A&P Chapter 4
Epithelial Tissue
General features
Cells are arranged in sheets and are densely packed.
Cells are adhered to adjacent cells via cell junctions.
Epithelial cells attach to a basement membrane.
Epithelial tissue is avascular but has a nerve supply.
Mitosis occurs frequently.
Significance: tight cell packing supports a protective and selective barrier; the basement membrane anchors tissue and enables communication with underlying connective tissue.
Surfaces of epithelial cells and the basement membrane
Apical (free) surface: faces external or internal lumen.
Lateral surfaces: connected to neighboring cells via cell junctions.
Basal surface: attached to the basement membrane.
Basal lamina and Reticular lamina form the basement membrane that underlies epithelium and anchors to connective tissue; provides support and filtration.
Connective tissue contains nerves and blood vessels that nourish the epithelium (epithelium itself is avascular).
Classification of epithelial tissue: covering and lining epithelia
Covering and lining epithelia are classified according to two features:
Shape of apical cells: squamous, cuboidal, columnar.
Number of cell layers: simple, pseudostratified, stratified.
Transitional epithelium is included in some classifications as a tissue type that can stretch.
Example mappings (from Table 4.1 in textbook): simple squamous, simple cuboidal, simple columnar, pseudostratified ciliated, stratified squamous, stratified cuboidal, stratified columnar, transitional (shape and layer combinations vary by tissue).
Glandular epithelium
A gland is a single cell or a mass of epithelial cells adapted for secretion.
Secretions of endocrine glands enter interstitial fluid and diffuse into the bloodstream without flowing through a duct.
Secretions of exocrine glands are released into ducts that empty onto a surface of a covering/lining epithelium (e.g., skin) or into a lumen (e.g., stomach, small intestine).
Endocrine glands (A) Endocrine Glands
Description: Secretions (hormones) enter interstitial fluid and then diffuse into the bloodstream without passing through a duct.
Location (examples): pituitary gland, pineal gland, thyroid and parathyroid glands, adrenal glands, pancreas, ovaries, testes, thymus.
Function: Hormones regulate many metabolic and physiological activities to maintain homeostasis.
Note: Endocrine glands are described in detail in Chapter 18.
Exocrine glands (B) Exocrine Glands
Description: Secretory products are released into ducts that empty onto a surface of covering/lining epithelium (skin surface or lumen of hollow organs).
Location (examples): sweat, oil, earwax glands of skin; salivary glands; pancreas (secretes into small intestine).
Function: Produce substances such as sweat, oil, earwax, saliva, or digestive enzymes.
Connective Tissue
General features
Consists of two basic elements:
Cells
Extracellular matrix – accounts for the functionality of the tissue
Connective tissue cells do not have any free surfaces.
Connective tissue is highly vascularized and has a nerve supply.
Exceptions: tendons and cartilage (relatively poor blood supply).
Extracellular matrix (ECM) in connective tissue (1 of 2)
ECM is located in the spaces between connective tissue cells.
ECM is composed of
fibers
ground substance
Function: ECM provides structural support and biochemical properties that determine tissue function.
ECM fibers (2 of 2)
Collagen fibers: strong and resist stretching but are not highly elastic; found in bone, cartilage, tendons, ligaments.
Elastic fibers: can stretch and return to original shape; found in skin, vessel walls, lungs.
Reticular fibers: thin collagen fibers forming fine networks; form stroma of soft organs (e.g., spleen).
These fibers contribute to the mechanical properties of connective tissues and shape tissue organization.
Classification of connective tissue (2 of 2)
Mature connective tissue categories:
Loose connective tissue
Dense connective tissue
Cartilage
Bone
Blood
Loose connective tissue
Areolar connective tissue: randomly arranged fibers and cells in a semi-fluid ground substance; found around nearly every body structure (e.g., subcutaneous tissue).
Adipose tissue: fat storage.
Reticular connective tissue: fine network of reticular fibers forming the stroma of soft organs.
Location example: subcutaneous tissue and around various structures; provides support and packing.
Dense connective tissue
Dense regular connective tissue: collagen fibers arranged in parallel bundles with rows of fibroblasts between them; forms tendons and ligaments (strength in one direction).
Dense irregular connective tissue: collagen fibers irregularly arranged with few fibroblasts; forms fascia, dermis, and other tissues needing strength in multiple directions.
Cartilage
Hyaline cartilage: contains a resilient gel-like ground substance; most abundant type; found at ends of long bones, nose, trachea, etc.; weakest type but provides smooth surface for movement.
Fibrous cartilage: thick bundles of collagen within ECM; found in intervertebral discs and menisci; strongest type of cartilage due to dense collagen.
Elastic cartilage: contains elastic fibers; found in the external ear and other structures requiring flexibility.
Bone tissue
Compact bone consists of osteons (also called Haversian systems).
An osteon has four parts:
Bone lamellae – concentric rings of ECM (mostly calcium and phosphate minerals and collagen fibers).
Bone lacunae – small spaces between lamellae containing osteocytes (mature bone cells).
Bone canaliculi – networks of canals projecting from lacunae containing the processes of osteocytes, enabling nutrient and waste movement.
Osteonic (Haversian) canal – contains blood vessels and nerves.
Spongy bone lacks osteons; contains trabeculae and spaces that often contain red bone marrow.
Periosteum: outer fibrous layer and inner osteogenic layer; contains periosteal vessels and nerves.
Medullary cavity: central cavity within long bones.
Bone tissue (visual summaries)
Spongy bone: bone trabeculae with spaces typically filled with red bone marrow.
Compact bone: osteons with concentric lamellae and central canal.
Periosteum surrounds bone; periosteal vessels supply the bone.
Blood (connective tissue overview)
Blood is a liquid connective tissue.
Components:
Blood plasma – fluid with dissolved substances (nutrients, wastes, enzymes, proteins, hormones, respiratory gases, ions).
Red blood cells (RBCs) – transport oxygen to body cells and help remove some carbon dioxide.
White blood cells (WBCs) – involved in immunity, allergic reactions, and phagocytosis.
Platelets – involved in blood clotting.
Muscular Tissue
General characteristics
Muscular tissue consists of muscle fibers, or myocytes, that use ATP to generate force.
Three types of muscle tissue:
Skeletal muscle
Cardiac muscle
Smooth muscle
Skeletal muscle
Striated and voluntary.
Attached to bones by tendons, enabling movement.
Structure includes long, cylindrical fibers with multiple nuclei and striations.
Cardiac muscle
Striated and involuntary.
Found in the heart wall.
Cells are joined end-to-end by intercalated discs to allow rapid electrical conduction and coordinated contraction.
Smooth muscle
Nonstriated and involuntary.
Located in walls of hollow internal structures (e.g., blood vessels, gastrointestinal tract).
Functions include constriction of vessels, propulsion of ingesta, contraction of the urinary bladder, etc.
Nervous Tissue
General characteristics
Two kinds of cells: neurons (nerve cells) and neuroglia, or glial cells (support cells).
Neurons
Basic parts:
Cell body (soma): contains nucleus and organelles.
Dendrites: short, branched processes; receptive portions.
Axon: long, single process; output portion that conducts nerve impulses to another neuron or target tissue.
Direction of message travel: typically from dendrites/soma through the axon to target tissues.
Myelin sheaths may surround axons to increase conduction speed.
Nervous tissue overview
Nervous tissue coordinates and controls body activities through rapid electrical signaling and chemical communication.
Excitable cells
Neurons and muscle fibers are excitable because they can respond to stimuli with electrical signals (action potentials).
Electrical excitability relies on voltage-gated channels in the plasma membranes.
These signaling mechanisms enable rapid communication and response across tissues and organs.
Exam 1 – What NOT to study (study guidance excerpt)
The following are listed as items NOT to study for Exam 1:
Clinical Connections
Ch 1
Table 1.2 – Eleven Systems of the Body
Section 1.6 – Aging and Homeostasis
Section 1.7 – Medical Imaging
Ch 2
Table 2.5 – Functional groups of organic molecules
Ch 3
Section 3.8 – Cellular Diversity
Section 3.9 – Aging and Cells, Cancer
Ch 4
Section 4.2 – Cell Junctions
Structural Classification of Exocrine Glands, with Figure 4.6
Embryonic Connective Tissue, with Table 4.3
Section 4.6 – Membranes
Section 4.10 – Tissue Repair
Section 4.11 – Aging
Note: This list is for exam preparation guidance and reflects content designated as not to study in that context.
Connections to broader concepts
Interdependence of tissue types:
Epithelial tissue provides covering, lining, and glandular functions; it often interfaces with connective tissue for support (basement membrane anchors epithelium to connective tissue).
Connective tissue provides support, structure, and transport (blood), with ECM composition dictating tissue properties (strength, elasticity, and resilience).
Muscular tissue converts chemical energy (ATP) into mechanical work; nervous tissue coordinates and regulates activity through rapid signaling.
Functional implications:
The avascularity of epithelia necessitates diffusion from underlying tissues for nutrients and waste removal; nerve supply supports sensory and motor functions.
Bone and cartilage provide rigid support and facilitate movement with skeletal muscles; bone contains a mineralized ECM for strength; cartilage provides flexible support and reduces friction.
Cardiac and smooth muscle enable involuntary control of circulatory and visceral systems, while skeletal muscle enables voluntary locomotion.
Practical relevance:
Understanding tissue structure-function relationships underpins interpretation of histology slides and the diagnosis of tissue-related pathologies.
References to terminology and concepts mentioned in the transcript
Epithelial tissue terms: epithelial sheet, basement membrane, basal lamina, reticular lamina, apical surface, avascularity, nerve supply, cell junctions.
Gland terminology: endocrine vs exocrine; duct, lumen, surface epithelium.
Connective tissue terminology: ECM, fibers (collagen, elastic, reticular), ground substance, vascularization, nerves.
Connective tissue mature classes: loose, dense, cartilage, bone, blood.
Cartilage types: hyaline, fibrous, elastic.
Bone structure: osteon, lamellae, lacunae, canaliculi, osteonic canal; periosteum; medullary cavity; trabeculae.
Blood components and functions: plasma, RBCs, WBCs, platelets.
Muscle types: skeletal, cardiac, smooth; features and functional roles.
Nervous tissue components: neurons, soma, dendrites, axons; neuroglia; electrical excitability and voltage-gated channels.