Thermoregulation

Question 1

Major Functions in the Skin

Answer 1

• Nutrition of the skin tissues
• Heat loss

Question 2

Dermal circulation

Answer 2

Cutaneous plexus
* A network of capillaries
* Located between subcutaneous layer and dermis
* Supplies adipocytes, hair follicles and sweat glands
Papillary plexus
* Formed from branches of the cutaneous plexus
* Gives rise to papillary loops

Question 3

Skin Vascularity

Answer 3

Arteriovenous Shunts
* Shunts blood between arteries and veins to conserve heat
* Have muscular walls innervated by the sympathetic division of the ANS
* Activation of sympathetic division results in blood flow to plexus and heat loss.
* Blood flow to skin & metabolism is influenced by to of surroundings.
Nervous Control
* Vasodilator control
* Vasoconstrictor control

Question 4

Sensory Nerves (Innervation and Skin)

Answer 4

• From pain, temp, and touch receptors
• Free nerve endings (dendrites of sensory nerve)
• Or sensory receptors:
  
  • Merkel Discs
  • Messiners Corpuscles–
    sensitive to light touch (in
    dermal papillae)
  • Pacinian corpuscles - sensitive
    to deep pressure and vibration
    (in reticular layer)

Question 5

Motor Nerves (Innervation and Skin)

Answer 5

• To sweat glands
• To erector pili muscle
• To blood vessels

Question 6

Sensory Nerves in Thermoregulation

Answer 6

• Detect increase or decrease in skin temperature
• Carry the information to the hypothalamus of the brain for
  thermoregulation

Question 7

Motor Nerves in Thermoregulation

Answer 7

• Activation of Sweat glands and pili muscle
• Contraction of skeletal muscle- shivering
• Shunting of blood in skin and limbs

Question 8

Metabolic rate

Answer 8

• the sum of all the catabolic and anabolic processes
• Rate at which heat is produced in the body
• The heat is produced as food is oxidised
• Energy from food = ATP + Heat
• Significant amount of energy used to synthesise ATP, but much of it is lost to environment as heat
• The heat produced is carried in H2O (plasma) throughout the body
• For body temperature to remain constant, heat must be lost to the
  environment at same rate it is generated

Question 9

Factors that Affect Metabolic Rate

Answer 9

• Exercise may increase BMR x15% (20% in well trained athlete)
• Nervous system, in stress ANS releases noradrenaline which increases BMR
• Hormones; adrenaline, noradrenaline, hGH, testosterone and thyroid hormones increase BMR
• Body T°; a 1°C rise in body To increases BMR X 10% (fever)
• Digestion of food increases MR X 10-20% (diet induced thermogenesis)
• Age; MR is higher in children
• Other factors:
• Sex (female MR is lower except in pregnancy)
• Climate (↓ if hot)
• malnutrition (↓ if malnourished)

Question 10

Homeostasis of Body T° Regulation

Answer 10

• Core T° is the body T° below the skin
• Shell T° is the surface T°
• Usually the core T° is higher
• If the heat loosing mechanisms give off more heat than is produced the core T° ↓
• If heat producing mechanisms generate more heat than is lost the core T° ↑

Question 11

Importance of temperature

Answer 11

• Too high core T° kills by denaturing protein (it also causes convulsions)
• Too low core T° causes arrhythmias (it also causes disorientation)
• Core Temperature kept between 36.7°C and 37.2°C by homeostatic control

Question 12

Evaporation

Answer 12

• Absorbs energy and cools surface where evaporation occurs
• Insensible water loss– each hour 20-25ml of water crosses epithelia and evaporates from alveolar surfaces and surface of skin (accounts for 20% of boy’s average indoor heat loss).
• Sensible heat loss– evaporation of sweat

Question 13

Radiation

Answer 13

• Objects warmer than environment lose heat as radiation
• Heat from sun is radiant heat
• More than 50% of heat you lose indoors is lost through radiation

Question 14

Conduction

Answer 14

• Direct transfer of heat through physical contact e.g. sitting on a cold chair
• Not effective way of gaining or
  losing heat – impact depends on the temperature of the object and the amount of skin surface area
  involved

Question 15

Convection

Answer 15

• Heat loss to cooler air that moves
  across the surface of your body. As
  body loses heat to air next to skin,
  the air warms and rises away from
  skin surface, and is replaced by
  cooler air which is then warmed
• Accounts for roughly 15% of
  body’s heat loss indoors

Question 16

Hypothalamic Thermostat

Answer 16

Tries to keep heat production and
heat loss in balance – i.e. maintain
Temp range

Question 17

Sensory thermoreceptors

Answer 17

(in skin, mucous membrane and in
hypothalamus) bring information to
hypothalamus of the brain

Question 18

Hypothalamus

Answer 18

has a special region called the Preoptic area output that has:
* heat losing centre
* heat production centre.
Preoptic area - regulates body temperature

Question 19

Heat Loss Centre (Heat loss)

Answer 19

stimulated when temperature at pre-optic area rises above its set
point

Question 20

Mechanisms for heat loss

Answer 20

1. Vasodilation
2. Perspiration
3. Decreased Metabolic Rate and Decreased Shivering
4. Increased Respiration
5. Behavioural change

Question 21

Vasodilation

Answer 21

inhibition of the ANS vasomotor output. This increases blood flow to the skin, warms the skin and increases heat transfer

Question 22

Perspiration

Answer 22

activation of the sweat glands and evaporation of H2O cools the skin

Question 23

Decreased Metabolic Rate and Decreased Shivering

Answer 23

mediated through hypothalamic
reflexes

Question 24

Increased Respiration

Answer 24

depth of breathing increased and breathing through the mouth will increase evaporation

Question 25

Behavioural change

Answer 25

seek shade or remove clothing

Question 26

Function of the Heat Promoting Centre (Heat gain)

Answer 26

to prevent hypothermia, or below-normal body temperature

Question 27

Mechanisms of heat gain

Answer 27

1. Vasoconstriction 2. Skeletal muscle 3. Sympathetic release 4. Thyroxine 5. Behavioural responses

Question 28

Vasoconstriction

Answer 28

increase vasomotor output (decrease blood flow to skin surface)

Question 29

Skeletal muscle

Answer 29

by shivering increases muscle tone and increases heat production.

Question 30

Sympathetic release

Answer 30

from adrenal gland (adrenaline and noradrenaline stimulate cellular metabolism, i.e. chemical thermogenesis)

Question 31

Thyroxine

Answer 31

increases cellular metabolism by increasing catabolic reaction

Question 32

Behavioural responses

Answer 32

put on more clothing or move to a heated area

Question 33

Shivering Thermogenesis

Answer 33

* muscle metabolism in contraction/relaxation * Gradual increase in muscle tone increases energy consumption of skeletal muscle tissue -> more energy used the more heat produced * Heat produced warms deep vessels where blood has been shunted * Shivering can increase rate of heat generation as much as 400%

Question 34

Non Shivering Thermogenesis

Answer 34

* increased metabolism (by liver) and BAT adipose breakdown * Involves release of hormones that increase tissue metabolic activity * Adrenal medulla – releases epinephrine, increasing glycogenolysis * Thyroid gland – releases thyroxine, increasing nutrient catabolism

Question 35

Pyrexia

Answer 35

-Fever * Usually bacterial or virus stimulated * Other causes are heart attack, tumour, surgery or trauma

Question 36

Mechanisms of Pyrexia

Answer 36

Phagocyte ingests bacteria ↓ Interleukin-1 secreted and circulated in the blood ↓ Prostaglandin production in the hypothalamus ↓ Resetting of T° thermostat

Question 37

Stages of fever

Answer 37

* Core T° thermostat ↑ 39.4°C,→ activation of the heat production mechanism resulting in vasoconstriction, increased metabolic rate and shivering→ Chill * When skin T° is increased to 39°C the chill disappears * When stress is removed the thermostat is reset→ the heat losing mechanism goes into operation. Resulting in Vasodilation and sweating. Crisis → T° is falling

Question 38

Why is T* increased during a fever?

Answer 38

* The high T° is beneficial: - Inhibits growth of bacteria - WBC delivered to site of infection faster - Increases Ab production - Increases rate of repair

Question 39

Complications of fever

Answer 39

* Dehydration * Acidosis – Blood pH * Permanent brain damage * Death of To rises to 44.5 – 45.5°C

Question 40

Heat Cramp

Answer 40

* Result of profuse sweating that removes NaCl from the body * Salt loss causes painful muscle contraction called heat cramp * Cramp in muscles used in working only felt when relaxed * Salted liquid relieves cramp.

Question 41

Heat Exhaustion

Answer 41

* Difficulty in maintaining blood volume * Normal or slightly low T°. * Cool clammy skin due to loss of fluid and electrolytes as sweat. * Muscle cramps, dizziness, vomiting, fainting, low blood pressure and low blood volume. * Body cannot compensate for low blood pressure. * Relieved by rest and salt tablets.

Question 42

Heat Stroke (sunstroke)

Answer 42

* Occurs when T° and relative humidity are high. * Body heat cannot be lost by evaporation and radiation * Decreased blood flow to skin and decreased sweating→ Core T° rises. * May destroy brain cells. * Relieved by immersion of the body in cool water (increased conduction) and rehydration.