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Biology A-level > 6C Homeostasis > Flashcards

6C Homeostasis Flashcards

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1
Q

Give two factors that can change your blood glucose concentration

A

Eating and exercise

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2
Q

Why must blood glucose concetration be carefully controlled?

A

All cells need a constant energy supply to work (glucose provides this)

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3
Q

What is the normal blood glucose conc.?

A

Normally around 90mg per 100cm^3 of blood

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4
Q

Which organ monitors blood glucose conc.?

A

The pancreas

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5
Q

When will blood glucose conc. rise?

A

After eating food containing carbohydrates

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6
Q

When will blood glucose conc. fall?

A

After exercising, as more glucose is used in respiration to release energy

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7
Q

What are the two hormones that control blood glucose conc.?

A
  • Insulin

- Glucagon

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8
Q

Does the nervous system or the hormonal system control blood glucose conc.?

A

The hormonal system

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9
Q

Where do insulin and glucagon come from?

A

They’re secreted from islets of Langerhans, which are cells in the pacreas

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10
Q

How do insulin and glucagon travel around the body?

A

Travel in the blood

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11
Q

Where do insulin and glucagon travel to in the body?

A

To their target cells (effectors)

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12
Q

What are the two types of cells found in islets of Langerhans?

A
  • Beta (β) cells

- Alpha (α) cells

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13
Q

What do Beta (β) cells in the pancreas do and where are they specifically found?

A

Secrete insulin into the blood

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14
Q

What do Alpha (α) cells in the pancreas do and where are they specifically found?

A

Secrete glucagon into the blood

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15
Q

What do insulin and glucagon act on?

A

Effectors, which respond to restore the blood glucose conc. to the normal level

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16
Q

What is the action of insulin?

A

It lowers blood glucose when it’s too high

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17
Q

What is glycogenesis activated by?

A

Insulin

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18
Q

What is glycogenolysis activated by?

A

Glucagon

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19
Q

What is gluconeogenesis activated by?

A

Glucagon

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20
Q

What is the action of glucagon?

A

It raises blood glucose conc. when it’s too low

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21
Q

What is another name for liver cells?

A

Hepatocytes

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22
Q

What are the two main roles of the kidneys?

A
  • Excrete waste

- Regulate blood water potential

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23
Q

Give an example of a waste product that the kideney excrete

A

Urea

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24
Q

Describe the process of ultrafiltration

A

As blood passes through capillaries in the cortex (outer layer) of the kidneys, substances are filtered out of blood & into long tubules that surround the capillaries

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25
Q

Describe the process of selective reabsorption

A

(Comes after ultrafiltration)

Useful substances, such as glucose & the right amount of water are then reabsorbed back into the blood

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26
Q

What happens after useful substances have been selectively reabsobed in th kidneys?

A

Remaining unwanted substances pass along the bladder & are excreted as urine

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27
Q

Where is blood filtered in the kidneys?

A

At the start of the nephrons

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28
Q

Name the structures that make up the kidney

A
  • Fibrous capsule
  • Cortex
  • Medulla
  • Renal pelvis
  • Ureter
  • Renal artery

DONT NEED TO KNOW THIS IGNORE IT
- Renal vein

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29
Q

What is the Fibrous capsule (kidneys)?

A

An outer membrane that protects the kidney

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30
Q

What is the Cortex (kidney)?

A

A lighter coloured outer regionmade up of renal (Bowman’s) capsules, convoluted tubules & blood vessels

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31
Q

What is the Medulla (kidney)?

A

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

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32
Q

What is the Renal pelvis (kidney)?

A

A funnel shaped cavity that collects urine into the ureter

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33
Q

What is the Ureter (kidney)?

A

A tube that carries urine to the bladder

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34
Q

What is the Reanl artery (kidney)?

A

Supplies the kidney with blood from the heart via the aorta

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35
Q

What is the Renal vein (kidney)?

A

Returns blood to the heart via the vena cava

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36
Q

What is the Loop of Henle?

A

A long, hairpin loop that extends from the cortex to the medulla of the kidney & back again

It is surrounded by blood capillaries

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37
Q

What is the Distal convoluted tubule (DCT)?

A

A series of loops surrounded by blood capillaries

Its walls are made of epithelial cells, but its surrounded by fewer capillaries than the proximal tubule

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38
Q

What are the component of a nephron?

A
  • Afferent arteriole
  • Efferant arteriole
  • Glomerular capillary
  • Renal (Bowman’s) capsule
  • Proximal convoluted tubule
  • Loop of Henle (Ascending & descending limb)
  • Blood capilaries
  • Distal convoluted tubule
  • Collecting duct
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39
Q

What is the Collecting duct?

A

A tube into which a no. distal convoluted tubules from a no. nephhrons empty

It is lined by epithelial cells & becomes increasingly wide as it empties into the pelvis of the kidney

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40
Q

What are the blood vessels found in each nephron?

A
  • Afferent arteriole
  • Glomerulus
  • Efferent arteriole
  • Blood capillaries
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41
Q

What is the Reanl (Bowman’s) capsule?

A

Closed end at the start of the nephron

It’s cup-shaped & surrounds a mass of blood capillaries known as the glomerulus

Inner layer of the renal capsule is made up of specialised cells called podocytes

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42
Q

What is the Proximal convoluted tubule?

A

A series of loops surrounded by blood capilaries

Its walls are made of epithelial cells which have microvilli

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43
Q

What is the Afferent arteiole?

A

Tiny vessel that ultimately arises from the renal artery & supplies the nephron with blood

It enters the renal capsule of the nephron where it forms the glomerulus

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44
Q

What is the glomerulus?

A

A many-branched knot of capillaries from which fluid is forced out of the blood

The glomorular capillaries recombine to form the efferent arteriole

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45
Q

What is the efferent arteriole?

A

Tiny vessel that leaves the renal capsule

It has a smaller diameter than afferent arteriole & causes an increase in blood pressure within the glomerulus

Efferent arteriole carries blood away from the renal capsule & branches to form blood capillaries

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46
Q

What role do capillaries play in the nephron?

A

Concentrated network of capillaries that surround proximalCT, loop of Henle & distalCT & from where they reabsorb reabsorb mineral salts, glucose & water

Capillaries merge to form venules that merge to form the renal vein

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47
Q

What is homeostasis?

A

The maintenance of a stable internal environment

Changes in your internal environment can affect your internal environment

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48
Q

Why is homeostasis important?

A

Keeping you internal environment stabel is vital for cells to function normally & to stop them being damaged

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49
Q

What are some of the most important important things to be maintained in homestasis?

A
  • Core body temp
  • Blood pH

Because temperature & pH affect enzyme activity & enzymes control the rate of metabolic reactions

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50
Q

What happens if temperature is too high?

A

(e.g. 40 degrees) Enzymes may become denatured

The enzymes’s molecules vibrate too much, which breaks the hydrogen bonds that hold them in their 3D shape

Shape of enzymes’s active site is changed & it no longer works as a catalyst

Means metabolic reactions less efficient

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51
Q

What happens if body temp is too low?

A

Enzyme activity is reduced, slowing the rate of metabolic reactions

52
Q

What temp is the highest rate of enzyme activity?

A

The optimum temp - 37 degrees

53
Q

What happens if blood pH is too high/low?

A

(highly alkaline or acidic) The enzymes become denatured

The hydrogen bonds that hold them in their 3D shape are broken, so the of the enzyme’s active site is changed & no longer works as a catalyst

54
Q

What pH is the highest rate of enzyme activity?

A

The optimum pH - usually around pH 7 (neutral)

Some enzymes work best at other pH’s e.g. enzymes found in the stomach

55
Q

Why is it important to maintain the conc. of blood glucose?

A

Cells need glucose for energy

Blood glucose conc. also affects the water potential of the blood

56
Q

What happens if the blood glucose conc. is too low?

A

Cells are unable to carry out normal activities as there isn’t enough glucose for respiration to provide energy

57
Q

What happens if blood glucose conc. is too high?

A

The water potential of blood is reduced to a point where water molecules diffuse out of cells into the body by osmosis

This can cause the cells to shrivel up and die

58
Q

How do homeostatic systems respond to a detected change?

A

By negative feedback

59
Q

What do homeostatic systems involve?

A
  • Receptors
  • A communication system
  • Effectors
60
Q

What do receptors do in homeostasis?

A

They detect when a level is too high or low & the info is communicated via the nervour system or the hormonal system to effectors

61
Q

What do effectors do in homeostasis?

A

They respond to counteract the change - bringing the level back to normal

62
Q

What is the mechanism that restores levels back to normal in homeostasis?

A

Called a negative feedback mechanism

63
Q

Can negative feedback work all the time?

A

Not all the time - it works within certain limits

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

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

64
Q

Why are there multiple negative feedback mechanisms in homeostasis?

A

Having more than one gives more control over changes in your internal environment

Means you can actively increase/decrease a level so it returns to normal - e.g. feedback mechanisms to reduce body temp & mechanisms to increase it

65
Q

What would happen if you only had one negative feedback mechanism?

A

All you could do would be turn it on and off - you could only change the level in one direction so it returns to normal

e.g. it’s a bit like trying to slow down a car with only an accelerator - you can only take your foot off the accelerator

66
Q

What do positive feedback loops do?

A

They amplify a change from the normal level

67
Q

How do effectors act in a positive feedback loop?

A

They respond by further increasing the level away form the normal

68
Q

What is positive feedback useful for?

A

It’s useful to rapidly activate something

e.g. a blood clot after an injury

69
Q

How does positive feedback work to form a blood clot after an injury?

A
  • Platlets become activated & release a chemical - this triggers more platelets to be activated & so on
  • Platelets very quickly form a blood clot at the injury site
  • The process ends with -ive feedback, when the body detects the blood clot has been formed
70
Q

When in a bad situation does poitive feedback happen?

A

It can happen when a homeostatic system breaks down

e.g. if you’re too cold for too long

71
Q

What sort of feedback happens in hypothermia?

A

Positive feedback

72
Q

Explain how positive feedback causes hypothermia?

A
  • Hypothermia is low body temp. (below 35 degrees)
  • It happens when heat’s lost from the body quicker than it can be produced
  • As body temp falls, the brain doesn’t work properly & shivering stops - this makes body temp fall even more
  • +ive feedback takes body temp further away from the normal level & it continues to decrease unless action is taken
73
Q

Is positive feedback involved in homeostasis?

A

It isn’t involved in homeostasis because it doesn’t keep your internal environment stable

74
Q

Does insulin lower or raise blood glucose levels?

A

It lowers blood glucose conc. when it’s too high

75
Q

Does glucagon lower or raise blood glucose levels?

A

It raises blood glucose conc. when it’s too low

76
Q

Describe the process which insulin lowers blood glucose conc.

A
  • Insulin binds to specific receptors on cell membranes of liver cells & muscle cells
  • Increases permeability of muscle-cell membranes to glucose, so cells take up more glucose. This involves increasing the no. channel proteins in cell membranes
  • Insulin also actives enzymes in liver & muscle cells that convers glucoes into glycogen
  • Cells are able to store glycogen in their cytoplasm as an energy store
  • Process of forming glycogenfrom glucose is called glycogenesis
  • Insulin also increases rate of respiration of glucose, especially in muscles
77
Q

Describe the process in which glucagon raises blood glucose conc.?

A
  • Glucagon binds to specific receptors on the cell membranes of liver cells
  • Glucagon activates enzymes in liver cells that break down glycogen into glucose
  • The process of breaking down glycogen is called glucogenolysis
  • Glucagon also activates enzymes that are involved in the formation of glucose from glycerol (a component of lipids) & amino acids
78
Q

Why are responses produced by hormones slower and why do they last longer?

A

They travel in the blood to their target cells - these responses are slower than those produced by nervous impulses

Hormones are not broken down as quickly as neurotansmitters, so the effects last longer

79
Q

Describe what happens when blood glucose levels are too high

A
  • Pancreas detects blood glucose conc. is too high
  • Beta cells secrete insulin, alpha cells stop secreting glucagon
  • Insulin binds to receptors on liver & muscle cells
  • Cells take up more glucose, glycogenesis is activated,, cells respire more glucose
  • Less glucose in the blood
80
Q

Describe what happens when blood glucose levels are too low

A
  • Pancreas detects blood glucose conc. is too low
  • Alpha cells secrete glucagon, beta cells stop secreting insulin
  • Glucagon binds to receptors on liver cells
  • Glycogenolysis is activated, gluconeogenesis is activated & cells respire less glucose
  • Cells release glucose into the blood
81
Q

What does insulin do to lower blood glucose conc.?

A

It makes glucose transporters availble for facilitated diffusion (e.g. GLUT4)

82
Q

What is the glucose transporter found in skeletal & cadiac muscles?

A

GLUT4

83
Q

What is the overall function of the kidneys?

A

Excrete waste and regulate blood water potential

84
Q

What is ultrafiltration in the kidneys?

A

As blood passes through capillaries in cortex (outer layer) of kidney substances are filtered out of blood into long tubules that surround the capillaries

85
Q

What is selective reabsorption in the kidneys?

A
  • Occurs after ultrafiltration

- Useful substances (glucose and water) are reabsorbed back in the blood

86
Q

What happens to remaining unwanted substances that don’t get reabsorbed?

A

They pass along the bladder and are excreted as urine

87
Q

What are the long tubules along the bundle of capillaries called?

A

Nephrons (around 1 million in each kidney)

88
Q

What is the process of blood filtration?

A

1) Blood from renal artery’s enters arteriolar in cortex
2) Each arteriole splits into the glomerulus (this is where ultrafiltration takes place)
3) The afferent arteriole takes blood into each glomerulus and the efferent arteriole takes filtered blood away from the glomerulus
4) High pressure in efferent arteriole forces molecules in blood out of capillary into Bowman’s capsule
5) Blood passes through 3 layers to get from capillaries to Bowman’s capsule
6) Large substances can’t pass through and substances that do are called the glomerular filtrate
7) Glomerular filtrate passed along rest of nephron and useful substances are reabsorbed
8) Filtrate flows through collecting duct and pass out of kidney though ureter

89
Q

What does the efferent arteriole do?

A

Takes filtered blood away from the glomerulus

90
Q

What does the afferent arteriole do?

A

Takes blood into each glomerulus

91
Q

Why does the efferent arteriole have high pressure?

A

Smaller in diameter so high pressure forces liquid and small molecules in the blood out of the capillary

92
Q

What are the 3 layers that molecules pass through form the capillary to Bowman’s capsule?

A
  • Capillary wall
  • Basement membrane
  • Epithelium in Bowman’s capsule
93
Q

Where does selective reabsorption take place?

A

As the glomerular filtrate flows along the PCT, through the loop of Henle, and along the DCT

94
Q

How’s does selective reabsorption take place?

A

1) Useful substances leave the nephrons into the capillary network
2) Epithelium of the PCT has microvilli (larger SA) for reabsorption of useful materials from glomerular filtrate to the blood
3) Useful solutes (glucose) are reabsorbed along PCT by active transport of facilitated diffusion
4) Filtrate that remains is urine which passes along ureter to the bladder

95
Q

What does urine usually consist of?

A
  • Water and dissolved salts
  • Urea
  • Hormones and excess vitamins
96
Q

How is the epithelium of the PCT adapted for reabsorption?

A

Has microvilli to provide a large surface area

97
Q

How does the second messenger process work?

A
  • Receptors for adrenaline & glucagon have specific tertiary structures, make them complementary in shape to their respective hormones
  • Adrenaline & glucagon bind to their receptors & activate the enzyme adenylate cyclase
  • Activated adenylate cyclase converts ATP into a chemical signal called a ‘second messenger’
  • The second messenger is called cyclic AMP (cAMP)
  • cAMP activates an enzyme called protein kinase A - Protein kinease A activates a cascade that breaks down glycogen into glucose
98
Q

What other hormone can increase blood glucose conc.?

A

Adrenaline

Just like glucagon, it also helps to increase blood glucose conc.

99
Q

Where is adrenaline secreted from?

A

The adrenal glands, which are located above the kidneys

100
Q

When is adrenaline secreted?

A

When there’s a low conc. of glucose in your blood, when you’re stressed & when you’re exercising

101
Q

What effect does adrenaline have on blood glucose concentrations?

A

Adrenaline binds to receptors in the cell membrane of liver cells

  • It activates glycogenolysis (breakdown of glycogen to glucose)
  • It inhibits glycogenesis (synthesis of glycogen from glucose)
102
Q

What is glycogenolysis?

A

The breakdown of glycogen to glucose

103
Q

What is glycogenesis?

A

The synthesis of glycogen from glucose

104
Q

What hormones does adrenaline control for blood glucose conc.?

A

It activates glucagon secretion & inhibits insulin secretion

This increases glucose conc.

105
Q

How does adreanile affect the body?

A

It gets the body ready for action by making glucose availble for muscles to respire

106
Q

How do adrenaline and glucagon act?

A

Via a second messenger

107
Q

Do adrenaline and glucagon bind to the inside or the outside of the cell?

A

They bind to receptors on the outside of the cell

They can activate glycogenolysis inside a cell via a second messenger

108
Q

What regulates the water potential of the blood?

A

Kidneys

109
Q

Why does water potential of the blood need to be kept constant?

A

Water is essential to keep the body functioning

110
Q

What ways to mammals lose water?

A
  • During excretion

- Sweating

111
Q

What is osmoregulation?

A

Kidneys regulating water potential in the blood

112
Q

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

A
  • More water is reabsorbed by osmosis into the blood from the tubules of nephrons
  • Urine is more concentrated (less lost during excretion)
113
Q

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

A
  • Less blood is reabsorbed by osmosis into the blood from the tubules of the nephrons
  • Urine is more dilute (less lost during excretion)
114
Q

Where does regulation of water mainly take place?

A
  • Loop of Henle
  • DCT
  • Collecting duct
115
Q

What is the function of the Loop of Henle?

A

Maintains a sodium ion gradient

116
Q

Where is the loop of Henle located?

A

In the medulla (inner layer) of the kidneys

117
Q

What is the loop of Henle made up of?

A
  • Descending limb

- Ascending limb

118
Q

How does the Loop of Henle control blood water potential?

A

1) At top of ascending limb Na+ are pumped into medulla by active transport, it’s not permeable to water so water stays inside (lowering water potential in medulla)
2) Because of this water in descending limb moves into the medulla by osmosis (not permeable to ions)
3) Water in medulla the reabsorbed into blood through capillary network
4) Near bottom of ascending limb Na+ diffuse out into medulla (further lowering water potential in medulla)
5) Water moves out of DCT by osmosis and reabsorbed into the blood
6) As ion concentration in medulla is high water moves out of the collecting duct by osmosis

119
Q

What are features of the ascending limb?

A
  • Ions are permeable

- Water is not permeable

120
Q

What are features of the descending limb?

A
  • Permeable to water

- Not permeable to ions

121
Q

What cells monitor water potential in the blood?

A

Osmoreceptors (part of brain called hypothalamus

122
Q

How do osmoreceptors respond when the water potential of blood decreases?

A

1) Water moves out of osmoreceptors by osmosis causing them to decrease in size
2) This sends signal to posterior pituitary gland which releases a hormone called ADH
3) ADH makes walls of DCT and collecting duct more permeable
4) More water is reabsorbed from these into medulla and into blood (small amount of concentration of urine produced)

123
Q

Why does blood ADH levels fall when your hydrated?

A

1) Water content of blood rises, so water potential increases
2) Detected by osmoreceptors
3) Posterior pituitary gland releases less ADH into blood
4) Less ADH means DCT and collecting duct become less permeable (less water reabsorbed)
5) Large amount of dilute urine is produced and more water is lost

124
Q

Where is ADH released?

A

Posterior pituitary gland

125
Q

How does the second messenger process work?

A
  • Receptors for adrenaline & glucagon have specific tertiary structures that make them complementary in shape to their respective hormones
  • Adrenaline & glucagon bind to their receptors & activate an enzyme called adenylate cyclase
  • Activated adenylate cyclase converts ATP into a chemical signal called a ‘second messenger’
  • The second messenger is called cyclic AMP (cAMP)
  • cAMP activates an enzyme called protein kinase A

Biology A-level (20 decks)

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