Thermoregulation Flashcards

Flashcards about thermoregulation, covering topics such as body temperature control, heat stress, and feedback mechanisms

Importance of Thermoregulation

Control over body temperature is crucial for enzymatic reaction rates, which are temperature-dependent and vital for life.

Effectors in Physiological Feedback Systems

Muscles (voluntary and involuntary) and glands are the effectors that bring variable/values back to the correct levels.

Normal Body Temperature Range

Normal range is 32°C-42°C, but thermoregulatory homeostatic mechanisms maintain core body temp within a much narrower range.

Effects of Temperature on Enzymes and Neurons

Enzymatic reactions are slowed with cold and disrupted by heat. Temperature spikes above the normal range denature proteins and depress neurons.

Heat-Loss Center Activation

Sweat glands activated: secrete perspiration, which is vaporized by body heat, helping to cool the body Skin blood vessels dilate: capillaries become flushed with warm blood; heat radiates from skin surface.

Heat-Promoting Center Activation

Skeletal muscles activated; shivering begins Skin blood vessels constrict: blood is diverted from skin capillaries and withdrawn to deeper tissues; minimizes overall heat loss from skin surface.

Thermoreceptors

Shell or peripheral receptors (numerous epidermal nerve endings) & Deep body receptors (cells located in hypothalamus respond to changes in core body temp).

Stimulation of the Hypothalamus during Heating

Skin (shell or peripheral) & core body (brain and organ) receptors stimulate The HYPOTHALAMUS which via the cerebral cortex, PNS & endocrine systems leads to conscious decisions & immediate unconscious decisions.

Stimulation of the Hypothalamus during Cooling

Skin (shell or peripheral) & core (brain) receptors stimulate The HYPOTHALAMUS which via the cerebral cortex, PNS & endocrine systems leads to conscious decisions & immediate unconscious decisions.

Heat Production in the Body

At rest, the liver, heart, brain, and endocrine organs account for most heat production. During exercise, heat production from skeletal muscles can increase 30-40 times.

Core & Shell Temperatures

The shell (i.e. the epidermis/skin), has the lowest temperature, and blood serves as major agent of heat transfer between core and surface. Organs in the body core will tend to be maintained at higher temperature.

Core Body Temperatures

Normal core temperature during the day is between 36.1- 37.8°C (or thereabouts). Core temperature fluctuates with a 24 hour cycle (circadian rhythm), reaching lows near 6 AM & highs near 6 PM.

Fever

Fever occurs when the hypothalamic set point is shifted higher by the action of circulating, inflammatory cytokines. Chemical reactions occur more quickly, infectiousness of many microbes is reduced, and Zn and Fe are sequestered by the liver.

The Feverish Response

The body reacts as if it is too cold (hence shivering while covered with blankets). Peripheral mechanism conserve and generate heat (e.g. shivering, vasoconstriction) until the body temperature increases to the elevated set point.

Heat Loss Mechanisms

Vasodilation of cutaneous arterioles→ increased heat loss Enhanced sweating → evaporative cooling Decreased muscle tone, reduces heat load Voluntary measures taken to reduce body heat.

Heat Promoting Mechanisms

Vasoconstriction of cutaneous blood vessels → decreased heat loss Incr. metabolic rate due to increases secretion of thyroxine and adrenaline Shivering & increased muscle tone: skeletal muscles generate heat, with piloerection (evolutionary hangover) Behavioural changes.

Heat Stress (Heat Exhaustion)

Elevated core body temperature (37.5-39 °C), mental confusion, & fainting dehydration (headache), may be difficulty maintaining BP heat-loss mechanisms are functional.

Heat Stroke (Hyperpyrexia)

When core temp. exceeds >40°C brain (and therefore hypothalamic activity) is depressed, and thermoregulatory control mechanisms work less well. Loss of control, sweating and blood flow to the periphery are reduced.

Heat Stroke - Signs

Will likely behave/speak inappropriately be confused, disoriented have a clammy, dry skin not request shade or fluid surface temp. may not feel high, but core temp. will tell the story.

Positive Feedback

Negative feedback  reduce or correct deviation from set point Positive feedback (pathological): error in signalling  increase deviation from set point (a vicious circle).

Haemostasis: +ve feedback

Break or tear occurs in blood vessel wall +ve feedback cycle is initiated Released chemicals attract more platelets Platelets adhere to site and release chemicals Feedback cycle ends when plug is formed.

Childbirth: +ve feedback

Obviously primary stimulus is gone once baby is born, and +ve feedback loop is then ‘disengaged”.