Thermoregulation

Question 1

Why is Thermoregulation Important?

Answer 1

-Body function relies on processes that are temperature-dependent.
-Metabolic rate is the heat energy that is produced per unit time.
-Changes in body temperature, the balance between heat production and loss.
-Hypothermia: abnormally low temperature, slows metabolic process, eventually, function stops.
-Hyperthermia: abnormally high temperature, which can denature proteins and lead to death.

Question 2

Poikilotherms?

Answer 2

-Fish, reptiles, and amphibians.
-Body temperature varies with the environment.
-Behaviour is important in maintaining preferred body temperature (PBT): Maintenance of PBT prevents lactic acidosis and maximises drug absorption, metabolism, and excretion.
-Environment critical in captive animals: temperature, UV light, humidity. Many diseases are related to husbandry.
-Can survive periods of food storage.

Question 3

Homeotherms?

Answer 3

-Mammals and birds.
-Maintain constant body temperature in a variety of environmental temperatures.
-High metabolic rate for heat production: high energy intake.
-Lecture focusses of homeotherms.

Question 4

Heat production?

Answer 4

-Metabolism.
-Food intake.
-Muscular activity.

Question 5

Heat loss?

Answer 5

-Radiation.
-Convection.
-Conduction.
-Evaporation.
-Excretion of urine and faeces.

Question 6

Homeostasis of thermoregulation?

Answer 6

-Regulated variable: Core body temperature.
-Sensor: thermosensors (hypothalamus, skin).
-Control center: Hypothalamus.
-Effectors: Blood vessels and sweat glands in the skin, as well as skeletal muscles.
-Effector Response: Change peripheral resistance, rate of sweat secretion, and shivering. Alter hear gain/losses.

Question 7

Monitoring body temperature?

Answer 7

-Thermometer.
-Core vs peripheral temperature measurement.:
1.) Heat is transported from the core to the periphery by blood.
2.) Within the thermoneutral zone (ambient temperature), animals can control skin temperature (maximises efficacy of feed for growth or production).
-Assess hydration status and cardiovascular function.

Question 8

Why don’t penguins’ feet freeze?

Question 9

Other countercurrent mechanisms?

Answer 9

-Carotid rete: sheep and other ungulates.
-Cold venous blood draining from the nose cools the brain’s blood supply.
-Not found in horse:
1.) Guttural pouches may provide function.
2.) Intracranial cavernous sinuses.

Question 10

Responses to increased and decreased core and peripheral temperature?

Answer 10

-Body temperature is maintained primarily by:
1.) Metabolic responses: below the thermoneutral zone.
2.) Vasomotor responses: within the thermoneutral zone.
3.) Evaporative responses: above the thermoneutral zone.

Question 11

Decreased core and skin temperature: physiological responses?

Answer 11

-Peripheral vasoconstriction: reduces blood flow to the skin.
-Counter-current heat exchange: cools blood heading to the periphery to prevent heat loss.
-Other mechanisms to prevent heat loss: insulation/ piloerection/ behavioural responses.
-Mechanisms of heat production: metabolism/ shivering and non-shivering thermogenesis.

Question 12

Mechanisms of heat production?

Answer 12

-Metabolism: most of the chemical energy is lost as heat.
-SHivering thermogenesis: rapid, involuntary cycle of contraction and relaxation of muscles.
-Non-shivering thermogenesis: stimulation of metabolism (brown adipose tissue).

Question 13

Increased core and skin temperatures: physiological responses?

Answer 13

-Sweating (notes species differences).
-Increased evaporation from skin and respiratory tract.
-Peripheral vasodilation.
-Decrease in heat production: decreased muscle tone, reduced adrenaline secretion.
-Behavioural responses.

Question 14

How do low environmental temperatures affect animal management?

Answer 14

-Care rehypothermia in newborns: use of heat lamps in lambing sheds.
-Insulation of animals in cold weather: calf jackets.
-The amount of powder in milk replacer needs to be increased to account for higher metabolic requirements and ensure growth.

Question 15

Thermoregulation in the Neonate?

Answer 15

-High body surface to body volume ratio.
-Less or even no insulation.
-Increase skin permeability.
-Lower energy supplies: limited amount of brown fat.
-Inability to display behavioural thermoregulation.
-Immature nervous system.
-Require ambient temperature much closer to set point temperature than adults.

Question 16

Hypothermia?

Answer 16

-Common in neonates and under anaesthesia.
-High surface-to-volume ratio.
-Low metabolic rate under anaesthesia.
-Can lead to increased morbidity and mortality, especially in sick patients.
-Cardiac arrhythmias: AF 30C VF 24-28C.
-Bradycardia.
-Impaired coagulation and wound healing.
-Decreased enzyme action of drugs.
-Prolonged duration of action of drugs.
-Decreased renal plasma flow.
-Decreased oxygen delivery to tissues.
-Lower anaesthetic requirements in anaesthetised animals.
-Shivering increases oxygen requirements.

Question 17

Prevention of hypothermia?

Answer 17

-Warm environmental temperatures.
-External heart sources.
-Insulation.
-In animals undergoing surgery: Warm fluids, HME Breathing systems, clipping, and scrub solution.

Question 18

Severe hypothermia?

Answer 18

-Warm water enemas.
-Bladder lavage.
-Gastric lavage.
-Peritoneal lavage.
-Vasodilation may worsen hypotension.

Question 19

Other causes of hypothermia?

Answer 19

-Sepsis.
-Shock.
-Endocrine disease (hypothyroidism, hypopituitarism, Addison’s).
-Intracranial disease (lesion in the hypothalamus).

Question 20

Hyperthermia?

Answer 20

-Hyperthermia: A general term used to describe an increase in body temperature above normal for that species, regardless of aetiology.
-Pyrexia: A specific term that refers to an increase in core body temperature due to an increase in the set point of the hypothalamus.
-Increased basal metabolic rate: 13%. for every C above normal.
-Increased oxygen and substrate requirement.
-Paraenchymal cell damage.
- T> 41C: irreversible brain damage.
- T> 43*C: death.

Question 21

Pyrexia?

Answer 21

-Infection.
-Immune-mediated disease.
-Neoplasia.
-Tissue trauma.

Question 22

Other causes of hyperthermia?

Answer 22

-Heat stroke.
-Hyperpyrexic syndrome.
-Exercise hyperthermia.
-Malignant hyperthermia.