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The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.
The basement membrane is the fusion of two lamina, the basal lamina and the reticular lamina (or lamina reticularis). The lamina reticularis is attached to the basal lamina with anchoring fibrils (type VII collagen fibers) and microfibrils (fibrillin). The two layers are collectively known 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-denselamina densa membrane is about 30–70 nanometers in thickness, and consists of an underlying network of reticular collagen (type IV) fibrils (fibroblast precursors) which average 30 nanometers in diameter and 0.1–2 micrometers in thickness. This type III collagen is of the reticular type, in contrast to the fibrillar collagen found in the interstitial matrix. In addition to collagen, this supportive matrix contains intrinsic macromolecular components.
The Lamina Densa (which is made up of type IV collagen fibers; perlecan (a heparan sulfate proteoglycan) coats these fibers and they are high in heparan sulfate) and the Lamina Lucida (made up of laminin, integrins, entactins, and dystroglycans) together make up the basal lamina.
Function and importance
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 (SAMs).
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 most notable examples of basement membranes is in the glomerular filtration of the kidney, by the fusion of the basal lamina from the endothelium of glomerular capillaries and the basal lamina of the epithelium of the Bowman's capsule, and between lungalveoli and pulmonary capillaries, by the fusion of the basal lamina of the lung alveoli and of the basal lamina of the lung capillaries, which is where oxygen and CO2 diffusion happens. Basement membrane is non cellular.
Some diseases result from a poorly functioning basement membrane. The cause can be genetic defects, injuries by the body's own immune system, or other mechanisms.
Genetic defects in the collagen fibers of the basement membrane cause Alport syndrome.
Noncollagenous domain basement membrane collagen type IV is autoantigen (target antigen) 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.
Breathing, controlled by the respiratory system, is a continuous process of which a person is normally unaware. If breathing stops, however, a person becomes acutely aware of the fact. An individual can go days without food and water and hours without sleep, but only five or six minutes without air. Anything beyond that would be fatal. The trillions of cells in the body need a constant and generous amount of oxygen to carry out their vital functions. As they use that oxygen, they give off carbon dioxide as a waste product. It is the role of the respiration system, working in conjunction with the cardiovascular system, to supply the oxygen and dispose of the carbon dioxide. Breathing describes the process of inhaling and exhaling air. The exchange of gases (oxygen and carbon dioxide) between living cells and the environment is a process known as respiration. The respiratory system, which controls breathing and respiration, consists of the respiratory tract and the lungs. The respiratory tract cleans, warms, and moistens air on its way to the lungs. The tract can be divided into an upper and a lower part. The upper part consists of the nose, nasal cavity, pharynx (throat), larynx, and upper part of the trachea (windpipe). The lower part consists of the lower part of the trachea, bronchi, and lungs (which contain bronchioles and alveoli). The nose is the only external part of the respiratory system. It is made of bone and cartilage (tough connective tissue) and is covered with skin. The two openings to the outside, called nostrils, allow air to enter or leave the body during breathing. The nostrils are lined with coarse hairs that prevent large particles such as dust, insects, and sand from entering. The nostrils open into a large cavity, the nasal cavity. This cavity is divided into right and left cavities by a thin plate of bone and cartilage called the nasal septum. The hard portion of the palate forms the floor of the entire nasal cavity, separating it from the mouth or oral cavity below. Three flat, spongy folds or plates project toward the nasal septum from the sides of the nasal cavity. These plates, called nasal conchae, help to slow down the passage of air, causing it to swirl in the nasal cavity. thick, gooey liquid. As the nasal conchae cause air to swirl in the nasal cavity, the mucus moistens the air and traps any bacteria or particles of air pollution. The cilia wave back and forth in rhythmic movement, and pieces of mucus with their trapped particles are swept along to the throat. The mucus is then either spat out or (more often) swallowed. Any bacteria present in the swallowed mucus is destroyed by the hydrochloric acid in the gastric juice of the stomach. Air is not only moistened in the nasal cavity but warmed, as well. A rich network of thin-walled capillaries permeates the mucus membrane (especially the uppermost concha), and the incoming air is warmed as it passes over the vessels. When air finally reaches the lungs, it is similar to the warm, damp air found in the tropics. The bones that surround the nasal cavity contain hollow spaces known as paranasal sinuses. The sinuses are also lined with mucous membrane containing cilia. The mucus produced in the sinuses drains into the nasal cavity. The main functions of the sinuses are to lighten the skull and to provide resonance (sound quality) for the voice. The pharynx or throat is a short, muscular tube extending about 5 inches (12.7 centimeters) from the nasal cavity and mouth to the esophagus and trachea. It serves two separate systems: the digestive system (by allowing the passage of solid food and liquids) and the respiratory system (by allowing the passage of air). The larynx, commonly called the voice box, forms the upper part of the trachea. The larynx is made of nine pieces of cartilage connected by ligaments. The largest of these cartilages is the shield-shaped thyroid cartilage, which may protrude at the front of the neck, forming the so-called Adam's apple. The upper cartilage is the epiglottis, a flaplike piece of tissue. During swallowing, the larynx rises up and the epiglottis folds down to cover the glottis, or the larynx's opening. This prevents food or liquids from passing into the lower respiratory tract. Mucous membrane lines the larynx. A pair of elastic folds in that lining form the vocal cords. During silent breathing, the vocal cords lie against the walls of the larynx. During speech, the cords are stretched across the opening of the larynx and air that passes through causes them to vibrate, generating sound waves. Various muscles produce tension on the cords, making them tighter (shorter) or looser (longer). The tighter the tension, the higher the pitch of the sound produced. Since men's larynges tend to be larger than women's, their vocal cords tend to be thicker and longer. The male voice thus tends to be lower in pitch. The trachea is a tough, flexible tube about 1 inch (2.5 centimeters) in diameter and 4.5 inches (11.4 centimeters) in length. Located in front of the esophagus, it is the principal tube that carries air to and from the lungs. The walls of the trachea are supported by 16 to 20 C-shaped cartilage rings. Elastic fibers in the tracheal walls allow the trachea to expand and contract during breathing, while the cartilage rings prevent it from collapsing. Mucous membrane containing cilia lines the trachea. The mucus produced by the membrane traps dust particles and other debris. The cilia move continuously in a direction opposite that of the incoming air, helping propel the mucus away from the lungs to the throat where it can be swallowed or spat out. The trachea divides behind the sternum (breastbone) to form a right and left branch called primary bronchi (singular: bronchus). Each bronchus passes into a lungâ€”the right bronchus into the right lung and the left bronchus into the left lung. The right bronchus is wider, shorter, and straighter than the left. As a result, accidentally inhaled objects (such as pieces of food) most often enter the right primary bronchus. By the time incoming air reaches the primary bronchi, it is warm, moistened, and cleansed of most particles or other impurities. The lungs are two broad, cone-shaped organs located on either side of the heart in the thoracic or chest cavity. They extend from the collarbones to the diaphragm, a membrane of muscle separating the thoracic cavity from the abdominal cavity. The base of each lung rests directly on the diaphragm. The rib cage forms a wall around the lungs, protecting them. At birth, the lungs are pale pink in color. As people age, their lungs grow darker. The inhaling of dirt and other particles increases this aging process, even scarring the delicate tissue of the lungs. Each lung is divided into lobes separated by deep grooves or fissures. The right lung, which is larger, is divided into three lobes. The left lung is divided into only two lobes. Combined, the two soft and spongy lungs weigh about 2.5 pounds (1.1 kilograms). A membrane sac, called the pleura, surrounds and protects each lung. One layer of the pleura attaches to the wall of the thoracic cavity; the other layer encloses the lung. A fluid (pleural fluid) between the two membrane layers reduces friction and allows smooth movement of a lung during breathing. After the bronchi enter the lungs, they subdivide repeatedly into smaller and smaller bronchi or branches. Eventually they form thousands of tiny branches called bronchioles, which have a diameter of about 0.02 inch (0.5 millimeter). This branching network of bronchial tubes within the lungs is called the bronchial tree. The bronchioles branch to form even smaller passageways that open into clusters of cup-shaped air sacs called alveoli (singular: alveolus). The average person has a total of about 700 million alveoli (which resemble clusters of grapes) in his or her lungs. These provide an enormous surface area-roughly the size of a tennis courtâ€”for gas exchange. A network of capillaries surrounds each alveolus. As blood passes through these vessels and air fills the alveoli, the exchange of gases takes place: oxygen passes from the alveoli int
Plasma membranes envelop all plant and animal cells and all single-celled eukaryotes and prokaryotes , separating them from their environments. Structurally, they resemble other cellular membranes, but differ slightly in their lipid composition and more drastically in their protein content from one cell to another and from intracellular membranes. These compositional similarities and differences, in turn, are reflected in the ways in which plasma membranes carry out their functions, facilitating solute transport, conducting signals, and anchoring cells to their environments. Like other membranes, plasma membranes are essentially lipid bilayers and exhibit a dynamic organization and fluidity characteristic of such "liquid crystalline" structures. The predominant lipids found in most plasma membranes include phospholipid and glycolipid; those in animal cells also contain significant amounts of cholesterol. Since cholesterol is a stiff, planar molecule and is thought to have a stabilizing influence on plasma membranes, scientists speculate its presence represents an adaptation by animal cells to the absence of the external cell wall that surrounds bacterial and plant cells. Plasma membranes also contain protein and glycoprotein in addition to lipid, of both the integral and peripheral varieties. These proteins perform the major functions associated with plasma membrane and they account for the major differences in plasma membranes among different cells of an organism. Plasma membranes transport nutrients into (and out of) cells and are responsible for facilitating the removal of carbon dioxide, the waste product of respiration. To perform these functions, they contain integral membrane proteins (IMP) that serve as carriers for glucose and a variety of amino acids and for HCO3>-(bicarbonate, the soluble form of carbon dioxide). All cells typically maintain cytoplasmic concentrations of Na+ (sodium) and K+ (potassium) at very different levels than found in their immediate environment: higher in the case of K+ and lower in the case of Na+ These ion gradients are maintained by another group of IMP called pumps, which actively transport these ions up their gradients, using energy supplied by metabolism . Membranes are also leaky to these ions, which diffuse across the plasma membrane and down their respective gradients through another class of IMPs called channels. Differences in the rates of ion diffusion produce differences in electrical charge across most membranes; these are measured as small differences in voltage and are called resting potentials. In so-called excitable cells, such as muscle fibers and neurons , channels may be opened by changes in resting potentials (or by signaling molecules binding to them). When this happens a wave of change in electrical potential may pass along the plasma membrane over the entire surface of the cell; these are called action potentials and represent the major way our nerves and sense organs communicate. Proteins integral to plasma membranes are involved in other forms of signaling as well. In these instances, an external signaling molecule, such as a hormone, binds very selectively to that portion of the IMP extending into the external environment (often involving the carbohydrates attached to the IMP). Such IMPs are more commonly called receptors, which differ in their binding specificity for various signaling molecules. When binding occurs, the receptor changes its overall structure (its conformation ) and that portion projecting into the cytoplasm becomes reactive in some manner. The cytoplasmic region might become an activated enzyme or it might, in turn, become "sticky" for a soluble cytoplasmic enzyme. In any event, the presence of an external signal is conveyed across the plasma membrane and is amplified by the activation of cytoplasmic enzymes, which continue the signaling process by producing second messengers. Under certain circumstances, the cytoplasmic "tails" of receptors are anchored to peripheral membrane protein components of the cytoskeleton , and the binding of a molecule to the extracellular surface releases the receptor from its anchorage. The IMP is then free to diffuse in the plane of the membrane and may become associated with other peripheral membrane proteins in the cytoplasm and aggregated into a specialized region of the plasma membrane called a coated pit. The coated pit then invaginates and forms a vesicle , by a process called endocytosis that removes the receptor (and its attached signal) from the cell surface. Integral membrane proteins of the plasma membranes also anchor cells to their environment: that is, to neighboring cells and to the proteins and glycoproteins of the extracellular environment (the extracellular matrix or ECM). The cytoplasmic portions of these IMP in turn are usually attached to peripheral membrane components of the cytoskeleton (such as microfilaments and intermediate filaments). Although these IMPs are not usually called receptors, their binding with the IMP of an adjacent cell or with the peripheral membrane proteins of the ECM is very selective, and a complex terminology has developed to characterize the very specific nature of these cell-cell and cell-matrix interactions and the IMP involved. Anchoring IMPs also resemble receptors insofar as changes in cell-cell and cell-ECM interactions mediated by these IMPs are often associated with changes in the cytoplasmic regions of the IMP, in this case to their attachments with the cytoskeleton. In this manner, some cells move from place to place (by changing their anchorage points), either normally in the case of circulating leukocytes and abnormally in the case of metastasizing cancer cells. Clusters of anchoring IMPs and their cytoskeletal elements are often referred to as desmosomes when the associations involve other cells and hemidesmosomes when the clusters attach to the ECM. Certain intercellular IMP associations are so tight they effectively seal adjacent cells to each other (without causing fusion of their membranes), forming so-called tight junctions. Tight junctions are especially common in epithelial tissue where their presence in bands around all the epithelia cells produces a very effective barrier against leakage of materials across the tissue through the extracellular space. Finally, certain IMPs may self-associate to form large, nonselective channels in the plasma membrane; such channels arise in close association with identical channels in neighboring cells, establishing cytoplasmic continuity among the cells so connected. These junctions are called gap junctions and they are thought to represent a major means of communications among neighboring cells making up a specialized tissue. Receptors and anchoring IMPs, and the plasma membranes containing them, differ respectively in the signals they can receive, in the second messengers they produce and in the selective nature of their anchorages. To a lesser extent, this is true of transport IMPs as well. These IMPs are the products of differential gene activation and they thus represent a major way in which specialized cells differ from each other. see also Cell Junctions; Membrane Structure; Membrane Transport Chris Watters Raven, Peter H., Ray F. Evert, and Susan E. Eichhorn. Biology of Plants, 6th ed. New York: W. H. Freeman and Company, 1999.
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Answers:1.a 2.c 3.c 4.b 5.d 6.a 7.yes yes yes no 8.no no no yes 9. large solids, liquids, specialize, waste 10.plants. cellulose 11. support and the prevent certain things from entering.
Answers:The respiratory system is an integrated network of organs and tubes that coordinates the exchange of oxygen and carbon dioxide between an organism and its environment. In humans, including mammals, the respiratory system begins with the nose and mouth; air enters the oral and nasal cavities, which combine to form the pharynx, which becomes the trachea. Air then travels down the various tubes to the lungs. Respiratory muscles mediate the movement of air into and out of the body. The alveolar system of the lungs functions in the passive exchange of molecules of oxygen and carbon dioxide, by diffusion, between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. The system also helps to maintain the acid-base balance of the body through the efficient removal of carbon dioxide from the blood. Good Luck!
Answers:I have a biology project that I'm working on and that was one of the questions so this is what I put. The nuclear membrane is a boundary and determines what comes in and goes out.
Answers:1. cell membrane gives the cell its shape as you see it under the microscope.that is the fluid mosaic model. 2.the cell membrane defines waht goes in and what is going out. it lets in water and nutrients and lets out waste materials.active and passive transport plus diffusion and osmosis apply here. 3.the phospholipid layer is strong and protects the organelles from shocks and pathogens. you should note that the cell membrane of a plant and an animal have slightly different structures and therefore functions vary.