Marieb s Human Anatomy and Physiology Marieb Hoehn Chapter 4 Tissues: The Living Fabric Epithelial Tissues Lecture 9 Lecture Overview Introduction to Tissues Epithelial Tissues Location General characteristics Functions Classification Glandular Epithelium 2 Where are Tissues in Our Organizational Scheme? Figure from: Hole s Human A&P, 12 th edition, 2010 3 1
Introduction to Tissues Tissue - a group of cells working together to perform one or more specific functions Histology the microscopic study of tissues Four primary types of tissues found in the adult : 1. Epithelial (covering/lining, protection, glands) [ pl. epithelia] 2. Connective (binding together, support, transport, energy) 3. Muscle (movement, heat production) 4. Nervous (information and short-term control) 4 Major Types of Epithelial Tissues Covering and Lining Epithelium External Surfaces, e.g., skin Internal surfaces 2 major types: 1. Those that communicate with outside, e.g., digestive, respiratory, reproductive and urinary tracts 2. Those that don t communicate with outside, e.g., chest cavity, abdominal cavity, endothelium of blood vessels and heart Glandular Epithelium Often lie in clusters deep to covering and lining epithelium Specialized for secretion into ducts, on to a surface, or into the blood 5 Functions of Epithelial Tissue Physical protection Protect from abrasion, dehydration, and destruction by chemical or biological agents Control of permeability Secretion Absorption Filtration Provide sensation Extensively innervated by sensory nerves May function in senses (smell, taste, etc.) Provide specialized secretions (glands) 6 2
Characteristics of Epithelial Tissue Specialized contacts with other cells Polarity (different ends of cell do different things) Avascularity (no blood supply) Regeneration (can divide to make new cells) Cellularity (lots of cells in close contact) Remember: Epithelial tissues always have a free surface and a basement membrane 7 Characteristics of Epithelial Tissue Specialized Contacts Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 8 Characteristics of Epithelial Tissue Polarity Outside surface note modifications Inner surface attached to underlying tissue by a basement membrane Figures from: Martini Visual A&P, 1 st edition, 2011 Notice the polarity and differential distribution of the cellular organelles 9 3
Characteristics of Epithelial Tissue Avascularity and Regeneration Does not contain blood vessels (avascular) Nutrients must be obtained by Diffusion from underlying tissue (125 µm limit) Absorption from free surface High rate of cell division and replacement Lost cells are continually replaced by dividing epithelial stem cells Rate of cell division (mitotic rate) is much higher than other tissues 10 Characteristics of Epithelial Tissue Cellularity Figure from: Hole s Human A&P, 12 th edition, 2010 - Cells are bound closely together - Little intercellular material - May form sheets; cells usually slough off in sheets 11 Modifications of Epithelial Cells Cilia movement of substances Microvilli greatly increase absorptive (surface) area Figures from: Martini, Anatomy & Physiology, Prentice Hall, 2001 12 4
Basal Lamina Formerly called: Basement membrane Two components: Lamina Lucida - glycoproteins and fine protein filaments - Barrier for passage of substances from underlying tissue into epithelium Lamina = thin layer Lamina Densa - bundles of coarse protein fibers - gives basal lamina its strength Figure from: Martini, Fundamentals of Anatomy & Physiology, Benjamin Cummings, 2004 13 Classification of Epithelial Tissues Epithelial tissues are classified according to both their: Shape Squamous (Thin, flat, irregular in shape) Cuboidal (Square or cuboidal) Columnar (Rectangular, tall) Type of layering (stratification) Simple (one layer) Stratified (two or more layers) Note that classification of stratified epithelium is based on the shape of the superficial, not deep, layers 14 Epithelial Tissues Figure from: Hole s Human A&P, 12 th edition, 2010 Simple squamous single layer of flat cells substances pass easily through line air sacs of lung, blood vessels, lymphatic vessels reduce friction, absorption/secretion Mesothelium lines ventral body cavities (serous membranes) Endothelium lines blood vessels 15 5
Epithelial Tissues Figure from: Marieb s Human A&P, 9 th edition, 2013 16 Epithelial Tissues Figure from: Marieb s Human A&P, 9 th edition, 2013 17 Epithelial Tissues Pseudostratified columnar single layer of elongated cells appear stratified, but they ARE NOT all cells attach to basement membrane; some do not reach surface often have cilia and goblet cells line respiratory passageways function: protection, secretion 18 6
Epithelial Tissues Figure from: Hole s Human A&P, 12 th edition, 2010 Stratified squamous many cell layers top cells are flat can accumulate keratin outer layer of skin line oral cavity, throat, vagina, and anal canal Main function is protection (abrasions, pathogens, chemicals) 19 Epithelial Tissues Figure from: Hole s Human A&P, 12 th edition, 2010 Transitional many cell layers cube-shaped and elongated cells line urinary bladder, ureters, and part of urethra Located in places where acute, short term stretching occurs 20 Glandular Epithelium Composed of cells that are specialized to produce and secrete substances Endocrine glands are ductless secrete directly into the blood Exocrine glands have ducts secrete into a duct or on to a surface Unicellular exocrine gland composed of one cell Example: goblet cell Multicellular exocrine gland composed of many cells Examples: sweat glands, sebaceous glands, salivary glands, etc. 21 7
Structural Types of Exocrine Glands Classified by: 1. Shape of secretory portion of gland 2. Branching pattern of the duct 22 Exocrine Glands Classified by: 1. Shape of secretory portion of gland 2. Branching pattern of the duct 23 Types of Glandular Secretions Merocrine glands fluid product exocytosis salivary glands pancreas sweat glands Holocrine glands secretory products whole cells sebaceous glands in hair follicles 24 8
Membranes A membrane is a combination of epithelium and connective tissue that covers and protects other structures and tissues. Technically, then, a membrane is an organ. Serous line body cavities that lack openings to outside reduce friction inner lining of thorax and abdomen cover organs of thorax and abdomen secrete serous fluid Cutaneous covers body skin Mucous line tubes and organs that open to outside world lining of mouth, nose, throat, digestive tract, etc. secrete mucus Synovial surround joint cavities 25 Epithelial Membranes Notice that each type of membrane is composed of TWO different types of tissues; epithelial and connective Figure from: Martini, Anatomy & Physiology, Prentice-Hall, 2001 26 Review of Epithelial Tissues Tissue - a group of cells working together to perform one or more specific functions Epithelial tissues are covering, lining, and glandular tissues that function in Physical protection Control of permeability Sensation Secretion Characteristics of epithelial tissue include Specialized contacts Polarity Avascularity Regeneration Cellularity 27 9
Review of Epithelial Tissues Covering and lining type tissue Characteristics: S-P-A-R-C Attached to underlying tissue by a basal lamina (basement membrane) Epithelial tissue always has a free surface Classified according to shape and number of layers 28 Review of Epithelial Tissues Glands are specialized epithelium Exocrine Secrete on to a surface or into a duct Multicellular exocrine glands are classified by: Shape of secretory portion of gland Branching pattern of the duct Endocrine - Secrete into the blood 29 Review of Epithelial Tissues Exocrine glands have several different mechanisms of secretion Merocrine Release of product from vesicles by exocytosis Most common mode of secretion Example: watery sweat used to cool skin Holocrine Entire cell is packed with secretion and then bursts Destroys cell Example: sebaceous glands associated with hair follicles Apocrine (may not be present in humans; listed here only for informational purposes) Loss of apical cytoplasm containing secretion, not entire cell Example: thick, sticky underarm perspiration 30 10
Review NAME OF ET SIMPLE SQUAMOUS SIMPLE CUBOIDAL SIMPLE COLUMNAR PSEUDO- STRATIFIED COLUMNAR DESCRIPTION STRUCTURE a single layer of flattened cells a single layer of cubeshaped cells with large centrally located nuclei a single layer of tall cells with basally located nuclei, goblet cells, & mucrovilli a single layer of tall cells with scattered nuclei, cilia, & goblet cells LOCATION linings of air sacs, capillaries, lymph vessels, body cavities; covering ventral organs linings of kidney tubules, ducts of glands lining of intestine lining of trachea, lining of fallopian tube FUNCTION diffusion, reduction of friction absorption, secretion protection, absorption, secretion protection, secretion 31 Review NAME OF ET DESCRIPTION STRUCTURE LOCATION FUNCTION STRATIFIED SQUAMOUS many layers of flattened cells keratinized = epidermis; non-keratinized = lining of vagina, anus, throat, mouth protection TRANSITIONAL several layers of cells that change shape under pressure lining of urinary bladder and ureters Distensibility (able to stretch) GLANDULAR simple cuboidal lining the ducts of glands secretion 32 11