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Biology > Topic 6 - Homeostasis > Flashcards

Topic 6 - Homeostasis Flashcards

1
Q

What is homeostasis

A

control systems that keep your internal environment roughly constant to stop cell damage

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2
Q

what happens to cells if blood glucose concentration is too low or too high

A
  • too high - the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis, the cells can shrivel up and die
  • too low - cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
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3
Q

what is a negative feedback response

A
  • change is counteracted to bring the level back to normal
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4
Q

what is a positive feedback mechanism

A
  • the change is amplified
  • further increase the level away from the normal level
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5
Q

When does bood glucose concentration level fall and rise

A
  • rise - after eating food containing carbohdrates
  • fall - after exercise
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6
Q

what are the 2 hormones involved in blood glucose control

A

insulin
glucagon

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7
Q

where is insulin and glucagon secreted from

A
  • insulin - beta cells in the islets of langerhans in the pancreas
  • glucagon - alpha cells in the islets of langerhans in the pancreas
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8
Q

How does insulin work

A
  • it lowers levels of blood glucose concentration when its too high
  • Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells
  • it increases the permeability of muscle cell membranes to glucose, so the cell take up more glucose. this involves increasing the number of channel proteins in the cell membranes
  • insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis)
  • the cells are able to store glycoen in their cytoplasm, as an energy source
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9
Q

what is glycogenesis

A

forming glycogen from glucose

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10
Q

what does glucagon do

A
  • rises blood glucose concentration levels
  • glucagon binds to specific receptors on the cell membranes of liver cells
  • glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
  • glucagon also activates enzymes that are involved in the formation of glucose from glycerol and amino acids (gluconeogenesis)
  • glucagon decreases the rate of respiration of glucose in cells
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11
Q

how does adrenaline increase blood glucose concentration

A
  • adrenaline is secreted from the adrenal glands when there is a low concentration of glucose in the blood, when youre stressed and exercising
  • adrenaline binds to receptors in the cell membrane of liver cells
  • it activates glycogenolysis
  • it inhibits glycogenesis
  • it also activates glucagon secretion and inhibits insulin secretion which increased glucose
  • adrenaline gets the body ready for action by making more glucose available for muscles to respire
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12
Q

what is the second messenger model for adrenaline and glucagon

A
  • adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase.
  • activated adenlyate cyclase converts ATP into a chemical signal called cAMP
  • cAMP activates an enzyme called protein kinase A.
  • it activates a chain of reactions that cause glycogenolysis
  • to produce glucose
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13
Q

what is type 1 diabetes caused by

A
  • The immune system attacks b cells in the islets of langerhans so they cannot produce insulin.
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14
Q

How is type 1 diabetes treated

A

insulin injections
controlling sugar intake

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15
Q

what causes type II diabetes

A
  • usually acquired later in life and linked with obesity
  • b cells dont produce enough insulin the body cells dont respond properly to insulin because insulin receptors dont respond properly.
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16
Q

how can type II diabetes be treated

A
  • eating healthy balanced diet
  • loosing weight
  • regular exercise
17
Q

how would you determine the concentration of a glucose solution

A
  1. make serial dilutions
  2. do a quantitative benedicts test on each solution
  3. use a colorimeter to measure the absorbance of the benedicts solution remaining in each solution
  4. use the results to make a calibration curve
18
Q

what is the function of the kidneys

A
  • excrete waste products like urea
  • regulate the water potential of the blood
  • ultrafiltration
  • selective reabsorption
19
Q

where, in the kidney, does ultrafiltration and selective reabsorption occur

A

nephrons

20
Q

what happens during ultrafiltration

A
  • blood from the renal artery enters afferent arterioles in the cortex of the kidney
  • each arteriole splits into a glomerulus - a bundle of capillaries looped inside the bowman’s capsule
  • the efferent arteriole is smaller in diameter than the afferent arteriole, so blood in the glomerulus is at high pressure.
  • the high hydrostatic pressure forces small moleucles and liquid out of the capillarie and into the bowman’s capsule
  • the liquid and small molecules pass through 3 layers to get into the bowman’s capsule and enter the nephron tubules ( a capillary wall, a basement membrane and the epithelium with gaps called podocytes)
  • larger molecules like proteins and blood cells stay in the blood
21
Q

what is the glomerulus

A

a bundle of capillaries inside the bowman’s capsule

22
Q

where is a nephron

A

in the cortex and medulla of the kidney

23
Q

list the structure of a nephron

A
  • afferent/efferent arteriole
  • glomerulus
  • bowman’s capsule
  • proximal convoluted tube (PCT)
  • loop of henle
  • distal convoluted tube (DCT)
  • collecting duct
24
Q

what happens during selective reabsorption of glucose

A
  • sodium ions are actively transported from the epithelial cells into the blood by tha sodium potassium ion pump
  • this creates a lower concentration of sodium ions in the epithelial cells compared to the lumen, so sodium inos diffuse down their gradient using a co transporter protein
  • this also binds to glucose, transporting glucose and sodium into the epithelial cells
  • the concentration of glucose is then higher in the epithilial cells compared to the blood so it moves down this concentration gradient via facilitated diffusion through a channel protein.
25
Q

how is the proximal convoluted tubule adapted for selective reabsorption

A
  • microvilli
  • co transporter proteins
  • high number of mitochondria
26
Q

what is the function of the liver

A

makes urea

27
Q

what are water potential receptors called and where are they found

A
  • osmoreceptors
  • hypothalamus of brain
28
Q

where is the cortex found on the kidney

A

outer layer of kidney

29
Q

what happens when you are dehydrated

A
  • osmoreceptors in the hypothalamus detect a low water potential
  • the posterior pituitary glandis stimulated and releases more ADH into the blood
  • more ADH means that the distal convoluted tubule and collecting duct become 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
30
Q

what happens when you are hydrated

A
  • osmoreceptors in the hypothalamus detect high water potential
  • posterior pituitary gland releases less ADH into the blood
  • less ADH meas that the distal convolute tubule and the collecting duct become less permeable so less water is reabsorbed into the blood
  • a large amount of dilute urine is produced and more water is lost
31
Q

what happens to concentration of urine as the medulla is thicker

A
  • longer loop of henle
  • sodium ion gradient is maintained for longer
  • more water reabsorbed from loop of henle by osmosis
32
Q

how is water selectively reabsorbed

A
  • Happens in the loop of Henle and collecting duct
  • in the ascending limb, sodium ions are actively transported out at the top, and diffuse out at the bottom
  • water cannot move as the limb is impermeable to water
  • water potential of the filtrate increases
  • the descending limb is hihgly permeable to water
  • water leaves by osmosis down the water potential gradient formed by the loss of sodium ions.
  • water is reabsorbed into the blood stream in the loop of henle and collecting duct
33
Q

where is ADH secreted from

A

posterior pituitary gland

Biology (17 decks)

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