Anatomy & Physiology: Histology, Tissues, and Integumentary System Study Guide

Histology and Tissues

Definitions and Overview

• Histology: The study of tissues, their structure, and function.

• Tissue: A group of structurally and functionally related cells and their extracellular matrix.

• Extracellular Matrix (ECM): The substance outside of the cells, consisting of ground substance and protein fibers.

Epithelial Tissue

• Definition: Epithelial tissue is named based on the number of cell layers and the shape of the cells.

• Location: Found lining and covering all body surfaces and hollow organs. Forms glands.

• General Description: Composed of epithelial cells and a thin basal layer of extracellular matrix.

Functions of Epithelial Tissue

• Protection: Provides a continuous surface to protect from external environment (e.g., keratin in epidermis of skin).

• Immune Defense: Specialized immune cells are embedded in epithelial tissues to protect against invading microorganisms.

• Secretion: Forms glands that produce substances such as oil or hormones.

• Transport: Selectively permeable barriers; certain substances can cross via passive or active transport.

• Sensation: Epithelial tissues are richly supplied with nerves that detect changes in the internal and/or external environment.

Classification of Epithelial Cells

• Simple Epithelium: One layer of cells (squamous, cuboidal, columnar).

• Stratified Epithelium: More than one layer of cells (usually squamous).

• Squamous: Flattened/squashed cells (e.g., alveoli in lungs for gas exchange).

• Cuboidal/Columnar: Cube-shaped or column-shaped cells (absorption and secretion, e.g., in kidney tubules or intestines).

Additional info: The function and location of each epithelial type depend on organ and tissue needs.

Specializations and Examples

• Keratinized Epithelium: Found on external surfaces (skin); cells are tough and water-resistant.

• Nonkeratinized Epithelium: Found on internal surfaces (mouth, esophagus, vagina); cells remain moist and can slough off.

• Cilia: Found in pseudostratified ciliated columnar epithelium (e.g., bronchioles, airways) to sweep out debris.

• Goblet Cells: Unicellular glands in simple columnar epithelium that secrete mucus (digestive and respiratory tracts).

Examples of Epithelial Types and Locations

• Simple squamous – alveoli (air sacs) in the lungs

• Simple cuboidal – renal tubules of the kidney

• Simple columnar – intestines/digestive system

• Pseudostratified ciliated columnar – bronchioles/airways

• Transitional – urinary bladder

• Stratified squamous – skin, inside cheeks of mouth

Connective Tissue

Overview and Functions

• Definition: Connective tissue is a diverse group of tissues with functions including connecting, binding, support, protection, transport, insulation, and energy storage.

• Locations: Found throughout the body: tendons, ligaments, bone, blood, cartilage, adipose tissue.

Types of Connective Tissue

• Connective Tissue Proper

• Cartilage

• Bone

• Blood

Functions of Connective Tissue (with Examples)

1. Connecting and binding (cartilage, dense regular tissue at joints)

2. Support (cartilage and bone support the weight of the body)

3. Protection (bones of the skull protect the brain; rib cage protects heart and lungs)

4. Transport (blood moves oxygen and nutrients, removes waste)

5. Insulation (adipose tissue prevents heat loss)

6. Energy storage (adipose tissue stores energy)

Extracellular Matrix (ECM)

• Composition: Made up of protein fibers (collagen, elastic, reticular) and ground substance.

• Function: Provides structural support, binds cells together, and regulates cellular functions.

• ECM Abundance: Loose connective tissues have less ECM; dense connective tissues and cartilage have more ECM.

Cells of Connective Tissue and Locations

Cell Type	Location/Example
Adipocytes	Adipose tissue, hypodermis, around internal organs
Fibroblasts	Areolar connective tissue, papillary dermis of skin
Mast cells	Areolar connective tissue, other loose connective tissues
Macrophages	Areolar connective tissue
Red blood cells	Blood, inside blood vessels
White blood cells	Blood, reticular tissue (lymph nodes, spleen)
Chondrocytes	Cartilage (all 3 types: hyaline, elastic, fibrocartilage)
Osteocytes	Bone tissue (femur, humerus, etc.)

Muscle Tissue

Types and Features

• Skeletal Muscle: Voluntary, multinucleate, striated, attached to bones (e.g., biceps brachii).

• Cardiac Muscle: Involuntary, striated, single and multi-nucleate, found in the heart.

• Smooth Muscle: Involuntary, single nucleus, no striations, found in walls of hollow organs (e.g., intestines, stomach).

Muscle Tissue Repair

• Epithelial tissues: Typically regenerate to repair damaged tissue.

• Connective tissues: Most regenerate well, except cartilage (limited ability).

• Muscle tissues: Cardiac and skeletal muscle repair by fibrosis (scar tissue formation).

Nervous Tissue

Cell Types and Functions

• Neurons: Send and receive signals; main parts are cell body, axon, dendrites.

• Neuroglial Cells: Support and nourish neurons and other nervous tissue.

Integumentary System (Skin)

Functions of the Skin

• Protection from mechanical trauma, pathogens, and the environment

• Sensation (sensory receptors)

• Thermoregulation (maintaining body temperature)

• Excretion of waste (sweat)

• Vitamin D synthesis

Membranes of the Skin

• Cutaneous membrane: Areolar connective tissue and dense irregular connective tissue

• Subcutaneous membrane (hypodermis): Adipose tissue

Layers of the Epidermis (Deep to Superficial)

1. Stratum basale (deepest layer)

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum (thick skin only)

5. Stratum corneum (most superficial, keratinized dead cells)

Skin Pigments

• Melanin: Orange/brown to black pigment

• Hemoglobin: Reddish-pink pigment

• Carotene: Yellow/orange pigment

Dermis and Hypodermis

• Dermis: Two layers: papillary (areolar connective tissue) and reticular (dense irregular connective tissue)

• Hypodermis: Subcutaneous layer of adipose tissue; not technically part of the skin

Skin Appendages

• Hair: Follicle, root, shaft

• Nails: Nail plate, body, root, cuticle, lunula

• Glands: Sebaceous (oil), sweat (eccrine and apocrine), mammary

Glands: Exocrine vs. Endocrine

• Exocrine glands: Release secretions to the surface via ducts (e.g., sweat, sebaceous glands)

• Endocrine glands: Release hormones directly into the blood (e.g., pituitary, thyroid)

Skin Pathology

Skin Cancer Types

• Basal cell carcinoma: Most common, arises from keratinocytes of the stratum basale

• Squamous cell carcinoma: Cancer of keratinocytes of the stratum spinosum

• Melanoma: Most dangerous, cancer of melanocytes; diagnosed using the ABCDE rule

Burns (Degrees and Severity)

1. First-degree: Superficial, only epidermis, minor sunburn

2. Second-degree: Damage to entire epidermis and part of dermis, blisters, possible scarring

3. Third-degree: Most damaging, skin destroyed down to muscle and bone, risk of fluid loss and infection