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BMEG 410 > 6 - Circulation > Flashcards

6 - Circulation Flashcards

1. Describe how pressure gradients, resistance and blood vessel radius affect blood flow. 2. Compare and contrast the structure of the major classes of blood vessel. 3. Describe the pressure changes across the vascular tree, systolic and diastolic pressure and the concept of mean arterial pressure. 4. Explain how arteriolar radius can change and what impact this would have on blood flow. 5. Describe the concept of total peripheral resistance and discuss how local and nervous control influences i

1
Q

Blood Flow

A

The rate of blood flow through a vessel (volume of blood passing through per unit of time) is directly proportional to the pressure gradient and inversely proportional to vascular resistance
F=change in P / R (resistance of vessels)

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2
Q

Pressure Gradient

A

the pressure difference between beginning and end of a vessel
– Blood flows from area of higher pressure to area of lower pressure

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3
Q

Resistance

A

measure of opposition of blood flow through a vessel

dependent on blood viscosity, vessel length, vessel radius

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4
Q

What is the major determinant of resistance to flow?

A

The vessel’s radius
Slight change in radius produces significant change in blood flow
R is proportional to 1/r^4

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5
Q

The Vascular Tree

A

The systemic and pulmonary circulations each consist of a closed system of vessels

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6
Q

Arteries

A

Carry blood away from heart to tissues –

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7
Q

Arterioles

A
  • Smaller branches of arteries

- major resistance vessels

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8
Q

Capillaries

A
  • Smaller branches of arterioles

* Smallest of vessels across which all exchanges are made with surrounding cells

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9
Q

Venules

A

Formed when capillaries rejoin

- Return blood to heart

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10
Q

What does the vascular tree consists of?

A

Arteries, Arterioles, Capillaries Venules, and veins

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11
Q

Veins

A

Formed when venules merge
- Return blood to heart
– Large radius offers little resistance to blood flow
– Also serve as blood reservoir

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12
Q

What 2 functions do arteries serve?

A
  1. Serve as rapid-transit passageways for blood from heart to organs
  2. Act as pressure reservoir to provide driving force for blood when heart is relaxing
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13
Q

How do arteries serve as rapid-transit passageways for blood from heart to organs?

A

Due to large radius, arteries offer little resistance to blood flow

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14
Q

How do arteries act as pressure reservoir to provide driving force for blood when heart is relaxing?

A

Arteries can be stretched and also recoil back to contract and push blood through.

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15
Q

What does arterial connective tissue contain?

A

– Collagen fibres: provide tensile strength

– Elastin fibres: provide elasticity to arterial walls

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16
Q

What does the force exerted by blood against a vessel wall depend on?

A

– Volume of blood contained within vessel

– Compliance of vessel walls

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17
Q

Systolic pressure

A

– Peak pressure exerted by ejected blood against vessel walls during cardiac systole
– Averages 120 mm Hg

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18
Q

Diastolic pressure

A

– Minimum pressure in arteries when blood is draining off into vessels downstream
– Averages 80 mm Hg

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19
Q

Arterial Pressure

A

the force exerted by blood against a vessel

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20
Q

Mean Arterial Pressure

A

Average pressure driving blood forward into tissues throughout cardiac cycle

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21
Q

Why is mean arterial pressure not the average pressure between the diastolic and systolic pressures?

A

Mean arterial pressure would be lower if we took the average, as diastole lasts longer than systole.

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22
Q

Radius supplying individual organs can be

adjusted independently to

A

– Distribute cardiac output (blood flow) among systemic organs, depending on body’s momentary needs
– Help regulate arterial blood pressure

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23
Q

Vasoconstriction

A

the narrowing of a vessel

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24
Q

Vasodilation

A

the enlargement in circumference
and radius of vessel
• Results from relaxation of smooth muscle layer
• Leads to decreased resistance and increased flow through that vessel

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25
Q

Vasocontriction And Vasodilation

A
  • The thick layer of smooth muscle surrounding each arteriole is richly innervated by sympathetic nerve fibres.
  • Smooth muscle is sensitive to many local chemical changes and to a few circulating hormones.
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26
Q

What are the mechanisms involved in adjusting arteriolar resistance?

A

Vasoconstriction and Vasodilation

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27
Q

How does smooth muscle regulate arteriolar resistance?

A
  • The thick layer of smooth muscle surrounding each arteriole is richly innervated by sympathetic nerve fibres.
  • Smooth muscle is sensitive to many local chemical changes and to a few circulating hormones.
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28
Q

Vascular Tone

A

Smooth muscle displays a state of partial constriction “at rest.”
It is the degree of constriction experienced by a blood vessel relative to its maximally dilated state.

29
Q

What are the two factors responsible for vascular tone?

A

– Myogenic activity of smooth muscle (i.e. activity produced by muscle without any external stimulation)
– Sympathetic stimulation (norepinephrine) of smooth muscle

30
Q

Local Control of Arteriolar Radius

A

Changes within other organs alter radius of vessels and adjust blood flow to organ

31
Q

What determines the amount of CO received by each organ?

A

The # and caliber of the arterioles supplying that area.

32
Q

Sympathetic stimulation (norepinephrine) of smooth muscle

A

used to adjust the total peripheral resistance

33
Q

Extrinsic Sympathetic Control of Arteriolar Radius

A
  • Local controls override sympathetic vasoconstriction for organ-specific regulation
  • No parasympathetic innervation to arterioles
34
Q

What are the local physical influences on arteriolar radius?

A

– Local application of heat or cold
– Chemical response to shear stress
– Myogenic response to stretch

35
Q

What are the local chemical influences on arteriolar radius?

A

– Local metabolic change

– Histamine release

36
Q

How are capillaries efficient?

A

As sites of exchange between blood and surrounding tissue cells, they are thin-walled, small-radius, extensively branched to maximize surface area and minimize diffusion distance
- Slow velocity through capillaries allows adequate time for exchange of materials

37
Q

Two types of passive exchanges in capillaries

A

– Diffusion (movement of solute due to
concentration gradient)
– Bulk flow (movement of water and solutes together due to pressure gradient)

38
Q

How does velocity of flow related to cross sectional area in the circulator system?

A

Velocity of flow is inversely proportional to the total cross-sectional area of all the vessels at any given level of the circulatory system

39
Q

What is the role of bulk flow?

A
  1. Important in regulating the distribution of ECF between the plasma and the interstitial fluid
  2. KEEP PLASMA FUNCTION CONSTANT to ensure that the circulatory system functions effectively
40
Q

Blood Brain Barrier (BBB)

A

Site of capillary exchange
Great control of brain interstitial fluid
Highly regulated

41
Q

Why is there a Blood Brain Barrier?

A
  • chemical fluctuations in the blood
  • harmful blood-borne substances reaching central neural tissue
  • Hormones that could act as neurotransmitters in the brain producing uncontrolled nervous activity
42
Q

How is control of brain interstitial fluid maintained? (BBB)

A

The only possible exchanges are through the capillary cells themselves, endothelial cells are connected with tight junctions

43
Q

The endothelial cells in brain capillaries are joined by what type of cell-cell adhesion?

A

tight junctions = NO PORES

pore size varies across organs, no pores in brain

44
Q

The Lymphatic System

A
  • Provides accessory route by which fluid can be returned from interstitial to the blood
  • Provide defense against disease
  • Extensive network of one-way vessels
45
Q

Initial lymphatics

A

– Small,blind-endedterminallymph vessels

– Permeatealmosteverytissueofthe body

46
Q

Lymph vessels

A

– Formed from convergence of initial lymphatics

– Eventually empty into venous system near where blood enters right atrium

47
Q

Causes of edema

A

– Reduced concentration of plasma proteins
– Increased permeability of capillary wall
– Increased venous pressure
– Blockage of lymph vessels

48
Q

Edema and Interstitial Fluid Accumulation

A

Swelling of tissues which occurs when too much interstitial fluid accumulates

49
Q

How does the venous system transports blood back to heart?

A

– Capillaries drain into venules
– Venules converge to form small veins that exit organs
– Smaller veins merge to form larger vessels

50
Q

Blood Volume Distribution

A 
Heart - 7%
Pulmonary - 9%
Systemic Arteries - 13%
Systemic Arterioles - 2%
Systemic Capillaries - 5%
Systemic Veins - 64%
51
Q

Venous Return

A 
• Driving pressure from cardiac contraction
• Sympathetically induced venous
vasoconstriction
• Skeletal muscle activity
• Effect of venous valves
• Respiratory activity
52
Q

Skeletal Muscle Pumping

A
  • Many of the large veins in the extremities lie between skeletal muscles.
  • When the skeletal muscle contracts, the veins are compressed.
  • This decreases the capacity of the veins and increases venous pressure.
  • Blood in the veins is squeezed forward toward the heart
53
Q

Venous Valves

A

• Ensures that blood flows towards the heart mechanically

54
Q

What drives the blood towards the heart in Venouse Valves?

A

Venous vasoconstriction and external venous compression drives the blood towards the heart

55
Q

How do venous valves help minimize the backflow of blood that may occur when a person stands up?

A
  • Veins have one way valves spaced every 2-4 cm apart.
  • These valves prevent the blood from flowing backwards and also counteracting the gravitational effects of upright posture.
56
Q

The Respiratory Pump

A

Inhalation and exhalation changes the pressure within our chest cavity

57
Q

How does the Respiratory Pump direct blood to the heart?

A

The pressure difference between the pressure within our chest cavity (5 mm Hg subatmospheric pressure) and the venous system in our limbs and abdomen (atmospheric pressure) in the Respiratory Pump squeezes blood from the veins in our lower extremities into the right atrium

58
Q

How is blood directed to the heart?

A

The Respiratory Pump (pressure) and Venous Valves (mechanical)

59
Q

Primary determinants of Blood Pressure

A

– Cardiac output
– Total peripheral resistance
– Mean arterial pressure = cardiac output x total peripheral resistance

60
Q

Hypertension

A

Blood pressure above 140/90 mm Hg

61
Q

Baroreceptors

A

Monitor mean arterial bp in the arteries that supply blood to brain

62
Q

Primary hypertension

A

– Catchall category for blood pressure elevated by variety of
unknown causes rather than by a single disease entity

63
Q

Secondary hypertension

A

– Occurs secondary to other known problems e.g. endocrine hypertension

64
Q

Complications of hypertension

A

Heart attack, stroke, heart failure

65
Q

Hypotension

A

blood pressure below 100/60 mm Hg

66
Q

Hypotension occurs when

A

– There is too little blood to fill the vessels

– Heart is too weak to drive the blood

67
Q

Orthostatic (postural) hypotension

A

Transient hypotensive condition when person moves from horizontal to vertical position

68
Q

Types of Shock

A

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BMEG 410 (12 decks)

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