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CAM201: Histology > Blood Vessels > Flashcards

Blood Vessels Flashcards

1
Q

Intima of Elastic Arteries

A

Simple squamous epithelium
Underling LCT with fibroblast-like cells, and some smooth muscle cells
Internal elastic lamina (may be difficult to see against high concentration of elastic lamellae in the media of elastic arteries)

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2
Q

Media of Elastic Arteries

A

Circularly arranged SMCs which interdigitate between fenestrated elastic lamellae

(elastic lamellae aid diffusion of nutrients, and SMCs secrete elastic and collagen fibres)

Collagen Fibres (limit stretch)

Outer portions may contain vasa vasorum

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3
Q

Adventitia of Elastic Arteries

A

LCT
Vasa Vasorum
Lymphatics, nerves
Adipose Tissue

Tethered to surrounding structures

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4
Q

What are elastic arteries? Diameter?

A

Largest arteries: aorta, carotids, subclavian, brachiocephalics

Receive blood under high pressure - act as conducting vessels that are highly compliant

Aorta: Wall thickness ~2mm to a lumen of ~25mm

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5
Q

What are Muscular Arteries? Diameter?

A

Distributing arteries.
E.g. femoral, radial arteries.
Wall thickness = ~1mm, lumen diameter = ~4mm

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6
Q

Intima of Muscular arteries

A 
Thinner than intima of elastic aa
Otherwise the same:
Simple sq epithelium
Underlying LCT with fibroblast-like cells and a few SMCs
Internal elastic lamina
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7
Q

Media of Muscular Arteries

A

Many concentric laters of smooth muscle
Fine elastic fibres (much less than elastic arteries)
A few collagen fibres (less than in elastic aa)
Has an External Elastic Lamina

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8
Q

Adventitia of Muscular Arteries

A

LCT

Some collagen and elastic fibres

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9
Q

What are arterioles? functions? Diameter?

A

Regulate blood flow into microcirculations
Major regulators of systemic blood pressure
Regulate peripheral resistance

Diameter <0.1-0.5mm generally

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10
Q

Intima of arterioles

A

Thinner than muscular arteries
Small endothelial cells
underlying connective tissue with fibroblast-like cells and some SMCs
Less well-defined internal elastic lamina, may be incomplete in parts

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11
Q

Media of arterioles

A

Generally ~-3 layers of SMCs: <6

No external elastic lamina

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12
Q

Adventitia of arterioles

A

Difficult to distinguish because is thinner and blends in with surrounding connective tissue

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13
Q

Function of the microcirculation?

A

Responsible for the diffusion of nutrients, waste, gases, and fluids via capillary beds

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14
Q

What is an arteriovenous shunt?

A

Regulates blood flow into capillary beds

Vasocontriction of arteriole = blood enters capillary bed

Vasodilation of arteriole = blood bypasses capillary bed because capillary bed has comparatively higher pressure

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15
Q

What is a Metarteriole?

A

Capillary-like structure with discontinuous smooth muscle layer

Acts as a local regulator of blood flow
Causes blood to bypass or enter capillary beds

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16
Q

Pre-capillary Sphincters?

A

Close when functional demans for blood, in a given capillary bed, is reduced

17
Q

Capillaries average diameter

A

5-10um

18
Q

Products of endothelial cells

A

Produce vasoactive substances

Primarily concerned with vasodilation, platelet adherence, or activation/inhibition of platelet adherence/activation

19
Q

Structure of a continuous capillary, and how they engage in exchange

A

Most common type

Simple squamous epithelium
Continuous Basal Lamina
Pericytes

Exchange:
Passive diffusion of gases through tight junctions

Active pinocytosis transportation of proteins through endothelial cells (this action is absent in endothelial cells of the BBB)

20
Q

Structure of Fenestrated Capillary

Where Are they found?

A

Found in kidneys, endocrine organs, small intestine
Have greater permeability than continuous capillaries

• Simple squamous endothelium
• Fenestrae (pore-like openings) are present through endothelial cells: 60-80nm diameter
o Allows easy passage of proteins smaller than plasma proteins
• Continuous basal lamina
• Pericytes are rarely present
• Diaphragm normally spans the pore, but not in the kidney (renal glomerulus)
o Diaphragm = radially arranged fibrils that normally span the pore to limit protein diffusion.

21
Q

Structure of Sinusoidal Capillaries

Where are they found?

A

Present in liver, spleen and bone marrow

Most permeable of the capillaries

  • Simple squamous epithelium
  • Larger fenestrae in epithelial cells: 30-40um diameter
  • Discontinuous basement membrane
  • Allows passage of blood cells
22
Q

Postcapillary Venules: function & structure

A

Resemble continuous capillaries
(simple sa endothelium, continuous basal lamina, pericytes)

Site of Diapedesis
Thus why lymphoid tissue has a high concentration of post-capillary venules

23
Q

Structure of general veins: Intima

A

o Simple squamous endothelium
o Subendothelial CT may be absent
• If there, fibroblast-like cells will be present
o No internal elastic lamina

24
Q

Structure of general veins: Media

A

o Thinner than arteries
o Contains a few SMCs
• SMCs are more irregularly organised compared with arteries

25
Q

Structure of general veins: Adventitia

A

o Thickest layer
o LCT
o Few nerve fibres
o Vasa vasorum in large veins (which may penetrate the media)

26
Q

Describe the valves of veins

A
  • Semilunar folds of tunica intima
  • Have core of elastic fibres
  • Covered by endothelium
  • Most numerous in veins of the limbs (prevent backwards flow)
27
Q

Structure of a large vein

A

Intima:
• Simple squamous endothelium
• Subendothelial connective tissue, with fibro-blast-like cells
• No internal elastic lamina

Media:
• Some irregularly arranged SMCs

Adventitia:
•	Longitudinally arranged SMCs 
o	Allow peristaltic pumping of blood (oppose gravity for return of blood)
o	Prevents over-distension of vessel
•	Vasa vasorum are present
28
Q

What is the lymphatic system?

A

Collects lymph from interstitium and drains it into venous return
• Via Right Lymphatic Duct and Thoracic duct which drain into the R and L brachiocephalic veins, respectively

Drains ~3L/day (~125ml per hour)

29
Q

Structure of Lymphatic capillary:

A

• Lumen lined by very thin endothelial cells
o No fenestrations
o No Tight Junctions
• Rudimentary, or absent, basement membrane
• No pericytes

Lumen held open by elastic myofibrils (anchoring filaments) that attach to collagen in the surrounding connective tissue

Lymph enters ‘blind sacs’ and is then transported in lymphatic vessels

30
Q

Structure of large Lymphatic Vessels:

A

• Lumen lined by very thin endothelial cells
o No fenestrations
o No Tight Junctions
• Rudimentary, or absent, basement membrane
• No pericytes
• Have valves!
• Large lymphatic vessels have some smooth muscle

CAM201: Histology (2 decks)

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