The Blood Vascular sy s tem BY DR. DALIA ELGAMAL Lecturer of Histology FOR PHARMACY STUDENTS

General Revision For BodyTissues:

Epithelial Tissue

B) Chromophils They take the regular histological stain. They

Blood Vessels Blood vessels are classified into: *Arteries *Veins *Capillaries *Arterio- Venous Connections -Arteriovenous anastomoses -Glomus

General Structure of Blood Vessels General Structure of Blood Vessels Generally the wall of any blood vessel is formed of 3 layers: 1- Tunica intima, which lies next to the lumen, is the innermost layer composed of simple squamous epithelium (endothelium) and the sub endothelial C.T.

2- Tunica media, the middle layer. Its structure is related directly to the function of the vessel, composed of helically arranged smooth muscle cells with some elastic and collagen fibers interspersed between them. 3- Tunica adventitia (the outermost layer). It is composed of ordinary C.T. containing fibroblast, Collagen and elastic fibers.

1- Large (Elastic) Arteries Aorta 1-Tunica intima: It is composed of an endothelium supported by a narrow subendothelial layer of C.T. The internal elastic lamina is present but indistinct. 2-Tunica media: (the thickest layer):

It consists of many fenestrated lamellae of elastic fibers alternating with circularly oriented layers of smooth muscle cells. 3- Tunica Adventitia: It is thin layer of loose fibroelastic C.T. containing vasa vasorum.

2- Medium sized (muscular) Arteries These include most vessels arising from aorta. Tunica intima: It is characteristically thin. The internal elastic lamina is prominent with an undulating surface. Tunica media: It is characterized by the presence of an abundant amount of smooth muscle cells that are circularly arranged.

Interspersed within the layers of smooth muscle cells are elastic and collagen fibers Tunica adventitia: It is composed of longitudinally oriented elastic and collagen fibers

Differences between medium sized arteries and veins

3- Large Veins Inferior vena cava Tunica intima: Has a thick subendothelial C.T. containing collagen fibers & few elastic fibers. A delicate internal elastic lamina may be present. Tunica media: It is very thin and contains few layers of smooth muscle cells & abundant C.T.

No external elastic Lamina is present. Tunica adventitia: It is the thickest layer The inferior vena cava has longitudinally arranged bundles of smooth muscle fibers. Contraction of these muscle fibers helps in propelling blood towards the heart against gravity.

4- Capillaries Capillaries form branching and anastomosing network between arterioles and venules. Their diameter is 8-10 Um slightly larger than the diameter of RBCs. Capillaries are formed of a single layer of squamous endothelial cells rolled into a tube.

The large number of pinocytotic vesicles on both surfaces of endothelial cells & in their cytoplasm is an identifying characteristic of capillaries. These vesicles are responsible for transport of macromolecules in both directions across the endothelial cytoplasm.

Pericytes are located along the outside of the capillaries and small venules and share the basal lamina of the endothelial cells. After injury, pericytes can differentiate to form new blood vessels & C.T. cells, thus participating in the repair process.

Types of Capillaries: 1- Continuous Capillaries: They are characterized by uninterrupted endothelial and continuous basal lamina. The edges of adjacent endothelial cells interdigitate with each other with a space of 20 nm between them. Site: muscles, C.T. and nervous tissue.

2- Fenestrated Blood capillaries: The endothelial cells have pores ( nm in diameter), and usually covered by a pore diaphragm. The basal lamina is continuous. Site: They are present in the intestinal mucosa, endocrine glands and choroid capillaries.

3- Blood Sinusoids : 3- Blood Sinusoids : They have an enlarged diameter of 30-40um & irregular path. The endothelial wall and the basal lamina are discontinuous. The fenestrae in the endothelial cells are without diaphragm. Site: Present in bone marrow, liver& spleen

5- Arterio- Venous Connections a-Arterio venous Anastomosis (AVAs): These are direct vascular connections between arterioles and venules that bypass the capillary bed They are abundant in skin where they are useful in thermoregulation.

When the AVAs are closed, the blood passes through the capillary bed; when shunts are open; a large amount of blood by passes the capillary bed and flows through the AVAs.

2-Glomera:( pleural of glomus): These are small organs present in nail beds and the tips of the fingers and toes. When the arteriole penetrates the C.T. capsule of the glomus, it develops a thick muscular wall which is richly innervated with adrenergic & cholinergic nerves. The glomera regulate the skin temperature.