TissuesChapter 4TissuesChapter 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 vesselsRegenerates 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, pituitaryExocrine 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 O2, 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 cellsExtracellular 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 - MesenchymeConnective tissue proper

Loose Dense

Supportive connective tissues Cartilage Bone (osseous) tissue

Fluid connective tissues Blood Lymph

Connective TissuesMajor Types of Connective Tissue

Figure 4-7

MESENCHYME

MesenchymeAn 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 ProperDepending on the arrangement of fibers, CT

proper can be classified into:

Loose CTsAreolarAdipose

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 cartilageElastic cartilageFibrocartilage

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 Ca3 (PO4)2 )

Because of the density of the matrix, osteocytes communicate & receive O2 / nutrients across canaliculi

Osseous tissue covered by fibrous periosteumWell 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