Homeostasis Flashcards

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1
Q

what is homeostasis?

A

the maintenance of an internal environment within restricted limits in organisms, to respond to the external environment
the ability to return to the optimum point

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2
Q

why is homeostasis essential for proper functioning of organisms?

A
  • to maintain a fairly constant internal environment (of pH and temperature) to let enzymes work at their optimum
  • changes to the water potential of blood and tissue fluid may cause cells to shrink and expand
  • allow for organisms to have a greater geographical range
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3
Q

what are the series of stages for the control of any self-regulating system?

A

OPTIMUM POINT, monitored by RECEPTOR, informs the COORDINATOR, send instructions to EFFECTOR, which creates a FEEDBACK MECHANISM

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4
Q

what is negative feedback?

A

when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off

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5
Q

what is positive feedback?

A

when a deviation from an optimum causes changes that result in an even greater deviation from the normal

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6
Q

what are hormones and how do they work?

A
  • produced in glands, secrete hormone directly into blood
  • carried in blood plasma to target cells
  • are effective in very low concentrations, but have widespread and long-lasting effects
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7
Q

what do the islets of Langerhan include?

A

alpha cells - larger and produce glucagon

beta cells - smaller and produce insulin

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8
Q

what is glycogenesis?

A

glucose into glycogen

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9
Q

what is glycogenolysis?

A

breakdown of glycogen to glucose

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10
Q

what is gluconeogenesis?

A

production of glucose from sources other than carbohydrates

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11
Q

what happens if the concentration of blood glucose increases too high?

A

lowers the water potential of the blood and creates osmotic problems that can cause dehydration

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12
Q

what are three factors that influence blood glucose concentration?

A
  • directly from diet
  • from hydrolysis in the small intestine of glycogen (glycogenolysis)
  • from gluconeogenesis
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13
Q

How does insulin reduce the concentration of glucose in blood?

A
  • increases rate of glucose absorption
  • increases respiratory rate of cells
  • increases rate of glycogenesis
  • increases rate of conversion of glucose to fat
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14
Q

what happens to beta cells when the blood glucose concentration reduces?

A

they reduce their secretion of insulin (=negative feedback)

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15
Q

how does glucagon increase the concentration of glucose in the blood?

A
  • attach to specific protein receptors on liver cell surface membrane
  • activate enzymes that convert glycogen to glucose
  • activate enzymes involved in gluconeogenesis (from amino acids and glycerol)
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16
Q

what happens to alpha cells when the blood glucose concentration increases?

A

they reduce their secretion of glucagon (=negative feedback)

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17
Q

how does adrenaline raise blood glucose concentration?

A
  • attaches to protein receptors on the cell-surface membrane of target cells
  • activate enzymes that cause the breakdown of glycogen to glucose in the liver
18
Q

what can we say about the use of the two hormones insulin and glucagon?

A

they act in opposite directions, and are antagonistic

19
Q

what are the two forms of diabetes?

A

Type I and Type II

20
Q

what causes Type I diabetes and when?

A

due to the body being unable to produce insulin, normally begin in childhood

21
Q

what causes Type II diabetes?

A

due to glycoprotein receptors on body cells being lost or losing their responsiveness to insulin, develops in people over 40 years

22
Q

how to control Type I diabetes?

A

by injections of insulin, managing carbohydrate intake + exercise

23
Q

how to control Type II diabetes?

A

regulating intake of carbohydrates + matching this to amount of exercise taken

24
Q

what are the 7 parts that make up the kidney?

A

fibrous capsule, cortex, medulla, renal pelvis, ureter, renal artery, renal vein

25
Q

what are the 9 parts and blood vessels associated with a nephron?

A

renal (Bowman’s) capsule, proximal convoluted tubule, Loop of Henle, distal convoluted tubule, collecting duct, afferent arteriole, glomerulus, efferent arteriole, blood capillaries

26
Q

what 5 features resist the movement of filtrate out of the glomerulus?

A

-capillary endothelial cells
connective tissue and endothelial cells of blood capillary
-epithelial cells of renal capsule
-hydrostatic pressure of the fluid in the renal capsule space
-low water potential of the blood in the glomerulus

27
Q

adaptations to allow glomerular filtrate from blood into renal capsule?

A
  • podocytes within inner layer of renal capsule, have spaces between them which allows for filtrate to pass between the cells rather than through them
  • endothelium of glomerular capillaries has spaces up to 100 nm between its cells
28
Q

the proximal convoluted tubule reabsorbs nearly 85% of filtrate. how are three ways that it is adapted to do so?

A

it has epithelial cells that have:

  • microvilli to provide a large SA to reabsorb substances from the filtrate
  • infoldings at their bases to give a large SA to transferr reabsorbed substances into blood capillaries
  • a high density of mitochondria to provide ATP for active transport
29
Q

what are the two regions of the Loop of Henle?

A
  • descending limb, narrow, thin walls that are highly permeable to water
  • ascending limb, wider, thick walls that are impermeable to water
30
Q

what happens at the distal convoluted tubule?

A

final adjustments are made to the water and salts that are reabsorbed
the pH is also controlled by selecting which ions to reabsorb

31
Q

what are the adaptations of the distal convoluted tubule?

A

the cells that make up the walls have microvilli and many mitochondria that allow them to reabsorb material rapidly from the filtrate, by active transport.

32
Q

how and why is the glomerular filtrate formed?

A

afferent arterioles -> glomerulus -> efferent arterioles
diameter of afferent greater than efferent and so there is a build up of hydrostatic pressure within the glomerulus
water and mineral ions are squeezed out of the capillary

33
Q

why do blood cells and large proteins not exist in the filtrate?

A

they are too large to pass through the glomerulus into the renal capsule

34
Q

what is the process of reabsorption of glucose and water by the PCT?

A

Na+ actively transported out into blood capillary - lowers Na+ conc
Na+ diffuse down a conc. gradient from lumen into epithelial cell lining - through carrier proteins by facilitated diffusion
specific carrier proteins that carry another molecule - co-transport
molecules that are co-transported into cells of PCT diffuse into blood - most other valuable molecules + water are reabsorbed

35
Q

what is the role of the Loop of Henle?

A

responsible for water being reabsorbed from the collecting duct, thereby concentrating the urine so that it has a lower water potential than the blood

36
Q

what are three ways in which the rise in solute lowers the water potential of blood?

A
  • too little water consumed
  • much sweating occurring
  • large amounts of ions being taken in
37
Q

how does the body respond to the drop in water potential of blood?

A
  • osmoreceptors in hypothalamus detect fall
  • water lost from osmoreceptor cells by osmosis
  • osmoreceptor cells shrink and hypothalamus produces antidiuretic hormone (ADH)
  • ADH passes to POSTERIOR pituitary gland, secreted into capillaries
  • ADH passes in blood to kidney, increases permeability to water of cell-surface membrane of cells making up DCT + collecting duct
  • specific protein receptors bind to ADH molecules, activates phosphorylase within cell
  • vesicles move to, and fuse with, its cell-surface membrane
  • aquaporins fuse with membrane and make the cell-surface membrane much more permeable to water
  • ADH increases permeability of c.d to urea, lowers water potential as urea passes out
  • water reabsorbed into blood - doesn’t increase but rather prevents it from getting lower. osmoreceptors send nerve impulses to thirst centre of brain
  • osmoreceptors detect rise in water potential and send fewer impulses
  • pituitary gland reduces release of ADH, permeability back to normal
38
Q

what are two ways in which the fall in solute raises the water potential of blood?

A
  • large volumes of water consumed

- salts used in metabolism or excreted not replaced in diet

39
Q

how does the body respond to the rise in water potential?

A
  • osmoreceptors detect rise, increases frequency of nerve impulses. pit. gland reduces release of ADH
  • less ADH = decrease in permeability of c.d to urea + water
  • less water reabsorbed
  • more dilute urine produced, water potential of blood falls
  • when normal again. osmoreceptors cause the pit. gland to raise ADH release back to normal levels
40
Q

what are both of these responses examples of?

A

negative feedback