Chapter 5 Tissues

Principal Types of Tissue Epithelial tissue Covers and protects the body surface Lines body cavities Secretion, excretion, absorption Forms many glands Connective tissue Supports the body and it parts Connects and holds parts together Transports substances and protects from foreign invaders Separated by large quantities of nonliving matrix

Principal Types of Tissue Muscle tissue Produces movement Contractility Nervous tissue Most complex tissue Communication between various parts of the body and in integration of their activities Generation of complex messages for the coordination of body functions

Embryonic Development of Tissues Tissues appear in the embyonic period of development First two months after conception Zygote divides repeatedly Blastocyst implants in uterus Gastrulation produces three primary germ layers Endoderm – epithelial tissue Mesoderm – epithelial, connective and muscle tissue Ectoderm – epithelial and nerve tissue Histogenesis The process by which the primary germ layers differentiate into different kinds of tissue

Epithelial Tissue Types and locations Epithelium is divided into two types: Membranous (covering or lining) epithelium Covers the body and some of its parts Lines the cavities, vessels, and tracts Glandular epithelium Grouped in solid cords or specialized follicles that form the secretory units of endocrine and exocrine glands

Epithelial Tissue Functions Protection Sensory functions Secretion Most important function of membranous epithelium Sensory functions Skin, nose, eye, and ear Secretion Glandular epithelium Hormones, mucus, digestive juices, and sweat Absorption Lining epithelium of the gut and respiratory tract allow for absorption of nutrients and exchange of gases between the lungs and the blood Excretion Lining of the kidney tubules makes the excretion and concentration of excretory products in the urine possible

Epithelial Tissue Generalizations about epithelial tissue Limited amount of matrix material Appear to be continuous sheet of cells when view under the microscope Membranous type is attached to a noncellular layer of adhesive, permeable material called the basement membrane Basement membrane is attached to connective tissue B.M. is synthesized by the epithelia and connective tissue Basal lamina - glycoprotein material made by epithelium Reticular lamina –fibers made by connective tissue

Epithelial Tissue Generalizations about epithelial tissue Avascular Contains no blood vessels Oxygen and nutrients must diffuse from capillaries in the connective tissue through the B.M. to reach epithelium Many desmosomes and tight junctions Capable of reproducing itself Frequent cell division Considerable wear and tear require rapid regeneration

Epithelial Tissue Classification of epithelial tissue Membranous (covering or lining) epithelium (Table 5-1) Classification based on cell shape (Figure 5-2) Squamous Cuboidal Columnar Pseudostratified columnar

Epithelial Tissue Classification of epithelial tissue (cont.) Classifications based on layers of cells (Table 5-1) Simple epithelium Cells in a single layer Stratified epithelium Cells are layered one on another Transitional epithelium Differing cell shapes in a stratified, or layered, sheet Stratified tissue types are named for the shape of the cells in their top layer only

Epithelial Tissue Classification of epithelial tissue (cont.) Classifications based on layers of cells (Table 5-2) Simple epithelium Simple squamous epithelium (Figures 5-2, 5-3, 5-4) One-cell layer of flat cells Permeable to many substances Examples: endothelium—lines blood vessels; mesothelium—pleura Simple cuboidal epithelium (Figure 5-5) One-cell layer of cuboidal cells Found in many glands and ducts

Simple Squamous Epithelium

Simple Cuboidal Epithelium

Epithelial Tissue Simple epithelium (cont.) Simple columnar epithelium (Figure 5-6) Single layer of tall, column-shaped cells Cells often modified for specialized functions goblet cells (secretion) cilia (movement) microvilli (absorption) Often lines hollow visceral structures

Epithelial Tissue Simple epithelium (cont.) Pseudostratified columnar epithelium (Figure 5-7) Columnar cells of differing heights All cells rest on basement membrane but may not reach the free surface above Cell nuclei at odd and irregular levels Found lining air passages and segments of male reproductive system Motile cilia and mucus are important modifications

Pseudostratified Ciliated Epithelium

Epithelial Tissue Stratified epithelium Stratified squamous (keratinized) epithelium Multiple layers of flat, squamous cells (Figure 5-8) Cells filled with keratin Covers outer skin on body surface Stratified squamous (nonkeratinized) epithelium (Figure 5-9) Lines vagina, mouth, and esophagus Free surface is moist Primary function is protection

Epithelial Tissue Stratified epithelium (cont.) Stratified cuboidal epithelium Two or more rows of cells are typical Basement membrane is indistinct Located in sweat gland ducts and pharynx Stratified columnar epithelium Multiple layers of columnar cells Only most superficial cells are typical in shape Found in in very few places in the body Located in segments of male urethra and near anus

Epithelial Tissue Stratified epithelium (cont.) Stratified transitional epithelium (Figure 5-10) Located in lining of hollow viscera subjected to stress (e.g., urinary bladder) Often 10 or more layers thick Protects organ walls from tearing by changing from cuboidal to squamous in appearance

Epithelial Tissue Glandular epithelium Specialized for secretory activity Exocrine glands—discharge secretions into ducts Endocrine glands—“ductless” glands; discharge secretions directly into the blood or interstitial fluid Structural classification of exocrine glands (Figure 5-12; Table 5-2) Multicellular exocrine glands are classified by the shape of their ducts and the complexity of their duct system Tubular and alveolar are saclike Simple exocrine glands—only one duct leads to the surface Compound exocrine glands—have two or more ducts

Exocrine Glands in the Stomach

Epithelial Tissue Glandular epithelium (cont.) Functional classification of exocrine glands (Figure 5-12) Apocrine glands Secretory products collect near apex of cell and are secreted by pinching off the distended end Secretion process results in some damage to cell wall and some loss of cytoplasm Mammary glands are good examples of this secretory type Holocrine glands Secretion products, when released, cause rupture and death of the cell Sebaceous glands are holocrine Merocrine glands Secrete directly through cell membrane Secretion proceeds with no damage to cell wall and no loss of cytoplasm Most prevalent gland type

Exocrine Glands