Cilia, Flagella, and Microvilli

Differences Between Cilia and Flagella

Cilia and flagella are cellular extensions that aid in movement. They differ in structure, number per cell, and function, but both are anchored to the plasma membrane by centrioles and have a 9+2 microtubule arrangement.

• Cilia: Short, multiple per cell; move substances over cell surfaces.

• Flagella: Long, usually only one per cell; propel the cell itself.

• Both are anchored by centrioles and have a 9+2 microtubule arrangement (9 pairs around the periphery, 2 in the center).

Example: Cilia line the respiratory tract and move mucus loaded with impurities up into the throat, where it can be swallowed and removed by the digestive system. The only human cell with a flagellum is the sperm cell, which uses its flagellum to propel itself through the female reproductive tract to reach the egg.

Structure and Function of Microvilli

Microvilli are finger-like extensions of the plasma membrane that increase the surface area for absorption. They are found on one side of certain cells, especially in the digestive tract and kidney tubules.

• Increase surface area for absorption.

• Found in areas with high absorption, such as intestines and kidneys.

• Composed of actin filaments (part of the cytoskeleton).

• Appear as a fuzzy border under the microscope.

Example: Microvilli line the cells of the intestine, increasing the surface area for nutrient absorption.

Epithelial Tissue

Types and Histology

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It exhibits polarity (apical and basal surfaces) and sits on a basement membrane (except glandular epithelium).

• Forms all glands (e.g., thyroid, adrenal, thymus).

• Exhibits polarity: apical and basal surfaces.

• Sits on a basement membrane (except glandular epithelium).

• Often found above connective tissue.

Example: In kidney sections, simple cuboidal epithelium lines tubules, while simple squamous epithelium forms thin barriers.

Classification of Epithelial Tissue

Epithelial tissues are classified by the number of layers and the shape of cells at the apical surface.

• Simple epithelium: One layer of cells.

• Stratified epithelium: Two or more layers.

• Cell shapes: squamous (flat), cuboidal (cube-shaped), columnar (tall).

Example: The outer layer of skin is stratified squamous epithelium, providing protection against abrasion.

Specialized Epithelial Types

• Simple Squamous Epithelium: Single layer of flat cells; allows rapid movement of materials (e.g., oxygen, carbon dioxide).

• Simple Cuboidal Epithelium: Single layer of cube-shaped cells; found in glands and kidney tubules, involved in secretion and absorption.

• Pseudostratified Columnar Epithelium: Appears to have multiple layers due to nuclei at different heights, but all cells touch the basement membrane; often ciliated, found in respiratory tract.

• Stratified Squamous Epithelium: Multiple layers of flat cells; keratinized type forms skin, nonkeratinized type lines mouth, esophagus, vagina.

• Transitional Epithelium: Specialized for stretching; found in urinary bladder, changes shape when stretched.

Tissue Preparation and Staining

Preparation Steps

Tissue preparation for microscopy involves fixing, dehydrating, sectioning, and staining tissues. Proper preparation is essential for clear visualization under the microscope.

• Fixing tissues preserves structure.

• Dehydration is done using alcohol steps (e.g., 90% to 75%).

• Sectioning creates thin slices for microscopy.

• Staining highlights specific structures (e.g., HME, hematoxylin and eosin).

Example: Students are instructed to study several tissue types before the next week and will examine tissue slides in the lab.

Microscopy Techniques

Types of Microscopes

Different types of microscopes are used to study tissues: compound light microscopes, transmission electron microscopes (TEM), and scanning electron microscopes (SEM). Each provides different levels of detail.

• Compound light microscopes use two lenses and light to magnify tissues.

• TEM provides detailed internal structure but is more expensive.

• SEM shows surface detail and is preferred when internal detail is not needed.

• SEM costs three to five times more than TEM.

Example: Microvilli can be observed under light microscopes, TEM, and SEM, each revealing different aspects of their structure.

Routes of Pathogen Entry and Protective Mechanisms

Entry and Protection

Pathogens can enter the body through cuts, the respiratory tract, or ingestion. The body has mechanisms to prevent pathogens from establishing, such as eating sterile food and having protective barriers in the respiratory tract.

• Pathogens can breach barriers via cuts, inhalation, or ingestion.

• Protective mechanisms exist but are not foolproof.

• Dental hygienists use eye protection to avoid exposure to pathogens.

Example: The body uses barriers such as skin, respiratory tract, and digestive tract to prevent disease transmission from patients' mouths.

HTML Table: Comparison of Cilia, Flagella, and Microvilli

Additional info:

• Some context and terminology were inferred from fragmented notes and standard academic sources.

• Details about tissue preparation, microscopy, and epithelial tissue classification were expanded for clarity and completeness.