Basic Organization of Human Body and Tissue Types
Student Learning Objectives
List general functions of 4 main tissue types:
Epithelial: Covers surfaces.
Muscle: Facilitates movement.
Connective: Provides support and protection.
Neural: Controls body functions.
State 5 Distinguishing Characteristics of Epithelial Tissue:
Polarity
Avascular and innervated
Specialized cell connections
Regenerative capacity
Nutritional support from connective tissue.
Classify major types of epithelial tissue:
Shapes: Squamous, Cuboidal, Columnar.
Layers: Simple, Stratified, Pseudostratified.
State cell type, fiber type, and major function of connective tissue proper.
Basic Organization of the Human Body
Cell:
The most basic unit of life.
Can survive independently and is capable of reproduction.
All cell types will eventually differentiate and become specialized.
Specialization leads to migration and binding together to form tissues.
Advantages of Specialized Cells/Tissues:
Division of Labor: Allows for highly sophisticated functioning.
Basic Organization of Human Body Continued
Functions of Different Tissue Types:
Epithelial: Covers surfaces.
Muscle: Facilitates movement.
Connective: Provides support and protection.
Neural: Controls body functions.
Composition of Organs: Most organs contain all four types of tissues.
Disadvantages of Differentiating:
Some cells may lose growth ability in adulthood.
Loss of these tissues can result in permanent disability of functions.
Study of Tissues
Definition of Tissue: Groups of similar cells sharing a common function.
Characteristics:
Cells are organized in three-dimensional structures and tightly packed together.
Cell membranes are connected by intracellular junctions.
Distinguishing Tissues:
Tissues can be distinguished by cell type, fiber type, and organization.
Much can be learned using light microscopy and well-stained tissue.
Major Tissue Type: Epithelial Tissue
General Characteristics:
Makes up the outermost layer of most organs.
Covers and lines cavities and hollow organs, with a thin basement membrane (lamina propria) anchoring epithelium to connective tissue below.
5 Distinguishing Characteristics of Epithelial Tissue
Polarity: Epithelial tissue has two surfaces differing in structure and function.
Apical Surface: Not attached to surrounding tissue, exposed to body cavities or organ cavities.
Basal Surface: Attached to underlying connective tissue.
Support and Nutrition:
Nutritionally supported by connective tissue; usually avascular (lacking blood vessels) but innervated (receives nervous input).
Nutrients diffuse through lamina propria from underlying vascular connective tissue.
Specialized Cell Connections:
Tight Junctions: Highly impermeable, creating a zipper-like seal around cells.
Desmosomes: Cellular rivets holding cells together, attached to cytoskeletal fibers.
Regeneration Capacity:
Cells are quickly regenerated, especially after damage due to environmental stress.
Nutritional Support: Nutrients from connective tissue diffuse through lamina propria as epithelial tissue is avascular.
Classifying Epithelial Tissue
Classified Based on:
Shape of Cells:
Squamous: Flat cells.
Cuboidal: Cube-shaped cells.
Columnar: Tall, elongated cells.
Number of Cell Layers:
Simple: One layer of cells.
Stratified: Two or more layers of cells.
Pseudostratified: Appears layered but is not.
Epithelial Tissue Examples
Simple Squamous Epithelium:
Characteristics: Single layer of thin flat cells, resembling floor tiles (e.g., fried eggs).
Functions: Easy passage of substances; found in alveoli of lungs, facilitating gas exchange (O2 and CO2).
Specialized names based on location:
Endothelium: Inner lining of blood vessels.
Mesothelium: Lining of serous membranes.
Simple Cuboidal Epithelium:
Structure: Single layer of cube-shaped cells with a central nucleus.
Functions: Secretion and absorption; found lining small ducts such as kidney tubules and thyroid follicles.
Simple Columnar Epithelium:
Structure: Single layer of elongated cells used for absorption or secretion.
Characteristics: Nuclei aligned near the basement membrane; may contain goblet cells producing mucus.
Locations: Lining of uterus, stomach, intestines; secretes digestive fluids or absorbs nutrients.
Pseudostratified Columnar Epithelium:
Structure: Single layer that appears layered, with nuclei at different levels.
Characteristics: Similar to simple columnar, with goblet cells.
Location: Lines respiratory passageways.
Stratified Squamous Epithelium:
Structure: Many cell layers thick, providing a protective layer; outermost cells are flat.
Functions: Protects underlying tissues; can be keratinized or non-keratinized.
Locations: Lines oral cavity, reproductive canals, rectum (non-keratinized) and outer layer of skin (keratinized).
Stratified Cuboidal Epithelium:
Structure: 2-3 layers of cube-shaped cells.
Functions: Provides better protection than a single layer; relatively rare.
Locations: Lines ducts of larger glands (e.g., mammary glands, sweat glands, pancreas).
Stratified Columnar Epithelium:
Structure: Top layer made of elongated cells; deeper layers may be cube-shaped.
Functions: Rare and provides some protection.
Location: Lines parts of male urethra and ducts of exocrine glands.
Transitional Epithelium:
Characteristics: Found in organs needing to stretch or relax (e.g., bladder).
Glandular Epithelium:
Composed of cells that produce and secrete substances into ducts.
Major Tissue Type: Connective Tissues
General Characteristics:
Most abundant tissue type in the body.
Cells are farther apart than epithelial cells, leading to lower density.
Contains an extracellular matrix (ECM) consisting of protein fibers and ground substance (non-fibrous proteins and fluid).
ECM consistency can vary from fluid to semisolid to solid.
Functions of Connective Tissue
Binds structures together and serves as the body's natural glue.
Provides structural support and protection for organs.
Absorbs impact, stores fat, and carries nutrients.
Protects against infections by containing immune cells.
Aids in tissue repair, usually with a good blood supply.
Most connective tissue cells have the capacity to divide.
Major Cell Types of Connective Tissue
Wandering Cells:
Temporarily appear in tissue, mainly immune cells.
Macrophages:
Specialized white blood cells conducting phagocytosis to defend against infection.
Mast Cells (Fixed):
Detect foreign particles; release histamine (causing inflammation) and heparin (preventing blood clotting).
Fixed Cells: Stays in the same tissue for an extended period. The type of fixed cell determines the connective tissue class.
Fibroblasts:
Most common fixed cell, large star-shaped cells that secrete fibers into the ECM.
Types of Connective Tissue
Connective Tissue Proper:
Loose:
Areolar.
Adipose.
Reticular.
Dense:
Regular.
Irregular.
Elastic.
Cartilage:
Hyaline.
Elastic.
Fibrocartilage.
Bone
Blood
Connective Tissue Fibers Produced by Fibroblasts
Collagen Fibers:
Provide tensile strength; parallel bundles, flexible but only slightly elastic.
Found in ligaments and tendons.
Elastic Fibers (Yellow):
Spring-like with branching, can stretch and return to shape.
Found in vocal cords and respiratory air passages.
Reticular Fibers:
Thin, branching fibers forming delicate, supporting networks.
Found in organs like the spleen and liver.
Loose Connective Tissue
Loose Areolar Connective Tissue:
Forms lamina propria under epithelial cells, with blood vessels nourishing nearby epithelial cells.
Contains mainly fibroblasts, sparse collagen, and elastic fibers in a gel-like ground substance.
Major Functions:
Universal packing material between tissues.
Provides flexibility and durability.
Stores fluids in the ground substance.
Loose Adipose Connective Tissue:
Contains adipocytes that store fat; when not filled, they resemble fibroblasts by pushing nuclei to one side.
Functions: Cushions and insulates organs, found behind eyeballs, surrounding major organs, and between muscles.
Loose Reticular Connective Tissue:
Composed of thin reticular fibers, supporting the walls of internal organs such as the liver and spleen.