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A Human Physiology > Arteries > Flashcards

Arteries Flashcards

1
Q

What is the vascular system?

A

The conducting pathways of the arterial and venous circulations, which run in parallel and are separated by dense networks of tiny vessels

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2
Q

What are the five composites of the arteries?

A

Adventitia, smooth muscle, elastic ,endothelium, pre-capillary sphincter

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3
Q

What does the adventitia do?

A

Provides structural strength and tethers vessels in place; in large vessels contains small blood vessels (vasa vasorum)

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4
Q

What does the smooth muscle do?

A

Supplies vessels with contractile power, regulating diameter of lumen

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5
Q

What does the elastic tissue do?

A

Gives mechanical strength and elastic properties

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6
Q

What does the endothelium do?

A

Filtering interface between blood and body; secretes vasoactive products

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7
Q

What does the pre-capillary sphincter do?

A

Controls blood flow to specific capillary beds selectively

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8
Q

What is smooth muscle?

A

Cells form layers and line cavities of hollow organs

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9
Q

What are features of smooth muscle?

A

Contractions are controlled by ANS; connected to each other electrically and mechanically (but not always); contract slowly but longly, without fatigue; has no sarcomere arrangement, and no NMJ

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10
Q

How is smooth muscle connected mechanically?

A

By specialised areas on membrane (dense bonds)

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11
Q

How is smooth muscle connected electrically?

A

By gap junctions on membrane; allows contraction as unit

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12
Q

How are contractile filaments arranged in smooth muscle?

A

Actin and myosin arranged in form of a lattice around the cell; actin is attached to cell via specialised areas in cytoplasm (dense bodies)

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13
Q

Where are neurotransmitters released from in smooth muscle?

A

As there are no NMJs, NTs are released non-specifically from varicosities

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14
Q

What is single unit smooth muscle?

A

Electrically coupled muscle cells by gap junctions; act as unit; blood vessels, intestines, uterus

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15
Q

What is multi-unit smooth muscle?

A

Not electrically coupled, so each cell needs to activated by a nerve; lung airways, large arteries

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16
Q

What is the implication of the lack of sarcomere arrangement in smooth muscle?

A

Myosin and actin can slide past each other without encountering ends of sarcomere, so less myosin and actin is needed (often ~50% myosin, can be 200% actin), and force of contraction can vary over a large range of lengths as actin and myosin still overlap

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17
Q

Why is it helpful that force of contraction can be maintained in smooth muscle over a larger range of lengths?

A

Most smooth muscles surround hollow structures and organs that undergo changes in volume; smooth muscle fibres retain ability to develop tension even with large increases in volume

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18
Q

How is contraction of smooth muscle regulated?

A

By Ca2+ entering the cell (instead of Ca2+ from SR); can be graded instead of all-or-nothing

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19
Q

What are the two types of action potentials in smooth muscle?

A

Pacemaker potential and slow waves

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20
Q

What are pacemaker potential action potentials?

A

Activates at regular intervals to allow regular contraction; intervals can change

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21
Q

What are slow waves?

A

A state of readiness, with fluctuations in polarisation below threshold; contract only when stimulus pushes slow waves upwards and meet threshold potential, firing action potentials successively as needed

22
Q

What determines if the process of action potentials forming from slow waves continues?

A

Depends how much slow wave is pushed up; if all slow wave if within threshold, continuous contractions occurs; if some slow wave is within threshold and some aren’t, contraction is interrupted

23
Q

How do action potentials stimulate muscular contraction in smooth muscles?

A

Depolarisation opens v-gated Ca2+ gates on sarcolemma; Ca2+ in; Ca2+ activates calmodulin; activated calmodulin activates myosin light-chain kinase; activated myosin light-chain kinase phosphorylates myosin; phosphorylated myosin is activated and binds to actin. Process only occurs if myosin is being phosphorylated at a higher rate than myosin light chain phosphotase is dephosphorylating myosin (which is always occuring)

24
Q

Where is the Ca2+ for smooth muscle contraction sourced from?

A

Extracellular fluid and sarcoplasmic reticulum

25
Q

How is flow of CV system changed?

A

MAP must be maintained, and venous pressure is small so can be ignored; arterioles alter levels of resistance to blood flow to distribute available amount of blood to where it is needed

26
Q

What is hyperemia?

A

Increase in blood flow according to metabolic needs of tissue in question (e.g. to deliver more oxygen, remove metabolites)

27
Q

What are chemical changes that take place locally when metabolic rate increases?

A

Tissue hypoxia; increased CO2, decreased pH, accumulation of K+, ATP, bradykinin, NO

28
Q

What is flow autoregulation?

A

Maintenance of blood flow rather than changing it

29
Q

What does flow autoregulation do when driving pressure increases?

A

When arterial pressure increases, a transient rise in blood flow occurs; increased flow removed the vasodilators; vessel constricts; flow returns to normal

30
Q

What is the stretch stimuli to muscle?

A

A myogenic response, based on metabolic factors

31
Q

What is the myogenic regulation of arteriole size?

A

An intrinsic regulation of smooth muscle to regulate flow; transient increase in pressure = increase in diameter of vessel = stretch in smooth muscle, which sends signal to smooth muscle, which constricts in response

32
Q

How is the arteriole size influenced by neural activity?

A

Sympathetic innervation; non-adrenergic and non-cholinergic fibres

33
Q

How does sympathetic innervation affect arterial size?

A

Release more NE on alpha-adrenergic receptors vasoconstricts (and opposite is true)

34
Q

How does innervation by non-adrenergic and non-cholinergic fibres affect arterial size?

A

Release of NO vasodilates (and possibly other unidentified vasoactive substances)

35
Q

What hormones cause vasodilation?

A

Adrenaline (on beta-2 receptors); atrial natriuretic peptide

36
Q

What hormones cause vasoconstriction?

A

Adrenaline (on alpha); angiotensin II; vasopressin

37
Q

What role does the endothelium have in controlling arterial size?

A

Major source of paracrines which regulate vessel size locally, allowing very specific regulation of flow

38
Q

What vasodilators does the endothelium release?

A

NO and prostacyclin

39
Q

What vasocontrictors does the endothelium release?

A

Endothelin-1

40
Q

How does shear stress affect the endothelium?

A

Affects bigger arteries, which respond to increased flow increasing force exerted on walls by dilating; increase NO and PGI2 and decrease ET1 in response to shear stress

41
Q

What are features of capillaries that enable them to carry out their function?

A

Numerous to reach each part of body; large SA; thin; low velocity

42
Q

Why are capillaries thin and create large SA?

A

Have just a single layer of endothelial cells; flow of gas proportional to SA, inversely proportional to thickness (Fick’s law)

43
Q

Why is velocity of capillaries so low?

A

Allows time during which diffusion can reach equilibrium

44
Q

What determines the flow in capillaries?

A

Total CSA (increased CSA = slower flow)

45
Q

What are the three types of capillary endothelial arrangements, and examples?

A

Continuous: muscle, nerve, fat, lymph nodes; fenestrated: glands, kidneys, intestines; discontinuous (sinusoids): liver, bone marrow, spleen

46
Q

What are three types of transport which occurs across endothelium of capillaries?

A

Diffusion, vesicle transport, bulk flow

47
Q

What is transported across endothelium by diffusion?

A

O2, Co2, glucose, amino acids, FAs

48
Q

What is transported across endothelium by vesicle transport?

A

Large molecules, e.g. proteins

49
Q

What is transported across endothelium by bulk flow?

A

Water, solutes

50
Q

How do you calculate net pressure in a capillary?

A

Hydrostatic - osmotic pressure

51
Q

What occurs when hydrostatic pressure > osmotic pressure?

A

Filtration

52
Q

What occurs when hydrostatic pressure < osmotic pressure?

A

Absorption

A Human Physiology (24 decks)

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