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Sec 3 Pure Bio > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

Define homeostasis

A
  • the maintenance of a constant internal environment

- process which ensures that composition of body fluids kept within narrow limits

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2
Q

Define internal environment

A
  • refers to conditions within body of organism
  • humans: blood and tissue fluids
  • stable internal environment, allow organism to be independent from changes in external environment/surroundings
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3
Q

Why does body temp need to be kept constant?

A
  • environmental conditions in surroundings constantly changing
  • enzymes in body can only work in specific range of temp
  • change in body temp may lead to enzyme inactivation or denaturation
  • high fever thus fatal
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4
Q

Why must tissue fluid be kept at constant pH and wp?

A
  • drastic change in pH, affect enzyme reactions in cells, harm body
  • drastic change in wp may cause cells to swell, burst; shrivel, affect reactions
  • composition of tissue fluid need to kept within very narrow limits to ensure constant pH and wp
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5
Q

Homeostasis involves negative feedback

A
  • in homeostatic control, body reacts to bring abt opposite effect to changes detected
  • if system/body disturbed, disturbance sets in motion a sequence of event that tends to restore a system to original state (negative feedback process)
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6
Q

Receptors/sense organs

A

-organs/structures in body that detect changes in body condition

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7
Q

Negative feedback process

A
  1. norm/set pt to be maintained
  2. stimulus: change in internal environment e.g. condition rises/decreases below normal
  3. receptor: detect stimulus, send signal to control centre
  4. corrective mechanism: bring abt reverse effect of stimulus
  5. feedback to stimulus once set pt reached, corrective mechanism stops
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8
Q

Examples of homeostasis in humans

A
  1. regulating body temp
  2. regulating blood glucose conc
  3. regulating wp
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9
Q

Regulation of blood glucose conc

A
  • glucose needed for cellular respiration, provide energy for vital activities
  • blood normally contains 70-90 mg of glucose per 100cm3 of blood
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10
Q

when blood glucose lvl rises above normal lvl

A
  1. normal set pt
  2. stimulus: blood glucose lvl rises above normal
  3. receptor: islets of langerhans in pancreas stimulated (control centre)
  4. corrective mechanism: islets of Langerhans secrete insulin into bloodstream, blood transport insulin to liver and muscles
    - insulin increases permeability of cell surface membrane to glucose, glucose absorbed more quickly
    - insulin causes liver and muscles to convert excess glucose to glycogen
    - glycogen stored in liver and muscles
  5. blood glucose conc decreases, provides negative feedback to receptor to reduce insulin production
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11
Q

when blood glucose lvl falls below normal

A
  1. normal set pt
  2. stimulus: blood glucose falls below normal
  3. receptor: islets of Langerhans in the pancreas stimulated
  4. corrective mechanism: islets of Langerhans secrete glucagon into bloodstream, blood transports glucagon to liver and muscles
    - glucagon causes conversion of stored glycogen back to glucose
    - from liver, glucose enters bloodstream
  5. negative feedback: blood glucose conc increases, provides feedback to receptor to decrease glucagon production
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12
Q

regulating blood water potential

A
  1. normal set pt
  2. stimulus: wp of blood increases/decreases (large intake of water/loss of water thru sweating)
  3. receptor: hypothalamus in brain stimulated
  4. corrective mechanism:
    - less/more ADH (anitdiuretic hormone) released by pituitary gland into bloodstream
    - less/more ADH transported to kidneys
    - cells in wall of collecting ducts become less/more permeable to water
    - less/more water absorbed into bloodstream
    - more/less water excreted, more concentrated/dilute
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13
Q

Role of skin

A
  • forms protective covering over body surface

- regulates temp and excretion

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14
Q

Structure of skin: Blood vessels (capillaries and arterioles) in dermis layer

A
  • blood vessels are present in dermis layer
  • constriction and dilation of arterioles caused by contraction of muscles in arteriole walls
  • constriction and dilation of arterioles help to regulate body temp
  • vasodilation vs vasoconstriction
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15
Q

Vasodilation

A
  • dilation of arterioles
  • more blood sent to blood capillaries in skin
  • e.g. blushing/flushed after vigorous activities
  • due to numerous blood vessels in skin dilating
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16
Q

Vasoconstriction

A
  • constriction of arterioles in skin
  • reduces amt of blood flowing thru capillaries in skin
  • become pale
17
Q

Structure of skin: Hair follicle

A
  • though embedded in dermis, produced by epidermis
  • Malpighian layer of epidermis sinks into dermis, form hollow tube called hair follicle
  • each hair grows inside the hair follicle
18
Q

Structure of skin: Hair papilla

A
  • a mass of tissue found at the base of the hair follicle
  • contains blood capillaries and nerves
  • covered with epidermal cells that constantly divide, pushing new cells outwards
  • cells that are pushed outwards gradually die, harden to form hair
19
Q

Structure of skin: Hair erector muscles

A
  • attached to hair follicles

- contracts, cause hair to stand on their ends, skin around hair raised, producing goose bumps

20
Q

Structure of skin: Sweat glands

A
  • a coiled tube formed by a downgrowth of epidermis
  • forms tight knot in dermis, surrounded by many blood capillaries
  • secreted sweat flows thru sweat duct to a sweat pore that opens at skin surface
  • secreted sweat mainly contains water, dissolved salts (sodium chloride), small amts of urea
  • considered an excretory organ as is contains small amts of metabolic waste products eg urea
  • sweat is secreted continuously, amt of sweat produced varies on the external and internal environmental conditions
  • small quantity of sweat, evaporates almost immediately
  • large quantity of sweat, droplets on skin/running streaks
  • sweat is a mean by which skin regulates body temp
21
Q

Structure of skin: Sensory receptors

A
  • detects changes in environment (stimuli)
  • eg nerve endings in the skin are sensory receptors
  • enable us to sense pain, pressure, temp changes in external environment
  • receptors that detect temp changes are called thermoreceptors (e.g. nerve endings)
22
Q

Subcutaneous fat

A
  • beneath dermis are several layers of adipose cells (adipose tissue)
  • fat is stored there
  • fat in these cells also act as an insulating layer, reduce heat loss
23
Q

How does our body produce and gain heat?

A
  • heat is produced within body as a result of metabolic activities e.g. cellular respiration
  • high lvls of cellular respiration takes plc in muscle and liver, large amt of heat released in these organs
  • heat is distributed to rest of body via bloodstream
  • heat also gained thru vigourous muscular exercise, consumption of hot food, being in warm environments
  • excess heat thus needs to be removed from body, prevent overheating
24
Q

How does our body lose heat

A
  • lost thru skin by radiation, convection and to a limited extent, conduction
  • by evaporation of water in sweat from surface of skin
  • in faeces or urine
  • exhaled air
25
Q

Shunt vessels

A
  • certain parts of skin contain shunt vessels
  • shunt vessels connect skin arterioles with skin venules
  • control amt of blood flowing thru skin capillaries
  • affect heat loss thru skin
26
Q

Shunt vessels constrict

A
  • skin arteriole dilates, shunt vessel constrict, increase blood flow to skin surface
  • more heat carried to skin surface, greater heat loss
27
Q

Shunt vessels dilate

A
  • skin arteriole constricts, shunt vessels dilate, less blood flow to skin surface
  • less heat carried to skin surface, less heat loss
28
Q

Hypothalamus

A
  • located in brain
  • monitors and regulates body temp
  • receives info abt temp changes from thermoreceptors in skin(detect temp from environment), and thermoreceptors in hypothalamus (detect temp of blood)
29
Q

WHat happens when body temp begins to rise

A
  • e.g. vigorous body activities, large amt of heat is produced,
  • heat produced accumulates in body, rise in body temp
  • change detected by hypothalamus, sends nerve impulses to relevant body parts
30
Q

Homeostatic processes that decreases body temp

A
  • dilation of arterioles in skin, constriction of shunt vessels allow more blood to flow thru blood capillaries in skin
  • more heat lost thru skin by radiation, convection and conduction
  • sweat glands become more active, increased production of sweat
  • more water in sweat evaporates from surface in skin, more latent heat of vaporization is lost from body (efficient means of losing heat)
  • decreased metabolic rate, reduces amt of heat released within body
31
Q

Why these homeostatic processes occur to decrease body temp

A
  • body absorbs heat when surrounding temp is higher than body temp
  • rise in external temp is detected by temp receptors, receptors immediately send nerve impulses to hypothalamus
  • absorbed heat mainly lost by evaporation of sweat from body
  • extra heat accumulated in body is removed so body temp maintained in normal range
32
Q

what happens when human body temp begins to fall

A
  • on cold day, rate of heat loss increases, esp at skin surface
  • drop in temp stimulates temp receptors in skin, rapidly send nerve impulses to hypothalamus
  • drop in temp ls also detected by hypothalamus
  • hypothalamus send nerve impulses to relevant body parts to enable homeostatic processes
33
Q

Homeostatic processes that increase body temp

A
  • constriction of skin arterioles, dilation of shunt vessels, less blood flows thru blood capillaries in skin
  • reduces heat lost by convection, radiation and conduction
  • sweat glands less active, decreased production of sweat
  • less water in sweat evaporates from surface of skin, less latent heat of vaporization lost from body
  • increased metabolic rate, increase amt of heat released within body
  • if all the above doesn’t work, shivering occurs
  • shivering is the reflex contraction of body muscles, spasmodic contraction of skeletal muscles increases amt of heat released within body, help raise body temp to rise to normal

Sec 3 Pure Bio (16 decks)

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