Lecture/Lab: Circulatory System Flashcards
tunica intima
inner endothelial layer
tunica media
muscular layer
tunica adventitia
layer of binding connective tissue.
The name “tunica adventitia”, in particular, bows to the fact that the circulation is a system derived from the mesodermal layer of the embryo, and is by default surrounded by mesodermal structures in the adult.
arteries
function is to control and partition the flow of blood, and buffer the pressure differential in the blood stream caused by the heart’s pumping action. The arterial system controls blood distribution down to the sub millimeter level in most organs, normally terminating in capillary beds
Capillary beds
function is to allow the transfer of gases and nutrients to those target organs
Veins
Blood is returned to the heart at relatively low pressure by a network of veins, that increase in diameter. The largest of the veins must work to buffer any change in blood volume, lest the heart be made to work against an excessive pressure gradient.
Veins tend to travel with companion arteries and nerves. Remember that an artery will always have a thicker tunica media than its companion vein. The companion vein usually appears larger in diameter.
What are the four possibilities for vessels of small size?
arterioles (the smallest branches of the arterial system), capillaries (whose lumen is comparable to the size of a single red blood cell), venules, and lymphatic vessels
Arterioles
have smooth muscle in their walls, a continuation of the circular smooth muscle of the muscular arteries that feed them.
Generally, arterioles have only one or two layers of smooth muscle.
Notice that the smooth muscle cell, which is a cigar-shaped cell has a nucleus that is elongated in a direction perpendicular to that of the endothelial cell nucleus, whose cell is shaped like an oval pancake. The contrast between the two adjacent nuclei, one cut longitudinally and one cut transversely, is often crucial to the identification of the arteriole.
Note also that the smooth muscle is more eosinophilic than the surrounding connective tissue. That layer (which may be only one cell thick) forms the tunica media of the arteriole. The endothelial cell forms the bulk of the tunica intima layer.
How to distinguish venules and capillaries?
Capillaries and venules are distinguished primarily on their size. Blood cells pass through capillaries in single-file. Thus, a capillary is roughly equal to, or less than the diameter of a red blood cell. Anything larger is a venule.
Venules
Whereas the venous system begins to attain a distinct tunica media as the vessels grow larger, smooth muscle is absent in the smallest venules, so the tunica media is also absent.
For comparably sized elements of the arterial and venous systems, the venous vessel will have a much thinner tunica media than the arterial vessel. One must develop an expectation for how much smooth muscle to see in a given sized vessel.
How to distinguish between continuous, fenestrated and sinusoidal capillaries?
can not be made in the LM, except perhaps indirectly, by inference based on the vessel’s location. (A capillary in the brain or among skeletal muscle will be of the continuous variety. A capillary in the intestines, or in an endocrine organ will be fenestrated. Sinusoidal capillaries are often larger in diameter, but even then you must infer from position within an organ that the vessel is a sinusoidal capillary. They are morphologically indistinguishable from venules in standard preparations).
Lymphatic vessel
The wall of a lymphatic vessel, even the large ones, consists only of the endothelium and a small amount of subjacent connective tissue.
The cells are not held in place as well as those of the veins, and their nuclei usually protrude into the vessel lumen. The smaller vessels have an angular appearance to their walls that is not apparent in veins, and the larger vessels may have valves within them.
Elastic arteries
The bulk of the wall forms the tunica media
Elastic lamellae and Lamellar units
alternating layers of smooth muscle and elastic fibers (elastic arteries).
The elastic fibers, if they were to be seen in a tangential section, would look like a fenestrated sheet (i.e., a solid layer with holes in it). Thus these layers are referred to as elastic lamellae. One of the repeating units, consisting of one layer of smooth muscle and one of its adjacent elastic lamellae, forms a structure referred to as a lamellar unit.
What is the difference between an elastic artery and a muscular artery?
From Google:
An elastic artery, like the aorta, is located closer to the heart and has a larger proportion of elastic tissue in its walls, allowing it to expand and recoil with each heartbeat to maintain steady blood flow, while a muscular artery has a thicker layer of smooth muscle, enabling it to actively regulate blood flow by constricting or dilating depending on the body’s needs
From Lab Doc:
Unlike the elastic artery, which is designed to buffer the pressure difference between systole and diastole, the muscular artery is primarily designed to control the distribution of blood as it branches. The lamellar units of the tunica media in muscular arteries are replaced with continuous layers of smooth muscle. The innermost elastic lamella, at the border of the tunica intima, is retained and strengthened, and is referred to as the internal elastic lamina (sometimes called internal elastic membrane). In larger muscular arteries, the outermost layer is also retained. It is termed the external elastic lamina.
internal elastic lamina
(sometimes called internal elastic membrane)
In muscular arteries, the innermost elastic lamella, at the border of the tunica intima, is retained and strengthened
Special veins
The largest veins, such as the vena cava, portal vein, and some select other veins, have a special morphology. They have the function of buffering changes in blood volume, and thus the capability to reduce their lumenal volume by contracting along their length. To carry out such contraction, smooth muscle fibers must be longitudinally arranged. Such longitudinal smooth muscle fibers are found in the tunica adventitia, and are characteristic of the largest veins.
epicardium
The outermost layer of the heart proper, the epicardium (visceral pericardium) is a serosa. It is a simple squamous epithelium plus a thin layer of subjacent collagenous connective tissue.
subepicardium
a layer of connective and adipose tissue, of varying thickness, that importantly contains the major cardiac vessels.
vasa vasorum
The vasculature of the tunica adventitia layer of very large vessels (aorta)
nervi vascularis
The innervation in the tunica adventitia of very large vessels
coronary sinus
draining deoxygenated blood from the heart muscle into the right atrium
Blood from the heart wall drains into the coronary sinus, then into the right atrium
Embolus
a thrombus, detached atheromatous plaque, or other foreign body that travels within the cardiovascular
system and lodges in a vessel, fully or partially occluding the vessel
arterial embolus
travels away from the heart through progressively smaller vessels
venous embolus
travels toward the heart through progressively larger vessels.
left and right CORONARY ARTERIES
the first branches of the aorta, supply the heart itself
