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BIO125 Physiology > Week 1 Principles of physiology II - Thermodynamics > Flashcards

Week 1 Principles of physiology II - Thermodynamics Flashcards

1
Q

Which of the following statements best describes homeostasis?

  1. Keeping the body in a fixed and unaltered state.
  2. Dynamic equilibrium.
  3. Maintaining a near-constant internal environment
  4. Altering the external environment to accommodate the body’s needs.
  5. Altering weather to accommodate the body’s needs.
A
  1. Keeping the body in a fixed and unaltered state.
  2. Dynamic equilibrium.
  3. Maintaining a near-constant internal environment
  4. Altering the external environment to accommodate the body’s needs.
  5. Altering weather to accommodate the body’s needs.
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2
Q

Which of the following features of a system is unlikely to lead to a stable homeostatic system?

A. Negative feedback.

B. Positive feedback.

C. Redundancy.
D. Complexity.

E. Alloftheabove.

A

A. Negative feedback.

B. Positive feedback.

C. Redundancy.
D. Complexity.

E. Alloftheabove.

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3
Q

Define homostasis in terms of thermodynamics.

A

The dynamic maintence of physiological variables within a predictable range

dymanic = variable may fluctuate, but still within a ‘normal’ range and the average value will be predictable over longer periods of time

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4
Q

What is the purpose of homeostasis (short and long term) & hierarchy of importance?

A

Short term: immediate survival

Long term: Health & wellbeing, reproductive capabilities

Key point: hierarchy of importance (priority), the variable that is of greater immediate importance may be maintained at the expense of other (long terms important) variables

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5
Q

Homeostasis hierarchy of importance: physiological variables required for short term

A
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6
Q

Homeostasis hierarchy of importance: physiological variables required for long term

A
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7
Q

What is an example of neuronal negative feedback reflex arc?

A

Control of body temperature

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8
Q

What are poikilotherms?

A

body temperature varies with the environmental temperatures

(turtle)

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9
Q

What are homeotherms?

A

core body temperature maintained within narrow constant range despite variations in the envrionmental temperatures

(humans –> source of body heat is internal - by-product of metabolism)

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10
Q

How does metabolism generate heat?

A

energy is required to preform all of the chemical reactions of the body at rest.

A minimum level of energy required to live is called the BMR and generates heat

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11
Q

Why control temperature?

A
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12
Q

Why is thermoregulation important?

A

cellular function –> homeostasis ensures optimal temp for cellular metabolism

normal body temp = 37 􏰀C

Variations are caused by:

  • Diurnal
  • Menstrual cycle
  • Exercise
  • Age
  • Ambient temperature
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13
Q

Thermoregulation: maintenance of the core temperature Tc.

What is core temperature?

A

the temperature of the body around the main internal organs

Core Temp 37.8 degrees

  • CNS, abdominal & throrasic cavities
  • highest temp
  • preciesely regulated

Shell Temp 20 - 40 degrees

  • skin & subcutaneous fat
  • generally cooler than core

Heat exchanged between core and shell by blood

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14
Q

What are the different ways to measure core temperature (Tc)?

A
  • Oral
  • Aural
  • Rectal
  • Oesophageal
  • GI Tract (temeprature pill)
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15
Q

What are the mechanisms of heat transfer?

A
  1. Radiation
  2. Convection
  3. Conduction
  4. Evaporation
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16
Q

Mechanisms of heat transfer: What is Radiation?

A
  • emission of heat energy from surface of warm body
  • via electromagnetic waves
  • if skin temp > environment temp body loses heat by radiation
17
Q

Mechanisms of heat transfer: What is Convection?

A
  • gravitationally induced heat transport, diven by the expansion of air or fluid on heating
  • hot air has lower density –> rise
  • Forced convection (strong winds) can increase heat loss
18
Q

Mechanisms of heat transfer: What is Conduction?

A
  • transfer of heat between objects in direct contact
  • rate of heat transfer depends on temp difference & conductivity
19
Q

Mechanisms of heat transfer: What is Evaportion? (insensible and sensible loss & humidity)

A

requires thermal energy, absorbed from skin > cooling body

Insensible loss

  • continuous (passive)
  • respiratory airways (air is humidified)
  • skin

Sensible loss

  • regulated by sympathetic nervous control
  • SWEATING – eccrine sweat glands
  • normal = 100ml/day, hot environment = 1.5L/day, vigorous exercise = 4L/day

Humidity

  • amount of H2O vapour present in the air
  • relative humidity (%)
  • relative humidity high > air almost fully saturated with H2O
  • > limited evaporative heat loss
20
Q

What is the heat balance equation?

A

HEAT INPUT = HEAT OUTPUT

Heat balance can also be disrupted, mechanisms then kick into place

21
Q

Heat Balance: what makes up Heat Imput and Output?

A

Heat Imput

Internal –> Oxidation of fuel (50% efficiency)

External –> environment

Heat Output

External

  • Radiation (50% heat energy lost)
  • Conduction (small amount of heat lost)
  • Convection (significant heat loss)
  • Evaporation
    • hot day = only mechanism for heat loss
    • relative humidity *
22
Q

Thermoregulation and the CNS: What is involved in the negative feedback relfex arcs?

A

The autonomic nervous system

Neurological integrating centers for physiological control are located in the midbrain and brain stem.

Controls:

  • Temperature (acting on muscles & skin)
  • Osmolarity (acting on kidneys)
  • Blood pressure/flow control (ascting on heart & blood vessles)
  • Blood gas/ventilation control (acting on respiratory muscles/lungs)
23
Q

Thermoregulation and the CNS: How is the hypothalamus involved?

A

thermoregulatory integrating centre of central and peripheral sensory information

  • posterior region (activated by cold)
  • anterior region (activated by heat)

May respond to very small changes in blood temperature (0.01C)

24
Q

Thermoregulation and the CNS: What are themoreceptors?

A

Afferent input points that send info to hypothalamus

  • Central Sensors (CBT) - hypothalamus, abdominal organs (brain, spinal cord, internal organs)
  • Peripheral Sensors (skin)
  • Deep Body Sensors (spinal cord, abdominal viscera, great viens)
25
Q

Thermoregulation and the CNS is debated. Why?

A
  • No one area is the centre for thermoregulation
  • Instead, there appears to be hierarchy extending through hypothalamus, brain stem and spinal cord
  • Lower brain stem and spinal structures can crudely sense changes in Tc and initiate certain responses
  • Medial and lateral parts of the preoptic nucleus, the anterior hypothalamus and nearby regions of the septum (the preoptic region) provide higher control
26
Q

How is thermoregulation triggered (the effectors)?

A
  1. Peripheral blood vessels
  2. Sweat glands – eccrine
  3. Skeletal muscles
27
Q

Thermoregulation Effectors: what are peripheral blood vessles?

A
  • vasoconstriction / vasodilation alters blood flow to skin
  • >> control conductive & radiative heat loss
28
Q

Thermoregulation Effectors: what are sweat glands (eccrines)?

A
  • control evaporative heat loss
  • ↑↓ sweat production (sympathetic control)
29
Q

Thermoregulation Effectors: what are skeletal muscles?

A
  • Shivering - increase in muscle tone
  • rapid involuntary rhythmic contractions (10-20/sec)
  • ALL energy liberated is converted to heat
  • 2-5 fold increase in heat within secs/mins
30
Q

What are skin vasomotor responses?

A

AIM = alter temp gradient between skin & environment

  • radius of blood vessels determines blood flow
  • skin blood flow varies (400-2500 ml/min)
31
Q

How are skin vasomotor responses controlled?

A

SYMPATHETIC NERVOUS SYSTEM

↑ sympathetic activity > vasoconstriction

  • ­ ↑ resistance ↓ BF ↓ skin temp
  • ↓ conductive & radiative heat loss

Conserves heat

↓ sympathetic activity > vasodilation

  • ↓ resistance ↑ BF ↑ skin temp
  • ↑ conductive & radiative heat loss

Loses heat

32
Q
A
33
Q

During cold exposure, what are the affects (Hypothalamus - posterior region)?

A
  • Vasoconstriction
  • Shivering
    • heat producing
    • skeletal muscles (­ increase muscle tone)
  • Piloerection
    • sympathetic NS
    • muscles at base of hair contract
    • creates dead space
      • decrease thermal gradient
  • Behavioural
    • hypothalamus & limbic system
    • voluntary
34
Q

During heat exposure, what are the affects (Hypothalamus - anterior region)?

A
  • Vasodilation
  • Sweating
    • Eccrine sweat glands
    • relative humidity essential
      • high humidity, evaporation slow
    • environmental temp
      • ONLY mechanism for heat loss
  • Behavioural
    • hypothalamus & limbic system
    • voluntary
35
Q

Define a fever. How does it work?

A

elevation of body temperature as result of infection / inflammation

  • Trigger = infection or inflammation
  • Response = WBCs proliferate & secrete chemical substances
    • endogenous pyrogens = “fever-inducers”
      • stimulate release of prostaglandins
    • increase hypothalamic set point
  • NB. intentional response of body notfailure of thermoregulatory system - increase temp augments immune response*
36
Q

How does aspirin work?

A

Acts on the prostaglandins, to not have a fever.

Sir John Vane, Nobel Prize 1982 “their discoveries
concerning prostaglandins and related biologically active substances”.

Instrumental in the understanding of how aspirin produces pain-relief and anti-inflammatory effects.

37
Q

Which of the following strategies would not help restore a high body temperature to normal?

  1. Non-shivering thermogenesis
  2. Sweating
  3. Flattening of skin hair
  4. Redistribution of blood flow to the periphery
  5. Shivering thermogenesis
A
  1. Non-shivering thermogenesis
  2. Sweating
  3. Flattening of skin hair
  4. Redistribution of blood flow to the periphery
  5. Shivering thermogenesis

BIO125 Physiology (17 decks)

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