Simple epithelial
The structure of cuboidal or columnar or squamous epithelium
Squamous Epithelium:
This is made up of flat disk like polygonal cells that are closely packed leaving no intercellular spaces. They appear like the arrangement of the tiles on the floor hence the epithelium is also known as the pavement epithelium. The cells of the tissue are connected by fine protoplasmic bridges and are slightly thicker at the centre. The nucleus is slightly flattened and is located at the centre of the cell.
Simple Squamous Epithelium is present in the inner lining of Bowman’s1 capsule in the kidneys, alveoli of the lungs, blood vessels etc.
Cuboidal Epithelium:
This tissue consists of cells that are usually squarish with a polygonal outline. In a surface view they appear as sheet of cells under the microscope. The cells have single nucleus located in the centre. The cubiodal epithelial cells are located in thyroid follicles, small salivary and pancreatic ducts, lining of the inner ear and proximal parts of the urinary tubules etc. Cubodial epithelium is also found in sweat glands, pigmented layer of retina and in the duct.
In the urinary tubules the cubodial cells have numerous tiny fingers like outgrowths called microvilli; these appear like a brush and the epithelium is often called brush bordered cuboid epithelium. The villi are supposed to increase the area for reabsorption of materials. The cuboidal epithlum that lines the ovaries and the seminiferous tubules in known as germinal epithelium. Cubodial cells play an active role in secretion, absorption and excretion.
The Term Paper on Stem Cell
Abstract There are several types of stem cells being used in stem cell research and therapy today. They are embryonic, adult and induced pluripotent stem cells. Each will be discussed further. This topic has stirred much moral, ethical and political debate as whether cells from fetuses should be used in this research. This impacts governmental policies on laws and funding. Another issue that must ...
Columunar Epithelium:
As the very name indicates this epithelium consists of columnar cells that are longer (taller) than broad. The tissue is made up of a single layer of cells. The outlines of the cells appear polygonal in a surface view. Each cell has a flattened and an oval end. There is a single nucleus in each cell which is elongated and usually located either in the centre or a little away from the centre. Usually some mucous secreting cells called Goblet cells are found in between the columnar epithelial cells that line the stomach and intestine.
The goblet cells have vacoule filled with mucous. The epithelial tissue containing the mucous secreting cells along with the underlying supporting connective tissue is usually referred to as the mucous membrane or mucosa.
Simple Columnar epithelial cells are found distributed in various organs like the lining of the gall bladder, bile ducts, gastric glands, intestinal galnds, pancreatic lobules etc.
In the intestine, the columnar epithelial cells that line the inner cavity are called microvilli and they are specialised for the absorption of water and digested food. The microvilli increase the surface area of absorption. These cells present in the small intestine constitute the brash bordered columnar epithelium.
Ciliated
Cilia are not hairs, but they are hair-like structures, and they beat back and forth. A paramecium has lots of cilia, and swims by beating them, like oars. A sperm has a single long flagellum that it swims with. A flagellum is essentially a long cilium. They have the same basic structure, just flagella are longer and usually occur singly.
The epithelial cells that line the trachea and bronchi are ciliated – likewise those that line the Fallopian tubes. These cilia beat back and forth, but the cells do not move, because they are fixed in position.
Such epithelium is covered by a layer of mucus, which traps particles, bacteria, etc., that may get in there, The beating cilia move that layer of mucus out of the organ, thereby helping get rid of whatever may have gotten in.
The Essay on Cells. Mitosis. DNA
Instructions: Read chapter 3 in your textbook and review the lecture notes and study resources provided by your instructor. Type your answer in the answer block provided for each question. Answer blocks should expand as you type. If you experience difficulty typing in the provided answer blocks, you may type your answers in a new document. Save a copy of the completed activity to your computer for ...
A pint or more of mucus is propelled up out of our lungs every day by this mechanism – and we swallow it. We usually don’t notice it, except when the mucus is particularly thick or there is an excessive amount of it.
In the Fallopian tubes, the cilia beat downward and help move the egg (or embryo) from the ovary to the uterus.
Those moving layers of mucus are very important because they are our first line of defense against infection of these organs. For example, smoking paralyzes the cilia in the respiratory tract. making smokers more susceptible to respiratory infections.
In this tissue the epithelial cells bear at their free ends thin elongated cytoplasmic processes called Cilia (Sing cilium).
Each cilium arises from a minute particle called basal granule or blepharoplast that lies internal to the cell membrane.
In between the ciliated epithelial cells are present mucous secreting goblet cells. The mucous spreads over the epithelium as a thin coating. The cilia have a beating action (move like the lashes of a whip) as a result of which the mucous and other substances are transferred over the epithelium from one place to another.
The cilia also help in shifting small solid particles entangled in the mucous. In this tissue the epithelial cells bear at their free ends thin elongated cytoplasmic processes called Cilia (Sing cilium).
Each cilium arises from a minute particle called basal granule or blepharoplast that lies internal to the cell membrane. In between the ciliated epithelial cells are present mucous secreting goblet cells. The mucous spreads over the epithelium as a thin coating
The cilia have a beating action (move like the lashes of a whip) as a result of which the mucous and other substances are transferred over the epithelium from one place to another. The cilia also help in shifting small solid particles entangled in the mucous.
CONNECTIVE
ADIPOSE
Adipose tissue is a fibrous connective tissue that is loose in structure. This tissue is filled with many cells which are called adipocytes. These cells are specialized to store triglycerides, or as they are more commonly called, fats. Each of these cells is filled with a large single drop of fat, which pushes the other components, the nucleus, cytoplasm, and others to the outside of the cell. The cell is bounded by the cell membrane, also called plasma membrane.
The Essay on Compact Bone Bones Tissue Cells
Chapter 7 I. Bone Structures. Bone Classification 1. 4 Classes - Long, Short, flat and irregular 2. Example of a long bone- forearm and thigh bones. 3. Short Bones are shaped like cubes 4. Ex. Of short bones are in wrists and ankle bones 5. Flat bones are plate like structures 6. Ex of Flat bones are plate like structures 7. Irregular bones vary in size 8. Irregular bones vary in size 9. Examples ...
BONE
The Structure (Physical Description) of bone tissue
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Above: Diagram illustrating the Structure of Long Bones |
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There are two main types of bone tissue, compact bone and spongy bone. Individual bones in the body can be formed from both of these types of bone tissue. The diagram on the right shows the physical structure of a typical “long bone”.
(If need be read about different types of bone – then come back to this page to continue.)
2.1 The structure of Compact Bone
Compact bone forms the outer layer of all bones and most of the structure of “long bones” – see diagram (right).
It contains few spaces and provides protection and support to the bone/s around which it is the outer-layer, as well as helping to enable the long bones to bear the stress placed on them by the weight of the body and the use to which the limbs are put, e.g. due any heavy physical work.
The basic unit of Compact Bone is an “osteon”, which is also known as a “Haversian System”.
Each Haversian System (unit) has a cylindrical structure that consists of four parts:
1. A central tube called a Haversian Canal, which contains blood vessels and nerves.
The Haversian Canal is surrounded by alternate layers of:
2. Lamellae (the word lamellae literally means “little plates”) are concentric rings of a strong matrix formed from mineral salts including calcium and phosphates and collagen fibres. The mineral salts result in thehardness of the bone structure, while the collagen fibres contribute its strength.
3. Lacunae are the small spaces between the lamellae in which contain the bone cells (called “osteocytes”) are located.
4. The lacunae are linked together by minute channels called canaliculi.
The canaliculi provide routes by which nutrients can reach the osteocytes and waste products can leave them.
The Essay on Stem Cells Adult Cell Types
The history of research on adult stem cells began about 40 years ago. In the 1960 s, researchers discovered that the bone marrow contains at least two kinds of stem cells. One population, called stem cells, forms all the types of blood cells in the body. A second population, called bone marrow stroma l cells was discovered a few years later. Stromal cells are a mixed cell population that generates ...
2.2 The Structure of Spongy Bone
Spongy Bone does not include osteons (the basic unit/s of Compact Bone – see above).
Instead, spongy bone consists of an irregular lattice of thin columns of bone called trabeculae (literally “little beams”), which contain lamellae, osteocytes, lacunae and canaliculi. The spaces between the trabeculae of some spongy bones are filled with red bone marrow.
Blood vessels from the periosteum (see diagram above-right), penetrate into the trabeculae lattice allowing the osteocytes in the trabeculae to receive nourishment from the blood passing through the marrow cavities.
Fibres:
There are three types of fibres secreted by connective tissue cells: collagen fibres, reticular fibres, and elastic fibres. The abundance and preponderance of different types of fibres varies in different CTs. Each type of fibre is formed by proteins made of long peptide chains.
Collagen fibres: The most common fibre type is the collagen fibre. These are flexible fibres with a high tensile strength. In typical preparations for the light microscope (LM), they appear as wavy lines of variable width and indeterminate length.
With the electron microscope, collagen fibres are seen to be made up of thread-like subunits called collagen fibrils. Each fibril, in turn, is made up of collagen molecules that are aligned, head to tail, in overlapping rows. Within each row, there is a gap beween the tail of one molecule and the head of the next. The fibril’s strength is due to covalent bonds between collagen molecules of adjacent rows – not the head to tail attachment within a row.
The collagen molecule (called tropocollagen) is composed of three intertwined polypeptide chains (each of which is called an alpha chain) that form a right-handed triple helix. Except for the ends of the chain, every third amino acid is a glycine. A hydroxyproline frequently precedes each glycine, and a proline frequently follows each glycine. Sugar groups are associated with the triple helix, so collagen is properly called a glycoprotein. (Figure 5.4, pg. 99 in Ross et al. gives a schematic diagram of the structure of collagen.)
The alpha chains that form the helix are not all alike, and, based on differences within the chains, as many as 16 types of collagen have been identified. They are classified by Roman numerals on the basis of chronology of discovery. Type I collagen is the most prevalent type of collagen, and constitutes about 90% of body collagen. It is the collagen found in the dermis of the skin, bone, tendon, organ capsules and many other areas. The fibres found in cartilage are finer, they consist of type II collagen. Type IV collagen is found in the basal lamina (of basement membrane) of epithelia. There is no need to memorize where the different types of collagen are found. A useful table for reference purposes is found in Ross et al. on page 100.
The Essay on Tissue Engineering Muscle By Micropatterning For Therapeutic Transplantation
Tissue Engineering Muscle by Micropatterning for Therapeutic Transplantation There is growing interest to treat patients with inherited or acquired muscular disorders by transplantation of cells to the site of dysfunction to restore normal function. One candidate cell source is skeletal muscle, which can be harvested from surrounding tissues for cell culture before injecting into the site of ...
Reticular fibres: Reticular fibres are closely related to collagen fibres. They are made of type III collagen fibrils (sometimes in association with type IV collagen).
The individual fibrils that constitute the reticular fibre are of narrow diameter and typically do not bundle to form thick fibres. Reticular fibres cannot be identified in routine preparations. They can be displayed with special silver preparations or with the periodic acid-Schiff (PAS) reaction because of their relatively high sugar content.
Reticular fibres were given their name because they are arranged in a mesh-like pattern. They provide a supporting framework for the cellular constituents of various tissues and organs, for example the liver. They are also found at the boundary of the CT and epithelium in loose CT, around adipocytes, small blood vessels, nerves and muscle cells.
In most locations, reticular fibres are produced by fibroblasts. However, the reticular fibres that support the stroma of hemopoietic and lymphatic tissue are made by special cells called reticular cells. Each reticular cell maintains a unique relationship to its fibre, surrounding it with its cytoplasm and thereby isolating it from its environment. (The thymus is an exception, it has no reticular fibres.)
Other areas where reticular fibres are not produced by fibroblasts include the endoneurium of peripheral nerves, where they are produced by Schwann cells (discussed under Nervous Tissue below), the tunica media of blood vessels and the muscularis externa of the alimentary canal. The tunica media and muscularis externa are made up of smooth muscle cells (described under muscle tissue below), and it is the smooth muscle cells themselves that secrete all the CT fibre types within those structures.
The Essay on Anatomy Of A Muscle Cell
Anatomy of Muscle Cells There are three types of muscle tissue in the human body. These muscle tissues are skeletal muscles, smooth muscles and cardiac muscles. Each of these muscle tissues has it very own anatomical makeup, which vary from muscle to muscle. The muscle cells in a muscle are referred to as muscle fibers, these fibers are skeletal muscle fibers, smooth muscle fibers and cardiac ...
Elastic fibres: Elastic fibres are thinner than collagen fibres and are arranged in a branching pattern to form a three dimensional network. They give tissue the ability to cope with stretch and distension. Elastic fibres are interwoven with collagen fibres in order to limit distensibility and to prevent tearing.
Elastic fibres are composed of two structural components: elastin and microfibrils. Elastin is a protein related to collagen but with an unusual polypeptide backbone that causes it to coil in a random way. The configuration of one molecule’s coiling is not permanent, it oscillates from one shape to another. The coiled elastin molecule can be stretched. When the force causing the stretch is withdrawn, the molecule recoils back to its former state. Two large amino acids unique to elastin, called desmosine and isodesmosine, cause elastin molecules to covalently bond to one another and form an elastin matrix. The entire matrix is engaged during the stretch and recoil of elastic tissue. (For a schematic drawing, see Fig. 5.9, pg. 104 of Ross et al.)
Microfibrils consist of a fibrillar glycoprotein. In developing elastic tissue, they appear before the elastin, and are believed to serve as an organizing structure for it. (Note: Don’t confuse microfibrils, an extracellular structure, with microfilaments, an intracellular structure made of actin.)
Elastic material is found in certain ligaments (elastic ligaments), some cartilage (called elastic cartilage) and in large arteries (elastic arteries).
In most cases, the elastic fibres are produced by fibroblasts. In the case of elastic arteries, it is produced by the smooth muscle cells of the tunica media. However, the elastic material produced by the smooth muscle cells does not contain microfibrils, only elastin, and as a result does not form elastic fibres. Instead, the elastin is laid down in fenestrated (having gaps or openings) sheets or lamellae arranged in concentric layers between layers of smooth muscle.
Elastic fibres do not stain very well with eosin and in routine preparations usually cannot be distinguished from collagen fibres. (Certain fixatives cause them to become somewhat refractile, and when this occurs, they can be distinguished from collagen fibres even with H&E staining.) Elastic fibres are selectively stained with special dyes such as orcein and resorcin-fuchsin.
The cells of connective tissues:
As mentioned above, many different kinds of cells can be found in CTs. In some CTs, there is a large diversity of cell types, in others, the diversity is very low. Some of the cells in CTs are fixed, that is, they are permanent residents in the connective tissue. Other cells are wandering, they are transient migrants who have entered the CT from the blood in response to specific stimuli. The list below summarizes some of the cells commonly found in connective tissues.
Fixed Cells:
Fibroblasts: Fibroblasts are the principal cells of connective tissue. They are responsible for the secretion of all types of fibres (collagen, reticular, elastin) and the complex carbohydrates of ground substance. A single fibroblast is believed to be able to secrete all the extracellular components, both sequentially and simultaneously. (A diagrammatic representation of collagen secretion by a fibroblast is shown in Fig. 5.5, pg. 101 of Ross et al.) In routine histological preparations, only the nucleus of the fibroblast can be identified, the cytoplasmic processes blend in with the surrounding collagen. The nucleus appears as an elongated or discoid structure. Like the nucleus of any cell, fibroblast nuclei stain blue with H&E, as nucleic acids avidly bind to basic dyes.
Chondroblasts & chondrocytes: These are the matrix-secreting cells of cartilage.
Osteoblasts & osteocytes: These are the matrix-secreting cells of bone.
Macrophages: Macrophages, also called histiocytes, are phagocytic cells derived from monocytes.
Adipose cells: Also called adipocytes, these cells are specialized to store neutral fat.
Mast cells: Mast cells have granules containing histamine, heparin and anaphylactic factors. When released in response to an antigen, they cause hypersensitivity reactions, allergy and anaphylaxis.
Undifferentiated mesenchyme cells: These are cells that retain the multiple potentials of embryonic mesenchyme cells. They are found in the tunica adventitia (the outer layer of CT) of venules.
Wandering Cells:
Lymphocytes: These are cells responsible for immune responses that circulate in the blood. Normally, only small numbers are found in the CTs throughout the body. The number increases dramatically at certain sites of tissue inflammation. They are also very numerous in the lamina propria of the respiratory and gastrointestinal tracts, where they are involved in immunosurveillance. The lamina propria is a layer of loose CT lying immediately beneath the epithelium.
Plasma cells: Plasma cells are derived from B-lymphocytes and produce antibodies against a specific antigen. They have a limited migratory ability and a short life.
Neutrophils: Neutrophils are white blood cells that act as phagocytes in the early stages of acute inflammation.
Eosinophils: Eosinophils are white blood cells that are found in the lamina propria of the GI tract, and at sites of allergic reaction and parasitic infection.
Basophils: Basophils are white blood cells that are similar to mast cells in having vasoactive agents released in response to an allergen.
Monocytes: Monocytes are white blood cells that will give rise to all the phagocytes of the mononuclear phagocytic system (see Ross et al., pg. 110, and Table 5.4, pg. 112).
In CT, they give rise to macrophages (histiocytes).
Classification of connective tissues:
Connective tissues are classified on the basis of types and relative abundance of cells, fibres and ground substance, and on the organization of fibres. The images below will introduce you to the diversity of connective tissues. You will study a number of these connective tissues in greater detail in some of the Blocks.
Loose (or areolar) connective tissue
This is a cellular type of connective tissue, with abundant ground substance and thin and relatively sparse fibres. It has a viscous gel-like consistency and is important for the diffusion of oxygen and nutrients from small vessels, and the diffusion of metabolites back to the vessels. The primary location of loose connective tissue is beneath epithelia that line the internal surfaces of the body, in association with the epithelia of glands and around small vessels. It is the initial site at which antigens, bacteria and other agents that have breached an epithelial surface can be destroyed.
What is gila (neurolgia)?
Answer:
The stromal tissue of the nervous system and consists of several types of specialized cells. This tissue holds the nervous system together and helps it ward off infection and injury with phagocytosis.
Nervous Nervous tissue sense stimuli and transmits signals from one part of an animal to another. The functional unit of the nervous tissue is the neuron, or nerve cell, which has a unique structure that is specialized to transmit signals called nerve impulses. A nerve cell consists a body and two or more extensions called dendrites and axons, which may be as long as a meter in humans.
They perform the major function of transmitting nerves impulses. Anatomically, a nerve tissue comprises of many neurons that are joined by the connective tissues.
Functions Are:
1. Sensory input
2. Integration
3. Controls of muscles and glands
4. Homeostasis
5. Mental Activity
MUSCLE
* Smooth Muscle Tissue.
Smooth muscle tissue is made up of thin-elongated muscle cells, fibres. These fibres are pointed at their ends and each has a single, large, oval nucleus. Each cell is filled with a specialised cytoplasm, the sarcoplasm and is surrounded by a thin cell membrane, the sarcolemma. Each cell has many myofibrils which lie parallel to one another in the direction of the long axis of the cell. They are not arranged in a definite striped (striated) pattern, as in skeletal muscles – hence the name smooth muscle . Smooth muscle fibres interlace to form sheets or layers of muscle tissue rather than bundles. Smooth muscle isinvoluntary tissue, i.e. it is not controlled by the brain. Smooth muscle forms the muscle layers in the walls of hollow organs such as the digestive tract (lower part of the oesophagus, stomach and intestines), the walls of the bladder, the uterus, various ducts of glands and the walls of blood vessels .
Functions of Smooth Muscle Tissue
* Smooth muscle controls slow, involuntary movements such as the contraction of the smooth muscle tissue in the walls of the stomach and intestines.
* The muscle of the arteries contracts and relaxes to regulate the blood pressure and the flow of blood.
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Smooth Muscle Tissue |
* Skeletal Muscle Tissue.
Skeletal muscle is the most abundant tissue in the vertebrate body. These muscles are attached to and bring about the movement of the various bones of the skeleton, hence the name skeletal muscles. The whole muscle, such as the biceps, is enclosed in a sheath of connective tissue, the epimysium. This sheath folds inwards into the substance of the muscle to surround a large number of smaller bundles, the fasciculi. These fasciculi consist of still smaller bundles of elongated, cylindrical muscle cells, the fibres. Each fibre is a syncytium, i.e. a cell that have many nuclei. The nuclei are oval in shaped and are found at the periphery of the cell, just beneath the thin, elastic membrane (sarcolemma).
The sarcoplasm also has many alternating light and dark bands, giving the fibre a striped or striated appearance (hence the name striated muscle).
With the aid of an electron microscope it can be seen that each muscle fibre is made up of many smaller units, the myofibrils. Each myofibril consists of small protein filaments, known as actin and myosin filaments. The myosin filaments are slightly thicker and make up the dark band (or A-band).
The actin filaments make up the light bands (I-bands) which are situated on either side of the dark band. The actin filaments are attached to the Z-line. This arrangement of actin and myosin filaments is known as a sacromere.
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A myofibril with actin and myosin filaments |
During the contraction of skeletal muscle tissue, the actin filaments slide inwards between the myosin filaments. Mitochondria provide the energy for this to take place. This action causes a shortening of the sacromeres (Z-lines move closer together), which in turn causes the whole muscle fibre to contract. This can bring about a shortening of the entire muscle such as the biceps, depending on the number of muscles fibres that were stimulated. The contraction of skeletal muscle tissue is very quick and forceful.
Functions of Skeletal Muscle Tissue
* Skeletal muscles function in pairs to bring about the co-ordinated movements of the limbs, trunk, jaws, eyeballs, etc.
* Skeletal muscles are directly involved in the breathing process.
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Skeletal Muscle Tissue |
* Cardiac (Heart) Muscle Tissue.
This is a unique tissue found only in the walls of the heart. Cardiac (Heart) Muscle Tissue shows some of the characteristics of smooth muscle and some of skeletal muscle tissue. Its fibres , like those of skeletal muscle, have cross-striations and contain numerous nuclei. However, like smooth muscle tissue, it is involuntary. Cardiac muscle differ from striated muscle in the following aspects: they are shorter, the striations are not so obvious, the sarcolemma is thinner and not clearly discernible, there is only one nucleus present in the centre of each cardiac fibre and adjacent fibres branch but are linked to each other by so-called muscle bridges. The spaces between different fibres are filled with areolar connective tissue which contains blood capillaries to supply the tissue with the oxygen and nutrients.
Functions of Cardiac (Heart) Muscle Tissue
* Cardiac muscle tissue plays the most important role in the contraction of the atria and ventricles of the heart.
* It causes the rhythmical beating of the heart, circulating the blood and its contents throughout the body as a consequence.
