Human Var Exam 3 Flashcards
Homeothermy
Thermoregulation that maintains a stable internal body temperature regardless of external influence
Bergmann’s Rule
As the effective climate becomes colder, body size increases, this is modeled as a cube or sphere. This is because smaller organisms have a higher surface area to volume ratio which facilitates heat loos through the skin and cools the body (beneficial in hot climates) while larger organisms have a lower surface area to volume ratio and radiate less body heat per unit of mass staying warmer
Ruff’s rule
As climate becomes cooler, body core breadth increases, modeled as a cylinder
Allen’s rule
As the effective climate cools, extremities decrease in relative length. A decreased limb diameter with increasing length is observed
Why does cold air need to be warmed and moistened?
If cold, dry air reaches the lungs, pulmonary vessels can constrict leading to pulmonary edema. Chronic exposure can also cause bronchial walls to thicken and functionally decline
Thompson’s rule
nose becomes narrower as the climate gets cooler/dryer, likely because narrower nose creates more turbulence of air and therefore more contact between air and nasal passage walls allowing it to remain warm and moist
Physiological responses to cold
Vasoconstriction - cold receptors trigger blood vessels to narrow to keep blood deeper and protect vital organs but CIVD increases flow to extremities to maintain function, occurs in cycles
Shivering - involuntary muscle contraction that produces heat
Non-shivering thermogenesis - heat is produced by hormonal action on adipose tissue increasing BMR, BAT short circuits ETC and produces heat rather than energy in response to cold
Short term cold acclimatization
Shivering became replaced by metabolic thermogenesis (lower metabolic rate) and reduced core temp at which shivering begins
Cold adaptation
Countercurrent heat exchange where blood is shunted to deep arteries along with oscillating vasoconstriction/vasodilation that reduces heat lost while maintaining tissue viability
Increased BMR
Increased insulation due to subcutaneous fat rising (BAT can increase metabolic rate)
High levels of physical activity/TEE contributes to thermoregulatory heat production
TRPM8
Gene for receptor for the sensation of moderate cold temperatures, positively selected for
Stages to sex determination
Chromosomal where gamete inherits either an XX or XY chromosome
Primary where gonads are driven by gonad forming genes (variation in gene copy number can occur and if individuals possessing a Y chromosome have extra copies of Wnt4 they can develop a rudimentary uterus/oviducts)
Secondary where the phenotype is driven by hormones produced by gonads
T vs DHT
T can be converted to DHT by 5-alpha-reductase and DHT forms external genitalia while Wolffian duct differentiation controlled by T. Y possessing individuals that lack the enzyme have functional testes that do not descend
Androgen insensitivity
Y possessing individuals make T via sry but androgen receptor cannot respond to T. Instead it responds to estrogen produced by adrenal glands so female external characteristics are produced but Mullerian ducts still degenerate
Genetic changes that select for darker pigmentation after hair gets lost
MC1R underwent positive selection and became the receptor located on the surface of melanocytes. DDB1 is associated with the UV response/melanoma risk and levels are regulated by UV exposure and MC1R signaling. MFSD12 also encodes a lysosomal protein that affects melanogenesis.
Heat Acclimatization
Intermittent (over 7-30 days) lowers core temp at which sweating begins, less heat storage, changes the sweating/vasodilation threshold, reduces the heart/metabolic rate but heart pumps more with each stroke, sweat becomes better distributed over body and carries less sodium, plasma volume increases
