Temperature Regulation- Dr. Shivani Flashcards
An increase in body T above what level is incompatible with life?
7 °C
What are processes that affect internal metabolism?
Basal metabolism
Dietary-induced thermogenesis (TID)
Specific dynamic action of food (SDA)
Thermogenic effect of food (TEF)
Physical exercise
Shivering thermogenesis
Non-shivering thermogenesis
What are the external mechanisms of thermoregulation?
Ingestion (hot food)
Ventilation (hot climate)
Radiation (short-wave from sun and long wave from surroundings)
What is shivering thermogenesis?
rhythmic oscillating contractions and relaxation of skeletal muscles due to activation of α & γ MN by the posterior Hypothalamus and heat production
What is non-shivering thermogenesis?
↑ in heat production which is not related to skeletal muscle activity (i.e., brown adipose tissue) via activation of beta receptors by cold stress
What are factors that affect heat production? (List the 2 major ones and 2 more factors)
Hormones **
SANS*****
Age
Stress
Gender
Climate
State of activity
Fever
What are some major hormones affecting heat production?
thyroid hormone thermogenic action stimulates Na+-K+-ATPase to increase metabolic rate and heat production
Adrenaline ,Noradrenaline
GH
What is radiation?
loss of heat (in the form of electromagnetic waves) from the body surface to surroundings (without physical contact)
What is convection?
conduction of heat aided by current of air or water which surround body surface
What is evaporation?
- Loss of energy from the skin and respiratory tract due to water evaporation
What does evaporation depend heavily on?
humidity of air
What is conduction?
loss of heat by transfer of thermal energy through direct contact with the surroundings especially to solid objects.
List the mechanisms of heat loss from the greatest influence to the least.
radiation
evaporation
convection
conduction
Be able to chart out the mechanism of thermogenesis in brown fat?
Chart it.
Where is the location of brown fat?
around blood vessels in the neck and the upper back, in the axillae, mediastinum and around the kidneys and adrenal glands
What is the brown color in brown fat due to?
Has a high density of mitochondria (brown color is due to mitochondrial cytochromes) and many small globules of fat
What tissue acts as an electronic blanket for the body?
brown fat
What is the thermoneutral zone?
25 – 30oC of environmental temperature.
Body temperature can be maintained without supplementary heat producing mechanisms or sweat secretion.
What are peripheral thermoreceptors?
(cold and warmth thermoreceptors of the skin)
What are central/ internal thermoreceptors?
inner organs and thermosensitive neurons
Do peripheral thermoreceptors provide feedback or feedforward control?
feedforward control
Do central/internal thermoreceptors provide feedback or feedforward control?
provide feedback contrl
Where is the thermostat of the body?
anterior HT- pre optic area
has set point
What is the heat promoting center of the body? Where does it receive input from? and what is activated?
Posterior HT
Receive inputs from central and peripheral thermoreceptors and activate effector mechanisms
What are the 3 ways of activation of the effector mechanisms for maintaining thermal homeostasis in the body??
- Sympathetic nervous system (sweat glands, blood vessels, adrenal medulla)
- Neuroendocrine pathway (HT, pituitary gland)
- Motor neurons to the skeletal muscles
Food and Appetite can increase or decrease in response to cold?
increase
When does ventricular fibrillation occur in a person losing heat?
ventricular fibrillation occurs at about 25 deg C
What is hyperthermia?
An increase in body T regardless of cause
Difference in heat exhaustion from heat stroke?
Heat exhaustion occurs there is excessive sweating, when water not replaced regulation fails and body T rises. (skin wet and cool from sweating)
While heat stroke is when the sweating mechanism fails the body T rises (skin is dry and hot)
IL 1 causes local release of what in the anterior hypothalamus leading to fever?
local release of PGs
How does aspirin work to help reduce set point in fevers?
When IL-6 is released after bacterial infection raising the hypothalmic set point PGE2 would cause the set point to be raised because IL1 causes local release of this in anterior hypothalamus
By blocking PGE2 which can be done because aspirin can block COX2 you prevent the elevated thermoregulatory point
What is malignant hyperthermia?
A defect in the SR Ca2+ release channel (RYR) (in some cases, a defect in the DHPR of the T-tubule), which becomes activated in the presence of anesthetics (i.e., halothane) or muscle relaxants (i.e., succinylcholine)
Treatment for malignant hyperthermia?
Treatment: dantrolene, a ryanodine receptor blocker DIRECTLY ACTING SKELETAL MUSCLE RELAXANT
What does malignant hyperthermia cause to happen?
↑ in metabolic rate and O2 consumption → ↑ heat production in skeletal muscle → dangerously high core body temperatures, tachycardia, hyperventilation, and hyperthermia
MOA of malignant hyperthermia?
A defect in the SR Ca2+ release channel (RYR) (in some cases, a defect in the DHPR of the T-tubule), which becomes activated leading to…
↑ release of Ca2+ into the myoplasm → prolonged muscle contraction (rigidity)
An otherwise healthy 15-month-old boy is brought to the emergency department by his mother 1 hour after having a single episode of generalized tonic-clonic seizure, which stopped spontaneously after 1 minute. He was sleepy initially but is now awake and alert. His mother reports that he has had a fever and runny nose for the past 3 days. His temperature is 40.1°C (104.2°F). Physical examination shows no abnormalities. Analysis of his cerebrospinal fluid shows 3 cells/mm3, a glucose concentration of 68 mg/dL, and a protein concentration of 35 mg/dL. Administration of a drug that acts through which of the following mechanisms of action is most appropriate in this patient?
A. Increasing frequency of Cl− channel opening
B. Blocking voltage-gated Na+ channels
C. Increasing duration of Cl− channel opening
D. Decreasing production of prostaglandin E2
E. Inhibiting transpeptidase cross-linking
F. Blocking T-type Ca2+ channels
D
What is the correct answer?
E ?
Most of the heat loss from an unclothed person at room temperature occurs by which of the following mechanisms?
a) conduction to air
b) conduction to objects
c) convection
d) evaporation
e) radiation
e? radiation
Which of the following mechanisms causes heat loss from a normal person when the environmental temperature is 106°f and the relative humidity is less than 10%?
a) conduction
b) convection
c) evaporation
d) radiation
C ?
A scuba diver explores an underwater lava flow where the water temperature is 102°f. which of the following profiles best describes the mechanisms of heat loss that are effective in this man?
B?
The diagram shows the effects of changing the set-point of the hypothalamic temperature controller. The red line indicates the body temperature, and the blue line represents the hypothalamic set-point temperature. Which of the following sets of changes occurs at point W, compared with point V?
E?
The diagram shows the effects of changing the set-point of the hypothalamic temperature controller. The red line indicates the body temperature, and the blue line represents the hypothalamic set-point temperature. Which of the following sets of changes occurs at point Y, compared with point V?
B?
The diagram shows the effects of changing the set-point of the hypothalamic temperature controller. The red line indicates the body temperature, and the blue line represents the hypothalamic set-point temperature. Which of the following sets of changes occurs at point X, compared with point V?
A?
