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Chapter 5
Lecture
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Histology
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Study of Tissues
Epithelial Tissue
Connective Tissue
Nervous and Muscular Tissue
Intercellular Junctions, Glands and
Membranes
• Tissue Growth, Development, Death and
Repair
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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
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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
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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
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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
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Sectioning Solid Objects
• Sectioning a
cell with a
centrally
located
nucleus
• Some slices
miss the cell
nucleus
• In some the
nucleus is
smaller
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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.
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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 5-9
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
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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
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Simple Squamous Epithelium
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Single row of flat cells
Permits diffusion of substances
Secretes serous fluid
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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
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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
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Pseudostratified Epithelium
• Single row of cells some not reaching free
surface
– nuclei give layer stratified look
• Secretes and propels respiratory mucus
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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
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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
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Nonkeratinized Stratified Squamous
• Multilayered surface epithelium forming moist,
slippery layer
• Tongue, oral mucosa, esophagus and vagina 5-18
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
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Transitional Epithelium
• Multilayered epithelium surface cells that change
from round to flat when stretched
– allows for filling of urinary tract
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– ureter and bladder
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
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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
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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 5-23
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
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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
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Areolar Tissue
• Loose arrangement of fibers and cells in
abundant ground substance
• Underlies all epithelia, between muscles,
passageways for nerves and blood vessels
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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
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Adipose Tissue
• Empty-looking cells with thin margins; nucleus pressed
against cell membrane
• Energy storage, insulation, cushioning
– subcutaneous fat and organ packing
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– 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
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attach muscles to bones
Dense Irregular Connective Tissue
• Densely packed, randomly arranged, collagen
fibers and few visible cells
– withstands stresses applied in different directions
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– deeper layer of skin; capsules around organs
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
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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
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fetal skeleton
Elastic Cartilage
• Hyaline cartilage with elastic fibers
• Provides flexible, elastic support
– external ear and epiglottis
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Fibrocartilage
• Hyaline cartilage with extensive collagen fibers (never
has perichondrium)
• Resists compression and absorbs shock
– pubic symphysis, meniscus and intervertebral discs
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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
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Bone Tissue (compact bone)
• Calcified matrix in lamellae around central canal
• Osteocytes in lacunae between lamellae
• Skeletal support; leverage for muscles; mineral
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storage
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
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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
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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
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Skeletal Muscle
• Long, cylindrical, unbranched cells with
striations and multiple peripheral nuclei
– movement, facial expression, posture, breathing,
speech, swallowing and excretion
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Cardiac Muscle
• Short branched cells with striations and
intercalated discs
– one central nuclei per cell
• Pumping of blood by cardiac (heart) muscle
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Smooth Muscle
• Short fusiform cells; nonstriated with only one central
nucleus
– sheets of muscle in viscera; iris; hair follicles and
sphincters
– swallowing, GI tract functions, labor contractions,
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control of airflow, erection of hairs and control of pupil
Intercellular Junctions
• All cells (except blood) anchored to each other or
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their matrix by intercellular junctions
Tight Junctions
• Encircle the cell joining it to surrounding cells
– zipperlike complementary grooves and
ridges
• Prevents passage between cells
– GI and urinary tracts
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Desmosomes
• Patch between cells holding them together
– cells spanned by filaments terminating on protein plaque
• cytoplasmic intermediate filaments also attach to plaque
• Uterus, heart and epidermis
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Gap Junctions
• Ring of transmembrane proteins form a water-filled channel
– small solutes pass directly from cell to cell
– in embryos, cardiac and smooth muscle
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Endocrine and Exocrine
Glands
• Secrete substances
– composed of epithelial tissue
• Exocrine glands connect to surface with a
duct (epithelial tube)
• Endocrine glands secrete (hormones)
directly into bloodstream
• Mixed organs do both
– liver, gonads, pancreas
• Unicellular glands – endo or exocrine
– goblet or intrinsic cells of stomach wall
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Exocrine Gland Structure
• Stroma = capsule and septa divide gland into lobes
and lobules
• Parenchyma = cells that secrete
• Acinus = cluster of cells surrounding the duct draining
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those cells
Types of Exocrine Glands
• Simple glands - unbranched duct
• Compound glands - branched duct
• Shape of gland
– acinar - secretory cells form dilated sac
– tubuloacinar - both tube and sacs
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Types of Secretions
• Serous glands
– produce thin, watery secretions
• sweat, milk, tears and digestive juices
• Mucous glands
– produce mucin that absorbs water to form a
sticky secretion called mucus
• Mixed glands contain both cell types
• Cytogenic glands release whole cells
– sperm and egg cells
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Holocrine Gland
• Secretory cells disintegrate to deliver their
accumulated product
– oil-producing glands of the scalp
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Merocrine and Apocrine
Secretion
• Merocrine glands release their
product by exocytosis
– tears, gastric glands,
pancreas, etc.
• Apocrine glands are merocrine
glands with confusing
appearance (apical cytoplasm
not lost)
– mammary and armpit sweat
glands
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Mucous Membranes
• Epithelium, lamina propria and muscularis mucosae
• Lines passageways that open to the exterior: reproductive,
respiratory, urinary and digestive
– Mucous (movement of cilia) trap and remove foreign particles
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and bacteria from internal body surfaces
Membrane Types
• Cutaneous membrane = skin
– stratified squamous epithelium over connective
tissue
– relatively dry layer serves protective function
• Synovial membrane lines joint cavities
– connective tissue layer only, secretes synovial fluid
• Serous membrane (serosa) –internal membrane
– simple squamous epithelium over areolar tissue,
produces serous fluid
– covers organs and lines walls of body cavities
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Tissue Growth
• Hyperplasia = tissue growth through
cell multiplication
• Hypertrophy = enlargement of
preexisting cells
– muscle grow through exercise
• Neoplasia = growth of a tumor (benign
or malignant) through growth of
abnormal tissue
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Changes in Tissue Types
• Tissues can change types
• Differentiation
– unspecialized tissues of embryo become
specialized mature types
• mesenchyme to muscle
• Metaplasia
– changing from one type of mature tissue to
another
• simple cuboidal tissue before puberty changes
to stratified squamous after puberty
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Stem Cells
• Undifferentiated cells with developmental
plasticity
• Embryonic stem cells
– totipotent (any cell type possible)
• source = cells of very early embryo
– Pluripotent (tissue types only possible)
• source = cells of inner cell mass of embryo
• Adult stem cells (undifferentiated cells in
tissues of adults)
– multipotent (bone marrow producing several
blood cell types)
– unipotent (only epidermal cells produced)
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Tissue Shrinkage and Death
• Atrophy = loss of cell size or number
– disuse atrophy from lack of use (leg in a cast)
• Necrosis = pathological death of tissue
– gangrene - insufficient blood supply
– gas gangrene - anaerobic bacterial infection
– infarction - death of tissue from lack of blood
– decubitus ulcer - bed sore or pressure sore
• Apoptosis = programmed cell death
– cells shrink and are phagocytized (no
inflammation)
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Tissue Repair
• Regeneration
– replacement of damaged cells with original
cells
– skin injuries and liver regenerate
• Fibrosis
– replacement of damaged cells with scar
tissue
• function is not restored
– healing muscle injuries, scarring of lung tissue in TB or
healing of severe cuts and burns of the skin
– keloid is healing with excessive fibrosis
(raised shiny scars)
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Tissue Engineering
• Production of tissues and organs in the lab
– framework of collagen or biodegradable polyester
fibers
– seeded with human cells
– grown in “bioreactor” (inside of mouse)
• supplies nutrients and oxygen to growing tissue
• Skin grafts already available
– research in progress on heart valves, coronary
arteries, bone, liver, tendons
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Wound Healing of a Laceration
• Damaged vessels leak
blood
• Damaged cells and mast
cells leak histamine
– dilates blood vessels
– increases blood flow
– increases capillary
permeability
• Plasma carries antibodies,
clotting factors and WBCs
into wound
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Wound Healing of a
Laceration
• Clot forms
• Scab forms on
surface
• Macrophages
start to clean
up debris
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Wound Healing of a
Laceration
• New capillaries grow
into wound
• Fibroblasts deposit
new collagen to
replace old material
• Fibroblastic phase
begins in 3-4 days
and lasts up to 2
weeks
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Wound Healing of a
Laceration
• Epithelial cells
multiply and spread
beneath scab
• Scab falls off
• Epithelium thickens
• Connective tissue
forms only scar
tissue (fibrosis)
• Remodeling phase
may last 2 years
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