Homeostasis

Question 1

what is homeostasis?

Answer 1

Homeostasis: maintainence of stable internal environment via self regulating processes in response to changing environmental changes

Question 2

what is a negative feedback loop?

whats a receptor?

whats an effector?

Answer 2

negative feedback loop: is control system that acts to maintain the level of some variable within a givin range following a disturbance

receptor (sensor): responds speifically to physiological variable (but not others)

Effector: a system that can act to restore the variable to its desired level

Question 3

why do we need regulation of body temp?

Answer 3

Why is body temperature regulated? Enzymes work best at opt. temps - otherwise denature

Question 4

how does thermoregulation occur?

Answer 4

stimulus causes body temp to rise:

-

Question 5

• how does normal body temp. differ in the body?

Answer 5

core temperature: brain and organs within thoracic and abdominal cavitites have highest temps

shell temperature: body surface and out extremities have lower temps

Question 6

what is core body temperature set point?

what does it represent?

can set point be reset?

Answer 6

• doesnt stay at 37.5 - fluctuates around a set point
• 37.5: represents the statistical mean of all the temp. measurements made from inds. in a pop.
• set point: independent of internal and external changes
• set point: can sometimes be reset (like in fever)

Question 7

how do we detect changes in temperature?

Answer 7

Peripheral thermoreceptors in the skin

• bare nerve endings
• two types:
  a) warm

b) cold

skin temp is perceived by comparing the relative activities of these two receptors: they signal which direction skin temp is going (> if cooling: increasing in firing of cold receptors and decrease in warm receptors)

Question 8

what happens when change in temperature is activated? (input vs output?)

which areas detect the change of temp from warm and cold?

what does this cause to change?

Answer 8

Goes to control centre: brain - specifically the hypothalamus:

Input:

• preoptic area (POA) monitors core temperature: recieves input from warm receptors from skin and and internal receptors
• paraventricular (PVN) and dorsomedial hypothalamic (DMH) nuclei: recieve input from cold receptors

Integration and Output to Effectors:

- Preoptic area (POA): regulate blood vessels in skin (vasoconstriction / dilation). stimulates posterior pituitary: conserves water

• paraventricular (PVN) and dorsomedial hypothalamic (DMH) nuclei: regulates skeletal muscle (shivering). brown fat stimulation (aka:) non-shivering thermogenesis.

Question 9

what acts as control centre for thermoregulation?

Answer 9

hypothalamus

Question 10

what do increases (2) and decreases (4) in body temperature cause in effectors?

Answer 10

heat increase / decrease stimulate effectors that will enhance / decrease heat loss

• To reduce heat gain:*
• Sweating initiated - (as long as air is dry, evap. of sweat is efficient)
• cutaneous vasodilation - blood flow near capillaries increases. heat lost by radiation. automated by autonomic nervous system by a reduction in vasomotor tone
• To increase heat gain:*

(adrenaline, catecholines and noradrenaline stimulate:)

• metabolic heat increased by vol. skeletal muscle contraction: shivering
• non-shivering thermogenesis: brown fat

- thyroid hormones increase o2 consumption on most cells: increases basal metabolic rate and heat production during cold

• cutaneous vasoconstriction: increase in sympathetic activity. mediated by noradrenaline on alpha adrenoreceptors. arteriovenous** **anastomoses are richly supplied by sympathetic adrenergic fibres

Question 11

what are the methods of heat loss?

Answer 11

1. evaoporation
2. conduction
3. convection
4. Radiation (loss of heat from IR rays / thermal energy)

Question 12

what are the types of sweat glands?

Answer 12

apocrine and eccrine

eccrine are the major sweat glands

Question 14

what is an arteriovenous anastomoses?

where found?

Answer 14

BV that provide a route for blood to bypass from the arterioles directly to venules, bypassing capillaries

• found in hands, feet, nose, ears and lip skins

Question 15

what is postive feedback?

e.g.?

Answer 15

when error signal acts to increase the initial deviation, pushing levels out of normal ranges

e.g. release of oxytocin to intensify the contractions of the smooth muscle of the uterus which becomes more active at end of preg.