human bio validation - body temp, water balance, breathing Flashcards
define thermoregulation
Maintaining the balance between heat production and heat loss
Constancy of body temperature is important for chemical reactions in cells to occur, as they are heat-sensitive
37˚ is optimum for cellular reactions
Heat produced at metabolic activity helps maintain this higher level
what is convection
Flow of air or currents can transfer heat
what is conduction
Transfer of heat from one object to another through physical contact
what is radiation
Transfer of heat from one object to another without physical contact
what is evaporation
The conversion of a liquid to a gas
what are thermoreceptors
temperature receptors
Central thermoreceptors: located in hypothalamus – detect body temperature
Peripheral thermoreceptors: located in the skin and some mucous membranes – detect outside temperatures
- Cold receptors: stimulated by environmental
temperatures lower than normal
Heat receptors: detect temperatures higher than normal
All are connected to the hypothalamus
Nerve impulses sent out by the hypothalamus help increase of decrease heat loss
explain the role of skin in thermoregulation
The diameter of arterioles to the skin is controlled by autonomic nerves, which can act to increase or decrease flow of blood to the surface
This thereby increases or decreases rate of heat loss (through radiation)
When large amounts of body heat must be lost and skin blood vessels are already at maximum dilation, sweating must occur
The production and transport of sweat to eh skin surface is stimulated by sympathetic nerves
Evaporation of sweat from the skin has a cooling effect: heat is removed from the skin when liquid sweat changes into vapour
Cooling of the skin results in cooling of the blood flowing through the skin
list some physiological responses of the body to prevent body temperature from falling
vasoconstriction of arterioles in the skin
shivering
piloerection
stimulation of adrenal medulla
increased production of thyroxine
explain how vasoconstriction of arterioles in the skin prevents heat loss
Impulses from he hypothalamus stimulate sympathetic nerves that cause blood vessels in the skin to constrict
blood is directed to internal organs to prevent heat loss from them
The skin becomes cooler because there is less warm blood flowing through it
Less heat will then be lost from body surface
explain how shivering prevents heat loss
A fall in body temp will cause the hypothalamus to send stimuli to the parts of the brain that increase skeletal muscle tone
These tremors are known as shivering and can increase body heat and production
explain how piloerection prevents heat loss
the contraction of piloerector muscles under the skin causes hair to stand on end, trapping an insulating layer of air
this help prevent radiation heat loss
this is relatively ineffective in humans due to lack of body hair
explain how stimulation of the adrenal medulla prevents heat loss
adrenal medulla i stimulates by sympathetic nerves
medulla secretes adrenaline and noradrenaline into the blood
hormones bring about an increase in cellular metabolism that leads to an increase in heat production
explain how the increased production of thyroxine prevents heat loss
increased production of thyroxine decreases metabolic rate
this response is slower but long lasting
the small change in metabolic rate that occurs between summer and winter is a result of this
list some psychological/behavioural responses to preventing heat loss
putting on an extra jumper
sheltering from a cold wind
turning on a heater
reducing surface area of body
list and explain some physiological responses to prevent body temperature from rising
vasodilation of arterioles in the skin
- increases blood flow through the skin
- skin becomes reddish in colour, surface temperature
rises and there is a greater heat loss through radiation
and convection
sweating
- above environmental temperatures of 28˚ sweating is
needed to increase heat loss
- occurs through evaporation
only effective in dry environments
decreased production of thyroxine (decreasing metabolic rate)
list some behavioural/psychological responses to prevent body temperature from rising
turning on a fan/air conditioner
removing external clothing
reducing physical activity
increase body surface area
what is heatstroke
when body temperature rises and the regulatory mechanisms cease. This can be fatal is brain cells are affected
what is heat exhaustion
occurs as a result of extreme sweating and vasodilation to heat loss
The loss of water in sweating reduces the volume of blood plasma and vasodilation reduces resistance to blood flow
Blood pressure decreases and heart output of blood decreases.
the person may collapse even if they have normal body temperature
what is hypothermia
occurs if a person’s core temperature falls below 33˚, the metabolic rate is so low that heat production is unable to replace heat loss and body temperature continues to fall
how is water loss controlled by the kidneys
- A decreased amount of water in the blood results in decreased concentration of the blood plasma to decrease. This means that the osmotic pressure of the blood is raised
- Osmoreceptors in the hypothalamus detect the increases osmotic pressure of the blood
- The hypothalamus stimulates the posterior globe of the pituitary gland to release ADH into the bloodstream
- ADH is carries all over the body by the blood but it affects its target organs which are the nephron tubules. The permeability to water of the distal convoluted tubules and collecting ducts is increased
- More water is reabsorbed into the blood plasma from the tubules and ducts
- The reabsorption of water increases the water concentration in the plasma so that the osmotic pressure of the blood is decreased
- The response has decreased osmotic pressure of the blood. This has eliminated/reduced the original stimulus that was increasing osmotic pressure of the plasma. Negative feedback has occurred.
how does the body restore water intake
- osmotic pressure is increased
- Osmoreceptors in a thirst centre in the hypothalamus detect high osmotic concentration in blood – other stimuli such as dry mouth are involved
- Stimulation of thirst centre makes person feel thirsty
- Conscious feeling of thirst stimulates a person to drink
- Fluid consumed is absorbed into plasma from alimentary canal
- As fluid circulates through body it enables intercellular and intracellular fluid to return to proper osmotic concentrations
- After drinking, thirst is no longer stimulated and desire to take in water ceases. This is a negative feedback loop.
explain how antidiuretic hormone (ADH) controls water loss
ADH is produced by the hypothalamus and released from the posterior lobe of the pituitary
ADH increases the permeability of the walls of the distal convoluted tubule and collecting duct
This reduced the volume of water in the filtrate and increase the concentration of the materials remaining
Conversely, when the concentration of ADH in the plasma is low, the tubules are not very permeable to water, and little water is reabsorbed into the plasma of the blood
explain how water is lost from the body
Water loss is continually lost from the body in sweat, urine, faeces and exhaled breath
During strenuous activity water loss can be high
As water is lost from blood, plasma becomes concentrated lower water content therefore higher osmotic pressure
Water moves from intercellular fluid into plasma by osmosis
Now intercellular fluid is concentrated and water diffuses out of the cells, so cells shrink from dehydration
