Temperature Regulation - Lec13

Question 1

What factors determine rate of heat produciton?

Answer 1

Heat is a metabolic byproduct from the inefficiency of various metabolic pathways

• BMR
• Muscle activity -shiver-
• Thyroxin
• Norepinephrine and epinephrine
• Increased cellular chemical activity
• Extra metabolism for digestion, absoraption and food storage

Question 2

What factors determine heat loss?

Answer 2

How rapidly heat can be conducted from body core to the skin

How rapidly head can be transferred from skin to surroundings
-from continuous venous pleus

Some heat is lost by the respiratory system

Question 3

Mechanisms of heat loss from skin surface

Answer 3

Radiation
Conduction
Convection
Sweating and evaporation/insensible perspiration

Question 4

Radiation

Answer 4

Heat loss in the form of infrared heat rays

Radiated by all objects not at absolute zero

If temperature of body is greater than ambient temp, more heat is radiated from the body than to the body

Amount transferred depends on the temp difference and ability of object to absorb energy

Question 5

Conduction

Answer 5

Kinetic energy of the molecules of the skin is transferrred to the air if the air is colder than the skin

Tranfer between two bodies when they are in close contact

Question 6

Convection

Answer 6

Removal of heat from the body by convection air currents

By air or fluid (such as water)

Question 7

Two enviromental mechanism of heat loss are.. .?

Answer 7

Wind and water

Wind’s cooling effect is propportional to the sq root of wind velocity

Loss of heat is many time greater in water than in air.

Question 8

Sweating - what stimulated its?

Answer 8

Stimulation factors for sweating:
-stimulation of anterior hypothalamus-pre-optic area in the brain electrically or by excess heat
Via cholinergic sympathetic fibers or norepinephrine

Question 9

How does aldosterone effect the composition of sweat?

Answer 9

it decreases the concentration of NaCl in sweat to conserve body salt

Released by adrenocortical glands.

Question 10

How are the concetrations of sweat different between a low stimulation of the duct versus a rapid/strong stimulation of the duct?

Answer 10

low stimulation - mostly water, very small [NaCl]; sweat is concentrated mixture of urea, lactic acid and potassium ion.

Question 11

What is the anterior pre-optic area of the hypothalamus? How does it help control body temperature?

Answer 11

“thermostatic body temperature”

warm-sensitive neurons increase firing rate to decrease body temperature - main function of anterior hypothalamus

cold-sensitive neurons increase firing rate when temperature falls - happens to more extent in the posterior hypothalamus

Question 12

Where is the primary motor area for shivering? What is it’s relationship with the anterior hypothalamic preoptic area? How is it activated?

Answer 12

dorsomedial part of posterior hypothalamus

mechanism for heat production (ant preoptic is heat loss)

excited by cold signals from skin and spinal cord

Question 13

What is chemical thermogenesis?

Answer 13

THe increase in cellular metabolism rate due to sympathetic stimulation

epinephrine and norepinephrine tell brown fat to uncouple oxidative phosphorylation utilizing ATP synthase to produce heat

Question 14

What is the set-point for thermal control?

Answer 14

a function of the activity of the warm-sensitve neurons of the pre-optic anterior hypothalamus

the set point is the level which sweating begins or shivering begins to return body to critical core temp (37 C)

Question 15

What physiological mechanisms alter the critical set point?

Answer 15

set point increases as skin temperature decreases

skin temperature changes

Question 16

How does Thyroxine effect cellular metabolism, body temperature and the anterior hypothalamic-reoptic areas?

Answer 16

another heat producing mechanism that takes weeks exposure to cold to take effect.

anterior hypothalamic reoptic area cools -> releases hormone to cause thyroid to stimulate itself to release thyroxine

thyroxine stimulates cellular metabolism by activating uncoupling protein

Question 17

what is a fever? what are pyrogens?

Answer 17

fever - body temperature above the usual range of normal

pyrogens - increase the set point temperature by increasing production IL-1, TNF, IL-6 and INF. IL-1 causes anterior pituitary to produce prostaglandins

Question 18

how do pryogens and prostaglandins affect fever?

Answer 18

increases temperature

Question 19

how does aspirin affect temperature?

Answer 19

decreases set-point temperature by inhibiting cyclooxygenase which results in decrease in production of prostaglandins

Question 20

febrile conditions

Answer 20

relating to thermocontrol

heat stroke, frostbite and hypothermia, heat exhaustion. malignant hyperthermia

Question 21

heat stroke

Answer 21

occurs when body temperature increases to point of tissue damage

sweating is impaired and core temperature increases

symptoms - dissiness, abdominal distress, vomiting, delirium, loss of consciousness

they are exacerbated by circulatory shock

Question 22

extreme control

Answer 22

hypothalamus loses ability to regulate control at around 85 degrees

because of a decreased rate of chemical heat production and sleepiness, which depresss activity of CNS heat control mech and prevents shivering

Question 23

heat exhaustion and malignant hypothermia

Answer 23

heat exhaustion

• caused by excessive sweating
• blood volume and arterial MP decreases -> fainting

malignant hypothermia - ambient temperature is so low that heat-generating mechanisms cannot maintain core temperature near set point

Question 24

hypothermia

Answer 24

ambient temperature is so low that heat-generating mechanisms cannot maintain core temperature near set point