Anatomy & Physiology: Skin, Tissues, and Glands Study Guide

Skin Structure and Function

Cells of the Epidermis

The epidermis is composed of several specialized cell types, each with distinct functions essential for skin health and protection.

• Keratinoctyes: Main cell type; produce keratin, vitamin D, and epidermal growth factors. Protect the immune system.

• Tactile (Merkel) cells: Sensory cells in the basal layer; detect touch via nerve fibers.

• Melanocytes: Produce melanin to protect against UV rays; found in the stratum basal and spinosum.

• Langerhans cells: Dendritic immune cells; migrate from bone marrow, found in spinosum and granulosum layers.

• Stem cells: Undifferentiated cells in the basal layer; give rise to new keratinocytes.

Strata of the Epidermis

The epidermis is organized into five distinct layers, each with unique characteristics and functions. The mnemonic "Come, Let's Get Sun Burned" helps recall the order from superficial to deep.

• Stratum corneum: Outermost layer; protects deeper layers, contains dead keratinocytes.

• Stratum lucidum: Found in thick skin (palms, soles); provides extra protection.

• Stratum granulosum: 3-5 rows of keratinized cells; contains lamellar granules for waterproofing and apoptosis.

• Stratum spinosum: 8-10 rows of keratinocytes; contains pre-keratin filaments, Langerhans cells, and melanocytes.

• Stratum basale: Deepest layer; site of cell division, contains stem cells, melanocytes, and Merkel cells.

Thick vs Thin Skin

Thick skin is found on the palms and soles, contains all five strata, and lacks hair follicles and sebaceous glands. Thin skin covers the rest of the body, has fewer layers, and contains hair follicles and sebaceous glands.

Dermis and Hypodermis

Dermis

The dermis is a connective tissue layer beneath the epidermis, providing strength and flexibility.

• Papillary layer: Areolar tissue, vascular, contains nerve endings and dermal papillae (fingerprints).

• Reticular layer: Dense irregular connective tissue, resistant to stretching, contains collagen and elastic fibers.

Hypodermis

The hypodermis (subcutaneous layer) consists of areolar and adipose tissue, serving as insulation and energy storage.

• Good site for drug injection due to proximity to blood supply.

• Contains subcutaneous fat for energy and heat production.

Skin Color and Pathological Changes

Normal and Pathological Colors

Skin color is determined by pigments and blood flow. Abnormal colors can indicate underlying health issues.

• Melanin: Brown-black pigment; provides UV protection.

• Hemoglobin: Red pigment in blood; gives skin a pinkish hue.

• Carotene: Yellow-orange pigment; accumulates in the skin.

• Abnormalities:

  • Cyanosis: Blue skin due to lack of oxygen.

  • Erythema: Redness from increased blood flow.

  • Hematoma: Bruising from blood clotting.

  • Jaundice: Yellowing from liver damage.

  • Pallor: Pale skin from decreased blood flow.

  • Albinism: White skin due to lack of melanin (genetic).

Skin Functions

• Protection from water loss, UV rays, air, and infections.

• Excretion of body fluids via sweat.

• Production of vitamin D and immune system support.

• Defense against antimicrobial pathogens.

Glands of the Skin

Types of Sweat (Sudoriferous) Glands

Sweat glands help regulate body temperature and excrete waste.

• Apocrine glands: Secrete sweat with proteins and fatty substances; found in axillary and genital areas; active during puberty.

• Merocrine (eccrine) glands: Most abundant; found in palms, forehead, and hands; secrete watery sweat for cooling.

Other Skin Glands

• Sebaceous glands: Secrete sebum (oil) to lubricate skin and hair; found in face, scalp, and other areas.

• Ceruminous glands: Produce cerumen (earwax); found in the ear canal.

Skin Cancer and Burns

Common Forms of Skin Cancer

• Basal cell carcinoma: Originates in stratum basale; rarely spreads.

• Squamous cell carcinoma: Originates in stratum spinosum; may spread.

• Malignant melanoma: Originates in melanocytes; spreads rapidly and is dangerous.

ABCDE Rule for Melanoma: Asymmetry, Border, Color, Diameter, Evolving.

Degrees of Burns

• 1st degree: Epidermis only; heals in 3-6 days (e.g., sunburn).

• 2nd degree: Epidermis and dermis; heals in 3-4 weeks.

• 3rd degree: Epidermis, dermis, hypodermis; may cause shock and infection, affects immune system, months to years to heal.

Tissue Types and Classification

Major Tissue Classes

• Epithelial tissue: Covers surfaces, lines cavities, forms glands.

• Connective tissue: Supports, binds, and protects organs.

• Nervous tissue: Conducts impulses, coordinates body functions.

• Muscular tissue: Enables movement.

Properties of Epithelium

• Lines external and internal surfaces.

• Has apical (top) and basal (bottom) surfaces.

• Attached to a basement membrane.

• Avascular (no blood supply).

Types of Epithelial Tissue

Epithelial tissues are classified by cell shape and number of layers.

• Simple squamous: Thin, flat; found in alveoli, kidney, blood vessels.

• Simple cuboidal: Square/rounded; found in liver, thyroid, mammary glands, kidney tubules.

• Simple columnar: Tall, column-shaped; found in GI tract, kidney, uterus.

• Pseudostratified columnar: Appears layered, but all cells touch basement membrane; found in respiratory tract.

• Stratified squamous (keratinized): Multiple layers, resistant to water; found in skin.

• Stratified squamous (non-keratinized): Moist surfaces; found in mouth, esophagus, vagina.

• Stratified cuboidal: Multiple layers; found in sweat glands, ovarian follicles.

• Stratified columnar: Protects and secretes; found in conjunctiva, pharynx, anus, male urethra.

• Transitional (urothelium): Stretches; found in bladder, ureters.

Connective Tissue

Common Properties

• Extracellular matrix (ground substance and fibers).

• Cells are not in direct contact.

• Highly vascular (except cartilage).

Connective Tissue Cell Types

• Fibroblasts: Produce fibers and ground substance.

• White blood cells: Immune defense.

• Adipocytes: Store triglycerides (fat).

Matrix and Fibers

• Matrix: Extracellular material (ground substance).

• Collagen fibers: Provide strength and framework.

• Elastic fibers: Provide elasticity.

• Reticular fibers: Thin collagen fibers; form supportive mesh.

Major Types of Connective Tissue

Type	Cellular Components	Matrix/Fibers	Function
Fibrous Connective Tissue	Fibroblasts, collagen fibers	Dense matrix	Support, protection, binding
Dense Regular Connective Tissue	Fibroblasts	Parallel collagen fibers	Resists tension; found in tendons, ligaments
Dense Irregular Connective Tissue	Fibroblasts	Randomly arranged collagen fibers	Withstands stress; found in dermis, capsules
Elastic Connective Tissue	Fibroblasts	Elastic fibers	Flexibility, recoil
Loose Connective Tissue	Fibroblasts, adipocytes	Loose matrix	Binding, cushioning, holding organs

Specialized Connective Tissues

• Reticular tissue: Mesh of reticular fibers; supports organs, found in lymph nodes, spleen.

• Adipose tissue: Stores fat; white and brown types.

• Cartilage: Stiff, rubbery matrix; types include hyaline, elastic, fibrocartilage.

• Bone: Spongy and compact; supports and protects.

• Blood: Fluid matrix; transports nutrients and cells.

Types of Cartilage

Type	Location	Function
Hyaline Cartilage	Trachea, larynx, skeleton	Flexibility, support
Elastic Cartilage	Ear, epiglottis	Elasticity, shape retention
Fibrocartilage	Pubic symphysis, intervertebral discs	Compression, shock absorption

Cell Junctions

Types of Junctions

• Tight junctions: Prevent passage of substances between cells.

• Desmosomes: Attach cytoskeletons of adjacent cells.

• Gap junctions: Allow small molecules to pass between cells.

• Hemidesmosomes: Anchor cells to basement membrane.

• Adherens: Attach structure to cytoplasm.

Glands and Membranes

Types of Glands

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

• Exocrine glands: Secrete via ducts to surfaces/cavities (e.g., sweat, salivary).

• Unicellular glands: Single cells (e.g., goblet cells in trachea).

• Multicellular glands: Tubular or alveolar structures; can be simple or compound.

Types of Secretions

• Serous glands: Watery secretions (e.g., sweat, milk).

• Mucous glands: Secrete mucus for lubrication.

• Mixed glands: Both serous and mucous (e.g., salivary glands).

• Cytogenic glands: Produce cells (e.g., bone marrow).

Major Membranes

• Cutaneous membrane: Skin; covers exterior body.

• Mucous membrane: Lines body cavities open to exterior.

• Serous membrane: Lines internal body cavities.

Tissue Growth, Change, and Repair

Modes of Tissue Growth

• Hyperplasia: Increase in cell number.

• Hypertrophy: Increase in cell size.

• Neoplasia: Abnormal tissue growth (tumors).

Ways Tissues Change Type

• Anaplasia: Loss of differentiation and function.

• Metaplasia: Change from one tissue type to another.

Tissue Repair

• New epithelial cells form via stem cells.

• Damaged tissue is replaced or repaired through cell division and differentiation.

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.