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A&P Winter > 21. Blood Vessels > Flashcards

21. Blood Vessels Flashcards

1
Q

Structure of Blood Vessels

A

1) Tunica intima/interna – closest to lumen
- simple squamous epithelium (endothelium) + basement membrane + C.T.

2) Tunica media
- Smooth muscle

3) Tunica externa – outermost
- C.T

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2
Q

Vasoconstriction v. Vasodilation

A

Vasoconstriction – decrease diameter of the lumen and increase blood pressure
Vasodilation – increase diameter of the lumen and decrease blood pressure

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3
Q

What’s diffrent about the structure of a capiliiary compared to other blood vesseles?

A

Capiliaries do NOT have these 3 layers

consist only of endothelium and a basement membrane

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4
Q

Blood pressure

A

the force exerted by the blood against the wall of a blood vessel (units = mmHg)

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5
Q

Systolic pressure v. Diastolic pressure

A

Systolic pressure: maximum pressure against the arterial wall during ventricular contraction. ~120 mmHg

Diastolic pressure: minimum pressure against the arterial wall during ventricular relaxation. ~80 mmHg

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6
Q

3 things that make up the arterial system

A

Elastic arteries + muscular arteries + arterioles

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7
Q

Elastic Arteries

A
  • include the aorta (its main branches) and the pulmonary trunk
  • presence of elastica interna/externa
  • act as pressure reservoir - expand and recoil to drive blood forward; felt as a pulse
  • BP is highest in the aorta and large systemic arteries
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8
Q

Muscular Arteries

A
  • medium-sized and branch to various organs
  • thickest tunica media with more smooth muscle cells and fewer elastic fibers; can’t recoil
  • considered to be distributing arteries because they deliver blood to specific body organs
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9
Q

Arterioles

A
  • microscopic vessels with diameters ranging from 10 to 300 μm
  • contains mostly smooth muscle with very few elastic fibers
  • smallest arterioles regulate flow into capillary beds
  • also known as resistance vessels
  • major drop in BP (~40mmHg) occurs between arteries and arterioles
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10
Q

Capillaries

A
  • Microscopic vessels with a diameter of only 8-10 μm
  • Wall has a single layer of endothelial cells and a basement membrane – NO muscular layer!
  • some capillaries contain pericytes along their walls that act to stabilize capillary wall and help control permeability
  • have a large surface area in order to function in the exchange of materials between the blood and interstitial fluid via diffusion and active transport
  • BP is about 35 mmHg at arteriole end and 17 mmHg at venule end
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11
Q

3 Structural Types of Capillaries

A

1) Continuous capillaries
2) Fenestrated capillaries
3) Sinusoids

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12
Q

Continuous capillaries

A
  • Location: skin and muscles
  • endothelial cells are continuous and have intercellular clefts (gaps)**
  • held together by tight junctions
  • allow limited passage of fluids and small solutes

Continuous since there’s no holes, pores or fenestration. (there are slight gaps between the cells, but its very very small since nothing can pass through). The brain is dif and there is zero gaps whatsoever.
• Most common (majority) of capiliares is continuous

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13
Q

Fenestrated capillaries

A
  • Location: villi of s.i., kidneys, endocrine glands
  • endothelial cells have fenestrations (pores)
  • greater permeability to fluids and small solutes
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14
Q

Sinusoids

A

Capiliary type
• Location: liver, bone marrow, lymphoid tissue
• endothelial cells have large fenestrations
• large intercellular clefts
• large lumen; incomplete basement membrane
• allow large molecules (blood cells and proteins) to pass between blood and tissues

Type 3 is for really large things. Very wide, very leaky, large pores. Lymphoid needs to move WBC out of spleen and explore. Liver is making a lot of albumin (maintain osmotic pressure), and other things that are larger like clotting factors. Doesn’t even have a complete basement membrane.

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15
Q

Capillary Beds

A
  • Organized into networks known as capillary beds
  • terminal arteriole –> metarteriole continuous with a thoroughfare channel–> joins postcapillary venule

• about 10-100 “true” capillaries branch off the metarteriole
• precapillary sphincter alternately relaxes/contracts to regulate flow into capillary bed
> relaxed (open): blood flows into capillaries, exchange occur
> contracted (closed): blood flow through capillaries stops

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16
Q

venules

A
  • receive blood from capillaries

* larger venules have several layers of smooth muscle

17
Q

Veins

A
  • venules join to form veins
  • vein walls are thinner than artery walls and typically a • vein looks collapsed
  • no elastic interna/externa
  • tunica media has few layers of smooth muscle cells and few elastic fibers
  • tunica externa consists of thick bundles of collagen fibers and elastic networks (often thicker than media)
  • veins are blood “reservoirs” as can hold ~60% of the blood volume
  • pressure gradient in veins is from about 15 mmHg to about 0 mmHg at the right atrium
  • must rely on factors other than pressure alone to help return blood back to heart (venous return)
18
Q

on factors other than pressure alone to help return blood back to heart (venous return)

A
  • gravity: only helps you above the heart level, it will hinder below the heart
  • presence of valves in veins (folds of tunica intima)
  • contraction of skeletal muscles =milking the veins. (You can’t stand still for more than 20min because your not doing this skel contraction so the blood starts pooling in your legs and you’ll eventually pass out, you start swaying, moving your feet to try to stimulate this contracting.)
  • respiratory pump: Inspire (breathing in) you decrease pressure in chest and increase pressure in abdomen, this pushes the blood in the direction of the heart.
  • sympathetic vasoconstriction: All vessels themselves also have smooth muscle (even if its just a bit) which can be told to sqeeze, and contract in order to push the blood towards the heart.
19
Q

Driving force of blood circulation is

A
  • blood pressure

* ↑ Pressure Difference, ↑ Blood Flow

20
Q

Blood Flow (formula)

A
  • is the volume of blood flowing through a vessel = cardiac output (CO)
  • F = CO
  • ↑ Pressure Difference, ↑ Blood Flow
21
Q

cardiac Output

A
  • Refers to the volume of blood pumped per minute by each ventricle of the heart
  • CO = stroke volume (SV) x Heart rate (HR)
  • eg. average adult cardiac output: CO = 70 ml/beat x 75 beats/min
22
Q

End Diastolic Volume (EDV)

A

total volume of blood in ventricle at end of ventricular relaxation phase (diastole)

23
Q

End Systolic Volume (ESV)

A

total volume of blood in ventricle after the ventricle has contracted and ejected about 60% of the blood from its chambers (40% of the blood usually remains in the ventricle)

24
Q

Stroke Volume

A
  • volume of blood pumped by each ventricle during each heart beat
  • Stroke volume = EDV - ESV

End Diastolic Volume (EDV)
End Systolic Volume (ESV)

25
Q

stroke volume is affected by two things:

A

i) Stretching of cardiac muscle fibers
- fibers are stretched by the volume of blood inside the ventricle at the end of diastole (EDV)

ii) Contractility of cardiac muscle fibers
- sympathetic nervous system activity and release of hormones epinephrine and norepinephrine will increase Ca2+ entry into muscle cytoplasm and increase the force of contraction

26
Q

Starling’s Law

A

a greater degree of stretch of fibers results in a greater force of contraction

27
Q

External Factors that affect Venous Return

A
  • increased respiratory movements
  • increase muscular activity to squeeze veins
  • sympathetic nervous system causing veins to constrict
28
Q

Blood volume changes that affect Venous Return

A

hormones such as the antidiuretic hormone (ADH) causes increase water uptake from kidneys if body gets dehydrated (increase blood volume)
\

29
Q

Baroreceptors

A

• pressure sensitive neurons located in the carotid sinus (internal carotid artery) and aortic arch

30
Q

If BP increases, then:

A
  • stretch baroreceptors more
  • send more impulses to CVC
  • stimulate inhibitory center
  • ↑ PNS output
  • release Ach at SA and AV nodes
  • result is a decrease in HR, a decrease in CO, and BP is decreased
31
Q

If BP decreases, then:

A
  • less impulses sent to CVC
  • stimulate acceleratory center
  • ↑SNS output
  • release NE at SA and AV nodes, and heart muscle
  • result is an increase in HR and force, an increase in CO, and BP is increased
32
Q

Peripheral Resistance

A

resistance to blood flow due to friction between the blood and the vessel wall
A) Blood viscosity (thickness of blood doesn’t change generally)
B) Vessel diameter (vessel diameter decreases, resistance to blood flow increases)

33
Q

Factors Affecting Vessel Radius

A

i) Sympathetic nerves
- CVC with output via sympathetic nerves to smooth muscle of arterioles and veins
- if sympathetic output increases, there is an increase in vasoconstriction

ii) Hormones
- Vasoconstriction: angiotensin II, epenephrine/norepeinephrine
- vasodilation: epenephrine

iii) Local factors
- O2, CO2, H+, and metabolites can alter arteriolar radius and influence state of capillary beds
- low O2, high CO2, high [H+], ↑ K+ will all cause VASODILATION

A&P Winter (10 decks)

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