Vascular plants known as tracheophytes, form a large group of plants that are defined as those land plants that have lignified tissues for conducting water and minerals throughout the plant. They have a specialized non-lignified tissue to conduct products of photosynthesis. Vascular plants include the clubmosses, ferns and angiosperms. Scientific names for the group include Tracheophyta and Equisetopsida sensu lato; the term higher plants should be avoided as a synonym for vascular plants as it is a remnant of the abandoned concept of the great chain of being. Vascular plants are defined by three primary characteristics: Vascular plants have vascular tissues which distribute resources through the plant; this feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to small sizes. In vascular plants, the principal generation phase is the sporophyte, which produce spores and is diploid. By contrast, the principal generation phase in non-vascular plants is the gametophyte, which produces gametes and is haploid.
They have true roots and stems if one or more of these traits are secondarily lost in some groups. The formal definition of the division Tracheophyta encompasses both these characteristics in the Latin phrase "facies diploida xylem et phloem instructa". One possible mechanism for the presumed switch from emphasis on the haploid generation to emphasis on the diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. In other words, elaboration of the spore stalk enabled the production of more spores, enabled the development of the ability to release them higher and to broadcast them farther; such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane is as follows, with modification to the gymnosperms from Christenhusz et al. Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al.
This phylogeny is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns are not monophyletic. Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements; the xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall contains the polymer lignin; the phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
The most abundant compound in all plants, as in all cellular organisms, is water which serves an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is transpired from the plant through its stomata to the atmosphere and replaced by soil water taken up by the roots; the movement of water out of the leaf stomata creates a transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules; the draw of water upwards may be passive and can be assisted by the movement of water into the roots via osmosis. Transpiration requires little energy to be used by the plant. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts. Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure.
It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is due to high temperatures, high humidity, darkness or drought. Xylem and phloem tissues are involved in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves by photosynthesis and transported to the growing shoots and roots for use in growth, cellular respiration or storage. Minerals are transported to the shoots to allow cell division and growth. Fern allies Non-vascular plant “Higher plants” or “vascular plants”
The basement membrane is a thin, extracellular matrix of tissue that separates the lining of an internal or external body surface from underlying connective tissue in metazoans. This surface may be epithelium and endothelium As seen with electron microscope, the basement membrane is composed of two layers, the basal lamina and the underlying layer of reticular connective tissue; the underlying connective tissue attaches to the basal lamina with collagen VII anchoring fibrils and fibrillin microfibrils. The two layers together are collectively referred to as the basement membrane; the basal lamina layer can further be divided into two layers. The clear layer closer to the epithelium is called the lamina lucida, while the dense layer closer to the connective tissue is called the lamina densa; the electron-dense lamina densa membrane is about 30–70 nanometers thick, consists of an underlying network of reticular collagen IV fibrils which average 30 nanometers in diameter and 0.1–2 micrometers in thickness.
In addition to collagen, this supportive matrix contains intrinsic macromolecular components. The lamina densa, whose collagen IV fibers are coated with the heparan sulfate-rich proteoglycan perlecan, the lamina lucida together make up the basal lamina. Integrins are not part of the basal lamina, they are part of desmosomes which are in the basement membrane but not the basal lamina. To represent the above in a visually organised manner, the basement membrane is organized as follows: Epithelial/mesothelial/endothelial tissue Basement membrane Basal lamina Lamina lucida laminin integrins nidogens dystroglycans Lamina densa collagen IV Attaching proteins collagen VII fibrillin Lamina reticularis collagen III Connective tissue The primary function of the basement membrane is to anchor down the epithelium to its loose connective tissue underneath; this is achieved by cell-matrix adhesions through substrate adhesion molecules. The basement membrane acts as a mechanical barrier, preventing malignant cells from invading the deeper tissues.
Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called carcinoma in situ. The basement membrane is essential for angiogenesis. Basement membrane proteins have been found to accelerate differentiation of endothelial cells; the most notable examples of basement membranes is the glomerular basement membrane of the kidney, by the fusion of the basal lamina from the endothelium of glomerular capillaries and the podocyte basal lamina, between lung alveoli and pulmonary capillaries, by the fusion of the basal lamina of the lung alveoli and of the basal lamina of the lung capillaries, where oxygen and CO2 diffusion happens. As of 2017 many other roles for basement membrane have been found that include blood filtration and muscle homeostasis; some diseases result from a poorly functioning basement membrane. The cause can be injuries by the body's own immune system, or other mechanisms. Genetic defects in the collagen fibers of the basement membrane cause Alport syndrome and Knobloch syndrome.
Non-collagenous domain basement membrane collagen type IV is autoantigen of autoantibodies in the autoimmune disease Goodpasture's syndrome. A group of diseases stemming from improper function of basement membrane zone are united under the name epidermolysis bullosa. Intima Kefalides, Nicholas A. & Borel, Jacques P. eds.. Basement membranes: cell and molecular biology. Gulf Professional Publishing. ISBN 978-0-12-153356-4. CS1 maint: Uses editors parameter
Vascular smooth muscle
Vascular smooth muscle refers to the particular type of smooth muscle found within, composing the majority of the wall of blood vessels. Vascular smooth muscle refers to the particular type of smooth muscle found within, composing the majority of the wall of blood vessels. Vascular smooth muscle is innervated by the sympathetic nervous system through adrenergic receptors; the three types of adrenoceptors present are: α 1, α 2 and β 2. The main endogenous agonist of these cell receptors is norepinephrine; the adrenergic receptors exert opposite physiologic effects in the vascular smooth muscle under activation: α 1 receptors. Under NE binding α 1 receptors cause vasoconstriction. Α 1 receptors are activated in response to shock or low blood pressure as a defensive reaction trying to restore the normal blood pressure. Antagonists of α 1 receptors cause vasodilation. Α 2 receptors. Agonists of α 2 receptors in the vascular smooth muscle lead to vasoconstriction. However, in clinical practice drugs applied intravenously that are agonists of α 2 receptors lead to powerful vasodilation, which causes a decrease in blood pressure by presynaptic activation of α 2 receptors in the sympathetic ganglia.
This presynaptic effect is predominant and overrides the vasoconstrictive effect of the α 2 receptors in the vascular smooth muscle. Β 2 receptors. Agonism of β 2 receptors causes low blood pressure. Usage of β 2 receptor agonists as hypotensive agents is less widespread due to adverse effects such as unnecessary bronchodilation in lungs and increase in blood sugar levels. Vascular smooth muscle contracts or relaxes to change both the volume of blood vessels and the local blood pressure, a mechanism, responsible for the redistribution of the blood within the body to areas where it is needed, thus the main function of vascular smooth muscle tone is to regulate the caliber of the blood vessels in the body. Excessive vasoconstriction leads to high blood pressure, while excessive vasodilation as in shock leads to low blood pressure. Arteries have a great deal more smooth muscle within their walls than veins, thus their greater wall thickness; this is because they have to carry pumped blood away from the heart to all the organs and tissues that need the oxygenated blood.
The endothelial lining of each is similar. Excessive proliferation of vascular smooth muscle cells contributes to the progression of pathological conditions, such as vascular inflammation, plaque formation, atherosclerosis and pulmonary hypertension. Mural cell Image of smooth muscle in the arterial walls Smooth muscle in stomach wall
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the outermost layer of the skin. There are three principal shapes of epithelial cell: squamous and cuboidal; these can be arranged in a single layer of cells as simple epithelium, either squamous, columnar, or cuboidal, or in layers of two or more cells deep as stratified, either squamous, columnar or cuboidal. In some tissues, a layer of columnar cells may appear to be stratified due to the placement of the nuclei; this sort of tissue is called pseudostratified. All glands are made up of epithelial cells. Functions of epithelial cells include secretion, selective absorption, transcellular transport, sensing. Epithelial layers contain no blood vessels, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane.
Cell junctions are well employed in epithelial tissues. In general, epithelial tissues are classified by the number of their layers and by the shape and function of the cells; the three principal shapes associated with epithelial cells are—squamous and columnar. Squamous epithelium has cells; this is found as the lining of the mouth, the blood vessels and in the alveoli of the lungs. Cuboidal epithelium has cells whose height and width are the same. Columnar epithelium has cells taller. By layer, epithelium is classed as either simple epithelium, only one cell thick or stratified epithelium having two or more cells in thickness or multi-layered – as stratified squamous epithelium, stratified cuboidal epithelium, stratified columnar epithelium, both types of layering can be made up of any of the cell shapes. However, when taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights, they can be confused with stratified epithelia; this kind of epithelium is therefore described as pseudostratified columnar epithelium.
Transitional epithelium has cells that can change from squamous to cuboidal, depending on the amount of tension on the epithelium. Simple epithelium is a single layer of cells with every cell in direct contact with the basement membrane that separates it from the underlying connective tissue. In general, it is found where filtration occur; the thinness of the epithelial barrier facilitates these processes. In general, simple epithelial tissues are classified by the shape of their cells; the four major classes of simple epithelium are: simple squamous. Simple squamous. Simple cuboidal: these cells may have secretory, absorptive, or excretory functions. Examples include small collecting ducts of kidney and salivary gland. Simple columnar. Non-ciliated epithelium can possess microvilli; some tissues are referred to as simple glandular columnar epithelium. These secrete mucus and are found in stomach and rectum. Pseudostratified columnar epithelium; the ciliated type is called respiratory epithelium as it is exclusively confined to the larger respiratory airways of the nasal cavity and bronchi.
Stratified epithelium differs from simple epithelium. It is therefore found where body linings have to withstand mechanical or chemical insult such that layers can be abraded and lost without exposing subepithelial layers. Cells flatten as the layers become more apical, though in their most basal layers the cells can be squamous, cuboidal or columnar. Stratified epithelia can have the following specializations: The basic cell types are squamous and columnar classed by their shape. Cells of epithelial tissue are scutoid shaped packed and form a continuous sheet, they have no intercellular spaces. All epithelia is separated from underlying tissues by an extracellular fibrous basement membrane; the lining of the mouth, lung alveoli and kidney tubules are all made of epithelial tissue. The lining of the blood and lymphatic vessels are of a specialised form of epithelium called endothelium. Epithelium lines both the outside and the inside cavities and lumina of bodies; the outermost layer of human skin is composed of dead stratified squamous, keratinized epithelial cells.
Tissues that line the inside of the mouth, the esophagus, the vagina, part of the rectum are composed of nonkeratinized stratified squamous epithelium. Other surfaces that separate body cavities from the outside environment are lined by simple squamous, columnar, or pseudostratified epithelial cells. Other epithelial cells line the insides of the lungs, the gastrointestinal tract, the reproductive and urinary tracts, make up the exocrine and endocrine glands; the outer surface of the cornea is covered with fast-growing regenerated epithelial cells. A specialised form of epithelium – endothelium forms the inner lining of blood vessels and the heart, is known as vascular endotheliu
The jugular veins are veins that take deoxygenated blood from the head back to the heart via the superior vena cava. There are two sets of jugular veins: internal; the left and right external jugular veins drain into the subclavian veins. The internal jugular veins join with the subclavian veins more medially to form the brachiocephalic veins; the left and right brachiocephalic veins join to form the superior vena cava, which delivers deoxygenated blood to the right atrium of the heart. The internal jugular vein is formed by the anastomosis of blood from the sigmoid sinus of the dura mater and the common facial vein; the internal jugular runs with the common carotid artery and vagus nerve inside the carotid sheath. It provides venous drainage for the contents of the skull; the external jugular vein runs superficially to sternocleidomastoid. There is another minor jugular vein, the anterior jugular vein, draining the submaxillary region; the jugular venous pressure is an indirectly observed pressure over the venous system.
It can be useful in the differentiation of different forms of lung disease. In the jugular veins pressure waveform, upward deflections correspond with atrial contraction, ventricular contraction, atrial venous filling; the downward deflections correspond with the atrium relaxing and the filling of ventricle after the tricuspid opens. Components include: The a peak is caused by the contraction of the right atrium; the av minimum is due to relaxation of the right closure of the tricuspid valve. The c peak reflects the pressure rise in the right ventricle early during systole and the resultant bulging of the tricuspid valve—which has just closed—into the right atrium; the x minimum occurs as the ventricle contracts and shortens during the ejection phase in systole. The shortening heart—with tricuspid valve still closed—pulls on valve opens, the v peak begins to wane; the y minimum reflects a fall in right atrial pressure during rapid ventricular filling, as blood leaves the right atrium through an open tricuspid valve and enters the right ventricle.
The increase in venous pressure after the y minimum occurs as venous return continues in the face of reduced ventricular filling. The jugular vein is the subject of a popular idiom in the English language, deriving from its status as the vein most vulnerable to attack; the phrase'to go for the jugular', means to attack decisively at the weakest point - in other words, to attack at the opportune juncture for a definitive resolution, or coup-de-grace. An alternate explanation for the phrase suggests "to go for the jugular" means to attack without restraint; the jugular vein system is essential but not weak or vulnerable, because this venous system is found deep in the body. Chronic cerebrospinal venous insufficiency
A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system; each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as Schwann cells that coat the axons in myelin. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium; the axons are bundled together into groups called fascicles, each fascicle is wrapped in a layer of connective tissue called the perineurium. The entire nerve is wrapped in a layer of connective tissue called the epineurium. In the central nervous system, the analogous structures are known as tracts; each nerve is covered on the outside by a dense sheath of the epineurium. Beneath this is a layer of flat cells, the perineurium, which forms a complete sleeve around a bundle of axons.
Perineurial septae subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium; this forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, meshwork of collagen fibres. Nerves are bundled and travel along with blood vessels, since the neurons of a nerve have high energy requirements. Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid; this acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation, the amount of endoneurial fluid may increase at the site of irritation; this increase in fluid can be visualized using magnetic resonance neurography, thus MR neurography can identify nerve irritation and/or injury.
Nerves are categorized into three groups based on the direction that signals are conducted: Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the mechanoreceptors in skin. Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands. Mixed nerves contain both afferent and efferent axons, thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. Nerves can be categorized into two groups based on where they connect to the central nervous system: Spinal nerves innervate much of the body, connect through the vertebral column to the spinal cord and thus to the central nervous system, they are given letter-number designations according to the vertebra through which they connect to the spinal column. Cranial nerves innervate parts of the head, connect directly to the brain, they are assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included.
In addition, cranial nerves have descriptive names. Specific terms are used to describe their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to "innervate" that section of the body or organ. Other terms relate to whether the nerve affects the same side or opposite side of the body, to the part of the brain that supplies it. Nerve growth ends in adolescence, but can be re-stimulated with a molecular mechanism known as "Notch signaling". If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells; this is referred to as neuroregeneration. The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud.
When one of the growth processes finds the regeneration tube, it begins to grow towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect. A nerve conveys information in the form of electrochemical impulses carried by the individual neurons that make up the nerve; these impulses are fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, the message is converted from electrical to chemical and back to electrical. Nerves can be categorized into two groups based on function: An afferent nerve fiber conducts sensory information from a sensory neuron to the central nervous system, where the information is processed. Bundles of fibres or axons, in the peripheral nervous system are called nerves, bundles of afferent fibers are known as sensory nerves.
An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as efferent nerves; the nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body. In vertebrates it consists of two main par
The vasa vasorum is a network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries and large veins. The name derives from Latin, meaning'the vessels of the vessels'. Studies conducted with 3-dimensional microcomputed tomography on pig and human arteries from different vascular beds have shown that there are three different types of vasa vasorum: Vasa vasorum internae, that originate directly from the main lumen of the artery and branch into the vessel wall. Vasa vasorum externae, that originate from branches of the main artery and dive back into the vessel wall of the main artery. Venous vasa vasorae, that originate within the vessel wall of the artery but drain into the main lumen or branches of concomitant vein. Depending on the type of vasa vasorum, it penetrates the vessel wall starting at the intimal layer or the adventitial layer. Due to higher radial and circumferential pressures within the vessel wall layers closer to the main lumen of the artery, vasa vasorum externa cannot perfuse these regions of the vessel wall.
The structure of the vasa vasorum varies with the size and location of the vessels. Cells need to be within a few cell-widths of a capillary to stay alive. In the largest vessels, the vasa vasorum penetrates the outer layer and middle layer to the inner layer. In smaller vessels it penetrates only the outer layer. In the smallest vessels, the vessels' own circulation nourishes the walls directly and they have no vasa vasorum at all. Vasa vasorum are more frequent in veins than arteries; some authorities hypothesize that the vasa vasorum would be more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This would lead to more vasa vasorum needed to supply the vessels sufficiently; the converse argument is that artery walls are thicker and more muscular than veins as the blood passing through is of a higher pressure. This means that it would take longer for any oxygen to diffuse through to the cells in the tunica adventitia and the tunica media, causing them to need a more extensive vasa vasorum.
A method of scanning is optical coherence tomography that gives 3D imaging. The vasa vasorum are found in large vein and arteries such as its branches; these small vessels serve to provide blood supply and nourishment for tunica adventitia and outer parts of tunica media of large vessels. In the human descending aorta, vasa vasorum cease to supply the arterial tunica media with oxygenated blood at the level of the renal arteries. Thus, below this point, the aorta is dependent on diffusion for its metabolic needs, is markedly thinner; this leads to an increased likelihood of aortic aneurysm at this location in the presence of atherosclerotic plaques. Other species, such as dogs, do have vasa vasorum below their renal vasculature, aneurysms at this site are less likely. Cerebral blood vessels are devoid of vasa vasorum. A relationship exists between changes in the vasa vasorum and the development of atheromatous plaques, it is not understood whether changes in the vasa vasorum in terms of their appearance and disappearance, is a cause or an effect of disease processes.
In 2009 Uffe Ravnskov and Kilmer S. McCully published review and hypothesis on vulnerable plaque formation from obstruction of vasa vasorum. In 2017 Haverich proposed that the formation of plaques is not from inside the vessel, but the result of inflammation of the vasa vasorum. Haverich noted that arteries fed by vasa vasorum are subject to development of arteriosclerotic plaques, he postulated. He noted. Damage by inflamed vasa vasorum leads to cell death within the wall and subsequent plaques formation. Vasa vasorum inflammation can be caused by viruses and fine dust among others. According to his view this concept conforms to observations that cardiac infarctions are more common when influenza has occurred or fine particles have been inhaled. Small vessels like vasa vasorum and vasa nervorum are susceptible to external mechanical compression, thus are involved in pathogenesis of peripheral vascular and nerve diseases. A tear in vasa vasorum situated in tunica media layer of aorta may start pathologic cascade of events leading to aortic dissection.
Presence of corkscrew collateral vessels in vasa vasorum is a hallmark of Buerger's disease and distinguishes it from Raynaud's phenomenon. T cells found. Inflammation and subsequent destruction of the vasa vasorum is the cause of syphilitic aortitis in tertiary syphilis. Obliterating endarteritis of the vasa vasorum results in ischemia and weakening of the aortic adventitia, which may lead to aneurysm formation in the thoracic aorta. Histology image: 05702loa – Histology Learning System at Boston University