Chapter 3: Histology

Epithelial Tissue

• covers organ surfaces, forms glands

• protection, absorption, secretion

• Characteristics

  • 1+ layers

  • closely adhered cells

  • Avascular - no blood vessels passing through

  • form surfaces

  • Basement membrane delivers nutrients

    • basal surface connects to basement membrane

    • apical surface is the “upper” part of the cell

• Classes of Epithelium

  • simple

    • every cell is connected to basement membrane

    • simple cuboidal, simple, cuboidal, simple columnar,

  • pseudostratified columnar

    • connected to basement membrane

    • goblet cells - specialized columnar cell that produces mucin

  • stratified

    • two or more layers

    • named by shape of the top layer

    • stratified squamous, stratified cuboidal, urothelium (transitional)

• Cell Shapes

  • Squamous

  • Cuboidal

  • Columnar

Simple Squamous

Simple Cuboidal

• single layer of square/round cells

• glandular

• often with brushed border

• absorption and secretion

• representative locations: liver, bronchioles, kidney tubules, most glands

Simple Columnar

• nucleus is elongated and oriented towards basal surface

• tend to have microvilli

• may possess goblet cells

• representative locations: stomach lining, intestines, gallbladder

• absorption secretion of mucus, movement of egg/embryo in uterine tube

Pseudostratified Columnar

• looks multilayered, but all cells attach to basement membrane

• often with goblet cells

• often ciliated

• representative locations: URI (nasal cavity → bronchi)

• portions of male urethra

• secretes and propels mucus

Keratinized Stratified Squamous Epithelium

• multiple cell layers becoming increasingly flat and scaly towards surface

• surface coverd with compact dead cells w/out nuclei

Non-keratinzed stratified squamous epithelium

• same as keratinized epithelium but without surface layer of dead cells

• resists abrasion and penetration by pathogenic organisms

• representative locations: tongue, vagina

Stratified Cuboidal

• two or more layers of cells, surface cells roughly square or round

• sweat glands, ducts

Urothelium (Transitional Epithelium)

• can distend without damage

• urinary tract

• protects underlying tissue from osmotic and acidic effects

Connective Tissue

• more matrix than cell volume

• specialized cells for supporting, binding, and protecting organs

• most prevalent tissue in the body

• Functions

  • binding of organs, support, physical protection, immune protection, movement, storage, heat production, and transport

Fibrous

• Fibers

  • Collagen - tough and flexible (white fibers of tendons/ligaments)

  • Reticular - thin collagen fibers (framework of spleen, lymph nodes)

  • Elastic - stretch and recoil; made of protein elastin (abundant in lungs)

• Cells Types

  • fibroblasts/fibrocytes: produce fibers and ground substance

  • leukocytes - neutrophils, lymphocytes, macrophages,

  • adipocytes

• Types

  • Loose Connective Tissue

    • areolar - abundant; binds epithelia to deeper tissue; a classification of “fascia”; abundant ground substance; network of collagen and elastic tissue in ground substance

    • Reticular connective tissue - (loose) network of reticular fibers and cells

  • Dense Regular Connective Tissue

    • highly organized, mostly made up of collagen fibers

    • many fibroblasts

    • slow to recover

    • is considered other classification of '“fascia”

  • Dense Irregular Connective Tissue

    • random arrangement of collagen fibers

    • resists stress (due to randomized structure)

    • Most of the dermis in skin

    • Protective “capsules”

  • Adipose Tissue

    • stores energy and provides protection

    • white - more abundant in adults

    • brown - more abundant in infants, for thermoregulation

Cartilage

• Cells/Structures of Cartilage

  • chondroblasts/chondrocytes

    • produce and maintain ECM

  • Lacuna

    • house mature chondrocytes

  • Fibroblasts

  • ECM

• Types of Cartilage

  • Hyaline Cartilage

    • dispersed collagen fibers, not usually visible

    • small clusters of 3-4 cells (cell nests) eclosed in lacunae

    • usually covered by perichondrium

  • Elastic Cartilage

    • elastic fibers form weblike mesh amid lucunae

    • always covered by perichondrium

    • external ear, epiglottis

  • Fibrocartilage

    • no perichondrium

    • parallel collagen fibers

    • rows of chondrocytes in lacunae between collagen fibers

    • menisci, intervertebral discs, pubic symphysis

    • resists compression and absorbs stress

Bone

• Types

  • Spongy (trabecular)

  • Compact (cortical)

    • arranged in osteons with a central canal

    • lamellae

    • lacunae with osteocytes,

    • canaliculi - little channels

Blood

• made of plasma and formed elements

  • plasma - water, salts, proteins

  • formed elements - erythrocytes (RBC), leukocytes (WBC), platelets

Nervous Tissue

• specialized for rapid communication with other cells

• the longest cells in body

• Nervous cell types

  • Neuroglia (glial) cells

  • Neurons

    • transmit information

    • parts of the neuron

      • neurosoma (cell body)

      • dendrites - receive information

      • axon - transmits signal

Muscular Tissue

• composed of elongated, excitable cells

• Types of muscular tissue

  • Skeletal muscle

    • cells: muscle fibers

    • voluntary

    • striated *

  • cardiac muscle

    • cells: cardiomyocytes

    • striated *

    • intercalated discs

    • involuntary

  • Smooth muscle

    • cells: fusiform myocytes - tapered at ends

    • non-striated *

    • involuntary

• Skeletal Muscle

  • attached to bones

  • arranged in long muscle fibers parallel to each other

  • each cell (fiber) is multi-nucleated - nuculei play critical role in protein development

• Cardiac Muscle

  • cardiomyocytes form most of the heart wall

  • arranged in long muscle fibers that are branched

  • striated

  • intercalated discs with gap junctions

  • involuntary

• Smooth muscle

  • fusiform (spindle-shaped) myocytes found in walls of hollow organs

  • non-striated

  • involuntary

Tissue Growth and Development

Growth

• * Hyperplasia - cell multiplication

  • growth

  • repair

• * Hypertrophy - enlargement of cell

• Neoplasia - tumor development

Changes

• differentiation - specialization of form or function

  • e.g., stem cells

• metaplasia - changes from one tissue to another

  • e.g., ossification of cartilage

Repair

• regeneration - replacement of dead cells

• fibrosis - scar tissue development

  • occurs in circumstances of extensive damage

Shrinkage and Death

• atrophy - reduction in size/number

  • “use it or lose it”

  • shrinkage

• necrosis - pathological death of tissue

  • infarction - blood supply cut-off

  • gangrene - inadequate blood supply (necrosis)

    • more often a chronic condition

• apoptosis - programmed cell death, normal function