Viral Diseases - Physiology

Question 1

Define homeostasis

Answer 1

A self-regulating process by which biological systems maintain stability while adjusting to change external conditions

Question 2

What mechanism is homeostatic contol by?

Answer 2

Negative feedback mechanism

Question 3

Describe the role of the hypothalamus

Answer 3

• Control centre
• Heat loss centre - preoptic and antrior nuclei
• Heat conservation centre - poseteior hypothlamic nuclei

Question 4

Describe the three interdependant components in homeostatic control mechanisms

Answer 4

1. Sensor - A receptor detects a change in the external environment
2. Control centre - The sensor sends the infomration to the control centre, whcih determines the necessray response
3. Effecors-the control centre sends signals to tissues and organs known as effectors. They make adjustment to bring the relevant varible back to set point

Question 5

a) What is the critical body core temperature?
b) What is the cricial body core temperature mainly dependant on?

Answer 5

a) 37.1 degrees celcius
b) Degree of activity

Heat temperture receptors in the hypothalamus in the anterior hypothalamic-preoptic area

Question 6

Describe the receptors involved in thermoregulation

Answer 6

Peripheral receptors

• Skin has both warmth and cold receptors
• Detect changes in skin temperature
• 10x as many cold receptors as warmth receptors

Central receptors

• Hypothalamus
• Detect chages in core body temperatyre
• Detect mainly cold than warm - concerned with preventing hypothermia

Question 7

a) What is hypothermia?
b) What is hyperthermia?

Answer 7

a) When the core body temperaure falls below 35 degrees celcius
b) When the core body temeperature rises above 40 degrees celcius

Question 8

a) What is the main sensory of temepraure
b) What is the control centre for temperature
c) What are the effectors for adjusting temperature?

Answer 8

a) Skin
b) Hypothalamus
c) Skin and muscles

Question 9

Describe the homeostatic control of temperature when the body is cold

Answer 9

Arteriolar vasoconstriction

• Reduces blood flow to prevent heat loss

Piloerection

• Sympatheic stimulation causes erector pili muscles attatched to hair follicle to contract
• Thicker layer of insulatin air trapped next to skin

Increase in thermogenesis

• Shivering - increase msucular activity generates heat
• Chemical excitation of heat production
• Thryoxine increases heat production

Sweating almost ceases

• minimal heat loss through evaporation

Question 10

Describe homeostatic control of temperarture when the body is too hot

Answer 10

Vasodilation

• Increase blood flow to skin increases heat loss

Sweating

• Evaporation of water in sweat leads to heat loss

Decrease in heat production

• Shivering and chemical thermogenesis strongly inhibited

Question 11

Describe the pathophysiology of fever

Answer 11

1. Fevere producing stimuli (pathogens) e.g. viruses, fungi
2. Activates immune system (macrophages and T-lymphocytes)
3. Cytokines (signalling molecules) breach the blood brain barrier and make way to hypothalamus
4. Hypothalamus increases temperature set level
5. Creates a hostile environment for pathogens

Question 12

Why do people shiver with a high temperature?

Answer 12

1. Higher temperature set level to make evenrionment hostile for patients
2. Person is below new termperature set level
3. Need to get hotter to meet temperature set level
4. Does this by shivering