CIRCULATORY SYSTEM I. How do vampires like to travel? By blood vessel!

I. There are two major components of the circulatory system. 1. heart 2. arteries 3. arterioles 4. capillaries 5. venules 6. veins A. The cardiovascular system:

B. The lymph vascular system 1. blind ended lymphatic capillaries that collect lymph fluid from tissues 2. larger lymphatic vessels that connect with one and other and finally empty collected lymph into large veins in the neck where the lymphatic and cardiovascular systems merge.

II. General cardiovascular circulation A. Two major components 1. arterial system 2. venous system

B. Together these two systems form two major circulatory loops BioBookcircSYS.html#Vertebrate Cardiovascular Syste 1. systemic loop 2. pulmonary loop

C. Diagram of general pattern of cardiovascular circulation

III. Structure of vessels I - General structure of larger blood vessels. A. Blood vessels larger than capillaries are encircled by 2 or more of the following tissue layers. In most instances, all 3 layers are present. tunica intima tunica media tunica adventitia

1. tunica intima (often referred to as the "intima"). Starting from the inside of the blood vessel and moving outward. a. layer of simple squamous epithelium called endothelium. b. the endothelial layer is encircled by a subendothelial layer of loose connective tissue that may contain some smooth muscle cells.

c. In arteries, the intima often appears scalloped (wrinkled) in sections due to contraction of the smooth muscle cells present in the subendothelial layer. 1. tunica intima

2. tunica media ("media") III. Structure of vessels I - General structure of larger blood vessels. a. this layer encircles the intima b. consists of circumferential smooth muscle with extracellular matrix secreted by the muscle cells collagen, elastin, various proteoglycans c. in muscular arteries a layer of elastin called the internal elastic lamina separates the intima and media

e. in large blood vessels, the media receives nutrients from arterioles/capillaries that branch off of arterioles in the adventitia and extend into it. 2. tunica media (or "media") d. in larger muscular arteries, an external elastic lamina separates the media from the outer adventitial layer. bank/chapter_3/Slide_58_artery/pages/b htm

3. tunica adventitia (or "adventitia") III. Structure of vessels I - General structure of larger blood vessels. a. connective tissue layer with high content of collagen and elastic fibers in extracellular matrix between fibroblasts b. this layer gradually becomes continuous with the connective tissue of the organ/tissue the vessel is in

ulatory/o_c_10.html c. in larger vessels a network of small blood vessels called the vasa vasorum is present in the adventitia. Branches of these vessels (arterioles, capillaries) venules) will extend into the tunica adventitia and the outer half of the media. * these provide nutrients to cells in the adventitia and media.

IV. Structure of vessels II - General relationship between tunics and arterial and venous vessels

V. Structure of vessels III - Arteries A. Large elastic arteries (e.g. descending aorta and large branches thereof) 3. lots of elastin in tunica media that gives these vessels yellow color in life 1. very thick tunica intima consisting of the endothelium with a relatively thick sub-endothelial layer of loose connective tissue. An internal elastic lamina may or may not be present sub-endothelial basal lamina of intima may not be present

4. media consists of concentrically arranged sheets of elastin fibers smooth muscle cells collagen fibers. The number and thickness of the elastic layers increases with age 5. tunica adventitia is usually relatively thin with a vasa vasorum (network of blood vessels) A. Large elastic arteries (e.g. decending aorta and large branches thereof)

B. Muscular arteries 1. essentially all the named and unnamed arteries in the body, except for the large elastic arteries, are muscular arteries. 2. tunica intima very thin - consists of endothelium and a flattened subendothelial layer of collagen and elastic fibers. A predominant feature of the intima is the internal elastic lamina. MPLES/Exmusart.htm lar.htm

5. larger muscular arteries may have an external elastic lamina. 6. adventitia is well developed and may be thinner than media. 4. spasmodic contraction of the media smooth muscle helps prevent hemorrhaging during injury. 3. the tunica media is the major identifying characteristic. It consists of a thick smooth muscular layer with as many as 40 layers of smooth muscle encircling the artery. B. Muscular arteries lar.htm

C. Arterioles 1. arterioles are small arteries, mm in diameter 2. tunica intima consists of the endothelium - no sub-endothelial layer of loose connective tissue 3. media is muscular and composed of 1-3 layers of smooth muscle 4. adventitia is fairly prominent atory/images/ff518.jpg

D. Metarterioles 1. metarterioles connect larger arterioles to capillaries 2. less than 40  m in diameter 3. consist of endothelium surrounded by a few discontinuous smooth muscle fibers 4. Smooth muscle cells act as sphincters that control the flow of blood through capillary beds

VI. Structure of vessels IV A. Capillaries 1. usually 7-9  m in diameter, but may be as small as 5  m or as large as 12  m in diameter or even up to 40  m in the case of sinusoidal capillaries. 2. wall consists of a simple squamous epithelium called endothelium. This is just the continuation of the endothelium that lines the whole circulatory system, without the various additional connective tissue and muscular layers that we find surrounding larger blood vessels.

3. this simple squamous epithelium is surrounded by a basal lamina. 4. cells called pericytes may be sporadically found between the basal lamina and the endothelial cells. These cells may be able to contract and thus constrict capillaries

VI. Structure of vessels IV 5. The circumference of the endothelial wall of a capillary is formed by 2-3 squamous cells A. Capillaries a. held together by occluding or gap junctions b. nuclei bulge into the capillary lumen (as opposed to pericytes).

circulatory/o_c_4.html A. Capillaries - examples

6. The walls of certain types of capillaries a. may have fenestrae (holes, sometimes with diaphragms) penetrating the squamous endothelial cells b. or there may be spaces (pores) between adjacent endothelial cells

B. There are 3 types of capillaries. 1. continuous capillaries a. no fenestrae or pores in wall b. most capillaries are of this type

2. fenestrated or perforated capillaries a. fenestrations (or pores) penetrate the endothelial cells - may have diaphragm. b. found in tissues where rapid exchange of substances occurs (found principally in capillaries of the villi of the intestinal wall and glomeruli of the kidney).

3. Sinusoids and sinusoidal capillaries a. highly convoluted and with enlarged diameter (30-40  m) b. open spaces are present between the endothelial cells c. many small multiple fenestrations without diaphragms penetrate the endothelial cells

d. phagocytic cells are present in and around the endothelial layer e. the endothelium lacks a continuous basal lamina g. found mainly in liver and hematopoietic organs such as bone marrow and spleen. f. In some cases the endothelium itself may be discontinuous

3. sinusoidal capillaries

Sinusoid in liver Sinusoid in spleen

C. So, in the case of capillaries with fenestrations or spaces between endothelial cells, we can see that these vessels are constructed to allow for the easy passage of materials (macromolecules) and sometimes cells (e.g. monocytes) into and out of the circulatory system. E. In continuous, as well as other types of capillaries, macromolecules can also be passed into or out of the circulatory system by what might be called transcellular pinocytosis. D. This can occur through fenestrations or spaces between cells. Capillaries