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Physiology > Regulation Of Circulation And Specialised Circulations > Flashcards

Regulation Of Circulation And Specialised Circulations Flashcards

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1
Q

What are the three distinct layers of the blood vessels?

A

Tunica intima - innermost endothelium
Basal membrane - fenestrated
Adventia - contains more collagen for new smooth muscle production

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2
Q

How do elastic arteries work?

A

They have elastin proteins that allow them to stretch to take the volume of blood at the pressure generated by the left ventricle

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3
Q

Given an example of an elastic artery

A

The aorta
Branches coming for the aorta

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4
Q

What is the importance of elasticity?

A

It maintains the diastolic pressure in the arterial system and contributes to the after load of cardiac output

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5
Q

Where does the majority of the resistance of the arterial system come from?

A

Arterioles

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6
Q

Why are pressures generated by the right side of the heart lower?

A

The pulmonary arteries are wider and more compliant

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7
Q

What are conduit arteries?

A

They are more muscular and feed blood to the smaller arteries of the organs

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8
Q

How do conduit arteries avoid compression at areas such as joint?

A

They have thick walls that prevent compression and collapse

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9
Q

What is the innervation of conduit arteries?

A

They have denser noradrengeric innervation of sympathetic vasoconstrictor fibres.
Cause vasoconstriction when active

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10
Q

What are small arteries or arterioles?

A

They are the resistance vessels where pressure falls sharply from one end to the other - pre-capillary spinsters

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11
Q

What innervation is there to arterioles?

A

Dense sympathetic noradrenergic innervation causing vasoconstriction
Can effectively determine the number of capillaries in which blood flows

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12
Q

What happens when sympathetic innervation is removed to arterioles?

A

This causes vasodilation to reduce resistance to blood flow and increase perfusion of capillary beds

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13
Q

What effect do metabolites produced during muscle activation cause?

A

They dilate local vessels to that area

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14
Q

What are capillaries?

A

They are the exchange part of the circulation as the walls are extremely thin and comprise of a single layer of endothelium

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15
Q

Why do capillaries provide little resistance to flow?

A

Because of the sheer number of capillaries in all systemic tissues

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16
Q

What three things that filtration across the capillaries depend on?

A

Balance of hydrostatic pressure within the capillary
Tissue pressure if surround tissues
Starlings forces - the colloid osmotic pressures in the vessels and extracellular fluid

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17
Q

What is oedema?

A

Vessels become leaky to water under situations such as inflammation leading to oedema

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18
Q

Where does diapedesis occur?

A

At capillaries

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19
Q

What is diapedesis?

A

The movement of WBC from the circulatory system and towards the site of tissue damage/infection

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20
Q

Explain the steps of diapedesis

A

i) chemotaxins are released bu damaged tissue
ii) They cross the endothelium and attract and activate WBC - neutrophils
iii) Neutrophils then stick to the endothelium and begin separating their cells
iv) A pododcyte of the neutrophil will extend through the gap and others will follow it towards the site of injury

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21
Q

What are arteriovenous anastomoses

A

They are shunt vessels found mostly in the skin that connect arterioles to venues directly
Bypassing capillaries

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22
Q

What innervation do arteriovenous anastomoses have?

A

Dense sympathetic innervation from the hypothalamic areas involved in temperature regulation

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23
Q

How is heat lost through the skin?

A

Removal of sympathetic innervation to the arteriovenous anastomoses so that blood can flow into the deep subcutaneous venous plexus

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24
Q

How are venules different from veins?

A

They are much smaller and more numerous

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25
What prevents back flow of blood in veins?
Semilunar valves Absent in large central veins and veins of the head
26
Do venules offer resistance to blood flow?
No very little resistance is offered
27
What innervation do venules have?
Sympathetic noradrengeric When innervated will vasoconstrict to route more blood back to the heart
28
How do muscle help veins?
Muscle contraction squeezes thin walled veins and pushes the blood along towards the heart
29
What do lymphatic vessels do?
They help maintain fluid balance in extracellular fluid They help mop up fat droplets They also have an immune function
30
How do lymphatic vessels work?
The endothelial cells are less tightly packed together so they are leaky, this allows fluid to enter from the surround extracellular fluid They have valves to ensure one way flow They return the fluid to the vena cava
31
What is vascular pressure?
The pressure created by the left the ventricle
32
What is the journey of vascular pressure?
They left ventricle develops a systolic pressure of 120mmHg From the aorta it drops to 80mmHg - pressure is now pulsatile In arterioles the pressure drops to 50mmHg - due to high resistance Pressure continues to fall through capillary beds By the time it reaches the vena cava it is close to zero
33
What is pulse pressure?
The difference between systolic and diastolic pressures
34
What is a normal pulse pressure?
40mmHg But it increases as you get older
35
Why does pulse pressure change with age?
Elastin fibres are lost and replaced with collagen fibres, and vessels become stiffer and less complaint
36
What is mean arterial pressure?
The diastolic pressure + 1/3 systolic pressure Normally it is around 93mmHg
37
Why are pulmonary pressures lower than systemic pressures?
Resistance in pulmonary flow is lower Because the vessels are wider and more compliant Systemic pressures must get around the whole body, pulmonary pressures only need to reach the lungs
38
Why are veins more compliant than arteries
They have less muscle mass Greater distension and blood volume carried
39
What is the difference in veins between low pressure and high pressure?
Low pressures - veins are relatively collapsed High pressures - they distend and become rounder
40
What innervation do veins have?
Moderate degree of sympathetic This increases activity of smooth muscle contractions and stiffen the vessel
41
What is the Frank-Starling mechanism?
More in - more out
42
How are smooth muscle cells arranged?
Small dense bodies anchor the actin while myosin fibres suspend between them
43
What are the difference between smooth muscle cells and skeletal muscle cells?
They are smaller, long (20-500 micrometers) and thin (1-5 micrometers) They are interconnected by gap junctions - allows for rapid conduction
44
How does smooth muscle function?
It has underlying rhythmical contractions, that produce phasic, slow rhythmical contractions Forces generated are smaller and can be maintained for longer periods (hours / days)
45
Steps to smooth muscle contraction
i) sympathetic nerves release noradrenaline ii) G-protein coupled receptors release second messengers (DAG) which open calcium channels - rapids calcium increase iii) Depolarisation can cause calcium to come in from the extracellular fluid as well iv) calcium induced calcium release - calcium binds of receptors on sarcoplasmic reticulum v) Calcium or 2nd messengers may also interact with ion channels to cause depolarisation vi) increased calcium binds to calmodulin this complex activated enzyme myosin light chain kinase vii) Myosin is then phosphorylated and cross bridging commences viii) contraction can maintain even after dephosphorylation
46
What is Poiseuille’s law?
That flow of a fluid is directly proportional to the viscosity of blood and the length of the vessel While being inversely proportional to the 4th power of the radius of the vessel
47
What effect does radius have on resistance to flow?
A small decrease in radius will cause a large increase in resistance and consequently reduction in flow
48
Define viscosity
Viscosity of blood is the resistance of fluid against flow
49
What is the equation for arterial pressure?
Pa = CO x TPR
50
What is the equation of cardiac output?
CO = SV x HR
51
Why is the equation for arterial blood pressure important?
It shows the three elements that medications target to alter arterial BP
52
Why is vascular resistance important?
Without resistance there would be maximal dilation and maximal flow, and this would exceed the maximal CO we are capable of by a factor of two
53
What is basal tone?
The balance of dilator and constrictor influences acting on smooth muscle
54
What are the extrinsic influences?
Nervous control Circulating hormones
55
What are the intrinsic factors ( local within organ)?
Myogenic response Temperature and pressure Tissues metabolites Vasoactive chemicals and autocoids Endothelial secretions (e.g. nitric oxide)
56
What are the two sources of calcium for smooth muscle use?
Influx from surrounding extracellular fluid Internal stores of the sarcoplasmic reticulum
57
What is active vasoconstriction?
Sympathetic nerves nerves release noradrenaline which bind to adrenoreceptors and cause vasoconstriction
58
What is passive vasodilation?
Sympathetic nerve activity decreases
59
What causes active vasodilation?
Some sympathetic nerves will cause vasodilation by the release of ACh
60
How does the sympathetic neuroeffector junction work?
Adrenergic receptors are distributed all over the smooth muscle so when transmitter is released it diffuses and interacts with receptors all around the varicosities
61
Where does acetylcholine work during sympathetic innervation?
The sympathetic ganglionic synapse
62
Where does noradrenaline work during sympathetic innervation?
At the neuroeffector junction
63
Where do cotransmitters work?
On the postsynaptic membrane of the target tissues
64
Where do neuromodulators work?
On the sympathetic nerve terminals from which they’re released
65
What receptors does noradrenaline have a greater affinity for?
Alpha receptors Coupled to G protein and Gq
66
What receptors does adrenaline have a greater affinity for?
Beta receptors Coupled to Gs G protein
67
How does sympathetic innervation reach the blood vessels?
Promoter neurones travel to the spinal cord, synapse with preganglionic neurones, exit the spine and travel to sympathetic ganglia then synapse with postganglionic neurones

Physiology (9 decks)

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