Tissues Tissues n Cells work together in functionally

Tissues

Tissues n Cells work together in functionally related groups called tissues n How is this done? n n n Attachments communication Types of tissues: 1. 2. 3. 4. Epithelial – lining and covering Connective – support Muscle – movement Nervous – control

Epithelial Tissue – General Characteristics & Functions Covers a body surface or lines a body cavity n Forms most glands n Functions of epithelium n Protection n Absorption, secretion, and diffusion n Filtration n Forms slippery surfaces (mucus secretion) n

Special Characteristics of Epithelia n Cellularity n n Specialized contacts n n n at the basal surface, both the epithelial tissue and the connective tissue contribute to the basement membrane Avascular n n epithelial tissues always have an apical and basal surface Support by connective tissue n n may have junctions for both attachment and communication Polarity n n cells are in close contact with each other with little or no intercellular space between them nutrients must diffuse from basal layer Innervated Regenerative n epithelial tissues are highly mitotic

Special Characteristics of Epithelia

Classifications of Epithelia n First name of tissue indicates number of layers n Simple – one layer of cells n Stratified – more than one layer of cells

Classifications of Epithelia n Last name of tissue describes shape of cells n Squamous – cells wider than tall (plate or “scale” like) n Cuboidal – cells are as wide as tall, as in cubes Columnar – cells are taller than they are wide, like columns

Naming Epithelia n Naming the epithelia includes both the layers (first) and the shape of the cells (second) n n The name may also include any accessory structures n n i. e. stratified cuboidal epithelium Goblet cells Cilia Keratin Special epithelial tissues (don’t follow naming convention) n n Psuedostratified Transitional

Simple Squamous Epithelium n Description n n single layer of flat cells with disc-shaped nuclei Special types n Endothelium (inner covering) n slick n lining of hollow organs Mesothelium (middle covering) n Lines peritoneal, pleural, and pericardial cavities n Covers visceral organs of those cavities

Simple Squamous Epithelium n n Function n Passage of materials by passive diffusion and filtration n Secretes lubricating substances in serous membranes Location n Renal corpuscles (kidneys) n Alveoli of lungs n Lining of heart, blood and lymphatic vessels n Lining of ventral body cavity (serosae/serous

Simple Squamous Epithelium If it’s from a mesothelial lining Simple squamous lining the walls of the capillary

Simple Cuboidal Epithelium n Description n n Function n n single layer of cube-like cells with large, spherical central nuclei secretion and absorption Location n kidney tubules, secretory portions of small glands, ovary surface

Simple Cuboidal Epithelium

Simple Columnar Epithelium n Description n single layer of column-shaped (rectangular) cells with oval nuclei n Some bear cilia at their apical surface n May contain goblet cells n Function Absorption; secretion of mucus, enzymes, and other substances n Ciliated type propels mucus or reproductive cells by ciliary action n

Simple Columnar Epithelium n Location n Non-ciliated form n Lines digestive tract, gallbladder, ducts of some glands n Ciliated form n Lines small bronchi, uterine tubes, and uterus

Pseudostratified Columnar Epithelium n Description All cells originate at basement membrane n Only tall cells reach the apical surface n May contain goblet cells and bear cilia n Nuclei lie at varying heights within cells n n Gives n false impression of stratification Function n secretion of mucus; propulsion of mucus by cilia

Pseudostratified Columnar Epithelium n Locations n Non-ciliated type n Ducts of male reproductive tubes n Ducts of large glands n Ciliated variety n Lines trachea and most of upper respiratory tract

Stratified Epithelia Contain two or more layers of cells n Regenerate from below n Major role is protection n Are named according to the shape of cells at apical layer n

Stratified Squamous Epithelium n Description Many layers of cells – squamous in shape n Deeper layers of cells appear cuboidal or columnar n Thickest epithelial tissue – adapted for protection n

Stratified Squamous Epithelium n Specific types n Keratinized – contain the protective protein keratin n Non-keratinized – forms moist lining of body openings Function n n Surface cells are dead and full of keratin Protects underlying tissues in areas subject to abrasion Location n n Keratinized – forms epidermis Non-keratinized – forms lining of esophagus, mouth, and vagina

Stratified Squamous Epithelium Non-keratinized vs. Keratinized

Transitional Epithelium n Description Basal cells usually cuboidal or columnar n Superficial cells dome-shaped or squamous n n Function n n stretches and permits distension of urinary bladder Location n Lines ureters, urinary bladder and part of urethra

Transitional Epithelium Relaxed state Stretched state

Epithelial Surface Features n Apical surface features n Microvilli – finger-like extensions of plasma membrane n Abundant in epithelia of small intestine and kidney n Maximize surface area across which small molecules enter or leave n Act as stiff knobs that resist abrasion

Epithelial Surface Features n Apical surface features n Cilia – whip-like, highly motile extensions of apical surface membranes n Contains a core of nine pairs of microtubules encircling one middle pair n Axoneme – a set of microtubules n Each pair of microtubules – arranged in a doublet n Microtubules in cilia – arranged similarly to cytoplasmic organelles called centrioles n Movement of cilia – in coordinated waves

A Cilium