Epithelium and Cell Structure

• Epithelium is a body tissue covering internal and external surfaces, lining cavities and organs, and forming glands.
• Its functions include protection, secretion, and absorption, varying by location.
• Organs consist of four tissue types: epithelial, connective, muscular, and nervous.
• All substances entering or leaving organs must cross epithelial tissue.
• Examples include skin epidermis, intestinal lining, respiratory tract lining, abdominal cavity lining, and sweat glands.

Epithelial Cells

• Epithelial tissue comprises cells of varying shapes arranged in single or multiple layers.
• Cells are the smallest living units making up organisms and body tissues. Your body has over 30 trillion cells.
• Cells have three main parts; the membrane, nucleus, and cytoplasm.
• Cell membrane: Surrounds the cell, regulating substance passage.
• Nucleus: Contains most of the cell's DNA.
• Cytoplasm: Fluid inside the cell containing functional parts.
• Some have surface characteristics aiding functions:
  • Microvilli: Non-motile, finger-like structures increasing surface area for absorption. Intestinal cells use microvilli to absorb nutrients and protect against bacteria.
  • Cilia: Motile, hair-like structures moving cells/substances along the surface. Respiratory tract cells trap and move dust towards nostrils. Fallopian tube cells move eggs to the uterus.
  • Stereocilia: Specialized microvilli resembling cilia, important for hearing and balance in the inner ear.

Types of Epithelial Cells

• Epithelial cells differ in type due to the tissue's varied functions.
• Epithelial cells are classified by shape:
  • Squamous: Flat and sheet-like.
  • Cuboidal: Cube-like with equal dimensions.
  • Columnar: Column-like, taller than wide.
• Cells are also classified by their arrangement:
  • Simple: Single layer of cells.
  • Stratified: Multiple layers of cells.
  • Pseudostratified: Single layer of closely packed cells appearing layered.
• There are several types depending on shape and layering:
  • Simple squamous: Lines vessels and cavities, regulating substance passage.
  • Simple cuboidal: Found in glandular tissue and kidney tubules.
  • Simple columnar: Specialized for absorption, often with cilia or microvilli, lining the stomach and intestines.
  • Stratified squamous: Protective, guarding against microorganisms and water loss. The epidermis is composed of this.
  • Stratified cuboidal: Uncommon, in salivary and sweat gland excretory ducts.
  • Stratified columnar: Uncommon, found in the conjunctiva lining eyelids, providing protection and mucus secretion.
  • Pseudostratified columnar: Found in the upper respiratory tract, usually ciliated.
• Epithelial cells can be categorized by their special functions:
  • Transitional: Multiple layers flatten when stretched, lining the urinary tract.
  • Glandular: Specialized for producing and secreting substances in glands.
  • Olfactory: Contains olfactory receptor cells with cilia that detect odors in the nasal cavity.

Epithelium Functions

• Epithelial tissue provides protection to underlying tissues, such as blood vessels, muscles, and internal organs. Intestinal cilia protect against bacteria.
• Glandular epithelium secretes enzymes, hormones, and fluids.
• Epithelial linings in internal organs allow absorption of substances like nutrient absorption in the intestines.
• Kidney epithelium excretes waste, while sweat glands excrete sweat.
• The respiratory tract epithelium filters dirt from inhaled air, and kidney epithelium filters blood.
• Simple squamous epithelium facilitates molecule movement from high to low concentrations, assisting in filtration, absorption, and secretion.
• Sensory nerve endings in epithelial tissue enable sensory reception, like stereocilia in the ear enabling hearing and balance. Tastebuds are embedded in the tongue's stratified squamous epithelium.

Conditions Affecting Epithelial Tissue

• A major concern is the potential for malignancy development, like adenocarcinoma or papillary thyroid carcinoma.
• Adenocarcinoma impacts glandular tissue is the most common cancer type affecting organs.
  • Nearly all prostate cancers
  • Most breast cancers
  • 96% of colorectal cancers
  • 95% of pancreatic cancers
  • 40% of non-small cell lung cancers
• Papillary thyroid carcinoma comprises 80% of thyroid cancers. It is slow-growing and highly treatable.
• Conditions associated with epithelial tissue:
  • Asthma: Bronchial epithelium becomes fragile, causing airway narrowing and mucus production.
  • Celiac disease: Immune system damages intestinal microvilli upon gluten ingestion, impairing nutrient absorption.
  • Human papillomavirus (HPV) strains 1-4: Causes warts on the epidermis.
  • Vertigo: Stratified squamous epithelial cell collection (cholesteatoma) in the ear affects balance and hearing.

Epithelial Cell Tests

• Pathology is the lab examination of cells and fluids for diagnosis, conducted by a pathologist.
• Tests include:
  • Epithelial cells in urine: Part of urinalysis. High amounts may indicate infection or kidney disease.
  • Pap smear: Checks for abnormal cervical cells.
  • Biopsy tests: Tissue examination for disease signs.
  • Cytology tests: Examination of cells from bodily tissues or fluids to determine a diagnosis.