FALL SEMESTER 2024

Instructor: Anthony Uzwiak Made by: Ruby :x

uzwiak@dls.rutgers.edu

Structural Organization

An understanding of the various primary tissue types present in the human body is essential for understanding the structure and function of organs.

Topics included:

1. Identity the four basic tissue types, their general characteristics, and describe their contribution to more complex body structures

2. Describe the common characteristics of epithelial tissue

3. Classify the subtypes of epithelial tissue and describe characteristics associated with each subtype

4. Describe the common characteristics of connective tissue

5. Classify the subtypes of connective tissue and describe characteristics associated with each subtype

6. Classify the subtypes of muscle tissue and describe characteristics associated with each subtype

7. Classify the subtypes of nervous tissue and describe characteristics associated with each subtype

Classes of Tissue

Tissue, as you may now, are a group of closely associated cells performing a similar function. Histology is the study of tissue structure.

Epithelial

Epithelial tissues cover and protect surfaces inside and outside of the body.

Functions of Epithelial Tissue

• Protection

  • Acts as a barrier and protects underlying structures from abrasion

  • Prevents substances from moving through it (toxic molecules and microorganisms).

• Absorption

  • Contain carrier proteins which regulate the absorption of materials.

• Filtration

  • Permits passage such as oxygen or carbon dioxide through

• Secretion

  • Sweat

  • Enzymes

Characteristics of Epithelial Tissue

• Mostly composed of cells: Cellularity

  • Close-packed cells with limited extracellular material

• Cover body surfaces

• Have an exposed surface

  • I.e, skin exposed to air; stomach lining exposed to food: the surface that is exposed is called apical (free) surface.

• Cellular organization— attaches at the basal surface

  • Surface of cells that are anchored in place is called the basal surface

    • Material is called the basement membrane

    • Made up of two layers: basal lamina and reticular lamina

      • Can be further divided into lamina lucia and lamina densa.

      • Made up of extracellular material secreted by epithelial cells— important role in supporting/guiding cell migration in tissue repair

      • Deep to the basement membrane is the reticular lamina.

    • Between the epithelial cells (where epithelial cells are connected to each other) is the lateral surface.

  • All epithelial sheets are supported by connective tissue.

• Cellular Connections

  • Tight junctions, desmosomes, and gap junctions

  • Tight junctions: held tightly together with proteins

  • Desmosomes: proteins extended from the cytoplasm of one cell into the cytoplasm of neighboring cells. Strong connection— etc; muscles

• Avascular (meaning no blood vessels)

• Innervated

  • Receives nervous innervation, includes nerves

• Capable of regeneration

  • Replaced rapidly by cell division

  • Cell loss due to friction and contact with hostile environments

Classification of Epithelial Tissue

Epithelial cells are classified by the number of cell layers and shape of superficial cells. There are four major types of epithelium.

Layers

• Simple (1 layer)

  • Single cell layer

  • Areas of absorption and filtration

• Stratified (2+ layers)

  • Two or more cell layers

  • Areas of high abrasion

Cell Shape

• Squamous

  • Flattened

  • Scale-like

    • “Squished”

• Cuboidal

  • Boxlike

  • As tall as wide

    • “Cube”

• Columnar

  • Tall

    • “Column”

Special Types

• Transitional

  • Changes the number and layers and shape to have more surface area

• Pseudostratified

  • One ayer but looks like more due to different sizes of cells

  • Has cilia on apical side

Shape of Nucleus

The shape of the nucleus conforms to the cell shape.

• Squamous—disc shaped

• Cuboidal—spherical

• Columnar—elongated from top to bottom

Types of Simple Epithelia

Simple Squamous Epithelia

Function:

• Diffusion, secretion, and filtration

• Needed when fluids or air must readily travel for diffusion

Location:

• Endothelium

  • Lining of the lymphatic system

  • Lining of all organs in cardiovascular system

• Mesothelium

  • Serous membrane linings of ventral body cavity

• Alveoli or capillary beds

Simple Cuboidal Epithelia

Function:

• Secretion and absorption

Location:

• Kidneys (nephron cells)

• Plexus of the brain

• Lining of lung bronchioles

• Surfaces of ovaries

Microvilli may be present to increase surface area.

Simple Columnar Epithelia

Function:

• Absorption (specifically pinocytosis), protection, and secretion

Location:

• Digestive tract, GI tract

Modifications:

• Dense microvilli on apical surface

• Goblet cells that secret protective lubricant

Pseudostratified Columnar Epithelia

• Single layer of cells that vary in height

• Only tallest reach apical surface

  • Always ciliated

    • Cilia propel trapped matter out

  • Goblet cells secrete mucus

    • Mucus traps particulate matter

  • Nuclei are located at different heights

Function:

• Absorption and secretion

Location:

• Respiratory system (nasal cavities)

• Reproduction

Types of Stratified Epithelia

Stratified epithelia typically have two or more layers.

• Regenerate from below via mitotic division

  • Basal cell divide

  • Move apically to replace older surface cells

• Durable

• Provide protection

Stratified Squamous Epithelia

• Surface cells are squamous

• Deep layers consist most often of cuboidal

• Stratified squamous is categorized as non keratinized (moist) or keratinized.

  • Non keratinized are living cells in the deepest and superficial layers— a layer of fluid covers superficial layers, making them moist

  • Keratinized are living cells only in the deepest levels, and the superficial layers are composed of dead cells

Function:

• Protects against abrasion; mechanical protection wherever there is friction

Location:

• Areas of abrasion

  • I;e, tongue or epidermis

• Forms external surface of the body

  • Extends into all body openings

  • Outer layer (epidermis) is keratinized

• Surface cells are flattened and atrophied

Stratified Cuboidal Epithelia

• Rare

Function:

• Movement and secretion

Location:

• Glands

• Ureter

Stratified Columnar

These are rare.

Function:

• Protective and secretion

Location:

• Location of eyelids

• Urethra

Transitional Epithelia

Function:

• Accommodates fluctuations in the volume of fluid in an organ/tube

  • Need for more surface area

Location:

• Lining of urinary organs

  • Apical cells can change shape to accommodate stretching

Classification of Glandular Epithelia

Epithelial tissue is capable of secretion. Specialized secretory organs called glands are responsible for secretion. They consist of one or more cells that make/secrete a product.

• Secretion refers to the aqueous product of glandular cells and the process of making that product.

  • Formation involves active processes.

    • Made in ER, packed in Golgi, and secreted by exocytosis

There are two types of glands— exocrine and endocrine.

• Exocrine

  • Secreted via ducts

    • Onto body surfaces or cavities

• Endocrine

  • Ductless

  • Secrete directly into extracellular space

There are three specific distinctions of glands— duct structure, secretory structure, and mode of secretion.

Structure of Exocrine Glands

First, let’s distinguish between the duct structure and secretory structure.

The duct is the tube in contact with the epithelial tissue free surface, which transports secreted material.

• The duct can be:

  • Simple— single, unbranched duct

  • Compound— branched duct

The secretory portion of the gland is found deeper within the epithelium, composed of cells responsible for producing the secreted material (secretory cells).

• The secretory portions of the glands can be:

  • Tubular— straight, narrow tube with the same width as the duct

  • Acinar— a saclike structure whose width is greater than the width of the duct

They both are supported by connective tissue, which supplies blood and nervous fibers.

The fibrous capsule may penetrate the gland and divide it into lobes.

Three major categories of the exocrine glands are unicellular, simple, and compound.

Unicellular:

Some exocrine glands are composed of a single cell, making them unicellular.

• Goblet cells that secrete mucus are unicellular.

Simple:

Simple glands are multicellular glands with a single, unbranched duct.

Some example of simple glands are:

• Simple tubular

  • Glands forming a straight tube with no branching

• Simple branched tubular

  • Glands with several tubular secretory portions branching rom single duct

• Simple acinar

  • Glands with a single saclike secretory portion

• Simple branched acinar

  • Several acinar secretory proportions branching from single duct

Compound:

Compound glands are multicellular glands that have several branched ducts. The secretory portions can be tubular or acinar, or a mixture of both.

Some example of compound glands are:

• Compound tubular

  • Glands with multiple ducts, each with a narrow tubular secretory portion

• Compound acinar

  • Glands with multiple ducts, each with several saclike secretory portions

• Compound tubuloacinar

  • Glands with multiple ducts, each with several tubular and acinar secretory portions

Modes of Secretion by Exocrine Glands

The cells of the secretory portion have three modes of secretion (or a combination). These three modes are merocrine, apocrine, and holocrine.

Merocrine glands secrete via exocytosis without altering secretory cell. It is the most common gland.

Apocrine glands accumulate products just beneath the free surface.

• Top of the cell is removed, and products are released.

  • The cell is then repaired

Holocrine glands accumulate products until the cell bursts— releases secretory products, and then dies.