Blood Vessels

Blood Vessels

By
Dr.Alaa Al-sahlany
Jan 13, 2021

TYPES OF BLOOD VESSELS

1. Arteries: (a) Large artery (b) Medium sized artery

2. Arterioles

3. Capillaries

4. Venules

5. Veins:(b) Large vein (a) Medium-sized vein

General Structure

(a) Tunica intima

Is composed of lining endothelium (simple squamous epithelium) and subendothelial connective tissue.

Sometimes Tunica intima is demarcated from tunica media by internal elastic lamina

.

(b) Tunica media

Is made of smooth muscle and connective tissue.

Sometimes it is thickened and demarcated from adventitia by external elastic lamina

(c) Tunica adventitia

It is composed of elastic connective tissue.

It carry small blood vessels (vasa vasorum) and sympathetic fibers.

1. Large (Elastic )artery

Aorta and its branches are examples

Presence of elastic fibers in the wall allows it to expand during contraction (systole) and to recoil during relaxation (diastole) of heart.

Tunica media mainly made of elastic lamellae

2. Medium-sized(Muscular )artery

Radial and ulnar arteries are examples

Presence of smooth muscle in its wall helps to control pressure of blood through

vasoconstriction or vasodilatation.


Tunica media consists mainly of smooth muscle cells. Hence the name muscular artery

Myocardial infarction

( complete occlusion of artery)
Angina
(stenosis of artery)

ARTERIOLE

It has a thick wall relative to the size of its small lumen

Serve as flow regulators for the capillary beds

CAPILLARIES

Arterioles break up into small blood vessels called capillaries which are the smallest diameter blood vessels

They are involved in exchange of gases, nutrients and metabolites between blood and tissue.

Tissues with high metabolic rates have abundant capillary network (e.g. liver, cardiac muscle).

Types of capillaries

1. Continuous capillary
It is the commonest type of capillary present in muscle, brain, etc.


The endothelial cells form a continuous lining of the capillary

2. Fenestrated capillary

Characterized by the presence of pores(fenestrations) in the endothelial cells.

These pores are allows substances and molecules to pass through.

The permeability of fenestrated capillary is much greater than that of continuous capillary therefore found in tissues in which rapid exchange of substances occur

3. Sinusoidal capillary

Found in liver and haemopoietic organs like bone marrow and spleen and liver.

Lumen is lined by discontinuous endothelium (the basal lamina is discontinuous) forming gaps that permit the passage of blood cells and large

Telangiectasia(dilated capillaries)

Spider angioma

Venules

Venules receive blood from capillaries

Only postcapillary venules take part in exchange of metabolites between blood and tissue as do capillaries.

Venules are sensitive to inflammatory mediators resulting in leakage of fluids and white blood cells

Due to leakage of fluid from venules to tissue

as response to histamine


VEINS
Veins are thin-walled blood vessels that carry blood from capillaries to heart.

They are often provided with valves which serve to prevent the reflux of the blood

2. Large vein

Superior vena cava and inferior vena cava are examples

Tunica media:

It is thin or absent.

Tunica adventitia:

It is the thickest coat.

1. Medium-sized vein

Medium-sized vein differs from medium-sized artery in having a collapsed lumen


Tunica adventitia:
It is the thickest coat.

Varicose veins

Valves are non-functioning


Lymphatic vessels

The lymphatic vessels are unidirectional(have valves), conveying fluid (only from tissues)

The largest lymphatic vessel ( draining most of the body and emptying into the veins on the left side) is the thoracic duct. The other main channel is the right lymphatic trunk

Because of their greater permeability, lymphatic capillaries are more effective than blood capillaries in removing protein-rich fluid from the extracellular spaces
.

Before lymph is returned to the blood, it passes through lymph nodes, where it is exposed to the cells of the immune system













Elephantiasis
Lymphatic obstruction