Muscle tissue

Muscle Tissue 

If it contracts, it's muscle:

Muscle tissue is categorized on the basis of a functional property: the ability of its cells to contract. In muscle tissue, the bulk of the cytoplasmic volume consists of the contractile protein fibrils actin and myosin. Muscle is responsible for movement of the body and changes in the size and shape of internal organs. Muscle cells are generally referred to as muscle fibres. (Note that the term "fibre" is used both for muscle cells, and for the extracellular elements, eg. collagen, produced by connective tissue cells.) Muscle fibres are typically arranged in parallel arrays, allowing them to work together effectively.

The structure and physiology of muscle will be studied in detail in the Homeostasis and Development Block. Here, we will discuss only the identifying features of the different types of muscle. Additional information on the histology of muscle is found in Ross et al., chapter 10.

The three types of muscle:

Three types of muscle tissue can be identified histologically: skeletal muscle, cardiac muscle and smooth muscle. The fibres of skeletal muscle and cardiac muscle exhibit cross striations at the light microscope level and they are both referred to as striated muscle.

Skeletal muscle
Skeletal muscle constitutes the muscle that is attached to the skeleton and controls motor movements and posture. There are a few instances where this type of muscle is restricted to soft tissues: the tongue, pharynx, diaphragm and upper part of the esophagus. (Some people use the term visceral striated muscle in the foregoing examples, but since it is identical in structure to the muscle that moves the skeleton, we won't bother with the extra term.)
Skeletal muscle fibres (cells) are actually a multi nucleated syncytium formed by the fusion of individual small muscle cells or myoblasts, during development. They are filled with longitudinally arrayed sub units called myofibrils. The myofibrils are made up of the myofilaments myosin (thick filaments) and actin (thin filaments). The striations reflect the arrangement of actin and myosin filaments and support structures. The individual contractile units are called sarcomeres. A myofibril consists of many sarcomeres arranged end to end. The entire muscle exhibits cross-striations because sarcomeres in adjacent myofibrils and muscle fibers are in register. The most obvious feature in longitudinal sections of skeletal muscle is the alternating pattern of dark and light bands, called respectively the A (anisotropic) and I (isotropic) band. The I band is bisected by a dense zone called the Z line, to which the thin filaments of the I band are attached.
The nuclei are located peripherally, immediately under the plasma membrane (sarcolemma). The thickness of individual muscle fibres varies (depending for example on location in the body and exercise) but each fibre is of uniform thickness throughout its length. Skeletal muscle fibres do not branch.
Connective tissue elements surround muscle fibres. Individual muscle fibres are surrounded by a delicate layer of reticular fibres called the endomysium. Groups of fibres are bundled into fascicles by a thicker CT layer called the perimysium. The collection of fascicles that constitutes one muscle is surrounded by a sheath of dense CT called the epimysium, which continues into the tendon. Blood vessels and nerves are found in the CT associated with muscle. The endomysium contains only capillaries and the finest neuronal branches.

Summary: Skeletal muscle fibres bear obvious striations, have many peripherally located nuclei, are of the same thickness throughout their length and do not branch.



Cardiac muscle
Cardiac muscle is the type of muscle found in the heart, and at the base of the venae cavae as they enter into the heart. Cardiac muscle is intrinsically contractile but is regulated by autonomic and hormonal stimuli.
Cardiac muscle exhibits striations because it also has actin and myosin filaments arranged into sarcomeres. Generally these striations do not appear as well-defined as in skeletal muscle. (At the ultrastructural level, some differences in the arrangement of the sarcoplasmic retiuculum and T tubules can be seen. Cardiac muscle also has a much greater number of mitochondria in its cytoplasm. More details on the anatomy and physiology of muscle will be discussed in H&D and Cardiovascular Blocks.)
At the light microscope level, a number of features distinguish cardiac from skeletal muscle. Cardiac muscle cells have only one or two nuclei, which are centrally located. The myofibrils separate to pass around the nucleus, leaving a perinuclear clear area (not always evident in standard preparations). This clear area is occupied by organelles, especially mitochondria (which are of course not visible in LM). As in skeletal muscle, individual muscle fibres are surrounded by delicate connective tissue. Numerous capillaries are found in the connective tissue around cardiac muscle fibres.
Cardiac muscle cells are joined to one another in a linear array. The boundary between two cells abutting one another is called an intercalated disc. Intercalated discs consist of several types of cells junctions whose purpose is to facilitate the passage of an electrical impulse from cell to cell and to keep the cells bound together during constant contractile activity. Unlike skeletal muscle fibres, cardiac muscle fibres branch and anastomose with one another. Although made up of individual fibres, heart muscle acts as a functional syncytium during contraction for the efficient pumping of blood.
Specialized fibres, called Purkinje fibres, arise from the atrioventricular node and travel along the interventricular septum toward the apex of the heart, sending branches into the ventricular tissue. Purkinje fibres are of larger diameter than ordinary cardiac fibres, with fewer myofibrils and an extensive, well-defined clear area around the nucleus. They conduct impulses at a rate about four times faster than that of ordinary cardiac fibres and serve to coordinate the contraction of the atria and ventricles.

Summary: Cardiac muscle fibres are striated, have one or two centrally located nuclei, branch and anastomose with other fibres, and are joined to one another by intercalated discs.

Smooth muscle
Smooth muscle is the intrinsic muscle of the internal organs and blood vessels. It is also found in the iris and ciliary body of the eye and associated with hair follicles (arrector pili). No striations are present in smooth muscle due to the different arrangement of actin and myosin filaments. (The arrangement of the filaments and mechanism of contraction is described on pg. 230-234, ch. 10 of Ross et al.) Like cardiac muscle, smooth muscle fibres are intrinsically contractile but responsive to autonomic and hormonal stimuli. They are specialized for slow, prolonged contraction.
Smooth muscle fibres are generally arranged in bundles or sheets. Each fibre is fusiform in shape with a thicker central portion and tapered at both ends. The single nucleus is located in the central part of the fibre. Fibres do not branch. They range enormously in size, from 20 (in wall of small blood vessels) to 500 (in wall of uterus during pregnancy) micrometers. Smooth muscle fibres lie over one another in a staggered fashion (tapered part of one fibre over thicker part of another). In longitudinal sections, it is often not possible to distinguish the fibre boundaries, and smooth muscle may closely resemble connective tissue (bundles of collagen). Where smooth muscle bundles are interlaced with bundles of connective tissue (eg. in the uterus), one can distinguish the smooth muscle by the orientation of the nuclei (all oriented in the same direction), and the greater abundance of nuclei per unit area (every smooth muscle cell has a nucleus, fibroblast nuclei are more scattered in bundles of CT). Also, smooth muscle nuclei often have a corkscrew shape in longitudinal section due to contracton of the muscle fibre during fixation. In cross section, smooth muscle appears as profiles of various sizes, depending on whether the cut went through the thick central part or tapered end of any individual fibre. Nuclei are seen only in the thicker profiles.
One distinguishing physiological feature of smooth muscle is its ability to secrete connective tissue matrix. In the walls of blood vessels and the uterus in particular, smooth muscle fibres secrete large amounts of collagen and elastin.

Summary: Smooth muscle fibres are fusiform with tapered ends, have a single centrally located nucleus, and do not exhibit striations.

Histology of the Heart

Histology of the Heart

The major part of the heart is constituted of cardiac muscle. This kind of muscle is found only in the heart and in the tunica media of the terminal parts of the venae cavae as they enter the heart. The layer of the heart consisting of cardiac muscle is called the myocardium. Its inner surface of the myocardium is lined with endocardium, and the outer surface with epicardium.

The Myocardium: 

Cardiac muscle is similar to skeletal muscle in many ways. Both types appear striated as a result of the arrangement of the actin and myosin filaments in the sarcomeres of the muscle fibres. The sarcolemma (plasma membrane) of both types has invaginations called T-tubules that spread depolarization throughout the cell. The signal is transmitted to the terminal cisternae of the sarcoplasmic reticulum, which are adjacent to the T-tubules. The release of calcium from the cisternae allows contraction to take place. The mechanism of muscle contraction (sliding filament) is the same in the cardiac and skeletal muscle.
There are differences in cardiac and skeletal muscle observable at the light microscope and ultrastructural level. Cardiac muscles fibres are of smaller diameter (about 15 micrometers) than most skeletal muscle fibres (10-100 micrometers). Cardiac muscle fibres are formed by individual muscle cells with one or two centrally placed nuclei, while skeletal muscle fibres are multinucleated protoplasmic units in which the nuclei are peripherally located. Cardiac muscle fibres branch and anastomose, skeletal muscle fibres do not. Cardiac muscle fibres are arranged in a linear array, each fibre is about 85-100 micrometers long. The junction between two cardiac muscle cells, called an intercalated disk, is another distinguishing feature. The intercalated disk is made up of three types of cell junctions: fascia adherentes, desmosomes and gap junctions.
At the ultrastructural level, the arrangement of T-tubules is more regularly organized in skeletal muscle, and they are found at the A-I junction, in contrast to the Z-line in cardiac muscle. T-tubules are usually associated with two terminal cisternae (triad) in skeletal muscle, versus one (diad) in cardiac muscle. The cisternae of skeletal muscle are much larger than those of cardiac muscle. Cardiac muscle is more vascularized and has more abundant mitochondria than does skeletal muscle (40% of volume vs. 2%), it also contains glycogen granules between the myofibrils. Physiologically, cardiac muscle is intrinsically rhythmic (contracts without outside stimulation) although it is regulated through nervous and hormonal mechanisms. The rate of cardiac muscle contraction is set by the sinoatrial node, whose intrinsic rhythm is the most rapid.

Cardiac muscle in longitudinal section

Figure 1 shows cardiac muscle in longitudinal section. The striations can be seen along the length of the muscle fibres. [The striations are easier to see when looking through the microscope, they are not as obvious on these scanned computer images.] The nuclei of the cardiac muscle cells lie in the middle of the cells. In a good face-view section, the nucleolus is well-stained and the rest of the nucleus has a delicate pattern. The myofibrils separate to bypass the nucleus, and there is often a perinuclear region in which no striations are seen. This region contains cytoplasmic organelles not directly involved in contraction.
Each muscle fibre is surrounded by an endomysium of delicate connective tissue with a rich capillary network. Although the reticular fibres of the endomysium are not usually seen, you will see the nuclei of fibroblasts between the muscle fibres and also many capillaries running alongside them. Fibroblast nuclei tend to be more flattened and darker staining than those of cardiac muscle cells and are of course peripherally located. [In your sections, you won’t be able to identify each nucleus. Find a good cardiac muscle nucleus with the features described above, then look for ones that look similar.]
Intercalated disks appear as slightly darker lines perpendicular to the length of the cardiac muscle fibres. Depending upon the preparation and the staining, intercalated disks can be obvious or barely identifiable.

Branching in cardiac muscle fibres

Figure 2 shows another longitudinal section of cardiac muscle. In this section, several cardiac fibres are seen branching.

Cross section of cardiac muscle

Figure 3 shows cardiac muscle fibres in cross section. The cut ends of the myofibrils appear stippled. When cross sections of myofibrils appear irregular, it probably indicates an area of branching. The nuclei of cardiac fibres are found near the middle of the cross section, sometimes a paler perinuclear region can be seen. Connective tissue runs between bundles of muscle cells, these bundles may become more widely separated during tissue preparation. Fibroblast nuclei will be found within the connective tissue or at the periphery of a muscle fibre (since each muscle fibre is also individually wrapped in endomysium). Many capillaries can be seen among the cardiac muscle fibres. The small empty circles among the muscle fibres are all capillaries (except for those larger than one RBC, they represent pre- or post-capillary vessels). The thickened areas of the capillary walls are endothelial cell nuclei. A large blood vessel, containing RBCs, is wrapped around a muscle bundle to the right of the figure, and a much smaller vessel (but too large to be a capillary), is a bit to the left of the large vessel. The endothelial cell nucleus in the smaller vessel is prominent.
The heart has a "skeleton" , which is the site for the origin and insertion of cardiac muscle. It consists of a fibrous ring surrounding each of the four orifices (aortic, pulmonary, tircuspid and mitral). The heart valves are attached to the cardiac skeleton.
Impulses originating in the sinoatrial node (SA node or pacemaker) pass along the cardiac muscle fibres of the atria and along internodal tracts of modified muscle fibres to the atrioventricular node (AV node) near the tricuspid valve. The AV node provides the only bridge between atrial and ventricular muscle. From the AV node, impulses pass across the fibrous skeleton of the heart to the ventricles via the AV bundle of His. The bundle of His divides into a right and left branch (the latter with 2 fascicles) which travel along the ventricular septum to the apex of the heart and then reverse their direction.
The branches of the bundle of His give off fibres, called Purkinje fibres, which are modified cardiac muscle cells with a diameter about twice that of regular fibres (30 vs. 15 micrometers). Purkinje fibres contain fewer myofibrils than regular cardiac muscle fibres and have large concentrations of glycogen. Their nuclei tend to be surrounded by a large perinuclear space with the myofibrils well toward the periphery of the muscle fibre. Purkinje fibres are much faster conducting than regular cardiac muscle fibres, with which they make contact via gap junctions. The impulse initiated in the SA node cause the atria to contract first and expel blood into the ventricles. The impulse is also carried along the internodal fibres to the AV node, bundle of His and its branches and then to the Purkinje fibres. Contraction of the ventricles begins at the apex and continues in a wavelike fashion toward the base, forcing blood into the aorta and pulmonary trunk.

Longitudional section of Purkinje fibers

Figure 4 shows Purkinje fibres in longitudinal section. Because of the lower density of myofibrils, Purkinje fibres appear paler than regular cardiac muscle fibres (a few of which can be seen at the bottom of the figure). A prominent perinuclear region is seen around several nuclei, and intercalated disks are evident. As in other cardiac muscle, capillaries are abundant. A capillary can be seen branching from a larger vessel near the middle, top third of the figure.
The Purkinje fibres shown in Figure 4 were scanned from. In this slide, collagen stains blue (Masson trichromic). This blue might be helpful in guiding you to the Purkinje fibres when you look at the slides under your microscope, as they are found in a layer of CT called the subendocardial layer (see below). (Little CT was visible in Figure 4, it would have been toward the top of the figure beyond the field of view).

Cross section of Purkinje fibres

Figure 5 shows Purkinje fibres in cross or oblique section embedded in the CT of the subendocardial layer. The wide diameter of the fibres and the large perinuclear region devoid of myofibrils can be seen clearly.

Regular cardiac fibres in cross section

 Figure 6 shows regular cardiac muscle fibres in cross section. It can be seen that the fibres are of smaller diameter, stain more darkly because of a higher density of myofibrils, and have a smaller perinuclear region than the Purkinje fibres of Figure 5.

The Endocardium: 

The endocardium lies on the luminal side of the myocardium. Its inner surface is covered with endothelial cells – the squamous epithelium lining the inside of the heart and blood vessels. Beneath the endothelium is a layer of fairly loose, well-vascularized connective tissue, this becomes a bit denser closer to the myocardium. The thickness of the endocardium varies inversely with the thickness of the myocardium. In other words, it is thicker in the atria than in the ventricles, as the muscular walls are more substantial in the ventricles. The layer of CT closest to the myocardium is slightly looser and is called the subendocardial layer. It contains veins and nerves, as well as the Purkinje fibres when present.
Figures 7 and 8 show the endocardial layer of the atrium and ventricle, respectively. At this magnification, the nuclei of the endothelial cells are barely distinguishable. The difference in the thickness of the endocardium between the atrium and ventricle is evident, both figures were scanned at the same magnification. Part if the myocardium is visible in both figures. No veins or nerves (or Purkinje fibres) are seen in the fields of view.

Endocardium of atrium

Endocardium of ventricle

The Epicardium: 

The epicardium is the delicate, inner visceral layer of the pericardium. We do not see the outer, fibroelastic parietal layer of the pericardium on our slides. The outer part of the epicardium is lined with mesothelium: the epithelium lining the walls and contents of the closed cavities of the body, such as the thoracic, pericardial and abdominal cavities. Large blood vessels and nerves are found in the epicardium, and adipose tissue can be abundant.

Low power view of epicardium

Figure 9 shows a low power view of the epicardium of the ventricle. Part of the myocardium is also visible. In the field of view shown here, there is a large amount of adipose tissue within the connective tissue of the epicardium. A nerve bundle and several blood vessels can also be seen. The mesothelial lining (at the top) is not really distinguishable.

Higher power view of the epicardium

A higher power view of the epicardium is shown in Figure 10. The nerve is the same as the one in Figure 9 and can be used for orientation. Blood vessels are more easily identified (brighter red due to RBCs). The nuclei of the mesothelial cells can be distinguished (albeit with difficulty) at this magnification.

Gland

Glandular epithelium:

A)Presence or absence of ducts

 •Exocrine – ducted

 •Endocrine - ductless

B)Uni- or multicellular

C)Mode of secretion

D)  Secretion products

Gland categories :

1)  Exocrine - glands that exude secretions into a ductule system. Have two parts, acinous = secretory bulb and ductule.

2)  Endocrine - glands exuding secretions directly into body fluids, ultimately blood.

3)  Mixed - glands combining both the above characteristics (e.g. pancreas) in the same cell

Cellular composition :

1)Unicellular - single cell gland, Goblet cell;  mucous secreting.  GI tract, respiratory ducts. Secretion process alters cell and nucleus shape.

2)  Multicellular - 

  a)  intra epithelial gland - gland is entirely within a layer of epithelium. Common in pseudostratified columnar  epithelium.

 b)  extra epithelial gland - in Connective Tissue below epithelium; may   have different shapes; tubular  and  acinar

Modes of Secretion(how products leave the cell)

1)  Merocrine - secretion does not affect the well-being of the cell = sweat glands.

2)  Apocrine - small part of the cell cytoplasm is lost with the secretion; the cell is damaged   but not killed = mammary glands.

3)  Holocrine - great deal of cytoplasm is lost with the secretion; the cell dies.Sebaceous   glands.

Secretion product

1)  serous - thin, watery fluid, product of serous cells, small pink staining cuboidal cells with spherical to elliptical nuclei; salivary glands,sweat glands, pancreatic acinar

.2)  mucous - thicker, viscous secretion, product of mucous cells, large blue staining cuboidal cells with flat, elongate nuclei; GI tract, oral   cavity.

3)  mixed serous-mucous - oral cavity, salivary.

4) sebaceous - thick, lipid rich secretions of cuboidal cells in certain skin regions - face, nose, axillary and pubic regions.

Myoepithelium:

Myoepithelium - specialized squamous epithelial cells with powers of contraction;

Surround glandular acini and ducts of many glands,

Contain actin, myosin, cytotokeratin =definitely epithelial in origin, not muscle...

Tissue

Epithelial tissue:
It may be defined as collection of closely  aggregated polyhedral cells with very little intercellular substance covering internal and external surfaces of the body.

Functions:
1)Protection of the underlying structure
2)Secretion
3)Absorption

There are two major categories of epithelia:
Membranous and Glandular.

1.Membranous epithelia are located throughout the body and form such structures as the outer layer of the skin; the inner lining of body cavities, tubes, and ducts; and the covering of visceral organs.

2.Glandular epithelia are specialized tissues that form the secretory portion of glands.
Membranous epithelia are histologically classified by the number of layers of cells and the shape of the cells along the exposed surface.
3.Epithelial tissues that are composed of a single layer of cells are called simple; those that are layered are said to be stratified.
4.Squamous cells are flattened; cuboidal cells are cubeshaped; and columnar cells are taller than they are wide.

Simple Epithelia:
Simple epithelial tissue is a single cell layer thick and is located where diffusion, absorption, filtration, and secretion are principal functions.

Simple Columnar Epithelium:
Simple columnar epithelium is composed of tall, columnar cells. The height of the cells varies, depending on the site and function of the tissue.
Each cell contains a single nucleus which is usually located near the basement membrane . Simple columnar epithelium is found lining the inside walls of the stomach and intestine.

Simple Squamous Epithelium:
Simple squamous epithelium is composed of flattened, irregularly shaped cells that are tightly bound together.
Each cell contains an oval or spherical central nucleus. This epithelium is adapted for diffusion and filtration.
It occurs in the pulmonary alveoli within the lungs (where gaseous exchange occurs), in portions of the kidney (where blood is filtered),
n the inside walls of blood vessels, in the lining of body cavities, and in the covering of the viscera.

Simple Cuboidal Epithelium:
Simple cuboidal epithelium is composed of a single layer of tightly fitted cube-shaped cells. This type of epithelium is found lining small ducts and tubules that have excretory,  secretory,or absorptive functions.
It occurs on the surface of the ovaries, forms a portion of the tubules within the kidney, and lines the ducts of the salivary glands and pancreas.

Simple Ciliated Columnar Epithelium:
Simple ciliated columnar epithelium is characterized by the presence of cilia along its free surface. By contrast, the simple columnar type is unciliated.
Cilia produce  wavelike movements that transport materials through tubes or passageways. This type of epithelium occurs in the female uterine tubes to move the ovum (egg cell) toward the uterus.

Pseudo-stratified Ciliated Columnar Epithelium:
As the name implies, this type of epithelium has a layered appearance (strata = layers). Actually, it is not multilayered (pseudo = false), because each cell is in contact with the basement membrane.
The tissue appears to be stratified because the nuclei of the cells are located at different levels.
It is found lining the inside walls of the trachea and the bronchial tubes; hence, it is frequently called respiratory epithelium. Its function is to remove foreign dust and bacteria entrapped in mucus from the lower respiratory system.

Stratified Epithelia :
Stratified epithelia have two or more layers of cells. Stratified epithelia have a primarily protective function that is enhanced by rapid cell divisions.

Stratified Squamous Epithelium:
Stratified squamous epithelium is composed of a variable number of cell layers that are flattest at the surface.There are two types of stratified squamous epithelial tissues: keratinized and nonkeratinized.

1. Keratinized stratified squamous epithelium:
 It contains keratin, a protein that strengthens the tissue. Keratin makes the epidermis (outer layer) of the skin somewhat waterproof and protects it from bacterial invasion
 The outer layers of the skin are dead, but glandular secretions keep them soft.

2. Nonkeratinized stratified squamous epithelium:
 It lines the oral cavity and pharynx, nasal cavity, vagina, and anal canal. This type of epithelium, called mucosa (myoo-ko′sa˘),is well adapted to withstand moderate abrasion but not fluid loss.

Stratified Cuboidal Epithelium:
Stratified cuboidal epithelium usually consists of only two or three layers of cuboidal cells. This type of epithelium is confined to the linings of the large ducts of sweat glands, salivary glands, and the pancreas, where its stratification probably provides a more robust lining than would simple epithelium.

Transitional Epithelium:
Transitional epithelium is similar to nonkeratinized stratified squamous epithelium except that the surface cells of the former are large and round rather than flat, and some may have two nuclei.
Transitional epithelium is found only in the urinary system, particularly lining the cavity of the urinary bladder and lining the lumina of the ureters.
This tissue is specialized to permit distension (stretching) of the urinary bladder as it fills with urine
The inner, exposed cells actually transform from being rounded when the urinary bladder is empty to being somewhat flattened as it distends with urine.

Connective tissue is the most abundant tissue in the body. It supports other tissues or binds them together and provides for the metabolic needs of all body organs. Certain types of connective tissue store nutritional substances; other types manufacture protective and regulatory materials.
A. Embryonic connective tissue

B. Connective tissue proper
1. Loose (areolar) connective tissue
2. Dense regular connective tissue
3. Dense irregular connective tissue
4. Elastic connective tissue
5. Reticular connective tissue
6. Adipose tissue

C. Cartilage
1. Hyaline cartilage
2. Fibrocartilage
3. Elastic cartilage

D. Bone tissue

E. Blood (vascular tissue)

Histology of blood vessels

 Histology of blood vessels
 
The walls of arteries and veins are composed of endothelial cells, smooth muscle cells and extracellular matrix (including collagen and elastin).
 These are arranged into three concentric layers:
1. Intima
2. Media
3.Adventitia.

The intima is the inner layer abutting the vessel lumen.
The adventitia is the outer layer abutting the perivascular soft tissue.
The media is sandwiched between the intima and adventitia.

The intima is the thinnest layer.  It is composed of a single layer of endothelial cells and a small amount of subendothelial connective tissue.
The intima is separated from the media by a dense elastic membrane called the internal elastic lamina.
The media is the thickest layer and provides structural support, vasoreactivity and elasticity.  It is composed of smooth muscle cells, elastic fibres and connective tissue, which vary in amount depending on the type of vessel. Smooth muscle cells contract (vasoconstriction) or relax (vasodilatation), which is controlled by autonomic nerves (nervi vasorum) and local metabolic factors.  Elastic fibres allow the vessel to expand with systole and contract with diastole, thereby propelling blood forward.  The media is separated from the adventitia by a dense elastic membrane called the external elastic lamina.
The adventitia is composed of connective tissue, nutrient vessels (vasa vasorum) and autonomic nerves (nervi vasorum).
The intima and inner part of the media are nourished by diffusion of oxygen and nutrients from blood in the lumen, and the adventitia and outer part of the media are nourished by vasa vasorum

Arteries:
The walls of arteries are thicker than that of veins to withstand pulsatile flow and higher blood pressures.  As arteries become smaller, wall thickness gradually decreases but the ratio of wall thickness to lumen diameter increases (ie. relative lumen size decreases).
Arteries are divided into three types according to size and function.  The constituents of the media of these vessels differ in their relative amounts accordingly.
Large elastic arteries (aorta, large aortic branches [eg. innominate, subclavian, common carotids, iliacs] and pulmonary arteries) – the media is abundant in elastic fibres that allow it to expand with systole and recoil during diastole, thereby propelling blood forward.
Medium-sized muscular arteries (other aortic branches, eg. coronary and renal arteries) – the media is abundant in smooth muscle cells that vasoconstrict or vasodilate, thereby controlling lumen diameter and regional blood flow.
Small arteries and arterioles (in the substance of organs and tissues) - the media is abundant in smooth muscle cells that vasoconstrict or vasodilate.  In vessels of this size, smooth muscle contraction causes dramatic changes in lumen diameter, thereby controlling systemic blood pressure as well as regional blood flow.

Capillaries:
Capillaries connect arterioles with venules.  They consist only of a single layer of endothelial cells on a basement membrane.  There is no media or adventitia.  The diameter is just wide enough for passage of a red blood cell, therefore flow is very slow.  These features facilitate exchange of oxygen, nutrients and other substances between blood and tissues.

Veins:
Post capillary blood flows into venules and then into progressively larger veins.
Compared to arteries, veins have larger diameters and thinner walls.  They therefore have larger lumens and contribute capacitance to the circulation, holding approximately two thirds of all circulating blood.
The intima and adventitia are similar in structure and function to arteries but the media is much thinner due to significantly less smooth muscle and elastic tissue.  Veins therefore do not have the same capacity for elastic recoil and vasoconstriction as arteries.  Blood is propelled forward by contraction of surrounding muscles and pressure gradients created during inspiration and expiration.  Reverse flow is prevented by the presence of venous valves.
The flaccid walls of veins predispose them to compression and penetration by tumour and inflammatory processes.

Thanks for reading !!! :D