TISSUES Tissues are groups of cells that work together to perform similar functions. Tissues characteristics will determine the function of the organ. There are four types of tissue: epithelial, connective, muscle, nervous. Each type performs specific functions that maintain homeostasis. Histology is the study of tissue. EPITHELIAL TISSUE Location: Lines and covers body s surface or inner cavities & forms glands in the body Functions: protection, secretion, absorption, filtration, propulsion, excretion Characteristics: 1. Cells are tightly packed together forming a continuous sheet. Adjacent cells are bound together by lateral contacts tight junctions or desmosomes. 2. Cells have polarity --- cell regions near the apical surface differ from those near the basal surface in both structure and function. Apical surface free or unattached surface that lines external surfaces or inner cavity of organs; can be slick, smooth or modified with cilia or microvilli. Microvilli are fingerlike extensions of plasma membrane that increase the exposed surface area for absorption and secretion. The microvilli are so dense that the cell has a fuzzy appearance called a brush border. Basal surface the lower attached surface of the epithelium. The basal surface is attached to the basement membrane which is composed of noncellular material secreted by both the epithelial cells and the underlying connective tissue. The basement membrane reinforces the epithelial sheet and resists stretching and tearing. The basement membrane is actually composed of 2 layers basal lamina (superior) & reticular lamina (inferior). The basal lamina is a noncellular, adhesive sheet composed of glycoproteins and collagen fibers acts as a selective filter that determines which molecules diffuse form the underlying connective tissue. The reticular lamina is a network of collagen fibers. 3. Innervated - contain nerves. 4. Avascular Epithelium has no blood vessels instead gets nutrient by diffusion from underlying connective tissue. 5. Regenerates rapidly stimulated by loss of apical-basal polarity and lateral contacts or nutrient availability. Classification: Epithelial are classified by their cellular arrangement (simple or stratified) and shape. Stratified epithelium is named for cells at the apical surface. 1
TYPES OF EPITHELIAL TISSUE: A. SIMPLE SQUAMOUS Two other locations endothelium (lining of lymphatic vessels, blood vessels and heart) and mesothelium (serous membranes in ventral body cavity) B. SIMPLE CUBOIDAL 2
C. SIMPLE COLUMNAR D. PSEUDOSTRATIFIED COLUMNAR 3
E. STRATIFIED SQUAMOUS F. STRATIFIED CUBOIDAL rare; found in some sweat and mammary glands. Typically two cell layers thick. G. STRATIFIED COLUMNAR rare; small amounts in pharynx, male urethra and lining of some glandular ducts. H. TRANSITIONAL EPITHELIUM 4
I. GLANDULAR EPITHELIUM involved in production and secretion of aqueous fluid into ducts or into bloodstream. Endocrine glands secretions released directly into blood or lymph and travel to specific target organs. Exocrine glands secretions released through ducts onto body surfaces or into body cavities. Examples include mucous, sweat and oil. Mucous and goblet cells line the intestines and respiratory tracts and produce mucus. CONNECTIVE TISSUE Location: most abundant tissue underlies epithelial & surrounds nerves and blood vessels Functions: support, attachment, insulating, protection, storage, transport Characteristics: 1. Composed of scattered cells & nonliving extracellular material called matrix. Matrix fills space between cells and is composed of ground substance and fibers. Composition and arrangement of cells and matrix vary. Ground substance serves as a medium through which solutes diffuse between capillaries and cells. Components include interstitial fluid, cell adhesion proteins and proteoglycans (trap water in various amounts). Fibers provide support. Collagen fibers are strong flexible to resist stress. Elastic fibers provide strength and stretching capabilities. Reticular fibers are thin branched collagen fibers that form networks that offer more give. Cells Blast cells are immature forms that secrete ground substances and fibers; fibroblast, chondroblast, osteoblast and hematopoietic stem cells in bone marrow. Cyte cells are mature forms that maintain the matrix; chondrocytes and osteocytes. Fat cells store nutrients. White blood cells respond to injury, mast cells initiate local inflammatory response by releasing heparin (anticoagulant) and histamine (promotes inflammation). Macrophages engulf dead cells. 2. Vascularity varies most have a good blood supply 3. Common Embryonic Tissue mesenchyme cells Classification: Connective tissues are classified based on cells, fibers and consistency of matrix. Types: connective tissue proper, cartilage, bone and blood. Connective tissue proper is divided into two subclasses: loose connective tissue and dense connective tissue. 5
TYPES OF CONNECTIVE TISSUE: A. AREOLAR TISSUE (loose) most widely distributed; serves as a reservoir of water and salts for surrounding tissues. Supports and bind other tissues called tissue fluid. B. ADIPOSE TISSUE (loose) 6
C. RETICULAR (loose) D. DENSE REGULAR 7
E. DENSE IRREGULAR F. DENSE ELASTIC 8
G. CARTILAGE Cells are avascular; get nutrients from membrane surrounding it. Lacks nerve fibers and is composed of 80% water. 3 types: hyaline, elastic and fibrocartilage HYALINE CARTILAGE FIBROCARTILAGE 9
ELASTIC CARTILAGE H. BLOOD HEMATOPOIETIC TISSUE 10
I. OSSEOUS TISSUE - BONE MUSCLE TISSUE Muscle tissues consist of fibers (cells) that are modified for contraction and thus provide motion, maintenance of posture and heat production. 3 types skeletal, smooth and cardiac muscle SKELETAL MUSCLE 11
SMOOTH MUSCLE CARDIAC MUSCLE 12
NERVOUS TISSUE Nerve tissues are made up of cells called neurons and neuroglia. Neurons receive impulse from stimuli, convert stimuli into impulse & conduct impulse to other neurons, muscles or glands. Neurons do NOT regenerate. Neuroglia cells protect and support neurons and are capable of regenerating. TISSUE REPAIR Tissue repair is determined by the type of tissue damaged and the severity of the tissue damage. Regeneration - replacement of destroyed tissue and original function is restored. Fibrosis - dense connective tissue replaces destroy tissue and the original function is lost. Regenerate extremely well epithelial tissue, bone, areolar, dense irregular, hematopoietic Moderate regenerating capacity smooth muscle, dense regular Virtually no functional regenerative capacity cardiac muscle, nervous tissue Events of tissue repair 1. Inflammation occurs inflammatory chemicals released; local blood vessels become permeable to allow WBC, fluid, clotting proteins and other plasma proteins to seep into injured area; clotting occurs. 2. The clot is replaced by granulation tissue. Fibroblast produce collagen fibers to bridge gap; macrophages phagocytize dead cells and debris; surface epithelial cells multiply and migrate over granulation tissue. 3. Regeneration and fibrosis effect permanent repair. Area mature and contract and epithelium thicken; fully regenerated epithelium with underlying scar tissue form. 13
MEMBRANES Cutaneous membranes (SKIN) a dry membrane with a superficial epidermis composed of stratified squamous epithelium and underlying dermis is dense irregular connective tissue. The main function is protection. Mucous membranes (mucosa) composed of varies types of epithelium resting on areolar connective tissue called lamina propria. Lines body cavities open to the exterior and organs of the respiratory, digestive, urinary and reproductive tracts. The mucosa is adapted for secretion of mucus. Serous Membranes (serosa) moist membrane found in ventral body cavities. The walls of ventral cavities and outer surface of visceral organs are covered by a thin, double-layered membrane. Serosa is composed of simple squamous epithelium with underlying areolar connective tissue. The main function is lubrication and cushioning. Serous membranes occur in pairs. The parietal layer lines a specific portion of the wall of the ventral body cavity. The visceral layer covers the outside of the organs in the cavity. The serous space between the layers is filled with lubricating fluid called serous fluid. The fluid is secreted by both layers and allows organs to slide without friction. The membranes lining the abdominal cavity and organs are called peritoneum. The membranes lining the thoracic cavity and the lungs are called pleura. The membranes lining pericardial cavity and covers the heart is called pericardium. 14