Importance of temperature regulation

metabolic reations → enzymes → optimum temperature → efficient ⇒ maintain steady metabolic rate

Too low/high → body malfunction/death

33 35 36.6-37.5 37.5 42

28 42 death

Key: balance geat gain and heat loss

Skin structure

Epidermis

1. Malpighian layer

Cells actively dividing to produce new cells
/ Produce pigment melanin -- skin colour, absorb UV
/ Produce vitamin D

2. middle layer

• Cells produced by Malpighian layer
• contents → replaced by fibrous protein keratin when pushed → skin surface
• ⇒ nuclei disappear → die

3. cornified layer

• Flattened, dead cells
• shed and replaced by inner layer cells
• Function: Barrier to prevent invasion of pathogens
  / minor mechanical injuries
  / waterproof → minimize water loss

Dermis

Hair

• Hair follicles: sac-like structure, hair root dev hair
• Hairs
• Erector muscles contract → hair erect;
  relax → lies flat

Sebaceous glands

• Open into follicles
• Sebum: keeps skin soft, waterproof
  Antiseptic, inhibit baterial and fungal growth

Sweat glands

• Coiled, tubular
• Sweat: water, minerals, metabolic wastes
• Sweat duct → sweat pore
• sweating: cools the skin, excretes metabolic waste

Sensory receptors and nerves

• Sensory receptors: temp, touch, pain
• sensory neurones, motor neurones

Blood vessels

Shunt vessels: connect arterioles ↔ venules
→ Blood bypass capillaries, regulate temperature

Subcutaneous fat

Underneath dermis
Thickness varies
Insulating layer to reduce heat loss
Source of energy reserve

Regulation mechanisms

Control centre

thermoreceptors in skin vs thermoreceptors in hypothalamus (in brain)

1. Heat gain centre (+ heat)
2. Heat loss centre (- heat)

Arterioles

When too cold: constrict = vasoconstriction. → reduce blood flow to capillaries near skin surface __ more blood flows through shunt vessel → less heat lost to surroundings by conduction, convection and radiation.

When too hot: dilate = vasodilation. → increase blood flow to capillaries near skin surface __ less blood flows through shunt vessel → more heat lost to surroundings by conduction, convection and radiation.

Sweating

When too cold: Sweat glands secrete less sweat → heat loss by evaporation is reduced

When too hot: Sweat glands secrete more sweat → heat loss by evaporation is increased (sweat absorbs heat)

Erector muscles

When too cold: erector muscles contract → hairs erect. For thick fur mammals(not humans with few short hairs), traps thicker layer of still air, less heat loss by conduction and convection because air is a good heat insulator

When too hot: erector muscles relax → hairs lie flat. For thick fur mammals(not humans with few short hairs), thinner layer of still air, more heat loss by conduction and convection

Subcutaneous fat (long term)

Too cold: thicker layer → fat is good insulator of heat → less heat loss by conduction and convection

Too hot: thinner layer → reduce insulating effect → more heat loss by conduction and convection

Shivering

Too cold: heat gain centre in hypothalamus: sends more freq. nerve impulses to skeletal muscles → contract in short bursts (aka shivering)

Involuntary, generates extra heat from increased cellular respiration in skeletal muscles

Thyroxine (long term)

Too cold: hypothalamus → pituitary gland → thyroid gland: more active → secretes more thyroxine (hormone) → increases metalbolic rate of body cells → more heat

Behaviours

Voluntary
Too cold: wear more clothes, hot food & drinks, heater, do exercise

Too hot: fewer and thinner clothes, seek shade from sunlight (radiation), fan/ air conditioner (convection and evaporation of sweat)