Lecture 8 - Thermoregulation

2 major functions of the blood in skin?

• nutrition

• Heat loss

What is the cutaneous plexus?

A network of capillaries between sub cutaneous and dermis

Supplies adipocytes, hair follicles, and sweat glands with blood

What is the papillary plexus ?

Branches of cutaneous plexus

Gives rise to capillary loops

What are arteriovenous shunts

Shunts between arteries and veins to conserve heat

What influences the blood flow to skin and metabolism

Temperature of surroundings

3 types of nerve endings

Merkel discs, messiness corpuscles and pacinian corpuscles

What are messiners corpuscles sensitive too?

Light

What are pacinian corpuscles sensitive to?

Deep pressure and vibration

What do sensory nerves do in response to temp

• detect increase or decrease

• Carry info to hypothalamus

What do motor neurons do in response to temp?

• activate sweat galnds and pills muscle

• Contracts skeletal muscle (shiver)

• Shunts of blood

What is metabolic rate?

Sum of all chemical reactions (anabolic and catabolic)

Rate at which heat is produced

How does body temp remain constant?

Heat must be lost to environment at same rate it is generated

Factors affecting metabolic rate - 7

1. Exercise ^

2. Nervous system - noradrenaline increases BMR

3. Hormones ^

4. Body temp ^

5. Digestion ^

6. Age ^ in children

7. Other e,g sex, climate and malnutrition

• females BMR is lower

Which temp is higher core or shell?

Core usually

Effect of high core temp?

Protein denaturation

Effect of low core temp?

Arrhythmias and disorientation

Core temp range

36.7 and 37. 2

4 processes of heat loss

1. Evaporation (20%)

2. Conduction (direct transfer)

3. Radiation (more than 50%)

4. Convection ( 15%)

Role of hypothalamic thermostat?

Tries to keep heat production and heat loss in balance

What brings info to the brain surrounding temperature?

Sensory thermoreceptors

5 heat loss mechanisms

1. Vasodilation - increased blood flow

2. Perspiration - sweating

3. Decreased metabolic rate and shivering - reflexes

4. Increased respiration - deeper breaths

5. Behavioural changes - seek shade, remove clothing

5 heat gain mechanisms

1. Vasoconstriction - decrease blood flow

2. Skeletal muscle - shivering

3. Sympathetic release - adrenal gland

4. Thyroxine - increases metabolism

5. Behavioural - put on more clothes, change are a

Non shivering thermogenesis

• increase metabolism by liver

• Release of hormones

• Adrenal medulla and thyroid

What temp indicates a fever?

37.2+

What generally stimulates a fever?

Bacterial or viral infections

Mechanism of Pyrex is fever

1. Phagcyte ingests bacteria

2. Interleukin 1 secreted and circulated

3. Prostaglandin produced in hypothalamus

4. Resetting of thermostat

Fever stage 1

Activation of heat procduction mechanisms e,g shivering, vasoconstriction increased metabolic rate

CHILL

Fever stage 2

Temp reaches 39 degrees Celsius - chill disappears

Fever stage 3

Stress is removed and thermostat reset

Heat loss mechanisms

4 benefits of temperature increase

1. Inhibits bacterial growth

2. Fast delivery of WBCs to infection

3. Increases ab production

4. Increased rate of repair

4 complications of temp increase

1. Dehydration

2. Acidic blood

3. Permanent brain damage

4. Death

How do heat cramps occur

Loss of NaCl due to sweating

Felt when muscles are relaxed

Electrolytes to relieve

Heat exhaustion

Difficult in maintaining blood volume in a normal or slightly low temp

Cool clammy skin - oss of electrolytes and fluid

Heat stroke

High temperatures and humidity

Body heat cannot be lost by evaporation or radiation

Decreased blood flow and sweating