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Biology > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is homeostasis?

A

The maintenance of internal environments within restricted limits in organisms for optimum cell function/enzyme activity

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2
Q

Examples of conditions that need to be controlled in the body

A
  • blood pressure
  • body temperature
  • blood glucose concentration
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3
Q

What is an example of positive feedback within the body?

A
  • propagation of an action potential - more diffusion of sodium ions = more sodium ion channels stimulated to open
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4
Q

What are the examples of negative feedback within the body?

A
  • control of blood pressure
  • control of blood water potential
  • control of blood glucose concentration
  • control of blood calcium ion concentration
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5
Q

Why does blood glucose concentration need to be controlled?

A
  • if blood glucose levels rise, water potential of the blood decreases causing water to move out of cells eg. red blood cells, therefore red blood cells shrivel and oxygen cannot be transported around the body
  • if blood glucose levels fall, there will be insufficient respiratory substrates needed for respiration
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6
Q

What is the second messenger model and how does it regulate blood glucose concentration?

A
  • adrenaline/glucagon binds to receptors on the cell-surface membrane
  • this causes the protein to change shape which activates adenyl cyclase
  • adenyl cyclase converts ATP to cyclic AMP
  • cAMP acts as a second messenger which binds to protein kinase and activates it
  • protein kinase catalyses the conversion of glycogen to glucose, which moves out of liver cells via facilitated diffusion into the bloodstream through channel proteins
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7
Q

What type of cells is the pancreas partly made up from?

A
  • hormone-producing cells called islets of Langerhans which contain:
  • alpha cells - secrete glucagon
  • beta cells - secrete insulin
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8
Q

What is glycogenesis?

A

the conversion of glucose to glycogen

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9
Q

What is glycogenolysis?

A

the breakdown of glycogen to glucose

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10
Q

What is gluconeogenesis?

A

the production of glucose from other sources other than carbohydrates such as amino acids and glycerol

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11
Q

How is blood glucose concentration lowered?

A
  • beta cells in the islet of Langerhans have receptors that detect a rise in blood glucose concentration
  • this stimulates the secretion of insulin which binds to complementary receptors on liver cell membranes
  • this increases the liver cells permeability to glucose, so more glucose is absorbed
  • this also activates enzymes which stimulate the conversion of glucose to glycogen
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12
Q

How is blood glucose concentration increased?

A
  • receptors on alpha cells in the islets of Langerhans detect the decrease in blood glucose concentration
  • this stimulates alpha cells to release glucagon, and the release of adrenaline from the adrenal gland
  • glucagon binds to complementary receptors on liver cells stimulating glycogenolysis and gluconeogenesis
  • second messenger model occurs to activate enzymes to hydrolyse glycogen into glucose
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13
Q

How does the release of insulin cause more glucose to be absorbed?

A
  • attaches to receptors on the surface of target cells which changes the tertiary structure, so more glucose is absorbed via facilitated diffusion
  • vesicles containing protein channels fuse with the membrane so more glucose is absorbed from the blood
  • activates enzymes involved in the conversion of glucose to glycogen
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14
Q

What other method can be used to decrease blood glucose concentration?

A

increased rate of respiration - more glucose used in glycolysis as a respiratory substrate

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15
Q

What is type 1 diabetes?

A

the immune system attacks beta cells in the islets of Langerhans, which prevents the release of insulin so glycogenesis is not stimulated - autoimmune disease

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16
Q

What is type 2 diabetes?

A

receptors on target cells become unresponsive to insulin - insulin is secreted but glycogenesis is not stimulated

17
Q

Why is glycogen a better storage molecule than glucose?

A
  • large - cannot cross cell membrane
  • insoluble - cannot affect water potential
  • glucose is small and soluble
18
Q

What are the blood vessels within the kidney?

A
  • renal artery - supplies the kidney with blood from the heart
  • renal vein - returns blood to the heart
19
Q

What are the structures within the nephron?

A
  • Bowman’s capsule - surrounded by a mass of capillaries called the glomerulus with high hydrostatic pressure - where ultrafiltration occurs
  • proximal convoluted tube where selective reabsorption occurs
  • loop of henle
  • distal convoluted tube
  • collecting duct
20
Q

What are the afferent and efferent arterioles?

A
  • afferent arteriole supplies the nephron with blood and the efferent arteriole moves blood away from the nephron
  • the efferent arteriole has a smaller diameter which increases hydrostatic pressure, leading to ultrafiltration
21
Q

How is glomerular filtrate formed by ultrafiltration?

A

There is high hydrostatic pressure in the renal artery because the diameter of the efferent arteriole is small leading to higher pressure. This pushes small molecules such as ions, urea and water through pores in the capillary endothelium and the basement membrane. Larger molecules such as cells and proteins remain.

22
Q

How is the proximal convoluted tubule adapted for selective reabsorption?

A
  • microvilli - provide a large surface area
  • carrier and channel proteins - in the membrane for active transport and facilitated diffusion
  • many mitochondria - needed to provide ATP for active transport
23
Q

How does selective reabsorption occur in the proximal convoluted tubule (PCT)?

A
  • sodium ions are actively transported out of the PCT which lowers the concentration inside the cells
  • sodium ions diffuse down their concentration gradient from the lumen of the PCT into epithelial cells by facilitated diffusion - glucose is also carried across via a co-transport protein
  • concentration in epithelial cells is greater than the bloodstream so glucose diffuses out
24
Q

What are the 2 regions in the loop of henle?

A
  • descending limb - highly permeable
  • ascending limb - impermeable
25
Q

What is the countercurrent multiplier in the loop of henle?

A
  • sodium ions are actively transported out of the ascending limb using energy from ATP hydrolysis, which decreases the water potential of the medulla. Normally water would move out however because the walls are impermeable no water can move out by osmosis
  • the walls of the descending limb are however permeable, therefore water moves out by osmosis into capillaries and has the lowest water potential at the bottom of the descending limb
  • at the base of the ascending limb, sodium ions diffuse out because concentration is very high, therefore water potential increases
  • as the filtrate moves up the ascending limb, solute concentration decreases as ions diffuse out which decreases the water potential of the medulla
  • therefore water can diffuse out of the entire length of the collecting duct down a concentration gradient
26
Q

What process occurs in the distal convoluted tubule?

A

materials can be reabsorbed from the filtrate via active transport

27
Q

What happens when the water potential of blood increases?

A
  • this is detected by osmoreceptors in the hypothalamus which stops ADH from being secreted by the pituitary gland
  • therefore less ADH will bind to complementary receptors on the membrane of the collecting duct
  • this means less vesicles containing aquaporins fuse with the membrane, so less water will move out of the collecting duct by osmosis
  • this leads to higher volume, lower concentration urine
28
Q

What happens when the water potential of blood decreases?

A
  • this is detected by osmoreceptors in the hypothalamus which stimulates ADH to be secreted by the pituitary gland
  • therefore more ADH will bind to complementary receptors on the membrane of the collecting duct
  • this stimulates the enzyme phosphorylase
  • this enzyme causes more vesicles containing aquaporins fuse with the membrane, so more water will move out of the collecting duct by osmosis down a concentration gradient because the membrane becomes more permeable to water
  • this leads to lower volume, higher concentration urine
29
Q

What part of the body releases ADH into the blood?

A

posterior pituitary

30
Q

What is the effect of ADH on the collecting duct?

A
  • stimulates increased aquaporins in the membrane
  • therefore increased permeability to water
  • so more water reabsorbed by osmosis
31
Q

How are animals able to hibernate without food?

A
  • fat stores are used in respiration so less energy from the food stores is required due to low metabolism and low rate of respiration, as there is little movement
  • gluconeogenesis using glycerol, fatty acids and amino acids
32
Q

Why does a thicker medulla lead to a higher concentration of urine?

A
  • thicker medulla = longer loop of henle
  • more sodium ions are moved out which maintains a sodium ion gradient for longer
  • therefore the water potential gradient is maintained for longer, so more water is reabsorbed from the collecting duct by osmosis

Biology (29 decks)

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