Histology and Tissue Anatomy: Epithelial, Connective, Muscle, and Nervous Tissues

What is a tissue?

Groups of similar cells and extracellular material (extracellular matrix) working together for a common function.

What is the study of tissues called?

Histology.

What is epithelium composed of?

One or more layers of closely packed cells with little to no extracellular matrix.

What are the four primary types of tissues?

Epithelial, connective, muscle, and nervous tissues.

What are the three primary locations of epithelial tissue?

Covers body surfaces, lines body cavities, and forms the majority of glands.

What does cellularity mean in epithelial tissue?

The tissue is composed almost entirely of tightly packed cells.

Describe the three surfaces of epithelial tissue polarity.

Apical surface: Exposed to environment/internal space, may have microvilli/cilia. Lateral surface: Intercellular junctions with adjacent cells. Basal surface: Attached to connective tissue via the basement membrane.

How do epithelial tissues obtain nutrients despite being avascular?

Across the apical surface or via diffusion from the basal surface.

Why can epithelial tissue detect environmental changes easily?

It is richly and extensively innervated.

What capacity allows epithelial tissue to continually replace lost cells?

High regeneration capacity.

What are the four primary functions of epithelial tissue?

Physical protection, selective permeability, secretions, and sensations.

Define Simple Epithelium and its primary functions.

One cell layer thick; all cells contact the basement membrane. Primary functions: Filtration, absorption, or secretion.

Define Stratified Epithelium and where it is found.

Two or more layers of cells; only the basal layer contacts the basement membrane. Found in areas subjected to mechanical stress.

What is Pseudostratified Epithelium?

Appears layered but isn't; all cells contact the basement membrane, though not all reach the apical surface.

Describe Squamous, Cuboidal, and Columnar cell shapes.

Squamous: Flat, wide, irregular; flat nucleus. Cuboidal: Tall as wide; central spherical nucleus. Columnar: Slender, taller than wide; oval nucleus in basal region.

What is unique about Transitional cells?

They can change shape depending on the stretch of the epithelium (limited to the urinary tract).

What are the characteristics and functions of Simple Squamous Epithelium?

Single layer of flat cells; thinnest barrier for rapid diffusion, filtration, and secretion in serous membranes.

Where is simple squamous epithelium located?

Air sacs of lungs (alveoli), vessel walls (endothelium), and serous membranes of body cavities (mesothelium).

What are the characteristics and locations of Simple Cuboidal Epithelium?

Single layer of uniformly shaped cells (tall as wide) with a central spherical nucleus. Designed for absorption/secretion. Found in kidney tubules, thyroid follicles, ovary surface, and exocrine gland ducts.

What structures characterize Nonciliated Simple Columnar Epithelium?

Contains microvilli (brush border) and unicellular goblet cells that secrete glycoprotein (mucin) to form mucus.

Where is nonciliated simple columnar epithelium found?

Lines most of the digestive tract from the stomach to the anal canal.

What is the function and location of Ciliated Simple Columnar Epithelium?

Cilia project from the apical surface to move mucus/oocytes. Interspersed with goblet cells. Lines bronchioles and uterine tubes.

What is the function and location of Ciliated Pseudostratified Columnar Epithelium?

Protective function; goblet cells secrete mucin to trap foreign particles moved by cilia. Located in large passageways of the respiratory system.

Where does Nonciliated Pseudostratified Columnar Epithelium occur?

Rare; lacks cilia/goblet cells. Serves a protective function mainly in the male urogenital tract (urethra and epididymis).

Describe Keratinized Stratified Squamous Epithelium.

Multiple cell layers; superficial layers consist of dead cells lacking nuclei and filled with keratin. Protects against abrasion. Found in the epidermis of the skin.

Describe Nonkeratinized Stratified Squamous Epithelium and its locations.

Multiple layers of living cells containing visible nuclei; kept moist with secretions. Lacks keratin. Lines oral cavity, pharynx, esophagus, vagina, and anus.

What is the function and location of Stratified Cuboidal Epithelium?

Two or more layers; superficial cells are cuboidal. Provides protection and secretion. Forms walls of ducts in sweat glands, male urethra, and ovarian follicles.

Where is the rare Stratified Columnar Epithelium found?

Two or more layers with columnar cells at the apical surface. Protects and secretes. Found in large ducts of salivary glands and parts of the male urethra.

Explain the relaxed vs. stretched state of Transitional Epithelium.

Relaxed: Basal cells cuboidal/polyhedral, apical cells large, rounded, and binucleated. Stretched: Apical cells flatten to accommodate urine volume changes in the bladder, ureters, and urethra.

Compare Endocrine and Exocrine glands.

Endocrine: Lack ducts; secrete hormones directly into the blood. Exocrine: Connected to epithelial surface by a duct (epithelium-lined tube) to transport secretions.

What is the most common unicellular exocrine gland?

The goblet cell (does not contain a duct).

What are acini in multicellular exocrine glands?

Cell clusters that produce secretions, surrounded by a fibrous capsule.

Classify exocrine glands by their anatomic forms.

Simple: Single, unbranched duct. Compound: Branched ducts. Tubular: Secretory portion same diameter as duct. Acinar: Secretory portion forms an expanded sac. Tubuloacinar: Contains both tubules and acini.

Differentiate Merocrine, Apocrine, and Holocrine secretion methods.

Merocrine: Released by exocytosis via vesicles (e.g., tear/salivary glands). Apocrine: Apical membrane pinches off (e.g., mammary glands). Holocrine: Entire ruptured cell becomes the secretion (e.g., sebaceous oil glands).

What are the shared basic characteristics of Connective Tissue (CT)?

Most diverse, abundant, and widely distributed type. It is vascular (degree varies) and has variable regenerative capacity (bone/blood high, cartilage none). Cells are generally not in direct contact.

What three basic components do all connective tissues share?

Cells, protein fibers, and ground substance. (Ground substance + protein fibers = extracellular matrix).

Distinguish between Resident cells and Wandering cells in CT.

Resident cells: Stationary; support, maintain, and repair ECM (e.g., fibroblasts, adipocytes). Wandering cells: Continuously move through CT for immune protection.

Describe Collagen, Reticular, and Elastic fibers.

Collagen: Strong and flexible; provides tensile strength. Reticular: Thin, branched fibers that form a supportive network. Elastic: Stretchable fibers that allow tissues to return to their original shape.

What is ground substance and how does its consistency vary?

Molecular material produced by CT cells surrounding cells and fibers. Varies from viscous (blood), semisolid (cartilage), to solid (bone).

What are the six primary functions of Connective Tissue?

Physical protection, support/structural framework, binding of structures, storage, transport, and immune protection.

What embryonic tissue is the common origin source of all adult CT cells?

Mesenchyme.

What are the properties and locations of Areolar CT?

Loose organization of collagen/elastic fibers; predominant cell is the fibroblast; highly vascular. Located in papillary layer of dermis, subcutaneous layer, and surrounding organs/nerves.

Contrast Loose Connective Tissue and Dense Connective Tissue.

Loose CT: Fewer cells/fibers, abundant ground substance; acts as body's 'packing material' (Areolar, Adipose, Reticular). Dense CT: Mostly tightly packed protein fibers, less ground substance; collagen predominates (Dense Regular, Dense Irregular, Elastic).

What are the two types of Adipose CT?

White adipose: Stores energy, acts as an insulator, cushions structures. Brown adipose: Found in newborns, generates heat, lost as we age.

What is the function and location of Reticular CT?

Forms a meshwork of reticular fibers, fibroblasts, and leukocytes to provide the structural framework (stroma) of lymphatic organs (spleen, thymus, lymph nodes, bone marrow).

Describe Dense Regular CT properties and why it takes a long time to heal.

Tightly packed, parallel collagen fibers with few blood vessels, leading to slow healing. Found in tendons and ligaments where stress is applied in a single direction.

What is Dense Irregular CT and where is it found?

Clumps of collagen fibers extending in all directions to withstand stress in multiple directions; highly vascularized. Found in the dermis, periosteum of bone, perichondrium of cartilage, and organ capsules.

What characterizes Elastic CT and its locations?

Branching, densely packed elastic fibers with few fibroblasts; able to stretch and recoil. Located in walls of large arteries (aorta), trachea, and vocal cords.

What are mature cartilage cells called and where are they housed?

Chondrocytes, which are housed in small pockets called lacunae within a firm, semisolid extracellular matrix.

What are the traits and locations of Hyaline Cartilage?

Most common type; clear, glassy appearance under the microscope; surrounded by perichondrium. Found in nose, trachea, larynx, costal cartilage, ends of long bones, and fetal skeleton.

What unique role does Fibrocartilage serve?

Weight-bearing cartilage that resists compression; parallel collagen bundles with sparse ground substance; lacks a perichondrium. Found in intervertebral discs, pubic symphysis, and knee menisci.

What is Elastic Cartilage and where is it located?

Densely packed elastic fibers making it resilient and highly flexible; surrounded by a perichondrium. Located in the external ear and epiglottis.

What are bone cells called and what elements form its matrix?

Osteocytes (housed in lacunae). The solid extracellular matrix contains organic components (collagen/glycoproteins) and inorganic components (calcium salts).

Compare Compact Bone and Spongy Bone structural configurations.

Compact bone: Perforated by neurovascular canals; organized into cylindrical structures called osteons. Spongy bone: Located in the interior; lacy latticework structure that is strong yet lightweight.

What is Lymph tissue derived from?

Derived from blood plasma; contains no cellular components or fragments, and is ultimately returned to the bloodstream.

What are the key traits of Skeletal Muscle Tissue?

Long, cylindrical parallel cells; multinucleated; shows alternating light/dark bands (striations). Under voluntary control of the somatic nervous system; moves the skeleton.

Describe Smooth Muscle Tissue and where it is located.

Also called visceral muscle tissue; lacks striations. Cells are spindle-shaped with a single central oval nucleus. Involuntary control. Found in walls of intestines, stomach, airways, bladder, uterus, and blood vessels.

What structures connect Cardiac Muscle cells and promote rapid electrical conduction?

Intercalated discs connect short, branching cells. They possess 1-2 nuclei, are striated, involuntary, and confined to the myocardium layer of the heart wall.

What are the two major cell types in Nervous Tissue?

Neurons: Receive, process, and transmit nerve impulses. Glial cells: Outnumber neurons; non-conductive cells responsible for protection, nourishment, and support of neurons.

Describe the three main parts of a Neuron.

Cell body: Houses the nucleus and organelles. Dendrites: Shorter, numerous processes that receive incoming signals. Axon: Single long process carrying outgoing signals away from the cell body.

What constitutes an Organ?

Two or more tissue types working together to perform specific complex functions.

What are the four types of Body Membranes?

Mucous membrane (mucosa), Serous membrane, Cutaneous membrane, Synovial membrane.

Classify the levels of Stem Cell potency.

Totipotent, Pluripotent, Multipotent, Unipotent.

Define Hypertrophy, Hyperplasia, and Atrophy.

Hypertrophy: Increase in cell size. Hyperplasia: Increase in cell number. Atrophy: Shrinkage of tissue by decrease in cell number or size.

Differentiate Metaplasia, Dysplasia, and Neoplasia.

Metaplasia: Mature epithelium transforms into a different form. Dysplasia: Abnormal tissue development (can be precancerous). Neoplasia: Out of control growth developing into a benign or malignant neoplasm.

Contrast Tissue Necrosis and Cell Apoptosis.

Necrosis: Pathological tissue death due to irreversible damage, triggering an inflammatory response. Apoptosis: Programmed cell death removing old/abnormal cells seamlessly without causing inflammation.