2) Temperature Regulation

What is Uthoff’s Phenomenon?

→ temporary worsening of vision (blurring/dimming) when core body temp increases-

• seen in pt with demyelinating diseases (e.g., MS)

• Heat impairs signal transmission in previously damaged (demyelinated) nerves

 Humans maintain an average body temperature of…

98.6°F or 37° C

When is body temperature typically at its lowest and highest?

Morning (AM) = lowest

Evening (PM) = highest

How does age affect body temperature?

↑ age = ↓ body temp

Where is the body’s temperature regulatory center located?

Hypothalamus - determines the "set point"

Which specific hypothalamic areas control temperature and shivering?

Anterior hypothalamic area controls body temp

Posterior hypothalamic area controls shivering

List 4 main ways the body generates heat.

1. Thyroid hormone production

2. SNS activation

3. Shivering

4. Behavioral components (e.g., seeking warmth)

Why are thyroid hormones considered thermogenic?

1. ↑ Na-K-ATPase activity

2. ↑ O₂ consumption

3. ↑ metabolic rate

4. ↑ heat production

How does thyroid activity differ in heat vs. cold intolerance?

Hyperthyroidism (↑TH) causes heat intolerance

• ↑ BMR, ↑ O₂ consumption, ↑ heat production

Hypothyroidism (↓ TH) causes cold intolerance

• ↓ BMR, ↓ O₂ consumption, ↓ heat production

What role does the SNS play in heat conservation?

→ Synergistic with and depends on presence of a thyroid response

• Stimulation of β-adrenergic receptors in brown fat → ↑ metabolic rate & heat production without shivering

• Stimulation of α₁ adrenergic receptors in skin → vasoconstriction of superficial vessels to prevent further heat loss + shunt blood to your core + stimulates arector pili muscles (goose bumps)

Why does being cold make you need to urinate?

Peripheral vasconstriction ↑ BP → stimulates urine production to ↓ BP by ↓ volume (peeing)

What is the primary role of Brown Fat? Where is it found?

Role: Non-shivering thermogenesis

• this is critical in neonates (making up 5% of their body mass)

Location: Back, along the upper half of the spine and toward the shoulders

How does brown fat change with age?

↑ Age = ↓ Brown fat

Compare White fat and Brown fat.

White fat

• single lipid droplet (“look” empty)

• less capillaries

Brown fat

• multiple smaller droplets

• ↑ (iron-containing) mitochondria + lacy cytoplasm

• more capillaries to supply the tissue with O₂ and nutrients + distribute produced heat throughout the body

How does Brown Fat produce heat instead of ATP even though it has mitochondria?

→ it has Thermogenin (uncoupling protein-1)

• this allows H⁺ to flow back through the mitochondrial membrane quickly, generating heat instead of ATP

What is the most effective way for the body to generate heat in a short time?

Shivering (rhythmic skeletal muscle contraction)

Which nerve fibers mediate the shivering response?

• α-motor fibers fire skeletal muscles

• γ-motor fibers keep spindles taut for repeated firing

How does Shivering change with age?

↑ Age = ↓ shivering

What is the medical term for severe or violent shivering?

Rigors

How does the body cool itself through the skin?

1. Vasodilation of peripheral blood vessels → shunts blood to surface → heat loss

2. Stimulation of eccrine sweat glands → sweat

3. Behavioral components (getting out of the sun, removing excess clothing, etc)

What is the rate of perspiration for a human?

greater 3L /hour

What is Syringoma?

→ Benign growth of eccrine sweat glands in the lids

• Begins at puberty

• not treated except for cosmesis

What is a patient with a fever called?

Febrile

How does fever assist in immune defense?

1. Move temps above optimal temp for microbe growth and replication

2. Strengths CD-8 lymphocytes function

List the steps explainng the physiological cause of a fever.

1. Pyrogens (pus) trigger IL-1 release

2. Prostaglandin production

3. ↑ hypothalamic set point

4. ↑ temp

How do aspirin and ibuprofen reduce fever?

1. Inhibit cyclooxygenase (COX)

2. ↓ prostaglandin production

3. No increase in hypothalamic set point

4. ↓ Fever

True or False: Acetominophen, aspirin and ibuprofen can all be used to reduce fever.

False - Acetominophen less effective for fever

What’s the difference between Heat Exhaustion and Heat Stroke?

Heat Exhaustion (wet)

→ excessive sweating and dehydration → ↓blood volume, ↓ BP, fainting

Heat Stroke (dry)

→ DRY, hot skin with potential tissue damage that can occur due to ineffective heat reduction methods

• temp >104°F

What is Malignant Hyperthermia?

→ complication of inhaled anesthetics caused by an inherited muscle receptor defect that keeps Ca²⁺ channels open

• leads to continuous muscle contraction & massive heat production

• heat dissipating mechanisms can’t keep up

How do you distinguish HSV from VZV Keratitis on a stain?

• HSV has sharp edges and knobs at the ends (dendrite)

• VZV has a feathery pattern with no end knobs (pseudodendrite)