Chapter 4Histology

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Histology

• Study of Tissues• Epithelial Tissue• Connective Tissue• Nervous and Muscular Tissue • Intercellular Junctions, Glands and Membranes• Tissue Growth, Development, Death and Repair

The Study of Tissues• 200 Different cell types• Four primary tissue classes– epithelial tissue– connective tissue– muscular tissue– nervous tissue

• Histology (microscopic anatomy)– study of tissues organ formation

• Organ = structure with discrete boundaries– composed of 2 or more tissue types

Features of Tissue Classes• Tissue = similar cells and cell products– arose from same region of embryo

• Differences between tissue classes– types and functions of cells– characteristics of matrix (extracellular material)• fibrous proteins • ground substance

– clear gels (ECF, tissue fluid, interstitial fluid, tissue gel)– rubbery or stony in cartilage or bone

– space occupied by cells versus matrix• connective tissue cells are widely separated • little matrix between epithelial and muscle cells

Embryonic Tissues

• Embryo begins as single cell– divides into many cells and layers (strata)

• 3 Primary germ layers– ectoderm (outer)

• forms epidermis and nervous system

– endoderm (inner) • forms mucous membrane lining GI tract and respiratory system and

digestive glands

– mesoderm (middle) becomes mesenchyme• wispy collagen fibers and fibroblasts in gel matrix• gives rise to muscle, bone, blood

Tissue Techniques and Sectioning

• Preparation of histological specimens– fixative prevents decay (formalin)– sliced into thin sections 1 or 2 cells thick– mounted on slides and colored with histological

stain• stains bind to different cellular components

• Sectioning reduces 3-dimensional structure to 2-dimensional slice

Sectioning Solid Objects

• Sectioning a cell with a centrally located nucleus

• Some slices miss the cell nucleus

• In some the nucleus is smaller

Sectioning Hollow Structures

• Cross section of blood vessel, gut, or other tubular organ.

• Longitudinal section of a sweat gland. Notice what a single slice could look like.

Types of Tissue Sections

• Longitudinal section– tissue cut along longest

direction of organ

• Cross section– tissue cut perpendicular

to length of organ

• Oblique section– tissue cut at angle

between cross and longitudinal section

Four primary tissue classes

• Epithelial tissue• Connective tissue• Muscular tissue• Nervous tissue

Epithelial Tissue

• Layers of closely adhering cells• Flat sheet with upper surface exposed to the

environment or an internal body cavity• No blood vessels– underlying connective tissue supplies oxygen

• Rests on basement membrane– thin layer of collagen and adhesive proteins– anchors epithelium to connective tissue

Simple Versus Stratified Epithelia• Simple epithelium

– contains one layer of cells– named by shape of cells

• Stratified epithelium– contains more than one layer– named by shape of apical cells

Simple Squamous Epithelium

• Single row of flat cells• Permits diffusion of substances• Secretes serous fluid• Alveoli, glomeruli, endothelium, and serosa

Simple Cuboidal Epithelium

• Single row cube-shaped cells with microvilli• Absorption and secretion, mucus production• Liver, thyroid, mammary and salivary glands,

bronchioles, and kidney tubules

Simple Columnar Epithelium

• Single row tall, narrow cells– oval nuclei in basal half

of cell• Absorption and secretion;

mucus secretion • Lining of GI tract, uterus,

kidney and uterine tubes

Pseudostratified Epithelium

• Single row of cells some not reaching free surface– nuclei give layer

stratified look• Secretes and propels

respiratory mucus

Stratified Epithelia• More than one layer of cells • Named for shape of surface cells– exception is transitional epithelium

• Deepest cells on basement membrane• Variations– keratinized epithelium has surface layer of dead

cells– nonkeratinized epithelium lacks the layer of dead

cells

Keratinized Stratified Squamous

• Multilayered epithelium covered with dead squamous cells, packed with keratin– epidermal layer of

skin• Retards water loss and

barrier to organisms

Nonkeratinized Stratified Squamous

• Multilayered surface epithelium forming moist, slippery layer

• Tongue, oral mucosa, esophagus and vagina

Stratified Cuboidal Epithelium

• Two or more cell layers; surface cells square

• Secretes sweat; produces sperm and hormones

• Sweat gland ducts; ovarian follicles and seminiferous tubules

Transitional Epithelium

• Multilayered epithelium surface cells that change from round to flat when stretched– allows for filling of

urinary tract– ureter and bladder

Four Types of Connective Tissue

1. Fibrous– Loose– Dense

2. Cartilage3. Bone– Spongy– Compact

4. Blood

Connective Tissue

• Widely spaced cells separated by fibers and ground substance

• Most abundant and variable tissue type• Functions– connects organs– gives support and protection (physical and immune)– stores energy and produces heat– movement and transport of materials

Cells of Connective Tissue

• Fibroblasts produce fibers and ground substance• Macrophages phagocytize foreign material and activate

immune system– arise from monocytes (WBCs)

• Neutrophils wander in search of bacteria• Plasma cells synthesize antibodies– arise from WBCs

• Mast cells secrete – heparin inhibits clotting– histamine that dilates blood vessels

• Adipocytes store triglycerides

Fibers of Connective Tissue• Collagen fibers (white fibers)– tough, stretch resistant, yet flexible– tendons, ligaments and deep layer of the skin

• Reticular fibers– thin, collagen fibers coated with glycoprotein– framework in spleen and lymph nodes

• Elastic fibers (yellow fibers)– thin branching fibers of elastin protein– stretch and recoil like rubberband (elasticity)– skin, lungs and arteries stretch and recoil

Connective Tissue Ground Substance

• Gelatinous material between cells – absorbs compressive forces

• Consists of 3 classes of large molecules– glycosaminoglycans – chondroitin sulfate• disaccharides that attract sodium and hold water• role in regulating water and electrolyte balance

– Proteoglycan (bottlebrush-shaped molecule) • create bonds with cells or extracellular macromolecules

– adhesive glycoproteins• protein-carbohydrate complexes bind cell membrane to

collagen outside the cells

Fibrous Connective Tissue Types

• Loose connective tissue– gel-like ground substance between cells– types

• areolar• reticular• adipose

• Dense connective tissue– fibers fill spaces between cells– types vary in fiber orientation

• dense regular connective tissue• dense irregular connective tissue

Loose Connective: Areolar Tissue

• Loose arrangement of fibers and cells in abundant ground substance

• Underlies all epithelia, between muscles, passageways for nerves and blood vessels

Loose Connective: Reticular Tissue

• Loose network of reticular fibers and cells• Forms supportive stroma (framework) for lymphatic

organs• Found in lymph nodes, spleen, thymus and bone

marrow

Loose Connective: Adipose Tissue

• Empty-looking cells with thin margins; nucleus pressed against cell membrane

• Energy storage, insulation, cushioning– subcutaneous fat and organ packing– brown fat (hibernating animals) produces heat

Dense Regular Connective Tissue

• Densely, packed, parallel collagen fibers– compressed fibroblast nuclei

• Tendons and ligaments hold bones together and attach muscles to bones

Dense Irregular Connective Tissue

• Densely packed, randomly arranged, collagen fibers and few visible cells– withstands stresses applied in different directions – deeper layer of skin; capsules around organs

Connective: Cartilage

• Supportive connective tissue with rubbery matrix

• Chondroblasts produce matrix– called chondrocytes once surrounded

• No blood vessels– diffusion brings nutrients and removes wastes– heals slowly

• Types of cartilage vary with fiber types– hyaline, fibrocartilage and elastic cartilage

Hyaline Cartilage

• Rubbery matrix; dispersed collagen fibers; clustered chondrocytes in lacunae– supports airway, eases joint movements

• Ends of bones at movable joints; sternal ends of ribs; supportive material in larynx, trachea, bronchi and fetal skeleton

Elastic Cartilage

• Hyaline cartilage with elastic fibers • Provides flexible, elastic support– external ear and epiglottis

Fibrocartilage- Fibrous Cartilage

• Hyaline cartilage with extensive collagen fibers (never has perichondrium)

• Resists compression and absorbs shock– pubic symphysis, meniscus and intervertebral discs

Connective: Bone

• Spongy bone - spongy in appearance– delicate struts of bone– covered by compact bone – found in heads of long bones

• Compact bone - solid in appearance– more complex arrangement– cells and matrix surround vertically oriented blood

vessels in long bones

Compact Bone

Bone Tissue (compact bone)

• Calcified matrix in lamellae around central canal• Osteocytes in lacunae between lamellae • Skeletal support; leverage for muscles; mineral storage

• Variety of cells and cell fragments; some with nuclei and some without

• Nonnucleated pale pink cells or nucleated white blood cells

• Found in heart and blood vessels

Connective: Blood

Nerve Tissue

• Large cells with long cell processes– surrounded by smaller glial cells lacking processes

• Internal communication between cells– in brain, spinal cord, nerves and ganglia

Muscle Tissue

• Elongated cells stimulated to contract• Exert physical force on other tissues– move limbs– push blood through a vessel– expel urine

• Source of body heat• 3 histological types of muscle– skeletal, cardiac and smooth

Skeletal Muscle

• Long, cylindrical, unbranched cells with striations and multiple peripheral nuclei– Voluntary movement, facial expression, posture, breathing,

speech, swallowing and excretion

Cardiac Muscle• Short branched cells

with striations and intercalated discs– one central nuclei per

cell

• Pumping of blood by cardiac (heart) muscle

Smooth Muscle

• Short fusiform cells; nonstriated with only one central nucleus– Involuntary movements– sheets of muscle in viscera; iris; hair follicles and sphincters – swallowing, GI tract functions, labor contractions, control of

airflow, erection of hairs and control of pupil