Week 3-4 Flashcards
1
Q
What factors affect heat storage?
A
Metabolism - work - evaporation +/- conduction +/- convection +/- radiation
2
Q
What is conduction?
A
The transfer of heat to a moving gas or liquid
3
Q
What are the effectors to decrease temperature?
A
Skin blood vessels (dilate)
Sweat glands
Endocrine tissue
Behaviour
4
Q
What are the effectors to increase temperature?
A
Skin blood vessels (constrict) Arrector pili muscles Skeletal muscles Endocrine tissue Behaviour Brown adipose tissue
5
Q
Where are the central chemoreceptors found?
A
Hypothalamus (preoptic anterior hypothalamus)
Spinal cord
Viscera
Great veins
6
Q
Where are the peripheral thermoreceptors?
A
Skin, oral and urogenital mucosa
7
Q
How is temperature information conveyed to the brain?
A
Spino-thalamo-cortical pathway > discriminative temperature sensation
Spino-reticulo-hypothalamic pathway > thermoregulation
8
Q
What pathway is responsible for discriminative temperature sensation?
A
Spino-thalamo-cortical pathway
9
Q
What pathway is responsible for sensation for thermoregulation?
A
Spino-reticulo-hypothalamic pathway
10
Q
What is the classical model of thermoregulation?
A
Proposes a set point for temperature control:
The hypothalamus compares temperature signals to a set point
11
Q
What is non-shivering thermogenesis?
A
Heat is produced by brown adipose tissue, via mitochondrial uncoupling
12
Q
What 3 factors does stroke volume depend on?
A
Preload
Contractility
Afterload
13
Q
What is preload?
A
The degree of stretch of cardiomyocytes prior to contraction
14
Q
What influences contractility?
A
Sympathetic nerve activity
Frank-Starling mechanism
15
Q
Core body temperature range?
A
36 - 37.5’C
16
Q
When can core body temperature measurements vary?
A
Time of day (cooler in evening)
Time of month (higher in luteal phase)
Age
Pathology
17
Q
What is the role of thermoregulation?
A
Maintain core body temperature
18
Q
What 3 factors are the rate of evaporation dependent on?
A
Temperature and relative humidity
Amount of skin surface
convective currents around the body
19
Q
The majority of central thermoreceptors are…
A
Warm-sensitive neurons
20
Q
The majority of peripheral thermoreceptors are…
A
Cold-sensitive neurons.
21
Q
How do cold-sensitive peripheral thermoreceptors transmit impulses?
A
Via thin myelinated A-delta fibres
22
Q
How do warm-sensitive peripheral thermoreceptors convey impulses?
A
Via unmyelinated C fibres
23
Q
What are TRPs?
A
Transient receptor potential ion channels: a superfamily of proteins expressed in cell membranes.
Subtypes for specific temperature ranges
24
Q
Where does information from skin afferents (cold and warm) enter the spinal cord?
A
Dorsal horn (lamina I)
25
Outline the spino-reticulo-hypothalamic pathway (for thermoregulation)
Second-order neurons (lamina I)
> lateral parabrachial nucleus reticular formation
>> median preoptic nucleus (hypothalamus)
26
What is sweating activated by?
Sympathetic cholinergic nerves
27
How is vasodilation achieved to regulate the core body temperature?
Initially: withdrawal of noradrenergic sympathetic vasoconstriction
Later: cholinergic sympathetic nerves
28
What happens if heat loss mechanisms fail?
Heatstroke
Seizures
Brain, liver and kidney damage
Death (extreme)
29
How is vasoconstriction achieved to regulate the core body temperature?
Adrenergic sympathetic nerves
30
What is piloerection?
Goosebumps
31
How is piloerection evoked?
By an increase in sympathetic neural discharge to skin: alpha-1-adrenergic response
32
Where is brown adipose tissue located?
```
Supraclavicular region
Neck
Mediastinum
Para-aortic region
Supra-renal region
```
33
What does brown adipose tissue do regarding thermoregulation?
Is the site of non-shivering thermogenesis: the cells make heat via mitochondrial uncoupling
34
Approximately how much ATP is stored in the body?
250g
35
What are the 7 factors affecting the maximal oxygen consumption rate?
```
Age
Genetics
State of physical health
Environment
Mode of activity performed
Gender
Intensity and volume of training
```
36
What are the 3 adjustable factors affecting the maximal oxygen consumption rate?
State of physical health
Mode of activity performed
Intensity and volume of training
37
What are the 3 physiological determinants of the maximal oxygen consumption rate?
Lungs
Heart
Muscle
38
What is the Fick Principle?
An equation determining the maximal oxygen consumption rate:
| V.O2max = cardiac output x (difference on the contents of O2 in the arterial and venous blood)
39
What determines cardiac output?
Heart rate x stroke volume
40
What is stroke volume dependent on?
Contractility and end-diastolic volume
| Negatively by afterload?
41
What is an ionotrope?
An agent that alters the force/strength of a muscular contraction
42
What ionotropes contribute to increased contractility of the heart?
Catecholamines: noradrenaline and adrenaline
| Beta-agonists
43
What is blood pressure dependent on?
Cardiac output x total peripheral resistance
44
What contributes to an increase in heart rate up to 100bpm?
Vagal withdrawal
45
What contributes to an increase in heart rate above 100bpm?
Sympathetic drive
46
What contributes to an increase in end-diastolic volume, and hence to an increase in stroke volume (during exercise)?
Venoconstriction in splanchnic vessels
Skeletal muscle pump
Respiratory pump
47
What 3 factors contribute to increased cardiac contractility during exercise?
Increased circulating catecholamines (NE and E)
Increased sympathetic nerve activity
Increased heart rate (Bowditch effect, minimal)
48
What changes in blood pressure occur during moderate intensity exercise?
Increase in systolic,
Decrease in diastolic,
Slight increase in Mean Arterial Pressure
49
What direct and indirect vasodilatory influences occur in skeletal muscle during exercise?
Increased H+/lactate
Increased K+
Increased CO2, decreased O2
Endothelial-derived vasodilator factors e.g. nitric oxide
50
How is O2 extraction increased in exercising muscle?
Increased capillary density
Increased myoglobin
Increased mitochondrial density
Increase in oxidative enzymes (making ATP)
51
What are the 5 core components considered when designing a cardiorespiratory exercise programme?
```
Mode
Intensity
Frequency
Duration
Progressive
```
Also safety
52
What is sarcopenia?
Muscle loss with ageing
53
Role of muscular/medium arteries
Allow vessels to regulate blood supply by constricting or dilating (smooth muscle)
54
Outline the vasodilator theory of local response to low oxygen
Decreased oxygen concentration in blood
> increased vasodilator substance formation
>> increased diffusion of vasodilators to interstitial fluid
>>> decreased resistance at local precapillary sphincters and metarterioles
55
What is reactive hyperaemia?
Blood flow is blocked to a tissue. Increased vasodilatory metabolites > decreased resistance
When blood flow is restored, large compensatory blood flow is received due to vasodilated capillary bed.
Causes increased stress on endothelium >> release of NO >>> further dilation
56
What is active hyperaemia?
1. Increased metabolic demand due to increased tissue activity
2. Vasodilator substances formed by metabolism
3. Vasodilation > decreased resistance >> increased blood flow
57
Outline the oxygen/nutrient demand theory of local response to low oxygen
Oxygen is required for smooth muscle contraction, therefore if there is too little oxygen in the blood, the smooth muscle will dilate resulting in lower resistance
58
What are the 2 theories regarding acute local control of blood flow?
Vasodilator theory
| Oxygen/nutrient demand theory
59
What are 2 examples of the vasodilator theory of local response to low oxygen?
Reactive hyperaemia
| Active hyperaemia
60
In which tissues is autoregulation of local blood flow especially important?
Brain
| Heart muscle
61
Outline the metabolic theory of autoregulation of blood flow
1. Increased blood pressure
2. Increased blood flow
3. Decreased metabolite concentration
4. Decreased vasodilation
5. Increased resistance
6. Decreased blood flow
62
Outline the myogenic theory of autoregulation of blood flow
Sudden stretch of vessel wall
> stretch opens Ca++ channels
>> smooth muscle contracts
63
What 3 mechanisms/reflexes affect contractility of the heart muscles?
Bainbridge reflex
Bowditch effect
Frank-Starling mechanism
64
Explain the Frank-Starling Mechanism
Increase in venous return
> increased volume of blood in ventricles after diastole
>> increased cardiac contractility
>>> increased cardiac output
65
Explain the Bainbridge Reflex
Increased atrial pressure
> increased cardiac contractility
>> increased heart rate
66
Explain the Bowditch Effect
Increased heart rate (during exercise)
| > increased contractility
67
How is cardiac contractility decreased?
Parasympathetic (vagal) STIMULATION
| Sympathetic INHIBITION
68
How is cardiac contractility increased?
Catecholamines and beta-agonists
Sympathetic STIMULATION
Increased venous return (Frank-Starling Mechanism)
Increased heart rate during exercise (Bowditch Effect)
Increased atrial pressure (Bainbridge Reflex)
69
Vasoconstrictor nerve terminals release predominantly which chemical?
Norepinephrine
70
How does norepinephrine act to contract smooth muscle and vasoconstrict?
Acts on alpha adrenergic receptors of smooth muscle
71
What effect does sympathetic stimulation have on the adrenal medulla?
Stimulates the secretion of epinephrine and norepinephrine
72
Explain the volume reflex
Stretching of the atria
> kidney arterioles dilate, increasing fluid filtration
>> hypothalamus reduces ADH production
73
What's the difference between atherosclerosis and arteriosclerosis?
Atherosclerosis - a blood vessel is partially or totally occluded due to plaque formation in the vessel wall.
Arteriosclerosis - the elasticity of the blood vessel walls is reduced, resulting in a reduction of the Windkessel effect
74
How is afterload increased? What effect does it have?
Constricting blood vessels
| > impairs pumping
75
Define oxygen consumption (VO2)
The amount of oxygen taken up by the lungs.
76
Define cellular oxygen consumption
The amount of oxygen taken up/used by the cells
77
When are oxygen consumption and cellular oxygen consumption equal?
When the body is at a steady state.
78
Define maximum oxygen consumption (VO2max)
The maximal amount of oxygen the body can take up
79
The endothelium has a role in...
```
Mechanics of blood flow
Regulation of coagulation
Leukocyte adhesion
Vascular smooth muscle growth
Barrier to transvascular diffusion of liquids and solids
```
80
What are the 3 classifications of capillaries based on permeability?
Continuous
Fenestrated
Sinusoidal
81
What are sinusoidal capillaries?
Capillaries with a large diameter and large fenestrae
| Present in liver especially
82
What are intercellular clefts and what is their function in capillaries?
Channel between 2 adjacent endothelial cells
| Transport of water and soluble ions
83
What are caveolae and what is their function in capillaries?
Plasmalemma vehicles - vesicles made of caveolins (proteins associated with cholesterol and sphingolipids)
Transport larger molecules e.g. proteins, can form vesicular channels
84
What is caveolin?
A protein associated with cholesterol and sphingolipids
| Makes caveolae
85
What are the 4 mechanisms for long-term local blood pressure regulation?
Angiogenesis
Collateral circulation
Eutrophic remodelling of small blood vessels
Hypertrophic remodelling of large blood vessels
86
How does collateral circulation contribute to long-term local blood pressure regulation?
New blood vessels formed around a blocked vessel
| Dilation of existing collaterals
87
Explain hypertrophic remodelling of large blood vessels due to increased blood pressure.
Increase in size and number of vascular smooth muscle cells
| Cross-linking of collagen and fragmentation of elastin in ECM
88
Give examples of vasodilatory metabolites associated with local control of blood flow
```
Adenosine (from ATP degradation)
Adenosine phosphates
CO2
K+ ions
H+ ions (from lactic acid)
```
89
What is net filtration pressure in a capillary determined by?
+ Capillary pressure
+ Interstitial colloid osmotic pressure
- Interstitial fluid pressure
- Plasma colloid osmotic pressure
90
What is the Starling hypothesis?
That the net filtration across a capillary wall is approximately zero i.e. that the filtration and reabsorption is approximately equal
91
What are the 3 elements making up the interstitium?
Solid (collagen, proteoglycan fibres)
Gel (like plasma)
Liquid (small channels)
92
What is the function of the lymphatic system?
Reabsorb extravascular proteins, colloids etc. and return to circulation
93
What is peripheral vascular disease?
Atherosclerosis of peripheral arteries resulting in stenosis/thrombosis/embolism/aneurysm
94
Name 4 retinal vascular diseases
Haemorrhage
Cotton wool spots
Microaneurysm
Retinal artery occlusion
95
Define lymphoedema
Swelling of the tissue due to inadequate lymphatic drainage.
| Doesn't have to be lymphatic, can be due to any imbalance of Starling forces
96
Name 3 primary lymphoedema conditions
```
Distal obliteration (ankle, onset at puberty, affects females)
Proximal obliteration (leg, any age)
Congenital hyperplasia (leg, at birth and progressive)
```
97
What are the current treatments for lymphedema?
Exercise
Massage
Pneumatic compression
Compression garments
98
What signals govern the cardiac output during constant workload exercise?
1. central command, vagal withdrawal, muscle pump, sensory nerve activity due to movement
2. vasodilation in active muscle, stimulation of cardiovascular system (vasodilator factors)
3. baroreceptor reflex stabilisation
