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Secondary 3 Biology > homeostasis > Flashcards

homeostasis Flashcards

1
Q

what is homeostasis?

A
  • maintainance of a constant internal environment
  • ensures that the internal conditions of an organism are kept constant all the time
  • ensures the organism is independent of changes in external environment
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2
Q

what are the internal conditions that should be kept constant?

A
  1. temperature
  2. pH level
  3. water potential
  4. blood glucose concentration
  5. carbon dioxide concentration
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3
Q

describe temperature as a condition?

A
  • enzymes in body can only work within a certain range of temperatures
  • change in temperature: inactive or denatured
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4
Q

describe pH level as a condition?

A
  • affects enzyme activity and rate of cellular reactions
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5
Q

describe water potential of a condition?

A
  • composition of tissue fluid has to be maintained to ensure w.p. of cells is kept constant
  • changes in w.p of blood plasma affects body cells
  • body cells may shrink and crenate or burst in solutions with w.p. different from cytoplasm
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6
Q

describe blood glucose concentration as a condition?

A
  • glucose in food is required for tissue respiration which releases energy for cells to carry out activities
  • glucose levels increase after meals and decrease after physical exertion
  • if blood glucose concentration changes, it can be dangerous
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7
Q

what are the homeostasis terms?

A

Stimulus : change in internal environment
Receptor: organ that detects the stimulus and sends signals to control centre
Corrective mechanism: brings about the reverse effect of stimulus
Negative feedback: a set of corrective mechanism triggered due to a change in the internal environment detected by receptor to bring about reverse effect of stimulus
to restore normal conditions
Norm: set point to be maintained

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8
Q

what happens when the condition is above normal?

A
  1. normal
  2. stimulus (rises)
  3. receptor (detects)
  4. control centre
  5. corrective mechanism
  6. condition decreases
  7. normal
    feedback is sent from condition to receptor
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9
Q

what happens when condition is below normal?

A
  1. normal
  2. stimulus (decreases)
  3. receptor (detects)
  4. control centre
  5. corrective mechanism
  6. condition rises
    feedback is sent from condition to receptor as condition rises/decreases
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10
Q

what happens when blood glucose concentration is above normal level?

A

stimulus: blood glucose conc rises above normal
↓
receptor : islets of Langerhans in pancreas is stimulated
↓
corrective mechanism: islets of Langerhans secrete insulin into bloodstream. Blood transports insulin to the liver and muscles. Insulin to permeability of cell surface membrane to glucose. Glucose is absorbed more quickly by cells. Insulin causes liver and muscles to convert excess glucose to glycogen, which is stored in liver and muscles
↓
blood glucose concentration decreases. This provides feedback to receptor to reduce insulin production
↓
Decrease back to normal

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11
Q

when happens when blood glucose concentration is below normal level?

A

stimulus: blood glucose conc. falls below normal
↓
receptor : islets of Langerhans in pancreas stimulated
↓
corrective mechanism: islets of Langerhans secrete glucagon into the bloodstream. Blood transports glucagon to liver and muscles. Glucagon causes the conversion of stored glycogen back to glucose. From liver, glucose enters bloodstream
↓
Blood glucose concentration increases. This provides a feedback to receptor to decrease glucagon production
↓
Increases back to normal

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12
Q

when happens when blood w.p. is above normal level/below normal level?

A

stimulus: w.p of blood increases/dec
↓
receptor: hypothalamus stimulated
↓
corrective mechanism: less ADH is released by the pituitary gland into the bloodstream. Less ADH transported to kidneys. Cells in walls of collecting ducts become less permeable to water. Less water reabsorbed into the bloodstream. More water excreted. Urine is more diluted. More urine produced
↓
feedback sent as w.p of blood decreases
↓
w.p. decreases back to normal

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13
Q

what is the structure of the human skin?

A
  • epidermis (outermost layer)
  • dermis
  • hair
  • sweat gland
  • sensory receptors
  • subcutaneous fat
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14
Q

what is the function of the epidermis?

A
  • cornified layer, forms outermost surface of skin, consists of dead dry cells called keratin deposits. Dead cells are continuously shed
  • granular layer, middle layer of epidermis. consists of living cells that move upwards. cells eventually die and form cornified layer
  • malpighian layer, innermost layer. Consists of actively dividing cells that contain melanin
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15
Q

what is the function of the dermis?

A
  • below Malpighian layer
  • upper part thrown into ridges or
    pupillae(folds)
  • has numerous blood capillaries supplying blood to skin
  • when arterioles dilate, more blood flows to skin surface blood capillaries (vasodilation)
  • when arterioles constrict, less blood flows to skin surface blood capillaries (vasoconstriction)
  • vasodilation and vasoconstriction play a role in body temperature regulation
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16
Q

what is the function of the hair?

A
  • embedded in dermis
  • malpighian layer sinks into dermis to form hair follicles
  • hair papilla found at base of hair follicle consists of blood capillaries and nerves
  • covered in epidermal cells that constantly divide and push new cells outwards
  • cells that are pushed outward die and form hair
  • hair erector muscles attached to hair follicles contract and cause hairs to stand, resulting in ‘goose pimples’
  • sebaceous glands open each hair follicle. They secrete sebum which lubricates the hair, keep skin soft and prevents microbial growth
17
Q

what is the function of the sweat gland?

A
  • coiled tube formed by down growth of epidermis
  • richly surrounded by blood capillaries
  • secretes sweat continuously which flows through sweat duct and sweat pore to skin surface
18
Q

what is the function of the sensory receptors?

A
  • nerve endings in skin

- sense pain, pressure and temperature (thermoreceptors)

19
Q

what is the function of the subcutaneous fat?

A
  • beneath dermis
  • consists of adipose cells which stores fat
  • insulating layer, reduce heat loss
20
Q

what happens for temperature regulation when there is heat gained by the body?

A
    • being in warm environments
    • intake of hot food and drinks
    • during physical exertion or exercise
    • metabolic activities
21
Q

what happens for temperature regulation when heat is lost by the body?

A
    • from skin surface via conduction, convection and radiation
    • evaporation of water in skin
    • expired air from lungs
    • faeces and urine
22
Q

what happens when temperature is higher than normal?

A
  1. stimulus: blood and skin temperature increases
  2. receptor and control centre : temperature receptors in skin detect change and send nerve impulses to brain. Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
  3. corrective mechanism:
    - dilation of arterioles in your skin and constriction of shunt vessels allow more blood to flow through blood capillaries. in skin. This allows more heat to be lost through skin by radiation, conduction and convection
    - sweat glands become more active, resulting in increased production of sweat. As more water in the sweat evaporate from the surface of skin, more latent heat of vapourisation is lost from body
    - efficient way to lose heat
    - decreased metabolic rate, to reduce amount of heat released within body
  4. as blood temperature decreases, feedback is sent to receptor
  5. blood temperature decreased to normal
23
Q

what happens when temperature is lower than normal?

A
  1. stimulus: blood and skin temperature decreases
  2. receptor and control centre: temperature receptors in skin detect change and send nerve impulses to brain. Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
  3. corrective mechanism:
    - constriction of arterioles and dilation of shunt vessels so that less blood flows through blood capillaries in skin. Reduces the heat lost by convection, conduction and radiation
    - sweat glands become less active resulting in decreased production of sweat. As less water in the sweat evaporates from surface of the skin, less latent heat of vapourisation is lost from body
    - increased metabolic rate to increase amount of heat released within body
    - shivering, a reflex contraction of your body muscles occurs. This spamodic contraction of the skeletal muscle increases amount of heat released and helps to raise body temperature to normal
  4. as it increases, feedback is sent to receptor
  5. blood temperature increases to normal

Secondary 3 Biology (13 decks)

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