32-BodyTemp Flashcards
homeothermic
organism that regulates body temperature internally (eg humans)
poikilothermic
organism that regulates body temperature externally (eg reptiles)
primary source of heat loss
skin
secondary source of heat loss
lungs
primary source of heat production
cellular metabolism
sympathatic vasomotor response to decrease in environmental temperature
NE -> alpha adrenergic R -> vasoconstriction of cutaneous arterioles
sympathatic vasomotor response to increase in environmental temperature
ACH ->
-> vasodilation of cutaneous arterioles
VIP ->
VIP
vasoactive intestinal peptide
sympathetic effector of sweating
ACH -> incr sweat production
endocrine effector of cellular metabolism
thyroid hormone -> incr cellular metabolism -> incr heat production
neural effector of shivering-induced thermogenesis
ACH (not sympathetic) -> asynchronous skeletal muscle contraction (both extensors and flexors)
neural effector of BAT thermogenesis
postganglionic sympathetic: NE -> beta-3 adrenergic R -> incr in UCP
endrocrine effector of BAT thermogenesis
thyroid hormone
UCP
uncoupling protein
uncouples glucose oxidation from ATP production, produces heat instead
fiber type of cold receptors
A-delta
fiber type of warm receptors
C
cold transient receptor potential (TRP) channel in periphery
TRPM8 - DRG and trigeminal, menthol, <27 deg C
heat transient receptor potential (TRP) channel in periphery
TRPV3 - keratinocytes, DRG (low), brain and tongue, 33-40 deg C
Peripheral pathway of pain and temperature
spinothalamic tract
Peripheral pathway for thermoregulation
spino-parabrachial pathway
Site of thermoregulation control in hypothalamus
Anterior hypothalamus/preoptic area
heat transient receptor potential (TRP) channel in hypothalamus
TRPV4 - found in OVLT and medial preoptic; responds to 25-35 deg C, osmolality
Fever produced by
endogoneous pyrogens, released by macrophages in response to bacterial or viral particles
endogenous pyrogens - examples
cytokines: interleukin-1,-6, and tumor necrosis factor alpha
Endogenous pyrogens act on
neurons in anterior hypothalamus / preoptic area
Mechanism of action of pyrogens
act on cytokine receptors in AH/POA -> incr. induction of COX-2 -> incr. formation of prostaglandins (esp. PGE_2)
COX-2
cyclooxygenase-2, induced by pyrogens acting on cytokine receptors, leads to prostaglandin formation
Mechanism of NSAIDs in reducing fever
NSAIDs = non-steroidal anti-inflammatory drugs
Block COX-2 activity -> decr. PGE_2
Cytokines cross blood brain barrier via
circumventricular organs:
- median eminence
- area postrema
- pineal
- subfornical organ
- -* organum vasculosum of the lamina terminals (OVLT) - located near POA of hypothalamus
OVLT
organum vosculosum of the lamina terminals (OVLT) - site of BBB crossing of cytokines
Site of action of PGE in POA
temperature-insensitive (I) neurons and warm (W) neurons
Role of DMH in thermoregulation
DMH=dorsal medial hypothalamus Receives inhibitory (GABAergic) projections from warm neurons in AH/POA Sends excitatory (glutaminergic) projections to sympathetic premotor neurons in raphe nucleus
Role of raphe pallidus in thermoregulation
Raphe pallidus neurons in medulla
Receive direct inhibitory (GABAergic) input from warm neurons in AH/POA
Send excitatory project to IML of spinal cord -> activate sympathetic vasomotor response
