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Biology A-Level > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Define Homeostasis

A

Using control systems to maintain a stable internal environment

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2
Q

Why is it vital to keep your internal environment stable?

A

For cells to function normally and to stop them being damaged

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3
Q

What happens when the body temperature is too high?

A
  • Enzymes denature
  • Vibrate too much, breaks the H bonds that hold the 3D shape
  • Metabolic reaction are less efficient
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4
Q

What happens when the body temperature is too low?

A
  • Enzyme activity is reduced
  • Slows down rate of metabolic reaction
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5
Q

What is the optimum temperature for the highest rate of enzyme activity?

A

37oC

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6
Q

What happens when the blood pH is too high or too low?

A
  • Enzymes denature
  • H bonds holding 3D shape are broken
  • Shape of active site changes and no longer work as catalyst
  • Metabolic reactions are less efficient
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7
Q

What is the optimum pH for the highest rate of enzyme activity?

A

pH 7

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8
Q

What happens when the blood glucose concentration is too high?

A
  • Water potential of blood is reduced
  • Water leaves cell into blood via osmosis
  • Cells shrivel up and die
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9
Q

What happens when the blood glucose concentration is too low?

A
  • Cells unable to carry out normal activities
  • Not enough glucose for respiration to provide energy
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10
Q

What does the homeostatic system involve?

A
  • Recepors
  • Communication system
  • Effector
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11
Q

What does the receptor do?

A

Detect when levels are too high or too low

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12
Q

Which mechanism restores the level back to normal?

A

Negative feedback mechanism

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13
Q

Negative feeback works…

A

W/in certain limits- change too big, effector may not be able to counteract it

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14
Q

Homeostasis involves ____ negative feedback mechanism

A

Multiple

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15
Q

What does having multiple negative feedback mechanism mean?

A
  • Can actively inc or dec level so it returns to normal
  • More control
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16
Q

What happens when you only have one negative feedback mechanism?

A
  • Can only actively change level in 1 direction
  • Slower response
  • Less control
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17
Q

Positive feedback ___ change from normal level

A

Amplify

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18
Q

How does effectors respond in positive feedback mechanisms?

A

Further increase level away from normal level

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19
Q

When is positive feedback useful?

A
  • Rapidy activate something eg. Blood clot
  • Homeostatic system breaks down eg. Hypothermia
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20
Q

Is positive feedback involved in homeostasis? Why?

A
  • No
  • Doesn’t keep internal env stable
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21
Q

The concentration of glucose in the blood is usually around…

A

90 mg per 100cm3

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22
Q

When does glucose conc increase?

A

After eating food containing carbs

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23
Q

When does glucose conc fall?

A

After exercise, glucose used for respiration to release energy

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24
Q

Which 2 hormones control blood glucose conc?

A
  • Insulin
  • Glucagon
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25
Q

Where are insulin and glucagon secreted from?

A
  • Cluster of cells in pancreas called Islets of Langerhans
  • Beta cells secrete insulin
  • Alpha cells secrete glucagon
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26
Q

Outline how insulin lowers blood glucose conc when it’s too high

A
  • Binds to receptor on cell membrane of liver cells and muscle cell, inc permeability of muscle cell membrane to glucose, cells take up more glucose- involves inc no. channel proteins
  • Activates enzymes that convert glucose to glycogen, cells able to store glycogen as energy source (glycogenesis)
  • Inc rate of respiration of glucose
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27
Q

Outline how glucagon inc blood glucose conc when it’s too low

A
  • Binds to receptors on cell membrane of liver cells
  • Activates enzymes in liver cells that break down glycogen to glucose (glycogenolysis)
  • Activates enzymes involved in formation of glucose from glycerol + aa (non-carbs = gluconeogenesis)
  • Dec rate of respiration of glucose
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28
Q

Outline what happens when the blood glucose conc falls

A
  • Pancrease detects too low
  • A- secrete glucagon, b- stop screting insulin
  • Glucagon binds to liver cell
  • Glycogenolysis activated
  • Gluconeogenesis activated
  • Cells respire less glucose
  • Cells release glucose to blood
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29
Q

Outline what happens when the blood glucose conc rise

A
  • Pancrease detects too high
  • A- stop secreting glucagon, b- secrete insulin
  • Insulin binds to muscle + liver cell
  • Cells take up more glucose
  • Glycogenesis activated
  • Cells respire more glucose
  • Less glucose to blood
30
Q

Outline how insulin makes glucose transporters available for facilitated diffusion

A
  • Skeletal + cardiac muscle cells contain channel protein GLUT4 - glucose transporter
  • Insulin levels low, GLUT4 stored in vesicles in cytoplasm
  • Insulin binds to receptors on cell surface membrane, triggers movement of GLUT4 to membrane
  • Glucose can then be transported into cell through GLUT4 via. FD
31
Q

Which gland secretes adrenaline?

A

Adrenal gland

32
Q

When is adrenaline secreted?

A
  • Low conc of glucose in blood
  • Stressed
  • Exercising
33
Q

Outline the function of adrenaline

A
  • Binds to receptors in cell membrane of liver cells
  • Activates glycogenolysis
  • Inhibits glycogenesis
  • Activates glucagon secretion
  • Inhibits insulin secretion
  • More glucose available for muscles to respire
34
Q

Describe the second messenger model of adrenaline and glucagon

A
  • Adrenaline and glucagon bind to receptor
  • Activate enzyme adenylate cyclase
  • Converts ATP to chemical signal- second messenger
  • Cyclic AMP
  • Activates enzyme protein kinase A
  • Activates cascade breaking glycogen to glucose
35
Q

Define diabetes mellitus

A

Condition where blood glucose conc can’t be controlled

36
Q

How is type 1 diabetes acquired?

A
  • Immune system attacks b cells in islet of langerhans so can’t produce insulin
  • Genetic predispositioning
  • Triggered by viral infection
37
Q

Define hyperglycaemia

A

After eating, glood glucose level rises and stays high

38
Q

How is type 1 diabetes treated?

A
  • Insulin therapy:
  • Regular insulin injection
  • Insulin pump (continuous)
39
Q

Define hypoglycaemia

A

Dangerous drop in blood glucose level

40
Q

How do you avoid a sudden rise in glucose?

A
  • Eating regularly
  • Control carbohydrate intake
41
Q

How is type 2 diabetes acquired?

A
  • Obesity
  • More likely with family history
  • Lack of exercise
  • Age
  • Poor diet
42
Q

Why does type 2 diabetes occur?

A
  • B cells dont produce enough insulin
  • Body’s cell don’t respond properly to insulin bc insulin receptors don’t work, so cells don’t take up enough glucose- high blood glucose conc
43
Q

How is type 2 diabetes treated?

A
  • Eating healthy
  • Balanced diet
  • Losing weight
  • Regular exercise
  • Glucose-lowering medication (if diet and exercise can control it)
  • Insulin injections
44
Q

How do health advisors respond to the inc in type 2 diabetes?

A
  • Eat diet low in fat, sugar and salt
  • Regular exercise
  • Lose weight
  • Educate people
  • Challenged food industry to reduce advertising junk food and use clearer labels
45
Q

How do food companies respond to the inc in type 2 diabetes?

A
  • Use sugar alternatives
  • Reducing sugar, fat and salt content
46
Q

What is the normal conc of glucose in the urine?

What does it mean when the conc is higher?

A
  • 0-0.8mM
  • Indicates diabetes
47
Q

How is quantitative benedict’s reagent different to normal benedict’s reagent?

A

When heated w/ glucose, initial blue colour is lost but brick red ppt isn’t produced

48
Q

Which method do you use to determine the conc of glucose in urine?

A

Colorimetry

49
Q

Higher the conc of glucose the more/less blue colour will be lost/produced, increasing/decreasing absorbance of solution

A
  • More
  • Lost
  • Decreasing
50
Q

Outline how to do a serial dilution?

A
  • 5 test tubes in racks
  • Add 10cm3 of initial 4mM glucose sol to 1st test tube and add 5cm3 of distilled water to other 4 test tube
  • Using pipette, draw 5cm3 of sol to second test tube (half conc - 2mM)
  • Repeat 3 times to create 1mM, 0.5mM and 0.25mM
51
Q

Outline the method used to determine the conc of glucose in a uring sample

A
  • Need several glucose solutions of diff, known conc (serial dilution)
  • Need to make a calibration curve:
  • Do quantitative benedict’s test on each solution (plus water as control)
  • Use colorimeter w/ red filter
  • Make calibration curve - absorbance against glucose conc
  • Can test unknown sol
52
Q

Outline the function of the kidneys

A
  • Excrete waste products
  • Regulate water potential of blood
53
Q

Label a nephron

A
  • Afferent arteriole
  • Glomerulus
  • Efferent arteriole
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
54
Q

Where does selective reabsorption take place?

A
  • PCT
  • Loop of henle
  • DCT
55
Q

Where does ultrafiltration occur?

A

Bowman’s capsule

56
Q

Describe how ultrafiltration produces glomerular filtrate (5)

A
  • Hydrostatic pressure
  • Small molecules
  • Pass through basement membrane
  • Protein too large to pass
  • Presence of pores/podocytes
57
Q

Name 4 substances present in the glomerular filtrate

A
  • Urea
  • aa
  • Fatty acids
  • Ions
58
Q

Outline how the proximal convoluted tubule are adapted for reabsorption

A
  • Infolding inc SA
  • Microvilli inc SA
  • Lots of mitochondria
59
Q

Describe the process of selective reabsorption

A
  • Useful filtrate (glucose) are reabsorbed along PCT by AT and FD
  • Water enters blood by osmosis bc water potential of blood is lower than filtrate
  • Filtrate that remains is urine
60
Q

What is urine made up of?

A
  • Water
  • Dissolved salts
  • Urea
  • Hormones
  • Excess vitamins
61
Q

What does urine not usually contain?

A
  • Proteins- too big to be filtered out
  • Blood cells- too big to be filtered out
  • Glucose- actively reabsorbed
62
Q

Give ways water is lost in the body?

A
  • Excretion
  • Sweat
  • Breathing
63
Q

Define osmoregulation

A

Regulation of the water potential of the blood

64
Q

What happens when the water potential of the blood is too low (dehydrated)?

A
  • More water is reabsorbed into the blood
  • Via osmosis
  • Urine is more conc so less water is lost during excretion
65
Q

What happens when the water potential of the blood is too high?

A
  • Less water is reabsorbed into the blood
  • Urine is dilute, more water is lost during excretion
66
Q

Where does the regulation of water potential mainly take place?

A
  • Loop of henle
  • DCT
  • Collecting duct
67
Q

Describe how the loop of henle maintains a sodium ion gradient

A
  • Ascending limb, Na+ pumped out into medulla using AT
  • AL impermeable to water so water stays inside tubule, creates low WP in medulla
  • Water moves out of descending limb into medulla via osmosis
  • Filtrate more conc
  • Water in medulla is reabsorbed into blood through capillary network
  • Bottom of AL Na+ diffuse out medulla, further lowering WP
68
Q

Describe what happens in the collecting duct

A
  • High ion conc in medulla lowers wp
  • Causes water to move out collecting duct via osmosis
  • Water in medulla is reabsored into blood via capillary network
69
Q

Which cells moniter the water content of blood?

A

Osmoreceptors in the hypothalmus

70
Q

When is ADH (antidiuretic hormone) secreted?

A

Water potential of blood inc

71
Q

Explain the role of ADH in the production of concentrated urine

A
  • When water potential of blood is too low, osmoreceptors in hypothalamus detect it
  • Post pituitary gland secretes more ADH
  • ADH increases permeability in DCT and collecting duct
  • More water reabsorbed into blood via osmosis

Biology A-Level (10 decks)

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