Histology IHistology IHistology I

Dr. Carmen E. RexachAnatomy 35

Mt San Antonio College

Histology• Study of tissues • Tissues = a group of cells

performing a common function

• Microscopic anatomy• Includes how different

tissues are arranged to form organs and other structures

Extracellular matrix: cell surface

• Composition– Fibrous structural and adhesion proteins

embedded in gelatinous polysaccharide ground substance

• Function– Binds cells together to form tissues

Extracellular matrix: cell surface

Cell Junctions• Tight junctions

– Near apical surface• Adhering junctions

– Below tight junctions• Desmosomes

– Sites that stretch• Gap junctions

– Shared cytoplasm

Tissue sections

Longitudinal sections Transverse or cross section

Tissue sections

Primary tissue classes

• Epithelial• Connective

• Differences– Matrix

• variation• Primary constituents

– Fibrous proteins– Ground substance

– Amount of cells vs matrix

• Nervous• Muscular

Epithelial tissue• Composition

– One or more layers of closely adhering cells– Apical surface and basal surface– Rest on a basement membrane– Avascular– Supported by connective tissues

• Function– Cover organ surfaces– Form secretory tissue– Form ducts of glands

Classification

• Criteria– Number of cell layers– Morphology of the

surface cells• Two major categories

– Simple (one layer)– Stratified (two or more

layers)

Cell shape• Squamous

• Cuboidal

• Columnar

• Acinar

Simple Epithelia

• General– All cells touch basement membrane

• Exception: Pseudostratified columnar

• Categories– Simple squamous– Simple cuboidal– Simple columnar– Pseudostratified columnar

Simple Epithelia

Microvilli vs. Cilia

Microvilli are folds in the apical surface of the plasma membrane. They increase cell surface area.

Cilia are composed of microtubules and project from the apical surface. Function: to move things across the cell surface

Acini

• Acinar cells are often arranged in a circle (acinus, acini), creating structures that resemble flowers or a pie that’s been cut into slices.

• Many exocrine glands are composed of acini.

Stratified Epithelia• General characteristics

– Up to 20 or more cell layers– Named for shape of surface cells

• Exception: transitional epithelium• Stratified squamous

– Most common– Exfoliation– Keratinized tissue (cornified)– Nonkeratinized

Stratified epithelia

Transitional epithelium

Note the “dome cells” at the apical surface

Connective Tissue

• Less cells, more ECF (ground substance)• Variable, widely distributed, most

abundant• Three categories of mature tissue

– Fibrous CT– Supportive CT (bone, cartilage)– Fluid CT (blood)

Functions

• Binds organs• Support• Protection

– Physical– Immune

• Movement• Storage• Heat production• Transportation

Fibrous Connective Tissue: Components

• Cells– Fibroblasts– Macrophage– Leukocytes– Plasma Cells– Mast Cells– Adipocytes

• Fibers – Collagenous– Reticular– Elastic

• Ground substance

Types of Fibrous CT• Loose

– Lots of ground substance– dissolves in vitro– Types

• Areolar, reticular, adipose• Dense

– Fiber is predominant component– Types

• Dense regular, dense irregular

Loose CT

Areolar connective tissue

Reticular connective tissue

Adipose connective tissue

Areolar Connective Tissue• Cells

– All six types• Matrix

– Predominately collagenous– Some elastic/reticular

• General– Very vascular– Loosely organized– Varied– Underlies almost all

epithelial tissue

Reticular• Reticular fibers and fibroblasts• Stroma of organs and tissues such as

lymph nodes, spleen, thymus, bone marrow

Adipose Tissue

• Adipocytes most abundant cell type

• Supported by areolarCT, reticular CT, blood vessels

• Function: energy storage

• White fat vs. Brown fat

Dense Connective Tissue• Dense Regular

– Closely packed parallel collagen fibers + fibroblasts

– Tendons and ligaments

– Yellow elastic tissue• Elastic fibers• Fibroblasts with

larger nuclei– Wavy elastic sheets

in walls of medium/large arteries

• Dense Irregular– Collagen fibers in

random arrangement + fibroblasts

– Dermis, protective capsule around organs, fibrous sheet around bones, etc.

– Similar to areolar, but less “open”space

Dense Connective Tissue

Dense Regular Dense Irregular

Cartilage• Flexible matrix• Avascular except when

transforming to bone• External ear, tip of nose,

larynx• Cells

– Chondroblasts• secrete matrix

– Chondrocytes• trapped in lacunae

• Three types– Hyaline– Elastic– Fibrocartilage

Hyaline Cartilage• Matrix

– smooth, frictionless – mix of collagen, elastin,

chondroitin (a glucosaminoglycan)

• Cells– Cell nests

• Usually covered by perichondrium– Dense irregular CT covering– inner layer produces new

chondrocytes• Examples:

– Costal cartilage– Nasal septum– C-ring cartilage of trachea– Fetal skeleton

Elastic Cartilage

• Matrix– Web-like mesh of

elastic fibers– Appearance of fur

• Perichondriumalways present

• Examples:– Pinna– Epiglottis

Fibrocartilage• Characteristics

– Parallel collagen fibers

– Rows of chondrocytes in lacunae

– No perichondrium• Examples

– Pubic symphysis– Intervertebral

discs– Menisci of the

synovial joints

Bone• Two forms

– Spongy• Heads of long

bone• Named for

appearance– Compact

• No visible spaces• Dense calcified

tissue• External surface

of all bone

• Structure of compact bone– Haversian canal– Osteon– Lamellae– Lacunae– Canaliculi

• Periosteum

Compact Bone

Blood• Plasma + formed

elements• Erythrocytes• Leukocytes

– Neutrophils– Basophils– Eosinophils– Monocytes– Lymphocytes

Hemopoiesisformation of formed elements

Nervous Tissue

• Excitable tissue• Function

– Rapid communication

• Cell types– Neurons– Neuroglia

Neurons

• impulse: an all or none electrical event

• neurotransmitters: chemical messengers released by neurons

Neuron

Neuroglia (nerve glue)

• 6 subtypes• highly branched

like neurons• not capable of

impulses• perform supportive

(connective tissue type) functions

astrocyte

Nerves: Cross section

Muscular Tissue• Contracts when stimulated• Three types

– Skeletal• Striated, multinucleated, voluntary• Muscle fibers

– Cardiac• Striated, uninucleate, involuntary• Short branching cells• Intercalated discs

– gap junctions– desmosomes

– Smooth• No striations, uninucleate, involuntary• Short fusiform cells• Visceral muscle

Muscular Tissue

Skeletal Muscle

Cardiac muscle

Smooth muscle