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Transcript
Physiology 2015 Tissues Tissues: The Cell Theory states that the cell is the basic unit of structure and function. When a group of cells with similar structure are found together performing a common function and possess similar extra-cellular substances located between the cells the result is a tissue. The microscopic study of tissue structure is called histology, which you have been and will continue to cover in lab. Our objective for this unit - is to discuss how the structure of specific tissues, (and the cells that comprise the tissue) relate to the tissue’s function as well as the growth, aging and trauma of tissues and the changes that occur. The four basic tissue types are: A. Epithelium or epithelial is found throughout the body where it covers internal and external surfaces. It also forms most of our glands. a. Common features – most epithelial tissue posses the following characteristics i. Very little extra-cellular matrix between cells. ii. Free surface – side of cells not in contact with other cells iii. Basement membrane – 1. attaches epithelial cells to underlying tissues 2. produced by the epithelial cells and the underlying cells 3. composed of carbohydrates and proteins b. General Functions of Epithelial Tissue i. Protecting underlying structures – epithelium of the oral cavity protects the underlying structures from abrasion ii. Acting as barriers – prevents the movement of many substances through, i.e. the skin acts as a barrier to water and prevents the water loss from the body. iii. Permitting the passage of substances – allows the movement of certain substances through. i.e. oxygen and carbon dioxide are exchanged between the air and blood by diffusion through the epithelium in the lungs iv. Secreting substances – examples are sweat and mucus glands v. Absorbing substances – epithelial in the intestinal tract absorb digested nutrients, vitamins and ions c. Classification/Types of Epithelia (refer to your coloring packet) Number of Layers Simple – one layer Cell Shape Squamous Cuboidal Columnar Pseudostratified (modified form of simple) Columnar Stratified – more than one layer Squamous – Keratinized – outer skin layer with a layer of dead cells – dry Non – keratinized – found in the mouth – moist and protects against abrasion Transitional (modified form of stratified) Cuboidal to columnar when NOT stretched i.e.empty bladder Squamous-like when stretched – i.e. full bladder d. Structural and Functional Relationships i. Cell Layers and Shapes – the number of cell layers and the shapes of the cells reflect the function that they perform 1. Two important functions based on number of layers a. controlling passage of materials through i. Simple epithelium (single layer) found in tissues in which the main function is movement of materials as in diffusion of gases or nutrients b. protecting the underlying tissues i. Stratified epithelium (more than one layer) adapted for protective function. As outer cell layers are damaged they are replaced by the cells at the deeper layers. 2. Functions differ based on cell shape a. Cells that are flat and thin deal with diffusion, for example the cells that make up the alveoli in the lungs c. Cuboidal or columnar cells deal with secretion and absorption. These cells are larger and contain more organelles that also reflect the function. i. For example – the stomach is lined with simple columnar epithelium, which contains many secretory vesicles filled with mucus. When released the mucus protects the stomach lining from the digestive enzymes and acid. 3. Shape and Number of layers can change a. if cells are subjected to long term irritation or other abnormal conditions. ii. Cigarette smokers – pseudostratified ciliated epithelium which produces mucus and helps to clean out respiratory tract is replaced by stratified squamous epithelium that is more resistant to irritation, but does not perform cleaning functions. 1. Lung cancer can result from the changes in the epithelial tissue ii. Free Cell Surfaces – epithelia have a free surface, which is not in contact with other cells and lies away from underlying tissues. The special features found on the free surface reflect their function. 1. Smooth surfaces – reduce friction as in blood vessels 2. Microvilli – increase cell surface area as seen in the intestine for absorption and secretion 3. Cilia – move material along the surface of the cells as in the nasal cavity and trachea, usually with the aid of mucus produced by specialized cells called goblet cells B. Connective Tissue is a diverse group of tissues ranging from a liquid (blood) to semi solid (cartilage) to a solid (bone). All of these tissue posses a common characteristic, a large amount of extra-cellular material (matrix) that separates the cells. a. Common Structural Features – i. Extra-cellular material has 3 major components 1. protein fibers – 3 types a. collagen – resemble microscopic ropes, are flexible but resist stretching b. reticular – short collagen fibers that branch to form a support network c. elastic – fibers with the ability to recoil to original shape after having been stretched 2. ground substance – shapeless, colorless background in which the protein fibers and cells sit a. made of a protein called prosteoglycan (protein with a polysaccharide attached) 3. water a. large amounts of water are trapped between the polysaccharides of the prosteoglycan molecule ii. connective tissue cells are named by their function a. -blast cells produce matrix b. -cyte cells maintain the matrix c. -clast cells break down the matrix b. Functions of Connective Tissue – due to the diversity of cell structure within this tissue category, there is also functional diversity. Here are the major categories of function. i. Enclosing and separating – sheets form capsules that cover organs and layers that separate tissues and organs – i.e. separation of muscles, blood vessels and nerves from on another ii. Connecting tissues to one another – example tendons connect muscle to bone and act as strong cables. iii. Supporting and moving – bones are rigid support for the body and cartilage, which is semi rigid, supports the nose, ear and joint surfaces. Joints allow one part of the body to move relative to another iv. Storing – many of the connective tissues are reservoirs for minerals and ions needed for metabolic reactions. Bones store calcium and phosphate, while adipose tissue stores high energy molecules. v. Cushioning and Insulating – adipose tissue cushions and protects many of the organs, for example the kidneys and the heart and provides and insulation layer under the skin that helps to conserve heat. vi. Transporting – blood transports a number of materials throughout the body including oxygen and enzymes, hormones and cells of the immune system. vii. Protecting – Bones protect underlying structures, for example the rib cage and immune system cells protect the body from toxins and bacterial infection. c. Classification/Types of Connective Tissues and where they are found C. Muscle Tissue - is responsible for the movement of the internal organs and the framework of the body due to its special property the ability of contraction. 1. 3 types of muscle ___________________ ____________________ _______________________ a. Skeletal muscle i. ii. iii. iv. v. Meat of animals and what you eat Makes up 40 % of a person’s body weight Attaches to the skeleton Enables body movement Muscle cells are long, cylindrical and have several nuclei per cell vi. Striated or striped due to the banding patterns of the muscle protein (actin and myosin) fibers vii. Voluntary b. Cardiac muscle i. Muscle of the heart (myocardium) and responsible for pumping blood ii. Involuntary (unconscious) control iii. Striated, with one nucleus per cell iv. Specialized gap junctions present called intercalated discs – allows for fast spread of bio-electrical signal c. Smooth Muscle i. Forms the walls of hollow organs (except the heart) ii. Found also in skin and eyes iii. Involuntary iv. Tapered at each end, one nucleus and not striated D. Nervous System – Nerve tissue is responsible for controlling and coordinating many bodily activities. Many of these functions depend on the ability of the nervous tissue cells to communicate with one another and with other cells by electrical signals called action potentials. 1. composed of neurons and support cells a. neurons or nerve cell i. responsible for the conduction of the action potential ii. made of 3 parts 1. cell body (soma) 2. dendrites 3. axons b. support cells called neuroglia i. do not conduct electrical impulses ii. function to nourish, protect and insulate the neurons iii. form myelin sheath around axon of cell 1. gaps in myelin sheaths called Nodes of Ranvier serve as sites for accelerating an impulse 2. 3 categories of nerve cells a. Sensory neurons i. Found in eyes, ears, surface of skin ii. Receive information about the body’s condition and the external environment b. Motor neurons i. Found in brain and spinal cord ii. Conducts impulses out of central nervous system towards muscles and glands and stimulates them c. Interneurons i. Found in brain and spinal cord ii. Integrate information – conducts information between neurons within the central nervous system II: Tissue Inflammation, Repair, Aging and Death A. Tissue Inflammation – a consequence of injury; is a body’s response to maintain homeostasis when tissues are damaged. Inflammation mobilizes the body’s defenses, isolates and destroys microorganisms, foreign materials and damaged cells so that tissue repair can proceed. a. five major responses/symptoms a. heat b. redness c. pain d. swelling e. disturbance of function b. responses initiated by release of chemicals called mediators of inflammation which act on injured tissue and associated blood vessels a. histamine – causes vessels to dilate and become more permeable i. produce responses of redness and heat ii. also allow materials and blood cells to move out of the blood vessels and into the damaged tissue with its antibodies, oxygen and clotting factors b. pain is caused by either i. nerve cell endings are directly damaged ii. as a consequence of fluid accumulation (edema) from the vessels with increased permeability c. pain, limitation of movement due to the edema, and tissue destruction all contribute to disturbance of function E. Tissue Repair - the substitution of viable cells for dead ones; can be achieved by regeneration or replacement and is determined by the type of tissues and severity of the wound. a. Regeneration – new cells are the same type as those that were destroyed and normal function resumes b. Replacement – new type of tissue develops that causes scar (accumulation of connective tissue) production and the loss of some tissue function - usually occurs when the wound is severe F. Tissue Aging – some changes are obvious while others subtle. a. Affect cells and the extra-cellular matrix produced by those cells b. Cells divide more slowly as one ages c. Collagen fibers become more irregular in structure, even though they increase in number. i. As a result, tissues with collaged (i.e. tendons) become less flexible and more fragile d. Elastic fibers fragment and bond to calcium ions and become less elastic e. Reduced flexibility and elasticity are causes of wrinkles as well as increased tendency for bones to break