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Transcript
Chapter 5 Tissues 5.1 Introduction • Cells are the basic unit of structure and function in the humans. • Cells are then organized into groups called tissues. – Tissues are composed of similar cells specialized to carry out a particular function. • In humans there are 4 major types of tissue: – Epithelial – protective coverings • Function – secretion and absorption – Connective – support soft body parts and binds structures together – Muscle – produce and control body movement – Nervous – conduct impulses that control and coordinate body activity Epithelial Tissues • Found throughout the body • Covers organs, forms inner lining of body cavity, lines hollow organs (stomach) • Always has a free (apical) surface exposed to the outside or internally to an open space. • The underside is attached or anchored to connective tissue by the basement membrane. – Basement membrane- a thin nonliving layer • Do not contain blood vessels – Underlying connective tissues are very abundant with blood vessels • **This is why you only bleed if you get a deep cut** • Divide often – Allows cuts to heal quickly • Tightly packed – Makes them effective coverings • Other functions: secretion, absorption, and excretion • Classified based on their shape: – Squamous- flattened – Cuboidal – cube shaped – Columnar – elongated, tall – Stratified- 2 or more layers – Simple – single layer Simple Squamous Epithelium • Single layer of thin flattened cells • Fit tightly (like tiles) • Nuclei are broad and thin (in depth) • Substances easily pass through this layer – Common sights of diffusion and filtration • Ex.) alveoli in lungs (exchange O2 and CO2) – They are easily damaged because they are so thin Simple Cuboidal Epithelium • • • • • • • • Single layer of cube shaped cells Centrally located spherical nuclei Not tightly packed Covers ovaries and most of the kidneys Free side faces the lumen (hollow channel) Function In kidneys: secretion and absorption In glands: secrets glandular products Simple Columnar Epithelium • Elongated (longer than wide) • Single layer of cells • Elongated nuclei; found close to the basement membrane • Can be ciliated – In female reproductive tract cilia aides in movement of the egg through the uterine tube to the uterus • Nonciliated simple columnar epithelium lines uterus and parts of the digestive tract (stomach and large intestines) • Because of the elongation, tissue is thick (protects underlying tissue) • Secrets digestive fluids and absorb nutrients • Goblet cells are found among the cells – They secrete a protective fluid called mucus onto the free surface of the tissue. Pseudostratified Columnar Epithelium • Appear to be stratified but actually aren’t • Nuclei are at 2 or more levels in a row of aligned cells. • Vary in shape • All reach the basement membrane, but not all each the free surface • Common for them to have cilia on the free surface • Goblet cells secret mucus which the cilia then moves away – Line respiratory system – trap dust or other particles and sweep it away Stratified squamous epithelium • Many layered; very thick • Cells divide in deep layers and new ones push the older farther outward where they are flattened • Named for the shape of the top layer of cells • Form outer layer of skin (epidermis) • As skin cells age they accumulate keratin (a protein) then harden and die • Keratinization – produces a covering of dry tough, protective material that prevents water and other substances from escaping underlying tissues. – Also blocks microorganisms and other chemicals from entering • Lines the oral cavity, esophagus, vagina and anal canal – **do NOT keratinize: they stay soft, moist, and all cells on it’s free surfaces stay alive** Stratified Cuboidal Epithelium • 2 or more layers of cuboidal cells • Provide protection • Line larger ducts (lumen) in mammary glands, sweat glands, salivary glands and pancreas • Lining of developing ovarian follicles and seminiferous tubules (parts of the female and male reproductive system) Stratified Columnar Epithelium • Several layers of cells • Superficial cells of consist of columnar cells • Basal layers consist of cuboidal • Found in male urethra and ductus deferens and the pharynx Transitional epithelium • Specialized to change in response to increased tension • Forms inner lining of urinary bladder and lines the ureters and superior urethra • When the walls of one of the organs contracts the tissue consists of several layers of cuboidal cells; when the organ distends tissue stretches and physical relationship among the cells changes – ***expandable lining*** • Forms barrier that helps prevent the contents of the urinary tract from diffusing back into the internal environment. Glandular Epithelium • Cells specialized to produce and secrete substances into ducts or into body fluids • Secrete products into ducts that open onto surfaces -> exocrine glands – Ex.) skin; digestive tract • Endocrine glands- secrete their products into tissue fluid or blood Exocrine Glands • Classified according to the ways they secrete their products – 1. merocrine glands – release fluids by exocytosis • Ex.) salivary, pancreatic and sweat glands • Apocrine glands – Loose small parts of their glandular bodies during secretion • Ex.) mammary glands, ceruminous lining inner ear canal • Holocrine glands – Disintegrate entire cell, fills with secretory product • Ex.) sebaceous gland (The sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals.) • Most exocrine glands are merocrine • Merocrine can be classified by the mucus or serious fluid they secrete – 1. serous fluid- watery and high in enzymes • Lubricants – 2. Mucus- thicker fluid, rich in glycoproteins (mucin) • Protection in digestive, respiratory and reproductive systems • *mucus and goblet cells secrete mucus in different parts of the body* 5.3 Connective Tissue • General characteristics – Bind structures – Provide support – Serve as frame works – Fill spaces – Store fat – Produce red blood cells – Protect against infections – Help repair tissue damage – are spaced further apart than epithelium cells – Contain extracellular matrix between them • Extracellular matrix- molecules that fill spaces between cells; consisting mostly of protein fiber networks – Consistency of extracellular matrix varies from fluid to semisolid to solid – Most an divide – Varying degrees of vascularity; most have good blood supply Major Cell Types • Contain a varitey of cell types – 1. fixed- reside in tissue for long time (fibroblasts and mast cells) – 2. wandering – move and appear temporally often in response to a wound or infection (macrophages) Fibroblasts • Most common type of connective tissue • Produce fibers by secreting proteins into the extracellular matrix of connective tissue Macrophages • Also known as histiocytes • Originate from white blood cells • Almost as numerous as fibroblasts in connective tissue • Specialized to carry out phagocytosis • Can move about • Function as scavenger/defense cells that clear foreign particles from tissues Mast Cells • Large and widely distributed • Found near blood cells • Release heparin (prevents blood clotting) • Release histamine (assoc. with inflammation and allergies) Connective Tissue Fibers • Fibroblasts produce 3 types: – 1. collagenous – 2. elastic – 3. reticular Most abundant Collagenous fibers • • • • • Thick threads of protein (collagen) Grouped in long, parallel bundles Flexible but only slightly elastic Have great tensile strength (resist pulling force) Important in holding structures together like: – Ligaments – bone to bone – Tendons – muscle to bone • Tissue with lots of collagenous fibers are dense connective tissue • Often appear white (white fibers) • Loose connective tissues have few collagenous fibers (compared to dense connective tissue) Elastic Fibers • made of elastin – Elastin is a spring like protein • Form complex network (they branch) • Weaker than collagenous fibers, easily stretched and deformed – Will return to original shape with the force is removed • Common in body parts subject to normal stretching (vocal chords) Reticular Fibers • Thin collagenous fibers • Highly branched • Form delicate support Categories of Connective tissue • 2 major categories – 1. connective tissue proper • Loose and connective tissue – 2. Specialized connective tissue • Cartilage, bone and blood** – Blood is considered a connective tissue because it has a matrix. The living cell types are red blood cells, also called erythrocytes, and white blood cells, also called leukocytes . The fluid portion of whole blood, its matrix, is commonly called plasma. Loose connective tissue • Includes areolar, adipose and reticular connective tissue • 1.) areolar tissue- forms delicate, thin membranes throughout the body – Made mostly of fibroblasts – Cells are spaced far apart – Separated by a gel-like ground substance that contains many collagenous and elastic fibers that fibroblast secret. – Binds skin to underlying organs and fills space between muscles – Lies beneath most layers of epithelium • 2.) adipose tissue (fat) – Develops when certain cells (adipocytes) store fat as droplets in their cytoplasm and enlarge – When cells become so abundance they crowd other cell types and form adipose tissue – Lies beneath the skin, and is also found: • • • • • • Between muscles Around kidneys Behind eyes In some abdominal membranes On the surface of the heart Around joints – Cushions joints and some organs such as the kidneys – Insulates beneath the skin and stores energy in fat molecules • 3.) Reticular connective tissue – Composed of thin, collagenous fibers in a 3D network – Provides framework for internal organs • Ex.) liver and spleen Dense Connective Tissue • Consists of many closely packed, thick collagenous fibers with a network of elastic fibers (mostly fibroblasts) • Very strong – allows for high pulling force • Binds with body parts as tendons and ligaments • Also in protective white layer of the eye and deep skin layer • Blood supply is poor; slowing healing Cartilage • Ridged connective tissue • Provides support, framework and attachments, protects underlying tissue • Forms structural models for many developing bones • Extracellular matrix is abundant and composed of collagenous fibers • Cartilage cells are called chondrocytes. – Covered in a connective tissue called perichondrium • Where nutrients diffuse through them to the cartilage • Heals very slowly and chondrocytes do not divide often 3 Types of Cartilage • 1.) Hyaline – Most common – Looks like white glass – Very find collagenous fibers – Found at the end of bones and in the soft part of the nose – Important in the growth and development of bones • 2.) Elastic Cartilage – Dense network – More flexible than hyaline – Provide framework of external ear parts and larynx. • 3.) Fibrocartilage – Very tough – High in collagenous fibers – Acts as a shock absorber • Forms pads between the vertebra in the spinal column • Cushions bones in your knees and pelvic girdle Bone • Most ridged connective tissue • Hardens due to mineral salts: calcium carbonate and calcium phosphate • High in collagenous fibers • Internally supports body structures • Also protects the cranial and thoracic cavities • Contains red blood cells (produced in the marrow) • Bone matrix is deposited in thin layers called lamellae • Bone cells are called osteocytes – Located in the lacunae and evenly disrupted • Osteons are a units made up of: – Osteocytes – Layers of extracellular matrix Clustered together around a central canal • Also known as the Haversian system named for Clopton Haversian. • Each canal contains a blood vessel • Material moves rapidly between blood vessels and bone cells Blood • Transports a variety of materials between interior body cells and those that exchange with the environment. • Blood is composed of 2 main parts: – 1.) blood plasma – fluid extracellular matrix – 2.) Formed Elements • Red blood cells, white blood cells. And platelets • Most blood is formed in the marrow of the long bones. 5.4 Types of Membranes • 5 types: – 1. epithelial membranes- thin sheet like structures composed to epithelium and underlying connective tissue. • 3 major types – Serous – Mucous – cutaneous – Serious membranes- line body cavities that lack openings to the outside • Consist of a layer of simple squamous epithelium and thin layer of loose connective tissue • Secrete serious fluid – Mucous membrane- line cavities and tubes that open to the outside of the body (ex.) oral and nasal cavities) • Consist of epithelium cells, goblet cells, and loose connective tissue • Cutaneous membranes – the skin • Synovial membrane- lines the joints 5.5 Muscle Tissue • General characteristics – Able to contract – Elongated cells often called muscle fibers • Can contract (shorten and thicken) – As they contract muscle fibers pull on the ends that are attached, which causes movement. – 3 types • Skeletal (approx. 40% of the body) • Smooth • Cardiac Skeletal Muscle Tissue • Found in muscles that usually attach to bones and controlled by conscious effort (voluntary muscle tissue) • Have striations – alternating light and dark cross markings • Each cells has multiple nuclei Smooth Muscle Tissue • • • • Named because cell don’t have striations Shorter than skeletal muscles and spindle shaped Centrally located nucleus Involuntary muscles Cardiac Muscle Tissue • Found only in the heart • Cells are striated and branched, single nucleus • Where cells touch each other is a special cell junction called intercalated disc • Involuntary muscle 5.6 Nervous Tissue • Found in the brain, spinal cord, peripheral nerves • Basic cells are called neurons • Respond to changes in the environment by transmitting electrical impulses along axons • As a result they can coordinate, regulate, and integrate many body functions. Nervous Tissue