Tissues Chapter 4 Tissues Chapter 4

Tissues Tissues are groups of cells and extracellular material that perform specific functions. The four tissue types, in varying combinations, form all of the structures of the human body. Histology - The study of tissues

Four Basic Tissue Types  Epithelial  Connective  Muscular  Neural (nervous) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Epithelial Tissue (epithelium) Characteristics  Cells closely packed & attached to each other  Apical cells exposed to external environment or internal surface  Cells attached to connective tissue at basement membrane  Avascular - Lack blood vessels  Regenerates easily - cells continually replaced

Epithelial Tissue Glandular - secretory structures derived from epithelia Endocrine glands - Secretion of product (hormones) into interstitial fluid and blood. e.g. – thyroid, pituitary Exocrine glands - Secretion of product onto a body surface. e.g. – sebaceous (oil), sudoriferous (sweat) Covering & lining epithelium - an avascular layer of cells that lines internal or external surfaces & covers organs within cavities; - always bound to CT creating an “epithelial membrane” Subtypes of epithelial tissue -

Epithelial Membranes  Epithelial tissue bound to connective tissue  Connection of tissues occurs at the basement membrane - noncellular meshwork anchors basal cells  Basement membrane creates a semi- permeable junction for diffusion of O 2, nutrients & wastes Epithelial Membranes

Epithelial membranes Types of epithelial membranes:  Mucous membranes (mucosa)  Serous membranes (serosa)  Cutaneous membrane (skin)

Mucous membranes (mucosa) Line body cavities that open to exterior environment Epithelial cells secrete mucus to moisten & protect surface Examples: digestive tract, respiratory passageway, urinary tract, reproductive passageways

Serous membranes (serosa) Line internal body cavities & cover organs within the cavity Always have two layers –  Parietal layer – lines cavity  Visceral layer – covers organs within cavity Epithelial cells secrete serous fluid, a watery fluid that lubricates surface of membranes Example: pleura, pericardium, peritoneum

Cutaneous membrane (a.k.a. skin) Covers & protects body surface from external environment Epithelial layer is epidermis Connective layer is dermis

Simple - one layer of cells Stratified – more than one layer of cells Pseudostratified – looks like more than one layer but all cells contact basement membrane  Cell shape Classifying covering & lining Epithelia :  Number of layers  Squamous - flat  Cuboidal – cube-shaped  Columnar - tall columns

Columnar cells may be modified with  microvilli  cilia  goblet cells Figure 4-3

Epithelial Tissue Table 4-1

Epithelial Tissue Simple Squamous Epithelium Figure 4-4(a)

Epithelial Tissue Simple columnar epithelium

Epithelial Tissue Stratified Squamous Epithelium Figure 4-5(c) 2 types: Keratinized Non-keratinized

Epithelial Tissue Pseudostratified Ciliated Columnar Figure 4-5(a)

Connective Tissue (CT) Characteristics:  Cells differ depending on specific type of CT (e.g. mesenchymal, fibroblasts, chondrocytes, osteocytes)  Cells usually widely spaced with intercellular matrix between  Usually well vascularized (exception: cartilage)  Usually do not regenerate easily  Repair ability varies depending on type of CT

Connective Tissues Components of Connective Tissues:  Specialized cells  Extracellular matrix Ground substance  Varies in consistency from liquid to gel-like to solid, depending on specific CT Protein fibers  Collagen – provides strength  Elastic – provides elasticity, resiliency  Reticular – provides support

Connective Tissues Whereas in epithelial tissue, the cell shape & layers were important to determine the function of the tissue, in connective tissues, the matrix of the tissue most directly determines the functional qualities of the tissue.

Classification of Connective Tissues  Embryonic CT - Mesenchyme  Connective tissue proper Loose Dense  Supportive connective tissues Cartilage Bone (osseous) tissue  Fluid connective tissues Blood Lymph

Connective Tissues Major Types of Connective Tissue Figure 4-7 MESENCHYME

Mesenchyme An embryonic CT with mesenchymal cells in a thick fluid ground substance with some collagen & reticular fibers. Mesenchyme is the precursor to all other forms of CT

Connective Tissue “Proper” Most common type of cell present is the fibroblast, but these CT’s may also contain adipocytes, macrophages, & other WBCs. The cells are surrounded by a syrupy ground substance that contains hyaluronic acid. Fibers vary & may be arranged loosely or densely packed together.

Connective Tissue Proper Depending on the arrangement of fibers, CT proper can be classified into: Loose CTs Areolar Adipose Dense CTs Dense regular (collagenous) Dense irregular

Areolar Connective Tissue Figure 4-9(a)

Adipose Connective Tissue Figure 4-9(b)

Dense Regular Connective Tissue Figure 4-9(c)

Dense Irregular Connective Tissue

Supportive Connective Tissues Chondrocytes in lacunae of interstitial fluid within a firm gel-like ground substance of chondroitin sulfate Avascular Covered by a fibrous perichondrium Three types of cartilage  Hyaline cartilage  Elastic cartilage  Fibrocartilage Cartilage

Hyaline Cartilage Figure 4-10(a)

Elastic Cartilage Figure 4-10(b)

Fibrocartilage Figure 4-10(c)

Supportive Connective Tissues  Osteocytes in lacunae of interstitial fluid within a calcified matrix  Matrix comprised of osteoid (mainly collagen) & calcium salts (mainly C a 3 (PO 4 ) 2 )  Because of the density of the matrix, osteocytes communicate & receive O 2 / nutrients across canaliculi  Osseous tissue covered by fibrous periosteum  Well vascularized tissue Bone (Osseous Tissue)

Osseous (Bone) Tissue Bone tissue classified on the basis of the pattern (functional unit) of the matrix Two types of bone tissue –  Spongy (cancellous)  Dense (compact)

Osseous Tissue Fig. 6-3 Spongy (cancellous) bone tissue:  Matrix arranged in trabeculae pattern surrounding marrow spaces  Marrow spaces of spongy bone contain red bone marrow

Osseous (Bone) Tissue  Compact (dense) bone tissue:  Matrix forms osteons (Haversian systems)  Osteons comprised of concentric lamellae (layers of matrix containing osteocytes) surrounding a central (Haversian) canal, which contains BVs  Osteocytes interconnected by canaliculi which radiate out across lamellae  BVs of central canals interconnect across perforating (Volkmann’s) canals

Fluid (liquid) Connective Tissues Cells + a liquid ground substance Blood  RBCs, WBCs, platelets + plasma Lymph  Lymphocytes (WBCs) + lymph fluid

Tissue Injuries and Repair Many different types of injuries can affect tissues – physical (e.g. cuts, bruises), thermal (e.g. burns), chemical, infections An injury usually harms multiple tissues simultaneously Tissues make coordinated response to restore homeostasis Two response processes  Inflammation  Repair (Regeneration)

Tissue Injuries and Repair Inflammation (a.k.a. the inflammatory response)  Homeostatic response designed to isolate the injured area & cleanup damaged tissue  Cells within CTs known as mast cells release chemicals (histamine, heparin) which cause vasodilation & increased capillary permeability

Tissue Injuries & Repair Vasodilation (resulting in increased blood flow) & increased capillary permeability lead to the 4 classic signs of inflammation: Warmth Redness Swelling Pain

Tissue Injuries and Repair Repair (Regeneration)  Response designed to repair/replace damaged tissues & restore function  Fibroblasts (CT cells) in damaged area & lay down collagen fibers to create scar tissue (fibrous tissue)

Tissue Injuries and Repair  Degree of replacement to original tissue type depends on type of tissue  Epithelial cells regenerate to replace the damaged epithelial tissues  CT proper, bone tissues & smooth muscle heal fairly well  Cartilage, neural tissue, skeletal & cardiac muscle tissues do not heal well at all