Partial 3 - Thermoregulation Flashcards
Heat production:
1) Basal metabolism (Exothermic reactions where most heat is generated by brain, heart, liver and glands at rest. Skeletal muscle produces 20-30% at rest, but can increase 30-40 times during exercise).
(2) Muscle activity (shivering)
(3) Thyroxine effect on cells
(4) Epinephrine effect on cells
(5) Temperature effect on cells.
Heat loss:
(1) Radiation (60%) when body temperature is greater than the surroundings
(2) Evaporation (22%) when the body temperature is near the surroundings
(3) Conduction (3%) when body is in direct contact with an object
(4) Convection (15%) which is heat loss due to air movement.
Thermoregulatory center is located in hypothalamus in?
Preoptic area
Heat loosing center mechanism
Dilates the arteries of the skin
Increases sweating
Increases respiration
Inhibits heat-promoting center
Heat promoting center mechanism
Constricts vessels of the skin
Stimulates arrector pili muscles
Leads to shivering
Inhibits heat-loss center
Heat exhaustion occurs when
an individual is exposed to high temperatures leading to heat-loosing centers being activated which decreases BP and blood to the brain
Compensatory mechanisms of heat exhaustion
SNS, Aldosterone and ADH
Symptoms of heat exhaustion
Headache Nausea Active sweating Skin being cool and pale Fainting
Heat stroke occurs when
when core temperature is 41 Celsius and happens to individuals with compromised hemostatic mechanisms (young children and Elderly) and healthy individuals under strenuous exercise.
Heat stroke leads to
Renal and splenic vasoconstriction Decreased peripheral blood flow Impaired thermoregulation Cerebral edema Increased intracranial pressure Protein denaturation
Complications of heat stroke
Rhabdomyolysis (breakdown of skeletal muscle)
Multiple organ failure (heart, liver, and kidney)
DIC
CNS hallucinations
Coma
Anhidrosis (Inability to sweat normally)
Causes of hyperthermia
Increased heat production
Drugs
Decreased heat loss
Increased heat production causes
External hyperthermia External heat stroke Malignant hyperthermia Neuroleptic malignant syndrome Lethal catatonia Thyrotoxicosis Pheochromocytoma Delirium tremens Status epilepticu Tetanus
Drugs that causes hyperthermia
β-blockers
Sympathomimetics
Anti-cholinergic
Salicylate toxicity
Decreased heat loss causes
Classic heat stroke
Occlusive dressings
Dehydration
Autonomic dysfunction
What leads to fever and how?
Pyrogens lead to fever by increasing the set point
Types of pyrogenes
Exogenous pyrogens (ex. bacteria, viruses, fungus, and allergens) Endogenous pyrogenes (ex. IL1, TNF, and IL-6).
Fever enhances host defences by
leading to increased neutrophil function (Enhanced migration and enhanced superoxide production), and increased mononuclear function (Enhanced interferon production and T-cell proliferation).
Fever alterates what
Endocrine alterations Autonomic alterations Behavioral changes Hematologic alterations Altered hepatocyte function
Endocrine alterations of fever
Increased production of CRH (which will increase ACTH and GC), GH, Aldosterone, insulin, glucagon, and acute phase reactants
Decreased production of TSH and ADH
Autonomic alterations of fever
Cutanenous vasoconstriction, increased HR, increased BP, and decreased sweating
Behavioural changes of fever
Seeking warmth Shivering Anorexia Somnolence (sleepiness) Malaise (general discomfort)
Hematologic alterations of fever
Leukocytosis, thrombocytosis, and decreased erythrocytosis
Altered hepatocyte function of fever
Increased production of acute phase proteins (CRP, serum amyloid A and fibrinogen)
Patterns of temperature change in fever
Intermittent
Remittent
Sustained
Relapsing
Intermittent fever
An intermittent fever is one in which temperature returns to normal at least once every 24 hours. These are commonly associated with conditions such as gram-negative/-positive sepsis, abscesses, and acute bacterial endocarditis
Remittent fever
In a remittent fever, the temperature does not return to normal and varies a few degrees in either direction.
Sustained fever
In sustained or continuous fever, the temperature remains above normal with minimal variations. These are seen in persons with drug-induced fever.
Relapsing fever
A recurrent or relapsing fever is one in which there is one or more episodes of fever, each as long as several days, with one or more days of normal temperature between episodes. Relapsing fevers may be caused by a variety of infectious diseases, including tuberculosis, fungal infections, Lyme disease, and malaria.
How many stages of fever?
4
First stage (prodromal stage) of fever
In prodromal stage body temperature rises, and there are nonspecific complaints such as mild headache and fatigue, general malaise, and fleeting aches and pains.
Second stage of fever
During the second stage there is sensation of being cold and the onset of generalized shaking, although the temperature is rising. When the shivering has caused the body temperature to reach the new set point of the temperature control center, the shivering ceases, and a sensation of warmth develops
Third stage of fever
In the third stage cutaneous vasodilation occurs, and the skin becomes warm and reddened
Fourth stage of fever
The fourth stage of the febrile response is marked by the initiation of sweating
During fever, the body switches from glucose to metabolism based on
Protein and fat breakdown
Metabolic acidosis can occur in fever if
Fat breakdown is rapid
Body temperature of 41 Celcius leads to
Delirium and seizures
Body temperature of 42 Celcius leads to
Coma, CNS damage and even death
Difference between fever and hyperthermia
(1) In fever, hypothalamic set-point is increased by cytokines, and peripheral mechanisms generate and conserve heat
(2) In hyperthermia hypothalamic set-point is normal, but peripheral mechanisms fail to match the set-point.
