Tissue Level of Organization

Tissue Level of Organization Lecture Notes

Introduction

  • Lecture presented by Chasity O’Malley at Palm Beach State College, with notes by Lori Garrett, Parkland College.

  • Copyright © 2018 Pearson Education, Inc.

Overview of Tissues

  • The human body contains trillions of cells that belong to approximately 200 different cell types.

  • Definition of Tissue: A tissue is defined as a group of similar cells and cell products that work together to perform a specific structural or physiological role in an organ.

  • Histology: The study of tissues and their arrangement into organs.

  • Cells are organized into four primary tissue classes:

    • Epithelial Tissue

    • Connective Tissue

    • Muscular Tissue

    • Neural (Nervous) Tissue

Characteristics of Primary Tissues

  • The four primary tissues differ based on:

    • Types and function of their cells

    • Characteristics of the matrix (extracellular material) surrounding the cells

    • Relative amount of space occupied by cells versus matrix.

The Tissue Level of Organization

  • The tissue level consists of:

    • Chemical Level: Molecules

    • Cellular Level: Cells

    • Tissue Level: Formed by extracellular materials and fluids that combine to create tissues with special functions, classified as:

    • Epithelial Tissue: Covers exposed surfaces, lines internal passageways and chambers, produces glandular secretions.

    • Connective Tissue: Fills internal spaces, provides structural support, and stores energy.

    • Muscular Tissue: Contracts to produce active movement.

    • Neural Tissue: Conducts electrical impulses and carries information.

Module 4.3: Epithelial Tissue

  • Epithelial tissues (epithelia) consist of sheets of closely packed cells; can be one or more layers thick.

  • Characteristics:

    • The upper surface is exposed to the body's surface or internal body cavity.

    • Covers body surfaces, lines body cavities, forms most gland tissue, often contains secretory or gland cells.

Gland Types from Epithelia

  • Glands derived from epithelia consist of:

    • Exocrine Glands: Secrete substances into ducts or tubes.

    • Endocrine Glands: Secrete hormones directly into the bloodstream.

Functions of Epithelial Tissue

  • Major functions include:

    • Physical protection

    • Control permeability

    • Provide sensation

    • Produce specialized secretions.

Communication and Structure of Epithelia

  • Epithelia are:

    • Avascular (no blood vessels)

    • Communicate via diffusion between cells.

    • Rests on a layer of loose connective tissue, depending on its blood vessels for nutrients and waste removal.

    • Adheres to underlying tissue via a thin basement membrane.

Basement Membrane

  • The basement membrane:

    • Layer between an epithelium and the underlying connective tissue.

    • Anchors the epithelium to the connective tissue below.

    • Basal Surface: Side facing the basement membrane.

    • Apical Surface: Side facing away from the basement membrane.

Basic Features of Epithelial Cells

  • Apical Surface Features:

    • Microvilli often found in the digestive, urinary, and reproductive tracts.

    • Cilia often found in cells lining the respiratory and reproductive tracts.

  • Base of Cells:

    • Basolateral surfaces consist of the base and lateral surfaces (attached to neighboring cells).

Epithelial Cell Shapes

  • Cell Shapes:

    • Squamous: Thin and flat.

    • Cuboidal: Small boxes.

    • Columnar: Slender rectangles.

  • Layering:

    • Simple Epithelium: Single layer.

    • Stratified Epithelium: Several layers; generally located in areas requiring protection.

Module 4.4: Interconnectivity of Epithelial Cells

  • For effective barriers, epithelia must:

    • Form complete covers and linings.

    • Replace damaged or lost cells.

Structures Connecting Epithelial Cells

  • Types of Intercellular Attachments:

    • Tight Junctions: Form barriers isolating basolateral surfaces from lumen contents.

    • Adhesion Belts: Strengthen the apical region and prevent distortion and leakage at occluding junctions.

    • Gap Junctions: Allow chemical communication between adjacent cells.

    • Desmosomes: Firmly attach neighboring cells by interlocking their cytoskeletons.

    • Hemidesmosomes: Attach deepest epithelial cells to the basal lamina.

Basal Lamina Structure

  • The basal lamina consists of:

    • Lamina Lucida: Clear layer containing glycoproteins and a network of fine protein filaments.

    • Lamina Densa: Contains coarse protein fibers, giving strength and filtering properties to the basal lamina.

Types of Intercellular Attachments (Continued)

  • Gap Junctions: Allow chemical communication, formed by connexons.

  • Desmosomes: Interlock cytoskeletons of adjacent cells, formed by cell adhesion molecules (CAMs) and intercellular cement containing proteoglycans, notably hyaluronan.

Module 4.5: Squamous Epithelia

  • Simple Squamous Epithelium:

    • Thin, flat, irregular shape; resembles fried eggs side by side.

    • Locations include:

    • Alveoli of lungs (for absorption/diffusion).

    • Lining ventral body cavity (mesothelium).

    • Lining heart and blood vessels (endothelium).

Stratified Squamous Epithelium

  • This type exists in areas experiencing severe mechanical or chemical stress and consists of several layers.

  • Example locations include:

    • Skin

    • Mouth

    • Throat

    • Esophagus

    • Rectum

    • Anus

    • Vagina

  • Types:

    • Keratinized: Tough, water-resistant, found on the skin's surface.

    • Nonkeratinized: Resists abrasion but can dry out, found in the oral cavity, pharynx, esophagus, anus, vagina.

Module 4.6: Cuboidal and Transitional Epithelia

  • Cuboidal Epithelium:

    • Cells resemble hexagonal boxes, with the nucleus centered.

    • Types:

    • Simple Cuboidal Epithelium: Found in linings of exocrine glands, ducts, parts of the kidney, thyroid gland.

    • Stratified Cuboidal Epithelium: Rare, found in ducts of exocrine glands like sweat glands.

Columnar Epithelium

  • Columnar Epithelium:

    • Cells appear rectangular; elongated nuclei near the basal lamina.

    • Types:

    • Simple Columnar Epithelium: Found in stomach, intestine, uterine tubes, kidney ducts.

    • Stratified Columnar Epithelium: Rare, only superficial cells are columnar in large ducts of salivary glands and pancreas.

    • Pseudostratified Columnar Epithelium: Appears stratified but is a single layer, cells typically have cilia, found in nasal cavities, trachea, larger airways of lungs.

Transitional Epithelium

  • Definition: Unusual stratified epithelium that stretches.

  • Example locations:

    • Urinary bladder

    • Urethra

    • Urine-collecting chambers of kidneys.

Characteristics of Glandular Epithelium

  • Glands: Collections of epithelial cells that produce secretions, can be either scattered cells or complex organs.

  • Types of Glands:

    • Endocrine Glands: Secrete hormones into interstitial fluid, then into bloodstream.

    • Exocrine Glands: Secrete into ducts that open onto epithelial surfaces.

Exocrine Gland Secretions

  • Three Types:

    • Merocrine Secretion: Product released from secretory vesicles by exocytosis, the most common type; includes mucin which mixes with water to form mucus for lubrication and protection.

    • Apocrine Secretion: Loss of apical surface and cytoplasm with secretion; example includes mammary glands producing milk.

    • Holocrine Secretion: Entire cell bursts, releasing secretions and killing the cell; replaced by stem cell division.

Structure of Multicellular Exocrine Glands

  • Classification:

    • Based on duct structure: Simple (single duct) or Compound (duct divides).

    • Based on secretory area structure: Tubular (ducts are tubular), Alveolar or Acinar (sac-like pockets), Tubuloalveolar or Tubuloacinar (both tubes and sacs).

Examples of Simple Exocrine Glands

  • Simple Tubular: E.g., intestinal glands.

  • Simple Coiled Tubular: E.g., merocrine sweat glands.

  • Simple Branched Tubular: E.g., gastric glands.

  • Simple Alveolar: E.g., sebaceous glands.

Examples of Compound Exocrine Glands

  • Compound Tubular: E.g., mucous glands in the mouth.

  • Compound Alveolar: E.g., mammary glands.

  • Compound Tubuloalveolar: E.g., salivary glands, pancreatic glands, and respiratory passage glands.

Unicellular Glands

  • Some glands are unicellular (individual mucous cells).

  • Example: Goblet cell, which secretes mucin; filled with large secretory vesicles at the apical cytoplasm.