CIRCULATORY SYSTEM I.
How do vampires like to travel?
By blood vessel!
I. There are two major components of the circulatory system.
A. The cardiovascular system:
1. heart
2. arteries
3. arterioles
4. capillaries
5. venules
6. veins
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.
http://www.cs.stedwards.edu/~kswank/LymphSyst.html
II. General cardiovascular
circulation
A. Two major components
1. arterial system
2. venous system
http://www.accessexcellence.org/AE/AEC/CC/art_vein.gif
B. Together these two systems form two
major circulatory loops
1. systemic loop
2. pulmonary loop
http://gened.emc.maricopa.edu/bio/bio181/BIOBK/
BioBookcircSYS.html#Vertebrate Cardiovascular Syste
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
http://www.medsch.wisc.edu/anatomy/histo/res/l/cv/cv21.jpg
http://www.mmi.mcgill.ca/Unit2/McKee/lect47histcapillariesbv.htm
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.
http://medic.med.uth.tmc.edu/edprog/images/Cv1.jpg
1. tunica intima
http://meded.ucsd.edu/hist-img-bank/chapter_3/Slide_58_artery/pages/a.2.58.2.1.htm
c. In arteries, the intima often appears scalloped (wrinkled) in sections due to
contraction of the smooth muscle cells present in the subendothelial layer.
III. Structure of vessels I - General structure of larger blood vessels.
2. tunica media ("media")
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
http://medic.med.uth.tmc.edu/edprog/images/Cv1.jpg
2. tunica media (or "media")
d. in larger muscular arteries, an
external elastic lamina separates the
media from the outer adventitial layer.
e. in large blood vessels, the media
receives nutrients from
arterioles/capillaries that branch off of
arterioles in the adventitia and extend
into it.
http://meded.ucsd.edu/hist-imgbank/chapter_3/Slide_58_artery/pages/b.2.58.2.2.htm
III. Structure of vessels I - General
structure of larger blood vessels.
3. tunica adventitia (or "adventitia")
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
http://128.218.123.161/IDS_100/vessels/fig2.html
http://medic.med.uth.tmc.edu/edprog/images/Cv1.jpg
http://medic.med.uth.tmc.edu/edprog/images/Cv1.jpg
http://www.finchcms.edu/anatomy/histology/organology/circ
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)
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.
2. sub-endothelial basal lamina of intima
may not be present
3. lots of elastin in tunica media that
gives these vessels yellow color in life
http://www.lab.anhb.uwa.edu.au/mb140/
A. Large elastic arteries (e.g. decending aorta and large branches thereof)
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)
http://www.lab.anhb.uwa.edu.au/mb140/
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.
http://www3.umdnj.edu/histsweb/lab7/lab7musleartery.html
http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab12b/EXA
MPLES/Exmusart.htm
http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Vascular/Vascu
lar.htm
B. Muscular arteries
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.
4. spasmodic contraction of the media
smooth muscle helps prevent
hemorrhaging during injury.
5. larger muscular arteries may have an
external elastic lamina.
6. adventitia is well developed and may be
thinner than media.
http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Vascular/Vascu
lar.htm
C. Arterioles
1. arterioles are small arteries, 0.04
- 0.4 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
http://www.finchcms.edu/anatomy/histology/organology/circul
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
http://128.218.123.161/IDS_100/vessels/fig12.html
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.
http://128.218.123.161/IDS_100/vessels/fig11.html
http://128.218.123.161/IDS_100/vessels/fig7.html
http://www.medscape.com/content/2004/00/46/94/469492/469492_fig.html
http://128.218.123.161/IDS_100/vessels/fig11.html
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
A. Capillaries
5. The circumference of the endothelial wall of a capillary is formed by 2-3
squamous cells
a. held together by occluding or gap junctions
b. nuclei bulge into the capillary lumen (as opposed to pericytes).
http://cal.vet.upenn.edu/histo/bloodvessels/capillary.html
A. Capillaries - examples
http://www.finchcms.edu/anatomy/histology/organology/
circulatory/o_c_4.html
http://www.udel.edu/Biology/Wags/histopage/colorpage/cbv/cav.GIF
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
http://128.218.123.161/IDS_100/vessels/fig6.html
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).
http://www.mmi.mcgill.ca/Unit2/McKee/lect47histcapillariesbv.htm
3. Sinusoids and sinusoidal capillaries
a. highly convoluted and with
enlarged diameter (30-40  m)
c. many small multiple
fenestrations without
diaphragms penetrate the
endothelial cells
b. open spaces are present
between the endothelial cells
http://www.finchcms.edu/anatomy/histology/organology/circulatory/images/ff549.jpg
d. phagocytic cells are present in and around the endothelial layer
e. the endothelium lacks a continuous basal lamina
f. In some cases the endothelium itself may be discontinuous
g. found mainly in liver and hematopoietic organs such as bone marrow and spleen.
3. sinusoidal capillaries
http://www.mmi.mcgill.ca/Unit2/McKee/lect47histcapillariesbv.htm
Sinusoid in spleen
Sinusoid in liver
http://www.medinfo.ufl.edu/year1/histo/images/k13h.jpg
http://www.finchcms.edu/anatomy/histology/organology/lymphoid/images/ff649.jpg
Capillaries
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.
D. This can occur through fenestrations or spaces between cells.
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.