Welcome to lab classes in histology of organ systems.
The aim of these lab classes is to provide students with educational resources necessary to acquire basic practical skills of each subject, ie recognize, locate and describe the types of cells, tissues and structures of each organ.
Each of these practical sessions are structured around three main elements:
- Definition of learning objectives.
- Description of structures, tissues and cell types of the system.
- Exercises location of structures / cell types in virtual slide (which is in other link).
- Differentiate between endocardium, myocardium and epicardium, and identify the tissues that compose them.
- Differentiate between atrium and ventricle.
- Locate the elastic and collagen fibers of the heart wall.
- Identify the cardiac muscle fibers in the myocardium and the connective tissue of endomysium.
- Identify capillaries: the lumen and the endothelium.
- Distinguish the types of capillaries in electron microscopy.
- Differentiate between capillary, venules and arterioles.
- Locate the different layers of the elastic artery wall.
- Locate the different layers of the muscular artery wall.
- Locate the different layers of the wall of a vein.
- Differentiate between muscular artery and elastic artery.
- Differentiate between a vein and an artery.
The cardiovascular system's mission is to transport the blood which carries oxygen and nutrients to tissues and remove from them, CO2 and metabolic waste.
The cardiovascular system along with the lymphatic system are the circulatory system.
In the vascular system, the heart pumps blood into the arterial system that distributes in the capillary network, which produces the exchange of substances, then the blood is collected by the venous system that returns to the heart where it enters a new pumping cycle.
Cardiovascular system elements have a common basic structure of three layers:
- The innermost layer is formed by a simple squamous epithelium (endothelium) that covers all the cavities of the cardiovascular system. Below the epithelium is a thin layer of connective tissue.
- The middle layer consists of a matrix of connective tissue in which muscle cells may be found.
- The outer layer consists of connective tissue.
While transporting blood, the heart and larger vessels the exchange of substances does not occur by diffusion , so these elements have their own blood supply system is known as "vasa vasorum".
The heart consists of two ventricles and two atria that in cross section are easily distinguished. 1
The ventricles are larger and its wall is much thicker than the atria.
Both the ventricular and atrial wall have three layers: 2
- Endocardium: It is the innermost layer. It consists of a simple squamous epithelium (endothelium) lining the cardiovascular cavities. Underneath endothelium you can see a thin layer of connective tissue.
- Myocardium: It is the thickest layer and it is composed of cardiac muscle cells between thin strips of connective tissue (endomysium). In the endomysium can see many small capillaries that are responsible for blood supplying the muscle cells. 3
- Epicardium: tTe epicardium may be considered as the pericardium visceral layer. It consists of an epithelium (mesothelium) and below it a layer of dense connective tissue.
The internal shape of the atrial wall is very irregular because the atrium has a great capacity to hold to contain blood strain provided by the venous system, before passing it to the ventricles to be pumped. 4
The atrial wall has the same layers that the ventricular wall, with some differences. The myocardium has a thickness much smaller than the ventricle. In the atrial endocardial connective tissue predominate elastic fibers, this can be seen very easily in slides stained with orcein - picroíndigocarmín technique, in which these fibers are stained in a very characteristic dark red. This technique, also, stains in blue-green collagen fibers, and thus the in the atrial epicardium shows elastic fibers, although collagen fibers predominate. 5
To regulate the flow of blood from the atria to the ventricle and from the ventricle into the arteries there are heart valves.
To secure the valves in the underlying tissue they are arranged in a ring of fibrous connective tissue which anchor the valves. 6
Heart valves can be seen as outgrowths of the endocardium. Its structure is simple, is bounded on both sides by endothelium and in between is a layer of connective tissue. 7
Purkinje fibers are modified cardiac muscle cells to favor the spread of the impulse. These cells are usually located in the subendocardial area and can be easily distinguished from the muscle cells of the myocardium. 8
The structure of the arterial wall follows the pattern of three layers of the cardiovascular system itself. These layers are: 9 10
- Tunica intima (endothelium + thin layer of subendothelial connective tissue)
- Tunica media (smooth muscle cells in a matrix of connective tissue)
- Tunica adventitia (connective tissue).
Tunica media is the thickest of these three layers, as the arterial system serves as high pressure conducting system.
Based on the composition of the tunica media are two types of arteries:
- Muscular arteries in which smooth muscle cells are located between fibers (mainly collagenous) connective tissue. 9 10
- Elastic arteries, characterized by the connective tissue present in the tunica media is rich in elastic fibers 11 12 (this looks very good in slides stained with orcein technique-picroíndigocarmín, which stains elastic fibers dark red). 13 These are elastic arteries are those that emerge from the cardiac ventricles (aorta and pulmonary) 14 that need expanded capacity that the elastic fibers were provided.
In both types of arteries, the tunica intima is separated from the tunica media by the inner elastic lamina (composed by elastic fibers).this film is seen very easily in muscular artery slides since it is the unique sheet of elastic fibers in the area. 15 There is also an external elastic lamina, which separates the tunica media of the tunica adventitia. This film is more difficult to distinguish, as opposed to internal, is thinner and is not continuous.
Veins have the same layered structure of the arteries, which receive the same names. 16
Veins, unlike arteries, are a blood return system, driving at low pressure. This is why the tunica media is much thinner than the arteries, which is very useful to distinguish from arteries. 17 18
In fact only in large-caliber veins tunica media can be distinguished as such, in the small-caliber dinner becomes nonexistent.
Veins have valves to prevent the return of blood flow.
CAPILLARIES, VENULES AND ARTERIOLES
The arterioles are the junction element between the arterial system and capillary network. Its mission is to supply blood to the capillary network. To regulate the flow of blood into the capillary network use muscular cells of the tunica media to prevent high pressure in the capillaries or breaks of their walls.
Arterioles have a three-layer structure of the arteries but very simplified, where very often only the endothelium is distinguished, a very thin layer of connective matrix, a single smooth muscle cells and adventitia connective which coincides with surrounding connective tissue. 19
The capillary network is the area of cardiovascular system in which produces the exchange of substances with the tissues. To facilitate this exchange, structure of the capillary wall is highly simplified and only consists of an endothelial cell. 20 21
The capillaries have a very small diameter, just enough to pass an erythrocyte, which sometimes has to change its morphology to pass.
According to its wall are three types of capillaries:
- Continuous Capillaries: The wall is absolutely continuous and transport of substances is through the endothelial cell, both active transport and passive transport. The basal lamina is well developed and continuous. These capillaries are found in the CNS, lungs, skeletal muscle and most connective tissues. 21
- Fenestrated capillaries: Endothelial cells have holes, so that the exchange of substances takes place facilitated by fenestration. The basal lamina is well developed and continuous. These capillaries are found in the renal glomeruli, endocrine glands and intestine. 22
- Sinusoidal capillaries (sinusoids): The wall is broken so there is no kind of barrier to the exchange of substances, this is also helped by the fact that the basal lamina is discontinuous. The sinusoids are found in bone marrow, liver and spleen.
The mission is venules is collect the blood from capillary network and drain into the venous system.
In the venules can not distinguish a muscular tunica media, so that the wall is reduced to the tunica intima and connective tissue of the tunica adventitia which merges with the underlying connective tissue of the organ where it is. 23
To distinguish between capillaries, venules and arterioles the main criteria are lumen diameter and wall structure. 23 24
- Locate the three layers of the ventricular wall (endocardium, myocardium and epicardium) in the virtual slide 25a
- Locate the mesothelium and the endothelium in the virtual slide 25a
- Locate capillaries in the endomysium of the myocardium in the virtual slide 26
- Locate the three layers of the atrial wall (endocardium, myocardium and epicardium) in the virtual slide 25b
- Locate the mesothelium and the endothelium in the virtual slide 25b
- Locate the atrial lumen and erythrocytes in the virtual slide 25b
- Locate elastic fibers in the endometrium handset in the virtual slide 27
- Locate elastic fibers in the tunica media of elastic artery in the virtual slide 27 28
- Locate the three layers of the arterial wall in the virtual slide 29
- Locate the tunica intima in the virtual slide 30
- Locate the elastic fibers and muscle cells in the arterial tunica media in the virtual slide 29
- Locate the inner elastic lamina in the virtual slide 30
- Distinguish between vein and artery in the virtual slide 31
- Locate the three tunics of both the vein and the artery in the virtual slide 31
- Locate capillaries and venules in virtual slide 32c
- Locate capillaries in the kidney glomeruli in the virtual slide 33b
- Locate hepatics sinusoids in the vistual slide 34
|Species / Animal group||Rat|
|Microscopy Method||Light field optical microscopy|
|Staining method||Masson's Trichrome|
|Section thickness||5-10 um|
This interactive image shows a cross section of rat heart stained with Masson trichrome technique.
It can be seen clearly atria and ventricles, and the initial portions of the aorta and pulmonary artery. It is also distinguished the ventricular septum that separates the ventricular cavity into two.
This class is opened to collaborations. If you wish to contribute with graphic or written material you can do so sending it from here. The author will receive it and then decide to include it or not, citing you as the source of the material.
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