ANP 1105A Anatomy & Physiology I Lecture 2A - Tissues PDF

ANP 1105A - Anatomy & Physiology I Basic Cellular Physiology & the Anatomy and Physiology of the Cardiovascular, Lymphatic & Respiratory Systems Lecture 2A – Tissues Presented by: Dr. Stephen Gee Faculté de médecine | Faculty of Medicine uOtta...

ANP 1105A - Anatomy & Physiology I Basic Cellular Physiology & the Anatomy and Physiology of the Cardiovascular, Lymphatic & Respiratory Systems Lecture 2A – Tissues Presented by: Dr. Stephen Gee Faculté de médecine | Faculty of Medicine uOttawa.ca Tissue: The Living Fabric (Chapter 4, pages 116-137) Don’t have issues, learn the tissues! Tissues Complex organisms, like humans, are made of collections of cells working together to perform a specific function. Tissues groups of cells similar in structure common function organized into organs 4 main tissue types Figure 4.1 Overview of four basic tissue types: epithelial, connective, muscle, and nervous tissues. How do we study tissue structure? Histology: study of tissues Fixation or freezing Cut into thin sections Stained with dyes (light microscopy) – 1850s T.E.M or heavy metals (electron. microscopy) – 1950s or antibodies conjugated to dyes Preservation can induce artifacts S.E.M. General Organization Tissues Tissues groups of cells similar in structure common function organized into organs. 4 main tissue types Figure 4.1 Overview of four basic tissue types: epithelial, connective, muscle, and nervous tissues. Epithelial Tissue (Epithelium) Sheet of cells - covers body surfaces or cavities e.g. surfaces of skin, digestive organs and respiratory tract Covering and lining epithelia On external and internal surfaces (e.g. skin) Glandular epithelia Secretory tissue in glands (e.g. salivary glands) Selective barrier – e.g. intestinal epithelium allows passage of certain substances (e.g. nutrients) but not others (e.g. toxins, microorganisms) bidirectional, highly regulated in healthy tissue and disease. Gut microbiome! (we are mostly bacteria!) Functions: protection, absorption, filtration, excretion, secretion, and sensory reception Special Characteristics of Epithelial Tissues Epithelial tissue has five distinguishing characteristics: 1. Polarity 2. Specialized contacts 3. Supported by connective tissues 4. Avascular, but innervated 5. Ability to regenerate Special Characteristics of Epithelial Tissues Polarity Epithelium Apical surface (top), is exposed to Apical surface surface or cavity Some apical surfaces are smooth, Borders open space but many have microvilli or cilia Basal surface Basal surface (bottom), faces inwards Next to underlying toward body connective tissue Attaches to basal lamina, an adhesive sheet that holds basal surface of epithelial cells to underlying cells Correct establishment and maintenance of cell polarity are crucial for normal cell physiology and tissue homeostasis Brush Border Epithelia  Special Characteristics of Epithelial Tissues Intercellular Contacts Epithelial cells need to fit closely together to form a barrier Specialized contact points bind adjacent epithelial cells together Lateral contacts include: Tight junctions – prevents substances from leaking between cells (regulated) Directional flow of ions, nutrients, etc Adherens junctions mediate cell- cell adhesion via proteins called cadherins. Desmosomes – prevents cells from pulling apart in tissues subjected to mechanical stress – (Desmoglein) Gap junctions - Intercellular communication mediated by connexins. Specialized Intercellular Contacts Apical Pathogens (reovirus, “Belt-like” cocksackie virus) Lateral Cell junction have different connecting proteins Basal and attach to different filaments e Forc More about cell junctions  Special Characteristics of Epithelial Tissues Supported by Connective Tissue All epithelia have a basement membrane (BM) Reinforces, resists stretching, tearing Defines epithelial boundary Consists of: Basal lamina – layer of extracelluar matrix (ECM) proteins Reticular lamina Deep to basal lamina Network of collagen (III) fibers Disease Relevance: Cancerous epithelial cells can penetrate BM and invade underlying tissues, resulting in spread of cancer (metastasis)  90% of cancer deaths upside down! Special Characteristics of Epithelial Tissues Avascular, but innervated ✗Blood vessels Nutrients, O₂ diffuse from connective tissue ✓Nerves (e.g. sensory nerve ending in the skin) Fun Fact: In one square inch of skin (including connective tissue) there are 4 yards of nerve fibers, 3 yards of blood vessels, 1300 nerve cells, 100 sweat glands, and 3 million cells Special Characteristics of Epithelial Tissues Regeneration Epithelial cells - high regenerative capacities Stimulated by loss of apical- basal polarity and broken lateral contacts Some cells exposed to friction, hostile substances  damage Must be replaced Requires adequate nutrients and cell division Wound healing Q. Where do new epithelial cells come from? Classification of Epithelia Based on: 1. Number of cell layers (1 or more) 2. Shape of cells Classification based on Cell Shape (b) Classification based on cell shape Squamous Cuboidal Columnar Squamous: flattened and scale-like Cuboidal: box-like, cube Columnar: tall, column-like In stratified epithelia, shape can vary in each layer, so classified according to the shape in apical layer Epithelium: Simple Squamous (a) Epithelium: simple squamous Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Air sacs of lung tissue Nuclei of squamous Function: Allows materials to pass by diffusion and filtration in sites where protection epithelial is not important but rapid diffusion is; cells secretes lubricating substances in serosae (linings of ventral body cavity). Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; serosae. Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (140×). Simple Squamous Epithelia Two special simple squamous epithelia have specialized names that reflect their locations Endothelium: lines the inner surface of the blood vessels, lymphatic vessels, and the heart. derived from ectoderm and endoderm in the early embryo Mesothelium: Form serous membranes - surround pericardium, peritoneum, pleura and internal reproductive organs (covers the organs' outer surfaces) derived from mesoderm Two membrane system with fluid in between Epithelium: Simple Cuboidal Centrally located, round nuclei Can have cilia Epithelium: Simple Columnar Epithelium: Pseudostratified Columnar (d) Epithelium: pseudostratified columnar “Pseudo” means false; Many cells are ciliated Description: Single layer of cells of differing heights, some not reaching the free surface; Goblet cell nuclei seen at different levels; may contain mucus-secreting cells and bear cilia. (contains mucus) Cilia Pseudo- stratified Function: Secrete substances, particularly mucus; propulsion of mucus by ciliary action. epithelial layer Location: Ciliated variety lines the trachea and most of the upper respiratory tract; nonciliated type in males’ sperm-carrying ducts and ducts of large glands. Basement membrane Trachea Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (780×). Cells vary in height and appear to be multi-layered and stratified, but tissue is in fact single-layered simple epithelium Stratified Epithelia Have two or more layers of cells New cells regenerate from below Basal cells divide and migrate toward surface More durable than simple epithelia because protection is the major role Stratified Squamous Epithelium (e) Epithelium: stratified squamous Description: Thick epithelium composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers. Stratified squamous epithelium Function: Protects underlying tissues in areas subjected to abrasion. Location: Nonkeratinized type forms the Nuclei moist linings of the esophagus, mouth, and vagina; keratinized variety forms the Basement epidermis of the skin, a dry epithelium. membrane Connective tissue Photomicrograph: Stratified squamous epithelium lining the esophagus (285×). Skin Keratinization Video Stratified Cuboidal Epithelium Quite rare Mostly found in ducts of larger glands Typically only two cell layers thick but has other, more basal layers (e.g. squamous) Functions: protection and secretion Sweat gland Parotid gland Mammary gland Stratified Columnar Epithelium Also very limited distribution in body Small amounts found in pharynx, in male urethra, and lining some glandular ducts Usually occurs at transition areas between two other types of epithelia Only apical layer is columnar columnar cuboidal Transitional Epithelium (f) Epithelium: transitional plaques uroplakin Transitional Epithelium (f) Epithelium: transitional Relaxed Stretched Glandular Epithelia Gland: One or more cells that makes and secretes an aqueous fluid called a secretion Classified by: 1. Site of product release: Endocrine: internally secreting (e.g. hormones) Exocrine: externally secreting (e.g. sweat) 2. Relative number of cells forming the gland Unicellular (e.g. goblet cells) or multicellular (e.g. salivary) Formation of multicellular exocrine and endocrine glands Endocrine glands Ductless Hormones: chemicals that travel through lymph or blood to target organs that respond in a characteristic way Major glands of the endocrine system include: Pineal gland Pituitary gland Pancreas Ovaries / Testes Thyroid and parathyroid glands Hypothalamus Adrenal glands Exocrine glands Secretions are released onto body surfaces, such as skin, or into body cavities More numerous than endocrine glands Secrete products into ducts Examples include: sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, prostate, pancreas, and liver. Can be: Unicellular Multicellular  Unicellular exocrine gland Microvilli Unicellular exocrine glands The only important unicellular glands are mucous cells and goblet Secretory vesicles cells containing Found in epithelial mucin linings of intestinal and respiratory tracts among columnar cells All produce mucin, a sugar-protein that can Golgi apparatus dissolve in water to form mucus, a slimy Rough ER protective, lubricating coating (protects from what?) Nucleus (a) (b) Multicellular exocrine glands composed of a duct and a secretory unit Usually surrounded by supportive connective tissue that supplies blood and innervation Connective tissue can form capsule around gland, and also extend into gland, dividing it into lobes Classified by: Structure Mode of secretion Acinus (secretory cells) Structural classification of multicellular exocrine glands Mechanisms of secretion in human exocrine glands Merocrine (eccrine) glands secrete their products by exocytosis as they are produced (most sweat glands, pancreas). In apocrine glands the secretory cells accumulate products just beneath the cell surface facing the duct; only the apex of the cell breaks off (sweat glands associated with hairy body parts). In holocrine glands, the entire secretory cell ruptures, releasing secretions and dead cell fragments (sebaceous oil glands). Apocrine sweat glands