Histology: Introduction & Epithelial Tissue PDF

Histology: Introduction & Epithelial Tissue Sections 5.1, 5.2, & 5.5a  What are tissues?  Aggregations of similar cells (and materials surrounding them) working together for a specific function  Why do we care?  True or False: Histology i...

Histology: Introduction & Epithelial Tissue Sections 5.1, 5.2, & 5.5a  What are tissues?  Aggregations of similar cells (and materials surrounding them) working together for a specific function  Why do we care?  True or False: Histology is tough  Cells working together with same goal(s) is the reason our organs function  But what about in real, everyday life?  Physical therapists  Physician’s assistants  Cardiac health  Pharmacology   PROBLEM SOLVING  Tissue Components  Cells ECM Cells  Extracellular matrix (ECM)  Fibrous proteins (fibers)  Ground substance  Ground Substance  AKA:  Tissue fluid  Extracellular fluid  Interstitial fluid  Amorphous, clear gel – varies in consistency  Functions:  Cells gain: water, gases, minerals, nutrients to cells  Cells release: waste, hormones, other products  Protection/shock absorption  How do cells join to form tissues?  Junctions between cells  Tight – seals space between cells  Prevents leaking (e.g., digestive juices in stomach)  Desmosomes – allows space between cells, but resists mechanical stress  Common between epithelial cells  Gap – pores/channels connecting cells  Connects cytoplasm to cytoplasm (like a tunnel)  E.g., some muscle cells (allows for almost simultaneous contraction)  4 Primary Categories of Tissues  Epithelial – covers  Connective – connects  Nervous* – communicates  Muscular* – contracts *We will cover these two tissues in depth later in the course  Epithelial Tissue  Closely adhering cells  Lines organs, forms exocrine glands  Lumen = cavity/open tube of organ/gland  Functions: Lumen  Protection Lumen  Secretion  Absorption  Filtration  Sensation  Epithelial Tissue – Common Features  Closely packed cells  Many tight junctions & desmosomes  Little ECM  Cell polarity  Apical surface = free surface (faces lumen)  Basal surface = attached to basement membrane  Epithelial Tissue – Common Features  Avascular  Innervated  High rate of regeneration  Why is this important in a covering or lining tissue?  Classification of Epithelial Tissue  Classified by:  Shape of cells  Number of layers of cells  Classification: # of Layers  1 = simple  > 1 = stratified  Looks like multiple layers, but not = pseudostratified Structure  function One layer  ? Multiple layers  ?  Classification: Shape  Squamous – flat (“scaly”)  Cuboidal – cube-shaped  Columnar – column-shaped (taller than wide)  If multiple layers, which layer do you look at for shape? Structure  function Thin cells  ? Thick cells  ? Top Hat – 3 Scenarios  Simple squamous epithelia  VERY thin single layer of cells  Allows for rapid diffusion of gases, nutrients  E.g., in air sacs of lungs & blood vessels  Secretes lubricating substances – Simple squamous decreases friction  E.g., lines body cavities (e.g., pleural & pericardial cavities)  Simple squamous epithelia by location  Endothelium –lines inside of  Mesothelium – lines inside of blood vessels & heart ventral body cavities  Simple cuboidal epithelium  Single layer of cube-shaped cells  Thicker barrier than simple squamous  More space for organelles such as mitochondria  energy for active transport  Microvilli (in some) – increase absorption  Goblet cells (in some) – secrete mucus (protective function)  Cilia (in some) – move mucus  Location examples:  Kidney tubules  Secretory glands (e.g., thyroid, salivary)  Simple columnar epithelium  Single layer of tall cells (lots of space for organelles)  Even thicker barrier than simple cuboidal  Functions  Microvilli (in some)  Goblet cells (in some)  Cilia (in some)  Location examples:  Lower digestive tract (stomach through intestines)  Goblet Cells  Produce secretion that (when mixed with water) becomes mucus  Mucus creates barrier  Traps unwanted particles (e.g., airway)  Protects tissues from digestive enzymes & acids  Home for microbiome in gut  Mucus creates layer of lubricant  Helps food/waste move through GI tract  Pseudostratified columnar epithelium  Single layer of tall cells that looks like multiple layers (BUT it’s not)  All cells connect to basement membrane  Function  Goblet cells  Cilia  Locations  Respiratory tract (nasal cavity, trachea, bronchi)  Stratified squamous epithelium  Multiple layers of flat(ish) cells  High turnover (exfoliation/desquamation)  Basal cells rounded, apical cells flatter  Most widespread epithelium Apical surface  Keratinized or non-keratinized  Functions  Resists abrasion  Resists water loss  Prevents pathogen invasion  Locations  Epidermis of skin Basal surface  Upper digestive tract (oral cavity, tongue, esophagus)  Keratinized stratified squamous epithelium  Cells produce keratin (protein)  Durable, protective  Makes surfaces tough, resistant  Apical layers dead, packed with keratin  Location  Epidermis of skin  Non-keratinized stratified squamous epithelium  Cells do NOT produce keratin  Apical layers still alive  Locations  Upper digestive tract (tongue, oral cavity, esophagus)  Vaginal canal  Stratified cuboidal epithelium  Multiple layers of cube-shaped cells  Function = secretion  Sweat  Hormones  Sperm production  Locations  Sweat glands  Ovaries  Seminiferous tubules  Urothelium  AKA transitional epithelium  Layers of rounded, dome-topped cells that can flatten (when organ stretches)  “Umbrella cells”  Has special proteins (uroplakins)  impermeable to urine  In urinary tract (particularly the urinary bladder)  Functions  Stretches to allow filling  Protects underlying tissue from osmotic damage (urine is hypertonic to intracellular fluid) Top Hat – one more scenario