Basic Histology and Connective Tissue Chapter 5

Histology, the Study of Tissues

Tissue Types

Connective Tissues

Histology is the Study of Tissues 200 different types of cells in the human body.

A Tissue consist of two or more types of cells that function together.

Four basic types of tissues:

epithelial tissue

connective tissue

muscular tissue

nervous tissue

An Organ is a structure with discrete boundaries that is composed of 2 or more tissue types.

Example: skin is an organ composed of epidermal tissue and dermal tissue.

Distinguishing Features of Tissue Types Types of cells (shapes and functions) Arrangement of cells Characteristics of the Extracellular Matrix:

proportion of water types of fibrous proteins composition of the ground substance

ground substance is the gelatinous material between cells in addition to the water and fibrous proteins

ground substance consistency may be liquid (plasma), rubbery (cartilage), stony (bone), elastic (tendon)

Amount of space occupied by cells versus extracellular matrix distinguishes connective tissue from other tissues

cells of connective tissues are widely separated by a large amount of extracellular matrix

very little extracellular matrix between the cells of epithelia, nerve, and muscle tissue

Embryonic Tissues An embryo begins as a single

cell that divides into many cells that eventually forms 3 Primary Layers:

ectoderm (outer layer)

forms epidermis and nervous system

endoderm (inner layer)

forms digestive glands and the mucous membrane lining digestive tract and respiratory system

mesoderm (middle layer)

Forms muscle, bone, blood and other organs.

Histotechnology Preparation of specimens for histology:

preserve tissue in a fixative to prevent decay (formalin) dehydrate in solvents like alcohol and xylene embed in wax or plastic slice into very thin sections only 1 or 2 cells thick float slices on water and mount on slides and then add color with

stains

Sectioning an organ or tissue reduces a 3-dimensional structure to a 2-dimensional slice.

Planes of Section

Longitudinal section

tissue cut along the longest direction of a structure

Cross section

tissue cut perpendicular to the length of a structure

Oblique section

tissue cut at an angle between a cross section and a longitudinal section

Two Dimensional Sections of Solid Three

Dimensional Objects

Slicing through a boiled egg is similar

to sectioning a cell

and its nucleus.

Slices 1 and 5

miss the yolk.

Yolk appears larger in section 3 than in

sections 2 and 4.

1 5

1 2 3 4 5

2 3 4

Sections of Complex Hollow Structures

Image A is a cross section of a curved

tubular structure like a

blood vessel or a

section of intestine.

Image B is a longitudinal section of a

spiraling, tubular

structure like a sweat

gland.

Notice what a single slice could look like.

A B

Epithelial Tissue (Epithelia) One or more layers of closely adhering cells. Forms a flat sheet with an unattached free surface (may be

exposed to the environment or an internal body cavity) and a basal surface attached to the basement membrane made of collagen.

Epithelia are avascular. Epithelial cells depend on diffusion of nutrients from capillaries in the underlying connective tissue or from the free surface.

Epithelia are innervated by sensory neurons. Basement membrane is a is semi-permeable layer of collagen

and adhesive proteins that anchors epithelial cells to underlying connective tissue.

The connective tissue under an epithelium is called the lamina propria.

Free Surface

Lamina Propria

Basal Surface

Naming Epithelia Epithelia are named for:

the number of layers of cells

simple epithelium = one layer of cells

stratified epithelium = more than one layer of cells

pseudostratified epithelium = simple that looks stratified

the shape of cells at the surface

squamous cuboidal columnar transitional

surface modifications cilia microvilli keratinization

Simple

Squamous

Epithelium

Single row of squamous (flat)

cells.

Can allow rapid diffusion of

substances or

secretion of fluid.

Example: lining of blood vessels or

lining of lung

alveoli

Simple Cuboidal Epithelium

Single row of cube-shaped cells

Functions include absorption, secretion, conduction

Example: most kidney tubules

Simple Columnar Epithelium

Single row of tall, narrow cells

Free Surface may have microvilli or cilia

Layer of microvilli is called the brush border

Functions: absorption, secretion (of mucus)

Example: Lines the intestines

Mucus

Microvilli

Absorptive Cell

Goblet Cell

Nucleus

Pseudostratified Epithelium

Single row of cells all attached to basement membrane Not all cells reach the free surface

nuclei of basal cells give a stratified appearance Secretes and propels respiratory mucus Example: lining of trachea

Basal

Cells

Goblet

Cells

Cilia

Mucous Membranes

Consists of a mucous-producing epithelium and underlying layers of connective tissue (lamina propria) and smooth muscle (muscularis mucosae).

Lines passageways that open to the exterior: digestive, respiratory, urinary and reproductive tracts.

Mucous forms a barrier and traps foreign particles or pathogens.

Epithelia of upper respiratory tract and parts of the reproductive tract (oviducts) are ciliated to sweep the mucous out of the body.

Stratified Epithelia

Composed of more than one layer of cells.

Always named for shape of surface cells.

Deepest cells sit on basement membrane and are the source of replacement cells for the epithelium.

Keratinization:

keratinized epithelium has surface layer of dead cells that contain abundant protein and are surrounded by lipids

nonkeratinized epithelium has living cells with nuclei in all layers

Nonkeratinized

Stratified

Squamous

Stratified epithelium of living cells forms an

abrasion-resistant,

moist, slippery layer.

Examples: lining of the mouth, esophagus,

vagina

Keratinized Stratified Squamous Epithelium

Surface layer of dead squamous cells surrounded by lipids and packed with granules of keratin protein.

Dead layer is keratinized or cornified. Retards water loss and prevents penetration of

microorganisms.

Example: skin

dead, keratinized

epithelial cells

living epithelial

cells

connective tissue

Stratified Cuboidal and Columnar Epithelium

In certain ducts, stratified columnar and cuboidal epithelia can occur. As epithelial types, both are

uncommon. Basal cells are typically cuboidal with

surface cells either columnar or cuboidal.

Example: large ducts of salivary glands

sweat gland duct kidney collecting duct

Stratified Columnar Epithelium

Transitional

Epithelium

Stratified epithelium with

rounded (domed)

surface cells.

Stretches to allow storage of urine.

Example: urinary bladder.

Quiz is on material up to this

point.

Intercellular Junctions

All cells except blood cells are anchored to each other or to the matrix surrounding them by intercellular junctions.

Tight Junctions

Tight junctions completely encircle the cell (like a sweat band around a persons head)

Tight Junctions form a zipper-like pattern of complementary grooves and ridges that prevent

substances and bacteria from passing between

cells.

Tight Junctions

Desmosomes Attachment between cells that holds them

together against mechanical stress (shearing forces).

A mesh of protein filaments connects integral membrane proteins and cytoskeletal proteins.

Abundant in muscle and skin

Hemidesmosomes attach

cells to the basement

membrane.

Desmosome

Hemidesmosome

Gap Junctions

Also called communicating junctions.

Cluster of tube-shaped transmembrane proteins that make channels between cells.

Small solutes and electrical signals pass directly from cell to cell and can synchronize the activity

of groups of cells.

Found in embryos, cardiac muscle and smooth muscle.

Gap Junction

Glands Glands secrete substances for elimination or for use

elsewhere in the body

Glands are composed predominantly of epithelial tissue

Exocrine glands maintain connection to the surface through a duct (examples: sweat glands, salivary glands)

Endocrine glands have no ducts but secrete their products (hormones) onto capillaries for absorption directly into bloodstream (pituitary, adrenal) or into interstitial fluid

Mixed organs have both types of glands:

pancreas secretes digestive enzymes into ducts and hormones into blood

gonads release gametes into ducts and secrete hormones into blood

Types of Glandular Secretions Serous

thin, watery secretions such as sweat, milk, tears and digestive juices.

Mucus

the sticky secretion called mucus is a glycoprotein, mucin, that absorbs water

Mixed Glands secrete both serous fluid and mucus

Note: Mucus is a noun. Mucous is an adjective. Mucus is secreted by mucous glands.

Cellular mechanisms of glandular secretion include:

1) merocrine

2) apocrine

3) holocrine

Merocrine Secretion

Cells of Merocrine Glands release their product by exocytosis.

Clusters of secretroy cells are called acini.

Products include tears, sweat, milk, pancreatic enzymes, gastric enzymes and acid

Duct

Acinus

1) Merocrine secretion is the most common type of glandular

secretion. Secretory cells produce secretory granules from the

Golgi. Secretory granules gather at the apical region of the

cell. Then, the granules membrane fuses with the apical membrane of the cell and the contents of the granule are

opened and released by the process of exocytosis.

Cellular Mechanisms of Glandular Secretion

2) Apocrine Secretion is a rare type of secretion dependent on

the action of sex hormones on glands. Granules in the

cytoplasm of secretory cells gather at the apical region of the

cell. Then, a part of the plasma membrane of the cell pinches

off a portion of the cytoplasm containing a granule. The vesicle

breaks down in the duct of the gland. Apocrine glands are

associated with hair follicles and become functional at puberty.

They respond to emotional or sensory stimuli (not to heat).

Examples of apocrine glands include the sweat glands in the

pubic and axillary regions.

Cellular Mechanisms of Glandular Secretion

3) Holocrine Secretion results from the breakdown and

discharge of entire secretory cells. This form of secretion is

unique to the sebaceous glands of the skin associated with

hair follicles.

Cellular Mechanisms of Glandular Secretion

Holocrine Secretion

Secretory cells proliferate at the base of the gland and move towards the duct as they mature. Once the cells are mature, they die and disintegrate. The cellular debris are released as the oily product of the cell.

Example: sebaceous glands are the oil-producing glands associated with hair follicles.

http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Epithelia/Epithel.htm

Connective Tissue Connective Tissues consist of widely spaced cells

suspended in an abundant extracellular matrix. The volume of the extracellular matrix is greater than the

volume of the cells.

Functions of Connective Tissues connects organs to each other divides body regions into compartments provides support, leverage and protection (physical and

immune)

covers and surrounds articular surfaces stores nutrients thermally insulates absorbs shock transports materials (water, nutrients, gases, waste,

hormones)

A Classification

Scheme for

Connective

Tissues

Embryonic Connective Tissue Mucoid Mesenchymal Tissue

Connective Tissue Proper Loose (areolar) Dense

Dense Regular Dense Irregular

Reticular Elastic

Specialized Connective Tissue Adipose

Yellow and White Brown

Hematopoietic

Supporting Connective Tissue Cartilage

Hyaline Cartilage Elastic Cartilage Fibrocartilage

Bone

Cells of Connective Tissues

All connective tissue cells are derived from mesoderm that developes in to mesenchymal cells as embryos develop.

Fibroblasts are the most abundant CT cell and they produce fibers and ground substance.

Adipocytes (fat cells) store triglycerides

Chondroblasts develop into chondrocytes as they produce cartilage

Osteoblasts develop into osteocytes as they produce bone

Hematopoietic Cells differentiate into blood cells Macrophages and Mast Cells can leave the blood and

enter the interstitial fluid between cells

Cells of Connective Tissues

Extracellular Matrix of Connective Tissue

The Extracellular Matrix is composed of:

Extracellular Tissue Fluid (mostly water, similar to blood plasma)

Protein Fibers

Ground Substance

Protein Fibers of the ECM Collagen Fibers

over a dozen distinct types of protein fibers

tough, flexible collagen fibers are abundant in tendons, ligaments, dermis of the skin, teeth, cartilage, bone

Reticular Fibers

thin, branched fibers that form a loose, interconnected network that hold cells, tissue fluid and ground substance

Located in distensible or spongy tissues (walls of blood vessels, dermis, lymph nodes, spleen, liver). Stain darkly with silver.

Elastic Fibers

also called yellow fibers because of their color in life

thin, straight fibers made of the protein elastin

stretch 150% resting length and recoil like a rubber band

give skin, lungs and arteries ability to stretch and recoil

Ground Substance of ECM Ground substance is a gelatinous or rubbery material mixed with CT fibers

and found in between CT cells.

Molecules have a negative charge that attracts Na+ which holds water. the water and salt help regulate electrolyte balance in tissues and help resist

tissue compression.

Ground substance consists of 3 classes of large molecules:

glycosaminoglycans (GAGs)

polymers of repeating disaccharides

important GAGs include chondroitin sulfate, glucosamine, hyaluronic acid, heparin

GAGs are especially abundant in cartilage, bone, tendon, joints, skin

proteoglycans

proteoglycans are GAGs linked to a protein core which form bottlebrush-shaped molecules (see structure on next slide)

adhesive glycoproteins

protein-carbohydrate complexes that stick cells to ECM

mark pathways for cell migration during development and healing

important glycoproteins include laminin and fibronectin

GAGs, Proteoglycans and Proteoglycan Aggregates

a proteoglycan

Proteoglycan Aggregate

The proteoglycan aggregate from cartilage, shown in the electron

micrograph on the left, is formed from a hyaluronate backbone attached to

proteoglycans. The middle diagram is of a small portion of the proteoglycan

aggregate showing core proteins of proteoglycans attached to a long

hyaluronate molecule. Chondroitin sulfate and keratan sulfate GAGs are

linked to core proteins forming many different proteoglycans. GAGs have a

repeating disaccharide structure.

Embryonic Connective Tissue

The Mucoid Mesenchymal Tissue of Embryonic Connective Tissue is semifluid with thin reticular fibers and relatively abundant mesenchymal cells and blood vessels. Whartons jelly of the umbilical cord is an example.

Wharton's Jelly Cyst in an Umbilical Cord

Connective Tissue Proper

Loose Connective Tissue (Areolar Tissue)

Dense Connective Tissue

Dense Connective Tissues

Dense Regular Connective Tissue

Dense Irregular Connective Tissue

Reticular Connective Tissue

Elastic Connective Tissue

Loose (Areolar)

Connective

Tissue Scattered cells include

thin fibroblasts, macrophages and mast cells.

Loose arrangement of thick, wavy collagen fibers (C) and thin dark-staining elastic fibers (EF).

Found under some types of epithelia including the mesentary of the digestive tract.

Contains nerves and blood vessels.

C

EF

Dense Regular Connective Tissue

Densely, packed, parallel collagen fibers

Fibroblasts sandwiched between fibers

Forms the strong, resilient tissue of tendons and ligaments

blood

vessel

Dense Irregular Connective Tissue

Densely woven collagen fibers with little open space and few cells

Withstands stresses applied in different directions

Forms the dermis of the skin and forms capsules around organs

Reticular Tissue

Loose network of thin, branched reticular fibers.

Supports cells in vascular, filtering organs like the liver lymph nodes, spleen, thymus and bone marrow.

Fibers are stained very dark with silver.

Elastic

Tissue Cross section of

the aorta shows

alternating layers

of muscle,

collagen fibers and

thinner, darker

staining elastic

fibers.

Special stains containing

solutions of metals

like silver are

needed to

visualize elastic

fibers.

People with Ehlers-Danlos

Syndrome usually have

hyperelasticity of the skin as shown

in these pictures. The unusually

elastic skin can be stretched much

further than normal skin because of

defective collagen synthesis in

connective tissues. This condition

also causes skin to be easily

bruised, heal poorly, and joints that

are unusually flexible (hyperflexible,

hypermobile).

Specialized Connective Tissue

Adipose Tissues

Unilocular (Yellow or White Fat)

Multilocular (Brown Fat)

Hematopoietic Tissue

Unilocular Adipose Tissue

White or yellow adipose cells are called unilocular adipocytes.

Unilocular adipocytes are large, empty-looking cells with the nucleus pressed against cell membrane (arrowhead). This shape is sometimes described as a signet ring.

Unilocular adipose is found beneath skin and surrounding organs. It is used for energy storage, insulation and for cushioning other tissues.

Multilocular Adipose Tissue

Brown Adipose cells are called multilocular adipocytes.

Multilocular adipose is found in human babies and in hibernating animals.

Cells have many mitochondria and many small droplets of fat. Multilocular adipocytes produce heat by breaking down stored fat. Heat is transferred to the blood through abundant capillaries.

Multilocular Adipose Tissue Distribution

Hematopoietic Connective Tissue (Blood)

Formed Elements are the blood cells classified as erythrocytes, leukocytes and platelets.

Non-formed Elements are the components of the blood plasma

erythrocyte

leukocytes

platelets

Supporting Connective Tissue

Cartilage

Hyaline Cartilage

Elastic Cartilage

Fibrocartilage

Bone

Compact Bone

Spongy Bone

Cartilage

Supportive connective tissue with a rubbery matrix

Cartilage is an avascular tissue (no blood vessels in the matrix) so cells rely on diffusion from a surrounding vascular membrane, the perichondrium, to deliver nutrients and remove wastes. (injured cartilage heals slowly if at all)

3 types of cartilage distinguished by the fibers of the extracellular matrix:

hyaline elastic fibrocartilage

Hyaline Cartilage

Fibrous, vascular capsule called the perichondrium covers a clear, non-fibrous matrix.

Chondrocytes produce the cartilage matrix. Each cell is in a pit called a lacuna.

Hyaline cartilage covers the ends of bones at all movable joints plus the sternal ends of ribs and is the supportive material in nose, larynx, trachea, bronchi.

Elastic Cartilage

Fibrous, vascular perichondrium

covers elastic

cartilage

The cartilage matrix has a

weblike mesh of

elastic fibers

among the

lacunae

Provides flexible, resilient, support

for the external

ear and epiglottis

Fibrocartilage

Chondrocytes in isolated clusters or rows in a matrix containing coarse, wavy collagen fibers.

Resists compression and absorbs shock Found in the pubic symphysis of the pelvis and the

intervertebral discs.

Bone

Bone matrix stores the minerals calcium and phosphorus.

Compact bone provides physical support for leverage during muscle contraction.

Spongy bone, also called trabecular or cancellous, fills the ends of long bones and supports the bone marrow.

Compact bone always covers spongy bone.

Compact Bone

Spongy Bone

Compact Bone and Spongy Bone

Muscle Tissue

Cells that respond to stimuli by contracting

Function is to exert physical force on other tissues

move bones

moves blood through vessels

expel urine and feces

3 types of muscle tissue: skeletal

cardiac

smooth

Skeletal Muscle

Long, cylindrical, unbranched cells with striations and multiple peripheral nuclei.

Function in movement, posture, breathing, speech, swallowing.

Cardiac Muscle

Short, striated cells connected to each other with intercalated discs.

Usually one central nucleus per cell. Sometimes cells are branched Found in heart and functions to pump blood.

Smooth Muscle

Short, fusiform cells; nonstriated with only one central nucleus.

Functions to control the diameter of openings in the gastrointestinal tract, respiratory tract, cardiovascular system

and parts of the reproductive system.

Neurons

Neurons may have long cell processes are usually surrounded by much smaller glial cells.

Neurons communicate with electrochemical signals at the tips of the axonal and dendritic processes.

Found in brain, spinal cord, nerves and ganglia.