Exploring Biomedicine 2024: Fever and Homeostasis

Homeostasis

the maintenance of a relatively stable internal environment not withstanding changes in the external environment

Reflexive homeostasis

self-regulating unconscious behaviour

Regulatory homeostasis

involves the endocrine and nervous systems (autonomic which is specific for homeostatic regulation)

What does homeostasis control in the body?

• temperature

• pH

• Ions

• Solvents

Why does the body need homeostasis?

to prevent the denaturation of proteins as denaturation causes loss in the 3D optimal shape of the protein

Ectotherm

organisms depending on environment for heat source

Endotherm

organism with varying metabolic heat production to compensate for heat loss to the environment

heteroderm

may use either strategy depending on biology e.g. hibernation

Feedback loops

ubiquitous in biology (everywhere)

Positive or negative

Negative feedback loop

self-regulatory

oscillates around equilibrium to find a stable point

What are the steps in negative feedback loop?

1. Stimulus

2. change detected by a receptor

3. input information sent along AFFERENT pathway

4. control centre with response system

5. output information sent along EFFERENT pathway

6. Effector activated

   1. Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis

What is positive feedback loop?

Amplification of the effect

e.g. blood clotting or contractions when giving birth

Visceral sensory system

sensory information from internal organs of the body (e.g. heart, blood vessels, lungs, GI tract, and bladder) that we are not consciously aware of

Somatic sensory system

sensory information from body wall (e.g. skin, skeletal muscles, bones, joints) that we are consciously aware of

Visceral motor system

smooth and cardiac muscle related activity (and glandular secretion)

involuntary

associated with homeostasis

Somatic motor system

skeletal muscle activity which is voluntary and leads to movement of joints and limbs

Autonomic Nervous System

visceral motor system conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

Sympathetic Nervous system

mobilises body during activity - keeps the body alive (pumps blood through the heart)

controls fight, flight, flee response

Arousing responses - increased heartrate and respiratory rate

activates adrenergic receptor also activating pathways for thermogenesis

Parasympathetic system

conserves energy

promotes house-keeping functions during rest

REST AND DIGEST

indigestion

occurs when not under threat

Endocrine system

chemical signaling molecules travel from cell released to the target cell via the circulatory system

gland releases chemical signaling molecule into blood vessel

then transported to receptor cell

What is another word for a chemical signaling molecule?

ligand (neurotransmitters, hormones, inflammatory mediators

How do ligands work?

bind to specific receptors to allow a response and if a cell doesn’t have a receptor there will be no response

What is ligand specificity?

different chemicals act as signaling molecules and so the receptor is specific to the ligand (lock and key)

Neurotransmitters

released in small pockets at the synapse

What is action-decreet neurotransmitters

restricted to receptors at the synapse

Noradrenaline

released by neurons of the sympathetic nervous system to evoke fear, fight, or flight response

activates class of receptors called adrenergic receptors

Endocrine Hormones

released into the circulatory system and affect any cell in the body with the specific receptor protein

Adrenaline

secreted by adrenal gland under sympathetic control

activates a class of receptors called adrenergic receptors

thyroid hormone

secreted by thyroid gland under hypothalamic regulation

increases energy expenditure

T3 and T4 activate pathways inside the cell leading to increased heat production

circadian rhythm

24-hr cycles part of the body’s internal clock, running in the background to carry out essential functions and sleep processes

What is the main cause of circadian rhythm?

core temperature affects activity and function of hormones inside the body

List the visceral reflexes involved in regulating core body temperature

metabolism - shivering, skin blood flow, sweating

What is shivering thermogenesis

somatic regulation

endocrine system

what is non-shivering thermogenesis?

sympathetic regulation of the endocrine system

how does skin blood flow affect body temperature?

sympathetic system of vasoconstriction or active vasodilation

What system causes sweating?

sympathetic system

What are behavioural changes an organism may perform to thermoregulate?

posture changes, temperature choice, altering microenvironment

What is fever?

altered temperature regulated set point higher than normal

how is the immune response activated?

Infectious agent activates immune system

release of inflammatory mediator to endothelial cell

stimulation of prostaglandin secretion into the blood

What are observations of fever?

Stimulated prostaglandin production

alters neuronal activity in the hypothalamus leading to altered set point

aspirin blocks the production of prostaglandin

What are physiological benefits to fever?

• impacts protein operations in bacterial cells

• slows viral replication rate because human cells do not operate as efficiently at higher temperatures

• activates/enhances immune response

• some proteins operate better at higher body temperatures

• selectively activated during infection

What are disadvantages of fever?

sepsis - uncontrolled inflammatory response leading to organ damage

What is sepsis?

1. local infection caused by bacteria

2. bacteria enter bloodstream

3. immune system responds to fight infection

4. bacteria and immune cells spread throughout the body causing uncontrolled inflammation

5. leads to organ damage and death if untreated