Week 1 Principles of physiology II - Thermodynamics Flashcards
Which of the following statements best describes homeostasis?
- Keeping the body in a fixed and unaltered state.
- Dynamic equilibrium.
- Maintaining a near-constant internal environment
- Altering the external environment to accommodate the body’s needs.
- Altering weather to accommodate the body’s needs.
- Keeping the body in a fixed and unaltered state.
- Dynamic equilibrium.
- Maintaining a near-constant internal environment
- Altering the external environment to accommodate the body’s needs.
- Altering weather to accommodate the body’s needs.
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. Negative feedback.
B. Positive feedback.
C. Redundancy.
D. Complexity.
E. Alloftheabove.
Define homostasis in terms of thermodynamics.
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
What is the purpose of homeostasis (short and long term) & hierarchy of importance?
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
Homeostasis hierarchy of importance: physiological variables required for short term
Homeostasis hierarchy of importance: physiological variables required for long term
What is an example of neuronal negative feedback reflex arc?
Control of body temperature
What are poikilotherms?
body temperature varies with the environmental temperatures
(turtle)
What are homeotherms?
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)
How does metabolism generate heat?
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
Why control temperature?
Why is thermoregulation important?
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
Thermoregulation: maintenance of the core temperature Tc.
What is core temperature?
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
What are the different ways to measure core temperature (Tc)?
- Oral
- Aural
- Rectal
- Oesophageal
- GI Tract (temeprature pill)
What are the mechanisms of heat transfer?
- Radiation
- Convection
- Conduction
- Evaporation
Mechanisms of heat transfer: What is Radiation?
- emission of heat energy from surface of warm body
- via electromagnetic waves
- if skin temp > environment temp body loses heat by radiation
Mechanisms of heat transfer: What is Convection?
- 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
Mechanisms of heat transfer: What is Conduction?
- transfer of heat between objects in direct contact
- rate of heat transfer depends on temp difference & conductivity
Mechanisms of heat transfer: What is Evaportion? (insensible and sensible loss & humidity)
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
What is the heat balance equation?
HEAT INPUT = HEAT OUTPUT
Heat balance can also be disrupted, mechanisms then kick into place
Heat Balance: what makes up Heat Imput and Output?
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 *
Thermoregulation and the CNS: What is involved in the negative feedback relfex arcs?
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)
Thermoregulation and the CNS: How is the hypothalamus involved?
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)
Thermoregulation and the CNS: What are themoreceptors?
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)
Thermoregulation and the CNS is debated. Why?
- 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
How is thermoregulation triggered (the effectors)?
- Peripheral blood vessels
- Sweat glands – eccrine
- Skeletal muscles
Thermoregulation Effectors: what are peripheral blood vessles?
- vasoconstriction / vasodilation alters blood flow to skin
- >> control conductive & radiative heat loss
Thermoregulation Effectors: what are sweat glands (eccrines)?
- control evaporative heat loss
- ↑↓ sweat production (sympathetic control)
Thermoregulation Effectors: what are skeletal muscles?
- 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
What are skin vasomotor responses?
AIM = alter temp gradient between skin & environment
- radius of blood vessels determines blood flow
- skin blood flow varies (400-2500 ml/min)
How are skin vasomotor responses controlled?
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
During cold exposure, what are the affects (Hypothalamus - posterior region)?
- 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
During heat exposure, what are the affects (Hypothalamus - anterior region)?
- Vasodilation
- Sweating
- Eccrine sweat glands
- relative humidity essential
- high humidity, evaporation slow
- environmental temp
- ONLY mechanism for heat loss
- Behavioural
- hypothalamus & limbic system
- voluntary
Define a fever. How does it work?
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
-
endogenous pyrogens = “fever-inducers”
- NB. intentional response of body notfailure of thermoregulatory system - increase temp augments immune response*
How does aspirin work?
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.
Which of the following strategies would not help restore a high body temperature to normal?
- Non-shivering thermogenesis
- Sweating
- Flattening of skin hair
- Redistribution of blood flow to the periphery
- Shivering thermogenesis
- Non-shivering thermogenesis
- Sweating
- Flattening of skin hair
- Redistribution of blood flow to the periphery
- Shivering thermogenesis
