Chapter 4
Histology
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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. Cartilage
3. 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
Connective: Blood
• 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
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