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Biology > Homeostatsis > Flashcards

Homeostatsis Flashcards

1
Q

Define homeostasis

A

maintaining a constant internal environment within restricted limits

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2
Q

Explain the importance of maintaining a body temperature close to normal in relation to enzyme activity

A

If body temperature is too high;
- hydrogen bonds break within enzymes, changes their tertiary structure and the shape of the active site. Less enzyme-substrate complexes form

If body temperature is too low;
- Enzymes have too low kinetic energy, less enzyme-substrate complexes, so metabolic rate is reduced

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3
Q

Explain the importance of maintaining blood pH close to normal in relation to enzyme activity

A

If blood pH is too high;
- hydrogen bonds break within proteins, changing their tertiary structure

If blood pH is too low;
- Hydrogen bonds break within proteins, changing their tertiary structure

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4
Q

Explain the importance of maintaining blood glucose close to normal in relation to water potential of blood and availability of glucose for respiration

A

If blood glucose is too high;
- Blood has a lower water potential than cells, water leaves cells into blood by osmosis. Cells lack water for metabolic reactions such as hydrolysis and as a solvent

If blood glucose is too low;
- Glucose is not provided to cells fast enough for a high enough rate of respiration

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5
Q

Define negative feedback and give an example in biology

A

Negative feedback reverses the direction of change back to its original level
e.g. When body temperature is above 37 degrees C, the body responds to decrease it back to original

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5
Q

In negative feedback, why is it important to have separate mechanisms for increasing and decreasing the factor?

A

Separate mechanisms are used to increase and decrease the factor, as this gives a greater degree of control

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6
Q

What are hormones? Where are they secreted from? How do they travel in the body? Where do they act? How long does their effect last?

A
  • Hormones are chemical messengers, secreted by glands which are transported by the blood stream
  • They only act at target cells which have complementary receptors
  • Their effect is widespread and long lasting
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7
Q

In which cells are insulin and glucagon produced?

A
  • Insulin is produced in Beta cells in Islets of Langerhans
  • Glucagon is produced in alpha cells in Islets of Langerhans
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7
Q

Define positive feedback and give an example in biology

A

Positive feedback is where the change in one direction is amplified i.e. an increase leads to a further increase
e.g. VG Na+ channels open which causes depolarisation which causes more VG Na+ channels to open

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7
Q

Explain the importance of maintaining blood water potential close to normal in relation to blood pressure and metabolic reactions

A

If blood water potential is too high;
- Water enters cells by osmosis. Too much can cause cell lysis. Lots of water in blood causes high blood pressure

If blood water potential is too low;
- water leaves cells by osmosis. Cells lack water for metabolic reactions like hydrolysis and as a solvent

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8
Q

Explain how insulin lowers blood glucose when it binds a receptor

A
  • Inserting more glucose channel proteins into the cell membrane so more glucose enters cell by facilitated diffusion
  • Activating enzymes to convert glucose to glycogen for storage (glycogenesis)
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9
Q

What are the target cells for insulin?

A

Liver and muscle cells

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10
Q

Explain how glucagon increases blood glucose when it binds to receptor?

A
  • Activating enzymes to hydrolyse glycogen to glucose (glycogenolysis)
  • Activating enzymes to convert glycerol/amino acids to glucose (gluconeogenesis)
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11
Q

What are the target cells for glucagon?

A

Liver cells

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12
Q

How does adrenaline increase blood glucose?

A
  • Adrenaline is released from adrenal gland
  • It binds receptors on liver cells
  • Enzymes are activated which hydrolyse glycogen to glucose (glycogenolysis)
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13
Q

Describe the second messenger model of adrenaline and glucagon action

A
  1. When glucagon and adrenaline bind their receptors they activate the enzyme adenylate cyclase
  2. Adenylate cyclase converts ATP to cyclic AMP (cAMP)
  3. cAMP is the second messenger and activates the enzyme protein kinase
  4. Activates enzymes to cause glycogenolysis (hydrolyse glycogen to glucose)
14
Q

Describe the role of the liver in glycogenesis, glycogenolysis and gluconeogenesis

A

Glycogenesis= activating enzymes to convert glucose to glycogen
Glycogenolysis= activating enzymes to hydrolyse glycogen to glucose
Gluconeogenesis= activating enzymes to convert glycerol/amino acids to glucose

15
Q

Explain how the formation of glycogen in liver cells due to insulin, leads to a lowering of blood glucose concentration (3)

A
  • glucose concentration insider the liver cell decreases
  • higher glucose concentration in the blood than cell creates concentration gradient
  • glucose enters cell by facilitated diffusion
16
Q

Describe the difference between type 1 and 2 diabetes

A
  • Type 1 cant produce insulin whereas type 2 diabetes can produce insulin
  • In type 2, receptors don’t respond to insulin whereas they do in type 1
  • Type 2 can be caused by obesity whereas type 1 cant
  • In type 1, beta cells are dead in the Islets of Langhans whereas they aren’t in type 2
17
Q

Explain how diabetes can be controlled by giving insulin and/or manipulation of diet

A
  • Type 1 can be controlled by injecting insulin as the beta cells in the Islets of Langhans have died. This isn’t the case for type 2
  • Type 1 can also be controlled by the manipulation of the diet. This involved eating complex carbohydrates (polysaccharides) rather than sugar (mono/disaccharides) as this prevents rapid increase in blood glucose. Absorbed more slowly than monosaccharides because glyosidic bonds need to be hydrolyzed first before absorption.
18
Q

Why cant insulin be taken orally instead of being injected?

A

Can’t be taken orally as insulin (a protein) would be digested or denatured by stomach acid

19
Q

Explain how diabetes can be controlled by regular exercise/loss of weight?

A
  • Type 2 can be controlled by regular exercise as more respiration so more glucose used so decreases concentration of glucose in cells so more glucose enters by facilitated diffusion
  • Type 2 can be controlled by loss of weight as obesity can be a cause of type 2
20
Q

Define osmoregulation

A

the control of blood water potential

21
Q

Name each part of the nephron and their functions

A
  • Glomerulus= bundle of capillaries which sits in the Bowman’s capsule
  • Basement membrane= membrane between the capillaries of the glomerulus and Bowman’s capsule
  • Bowman’s capsule= where ultrafiltration takes place
  • Proximal convoluted tubule= selective reabsorption occurs here which absorbs useful substances back into the blood
  • Loop of Henle= regulates blood water potential by maintaining a gradient of sodium ions in the medulla (osmoregulation)
  • Distal convoluted tubule= more reabsorption of water occurs here (effected by ADH)
  • Collecting duct= final place for reabsorption of water (effected by ADH)
22
Q

During ultrafiltration what layers do the substances pass through?

A
  1. Pores in the capillary endothelium
  2. Basement membrane
  3. Bowman’s capsule epithelium (made of Podocytes)
23
Q

During ultrafiltration, what is and isn’t filtered?

A

Water and other small molecules e.g. glucose and amino acids are forced out
Proteins and cells are too large so stay in the blood

24
Q

What is the name of the filtrate formed in ultrafiltration?

A

Glomerular filtrate

25
Q

How are the cells of the proximal convoluted tubule adapted for selective readsportion?

A
  • Many mitochondria for more aerobic respiration to produce more ATP for active transport
  • Microvilli increase surface area
  • Many channel/carrier proteins for facilitated diffusion
  • Many carrier proteins for active transport
  • Many ribosomes to produce carrier/channel proteins
26
Q

How are glucose and water reabsorbed at the proximal convoluted tubule?

A
  • Water is reabsorbed at the proximal convoluted tubule by osmosis as proteins decrease the water potential of the blood allowing water to move down a water potential gradient from the proximal convoluted tubule into the blood
  • Glucose is reabsorbed at the proximal convoluted tubule by co-transport with Na+ in the same way as in the small intestine
27
Q

Describe the steps by which the loop of Henle creates a more concentrated filtrate and allows for the reabsorption of water in the descending limb and collecting duct

A

Ascending limb of Loop of Henle;
1. Na+ are actively transported out which decreases water potential in the medulla
2. The ascending limb is impermeable to water so water remains in the tubule
3. Filtrate becomes less concentration

Descending limb of Loop of Henle;
1. The descending limb is permeable to water
2. Water moves out by osmosis into lower water potential of medulla
3. Na+ actively transported into the descending limb
4. Due to the loss of water and Na+ moving in, the filtrate becomes more concentrated down the descending limb
5. This creates an increasing Na+ concentration deeper into the medulla

Collecting duct;
1. A water potential gradient is maintained along the length of the collecting duct (where Na+ concentration is increasing)
2. Water will leave the collecting duct by osmosis into the medulla
3. Water is then absorbed into the surrounding capillaries

28
Q

Which part of the brain detects blood water potential and which part secretes ADH?

A

The osmoreceptors in the hypothalamus detects changes in blood water potential
ADH is released from the posterior pituitary gland

29
Q

Give the step by step process by which ADH causes more reabsorption of water when dehydrated. What effect on the urine does this have?

A
  1. Decrease in blood water potential
  2. In the hypothalamus in the brain, water moves out of osmoreceptors into blood by osmosis
  3. Posterior pituitary gland releases more ADH into the blood
  4. ADH causes the distal convoluted tubule and collecting duct membranes to become more permeable to water, more aquaporins inserted
  5. more water reabsorbed into the blood
  6. Urine volume becomes less and is more concentrated
30
Q

What is proteinurea? What causes it?

A

Proteinurea is where there’s a high quantity of protein in the urine
Damages to the basement membrane causes proteinurea as proteins are able to pass through

31
Q

Describe the stages of ultrafiltration

A
  1. There’s a high blood pressure in the glomerulus
  2. Water and other small molecules e.g. glucose and amino acids are forced out
  3. This forms the glomerular filtrate in the tubule
  4. Proteins and cells are too large to pass through, so stay in the blood
  5. Water and small molecules pass through the pores in the capillary endothelium, the basement membrane and then the bowman’s capsule epithelium
32
Q

If blood water potential is too high, what will happen at the kidney?

A
  • Less water reabsorbed
  • Greater urine volume
  • Lower urine concentration
33
Q

Describe how glucose is reabsorbed into the blood in the nephron (5)

A
  • Glucose is reabsorbed at the proximal convoluted tubule
  • Na+ ions are actively transported from the epithelial cell into the blood using energy from the hydrolysis of ATP and a carrier protein against its concentration gradient.
  • This maintains the Na+ concentration gradient between the tubule and epithelial cell
  • Glucose and Na+ are co-transported from the tubule into the epithelial cell using a carrier protein down the Na+ concentration gradient. This is facilitated diffusion
  • Glucose moves from the cell into the blood using a carrier protein via facilitated diffusion
34
Q

How does the length of the loop of Henle impact the amount of water reabsorbed from the collecting duct?

A

The longer the loop of Henle, the greater the Na+ concentration, deeper into the medulla. The water potential gradient is maintained for longer. More water is reabsorbed from the collecting duct by osmosis

Biology (26 decks)

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