Human Anatomy and Physiology Quiz

Tissue Organization

• Tissues are groups of similar cells and extracellular material that perform a shared function
• Examples of tissue functions: providing protection, support, and transport
• Histology is the study of tissues

Four Tissue Types

• Epithelial, connective, muscle, and nervous
• These tissues have varied structures and functions

Epithelial Tissue Characteristics

• Covers body surfaces and lines body cavities
• Forms the majority of glands
• Composed of one or more layers of closely packed cells
• Contains minimal or no extracellular matrix
• Lacks blood vessels

Cellularity

• Composed mostly of tightly packed cells

Polarity

• Has an apical surface exposed to the external or internal environment
• May have microvilli or cilia
• Has a lateral surface with intercellular junctions
• Has a basal surface attached to connective tissue

Attachment to Basement Membrane

• A complex structure produced by epithelium and connective tissue
• Consists of three layers: lamina lucida, lamina densa, and reticular lamina
• Contains collagen fibers and specific proteins and carbohydrates
• Forms a selective barrier between epithelium and connective tissue

Avascularity

• Without blood vessels
• Nutrients are obtained from the apical or basal surface

Extensive Innervation

• Detects changes in the surrounding environment
• High regeneration capacity: Cells frequently damaged or lost
• Deepest epithelial cells (stem cells) adjacent to the basement membrane continuously regenerate

Functions of Epithelial Tissue

• Physical protection: Protects external and internal surfaces
• Selective permeability: Some substances cannot pass
• Secretion: Specialized cells produce and release substances
• Sensations: Contains nerve endings for touch, pressure, temperature, pain, etc
• Specialized epithelium (neuroepithelium) houses cells for sight, taste, smell, hearing, and equilibrium

Epithelial Classification

• Two parts indicate classification:
  • First part: Number of cell layers (simple or stratified)
  • Second part: Shape of cells at their apical surface (squamous, cuboidal, columnar, transitional)

Simple Epithelium

• One layer thick
• All cells are in direct contact with the basement membrane
• Found in areas where stress is minimal
• Functions in filtration, absorption, and secretion

Stratified Epithelium

• Two or more cell layers thick
• Only the deepest layer is in contact with the basement membrane
• Found in areas subject to stress (better able to withstand wear and tear)

Pseudostratified Epithelium

• Appears layered due to nuclei at different levels
• All cells are attached to the basement membrane
• Some cells don't reach the apical surface; a type of simple epithelium

Squamous Cells

• Flat, wide, and irregular in shape
• Arranged like flattened floor tiles
• Nucleus flattened

Cuboidal Cells

• Approximately as tall as they are wide
• Nucleus is spherical and centrally located

Columnar Cells

• Slender and taller than they are wide
• Nucleus is oval

Transitional Cells

• Change shape based on stretch of the epithelium
• Polyhedral in shape when relaxed, flattened when stretched (e.g., Lining of the bladder)

Simple Squamous Epithelium

• Thinnest possible barrier. Consisting of single layer of flattened cells, spherical to oval nucleus.
• Allows rapid movement of molecules across surfaces.
• Forms lining of air sacs of lungs.
• Found lining blood and lymph vessel walls (called endothelium).
• Forms mesothelium (lining of cavities).

Simple Cuboidal Epithelium

• Contains uniformly shaped cells used for small ducts and glands.
• Single layer of cells, cuboidal in shape.
• Absorbs fluid across the apical surface.
• Secretes specific molecules (e.g., walls of kidney tubules, most glands, smaller ducts of exocrine glands, surface of ovary, thyroid gland).

Simple Columnar Epithelium (Nonciliated)

• Single layer of columnar cells ideal for secretory and absorptive functions.
• Often contains microvilli (collectively called a brush border).
• Often contains unicellular glands (goblet cells) that secrete glycoprotein (mucin) forming mucus.
• Lines most of the digestive tract

Simple Columnar Epithelium (Ciliated)

• Has cilia projecting from the apical surface to move mucus.
• Goblet cells are interspersed.
• Lines uterine tubes, helps move oocytes from the ovary to the uterus.
• Found in bronchioles.

Pseudostratified Columnar Epithelium

• Appears to consist of multiple cell layers but is actually simple, with nuclei scattered at different distances.
• Not all cells reach the apical surface.
• Houses goblet cells and may have cilia.
• Found in large passageways of the respiratory system, male urethra, and epididymis.

Stratified Squamous Epithelium (Nonkeratinized)

• Alive all the way to the apical surface
• Has microscopically visible cell nuclei
• Kept moist by secretions (e.g., saliva, mucus)
• Lacks keratin (protective protein) Lines the oral cavity, pharynx, esophagus, vagina, and anus.

Stratified Squamous Epithelium (Keratinized)

• Superficial layers are dead
• Cells lack nuclei; filled with keratin
• Cells in the basal region migrate toward the apical surface, fill with keratin, and die.
• Found in the epidermis.

Stratified Cuboidal Epithelium

• Contains two or more layers of cells; these cells are cuboidal in shape
• Primarily protective
• Forms walls of ducts of most exocrine glands (e.g. ducts of sweat glands)

Stratified Columnar Epithelium

• Two or more layers of cells.
• Cells at apical surface are columnar in shape.
• Protective and secretory functions.
• Found in large ducts of salivary glands; the membranous segment of the male urethra.

Transitional Epithelium

• Restricted to the urinary tract
• In relaxed state: Apical cells are large and rounded
• In stretched state: Apical cells are flattened
• Contains binucleated cells.

Glands

• Individual cells or multicellular organs
• Composed predominantly of epithelial tissue
• Secrete substances for use elsewhere or to eliminate wastes (like mucus, electrolytes, hormones, enzymes, urea)

Endocrine Glands

• Lack ducts
• Secrete hormones into interstitial fluid and blood
• Act as chemical messengers influencing cell activity elsewhere

Exocrine Glands

• Formed from invaginated epithelium in connective tissue
• Connected to epithelial surface by a duct (epithelium-lined tube for gland secretion)
• Includes sweat glands, mammary glands, and salivary glands

Unicellular Exocrine Glands

• Typically do not contain a duct
• Located close to the epithelium surface
• Goblet cell is the most common example

Multicellular Exocrine Glands

• Contain numerous cells, such as acini (cell clusters producing secretions)
• Contain ducts transporting secretions to the epithelial surface
• Often surrounded by a fibrous capsule, partitioned into lobes.

Method of Secretion

• Merocrine: Package secretions into vesicles and release them by exocytosis (e.g., lacrimal glands, salivary glands, some sweat glands, exocrine glands of the pancreas, gastric glands of the stomach)
• Apocrine: Pinch off a portion of the apical membrane along with secretory product; damaged cells repair; release is by exocytosis (e.g., mammary glands, some axillary and pubic sweat glands)
• Holocrine: Accumulates a product inside a cell until it ruptures releasing the product and the cell itself (e.g., oil-producing glands in the skin, sebaceous glands).

Connective Tissues: Cells in a Support Matrix

• Consists of cells, protein fibers, and ground substance.
• Most diverse, abundant, and widely distributed.
• Designed to support, protect, and bind organs.
• Examples include: tendons, ligaments, body fat, cartilage, bone, and blood.

Connective Tissue Support Matrix: Characteristics (Cells)

• Resident cells (stationary) are permanently housed within the connective tissue

  • Fibroblasts: Most abundant; produce fibers and ground substance.
  • Adipocytes (fat cells): Appear as small clusters. In large amounts, the tissue is termed adipose connective tissue.
  • Mesenchymal cells: Type of embryonic stem cell that replaces damaged cells, producing committed connective tissue cells.
  • Fixed Macrophages: Relatively large, irregular shaped cells. Derived from monocytes - phagocytize (engulf) damaged cells or pathogens; scattered throughout matrix.

• Wandering cells (mobile) are continuously moving through the connective tissue

• Mast cells: Small, mobile cells close to blood vessels, secrete heparin to inhibit blood clotting, and histamine to dilate blood vessels.

• Plasma cells: Formed when B-lymphocytes are activated by foreign material, produce antibodies to immobilize foreign materials.

• Free macrophages: Mobile phagocytic cells that function like fixed macrophages.

• Other leukocytes (neutrophils, lymphocytes): Phagocytize bacteria and attack and kill foreign materials.

Connective Tissue Support Matrix: Characteristics (Protein Fibers)

• Collagen fibers: Strong, flexible, resistant to stretching; numerous in tendons and ligaments.
• Reticular fibers: Thinner than collagen fibers; tough but flexible; abundant in stroma (connective tissue framework) of lymphoid organs (lymph nodes, spleen, liver)
• Elastic fibers: Branching wavy fibers that stretch and recoil easily; found in skin, lungs, and arteries.

Connective Tissue Support Matrix: Characteristics (Ground Substance)

• Nonliving material
• Produced by connective tissue cells
• Contains large molecules, and water.
• Can be viscous (e.g., blood) or semisolid (e.g., cartilage) or solid (e.g., bone).
• Ground substance + protein fibers = extracellular matrix

Connective Tissue Functions

• Physical protection; Support and structural framework; Binding of structures; Storage; Transport; Immune protection.

Clinical Views (Scurvy, Marfan Syndrome)

• Scurvy: Deficiency of vitamin C; needed for healthy collagen.
• Marfan syndrome: Genetic disease of connective tissue, skeletal, cardiovascular, and visual abnormalities. (abnormally long limbs, fingers, toe; malformed thoracic cage, vertebral column; easily dislocated joints, weakness in aorta, abnormal heart valves)

Tissues in Organs and Body Membranes

• Organs: Composed of two or more tissue types that work together to perform specific complex functions. (e.g. stomach - contains all four types)
• Body Membranes: Formed from epithelial tissue bound to underlying connective tissue; four types: mucous, serous, cutaneous, and synovial

Tissue Development and Aging

• Metaplasia: Change in a mature epithelium to a different form in response to the environment (e.g., smokers' trachea epithelium from pseudostratified ciliated columnar to nonkeratinized stratified squamous epithelium; chronic acid reflux - esophagus epithelium changes from nonkeratinized to simple columnar).
• Hypertrophy: Increased cell size
• Hyperplasia: Increased cell number
• Neoplasia: Abnormal tissue growth
• Atrophy: Shrinkage of tissue (due to normal aging, lack of use)
• Necrosis: Tissue death due to irreversible damage.
• Aging of Tissues: Changes in support, maintenance, replacement of cells; changes to structure and composition of tissues; declining amount of collagen, delayed tissue repair. Accelerated decline with poor diet and circulation problems.

Test your knowledge on human anatomy and physiology with this quiz. Questions cover a range of topics including connective tissue, epithelial cells, and various symptoms of diseases. It's a great way to solidify your understanding of the human body's structure and function.