Tissues: Levels of Organization and Types

White fat (WAT) cells

store lipids

Brown fat (BAT) cells

burn lipids to produce heat and energy

SWAT

gives adipose tissue its structural integrity.

Atoms

Make up molecules.

Molecules

Make up cells.

Cells

Make up tissues.

Tissues

Make up organs.

Organs

Make up organ systems.

Organ systems

Make up organisms.

Cells in the body

There are over 35 trillion cells.

Types of cells

There are approximately 200 types of cells.

Primary tissue types

All cells can be placed into one of the four primary tissue types: Epithelial, Connective, Muscular, Neural.

Cellularity

Cells are bound close together with no intercellular space.

Polarity

Refers to the structural and functional difference between the exposed apical surface and the attached basal surface.

Epithelioid cells

Epithelial cells without a free surface.

Attachment

The basal layer is attached to the basal lamina.

Avascularity

Epithelial tissues do not contain blood vessels.

Functions of Epithelial Tissue

Provides physical protection, controls permeability, provides sensation, and produces secretions.

Microvilli

Increases surface area for absorption of material, found on the apical surface of cells of the urinary and digestive tracts.

Stereocilia

Long microvilli, commonly found in the inner ear and male reproductive tract.

Ciliated epithelium

Moves substances over the apical surface, found lining the respiratory tract.

Intercellular connections

Extensive connection between the cells that holds them together and prevents the passage of chemicals and pathogens.

Basal lamina

The cell membrane attaches to the basement membrane, consisting of typically two layers.

Reticular lamina

Attaches to underlying connective tissue.

Epithelial Maintenance and Renewal

Must be replaced frequently due to exposure to disruptive enzymes, toxic chemicals, pathogens, and mechanical abrasion.

Simple epithelium

Epithelium has only one layer of cells, found in protected areas such as internal compartments of the body.

Stratified epithelium

Epithelium has two or more layers of cells, found in areas with mechanical or chemical stresses.

Squamous epithelium

Cells are relatively flat in appearance.

Cuboidal epithelium

Cells are shaped like cubes.

Columnar epithelium

Cells are longer than they are wide, shaped like columns.

Simple squamous epithelium

Consists of very delicate cells, reduces friction, absorbs and secretes material.

Stratified squamous epithelium

Located on the surface of skin and lines the mouth, anus, esophagus, vagina, providing protection against abrasion, pathogens, and chemicals.

Keratin

A protein produced by cells.

Nonkeratinized

Refers to mucosal lining that does not contain keratin.

Simple cuboidal epithelium

Epithelium located in the thyroid gland, ducts, and kidney tubules, functioning in secretion and absorption with very limited protection.

Stratified cuboidal epithelium

A rare type of epithelium found in the ducts of sweat glands, primarily functioning in secretion and absorption.

Simple columnar epithelium

Epithelium lining the stomach, intestines, gallbladder, uterine tubes, and collecting ducts of the kidneys, functioning in secretion, absorption, and protection.

Stratified columnar epithelium

Epithelium located in the pharynx, epiglottis, anus, mammary glands, salivary glands, and urethra, primarily functioning in protection.

Pseudostratified ciliated columnar epithelium

Epithelium with nuclei situated at different levels, found in the nasal cavity, trachea, and bronchi, functioning in protection and secretion.

Transitional epithelium

Epithelium consisting of many layers and a combination of cuboidal and oddly shaped cells, located in the urinary bladder, renal pelvis, and ureters, with the ability to stretch extensively.

Glandular epithelia

Epithelia that contain gland cells, classified based on type of secretion released, structure of the gland, and mode of secretion.

Exocrine glands

Glands whose secretions travel through ducts to the epithelial surface.

Serous glands

Exocrine glands that secrete watery fluid with enzymes.

Mucous glands

Exocrine glands that secrete glycoproteins called mucins (mucus).

Mixed exocrine glands

Glands that contain both serous and mucus secretions.

Endocrine glands

Glands whose secretions enter into the blood or lymph, primarily hormones.

Unicellular glands

Glands that secrete mucins, including goblet cells and mucus cells.

Goblet cells

Unicellular glands found within the trachea.

Mucous cells

Unicellular glands found within the salivary glands.

Multicellular glands

Glands that secrete mucins and produce secretory sheets.

Tubular gland

Gland where cells are arranged in a tube.

Alveolar (acinar) gland

Gland where cells form a blind pocket.

Tubuloalveolar (tubuloacinar) gland

A gland that combines tubular and alveolar structures.

Simple duct structure

Duct structure with no branching.

Compound duct structure

Duct structure with repeated branches.

Eccrine secretion

A method of secretion involving exocytosis, found in salivary glands.

Apocrine secretion

A method of secretion involving shedding of the apical portion of the cell, found in mammary glands.

Holocrine secretion

A method of secretion where the cell bursts apart, found in sebaceous glands.

Connective tissues

Tissues that have three main components: specialized cells, extracellular protein fibers, and matrix.

Matrix

The collective term for the extracellular component of any connective tissue made of protein fibers and the ground substance.

Functions of connective tissue

Includes establishing structural framework, transporting fluids, protecting organs, supporting other tissues, storing energy, and defending against microorganisms.

Connective Tissue Proper

Has a matrix of fibers (loose fibers and dense fibers)

Fluid Connective Tissue

Has a matrix of liquid (blood and lymph)

Supporting Connective Tissue

Has a matrix of fibers and, in some cases, insoluble calcium salts

Connective Tissue Proper

Two classes of connective tissue proper cells: Fixed cells and wandering cells

Fixed Cells

Cells that remain in the connective tissue and perform specific functions

Wandering Cells

Mobile cells that move through the connective tissue and respond to injury or infection

Fibroblasts

Produce connective tissue fibers

Fibrocytes

Maintain connective tissue fibers and matrix

Fixed Macrophages

Phagocytize pathogens and damaged cells

Adipocytes

Store lipid reserves

Mesenchymal Cells

Connective tissue stem cells that can differentiate into other cell types

Melanocytes

Synthesize melanin

Free Macrophages

Mobile/traveling phagocytic cells (derived from monocytes of the blood)

Mast Cells

Stimulate local inflammation

Lymphocytes

Participate in immune response; mobilize during infection or tissue injury

Neutrophils and Eosinophils

Types of white blood cells involved in immune response

Collagen Fibers

Designed to develop tensile strength, which is the ability to resist tension

Reticular Fibers

Support the structure of organs

Elastic Fibers

Contain protein called elastin

Areolar Tissue

Connects skin to muscle and provides minimal support but independent movement

Adipose Tissue

Cushions and insulates; consists of white fat (white adipose cells) and brown fat (brown adipose cells)

Reticular Tissue

Provides a supporting framework in organs like liver, spleen, and lymph nodes

Dense Regular Connective Tissue

Connects muscle to bone (tendons), muscle to muscle (aponeuroses), or bone to bone (ligaments)

Dense Irregular Connective Tissue

Provides strength and forms a fibrous capsule around organs

Fluid Connective Tissues

Includes blood and lymph

Blood

Transport oxygen and carbon dioxide; consists of erythrocytes, leukocytes, and platelets

Lymph

Involved with the immune system; consists of lymphocytes

Cartilage

Made of chondrocytes; has a gel matrix made of chondroitin sulfate

Bone

Solid matrix made of calcium phosphate; provides support and strength

Hyaline Cartilage

Provides flexible support and reduces friction in joints

Elastic Cartilage

Provides flexible support in structures like the auricle of the ear

Fibrous Cartilage

Resists compression and absorbs shock in pads within the knee joints

Epithelial Membranes

Consist of a sheet of epithelial cells and an underlying connective tissue

Mucous Membranes

Line digestive, respiratory, reproductive, and urinary tracts; provide a barrier against pathogens

Serous Membranes

Line body cavities and consist of a parietal and visceral layer

Cutaneous Membrane

Makes up the skin and consists of keratinized stratified squamous epithelium

Synovial Membrane

Lines joint cavities and produces synovial fluid to reduce friction

Embryonic Connective Tissue

Includes mesenchyme and mucoid connective tissue

Fascia

Layers of connective tissue that connect organs with the rest of the body