"Cytology & Histology" Lecture Notes PDF

Cytology &Histology Porf. Dr. Eman Abbas Moussa Lecturer (3) Tissues ◼ Cells work together in functionally related groups called tissues ◼ Types of tissues: 1. Epithelial – lining and covering 2. Connective – support 3. Muscle – movement 4. Nervous – co...

Cytology &Histology Porf. Dr. Eman Abbas Moussa Lecturer (3) Tissues ◼ Cells work together in functionally related groups called tissues ◼ Types of tissues: 1. Epithelial – lining and covering 2. Connective – support 3. Muscle – movement 4. Nervous – control Epithelial Tissue – General Characteristics & Functions ◼ Covers a body surface or lines a body cavity ◼ Forms most glands ◼ Functions of epithelium  Protection  Absorption, secretion, and ion transport  Filtration  Forms slippery surfaces Special Characteristics of Epithelia ◼ Cellularity  cells are in close contact with each other with little or no intercellular space between them ◼ Specialized contacts  may have junctions for both attachment and communication ◼ Polarity  epithelial tissues always have an apical and basal surface ◼ Support by connective tissue  at the basal surface, both the epithelial tissue and the connective tissue contribute to the basement membrane ◼ Avascular  nutrients must diffuse ◼ Innervated ◼ Regeneration  epithelial tissues have a high capacity for regeneration Special Characteristics of Epithelia Lateral Surface Features ◼ Factors holding epithelial cells together  Adhesion proteins link plasma membranes of adjacent cells  Contours of adjacent cell membranes  Special cell junctions ◼ Tight Junctions ◼ Adherens Junctions ◼ Desmosomes Lateral Surface Features – Cell Junctions ◼ Tight junctions (zona occludens) – close off intercellular space  Found at apical region of most epithelial types  Some proteins in plasma membrane of adjacent cells are fused  Prevent molecules from passing between cells of epithelial tissue Tight Junction Lateral Surface Features – Cell Junctions ◼ Adherens junctions (zonula adherens) – anchoring junction  Transmembrane linker proteins attach to actin microfilaments of the cytoskeleton and bind adjacent cells  Along with tight junctions, form the tight junctional complex around apical lateral borders of epithelial tissues Lateral Surface Features – Cell Junctions ◼ Desmosomes – two disc-like plaques connected across intercellular space  Plaques of adjoining cells are joined by proteins called cadherins  Proteins interdigitate into extracellular space  Intermediate filaments insert into plaques from cytoplasmic side Desmosome Lateral Surface Features – Cell Junctions ◼ Gap junctions – passageway between two adjacent cells  Let small molecules move directly between neighboring cells  Cells are connected by hollow cylinders of protein Gap Junction Basal Feature: The Basal Lamina ◼ Noncellular supporting sheet between the epithelium and the connective tissue deep to it ◼ Consists of proteins secreted by the epithelial cells ◼ Functions:  Acts as a selective filter, determining which molecules from capillaries enter the epithelium  Acts as scaffolding along which regenerating epithelial cells can migrate ◼ Basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane Epithelial Tissues Classifications & Naming of Epithelia ◼ First name of tissue indicates number of layers  Simple – one layer of cells  Stratified– more than one layer of cells Classification & Naming of Epithelia ◼ Last name of tissue describes shape of cells  Squamous – cells wider than tall (plate or “scale” like)  Cuboidal – cells are as wide as tall, as in cubes Columnar – cells are taller than they are wide, like columns Naming Epithelia ◼ Naming the epithelia includes both the layers (first) and the shape of the cells (second)  i.e. stratified cuboidal epithelium ◼ The name may also include any accessory structures  Goblet cells  Cilia  Keratin ◼ Special epithelial tissues (don’t follow naming convention)  Psuedostratified  Transitional Simple Squamous Epithelium ◼ Description  single layer of flat cells with disc-shaped nuclei ◼ Special types  Endothelium (inner covering) ◼ slick lining of hollow organs  Mesothelium (middle covering) ◼ Lines peritoneal, pleural, and pericardial cavities ◼ Covers visceral organs of those cavities Simple Squamous Epithelium ◼ Function  Passage of materials by passive diffusion and filtration  Secretes lubricating substances in serosae ◼ Location  Renal corpuscles  Alveoli of lungs  Lining of heart, blood and lymphatic vessels  Lining of ventral body cavity (serosae) Simple Squamous Epithelium Simple squamous lining the walls of the capillary Simple Cuboidal Epithelium ◼ Description  single layer of cube-like cells with large, spherical central nuclei ◼ Function  secretion and absorption ◼ Location  kidney tubules, secretory portions of small glands, ovary & thyroid follicles Simple Columnar Epithelium ◼ Description  single layer of column-shaped (rectangular) cells with oval nuclei ◼ Some bear cilia at their apical surface ◼ May contain goblet cells ◼ Function  Absorption; secretion of mucus, enzymes, and other substances  Ciliated type propels mucus or reproductive cells by ciliary action Simple Columnar Epithelium ◼ Location  Non-ciliated form ◼ Lines digestive tract, gallbladder, ducts of some glands  Ciliated form ◼ Lines small bronchi, uterine tubes, uterus Pseudostratified Columnar Epithelium ◼ Description  All cells originate at basement membrane  Only tall cells reach the apical surface  May contain goblet cells and bear cilia  Nuclei lie at varying heights within cells ◼ Gives false impression of stratification ◼ Function  secretion of mucus; propulsion of mucus by cilia Pseudostratified Columnar Epithelium ◼ Locations  Non-ciliated type ◼ Ducts of male reproductive tubes ◼ Ducts of large glands  Ciliated variety ◼ Lines trachea and most of upper respiratory tract Stratified Epithelia ◼ Contain two or more layers of cells ◼ Regenerate from below ◼ Major role is protection ◼ Are named according to the shape of cells at apical layer Stratified Squamous Epithelium ◼ Description  Many layers of cells – squamous in shape  Deeper layers of cells appear cuboidal or columnar  Thickest epithelial tissue – adapted for protection Stratified Squamous Epithelium ◼ Specific types  Keratinized – contain the protective protein keratin ◼ Surface cells are dead and full of keratin  Non-keratinized – forms moist lining of body openings ◼ Function  Protectsunderlying tissues in areas subject to abrasion ◼ Location  Keratinized – forms epidermis  Non-keratinized – forms lining of esophagus, mouth, and vagina Transitional Epithelium ◼ Description  Basal cells usually cuboidal or columnar  Superficial cells dome- shaped or squamous ◼ Function  stretches and permits distension of urinary bladder ◼ Location  Linesureters, urinary bladder and part of urethra Glandular Epithelium ◼ Ducts carry products of exocrine glands to epithelial surface ◼ Include the following diverse glands  Mucus-secreting glands  Sweat and oil glands  Salivary glands  Liver and pancreas  Mammary glands ◼ May be: unicellular or multicellular Unicellular Exocrine Glands (The Goblet Cell) ◼ Goblet cells produce mucin ◼ Mucin + water → mucus ◼ Protects and lubricates many internal body surfaces Multicellular Exocrine Glands ◼ Classified by structure (branching & shape) of duct ◼ Can also be classified by mode or type of secretion  Merocrine secretion – secretory vesicles released via exocytosis (saliviary glands)  Apocrine secretion – apical portion of the cell is lost, cytoplasm + secretory product (mammary glands)  Holocrine secretion – entire cell is destroyed during secretion (sebaceous gland) mode or type of secretion May also be classified by types of secretions from exocrine glands ◼ Serous  mostly water but also contains some enzymes  Ex. parotid glands, pancreas ◼ Mucous  mucus secretions  Ex. sublingual glands, goblet cells ◼ Mixes  serous & mucus combined  Ex. submandibular gland