CIRCULATORY SYSTEM II
VIII. Structure of vessels 6 - Venous vessels
A. post capillary venules (those venules directly connected to capillaries).
1. 30  m - 200  m in diameter (bigger than most capillaries)
2. consist of endothelium with incomplete layer of pericytes that are located
between the endothelial cells and the basal lamina of the endothelium.
http://www.finchcms.edu/anatomy/histology/organology/circulatory/images
VIII. Structure of vessels 6 - Venous vessels
A. post capillary venules
3. Wall lacks smooth muscle cells and instead has longitudinally arranged
fibroblasts and associated reticular fibers. These do not form a complete layer
around the vessel.
4. Note the difference between the
pre-capillary arteriole and postcapillary venule in this photograph.
The nuclei of circumferential smooth
muscle cells can be seen in the
arteriole, while they are lacking in the
venule.
http://www.finchcms.edu/anatomy/histology/organology/circulatory/images
http://www.mmi.mcgill.ca/Unit2/McKee/lect47histcapillariesbv.htm
B. venules (beyond the post-capillary venules)
1. 0.2 - 1 mm in diameter
2. intima usually lacks an obvious subendothelial layer of
connective tissue
3. thin media consisting of a few smooth muscle cells. As venule
size increases, the amount of smooth muscle increases.
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/vls2.GIF
B. venules
4. well developed adventitia rich in collagen fibers.
5. despite tunic investments, blood cells such as monocytes can still pass
through the walls of venules
a. the process utilized by monocytes to pass through capillary or venule walls is
called diapedesis - the act of a leukocyte squeezing through small spaces
between cells
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/vls2.GIF
C. small to medium sized veins
1. 1-9 mm in diameter
2. intima usually has a thin sub-endothelial layer of connective tissue
associated with endothelium. Sub-endothelial layer of C.T. is absent in
some cases.
http://www.auburn.edu/academic/classes/zy/hist0509/index_histology.html
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/savp1.GIF
C. small to medium sized veins
3. thin media
4. well developed adventitia rich in collagen fibers.
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/savp1.GIF
C. small to medium sized veins
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/avp.GIF
D. large veins
1. intima is well developed
2. media is muscular, but thin relative to that of muscular arteries with similar
lumen size. A few circular layers of smooth muscle are present amongst
abundant connective tissue.
3. adventitia is thickest and best developed tunic. Comprises most of wall of
vessel.
May contain longitudinal bundles of smooth muscle and
vasa vasorum.
4. this arrangement of longitudinal muscle in adventitia and circular in media
helps to strengthen wall and help prevent settling of blood in limb veins due
to gravity.
D. large veins
http://www.georgetown.edu/dml/educ/micro/cardio/17.htm
Human vena cava
•Intima thin - not resolvable at this magnification
•Media thin
•Adventitia - thick with bands of longitudinal smooth muscle,
vasa vasorum
5. in addition to this muscular arrangement, valves are also present in large
veins. These also help prevent back flow of blood.
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/valve1.GIF
6. skeletal muscle (in conjunction with the valves) is also helpful in
preventing backflow by propelling blood through veins in the correct
direction as the muscles contract.
http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookcircSYS.html#Vertebrate Cardiovascular Syste
IX. Heart
A. The heart is composed of
1. a fibrous connective tissue skeleton
2. Three layers or tunics
a. endocardium
b. myocardium
c. epicardium
3. valves
4. an electrical impulse conducting system
B. Tunics of the heart
1. endocardium - in a sense, simply a continuation of tunica intima
a. consists of 3 parts
* endothelium resting on a basal lamina and associated thin layer
of collangenous fibers
* Beneath the endothelium is the sub-endothelial layer of connective
tissue containing elastic fibers and a few smooth muscle cells
(some texts call this loose C.T. and others dense C.T.)
* Beneath that lies the subendocardial layer of loose connective
tissue that contains small blood vessels and nerves. In the
ventricle, the Purkinje fibers are associated with the
subendocardial zone.
1. endocardium - simply a continuation of tunica intima
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_13.html
2. Myocardium - consists of 2 components
a. fascicles of cardiac muscle cells that connect to the fibrous connective
tissue skeleton of the heart
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_14.html
b. Noncontactile, modified muscle cells that form the impulse (action potential) generating
and conducting system of the heart
* this system is composed of the atrioventricular and sinoatrial
nodes, and the Purkinje fibers
* Purkinje fibers - cardiac muscle
cells specialized for impulse (action
potential) generation and impulse
conduction
* the cells of this system generate
and conduct action potentials that
synchronize the heartbeat
a. autonomic nerve
b. Purkinje fibers c.
cardiac muscle
http://www.ttuhsc.edu/courses/cbb/histo/circsys/pg19jp.html
* Purkinje fibers are scattered along the innermost portion of the myocardium
in the ventricle, next to the endocardium
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_14.html
3. Epicardium - epithelium and connective tissue covering of heart. Also called
the visceral pericardium.
a. squamous to cuboidal epithelial external lining - a continuation of the
mesothelium that lines the pericardial cavity.
b. below this is a layer of connective tissue with high concentration of
elastic fibers - elastic layer
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_15.html
c. between the elastic layer and myocardium is the subepicardial layer which
consists of loose connective tissue containing nerves, arteries, veins, and
adipose tissue.
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_15.html
C. Valves - read in text, p. 117 (not much there).
X. A few words about the lymphatic vessels
A. System of thin walled vessels that runs throughout the body.
B. These vessels are lined with endothelium.
C. Larger lymphatic vessels are similar in structure to veins except with
thinner walls and with no clear cut separation between the 3 tunics (intima,
media, adventitia).
https://histo.life.uiuc.edu/histo/atlas/image.php?sname=w51a&
iname=40a15&oid=348
http://www.finchcms.edu/anatomy/histology/organology/circulatory/o_c_17.html
X. A few words about the lymphatic vessels
C. Lymph vessels begin with blind-ended capillaries
that originate in connective tissue of nearly all parts of
body.
D. These capillaries and associated small lymph
vessels converge into larger vessels that return fluid
expressed from arteries and veins into tissues to the
venous component of the blood circulatory system.
http://www.cs.stedwards.edu/~kswank/LymphSyst.html
E. All lymphatic vessels eventually drain into 2
large ducts, the thoracic duct (cisterna chyli)
and the less extensive right lymphatic duct
that, respectively, connect to the left and right
subclavian veins in the neck.
F. The lymph vessels are also a pathway by
which various cells of the immune system
can enter or leave the blood circulatory
system and tissues.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/I/ImmuneSystem.gif
http://www.cs.stedwards.edu/~kswank/LymphSyst.html
Thoracic duct (cisterna chyli, on left side, connects to left subclavian vein)
http://www.kumc.edu/instruction/medicine/anatomy/histoweb/vascular/vascular.htm
Lacteal - lymph vssel in lamina
propria of small intestine that
extends into a villus.
http://www.lab.anhb.uwa.edu.au/mb140/
http://www.finchcms.edu/anatomy/histology/organology/circulatory/images/ff561.jpg