Connective Tissue Cells example essay topic

Overview of Anatomy & Physiology Anatomy - is the study of the structure of the body parts & their relationship to one another. Physiology - concerns with the function of the bodys structural machinery - how the body works. Topics of Anatomy Gross Anatomy - is the study of the large body structures visible to the naked eye. It can be approached in different ways.

Regional Anatomy - is the study of all the structures in one particular region. Systematic Anatomy - is when anatomy is studied system by system. Surface Anatomy - is the study of the internal structures as they relate to the overlying skin surface. Microscopic Anatomy - is the study of structures too small to be seen without a microscope. Topics of Physiology They are usually divided into operations of specific organ systems. The Principle of Complementarity of structure & Function - Anatomy & Physiology are taught together because the functions always reflect the structure.

Levels of structural organization Chemical level - this includes atoms & molecules. Cellular level - is the smallest unit of living things. Tissue level - are groups of similar cells that have a common function. Organ level - an organ is at least two tissues that perform a specific function of the body. Organ System level - organs that work together to accomplish a specific function. Homework (pgs.

4-5) February 5, 1999 Summary of the Bodys Organ Systems Integumentary System - forms of the external body covering; protects deeper body tissue from injury; synthesizes vitamin D; site of cutaneous (pain, pressure, ect.) receptors, & sweat & oil glands. Skeletal System - protects & supports body organs; provides th framework the muscles use to cause movement; blood cells are formed within bones; stores minerals. Muscular System - allows manipulation of the environment, locomotion, & facial expression; maintains posture; produces heat. Nervous System - fast-acting control system of the body; responds to internal & external changes of the body by activating appropriate muscles & glands. Endocrine System - glands secrete hormones that regulate processes such as growth, reproduction, & nutrient use (metabolism) by body cells. Cardiovascular System - Blood vessels transport blood, which carries oxygen, carbon dioxide, nutrients, ect. ; the heart pumps blood.

Lymphatic System / Immunity - Picks up fluids leaked from blood vessels & returns it to the blood; disposes of debris in the lymphatic stream; houses white blood cells (lymphocytes) involved in immunity. The immune response mounts the attack against foreign substances within the body. Respiratory System - keeps blood constantly supplied with oxygen & removes carbon dioxide; the gaseous exchange occurs through the walls of the air sacs of the lungs. Digestive System - breaks down food into absorbable units that enter the blood for distribution to the body cells; indigestible foodstuffs are eliminated as feces. Urinary System - eliminates nitrogenous waste from the body; regulates water, electrolytes, & the acid-based balance in the blood. Male Reproductive System - overall function is the production of offspring.

Testes produce sperm & male sex hormones; ducts & glands aid in delivery of sperm to the female reproductive tract. Female Reproductive System - overall function is the production of offspring. Ovaries produce eggs & female sex hormones; remaining structures serve as sites for fertilization & the development of the fetus. Mammary glands of female breast produce milk to nourish the newborn.

Classwork (pgs. 6-8) February 8, 1999 Maintaining Life Necessary Life Functions Maintaining Boundaries - keeps its internal environment separate from the external environment (ex. - skin or cell membrane). Movement - all activities promoted by the muscular system; on the cellular level, muscle cells contracting is called contractility. Responsiveness - irritability is the ability to sense changes in the environment & then respond to them.

Digestion - is the process of braking down ingested food into simple molecules that can be absorbed into the blood. Metabolism - all chemical reactions that occur within the body. Excretion - is the process of removing wastes from the body; usually refers to urine. Reproduction - the making more of an organism; occurs asexually (one) or sexually (two).

Growth - an increase in size. Survival Needs The goal of the body system is to maintain life. There are several factors that need to be present, like: Nutrients - these contain the chemical substances used for energy & cell building. Oxygen - chemical reactions in the body require oxygen. Water - is the single most abundant substance in your body. Homeostasis Homeostasis - is the bodys ability to maintain a relatively stable internal condition, even though the outside world changes.

There are three factors in the homeostatic control organism: Receptor - sensor that monitors the environment. Control Center - analyzes input it receives & determines the appropriate action. Effector - provides the means to the response. Classwork (pgs. 8-13, & 16) February 9, 1999 Positive & Negative Feedback Most of the homeostatic control mechanisms are negative feedback mechanisms. The net effect is that the output of the system shuts off the original stimulus (ex. - heat & air conditioning in houses & glucose regulating {pgs.

9 -10, fig. 1.5}). Positive feedback mechanisms, (often referred to as cascades) the result or response enhances the original stimulus so that the output (activity) is accelerated {pg. 11, fig. 1.6}. Regional Terms Used to designate specific areas within the major body divisions. Axial - part that makes up the main axis of the body; head, neck, & truck. Appendicular - part that consists of the appendages or limbs; arms & legs. Body Planes In the study of Anatomy, the body is often sectioned along a flat surface called a plane.

A section is named for the plane along which it is cut. Sagittal plane - a vertical plane that divides the body into left & right halves. Median or Mid sagittal plane - a vertical plane that lies directly in the center (midline) of the body Frontal or Coronal plane - a vertical plane that divides the body into anterior & posterior parts. Transverse or Horizontal plane - a horizontal plane that divide the body into superior & inferior parts; also called a cross section. Body Cavities Within the axial portion of the body are two large cavities. They are closed to the out side & each contains internal organs.

Dorsal Body Cavity - contains two divisions. Cranial cavity - within which the brain is encased by the skull. Vertebral or Spinal cavity - runs within in the bony vertebral & encloses the spinal cord. Ventral Body Cavity - contains two divisions.

Thoracic cavity - surrounded by the ribs. Pleural cavities - each houses a lung, & the medial mediastinum. Pericardial cavity - within the mediastinum, encloses the heart, & surrounds the thoracic organs (esophagus, trachea, ect.) Abdominopelvic cavity - a dome-shaped muscle important in breathing. Abdominal cavity - contains the stomach, spleen, liver, intestines, & other organs. Pelvic cavity - contains the bladder, rectum, & reproductive organs.

Homework (pgs. 11-12, & 14) February 9, 1999 Homeostatic Imbalance Homeostasis is so important that most disease is regarded as a result of its disturbance, a condition called homeostatic imbalance. As we age, our body organs & control systems become less efficient. As a result, our internal environment becomes less & less stable. These events place us at an even greater risk for illness & produce the changes we associate with aging. Another important source of homeostatic imbalance occurs in certain pathological situations when the usual negative feedback mechanisms are overwhelmed & destroyed by the positive feedback mechanisms take over.

Some instances of heart failure reflect this phenomenon. Anatomical Position & Directional Terms To describe body parts & position accurately, we need an initial reference point & must use indications of direction. The anatomical reference point is a standard body position called anatomical position. In this position, the body is erect with feet together.

The terms right & left refer to those sides of the cadaver or the person being viewed - not to those of the observer. Directional terms allow us to explain exactly where one body structure is in relation to another. Anatomical terminology saves words & is less ambiguous; anatomical meanings are very precise. Orientation & Directional Terms Superior (cranial) - toward the head end or upper part of a structure or the body; above.

Example: The head is superior to the abdomen. Inferior (caudal) - away from the head end or toward the lower part of a structure or the body; below. Example: The navel is inferior to the chin. Anterior (ventral) - toward or at the front of the body; in front of.

Example: The breastbone is anterior to the spine. Posterior (dorsal) - toward or the back of the body; behind. Example: The heart is posterior to the breastbone. Medial - toward or at the midline of the body; on the inner side of. Example: The heart is medial to the arm.

Lateral - away from the midline of the body; on the outside of. Example: The arms are lateral to the chest. Intermediate - Between a more medial & more lateral structure; Example: The collarbone is intermediate between the breastbone & the shoulder. Proximal - Closer to the origin of the body part or the point of attachment of a limb to the body trunk. Example: The elbow is proximal to the wrist. Distal - farther from the origin of the body part or the point of attachment of a limb to the body trunk.

Example: The knee is distal to the thigh. Superficial - Toward or at the body surface. Example: The skin is superficial to the skeletal muscles. Deep - away from the body surface; more internal.

Example: The lungs are deep to the skin. Classwork (pg. 17) February 10, 1999 Body Cavities & Membranes Membranes in the Ventral Body Cavity The walls of the ventral body cavity & the outer surfaces of the organs it contains are covered by serous membrane. The one lining the cavity wall is the parietal serosa, which folds on itself to form the visceral serosa {pg. 17, fig. 1.10} for all the cavities. Other cavities Oral & Digestive cavity - oral cavity, commonly called the mouth Nasal cavity - located within & posterior to the nose. Orbital cavities - house the eyes & present them in an anterior position. Middle Ear cavities - carved into the temporal bone of the skull lie just medial to the eardrum; contain tiny bones that transmit sound vibrations.

Synovial cavities - are joint cavities; enclosed within fibrous capsules that surround freely movable joints of the body (ex. - elbow & knee capsules). Classwork (pgs. 109-113,119,132,134) February 12, 1999 Types of Tissues Histology is the study of tissues, it complements the study of gross anatomy. Tissues are groups of cells that are similar in structure & perform a common function.

Tissues are organizations of similar cells that are surrounded & often embedded in a nonliving intercellular material called a matrix. Four Principle Types of Tissues Epithelial tissue - is a sheet of cells that covers & protects the body surface; lines body cavities; moves substances in & out of the blood; & forms some glands. Connective tissue - supports the body & connects body parts; found everywhere in the body. Muscle tissue - produce most types of body movement.

Nervous tissue - most complex body tissue; specializes in communication between various parts of the body. Functions of the Epithelial Tissue Protection - the skin protects the body from mechanical, chemical, & invading bacteria. Sensory Functions - skin, nose, eyes. & ears. Excretion - found in the lining of the kidneys tubule makes it possible.

Filtration - also in kidneys; filters blood so it can be excreted. Secretion - secretes hormones, mucus, digestive juices, & sweat. Absorption - found in the lining of the gut & respiratory tract. This allows for absorption of nutrients from the gut; & exchange of gases between the lungs & heart. Classification of Epithelia Each epithelium is given two names. The first name indicates the # of cell layers present; the second describes the shape of its cells.

Simple Epithelia The simple epithelia are concerned with absorption, secretion, & filtration. Protection is not one of their specialties. Simple Squamous Epithelium - their cells are flattened laterally & their cytoplasm is spares; in a surface view, it resembles a tiled floor, perpendicularly they resemble fried eggs. This epithelium is found were filtration or the exchange of substances by rapid diffusion is a priority. Simple Cuboidal Epithelium - consists of a single layer of cubical cells & its spherical nuclei is stained darkly; looks like a string of beads when viewed microscopically. It functions are excretion & absorption.

Simple Columnar Epithelium - seen a as a single layer of tall, closely packed cells, aligned like soldiers in a row. Mostly associated with absorption & secretion. It lines the digestive tract from the stomach to the rectum. Pseudo stratified Columnar Epithelium - cells vary in height & rest on the basement membrane, but only the tallest reach the apical surface of the epithelium; the nuclei are located at different levels above the basement, thus giving a false (pseudo) impression. They secrete & absorb substances. Homework (pgs.

109-110) February 12, 1999 Special Characteristics of Epithelium Epithelial tissues have many characteristics that distinguish them from other tissues types. Cellularity. - Epithelial tissue is composed almost entirely of close-packed cell. Only a tiny amount of extracellular material lies in the narrow spaces between them.

Specialized contacts. - Epithelial cells fit closely together to form continuous sheet. Adjacent cells are bound together at many points by lateral contacts, including tight junctions & desmosomes. Polarity. - All epithelia have an apical surface, a free surface exposed to the body exterior or the cavity of an internal organ, & an attached basal surface. All epithelia exhibit polarity, meaning that cells near the apical surface differ from those at the basal surface in both structure & function.

Although some apical surfaces are smooth & slick, most have microvilli, finger like extensions of the plasma membrane. Microvilli tremendously increase the exposed surface area, & in epithelia that absorb or secrete substances, the microvilli are often so dense that the cell apic es have a fuzzy appearance called a brush border. Some epithelia, such as that lining the trachea, have motile cilia that propel substances among their surfaces. Lying adjacent to the basal surface of an epithelium is a thin supporting sheet called the basal lamina. This noncellular, adhesive sheet consists largely of glycoproteins secreted by the epithelial cells. Functionally, the basal lamina acts as a selective filter; that is, it determines which molecules diffusing from the underlying connective tissue will be allowed to enter the epithelium.

The basal lamina also acts as a scaffolding along which epithelial cells can migrate to repair a wound. Supported by connective tissue. - All epithelial sheets rest upon & are supported by connective tissue. Just deep to the basal lamina is the reticular lamina, a layer of extracellular material containing a fine network of collagen protein fibers that belong to the underlying connective tissue. Together the two laminae form the membrane basement. The basement membrane reinforces the epithelial sheet, helping it to resist stretching & tearing forces, & defines the epithelial boundary.

An important characteristic of cancerous epithelial cells is their failure to respect this boundary, which they penetrate to invade the tissue beneath. Innervated but avascular. - Although epithelium is innervated (supplied by nerve fibers), it is avascular (contains no blood vessels). Epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue.

Regeneration. - Epithelium has a high regenerative capacity. Some epithelia are exposed to friction & their surface cells removed by abrasion. Others are damaged by hostile substances in the external environment (bacteria, acid, smoke). As long as epithelial cells receive adequate nutrition, they can replace lost cells rapidly by cell division.

Classwork (pgs. 115-118) February 16, 1999 Stratified & Glandular Epithelia Stratified Epithelia Stratified epithelia consists of two or more cell layers. Stratified Squamous Epithelium - is the most widespread of the stratified; found in the exterior part of the skin. Stratified Cuboidal & Stratified Columnar - are rare; usually found in large ducts & some glands. Transitional Epithelium - found in the lining of urinary organs. Transitional epithelium can change shape in order to stretch.

Glandular Epithelia Epithelium of the glandular type is specialized for secretory activity. All glands are classified as exocrine or endocrine. Exocrine glands - discharge their secretory products into ducts (ex. salivary glands) Endocrine glands - are ductless; they discharge their secretions directly: hormones. Multicellular exocrine glands have two structural elements: ducts & secretory units. On the basis of their duct structures they are either simple glands - single unbranched ducts or compound glands - that have a branched duct. Then they are further described according to their secretory parts: Tubular - forms tubes.

Alveolar - small flask like sacs. Tubulo alveolar - both. Functional Classifications of Exocrine Glands. Methods by which they discharge.

Three types: Apocrine Glands - collect their products near the tips of the cell & then they release into a duct by pinching of (ex. mammary glands). Holocrine Glands - collect inside the cells & then they rupture (ex. sebaceous (oil) glands). Merocrine Glands - discharge directly through the cell membrane (ex. salivary glands). Homework (pgs. 119) February 16, 1999 Unicellular Exocrine Glands Unicellular exocrine glands are single cells scattered in am epithelial sheet amid cells with other functions. They have no ducts.

In humans, all such glands produce mucin, a complex glycoprotein that dissolves in water when secreted. Once dissolved, mucin forms mucus, a slimy coating that both protects & lubricates surfaces. The only important unicellular glands in humans are the goblet cells found sprinkled in the columnar epithelium cells lining the intestinal & respiratory tracts. Although unicellular glands probably outnumber multicellular glands, unicellular glands are the less well known of the two glands types.

Classwork (pgs. 119,122-126) February 17, 1999 Connective Tissue Connective Tissue is the most abundant tissue. Its major functions are: Binding & Support Protection Insulation & Blood Transportation Common Characteristics of Connective Tissue Common origin - derived from the mesoderm. Degrees of vascularity; some are vascularised, others are not. Extracellular matrix - this separates the living cells of the tissue. Two Classes of Connective Tissue The first is divided into four groups.

Loose Ordinary Tissue (Areolar) - found between other tissues or other organs; used in connection; it is a fluid. Adipose Tissue (Fat) - found under the skin & as padding at various points. Used for protection, insulation, & a reserve for food. Reticular Tissue - slender branching of reticular fibers forms the framework for the spleen, lymph nodes, & bone marrow; look like little strings that run in all directions.

Dense Fibrous Tissue - tendons & ligaments; they are bundles or callagenous fibers in parallel rows in a fluid matrix; they are thicker strings that run in one direction. The second class of connective tissue contains cartilage - has qualities intermediate between dense fibrous connective tissue & bone. It is avascular (no bloods run through it) & has no nerves. Hyaline Cartilage - is the most abundant tissue type in the body; provides firm support with some pliability. Elastic Cartilage - nearly identically like hyaline cartilage, but has more elastin fibers which gives this tissue a greater tolerance for repeated bending. Fibro cartilage - (fibrous cartilage) often found where hyaline cartilage meets a true ligament or tendon.

Found where strong support & ability to withstand heavy pressure are required. Homework (pgs. 120-122) February 17, 1999 Structural Elements of Connective Tissue Connective tissues have three main elements: ground substance, fibers, & cells. Ground substances make up the extracellular matrix. (Note: that the term matrix indicates the ground substance.) Ground Substance Ground Substance - is an amorphous (unstructured) material that fills the space between the cells & contains the fibers.

It is composed of instertitial fluid, cell adhesion proteins, & proteoglycans. Cell adhesion proteins, a group that includes fibronectin & lamina, sever mainly as a connective tissue glue that allows connective tissue cells to attach themselves to matrix elements. The proteoglycans consists of a protein core to which glycosaminoglycans (GAGs) are attracted. The strand-like GAGs which are large, negatively charged polysaccharides, stick out from the core protein like the fibers of a bottle brush. Important examples of GAGs in connective tissues are chondroitin sulfate, keratin sulfates, & hyaluronic acid.

The GAGs intertwine & trap water, forming a substance that varies from a fluid to a semi-stiff hydrated gel. The relative amounts & kinds of GAGs help determine the properties of the matrix. Example - The higher the GAG content, the stiffer the ground substance is. The ground substance holds fluids & functions as a molecular sieve, or medium, through which nutrients & other dissolved substances can diffuse between the blood capillaries & the cells. The fibers embedded in the ground substance makes it less pliable & impede diffusion somewhat. Fibers The fibers of the connective tissue provide support.

Three types of fibers are found in connective tissue matrix: Collagen Fibers - (white fibers), are constructed primarily of the fibrous protein collagen. Collagen molecules are secreted into the extracellular space, where the are assembled spontaneously into cross-linked fibers. Collagen fibers are extremely tough & provide high tensile strength to the matrix. Stress test show that collagen fibers are stronger than steel fibers of the same size.

Collagen fibers are the most abundant. Elastic Fibers - (yellow fibers), are formed largely from another fibrous protein, elastin. Elastin has a randomly coiled structure that allows it to stretch & recoil like a rubber band. The presence of elastin in the matrix gives it a rubbery, or resilient, quality. Connective tissue can stretch only so much before its thick, rope-like collagen fibers become taut.

Then, when the tension lets up, elastic fibers snap the connective tissue back to its normal length & shape. Elastic fibers are found where greater elasticity is needed (ex. skin, lungs, & blood vessel walls). Reticular Fiber - are fine callagenous fibers & are continuous with collagen fibers. They branch extensively, forming delicate networks that surround small blood vessels & support the soft tissue of organs. They are particularly abundant where connective tissue abuts other tissue types, for example, in the basement membranes of epithelial tissues, & around capillaries, where they form fuzzy nets. Cells Each major class of connective tissue has a fundamental cell type that exists in immature & mature forms.

The undifferentiated cells, indicated by the suffix blast, are actively mitotic cells that secrete the ground substance & the fibers characteristics of their particular matrix. The primary blast cell types by connective tissue class are: Connective tissue proper: fibroblast. Cartilage: chondro blast. Bone: osteoblast. Blood: hemocytoblast or hematopoietic stem cell. Once they synthesize the matrix, the blast cells assume their less active, mature mode, indicated by the suffix cute.

The mature cells maintain the health of the matrix. However, if the matrix is injured, they can easily revert to their more active state to repair & regenerate the matrix. (The hemocytoblast, the blood-forming stem cell found in bone marrow, always remains actively mitotic.) Additionally, connective tissue is home to an assortment of other cell types, such as nutrient-storing fat cells & mobile cells that migrate into the connective tissue matrix from the bloodstream. The latter include white blood cells (neutrophils, eosinophils, lymphocytes) & other cell types concerned with tissue response to injury, such as mast cells, macrophages, & antibody-producing plasma cells. This wide variety of cells is particularly obvious in our prototype, areolar connective tissue. The oval mast cells are typically found clustered in tissue spaces deep to an epithelium or along blood vessels.

These cells act as sensitive sentinels to detect foreign substances (ex, bacteria, fungi) & initiate local inflammatory responses against them. In the mast cell cytoplasm are conspicuous secretory granules containing: Heparin - an anticoagulant (a chemical that prevents the blood clotting) when free in the bloodstream, but its significance in human mast cells is uncertain Histamine - is released during inflammatory reactions, makes the capillaries leaky. Macrophages are large, irregularly shaped cells that avidly phagocytize a broad variety of foreign materials, ranging from foreign molecules to entire bacteria to dust particles. Macrophages also engulf & dispose of dead tissue cells, & they are central actors in the immune system. In connective tissues, they may be attached to connective tissue fibers or they may migrate freely through the matrix. Macrophages are peppered throughout loose connective tissue, bone marrow, & lymphatic tissue.

Those in certain sites are given specific names. They are called histiocytes in loose connective tissue, Kupffer cells in the liver, & micro glial cells in the brain. Although all these cells are phagocytes, some have selective appetites. For example, macrophages of the spleen primarily dispose of aging red blood cells, but they will not turn down other delicacies that come their way. Classwork (pgs. 128-134) February 18, 1999 Bone, Blood, Membranes, Nervous, & Muscle Tissues Bone (osseous) - due to its rock hardness it has the ability to support & to protect softer tissue.

Blood - the fluid within blood vessels; functions as the transport vehicle in the cardiovascular system. Membranes - a continuous multicellular sheet composed of at least two primary tissue types: an epithelium bound to an underlying layer of connective tissue proper. Cutaneous Membranes - are your skin. Mucous Membranes - lines cavities open to the exterior.

Serous Membranes - are moist membranes found in closed ventral body cavities (ex. pericardium, pleura). Nervous Tissue - Has two major cell types. Neurons - specialized cells that generate & conduct nerve impulses. Neuralgia - are supporting cells.

Muscle Tissue - made up of muscle fibers. Muscle cells possess mylofilaments. Skeletal Muscle - attached to bone, voluntary or stratified (lines); form the flesh of the body. Cardiac Muscle - occurs in the heart, it is striated & contains intercalated discs (junctions of branching cells). Smooth Muscle - visceral or involuntary; found in hallow internal organs. Homework (pgs.

136) February 18, 1999 Steps of Tissue Repair Tissue repair requires that cells divide & crawl, activities that are initiated by growth factors (wound hormones) released by injured cells. It occurs in two major ways: by regeneration - the replacement of destroyed tissue with the same kind of tissue- & by fibrosis - involves proliferation of fibrous connective tissue called scar tissue. Each of these occurs depends on: The types of tissue damaged. The severity of the injury. In skin, the tissue we will use as our example, repair involves both activities. Inflammation sets the stage.

The process begins while the inflammatory reaction is still going on. Let us briefly examine what has happened up to this point. Tissue injury sets the following inflammatory events into motion. First, because of the release of histamine & other inflammatory chemicals by injured tissue cells, macrophages, mast cells, & others, the capillaries dilate & become very permeable.

This allows white blood cells & plasma fluid rich in clotting proteins, antibodies, & other substances to seep into the injured area. Then the leaked clotting proteins construct a clot, which stops the loss of blood, holds the edges of the wound together, & effectively walls off, or isolates, the injured area, preventing bacteria, toxins, or other harmful substances from spreading to surrounding tissues. The portion of the clot exposed to the air quickly dries & hardens, forming a scab. The inflammatory events leave excess fluid, bits of destroyed cells, & other debris in the area. Most of this material is essentially removed from the area via lymphatic vessels or phagocytized by macrophages. At this point, the first step of tissue repair, organization, begins.

Organization restores the blood supply. During organization the temporary blood clot is replaced by granulation tissue. Granulation tissue is a delicate pink tissue composed of several elements. Thin, extremely permeable capillaries bud from intact capillaries nearby & enter the damaged area, laying down a new capillary bed; they protrude nub-like from the surface of the granulation tissue, giving it a granular appearance.

These capillaries are fragile & breed freely, as demonstrated when someone picks at a scab. Also present in granulation tissue are scattered macrophages & fibroblasts that synthesize new collagen fibers to bridge the gap permanently. As organization continues, macrophages digest & remove the original blood clot. The granulation tissue, destined to become scar tissue (a permanent fibrous tissue patch), is highly resistant to infection because it produces bacteria-inhibiting substances.

Regeneration &/or fibrosis effects permanent repair. While organization is going on, the surface epithelium begins to regenerate. Epithelial cells migrate across the granulation tissue just beneath the scab, which soon detaches. As the fibrous tissue beneath matures & contracts, the regenerating epithelium thickens until it finally resembles than of the adjacent skin. The end result is a fully regenerated epithelium, & an underlying region of scar tissue.

The scar may be invisible, or visible as a white thin line, depending on the severity of the wound. Classwork (pgs. 189-203) February 24, 1999 Skeletal System The adult Skeleton has 206 separate bones. There are two main divisions: Axial Skeleton - has 80 bones; the upper axis has 74; the inner ear has 6. Contains the skull. There are two major divisions: Cranium - brain case (has 8 bones): 1.

Frontal Bone - forehead. 2. /3. Parietal Bones - bulging top side of the cranium. 4. /5.

Temporal Bones - house the middle & inner ear structures. 6. Occipital Bone - creates the framework of the lower back part of the skull. 7.

Sphenoid Bone - resembles bat wings. 8. Ethmoid Bone - forms bony area between the nasal cavity & the orbits of the eyes. Face - (has 14 bones): 1.

/2. Maxillae Bones - upper jaw (upper lip); one on each side. 3. Mandible Bone - lower jaw. 4.

/5. Zygomatic Bones - cheeks 6. /7. Nasal Bones - bridge of the nose; one on each side. 8. /9.

Lacrimal Bones - helps form tear ducts. 10. /11. Inferior Nasal Concha e Bones - ledge protecting the nasal cavity. 12. Vomer Bone - completes the nasal septum.

13. /14. Palatine Bones - hard plate within the mouth. Appendicular Skeleton - consists of 126 bones. Classwork (pgs. 204-213) February 25, 1999 Regions of the Spinal Column Hyoid Bone - is below the skill, attached to the bottom of the tongue; single bone in the neck above the larynx & below the mandible; not attached to any other bone in the body (sesam oid).

Spinal Column; divided into three types of vertebrae: Cervical Vertebrae - neck (has 7 bones). Thoracic Vertebrae - found in the posterior part of the chest or the thorax (has 12 bones). Lumbar Vertebrae - found in the small of the back (has 5 bones). Sacrum - below the vertebral column, a single bone resulted by a fusion of 5 separate vertebrae.

Atlas - is at the top of the vertebral column, the head sits upon it; has no body & no spinous processes Axis - is below the atlas; has a body & a spinous processes. Coccyx - is below the sacrum, consists of 4 bones fused together (is a tail bone). Sternum - is the media part of the anterior chest. Ribs - 12 pairs or 24; in front (anterior), each of the first 7 ribs joins a costal cartilage that attach to the sternum. Then the next 3 join the cartilage of the ribs before, so they are attached to the sternum directly. The 11th & 12th pairs do not attach & are called floating ribs.

Classwork (pgs. 214-227) February 26, 1999 Appendicular Skeleton Bones of the limbs & their girdles are collectively called the appendicular skeleton because they are appended to the axial skeleton that forms the longitudinal axis of the body. Pectoral (Shoulder) Girdle Shoulder Girdle - consists of two bones, the anterior clavicle & the posterior scapula. Clavicles - collar bones, are slender, doubly curved long bones that can be felt along their entire courses as they extend horizontally across the superior thorax. Scapulae - shoulder blades, are thin, triangular flat bones. The Upper Arm Humerus - (arm) articulates proximally with the scapula at the shoulder, & distally with the radius & ulna at the elbow.

Radius - on the thumb side, has two proximal articulations, the humerus, & ulna. Ulna - on the little finger side, articulates proximally with the humerus & the radius, & distally with cartilage. 7 carpals - wrist. 5 metacarpals- framework of the hand. 14 phalanges - fingers. Pelvic (Hip) Girdle Hip Girdle- formed by a pair of coxal bones, which consists of three bones, which are separate during childhood & fused together during adulthood): Ilium - the large flaring bone that forms a major portion of a coxal bone.

Ischium - forms the posteroinferior part of the hip bone. Pubis - forms the anterior portion of the os coxa. The Lower Limb Femur - (thigh bone), is the largest, longest, & strongest bone in the body. Tibia - the longest & strongest bone in the lower leg; articulates proximally with the femur, & distally with the fibula & talus.

Fibula - is smaller & more deeply placed, proximally articulates with the tibia. 7 tarsal - ankles. 5 metatarsals - flat part of the foot. 14 phalanges - toes. Classwork (pgs. 261-262) March 05, 1999 General Function of the Muscular System There are four general functions of the skeletal system.

Movement - either body as a whole or parts of the body. Heat Production - muscles produce heat - since there are so many muscles, they are one of the most important parts of the mechanisms for maintaining homeostasis. Posture - continual partial contraction of muscles allow for standing, sitting, ect. Stabilizing Joints - muscles help keep everything in place. There are four characteristics that enable skeletal muscle tissue to function: Excitability - the ability to be stimulated, this causes them to be able to respond to regulatory mechanisms, such as nerve signals. Contractility - the ability to shorten, which allows muscles to pull on bones & produces movement.

Extensibility - the ability to stretch & return to the resting length. Elasticity - the ability of the muscle fiber to resume to its resting length after being stretched. Skeletal muscle cells, are composed of bundles of skeletal muscle fibers that extend the length of the muscle. They are long cells. They have the same structural parts as other cells, but they have different names: Sarcoma - cell membrane. Sarcoplasmic Reticulum - endoplasmic reticulum.

Sarco plasm - cytoplasm, it contains mitochondria & many nuclei. Myofibrils, are bundles of long fibers. They are made up of thick & thin filaments. Homework (pgs. 263-265) March 05, 1999 Attachments Most muscles span joints & are attached to bones (or other structures) in at least two places & when a muscle contracts, the movable bone, the muscles insertion, moves toward the immovable are less movable bone, the muscles origin. In the muscles of the limbs, the origin usually lies proximal to the insertion.

Muscle attachments, whether origin or insertion, may be direct or indirect. In direct attachments, the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage. In indirect attachments, the muscles connective tissue wrappings extend beyond the muscle as a rope-like tendon or a flat, broad aponeurosis. The tendon or aponeurosis anchors the muscle to the connective tissue covering of a skeletal element (bone or cartilage) or to the fascia of other muscles. The temporal is muscle of the head has both direct & indirect (tendinous) attachments. Of the two, indirect attachments are much more common in the body because of their durability & small size.

Since tendons are mostly tough collagen ic fibers, they can cross rough bony projections which would tear apart the more delicate muscle tissues. Because of their relatively small size, more tendons than fleshy muscles can pass over a joint - thus, tendons also conserve space. Myofibrils When viewed at high magnification, each muscle fiber is seen to contain a large number of rod-like myofibrils that run in a parallel fashion & extend the entire length of the cell. Each are 1-2 m in diameter, the myofibrils are so densely packed that the mitochondria & other organelles appear to be squeezed between then. There are hundreds to thousands of myofibrils in a single muscle fiber, depending on its size, & they account for about 80% of the cellular volume. The myofibrils are the contractile elements of the skeletal muscle cells.

Striations, Sarcomeres, & Myofilaments Striations - a repeating series of dark & light bands, are evident along the length of each myofibril. The dark bands are called A bands because they are anisotropic; that is, they can polarize visible light. The light bands, called I bands, are isotropic, or non polarizing. In an intact muscle fiber, the myofibril bands are nearly perfectly aligned with one another & this gives the cell as a whole a stripped (striated) appearance. Each A band has a lighter stripe in the midsection called the H zone (bright). The H zones are visible only in relaxed muscle fibers.

Each H zone is bisected by a dark line called the M line. The I bands also have a mid-line interruption, a darker area called the Z discs. A sarcomere is the region of the myofibril between two successive Z discs. About 2 m long, the sarcomere is the smallest contractile unit of a muscular fiber.

Thus, the functional units of the skeletal muscle are actually very minute proportions of the myofibrils, & the myofibrils are chains of sarcomeres aligned end-to-end like boxcars in a train. If we examine the banding pattern of a myofibril at the molecular level, we see that it arises from an orderly arrangement of two types of even smaller structures, called filaments or myofilaments, within the sarcomeres. The thick filaments extend the entire length of the A band. The more lateral thin filaments extend across the I bands & part way into the A band. The Z discs, also called a Z line, is a coined shaped protein sheet that anchors the thin filaments & also connects each myofibril to the next throughout the width of the muscle cell. The H zone of the A band appears less dense when viewed microscopically because the thin filaments do not overlap the thick ones in this region.

The M line in the center of the H zone is slightly darker because of the presence of fine strands that hold adjacent thick filaments together in that area. A longitudinal view of the mylofilaments is a bit misleading because it gives the impression that each thick filament interdigitate's with only four thin filaments. In areas where thin & thick filaments overlap, each thick filament is actually surrounded by a hexagonal arrangement of six thin filaments.