Circulatory System Ms. Hazel Anne L. Tabo

Circulatory System Blood and lymphatic vascular system Blood vascular system: 1) Heart – muscular organ 2) Arteries – efferent vessels of the heart; nutrient and O 2 to the tissues 3) Capillaries – a diffuse network of thin tubules; anastomose (converge and reconnect in a network) profusely in organs, capillary walls allow interchange between blood and tissue organs takes place. 4) Veins – afferent vessels; represent the convergence of the capillaries into a system of larger channels; carries products of metabolism and CO 2, etc.

Lymphatic vascular system: 1) Lymphatic capillaries – dead-end tubules, gradually join or anastomose in vessels of increasing size and terminates in blood vascular system (emptying in the large veins of the heart); carries the fluid of the tissue spaces (interstitial fluid) that contributes to the liquid part of the lymph. 2) Lymph glands – contributes to lymphocyte circulation & other immunologic factors 3) Spleen and Thymus – involved in development of lymphocytes

Capillaries Made up of single endothelium; (+) Tunica intima Ave. diameter: 7-9  m Epithelial cells form the walls are joined by zonula occludens 3 types: Continuous, Fenestrated, Sinusoidal

This capillary is formed by “continuous” endothelial cells and basal lamina that do not form openings, which would allow substances to pass the capillary wall without passing through both the endothelial cell and the basal lamina. Both endothelial cells and the basal lamina can act as selective filters.

Continuous capillary Pericytes – mesenchymal cells surrounding endothelial cells

The endothelial cell body forms small openings called fenestrations or pores, which allow components of the blood and interstitial fluid to bypass the endothelial cells on their way to or from the tissue surrounding the capillary. The fenestrations may represent or arise from pinocytotic vesicles which open onto both the luminal and basal surfaces of the cell. The extent of the fenestration may depend on the physiological state of the surrounding tissue (renal tissue), fenestration may increase or decrease depending on the need to absorb or secrete. The endothelial cells are surrounded by a continuous basal lamina, which can act as a selective filter.

Fenestrated capillary Ex: Kidney, Intestines, Endocrine Glands

Filtration in Glomerulus Last updated: 14 June 2010 / dgk

Fenestrated endothelial cells, which may not even form a complete layer of cells and incomplete basal lamina. They form large irregularly-shaped vessels, sinusoids or sinusoid capillaries. This allows a very free exchange of substances or even cells between bloodstream and organ is advantageous. Ex: liver, spleen, and red bone marrow

Artery Thick-walled blood vessels; (+) 3 tunics/layers Tunica intima (internal tunic) – lining the lumen of the vessel; made up of a) endothelial cell layer; b) subendothelium (loose CT and few smooth myofiber); c) internal elastic limiting membrane (inner elastic fiber layer) Tunica media (middle tunic) – mainly of smooth muscle cells in circular orientation, with interspersed elastic fibers or elastic lamina (fenestrated) for nourishment of deeper cells in the vessel wall.; the chief site of metabolic activities in the blood vessels Tunica adventitia (outer or adventitial tunic) – consists of connective tissue with collagen and elastic fibers Vasa vasorum – small arteries in the walls of large arteries and veins, nourishes by diffusion of metabolites from the bloodstream.

Vasa vasorum: In Arteries – Adventitial layer In Veins – reaches up to tunica media

Large Artery (Aorta) - T. intima: internal lamina is thicker than muscular arteries lamina - T. media: concentric elastic membranes with smooth muscles in between - T. adventitia: does not show external limiting membrane with elastic and collagen fibers Medium-sized and Small A. - wider lumen - “muscular arteries” - (+) internal elastic limiting membrane -thick tunica media with intermixed elastic material -Poor T. adventitia - no vasa vasorum Arterioles -<0.5  m diameter - Narrow lumen - tunica intima w/o subendo-thelial layer - (+) tunica media - (+) poor or absent tunica adventitia Metarterioles - Discontinued smooth muscle layer

Arteriole Muscular artery Large artery

Metarteriole A branch of arteriole with a discontinuous layer of smooth muscle. It in turn, branches into capillary network. Constriction of metarterioles: help to regulate circulation in capillaries. Precapillary Sphincter – a smooth muscle between metarteriole and start of capillary vessel, it can completely stop the blood flow in capillaries.

Vein Large Vein (Limb veins; Vena cava) - Wide lumen - T. intima: well- developed -T. media: with few smooth muscles and abundant CT - T. adventitia: Thick collagen fibers with smooth muscles Medium-sized and Small Vein mm diameter -wider lumen - (-) t. intima: (+) valves (+/-) subendothelial layer -thin tunica media with intermixed collagen fiber - Rich T. adventitia - no vasa vasorum Venule mm diameter - Wider lumen than arteriole - (+) tunica intima -Thin t. media -Rich t. adventitia Valves – elastic CT on both sides of vein endothelium; propel the blood to the heart

L: Venule; R: Arteriole

L: Wall layers of large vein R: Medium vein with valves.

Carotid bodies and Aortic bodies They are highly vascular and muscular tissues (chemoreceptors sensitive to catecholamines: epinephrine & norepinephrine) Location: Carotid A.: Near the bifurcation of the common carotid artery; Aortic B.: on the arch of the aorta Blood supply: Fenestrated capillaries Sensitive to low O 2 tension, high blood CO 2 and low arterial blood pH.

Type I cells (main cells) have granules secreting dopamine, serotonin and adrenaline (green arrows); Type II cells – sustentacular or supporting cells (orange arrows); C - fenestrated capillaries. C C C C C C

Images: mlwww.ouhsc.edu/histology/text%252...lar.ht ml es/vascular/vascular.htmwww.lab.anhb.uwa.edu.au/mb140/corepag es/vascular/vascular.htm histology/english/cardiovascular/Fig18_Ca rdiovascular.htmwww.courseweb.uottawa.ca/medicine- histology/english/cardiovascular/Fig18_Ca rdiovascular.htm