Download Stratified epithelium contains more than one layer named by shape

Chapter 5
Histology
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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
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
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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
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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
• 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
– 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
– 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
Intercellular
Junctions
• All cells (except blood) anchored to each other or
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
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
Gap Junctions
• Ring of transmembrane
proteins form a waterfilled channel
– small solutes pass
directly from cell to
cell
– in embryos, cardiac
and smooth muscle
Glands
• A gland is a cell or organ that secretes substances
in the body or releases them for elimination.
• 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
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
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
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
Holocrine
Gland
• Secretory cells disintegrate to deliver their
accumulated product
– oil-producing glands of the scalp
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
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 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
Membranes
Cutaneous Membrane
Serous Membrane
Synovial Membrane
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
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
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)
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)
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)
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
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
Wound Healing of a Laceration
• Clot forms
• Scab forms on
surface
• Macrophages
start to clean up
debris
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
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