Histology

The study of cells and tissues

Tissues – 4 basic types epithelial connective muscular nervous

Epithelium – forms internal or external linings of organs and glands, specialized for lubrication, resisting abrasion, water-proofing, absorption, and/or secretion; rests on basement membrane; basal to apical or luminal polarity; one free surface; cellularity; specialized cell junctions including desmosomes or tight junctions; rapid regeneration; nourishment by diffusion; no intrinsic vascularization or innervation

Epithelium (pl. epithelia) simple squamous stratified squamous simple cuboidal stratified cuboidal simple columnar pseudostratified columnar transitional glands endocrine – ductless exocrine – possess ducts

simple squamous stratified squamous flat, single layered multilayered with basal germinal layer e.g., endothelium of blood vessels e.g., epidermis of skin

simple cuboidal stratified cuboidal e.g., glands and their ducts e.g., glands and their ducts gall bladder, sexual ducts

simple columnar pseudostratified columnar cells tall, parallel cells tall, not parallel brush border or microvilli ciliated e.g., endothelium of intestines e.g., endothelium of trachea

transitional urinary bladder

glands – both excretory and secretory endocrine – ductless exocrine – possess ducts shape: tubular, alveolar, simple, complex

Connective Tissues Non-binding Connective Tissue blood/lymph

Binding Connective Tissue loose connective tissue dense connective tissue cartilage bone

Non-binding Connective Tissue blood/lymph

Loose Connective Tissue – little protein in extracellular matrix areolar – collagen, forms interstitia adipose – lipid droplets, fat

reticular – reticulin, net or filter structure of lymph organs (not shown)

Dense Connective Tissue – much protein in extracellular matrix regular – parallel collagen fibers irregular – nonparallel collagen fibers e.g., tendons e.g., dermis of skin

elastic – elastin, rebounds after deformation e.g., arteries

fibrous – fibrin, very tough joints e.g., intervertebral discs

Cartilage – extracellular matrix with glycosaminoglycans, chondroitin sulfate, hyaluronic acid; chondrocytes reside in lacunae; interstitial and appositional growth hyaline – collagen, most common type elastic – elastin, e.g., skeletal system e.g., pinna of ear, epiglottis

Bone – highly vascularized extracellular matrix of precipitated collagen and apatite [Ca3(PO4)2]; osteocytes reside in lacunae; appositional growth only

Muscular Tissue – Ca++ and ATP dependent contraction; thin filaments – actin,

troponin, meromyosin; thick filaments – myosin smooth muscle striated muscle skeletal striated muscle cardiac striated muscle

Smooth Muscle – spindle shaped cells, mononucleate, in walls of organs (e.g., digestive tract, blood vessels, skin), respond to hormones, stretch, and innervation by autonomic nervous system

Striated Muscle – myofilaments bundled into myofibrils forming ‘striated’ sarcomeres (alternating interdigitating bands of thick and thin filaments), juxtaposed to sarcoplasmic reticulum (ER sequesters Ca++) and transverse tubules (invaginations of sarcolemma); numerous mitochondria

Skeletal Striated Muscle – giant multinucleate linear cells of voluntary skeletal muscular system, syncytium, every cell innervated with motor endplate, responds to neurotransmitter acetylcholine; denervation results in atrophy

Cardiac Striated Muscle – myocardium of heart; branching cells joined at intercalated discs; syncytium but few nuclei; intercalated discs possess gap junctions (electrical connectivity) and desmosomes; cells depolarize spontaneously and wave of contraction passes from cell to cell; rate modulated by hormones and autonomic innervation

Nervous Tissue neuroglia or glial cells – structural, supportive, insulating neurons – excitatory

Neuroglia or glial cells

Neurons – excitatory; cell body or ‘neuron’; cell processes are axons and dendrites; slow transport of neurotransmitters from neuron to presynaptic vesicles of axon; membrane depolarization causes release of neurotransmitters into synapse which are bound by receptors of postsynaptic dendrites; neurotransmitters may be excitatory, inhibitory, or modifying to membrane depolarization of postsynaptic neuron