Download Prelab 3 Circulatory

Prelab Exercise 3 –CIRCULATORY SYSTEM
CIRCULATORY SYSTEM
Arteries and veins are classified according to their size and the histology of their walls.
In each case, one should analyze thoroughly the tissue composition of each of the three
tunicas: intima, media, and adventitia. The histology of the media and adventitia is
particularly important in determining the type of vessel. Although vessels are subdivided
into categories on the basis of size and composition of the wall, there are no abrupt
boundaries between categories. Rather, the histology changes gradually from the larger
to the smaller vessels (see summary table, below).
ARTERIES – there are several types of arteries: elastic arteries; muscular ateries and
arterioles.
Large conducting (“elastic”) arteries have a relatively thin intima (endothelium and thin
layer of CT). Also, smooth muscle cells interdigitate with prominent lamellae of elastic
fibers in the thicker media. The adventitia also contains elastic fibers along with dense
collagen fibers and is thinner (relatively speaking) than in muscular arteries. There are
also vasa vasorum and nervi vascularis in the adventitia.
Medium-size, distributing (“muscular”) arteries. In general, the muscular arteries
correspond to the smaller named arteries which you dissect in gross anatomy lab. The
intima and internal elastic lamina are well-developed. The media has a predominance of
smooth muscle, with sparse elastic fibers. The adventitia is relatively thicker than in the
elastic arteries (see the figure below).
1
Prelab Exercise 3 –CIRCULATORY SYSTEM
Arterioles. Arterioles contain only a few layers of smooth muscle in the media and are
quite small (40-200 µm diameter). These vessels provide much of the peripheral
resistance to blood flow and therefore are involved in the regulation of blood flow and
pressure.
CAPILLARIES
Capillaries consist of an endothelium with a basement membrane. They are specialized to
permit (and in some cases restrict) the passage of things between the blood stream and
the interstitial spaces. Review the fine structure of the three types of capillaries
(continuous, fenestrated, and discontinuous). Especially note how capillary structure
is adapted to the physiologic requirements of each organ. For example, compare the
capillaries of the brain to those of the liver.
2
Prelab Exercise 3 –CIRCULATORY SYSTEM
Types of microcirculation formed by small blood vessels. (1) The usual sequence of arteriole –>
metarteriole –> capillary –> venule and vein. (2) An arteriovenous anastomosis. (3) An arterial portal
system, as is present in the kidney glomerulus. (4) A venous portal system, with a second capillary bed, is
present in the liver.
3
Prelab Exercise 3 –CIRCULATORY SYSTEM
VEINS
Veins have larger lumens, much less smooth muscle, a thinner intima (without internal
elastic lamina) and a thick connective tissue adventitia. Valves appear at intervals
through the venous system.
Diagram comparing the structure of a muscular artery (left) and accompanying
vein (right). Note that the tunica intima and the tunica media are highly developed in the
artery but not in the vein.
4
Prelab Exercise 3 –CIRCULATORY SYSTEM
CHARACTERISTICS OF BLOOD VESSELS
ARTERIES
VESSEL
ADVENTITIA)
Elastic artery
DIAMETER
> 1 cm
INNER LAYER
(TUNICA INTIMA)
MIDDLE LAYER
(TUNICA MEDIA)
OUTER LAYER
(TUNICA
Endothelium
Connective tissue
Smooth muscle
Elastic lamellae
Connective tissue
Elastic fibers
Thinner than tunica
Endothelium
Connective tissue
Prominent internal
Smooth muscle
Collagen fibers
Relatively little
Connective tissue
Some elastic fibers
Thinner than tunica
elastic lamina
elastic tissue
Ext. elastic lamina
Endothelium
Connective tissue
Internal elastic
Smooth muscle
(8-10 cell layers)
Collagen fibers
Connective tissue
Some elastic fibers
Thinner than tunica
Smooth muscle
Thin, ill-defined sheath
media
Muscular artery
Large
2 - 10 mm
media
Small
0.1 - 2 mm
media
lamina
Arteriole
of
40-200 µm
Endothelium
Connective tissue
Capillary
4 - 10 µm
Endothelium
(1-2 cell layers)
None
connective tissue
None
VEINS
VESSEL
DIAMETER
INNER LAYER
(TUNICA INTIMA)
MIDDLE LAYER
(TUNICA MEDIA)
OUTER LAYER
(TUNICA
ADVENTITIA)
Venule
50 - 100 µm
Endothelium
Pericytes
Smooth muscle
Connective tissue
(1 or 2 cell layers) Some elastic fibers
Thicker than tunica
0.1 - 1 mm
Endothelium
Smooth muscle
(2 or 3 layers
continuous with
media
Small vein
Connective tissue
Some elastic fibers
Thicker than tunica
media
tunica intima)
Medium vein
1 - 10 mm
Endothelium
Connective tissue
Smooth muscle
Collagen fibers
Connective tissue
Some elastic fibers
5
Prelab Exercise 3 –CIRCULATORY SYSTEM
Internal elastic membrane
Thicker than tunica
media
in some cases
Large vein
> 1 cm
Endothelium
Connective tissue
Smooth muscle
(2-15 layers)
Cardiac muscle
Connective tissue
Some elastic fibers
Much thicker than
tunica
near heart
media. sm. mus.
fascicles
Collagen fibers
LYMPHATIC VESSELS
The smallest lymphatics are often difficult to distinguish from capillaries and small
venules except for their greater variability in form and cross-sectional area. Larger
lymphatics resemble small venous channels, but have somewhat thinner walls, less welldefined tunicas, and an abundance of valves. Lymphatic channels should contain lymph
fluid (and some lymphocytes) in contrast to venous and arterial channels, which will
contain all blood elements.
CHECK LIST
VESSELS: Understand the architecture of both arteries and veins. Be aware of the
approximate diameter, composition, organization and relative thickness of:
-tunica intima
-tunica media
-tunica adventitia
Define:
-endothelium
-vasa vasorum
-nervi vascularis
-internal elastic lamina
-external elastic lamina
-metarteriole
-arteriovenous anastomosis
-continuous and fenestrated capillaries
-pericytes
-lymphatic vessels with valves.
6
Prelab Exercise 3 –CIRCULATORY SYSTEM
THE HEART
Cardiac muscle is found in only one site in the body, namely the wall of the heart. The
structure of this type of muscle tissue was studied specifically during the Muscle lab.
This lab will consider the muscle in context of the entire organ.
The walls of all chambers possess similar layers: endocardium, myocardium, and
epicardium, but the relative thickness of these layers and the detailed organization of the
tissues composing them vary radically in different chambers. (Note the respective
continuity of these layers with tunica intima, tunica media, tunica adventitia of blood
vessels.) Also, there are highly specialized structures such as the valves and their
reinforcing mechanisms, which require careful analysis. Because the heart is fairly
complex, it becomes important in the study of any section to determine precisely where it
was cut with reference to the total cardiac anatomy.
The “cardiac skeleton” is dense connective tissue between the atrium and ventricles that
provide an anchoring point for cardiac muscle and that limit the direct spread of electrical
activity in atrial muscle to the ventricles. The thin leaflets of the atrioventricular valve
intervening between the two heart chambers attach to the cardiac skeleton.
The epicardium (visceral pericardium) and subepicardial fat are outside of the
myocardium. This is the location of the coronary blood vessels.
7
Prelab Exercise 3 –CIRCULATORY SYSTEM
The cardiac conduction system is comprised of specially modified cardiac muscle cells
(Purkinji fibers). These are designed to transmit the electrical signal from the A-V node
to the ventricles through various branches. Their location, and the direction of
transmission of the cardiac impulse is shown in the figure below.
CHECK LIST
Know the histology of the heart, including the morphology of atrium and
ventricle.
Recognize the epicardium, myocardium and endocardium.
Understand the structure and importance of the cardiac skeleton.
Explain the role of Purkinje fibers in the heart and know their structures.
8