the membrane?

A

When insulin binds to receptors on the cell-surface membrane.

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25
Q

How is glucose transported into the cell?

A

Through the GLUT4 protein by facilitated diffusion

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26
Q

What increases the blood glucose concentration other than glucagon?

A

Adrenaline

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27
Q

What is adrenaline?

A

A hormone that’s secreted from your adrenal glands

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28
Q

When is adrenaline released?

A

When there’s a low concentration of glucose in your blood due to stress or exercising

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29
Q

Where does adrenaline bind?

A

To receptors in the cell membrane of liver cells

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30
Q

What does adrenaline do (activate/ inhibit)?

A
  • It activates glycogenolysis (the breakdown of glycogen to glucose).
  • It inhibits glycogenesis (the synthesis of glycogen from glucose).
  • Activates glucagon secretion (increasing the glucose conc).
  • Inhibits insulin secretion (increasing the glucose conc).
  • Gets the body ready for action by making more glucose available for muscles to respire.
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31
Q

What do adrenaline and glucagon act with?

A

A second messenger

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32
Q

How can both adrenaline and glucagon activate glycogenolysis inside a cell?

A
  1. The receptors for adrenaline and glucagon have specific tertiary structures that make them complementary in shape to their respective hormones.
  2. Adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase.
  3. Activated adenylate cyclase converts ATP into a chemcial signal called a second messenger.
  4. The second messenger is called cyclic AMP (cAMP).
  5. cAMP activates an enzyme called protein kinase A. Protein kinase A activates a cascade that breaks down glycogen into glucose (glycogenolysis)
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33
Q

What do the kidneys do?

A

excrete waste and regulate blood water potential

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34
Q

Explain the process of excretion of waste products

A
  1. Blood enters through the renal artery and passes through the capillaries in cortex.
  2. As the blood passes through capillaries in the corex of the kidneys, substances of filtered out of the blood and into long tubules that surround the capillaries = ULTRAFILTRATION.
  3. Useful substances such as glucose and the right amount of water are then reabsorbed back into the blood = selective reabsorption.
  4. Remaining unwanted substances pass along to the bladder and are excreted as urin.
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35
Q

Where is blood filtered?

A

At the start of the nephrons

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36
Q

Describe how urea is removed from the blood

A
  1. Hydrostatic pressure / description of pressure / description of how pressure generated;
  2. Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule / glomeruli / renal capsule;
  3. Through basement membrane;
  4. Enabled by small size urea molecule;
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37
Q

Explain how urea is concentrated in the filtrate.

A
  1. Reabsorption of water / by osmosis;
  2. At the PCT / descending LoH;
  3. At the DCT / CD
  4. Active transport of ions / glucose creates gradient (in context);
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38
Q

Describe how ultrafiltration produces glomerular filtrate. (5)

A
  1. Blood pressure / hydrostatic pressure;
  2. Small molecules / named example;
  3. Pass through basement membrane / basement membrane acts as filter;
  4. Protein too large to go through / large so stays behind;
  5. Presence of pores in capillaries / presence of podocytes;
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39
Q

Some people who have diabetes do not secrete insulin.

Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin. (4)

A
  1. High concentration of glucose in blood;
  2. High concentration in tubule / in filtrate;
  3. Reabsorbed by facilitated diffusion / active transport; Requires proteins / carriers;
  4. These are working at maximum rate / are saturated;
  5. Not all glucose is reabsorbed / some is lost in urine;
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40
Q

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH).

Explain how these two features are adaptations to living in desert conditions. (6)

A
  1. More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
  2. By osmosis;
  3. From collecting duct / from end of second convoluted tubule;
  4. Due to longer loop of Henle;

For loop of Henle, maximum 2 marks:

  1. Sodium / chloride ions absorbed from filtrate in ascending limb;
  2. Gradient established in medulla / concentration of ions increases down medulla;

For ADH, maximum 2 marks:

  1. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
  2. Makes cells more permeable / inserts aquaporins in plasma membranes;
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41
Q

Explain ultrafiltration process

A
  1. Blood from the renal artey enters smaller arterioles in the cortex of the kidney.
  2. Each arteriole splits into a structure called a glomerulus - a bundle of capillaries lopped inside a Bowmans capsule.
  3. Ultrafiltration takes place in the bowmans capsule.
  4. The arteriole takes blood into each glomerulus = the afferent arteriole.
  5. The arteriole that takes blood away from the glomerulus = the efferent arteriole.
  6. The efferent is smaller in diameter than the afferent arteriole so the blood in the glomerulus is under high pressure.
  7. The high pressure forces liquid and small molecules in the blood out of the capillary and into the bowmans capsule.
  8. The liquid and small molecules pass through three layers into BC and enters nephron tubules - the capillary wall, a membrane and the epithelium of the BC.
  9. Larger molecules like proteins and blood cells can’t pass through, so stay in the blood. The substances that enter the BC are known as the glomerular filtrate.
  10. The glomerular filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way.
  11. Finally the filtrate flows through the collecting duct and passes out of the kidney along the ureter.
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42
Q

Summary of what ultrafiltration is

A

blood from renal artery enters smaller arterioles in the cortex of kidney

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43
Q

When does selective reabsorption take place

A

Takes place as the glomerular filtrate flows along proximal convoluted tubulue, through the loop of henle and along distal convoluted tubule.

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44
Q

Where do useful substances leave and where do they enter?

A

They leave the tubules of the nephrons and enter the capillary network that’s wrapped around them.

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45
Q

What does the epithelium of the wall of the PCT have that provides a large surface area?

A

Microvilli

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46
Q

What do microvillis provide

A

A large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood.

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47
Q

What solutes are reabsorbed along the PCT and how are they absorbed?

A

glucose by active transport and facilitated diffusion

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48
Q

How does water enter the blood?

What is it reabsorbed from?

A

By osmosis because the water potential of the blood is lower than that of the filtrate. Water is reabsorbed from the PCT, loop of henle, DCT and the collecting duct.

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49
Q

What is urine made up of?

A
  • Water and dissolved salts
  • Urea
  • Other substances such as hormones or excess vitamins
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50
Q

What does urine not usually contain?

A
  • Proteins and blood cells - they’re too big to be filtered out of the blood.
  • Glucose because it’s actively reabsorbed back into the blood.
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51
Q

What is osmoregulation?

A

The homeostatic control of water potential of the blood

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52
Q

When does diabetes occur?

A

When blood glucose concentration is not controlled

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53
Q

What is diabetes mellitus?

A

A condition where blood glucose concentration can;t be controlled

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54
Q

Type 1 diabetes

  • explain type 1 diabetes in terms of insulin
  • what have some scientists found
  • what is hyperglycaemia
  • what it can lead to
  • how its treated
  • why does the treatment need to be carefully controlled
  • what is hypoglycaemia
A
  • The immune system attacks the beta cells in the islets of langerhans so they can’t produce insulin.
  • Some scientists have found that some people have a genetic predisposition to developing Type 1 diabetes. They also think viral infections trigger it.
  • The blood glucose levels after eating rise and stays high - HYPERglycaemira (remember it as hyper = too much glucose/ energy).
  • Can lead to deaths if left untreated. The kidneys can’t reabsorb all this glucose, so some is excreted in the urine.
  • Type 1 diabetes is treated with insulin therpy. Most people need regular insulin injections thruout the day but some use an insulin pump to deliver insulin continuously.
  • Insulin therapy needs to be carefully controlled because too much insulin can produce a dangerous drop in blood glucose levels - HYPOglycaemia.
  • Eating regularly and controlling simple carbs intake helps avoid sudden rise in glucose.
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55
Q

Type 2 diabetes

  • when do people get it
  • what is it linked to
  • what are risk factors
  • Explain what it is in terms of insulin/ when it occurs
  • how can it be treated
    *
A
  • It usually occurs later in life than type 1.
  • Its linked to obesity and is more likely in family history
  • risk factors include; lack of exercise, age and poor diet
  • It occurs when beta cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin due to the insulin receptors on their membrane not working properly, so cells dont take up enough glucose. That means the blood glucose concentration is higher than normal.
  • It can be treated by eating healthy, balanced diet, losing weight and regular exercise.
  • Glucose lowering medication can be taken if diet and exercise can’t control it.
  • Insulin injections might eventually be needed
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56
Q

What do health advisors recommend to people to reduce risk of developing type 2 diabetes

A
  1. eat a diet that’s low in fat, suagr and salt with plenty of whole grains, fruit and vegetables.
  2. take regular excercise
  3. lose weight if necessary
  4. campaigns like NHS’s “change4life” aim to educate people on how to have a healthier diet and lifestyle.
  5. encourage food industries to reduce advertising of junk food to improve the nutrional value of their products and use clearer labels.
57
Q

How have some food companies attempted to make their products more healthy?

A
  • using sugar alternatives to sweeten food/ drinks
  • reducing the sugar, fat and salt content
58
Q

What’s used to determine the concentration of glucose solution?

A

Calorimetry

59
Q

What\s the concentration of glucose in urine

A

Very low

0-0.8mM

60
Q

What would it indicate if there’s a higher concentration of 0-0.8mM?

A

Diabetes

61
Q

Explain the step used to determine the concentration of glucose solution in a urine sample using calorimetry

A
  1. Quanitative benedicts reagent when heated with glucose will lose its blue coloue. A brick red ISN’T produced.
  2. You can use a colorimeter to measure the light absorbance of the solution after the quantitative benedicts test has been carried out.
  3. The higher the conc. of glucose, the more blue colour will be lost, decreasing the absorbance of the solution.
62
Q

What is serial dilution?

A

make several glucose solutions of different known concentrations

63
Q

Give the steps using serial dilution

A
  1. Line up five test tubes in a rack.
  2. Add 10cm3 of the initial 4mM glucose solution to the first test tube and 5cm3 of distilled water to other four test tubes.
  3. Then, using a pipette, draw 5cm3 of the solution from the first test tube, add it to the distilled water in the second test tube and mix the solution thoroughly. You now have 10cm3 of the solution that’s half as concentrated as the solution in the first test tube (it’s 2mM).
  4. Repeat the process three more times to create solutions if 1mM, 0.5mM and 0.25mM.
64
Q

What does the kidneys regulate?

A

The water potential of the blood

65
Q

Why is water essential?

A

To keep the body functioning

66
Q

What needs to be kept constant in the blood?

A

The amount of water

67
Q

How is water lost?

A
  • Excretion
  • Sweat
  • breathing
68
Q

What is osmoregulation?

A

The control of water levels and mineral ions (salt) in the blood.

69
Q

Give the location of osmoreceptors in the body of a mammal.

A

Hypothalamus.

70
Q

If the water potential of blood is too low, what does that mean for the body?

A

It’s dehydrated

71
Q

When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why. (only need point 1 and 2 to get full marks)

A
  1. Water potential of blood will decrease;
  2. So more water gets reabsorbed and moves from osmoreceptor into the blood from the tubules of nephrons by osmosis.
  3. That means the urine is more concentrated, so less water is lost during excretion.
72
Q

When is the urine more concentrated?

A

When a person is dehydrated and so less water is lost during excretion.

73
Q

When a person is too hydrated, the cell volume of an osmoreceptor increases. Explain why.

// explain what happens when a person is over hydrated

A
  1. Water potential of blood will increase/ is too high
  2. Less water is reabsorbed by osmosis into the blood from tubules of nephrons.
  3. Urine is more dilute, so more water is lost during excretion
74
Q

When is the urine more dilute?

A

when the body is too hydrated, more water is lost during excretion

75
Q

Where does the regulation of water potential take place?

A
  • Loop of Henle
  • DCT
  • Collecting duct
76
Q

The volume of water reabsorbed by the DCT and collecting duct is controlled by what?

A

Hormones.

77
Q

What does the loop of Henle maintain?

A

A sodium ion gradient

78
Q

Where is the loop of henle located?

A

In the medulla of kidneys

79
Q

What is the loop of henle made up of?

A

Two limbs;

  • descending limb
  • ascending limb
80
Q

What do the AL and DL control in the loop of henle?

A

The movement of sodium ions so that water can bd reabsorbed by the blood

81
Q

The control of water balance in the body involves negative feedback.

(i) Describe what is meant by negative feedback.

A

where a change triggers a response which reduces the effect of a change

82
Q

What is meant by homeostasis?

A

maintaining a constant internal environment;

83
Q

Giving one example, explain why homeostasis is important in mammals.

A

temperature / pH;

optimum for enzymes / effect of pH / temperature on enzyme activity;

84
Q

Cross-channel swimmers may suffer from muscle fatigue during which the contraction mechanism is disrupted. One factor thought to contribute to muscle fatigue is a decrease in the availability of calcium ions within muscle fibres.

Explain how a decrease in the availability of calcium ions could disrupt the contraction mechanism in muscles. (3)

A
  1. cannot interact with / move tropomyosin from binding sites on actin;
  2. myosin(heads) do not bind / actinomyosin not formed;
  3. does not activate ATPase / energy not released from ATP;
85
Q

Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours.

A
  1. Release of glucagon;
  2. Leads to formation of glucose in liver (cells);
  3. From non-carbohydrates / amino acids / fatty acids
86
Q

Apart from the yoghurt, it was important that all of the mice were given the same food each day.

Give two reasons why it was important that all of the mice were given the same food each day.

A
  1. Food is a factor affecting blood glucose / different foods contain different amounts of starch / glucose / sugar / carbohydrate;
  2. To keep starch / fibre intake the same / similar;
87
Q

When insulin binds to receptors on liver cells, it leads to the formation of glycogen from glucose. This lowers the concentration of glucose in liver cells.

Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration.

A
  1. Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;
  2. Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein);
88
Q

Adrenaline binds to receptors in the plasma membranes of liver cells.

Explain how this causes the blood glucose concentration to increase.

A
  1. Adenylate cyclase activated / cAMP produced / second messenger produced;
  2. Activates enzyme(s) (in cell so) glycogenolysis / gluconeogenesis occurs / glycogenesis inhibited;
89
Q

Diabetic people who do not control their blood glucose concentration may become unconscious and go into a coma. A doctor may inject a diabetic person who is in a coma with glucagon.

Explain how the glucagon would affect the person’s blood glucose concentration. (2)

A
  1. Glycogen to glucose / glycogenolysis by activating enzymes;
  2. Gluconeogenesis;
90
Q

Explain how the Loop of Henle works/ how water moves out

A
  1. Near the top of the ascending limb, Na+ ions are pumped out into the medulla using active transport.
  2. The ascending limb is impermeable to water, so the water stays inside the tubule. This creates a low water potential in the medulla because there’s a high concetration of ions.
  3. Water moves out descending limb, into medulla by osmosis. The filtrates then more concentrated.
  4. Bottom of ascending limb, Na+ ions diffuse into medulla, lowering water potential in medulla. (Ascending limb is impermable to water so stays in tubule again).
  5. Water moves out of DCT by osmosis and reabsorbed into the blood.
  6. The three stages increase the ion concentration in the medulla, which lowers the water potential.
  7. That causes water to move out of collecting duct by osmosis. The water in the medulla is reabsorbed into the blood through the capillary network.
91
Q

What controls water reabsorption

A

hormones

92
Q

What controls the water potential of the blood

A

osmoreceptors in th brain hypothalamus

93
Q

What happens when the water potential decreases?

A

Water moves out of osmoreceptor cells by osmosis causing a decrease in the volume. That sends a signal to other cells in the hypothalamus, which sends a signal to the posterior pituitary gland. That causes the posterior pituitary to release a hormone called ADH (antidiuretic hormone) into the blood.

94
Q

What does ADH stand for?

A

Antidiuretic hormone

95
Q

What does ADH make the walls of DCT and collecting duct?

A

More permeable to water so more water can be reabsorbed from these tubules into the medulla and into the blood by osmosis. A small amount of concentrated urine is produced which means less water is lost from the body.

96
Q

When is less water lost?

A

When the urine is concentrated

97
Q

How does ADH change the water content of the blood when it’s too low (dehydrated)?

A
  1. The water content of the blood drops, so its water potential drops.
  2. That is detected by osmoreceptors in the hypothalamus.
  3. The posterior pituitary gland is stimulated to release more ADH into the blood.
  4. More ADH means that the DCT and collecting duct becomes more permeable so more water is reabsorbed into the blood by osmosis.
  5. A small amount of highly concentrated urine is produced and less water is lost.
98
Q

How does ADH change the water content of the blood when it’s too high (hydrated)

A
  1. The water content of the blood rises, so it’s water potential increases.
  2. That’s detected by osmoreceptors in the hypothalamus.
  3. The posterior pituitary gland releases less ADH into the blood.
  4. Less ADH means that the DCT and CD become less permeable so less water is reabsorbed into the blood by osmosis.
  5. A large amount of dilure urine is produced and more water is lost.
99
Q

n humans, when the stomach starts to become full of food, receptors in the wall of the stomach are stimulated. This leads to negative feedback on the desire to eat. Suggest why this negative feedback is important.

A
  1. (Negative feedback) stops desire / wish to eat / appetite;
  2. (This) limits amount eaten / stops eating;
  3. Prevents / reduces risk of obesity / too much energy intake;
100
Q

In this investigation, the higher the concentration of sucrose in a rat’s mouth, the higher the frequency of nerve impulses from each taste receptor to the brain.

(3)

If rats are given very high concentrations of sucrose solution to drink, the refractory period makes it impossible for information about the differences in concentration to reach the brain. Explain why.

A
  1. (Refractory period) leads to discrete / separate nerve impulses / time when another nerve impulse can’t happen;
  2. When maximum frequency reached / exceeded, no further increase in information / all (higher) concentrations of sucrose seem the same;
101
Q

From which gland is ADH released?

A

pituitary

102
Q

Use the information given;

explain how ADH increases the movement of water from the lumen of the collecting duct into the blood.

A
  1. ADH causes vesicles containing aquaporins / aquaporins to be inserted into membrane / collecting duct wall / plasma;
  2. water enters cell through aquaporins;
  3. by osmosis / diffusion / down a water potential gradient;
  4. (from cell) to capillary;
  5. via interstitial fluid;
103
Q

Suggest why diabetes insipidus is more common in males. (2)

A
  1. because males only have one X chromosome / do not have Y chromosome;
  2. a single copy of the recessive allele will be expressed;
104
Q

A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how. (3)

A
  1. recessive alleles can be carried by individuals without showing effects / dominant allele always expressed;
  2. organism that are carriers more likely to reproduce / affected organism less likely to reproduce;
  3. therefore recessive alleles are more likely to be passed on / dominant alleles less likely to be passed on;
105
Q

Changes in your external environment can affect your..

A

internal environment (blood and tissue fluid that surrounds your cells)

106
Q

What does homeostasis involve?

A

The control systems that keep your internal environment roughly constant

107
Q

What is vital for cells to function normally

A

keeping the internal environment stable.

108
Q

What is particularly important to maintain?

A

The right core body temperature

Blood pH

109
Q

Why is it important to maintain the right core body temp ad pH of blood

A

Temperature and pH affect enzyme activity and the enzymes control the rate of metabolic reactions.

110
Q

What happens if the temperatures too high?

A
  1. Enzymes denature
  2. The enzymes molecules vibrate too much breaking the hydrogen bonds that hold them in their 3D shape
  3. The shape of active site now changed and no longer works as a catalyst.
  4. That means metabolic reactions are less efficient
111
Q

What happens if the temperature is too low?

A
  1. Enzyme activity reduced
  2. Slows the rate of metabolic reactions
112
Q

When do enzymes work best/ their highest rate of activity?

A

The highest rate of enzyme activity happens as their optimum temperature

37oC

113
Q

What happens if the pH too high or too low?

A
  1. Enzymes denatured
  2. Hydrogen bonds that hold the 3D shape are broken so shape of enzymes active site is changed
  3. no longer works as catalyst
  4. metabolic reactions less efficient
114
Q

optimum pH for highest enzyme activity

A

usually pH 7

some enzymes in the stomach tho work best in lower pH

115
Q

Why is it important to maintain the right concentration of glucose in the blood?

A

because cells need glucose for energy

and blood glucose conc. affects the water potential of blood

116
Q

What is the water potential of blood

A

The potential of water molecules to diffuse out of or into a solution

117
Q

If the blood glucose concentration is too high, how is the water potential of blood affected?

A

its reduced to the point where water molecules diffuse out of cells into blood by osmosis which causes cells to shrivel up and die.

118
Q

If the blood glucose concentration is too low, how is the water potential of blood affected?

A

cells unable to carry out normal activites as there isn’t eough glucose for respiration to provide energy

119
Q

What does homeostatic systems detect

A

a change and respond by negative feedback

120
Q

What does homeostatic systems involve

A

receptors

a communication system

effectors

121
Q

How is the information communicated?

A

Receptors

via. the nervous system or hormonal system to effectors

122
Q

why do effectors respond to when a level is too high or low?

A

to counteract the change (bring it back to normal)

123
Q

Negative feedback

A

Changes causes a response that leads to a reduction in that change.

The mechanism that restores the level to normal.

124
Q

Why does negative feedback only work in certain limits?

A

If the change is too big, then the effectors may not be able to counteract it.

i.e. a huge drop in body temperature caused by prolonged exposure to cold weather may be too large to counteract.

125
Q

What do multiple negative feedback mechanisms give and how?

A

more control because having more than one mechanism gives more control over changes in your internal environment than just one negative feedback mechanism

126
Q

Having multiple negative feedback mechanisms means you can ____ increase or decrease a level so it returns to normal

A

actively

127
Q

What would it mean if you had one negative feedback mechanism?

A

All you could do would be turn it on or turn it off. You’d only be able to actively change a level in one direction so it returns to normal.

128
Q

What would having one negative mechanism cause

A

a slower response

less control

129
Q

When does postive feedback mechanisms occur?

A

Happens when a homeostatic system breaks down i.e. if you’re too cold for too long

130
Q

What does a positive feedback mechanism do?

A

Amplifies the change

131
Q

How do the effectors respond to positive feedback mechanisms?

A

Further increase the level away from the normal level.

132
Q

What is positive feedback useful for?

A

Rapidly increasing something i.e. blood clot after an injury.

133
Q

Explain blood clots forming

A
  1. Platelets become activated and release a chemical - this triggers more platelets to be activated.
  2. Platelets very quickly form a blood clot at the injury site.
  3. The process ends with negative feedback when the body detects the blood clot has been formed.
134
Q

How does hypothermia involve positive feedback?

A
  1. Hypothermia is low body temp.
  2. It happens when heat’s lost from the body quicker than it can be produced.
  3. As the body temp. falls the brain doesn’t work properly and shivering stops - makes the body temp. fall even more.
  4. Positive feeback takes body temp. further away from the normal level, and it continues to decrease unless action is taken.
135
Q

Why isn’t positive feedback involved in homeostasis

A

Because it doesn’t keep your internal environment stable.

136
Q

How is urea concentrated in filtrate?

A
  1. Waters reabsorbed by osmosis
  2. At PCT
  3. At DCT
  4. By active transport
137
Q

How does a lack of insulin affect the reabsorption of glucose?

A
  1. Increase in conc. of glucose in the blood and tubule.
  2. Reabsorbed by facilitated diffusion.
  3. Proteins required.
  4. They work at a max. rate.
  5. Not all glucose reabsorbed/ some lost in the urine.
138
Q

How is urea removed?

A
  1. HSP
  2. Causes ultrafiltration thru the basement membrane
  3. Small size urea molecules out

a-level biology a2 (11 decks)

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