Homeostasis & Thermoregulation

Endotherms

An organism that internally regulate temperature.

Ectotherms

An organism that cannot internally regulate temperature.

How is Homeostasis controlled?

It is controlled via the Hypothalamus and Pre-optic area (POA).

Core Body Temperature = Hypothalamus POA set point temperature means?

The body is in temperature homeostasis.

Physiological response when core body temperature is too high?

Enhance heat loss:

Sweat

Panting

Cutaneous vasodilation

Physiological response when core body temperature is too low?

Enhance heat production:

Shiver

Increase metabolism

Cutaneous vasoconstriction

Two examples of regulated change in setpoint?

Torpor

Fever

Define Torpor

Regulated lowering of setpoint temp.

• Hibernation (less food, less O2, metabolism decreases)

• Set point goes down, body temperature goes down to match set point (in homeostasis when equal)

Define Fever

Regulated elevation of setpoint temp.

• Exposure to pathogens (bacteria, viruses)

• Bacterial infections: LPS on cell wall of bacteria that binds to receptor on human cell membrane and body recognizes as foreign and body emits fever response

  • LPS turns on inflammatory genes (cytokines)

• Caused by pyrogens = fever inducing molecules

Define Periodic Fever Syndromes

Rashes and High fevers but not associated with any pathogen

Location of the Hypothalamus

Directly above the pituitary gland.

Role of POA in thermoregulation

Contains warm- and cold-sensitive neurons that regulate temperature setpoint.

Exogenous pyrogen example?

LPS from bacterial cell walls.

Example of Endogenous Pyrogens

Cytokines produced by the body that induce fever.

Cause of periodic fever syndromes

Genetic mutations leading to increased IL‑1 production.

Treatment for IL‑1–driven fever syndromes

Block IL‑1 with monoclonal antibodies or IL‑1 receptor antagonists.

Non‑shivering thermogenesis

Uncoupler proteins dissipate proton gradient to generate heat instead of ATP.

Evolutionary benefit of fever

Increases resistance to pathogens.

Define Exogenous Pyrogen

A fever-inducing substance that comes from outside the body.

Define Endogenous Pyrogen

A fever inducing protein produced by your own body in response to infection, inflammation, or injury.