Epithelial Tissues and Cell Junctions Quiz

Histology of Epithelia and Glands

• Epithelia are tissues categorized by cell arrangement (layers) and cell shape.
• Epithelia line body surfaces, cavities, and form glands.
• Epithelial cells are tightly packed and are classified into simple (single layer) and stratified (multiple layers).
• Specific types include squamous (flat), cuboidal (cube-shaped), columnar (column-shaped), and transitional (variable shape).
• Epithelial tissues contain specialized surface features reflecting their functions of protection, secretion, absorption, and filtration.
• Epithelia are classified by both the cell arrangement and cell shape.

Tissue Overview

• A tissue is a group of cells with a common embryonic origin, working together for specialized functions.
• Tissues can be hard (bone), semisolid (fat), or liquid (blood).
• Histology is the science of studying tissues.
• Pathologists conduct laboratory studies of cells and tissues to diagnose diseases.

Types of Tissues

• Four types of tissues exist: epithelial tissue, connective tissue, muscular tissue, and nervous tissue.
• Epithelial tissue covers body surfaces and lines hollow organs, body cavities, ducts, and forms glands.
• Connective tissue protects, supports, and binds organs, storing energy and providing immunity.
• Muscular tissue generates force for body movement and heat.
• Nervous tissue detects body changes and responds via nerve impulses.

Development of Tissues

• Tissues derive from three primary germ layers: ectoderm, endoderm, and mesoderm.
• Epithelial tissues arise from all three germ layers.
• Connective tissue and most muscle tissues originate from mesoderm.
• Nervous tissue develops from ectoderm.

Cell Junctions

• Cell junctions are contact points between plasma membranes of tissue cells.
• Five common types are tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.
• Tight junctions fuse cells, seal off passageways, and are common in epithelial tissues like intestines and urinary bladder.
• Adherens junctions have plaque proteins, resist separation, and are linked via cadherins.
• Desmosomes have plaque proteins and keratin intermediate filaments, preventing epidermal cell separation.
• Hemidesmosomes anchor cells to the basement membrane via integrin glycoproteins and intermediate filaments.
• Gap junctions are channels for communication through connexins.

Epithelial Tissues

• Epithelial tissue is composed of cells arranged in continuous sheets, either single or multiple layers, tightly packed together.
• Tissues are classified by arrangement into layers, and shapes of cells.
• Three main functions include acting as a selective barrier, producing secretions onto the free surface, and acting as a protective barrier.
• Epithelial tissue comprises various specialized cell types reflecting their functions.

General Features of Epithelial Cells

• Epithelial cells have specialized surfaces: apical (free), lateral, and basal surface.
• Apical surfaces face body surfaces, body cavities, lumens, or ducts.
• Lateral surfaces face adjacent cells.
• Basal surfaces are opposite of apical surfaces and adhere to extracellular materials.

Basement Membrane

• The basement membrane is a double extracellular layer supporting epithelial tissue, serving as an attachment point.
• Basal lamina is closer to the epithelial cells.
• The reticular lamina is closer to connective tissue, containing collagen secreted by connective tissue cells.

Epithelial Tissues and Supplies

• Epithelia lack blood vessels (avascular).
• Blood vessels in underlying connective tissues nourish and remove wastes from epithelial cells.
• The high rate of cell division allows epithelium to repair and renew frequently.
• Epithelial tissue protects, filters, and plays numerous bodily roles.

Covering and Lining Epithelium

• Epithelial tissues can be classified by arrangement—simple (one layer) or stratified (multiple layers) and shape of cells.
• Shapes of cells include squamous (flat), cuboidal (cube-shaped), columnar (column-shaped), transitional (variable shape).

Specific Epithelial Types

• Simple squamous are thin, flat cells ideal for diffusion and filtration (e.g., alveoli in lungs; lining of blood vessels).
• Simple cuboidal are cube-shaped cells for secretion and absorption (e.g., kidneys, tubules in some glands).
• Simple columnar are tall column-shaped cells for secretion and absorption, sometimes ciliated for movement (e.g., intestines, uterine tubes).
• Pseudostratified columnar cells appear layered but all cells contact the basement membrane, often ciliated and found in respiratory tracts.
• Stratified squamous are multiple layers suited for protection and consist of keratinized and non-keratinized variants.
• Stratified cuboidal cells are rare, typically multi-layered, and function in protection.
• Stratified columnar cells are also rare, multi-layered, and provide protection and secretion.
• Transitional epithelium is found in urinary systems and can change in shape depending on stretch status.

Glands Overview

• Glands are classified as multicellular or unicellular, based on the organization of the secretory cells.
• Glands either secrete substances directly onto a body surface or into the blood circulation.
• Exocrine glands secrete onto a body surface via ducts.
• Endocrine glands secrete hormones directly into the blood.

Gland Secretion and Classification

• Exocrine glands have three release mechanisms—merocrine, apocrine, and holocrine.
• Merocrine release by exocytosis to the apical cell membrane, common in acinar cells.
• Apocrine release from apical cell surface by cytoplasm envelope, common in mammary glands.
• Holocrine release involves cell apoptosis and discharging contents, characteristic of sebaceous glands.

Multicellular Glands

• Multicellular glands have varying degrees of complexity, classified by duct arrangement and secretory portion shape (tubular, alveolar/acinous, or tubuloalveolar).
• Shapes of the ducts may be straight, branched, or coiled.
• Alveolar portions can be single or branched.

Other Gland Types

• Unicellular glands like goblet cells secrete mucus within other tissues and are found in columnar tissues.

The Skin

• The integumentary system constitutes the skin and its accessories.
• Different tissues form the largest organ in the body: the skin.
• Three primary regions—epidermis, dermis, and hypodermis.

Functions of the Skin

• Protection, sensation, thermoregulation, control of water loss, and metabolic functions.

Epidermis

• The epidermis is a keratinized stratified squamous epithelium
• The epidermis contains keratinocytes (the predominant cells), melanocytes, Langerhans cells, and Merkel cells.

Epidermis - Melanocytes, Langerhans, and Merkel

• Melanocytes produce pigment melanin for skin color, protecting from UV radiation.
• Langerhans cells are immune cells and antigen-presenting cells.
• Merkel cells function in touch sensation.

Epidermal Layers

• Stratum basale, the deepest layer, includes generative cells, melanocytes, and Langerhans cells.
• Stratum spinosum has flattened cells and spines (forming desmosomes).
• Stratum granulosum cells undergo apoptosis and contain keratohyalin, lamellar granules.
• Stratum lucidum is present only in thick skin.
• Stratum corneum, the outermost layer, contain a lot of flattened dead keratinocytes.

Dermis

• The dermis is a collagen- and elastic-fiber-rich connective tissue.
• Two regions are the papillary and reticular dermis.
• The papillary dermis contains loose areolar, collagen, and elastic fibers.
• The reticular dermis houses sweat and sebaceous glands, blood vessels, nerves, and collagen and elastic fibers.

Skin Cancers

• Basal cell carcinoma is commonly seen on sun-exposed areas, often developing from a pearly nodule.
• Squamous cell carcinoma develops from squamous cell epithelium, progresses rapidly, often resulting from actinic keratosis.
• Malignant melanoma arises from melanocytes, exhibiting asymmetry, irregular borders, varied colors, diameter changes over time, and symptoms.

This quiz tests your knowledge on various aspects of epithelial tissues and their characteristics, including junction types, secretions, and tissue origins. Explore concepts like hemidesmosomes, apocrine secretion, and the morphology of epithelial cells. Perfect for biology students seeking to deepen their understanding of these fundamental topics.