The Tissue Level of Organization

Anatomy I: by Larry Hernandez

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Tissue

• Collections of specialized cells and cell products that performs a limited number of functions

Histology

• The study of tissues

Epithelial (Covering)

• Covers exposed surface

• Lines internal passageways

• Forms glands

Connective (Support)

• Fills internal spaces

• Provides structure and strength to support other tissues

• Transport material

• Stores Energy

Muscle (Movement)

• Specialized for contraction

• Skeletal muscle, heart muscle, and walls of hollow organs

Neural (Control)

• Carries electrical signals from 1 part of the body to another

Primary Germ Layer

• Embryonic give rise to all four tissue types in adults

  • Ectoderm:

    • Nervous, epithelial (Epidermis)

  • Mesoderm:

    • Muscle, connective, epithelial (Endothelium + Mesothelium)

  • Endoderm:

    • Epithelial (Mucosa)

Epithelial Tissues

2 Categories:

• Epithelia:

  • Layers of cells covering internal or external surfaces

• Glands:

  • Structures that produce fluid secretions

Key Concept

• Tissues are: Collections of cells and cell products that preform specific, limited functions

• 4 Tissue types form all the structures of the human body

Special Structures and Functions Of Epithelial Tissues

Topic

Characteristics of Epithelia (Title)

Structures of Epithelia

• Cellularity:

  • Little extracellular matrix, mostly cells

• Contacts:

  • cells linked by tight junctions

• Polarity:

  • Apical (apex) + Basal surfaces, separate functions

• Attachment:

  • attached to Connective tissue (CT) via basal lamina

• Avascularity:

  • No blood vessels, diffusion of connective tissues

• Regeneration:

  • High turnover, stem cells at basal surface. (Once every day)

Functions of Epithelia:

• Provide physical protection:

  • abrasion, dehydration, infection

• Control Permeability:

  • semi-permeability covers all surfaces

    • Digestion: small intestine (absorbs) and digestive system lining

• Provide Sensation:

  • Sensory Neurons

• Produce specialized secretion (Glandular Epithelium)

  • Protection, chemical messages

Free Surface and Attached Surface

1. Apical Surface: Exposed to the environment may have:

   -Microvilli: absorption or secretion

   -Cilla: fluid movement

2. Basolateral Surface: attachment to neighboring cells via intercellular connections

Intercellular Connections

General Adhesion: Large Connections

1. CAMs (Cell Adhesion Molecules):

   • Connect adjacent membranes or binds extracellular materials (e.g. basal lamina)

2. Intercellular cement:

   • Thin layer of hyaluronan

   • (Proteoglycan):

     • Attach adjacent membranes

Specific Adhesion = Cell Junctions

1. Tight Junctions

2. Gap Junctions

3. Desmosomes

Cell Junctions

• Tight Junction:

  • Interlocking proteins, bind lipid portion of membrane, water tight seal.

• Gap Junction:

  • Connexons form channel, allow molecules to pass for communications

• Desmosomes:

  • CAMs + intercellular cement on dense area to cytoskeleton, resist streching and twisting

Cell Junctions: Gap Junction

Connexons form protein channels allow molecules to pass for communication

• Rapid Communications

• Allow ions to pass

• Coordinated contractions

Cell Junction: Tight Junction

• Between 2 cell membranes

• Interlocking proteins, binds lipids portion of membrane

• Prevents passage of water and solutes

Cell Junction: Desmosomes

• Cell Adhesion Molecules + intercellular cement on dense area are attached to the cytoskeleton

• Resist streching and twisting

1. Belt Desmosomes:

   • Continous band in apical region, attached to microfilaments

2. Button Desmosomes:

   • “Spot Weld”, attachment to intermediate filaments

3. Hemidesmosomes

   • Half button desmosomes at basal surface, attaches to basal lamina

Classes of Epithelia

• Based on shape and layers

• Shape: (All are hexagonal from the top)

1. Squamos: Flat, disc shaped nucleus

2. Cuboidal: Cube or sqaure, center round nucleus

3. Columnar: Tall, Basal oval nucleus

Layers

• Simple Epithelium:

  • Single layer of cells

  • Function: absorption, secretion, filtration

• Stratified Epithelium:

  • Two or more layer of cells

  • Function: protecton

Eight Types of Epithelial Tissue

1. Simple Squamos Epithelium

2. Stratified Squamos Epithelium

3. Simple Cuboidal Epithelium

4. Stratified Cuboidal Epithelium

5. Transitional Epithelium

6. Simple Columnar Epithelium

7. Pseudostratified Coulmnar Epithelium

8. Stratified Columnar Epithelium

Simple Squamos Epithelium

• Thin Delicate

• Locations: found in protected regions

  • Mesothelium (serosa), endothelium (blood vessels, heart), kidney tubules, cornea, and alveoli of lungs

• Functions: absorption, diffusion, filitration or secretion

Stratified Squamos Epithelium

• Basal Cells:

  • Look cuboidal, apical cell squamos

• Found on exposed surfaces

• Functions:

  • Provide protection from absorption, pathogens, and chemicals

• Two Types:

  • A.) Nonkeratinized = Muscosa

    • Kept Moist

    • All Cells nucleated

    • Location: mouth, esophagus, anus, and vagina

  • B.) Keratinixed = Epidermis

    • Dry, apical cells dead

    • Cells contain keratin protein to resist dehydration and add strength

Simple Cuboidal Epithelia

• Location:

  • Kidney Tubules

  • Pancreas

  • Salivary Glands

  • Thyroid

• Functions:

  • Secretion

  • Absorption

Stratified Cuboidal Epithelium

• Rare

• Typically Two Layers

• Location:

  • Some sweat glands

  • some mammary glands

• Function:

  • protection

  • excretion, and secretion

Transitional Epithelium

• Relaxed:

  • Looks like stratified cuboidal

• Stretched:

  • Looks Squamos

• Location:

  • Urinary Bladder

  • Ureters

• Function:

  • Tolerate Excessive stretching

Simple Columnar Epithelium

• Nuclei line up near the basal lamina

• Apical surface of cells often has microvilli = “brush border’ (In intestine)

• Goblet cells often present:

  • Secrete mucus

• Locations:

  • Stomach, intestine, gallbladder, uterine tubes and collecting ducts of kidney

• Functions:

  • Absorption or secretion

Pseudostratified Columnar Epithelium

• Several cells contact basal lamina

• Some too short to reach apical surface

• Nuclei scattered so it appears stratified

• Tall cells have cilia on apical surface

• Goblet cells (muscus) often present

• Location:

  • Nasal Cavity, trachea, bronchi, male reproductive tract, female uterine tubes

• Functions:

  • Move material across surface

Stratified Columnar Epithelium

• Rare

• 2 layers or mutiple layers with only apical layer columnar

• Location:

  • (Tiny parts of): pharynx, epiglottis, anus,mammary glands, salivary glands, urethra

• Function:

  • Minor protection

Cell Biology

Topic

Cell Biology: Listing

• Cell Membrane (1)

  • Osmosis, Diffusion

  • Cell Wall

• Cytoplasm (2)

  • Nutrient Water

• Nucleus (3)

  • Chromosomes/ Alleles

  • DNA/RNA

• Mitochondria and Golgi Apparatus (4)

• Ribosomes (5)

  • Proteins make things go

  • Protein synthesis

• Mitosis and Meiosis

Glandular Epithelia

1. Endocrine Glands: “Internally Secreting”

   • Secrete into intersitial fluid —> Blood

   • Secretions = hormones

   • Regulate and coordinate activities

     • e.g. pancreas, thyroid, pituitary

2. Exocrine Glands: “Externaly Secreting”

   • Secreting duct —> Epithelial Surface

     • e.g. dogestive enzymes, perspiration, tears, milk and mucus

   • Classified three ways:

     • 1.) Mode of Secretion

     • 2.) Type of secretion

     • 3.) Structure

A.) MODE OF SECRETION

1. Merocrine Secretion:

   • Product released form secretory vesicles by exocytosis

     • e.g. Mucus, Sweat

2. Apocrine Secretion:

   • Product accumulates in vesicles

   • Apical region of cell which vesicles is shed to release product

     • e.g. milk

3. Holocrine Secretion:

   • Product accumulates in vesicles

   • Whole cell is lysed to release product

   • Cells dies, must be replaced by stem cells

     • e.g. Sebum

B.) TYPES OF SECRETION

1. Serous Glands: Water + Enzymes

   • e.g. parotid salivary glands

2. Mucus Glands: Mucin

   • (+Water= Mucus)

   • e.g. goblet cells

3. Mixed Endocrine Glands:

   • (Serous + Mucus secretion)

   • e.g. submandibular salivary glands

C.) Gland Structure

• The exocrine gland can be classified

  • unicellular glands: 1 cell

    • e.g. Goblet cells which are scattered among epithelia

    • found in the intestinal lining

  • Multicellular Glands:

    • group of cells named for shape and structure