Blood Vessels PDF - Mansoura National University

BLOOD vessels Dr. Dalia Eita  Agenda ❑ Types of blood vessels ❑ Structure of large arteries and veins ❑ Structure of medium sized arteries and veins ❑ Structure of types of arterio-venous connections  ILOs ❑ Differentiate between types of blood vessels ❑ I...

BLOOD vessels Dr. Dalia Eita  Agenda ❑ Types of blood vessels ❑ Structure of large arteries and veins ❑ Structure of medium sized arteries and veins ❑ Structure of types of arterio-venous connections  ILOs ❑ Differentiate between types of blood vessels ❑ Identify structure of large arteries and veins ❑ Identify structure of medium sized arteries and veins ❑ demonstrate the structure of types of arterio-venous connections  ARTERIO- Arteries Veins VENOUS CONNECTION Large arteries: Large veins: Blood Aorta Inferior vena capillaries cava Medium sized Medium-sized Blood arteries veins Sinusoids Arterio-venous Arterioles Venules anastomosis (A-V shunts)  Large veins: inferior vena cava Characters: Has a very wide lumen with many valves. Has collapsed thin and flat wall. Tunica Similar to medium-sized vein intima Thin and contains only smooth muscle Tunica fibers. media very thick layer of loose C.T containing collagenous fibers, C.T Tunica cells, vasa vasorum and nerves. adven Also contains longitudinally arranged bundles of smooth titia muscle fibers. Large veins: inferior vena cava Large veins: inferior vena cava  ARTERIO-VENOUS CONNECTION Blood capillaries Thin walled tubular blood channels (conduct the blood from the terminal arterioles to the venules). Their diameter is 8-10 μm. Network of these vessels known as capillary beds.  Blood capillaries Histological structure: 1. Single layer of endothelial cells resting on a basal lamina. 2. Pericytes lie in between the endothelium and the basal lamina. 3. The cytoplasm of endothelial cells contains all the usual organelles besides numerous microfilaments, intermediate filaments and pinocytotic vesicles. 4. The cells hold together by zona occludens and gap junction. N. B. After tissue injury pericytes proliferate and differentiate to form new blood vessels and C. T. cells. Blood capillaries  Types of blood capillaries Continuous capillaries: No fenestrae are present. Site: in all kinds of muscle tissue, C. T., exocrine glands and nervous tissue. Fenestrated capillaries Large fenestrae are present in the cytoplasm of their endothelial cells. The fenestrae are closed by diaphragms that are thinner than a cell membrane. A continuous basal lamina is present. Site: present in the kidney, intestine and endocrine glands. Fenestrated capillaries without diaphragm: They have a very thick basal lamina. Site: Renal glomerulus capillary. Discontinuous sinusoidal capillaries: The basal lamina and endothelial cells are discontinuous. Multiple fenestrae without diaphragm are found in the endothelial cells. MEDICAL APPLICATION Junctions between endothelial cells of postcapillary venules are the loosest of the microvasculature. At these locations there is a characteristic loss of fluid from the circulatory system during the inflammatory response, leading to edema.  Blood Sinusoids These are dilated irregular blood spaces, (5-30) µm in diameter Sites: Bone marrow, spleen, liver, and endocrine glands. Histological structure: 1. They are lined by fenestrated endothelial cells (simple squamous epithelium). Their walls contain pores not covered by diaphragms. 2. The endothelium rests on a thin layer of reticular C. T. No basement membrane present. 3. Macrophages are present outside the sinusoidal wall, extending their pseudo-podia inside the wall to phagocytose any foreign body.  Capillaries Sinusoids Diameter: Uniform 8-10 μm. Irregular 5-30 μm. Lumen: Narrow. Wide. Sites: Present everywhere in the body. Present in certain sites: bone marrow, spleen, liver and endocrine glands. Structure: 1. Lining endothelium fenestrated or continuous. Fenestrated not covered with diaphragm. Absent. 2. Basement membrane Well developed. Present. Absent. 3. Pericytes Absent. Present. 4. Macrophages Function: Gas and nutrient exchange. According to the site.  Arterio-venous anastomosis (A-V shunts) Blood channels allow the blood to pass directly from the arteries and arterioles to the veins or venules without capillaries. Sites: 1.Exposed part as tips of fingers, toes, in external ear, nose, lip and tongue. 2.Internal organs as stomach, intestine, liver, endocrine gland, uterus, placenta and sympathetic ganglia. Structure: Similar to the arterioles on their arterial side and similar to the venules on the venous side. ❖ The intermediate segment of A-V shunt: a) The lumen decreases gradually towards the venous side. b) The internal elastic lamina disappears towards the venous side. c) The media is well-developed and rich in smooth muscles and contain myoepithelial cells which act as sphincter. d) The adventitia becomes thicker at the venous side. Function: 1.Conserve the body temperature; dilate in cold weather while constrict in hot weather. 2.Regulate the blood flow to the organs according to their need. 3.When dilate the venous return is increased and vice versa. Dr. Dalia Eita References ▪ Junqueira LC, Carneiro J: Junqueira’s Basic Histology. Text and Atlas, fourteenth edition, Copyright © 2016 by McGraw-Hill Education. ▪ Student medical histology book, Mansoura university.