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BLOCK C - CIRCULATION > Histology of Blood Vessels > Flashcards

Histology of Blood Vessels Flashcards

1
Q

The circulatory system consists of…
* heart
* vascular system (afferent and efferent blood vessels)

What are the functions of these structures?

A

Heart: Pumps blood
Afferent vessels (veins): Convey metabolism waste products and CO2 to the heart
Efferent vessels (arteries): Conduct nutrients and O2 to tissues

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2
Q

Describe the lymphatic network

A

Blind capillaries (tubules) converge into larger lymphatic vessels that drain into large veins

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3
Q

What is the lymph?

A

Fluid conducted by the lymphatic system, formed by plasma enriched with immunoglobins and lymphocytes produced by the lymphatic organs.

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4
Q

Name the types of vessels the blood moves through as it moves away from the heart

A

Heart
Large (elastic) arteries
Muscular arteries
Arterioles
Metarterioles
Capillary network
Post capillary venules
Venules
Medium/small (muscular) veins
Large veins
Heart

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5
Q

What are the 3 distinct layers of the wall of arteries and arterioles?

A

Intima
Media
Adventitia

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6
Q

The adventitia or arteries and arterioles often merges with…

A

dense or loose connective tissue surrounding the vessels

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7
Q

Do walls of veins and venules have equivalent layers to those in arteries and arterioles?

A

Yes but they are difficult to identify and their borders are often poorly defined

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8
Q

Describe the anastomosing (interconnected, web-like) microvasculature

A

Metarterioles are small vessels that connect arterioles to the capillary
network.
Postcapillary venules are small veins that collect blood from the capillary network.
The capillary network is located between the metarterioles and postcapillary venules and is the site of gas, nutrient and waste exchange.

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9
Q

Describe the capillary wall

A
  • Simple squamous endothelium with tight junctions sitting on a basement membrane and surrounded by reticular fibres.
  • Support is provided by vimentin filaments within the endothelial cells.
  • Absent or minor adventitia
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10
Q

How does the cross-sectional area of the aorta compare to that of the capillary network? How does the flow compare?

A

The total cross-sectional area of the capillary network is 800 times larger than that of the aorta.

The flow in capillaries is 0.3mm/sec compared to 320mm/sec in the aorta (i.e. much slower in capillaries).

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11
Q

Name two substances that increase the permeability of the capillaries.

A

Histamine
Bradykinin

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12
Q

Other than gas and nutrient exchange, name 3 other roles of the capillaries

A
  • thermoregulation
  • regulation of blood pressure
  • inflammation
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13
Q

Describe the classification of capillaries

A

Capillaries are classified based on their permeability.

  1. Impermeable capillaries
    * continuous capillaries
  2. Permeable capillaries
    * fenestrated capillaries
    * sinusoid capillaries
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14
Q

Describe continuous (impermeable) capillaries

A
  • Contain trans-endothelial channels
  • Contain pinocytic vesicles
  • Do not contain fenestrations (have tight junctions between endothelial cells with few or no gaps, creating a continuous lining)
  • Present in nervous tissue, skeletal, cardiac and smooth muscle, skin, lungs and lymphatic organs
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15
Q

Describe fenestrated (permeable) capillaries

A
  • Contain trans-endothelial channels
  • Contain pinocytic vesicles
  • Contain fenestrations (pores) with diaphragms
  • Enable larger particles and solutes to pass through the capillary wall, like albumin
  • Present in intestinal mucosa, pancreas, salivary glands, endocrine glands and renal glomerulus of the kidney
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16
Q

What is the endothelium? What are its 3 primary functions?

A

The endothelium is a thin layer of specialized cells that line the interior surface of blood vessels, lymphatic vessels and the heart.

  1. Permeability
  2. Metabolic function
  3. Production of vasoactive substances
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17
Q

What is the “permeability” function of the endothelium?

A

The endothelium has selective permeability, allowing it to control the movement of substances between the bloodstream, lymphatic system and surrounding tissues.

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18
Q

What are the 2 metabolic functions of the endothelium?

A
  1. Conversion of angiotensin I to angiotensin II (a hormone that regulates BP)
  2. Inactivation of vasoconstrictive and pro-inflammatory molecules: bradykinin (a potent stimulator of smooth muscle contraction) and serotonin, prostaglandins, norepinephrine, etc.
19
Q

Name two vasoactive substances produced by the endothelium and their effects.

A

Endothelin (vasoconstrictive)
Nitric oxide (relaxing factor, vasodilation)

20
Q

What is desquamation? What can it lead to?

A

Desquamation is when endothelial cells get detach and peel off the endothelial lining of blood vessels. This process can trigger fibrin aggregation by attracting platelets and result in the formation of thrombi.

21
Q

Describe the mechanism of action of endothelin

A

Endothelin released by endothelial cells will bind endothelin receptors on nearby smooth muscle cells. This leads to an increase in calcium ions in the muscle cell, causing it to contract.
Therefore, endothelin has vasoconstrictive effects of blood vessels.

22
Q

Describe the mechanism of action of nitric oxide

A

Nitric oxide released by endothelial cells activates an enzyme called guanylyl cyclase, which increases the levels of cGMP. cGMP reduces calcium levels in the muscle cells, causing it to relax. Therefore, nitric oxide has vasodilative effects on blood vessels.

23
Q

What is another name for fibrin? Briefly describe its function

A

Factor Ia

Fibrin is formed by the action of thrombin on fibrinogen as a result of the coagulation cascade. Fibrin combines with platelets to form a hemostatic plug (blood clot) over a wound in the blood vessels.

24
Q

What is an atherosclerotic plaque?

A

A buildup of fatty deposits and cholesterol in the walls of arteries. It can lead to endothelial injury and trigger blood clot formation, causing an occlusion of the blood vessels.

25
Q

Name some similarities and differences between the intima of muscular ateries and large elastic arteries.

A

In both cases, the intima comprises the endothelium (tight and gap junctions) and a thin subendothelium.
However, muscular arteries have a well-defined internal elastic limiting membrane (IELM) whereas large elastic arteries have a fenestrated IELM that is difficult to distinguish from the elastic layers in the media.

26
Q

Describe the differences between the media of muscular arteries and large elastic arteries.

A

The media of muscular arteries consists of 4-10 smooth muscle layers and of collagen type III.
The media of large elastic arteries is very thick (50 layers of smooth muscle) and contains fenestrated elastic membranes, collagen type II and chrondoitin SO4 proteoglycans.

27
Q

Describe the key difference between the adventitia of muscular arteries and large elastic arteries.

A

The adventitia of muscular arteries consists of dense connective tissue with or without vasa vasorum.
The adventitia of large elastic arteries consists of dense connective tissue, but also collagen type I and always contains vasa vasorum.

28
Q

Name two examples of large elastic arteries.

A

Aorta
Carotid artery

29
Q

Describe the similarities and differences between the intima or small/medium veins and large size veins.

A

Both consist of an endothelium and subendothelial layer with a poorly defined or absent IELM. However, small/medium veins do not have smooth muscle cells in their intima, whereas large veins do have some diffuse smooth muscle cells in the subendothelial layer. Also, large size veins have prominent valves.

30
Q

Describe the media of medium/small veins and large size veins.

A

Small/medium veins have a media that consists of incomplete layers (usually 2) of smooth muscle cells.
Large size veins have a media consisting of 5 layers or less of smooth muscle cells, separated by connective tissue and collagen

31
Q

Describe the adventitia of medium/small veins and large veins.

A

Medium/small vein have an adventitia that consists of dense connective tissue with or without vasa vasorum.
Large size veins have a thick adventitia - it is the thickest layer of large veins! It is made of dense connective tissue with vasa vasorum.

32
Q

Name two examples of large size veins

A

Superior vena cava
Inferior vena cava

33
Q

What are some key similarities and differences between the layers of arterioles and venules.

A

Intima:
Arterioles have a thin or absent subendothelium and fibrous or absent IELM. Venules have no subendothelium and no IELM.

Media:
Arterioles have a thin media with 1-2 layers of SM cells. Venules have an incomplete media, pericytes may be present.

Adventitia:
In both cases, thin without vasa vasorum.

34
Q

Which of the following has a larger diameter:
a) arterioles
b) venules

A

b) venules (0.2mm to 20um)

Arterioles have a smaller diameter (0.1mm to 10-15um)

35
Q

Sometimes arterioles may anastomose directly to venules, forming…

A

functional bypasses

36
Q

What type of function may the smooth muscle of metarterioles have?

A

Sphincter function (directs the blood directly to venules via anastomoses and regulate blood pressure).

37
Q

Arterioles are important for regulating…

A

systemic blood pressure

38
Q

Describe the wall of lymphatic vessels

A
  • Very thin endothelium (no occluding junctions or gap junctions)
  • No basement membrane associated with endothelium
  • Endothelial cells are anchored to the connective tissue fibres (type I and III collagen elastic fibres)
39
Q

Small and large lymphatics usually have…

A

valves (folds of the wall projecting into the lumen)

40
Q

What do large lymphatics have in their walls?

A

Smooth muscle cells

41
Q

Name an example of a large lymphatic

A

Thoracic duct

42
Q

The lymphatic vessels of the thoracic duct empty into the venous system at…

A

the junction of jugular and subclavian veins

43
Q

What are varicose veins?

A

They are swollen, twisted and enlarged veins that usually appear directly under the skin (esp. legs). They result from weakened of damaged valves in the veins, which lead to poor blood flow and cause blood to pool in the veins.

44
Q

Unlike other types of capillaries, sinusoids do not rest on a basement membrane. What structure ensures their integrity instead?

A

The endothelial cells of sinusoids are held in place by a large network of thick reticular fibres.

BLOCK C - CIRCULATION (10 decks)

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