Histology

The Tissue Level of Organization

Histology The study of tissues and how tissues

are combined in various ways to form organs & membranes of the human body.

The human body contains four primary types of tissues: Epithelial Connective Muscle Neural (nerve) tissue.

I. Epithelial Tissue Made of cells with little space

between cells. The cells are so tightly packed

together that blood vessels can’t penetrate between them and is called avascular.

Epithelial Tissue In certain areas of the body epithelial tissue may perform

the following functions: Control Permeability: Provide Sensitivity Provide Physical Protection: Produce Secretions:

Epithelial Tissue Two Types Covering & Lining and

Glandular.1.Covering & Lining Epithelia is

classified based on the number of cell layers and the cell shape.

2.Glandular Epithelia is classified based on if the tissue secretes its product into a gland or not.

Covering & Lining Epithelial Classification based on:

Number of cell layers.• Simple- single layer.• Stratified- many layers.• Pseudostratified- appears to be many layers

but is actually a single layer. Cell Shape.

• Squamous- Flat.• Cuboidal- Cube shaped.• Columnar- Rectangular.• Transitional- Cuboidal & Squamous.

Simple Squamous Flat cells with central nucleus. Function: Permits the efficient

diffusion of materials. Location: Lining of body cavities,

lines the walls of blood & lymphatic vessels, forms the walls of air sacs.

Simple Squamous

Simple Cuboidal Single layer of cube-shaped cells

with central nucleus, often have cilia and/or microvili.

Function: Forms the walls of small ducts and tubes that carry secretions.

Location: Kidneys, Liver, Glands.

Simple Cuboidal

Simple Columnar Single layer of rectangle cells whose

nuclei lie near the base (basal) of the cell.

Function: Absorb and secrete; mucus, enzymes, etc.

Location: Uterus, Stomach, Digestive Tract, Bronchi.

Simple Columnar

Stratified Squamous Multiple layers, only top layer is

squamous the deeper layers are cubiodal and or columnar.

Function: Covers areas that must resist wear & tear, protects openings of the body from abrasions.

Location: Esophagus, Mouth, Nose, Vagina, etc.

Stratified Squamous

Stratified Cuboidal Function: Protection. Location: Sweat Glands. Mammary

Glands, Salivary Glands.

Stratified Cuboidal

Stratified Columnar Function: Protection & Secretion. Location: Male Urethra, some large

ducts, rare in the body.

Stratified Columnar

Pseudostratified Columnar Appears to be multilayered but is

not. Function: Often contains cilia which

creates currents to move mucus. Location: Lines parts of respiratory

tract, such as the trachea & bronchi.

Pseudostratified Columnar

Pseudostratified

Transitional Multilayered cube-like cell shape. Function: Can stretch(elasticity) and

return to the original shape (extensibility).

Location: Lines Bladder, Urethra, Ureters.

Transitional

Glandular Epithelium Tightly packed cells that specialize in

manufacturing and secreting products. Two categories:

Exocrine: Releases products into ducts.• sweat & oil glands, salivary, and mucus

glands. Endocrine: Releases products into

extracellular space (blood)• pituitary gland, thyroid gland, and adrenal

gland.

II. Connective Tissue Is composed of scattered loosely packed

cells that are within a large amount of nonliving intercellular material.

It is vascular Its primary function is to hold other

tissues and organs in place. Two categories of connective tissue

Produces & Maintains-(matrix) Protects From Infection (white blood cells)

Connective Tissue 4 Types of connective tissue

• A. Connective tissue proper• B. Cartilage• C. Bone• D. Blood forming (spongy bone)

A. Connective Tissue Proper Types of connective tissue proper:

Areolar, Adipose, Reticular, Dense Connective.

1. Areolar Tissue: AKA: Loose Connective Tissue. Contains fibroblast(producing cells) and

macrophages (protecting cells). Function: Anchors and cushions organs,

vessels, nerves. Fights bacteria. Stores lipids.

Areolar Tissue

A. Connective Tissue Proper 2. Adipose Tissue:

Contains adipocytes (producing cells which contain deposits of fat).

Function: Provides reserve energy, insulates & protects organs.

Adipose Tissue

A. Connective Tissue Proper

3. Dense Connective Tissue Two Types:

•Dense Regular- Fibers are arranged in parallel fashion. Extremely resistant to stress.

• tendons (muscle to bone)• ligaments (bone to bone)

•Dense Irregular- Fibers are arranged in an interwoven meshwork. Forms an external wrapping.

• Location: Wrapped around bone, cartilage, kidneys, liver, spleen, and where the tendon connects to the bone.

Dense Regular

Dense Irregular

A. Connective Tissue Proper 4.Reticular

Location: Lymphoid organs Function: Form a soft internal skeleton

to support other tissues.

Reticular Tissue

B. Cartilage Harder than connective tissue

proper. Contains chondrocytes (producing

cells). There are three types of cartilage:

Hyaline, Elastic, Fibrocartilage.

B. Cartilage 1. Hyaline Cartilage-

Bluish-white in color. Most abundant of all three. Function: Supports and reinforces,

with-stands compression. Location: Forms embryonic skeleton,

upper respiratory tract, costal cartilage, moveable joints.

Hyaline Cartilage

B. Cartilage 2. Elastic Cartilage

Yellowish in color. Function: Maintains shape allows for

flexibility. Location: Ears, Nose, Epiglottis.

Elastic Cartilage

B. Cartilage 3. Fibrocartilage

Has an abundance of collagen. Is found in association with hyaline

cartilage. Function: Shock absorber. Location:intervertebral disc, pubis

symphysis, knee joint.

Fibro Cartilage

C. Bone Has dense intercellular material

composed of mineral salts and collagenous fibers.

Made up of osteocytes Also known as osseous tissue. Two Types of BoneTwo Types of Bone

Compact and Spongy.

C. Bone Compact Bone: Forms the bones of

the skeletal system. Function: Provide structural support,

stores calcium. Location: All bones, the hard outside

layer of bone.

Bone (compact)

C. Bone Spongy Bone: Found inside of compact

bone. Has blood forming tissue called red marrow. Function: to produce blood cells. Location: inside the bone of the skeletal

system. Blood: is a type of connective tissue known

as formed elements.• Also know as liquid tissue• Has both solid (formed elements) and liquid

components.

Red Blood Cells

Spongy Bone

III. Muscle Tissue made of specialized cells that

contain protein filaments which allow the cells to contract.

The protein fibers are arranged in parallel bundles.

The Three types of muscle are: Skeletal, Smooth, and Cardiac.

A. Skeletal Muscle Striated (has bands of stripes). Multi-nucleated Attaches to bone, is the primary

mover in the muscular system. Voluntary (you control). Function: Body movement.

Skeletal Muscle

B. Smooth Muscle Not striated, Single Nucleus. In the walls of blood vessels and

visceral organs. Involuntary (not consciously

controlled). Function: Movement of: food, blood

urine, child birth etc.

Smooth Muscle

C. Cardiac Muscle Striated, Single Nucleus Contains thick cell membranes

called intercalated disks. Found in the walls of the heart. AKA myocardium. Involuntary. Function: move blood in the

circulatory system.

Cardiac Muscle

IV. Nervous Tissue Has well developed properties of

conductivity and excitability. Transmits electrochemical signals. Two Types of Nervous Tissue:

Neurons-Basic functioning unit of nervous tissue conducts electrochemical messages.

Neuroglia- Cells of the spinal cord and brain that maintain and support neurons.

Nervous Tissue