CH3 Histology

Embryology

Formation of Tissues

Zygote

• Single cell produced after fertilization

• contains 46 chromosomes

Cleavage

Cell divisions during this stage produce a hollow ball of cells, takes about a week to complete

Blastocyst

Hollow ball of cells

Trophoblast

outer layer of the blastocyst that will form the placenta

Ectoderm

• cells that will form the epidermis of skin and epidermal derivatives

• nervous tissue and sense organs

• pituitary gland

• adrenal medulla

• enamel of teeth

• Lens of eye

Mesoderm

• cells that will form dermis of skin and epithelial lining of blood vessels, lymph vessels, and serous membranes

• muscle tissue

• connective tissue

• adrenal cortex

• heart, kidneys, ureters, internal reproductive organs, spleen

Endoderm

• cells that will form the epithelial lining of respiratory tract, GI tract, tympanic cavity, auditory tube, urinary tract, reproductive tract

• liver (most of)

• gallbladder

• pancreas

• palatine tonsils (portion of)

• thyroid gland

• parathyroid glands

• thymus

Epithelial tissue

• covers exposed surfaces

• lines internal passageways and chambers

• produces glandular secretions

Connective tissue

• fills internal spaces

• provides structural support

• stores energy

Muscular tissue

• contracts to produce movement

• includes skeletal muscle, cardiac muscle, and smooth muscle

Neural tissue

• conducts electrical impulses

• carries information

Epithelial, connective, muscular, neural

Four primary tissue types

Epithelial tissue

• No intercellular space, tightly packed cells

• Avascularity

  • no blood vessels

• Sheets and layers

  • sheets of cells

  • single or multiple layers thick

• regeneration of surface cells via stem cells

• polarity - structural and functional differences between top and bottom of cells

  • exposed apical surgace

  • have an attached basal surface

  • apical/basal surfaces are structurally and functionally different

Functions of epithelial tissue

• provides physical protection

  • from abrasion, dehydration, and destruction

• controls permeability

• sensory cells

  • general (touch)

  • neuroepithelia (sense organs)

• produces secretions

  • unicellular glands

  • glandular epithelia

Apical surface structures

Microvilli, stereocilia, cilia

Microvilli

Short, can move;

• increases surface area

• line urinary and digestive track

Stereocilia

long, rigid

• inner ear and male reproductive tract

Cilia

long, can move

• move substances over apical surface

• line respiratory tract

Intercellular connections

Give epithelium strength and stability

• holds cells together

• prevents passage of chemicals, water, pathogens

• Gap junctions, CAMs, tight junctions, hemidesmosome, and proteoglycans

• also bind cells to basal lamina

Epithelial renewal

• must be replaced frequently due to exposure/use

• disruptive enzymes

• toxic chemicals

• pathogens

• mechanical abrasion

• replaced through time via continual division of stem cells near basal lamina

Simple and stratified

Two types of layering

Simple epithelium

• one layer of cells

• protected internal compartments of body

Stratified epithelium

• two or more layers of cells

• areas of mechanical or chemical stresses

Squamous epithelium

relatively flat, “pancakes”

Cuboidal epithelium

shaped like cubes

Columnar epithelium

longer than wide; columns

Simple squamous epithelium

• Thin delicate layer

• reduces friction, controls vessel permeability, performs absorption and secretion

• lining body cavities

• lining heart and blood vessels

• alveoli

Stratified squamous epithelium

• physical barrier, some surfaces keratinized

• mucosal linings are nonkeratinized

• lining of orfices

• surface of skin

Simple cuboidal epithelium

• secretion, absorption

• thyroid gland

• renal tubules

• ducts

Stratified cuboidal epithelium

• secretion, absorption

• ducts of sweat glands

• ducts of mammary glands

• Lumen: center of duct/tube

Simple columnar epithelium

• highly polarized

• high secretion, high absorption

• stomach, intestine, gallbladder, uterine tubes, renal collecting ducts

• most have microvilli/cilia

Stratified columnar epithelium

• high activity areas

• protection

• pharynx, epiglottis, anus, mammary glands, salivary glands, and urethra

Pseudostratified ciliated columnar epithelium

• protection, secretion

• have cilia, actually a simple epithelium

• appears as stratified but is actually simple

• nasal cavity, trachea, bronchi, male reproductive tract

Transitional epithelium

• “stretchy”, expansion, recoil

• mainly cuboid, but mix of others

• renal pelvis, ureters, bladder

Glandular epithelium

Classified based on: type of secretion released, structure of gland, mechanism of secretion

Exocrine and endocrine

Types of glands

Exocrine glands

ducts to an epithelial surface, body opening, or space

Endocrine glands

into ECF then to blood stream or lymph, hormones

Serous, mucous, mixed

Types of exocrine glands

Unicellular

Mucins

• goblet cells (mucous cell)

• isolated from other glandular cells

Multicellular

• secretory sheets and clusters, mixed

Gland cells

Duct cells

Compound tubular gland

Ex. mucous glands in oral cavity

Compound alveolar gland

Ex. mammary glands

Compound tubuloalveolar gland

Eccrine secretion

• secretory product is packaged into secretory vesicles

• exocytosis

• can be continuous

• fastest secretion rate

• ex. salivary glands

Apocrine secretion

• product released during shedding of apical portion of cell

• non-continuous

• production in waves

• ex. mammary glands

Holocrine secretion

• lysis of entire cell

• typically oily products

• slowest production rate

• ex. sebaceous gland cells

Embryonic connective tissue

Connective tissue

Specialized cells, extracellular protein fibers, ground substance

• establishing body’s structural framework

• transport fluid and dissolved materials

• protect organs

• support, surround, and connect other tissues

• store energy

• defend body from mic0ororganisms

Matrix

• extracellular component of protein fibers and “ground substance” (fluid portion)

• Matrix of bone is calcified

• connective tissue cells embedded within it

collagen, reticular, and elastic fibers, ground substance

Fibers of connective tissue

Collagen fibers

high tensile strength, tendons and ligaments

Reticular fibers

structural mesh within organs

Elastic fibers

protein called elastin: “rubbery”, lines vasculature

Ground substance

Thick syrupy consistency, mix of proteins and carbohydrates

Connective tissue proper

matrix of loose fibers and dense fibers

Fluid connective tissue

watery matrix of dissolved proteins

• blood and lymph

Supporting connective tissue

dense matrix of fibers and may have insoluble calcium salts

• cartilage and bone

Loose connective tissue proper

Fibers create loose, open framework

• areolar tissue

• adipose tissue

• reticular tissue

Dense connective tissue proper

fibers are densely packed

• dense regular

• dense irregular

• elastic

Blood

contained in cardiovascular system

Lymph

contained in lymphatic system

Cartilage

solid rubbery matrix

• hyaline cartilage

• elastic cartilage

• fibrous cartilage

Bone

solid, crystalline matrix

Areolar tissue

• “Stuffing” of body

• light connection that allows movement between skin and muscle

• cushions organs

• within deep dermis of skin

Adipose tissue

• padding

• white fat: energy storage

• brown fat: thermogenesis

• Deep to the skin

Reticular tissue

• “structural sponge”

• matrix is stiffest of loose CT

• provides supporting framework

• liver, kidney, spleen, lymph nodes, bone marrow

Dense regular connective tissue

• ligaments

• tendons

• aponeuroses

• high tensile strength

• provides firm attachment, conducts pull of muscle, reduces friction, stabilizes relative positions of bones

• between skeletal muscles and skeleton, between bones or stabilizing positions of internal organs, covering skeletal muscles

Dense irregular connective tissue

• organ sheaths

• provides strength to resist forces applied from many directions, prevents over-expansion

• capsules of viceral orangs, periostea and perichondria, nerve and muscle sheaths, dermis

Elastic connective tissue

• “rubbery”

• springy and resilient

• stabilizes positions of vertebrae and penis, cushions shocks, permits expansion and contraction of organs

• Between vertebrae of spinal column, ligaments supporting penis, ligaments supporting transitional epithelia, in blood vessel walls

FCT matrix

Matrix of watery mixture of dissolved proteins

• blood and lymph

Blood

• erythrocytes (red blood cells): gas transport

• leukocytes (white blood cells): immune function

• thrombocytes (platelets): blood clotting

• plasma: matrix

Lymph

monitors for signs of infection, mainly lymphocytes (T and B cells), but some phagocytic cells

Cartilage

Contains chondrocytes

• gel matrix made of chondroitin sulfate

• cells reside in lacunae

• avascular

• have a fibrous perichondrium

  • cellular layer: maintenance

  • fibrous layer: connection to other structures

• most cartilage cannot repair severe damage

Hyaline cartilage

• tracheal rings

• costal cartilage

• joints

• provides stiff but somewhat flexible support

Elastic cartilage

• most flexible cartilage

• provides support but tolerates distortion without damage and returns to original shape

• auricle of external ear, epiglottis, auditory canal, cuneiform cartilages of larynx

Fibrous cartilage

• firmest, strongest cartilage

• resists compression, prevents bone-to-bone contact, limits relative movement

• pads within knee joint, between pubic bones of pelvis, intervertebral discs

Periosteum

External surface of bone

Endosteum

Internal surface of bone

Lamellae

mix of collagen fibers and calcium salts in bone

Membrane

Epithelia + connective tissue

• sheet of epithelial cells

• and underlying connective tissue

• mucous

• serous

• cutaneous

• synovial

Mucous membrane

coated with secretions of mucous glands, line most of digestive and respiratory tracts and portions of urinary and reproductive tract

Serous membrane

Line the peritoneal, pleural, and pericardial body cavities

Cutaneous membrane

covers skin/outer surface of the body

Synovial membrane

line joint cavities and produce the fluid within the joint

Sarcoplasm

Muscle tissue cytoplasm

Sarcolemma

Muscle tissue cell

Skeletal muscle tissue

• cells are long, cylindrical, striated, and multinucleate

• voluntary or reflex arcs

• combined with connective tissues and neural tissue in skeletal muscles

• moves or stabilizes the position of the skeleton

• hypertrophy not hyperplasia via myosatellites

Cardiac muscle tissue

• cells are short, branched, and striated, usually with a single nucleus, interconnected by intercalated discs

• myogenic

• branched: “mesh”

• scar tissue

• location: heart

• circulates blood, maintains blood pressure

Smooth muscle tissue

• cells are short, spindle-shaped, and nonstriated, with a single central nucleus

• can replicate

• reflex arcs are myogenic

• found in walls of blood vessels and in digestive, respiratory, urinary, and reproductive organs

• moves food, urine, and reproductive tract secretions

• involuntary

Neuroglia and neurons

Neural cell types

Neuroglia

supporting cells of neural tissue, can divide

Neuron

specialized to conduct electrical signals (action potential)

• longest cells in body

• incapable of cell reproduction

Dendrite

receives stimuli on neuron

Axon

transmits a signal (action potential) down neuron