Temperature Control in Humans

Premed Biology January 2015

37⁰ C (98.6 F)

What is your normal body temperature?

• Homothermic (constant & high body temperature) or Endothermic (warm blooded)– Birds & Mammals

• Poikilothermic ( Varying in temperature according to the surrounding or environment temperature) or Ectothermic ( cold-blooded)– Amphibians & Reptiles – Bask in warm temperature and hibernate in cold

temperature

• Regulation of body temperature is a type of homeostasis called “Thermoregulation”

• Thermoreceptor is a type of “sensory receptor” detects change in temperature

EFFECTOR RESPONSE TO LOW TEMP RESPONSE TO HIGH TEMP

Smooth muscles in Arterioles of skin

Contraction of muscles resulting in vasoconstrictionSkin turns blue

Muscles relax resulting in vasodilationSkin turns red

Sweat Glands No sweat Glands secrete sweat that evaporates

Erector pili muscle of skin Muscles contract raising skin hair (Goosebumps) to trap warm air

Muscles relax lowering hair for evaporation

Skeletal Muscles Contract resulting in shivering

No shivering

Adrenal & Thyroid glands Secrete adrenalin and thyroxine increasing metabolic rate (E.g. High metabolic rate in LIVER generating heat)

No gland secretion

Erector pili muscle (muscle connected to hair follicle) CONTRACTS in response to cold trapping warm air E.g. Goosebumps

Sensory Transduction • All Sensory processes begin with STIMULI (form of energy)

– Many (but not all) detect from outside body (Heat, light, pressure, chemicals)

• Sensory Receptor converts stimulus energy into a change in membrane potential

• Sensory information travels through nervous system as impulse or action potentials

• When action potential reaches the brain through sensory neurons, circuit of neurons process generating the PERCEPTION of stimuli

• Transduction of stimuli by sensory receptors subject to 2 modifications:

• 1. Amplification (Strengthening of sensory signal)• 2. Adaptation (Upon continuous stimulation,

receptors undergo a decrease in responsiveness)

Sensory Receptors

• Body contains 5 types of sensory receptors:

• 1. Mechanoreceptors for touch & pressure• 2. Thermoreceptors for temperature change• 3. Nociceptors for pain• 4. Chemoreceptors for taste and smell• 5. Electromagnetic receptors for light (spectrum)

Mechanoreceptors

• Sense physical deformation caused by mechanical energy (eg. Pressure, touch, stretch, motion and sound)

• Receptors that detect light touch or vibration are close to surface of skin.

• Strong pressure and vibrations are detected in deep skin layers.

Mechanoreceptors

• Vertebrae stretch receptors, are mechanoreceptors that detect muscle movement and triggers Knee-jerk-reflex

• Stretch receptors are dendrites of sensory neurons that spiral around skeletal muscle fibers

• Muscle fibers stretch sensory neurons depolarize nerve impulses spinal chord motor neuron Reflex Response

Chemoreceptors

• Transmit information about solute concentration, others about individual kinds of molecules

• Eg. Osmoreceptors in brain stimulate thirst, detect changes in total solute concentration in blood

• Receptors for O2, CO2, glucose, and amino acids

Electromagnetic Receptors

• Detect forms of electromagnetic energy• Light, electricity, and magnetism

Thermoreceptors

• Located in skin and anterior hypothalmus• Send information to body’s thermostat in

posterior hypothalmus

Pain Receptors

• Detect stimuli that reflect harmful conditions• Also called “Nociceptors”

• Some chemicals enhance perception of pain• Damaged tissues release prostaglandin, local

regulators of inflammation• Prostaglandins worsen pain by increasing

sensitivity

Sensory Receptors in Skin

• Physical stimulus Neural Signals

• Each receptor has own neural pathway to the CNS resulting in different sensations

• (E.g. Body temperature detected by thermoreceptors and send to Hypothalamus)