Histology: Epithelial Tissue Overview

Simple Squamous Epithelium

• Function: Allows simple diffusion of gases, nutrients, and waste across a thin membrane.
• Location: Air sacs of lungs, capillary walls, interior of the heart (endothelium), and lining ventral body cavities (mesothelium).

Simple & Stratified Cuboidal Epithelia

• Simple: Function in secretion, absorption, and protection (glandular cells). Location: Kidney tubules, secretory portion of the thyroid, and salivary glands.
• Stratified: Function in duct lining, secretion, absorption, and protection. Location: Sweat glands and mammary glands.

Simple Columnar Epithelium

• Function: Secretion of enzymes, mucus, or other substances; absorption.
• Location: Digestive tract.
• Goblet cells: Unicellular, mucous-secreting gland found in digestive and respiratory tracts.

Transitional Epithelium

• Function: Allows for distension without tearing the membrane.
• Structure: Modified stratified epithelium (cells change shape from round to flat).
• Location: Urinary bladder.

Pseudostratified Columnar Epithelium

• Function: Protection, secretion, and movement of mucous.
• Location: Nasal cavity, trachea, bronchi, and parts of the male reproductive tract.

Glands

• Glands: One or more cells that make and secrete a product. Two types of glands exist:
  • Endocrine Glands: Secrete hormones directly into the bloodstream.
  • Exocrine Glands: Secrete products onto a surface, including the skin surface.

Apocrine Secretion

• Ap- = separating from.
• Loss of cytoplasm along with the secretion through packed vesicles in the apical portion of the cytoplasm.
• Example: Milk production.

Merocrine/Eccrine Secretion

• Most common mode of secretion.
• Secretion released from secretory vesicles by exocytosis.
• Examples: Mucous that traps bacteria, lubricates and protects lumens, and sweat that cools the body.

Holocrine Secretion

• Gland cell bursts when the cell is packed with secretion.
• Example: Sebaceous glands (oil glands attached to hair follicles all over the body).

Skeletal Muscle

• Nucleus Number: Multiple.
• Striated: Yes.
• Voluntary/Involuntary: Voluntary.
• Cell Division: Limited.
• Function: Provides body heat and causes movement by shortening protein fibers pulling on bones or skin.

Smooth Muscle/Visceral Muscle

• Nucleus Number: Single.
• Striated: No.
• Voluntary/Involuntary: Involuntary.
• Cell Division: Limited.
• Function: Propels or squeezes substances through hollow organs by alternating between contracting and relaxing; makes up walls of vessels.

Cardiac Muscle/Myocardium

• Nucleus Number: Single.
• Striated: Yes.
• Voluntary/Involuntary: Involuntary.
• Cell Division: Limited.
• Function: Gap junctions between intercalated discs help muscle cells synchronize contractions.

Skin

• Function: Protection from external environment, excretion of salts, water, and wastes, maintaining internal temperature (insulation/sweating), melanin production (UV ray protection), water resistance (keratin protects against water loss), vitamin D synthesis (assists calcium metabolism), and sensation (touch, pain, pressure, temperature).
• Skin is the body's first line of defense against pathogens.

Stratum Corneum, Stratum Lucidum, Stratum Granulosum, Stratum Spinosum, Stratum Basale

• Layers of the skin.
• Stratum corneum: Outermost layer of dead cells that flake off. Stratum lucidum is located below it and only in palms and soles of the feet. Stratum granulosum cells are located below and stratum spinosum cells are located below that. And stratum basale is the bottom layer, which contains stem cells that produce new skin cells.

Melanin: Pros and Cons

• Pros: Protects DNA from ultraviolet rays.
• Cons: Blocks UV rays needed for vitamin D production, increasing the risk of not having enough vitamin D.

Sebaceous Glands

• Structure: Holocrine glands with ducts that open into hair follicles.
• Function: Secretes sebum (an oil) which softens and lubricates hair and skin, and is bactericidal.
• Location: All over the body except for palms and soles of the feet.

Sweat Glands: Apocrine

• Structure: Ducts empty into hair follicles.
• Function: Active at puberty and in stress/emotional situations.
• Location: Underarms, genitals, and around nipples.
• Secretion: Similar to sweat, with additional fatty acids and proteins; milky white to yellow; slight odor, which becomes unpleasant if decomposed by bacteria.

Sweat Glands: Merocrine/Eccrine

• Structure: Single coiled tube in the dermis; duct opens to a sweat pore.
• Function: Thermoregulation, response to stress, lowers pH, and acts as an antibiotic.
• Location: All over the body (forehead, upper lip, palms, soles).
• Secretion: Sweat (water, salts, wastes, and vitamins): pH 4–6. Dermcidin is an antibiotic in sweat that protects against bacterial growth.

Ceruminous Glands

• Function: Protects the ear drum, keeps the outer surface of the eardrum pliable and waterproofed, and blocks entry of foreign material.
• Location: Dermis of the ear canal.
• Secretion: Cerumen (earwax).

Explore the various types of epithelial tissues, including simple squamous, cuboidal, columnar, and transitional epithelia. Learn about their functions, locations, and specialized cells such as goblet cells. This quiz covers essential histological concepts relevant to human anatomy and physiology.