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Biology Paper 2 > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis?

A

The maintenance of a stable internal environment

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2
Q

What effect does temperature have on metabolic reactions?

A

Temperature too high- reactions stop as vibrations, due to an increase in kinetic energy and hydrogen bonds break that help hold enzyme’s 3D shape. Active site changes shape so enzyme and substrate no longer fit together and no longer functions as a catalyst
Temperature too low- enzyme activity reduced as kinetic energy reduced

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3
Q

How do you work out pH?

A

pH= -log10 (H+)

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4
Q

Effect of blood glucose Concentration levels on cells

A

If blood glucose concentration is too high- water potential of blood reduced- water molecules diffuse out of blood into to cells via osmosis which can cause cells to shrivel up and die
If blood Concentration is too low- cells cannot carry out functions as glucose needed for respiration to provide energy

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5
Q

What is a negative feedback mechanism?

A

Negative feedback keeps things around the normal level by counteracting change. Receptors detect change, information communicated via nervous system or hormonal system to effectors to bring levels to normal

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6
Q

Why do we have multiple negative feedback mechanisms?

A

Means levels can be actively increased and decreased which gives more control over changes in your internal environment

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7
Q

What is a positive feedback mechanism and give an example of a positive feedback mechanism

A

Effectors respond to further increase the level away from the normal level- it isn’t involved in homeostasis because it doesn’t keep your internal environment stable. Positive feedback is useful to rapidly active processes in the body for example after the formation of blood clots after an injury platelets become activated and release a chemical which releases more platelets this means platelets form very quickly from a blood clot at the injury site (process ends with negative feedback when body detects blood clot had been formed)

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8
Q

What cells does the Islet of Langerhans contain?

A

Alpha and beta cells

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9
Q

What is the role of the alpha cells?

A

Secrete glucagon into the blood

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10
Q

What is the role of the beta cells?

A

Secrete insulin into the blood

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11
Q

What is the role of insulin and how does it work?

A

Insulin lowers blood Concentration when it is too high, it binds to specific receptors on the cell membrane of muscle and liver cells (hepatocytes). This increases permeability of muscle cell membranes to glucose. This involves increasing the number of channel proteins in the cell membrane
Insulin also activas enzymes in muscle and liver cells which convert glucose into glycogen (glycogenesis) so cells are able to store glycogen as an energy source in the cytoplasm
Insulin also increases rate of respiration of glucose especially in muscle cells

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12
Q

What is the role of glucagon and how does it work?

A

Glucagon raises blood concentration when it is too low. It binds to specific receptors on the cell membranes of liver cells and activates enzymes that breakdown glycogen into glucose (glycogenolysis)
Also activates enzymes that are involved in the formation of glucose from gylcerol and amino Acids. This process of forming glucose from non carbohydrates is called gluconeogenesis.
Glycogen decreases rate of respiration of glucose in cells

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13
Q

Compare hormones to nerve impulses

A

Responses by hormones slower
Responses to hormones can occur all over the body of their target cells are widespread, unlike nerve impulses that are localised in one area.
Hormones tend to last longer as they are not broken down as quickly as neurotransmitters

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14
Q

How do negative feedback mechanisms control blood glucose concentration?

A

High- Pancreas detects blood glucose conc too high. B cells secrete insulin and A cells stop secreting glucagon. Insulin binds to receptors on liver and muscle cells (the effectors) effectors respond which leads to glucose levels returning to normal
Low- Pancreas detects blood glucose conc too low
A cells secrete glucagon and b cells stop secreting insulin. Glucagon then binds to receptors on liver cells (the effectors) effectors respond which leads blood concentration returning to normal

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15
Q

What type of protein is a glucose transporter? And what is its role

A

Channel Protein- allows glucose to be transported across a cell membrane

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16
Q

What is the name of the glucose transporter in skeletal and muscle cells?

A

GLUT4

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17
Q

What triggers the movement of GLUT4 into the membrane from the vesicles in the cytoplasm?

A

Insulin binding to receptors on cell surface membrane.

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18
Q

How can glucose be transported into the cell via the GLUT4 protein

A

Through facilitated diffusion

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19
Q

Where is adrenaline secreted from?

A

Adrenal gland found just above the kidneys

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20
Q

When is adrenaline secreted?

A

When there is low glucose conc in blood
During stress
During exercise

21
Q

Once adrenaline binds to receptors in the cell membrane of liver cells, how does it increase blood glucose concentration? (4 points)

A

Activates glycogenolysis
Inhibits glycogenesis
Activates glucagon secretion and inhibits insulin secretion which increases glucose concentration
Makes more glucose available for muscles to respire

22
Q

How does adrenaline and glucagon activate gylcogenolysis through the second messenger model?

A

When the two hormones bind to receptors on the cell membranes of liver cells , enzyme Adenylate Cyclase which converts ATP into Cyclic AMP (cAMP) which is the second messenger. cAMP activates enzyme protein kinase A. Protein kinase A activates a cascade that breaks down glycogen into glucose (gylcogenolysis)

23
Q

What is type 1 diabetes?

A

Where the immune system attacks the B cells in the Islet of Langerhans so they can’t produce any insulin and so after eating glucose levels stay high

24
Q

What is type 2 diabetes

A

Usually acquired later in life and occurs when B cells don’t produce enough insulin or when the body cells don’t respond properly to insulin. This is because the insulin receptors don’t function properly so cells don’t take up enough glucose so blood concentration is higher than normal

25
Q

What 2 lifestyle changes reduce risk of diabetes

A 
Healthier diets (decrease in sugar and fat)
Increase levels of physical activity
26
Q

Give three actions health advisors think the food industry needs to do to reduce the risk of people developing Type 2 diabetes

A

Reduce advertising of junk food
Improve nutritional value of their products
Use clearer labelling on products

27
Q

Give 5 risk factors associated with Type 2 diabetes

A

Obesity, lack of exercise, family history, more advanced age, poor diet

28
Q

What is 2 of the main functions of the kidneys?

A

To filter waste products out of the blood and reabsorb useful solutes (e.g glucose)
Regulate the body’s water content

29
Q

Where does ultrafiltration take place in the kidney?

A

The gromerulus inside the Bowman’s capsule

30
Q

What is the arteriole called that takes blood in each gromerulus called?

A

The afferent arteriole

31
Q

What is the arteriole called that takes the filtered blood away from the gromerulus called?

A

The efferent arteriole

32
Q

How does liquid and small molecules in the blood enter the bowman’s capsule?

A

The efferent arteriole is smaller in diameter compared to the afferent arteriole so the blood in the gromerulus is under high pressure, which forces liquid and small molecules in the blood out of the capillary and into the bowman’s capsule. ( Due to Hydrostatic pressure)

33
Q

What three layers does the liquid and small molecules need to get into the bowman’s capsule and enter the nephron tubules?

A

The capillary endothelium, basement membrane and the epithelium of the Bowman’s capsule

34
Q

What is the name of the cells that make up the epithelium of the Bowman’s capsule called?

A

Podocytes

35
Q

What molecules stay in the blood and don’t make up the gromerular filtrate

A

Proteins and blood cells and platelets

36
Q

What substances make up the gromerular filtrate?

A

Small molecules like nitrogenous waste, water and nutrients

37
Q

What adaptions does the PCT have to allow selective reabsorption of useful molecules?

A

Epithelium walls of PCT have microvilli to provide large surface area for reabsorption of useful materials in the gromerular filtrate from the tubules into the blood (in the capillaries)

38
Q

What processes are useful products absorbed along the PCT

A

Active Transport and facilitated diffusion

39
Q

Where is water reabsorbed from in blood (Specifically) and what is the name of the filtrate that remains?

A

From the PCT, loop of Henle, DCT and collecting duct.

Urine

40
Q

What substances are usually found in urine?

A

Water, dissolved salts, urea, hormones, excess vitamins

41
Q

Write the sequence of urine production

A

Gromerulus, Bowman’s capsule, Proximal convoluted tube, loop of Henle, distal convoluted tube (DCT), collecting duct, ureter and bladder

42
Q

How does the loop of Henle control the movement of sodium ions so that water can be absorbed by the blood (osmoregulation)?

A

1- Near top of ascending limb, Na+ ions actively pumped out into the medulla. Ascending limb impermeable to water so water stays inside the tubule. This creates low water potential in the medulla because high concentration of ions
2- lower potential in medulla means water moves out of descending limb (via osmosis) into the medulla. This makes gromerular filtrate more concentrated (the ions can’t diffuse out the defending limb is impermeable to them). The water in the medulla is reabsorbed into the blood through the capillary network
3- bottom of the ascending limb Na+ ions diffuse out into the medulla, lowering water potential of medulla (ascending limb impermeable to water so it stays in the tubule)
4- Water moves out the DCT by osmosis and is reabsorbed into the blood
5- ion concentration has been massively increased in first 3 stages so water potential lowered. Water potential moves out the collecting duct through osmosis. Water in blood, again, reabsorbed into the blood through the capillary network

43
Q

How is the water potential of the blood monitored?

A

By cells called osmoreceptors in a part of the brain called the hypothalamus

44
Q

How is ADH released into the blood

A

When water potential of blood decreases , water moves out osmoreceptor cells via osmosis which causes cells to decrease in volume. This sends a signal to other cells in the hypothalamus which send a signal to posterior pituitary gland. This causes posterior pituitary gland to release ADH into the blood

45
Q

How does ADH lower the amount of water lost from the body?

A

ADH molecules bind to receptors on the plasma membranes of cells in the DCT and the collecting duct.
When this happens, aquaporins (protein channels) allow water to pass through via osmosis, making the walls of the DCT and the collecting duct more permeable to water.
This means more water is reabsorbed into these tubules into the medulla and into the blood via osmosis.
Small amount of concentrated urine is produced which means less water is lost from the body

46
Q

What happens when dehydration occurs?

A
  • Water content of the blood drops so water potential drops
  • this is detected by osmoreceptors in the hypothalamus
  • this posterior pituitary gland is stimulated to release more ADH into the blood
  • More ADH means that the collecting duct are more permeable so more water is reabsorbed into the blood by osmosis
  • A small amount of highly concentrated urine is produced and less water is lost
47
Q

What happens when hydration occurs?

A
  • The water content of the blood rises so its water potential rises
  • This is detected by osmoreceptors in the hypothalamus
  • The posterior pituitary gland releases less ADH into the blood
  • Less ADH means that the DCT and collecting duct are less permeable so less water is reabsorbed into the blood by osmosis
  • A large amount of dilute urine is produced and more water is lost
48
Q

What happens to the gromerular filtrate in the proximal convoluted tubule?

A

Selective reabsorption takes place

Biology Paper 2 (5 decks)

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