Study Guide: Cells, Tissues, and the Integumentary System (Chapters 3–5)

Cells: The Living Units

Phases of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It consists of interphase (G1, S, G2) and the mitotic phase (mitosis and cytokinesis).

• G1 phase (Gap 1): Cell grows and carries out normal functions.

• S phase (Synthesis): DNA replication occurs.

• G2 phase (Gap 2): Cell prepares for division; organelles duplicate.

• M phase (Mitosis): Division of the nucleus and cytoplasm.

Example: Skin cells rapidly progress through the cell cycle to replace lost or damaged cells.

Phases of Mitosis and Meiosis

Mitosis and meiosis are processes of nuclear division. Mitosis produces two identical daughter cells, while meiosis produces four genetically unique gametes.

• Mitosis Phases: Prophase, Metaphase, Anaphase, Telophase

• Meiosis Phases: Meiosis I (Prophase I, Metaphase I, Anaphase I, Telophase I), Meiosis II (Prophase II, Metaphase II, Anaphase II, Telophase II)

• Similarities: Both involve chromosome segregation and cell division.

• Differences: Meiosis includes two divisions and crossing over, resulting in genetic diversity.

Example: Mitosis occurs in somatic cells; meiosis occurs in gamete formation.

Cell Growth and Death

• Hyperplasia: Increase in cell number (e.g., callus formation on skin).

• Hypertrophy: Increase in cell size (e.g., muscle growth from exercise).

• Atrophy: Decrease in cell size or number (e.g., muscle wasting from disuse).

• Apoptosis: Programmed cell death, essential for development and homeostasis.

• Necrosis: Uncontrolled cell death due to injury or disease, often causing inflammation.

Importance: Apoptosis removes damaged cells without inflammation; necrosis can damage surrounding tissue.

Tissue: The Living Fabric

Characteristics of Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It is characterized by:

• Cellularity (closely packed cells)

• Polarity (apical and basal surfaces)

• Attachment to a basement membrane

• Avascularity (no blood vessels)

• Regeneration (rapid cell division)

Types of Epithelia

• Simple epithelia: Single cell layer (e.g., simple squamous in alveoli)

• Stratified epithelia: Multiple layers (e.g., stratified squamous in skin)

• Shapes: Squamous (flat), cuboidal (cube-shaped), columnar (tall)

Functions: Protection, absorption, filtration, secretion

Locations: Skin, lining of digestive tract, glands

Glands and Their Types

• Gland: One or more cells that secrete a product.

• Exocrine glands: Secrete onto body surfaces or into ducts (e.g., sweat glands).

• Endocrine glands: Secrete hormones into the bloodstream (e.g., thyroid gland).

• Unicellular glands: Single-celled (e.g., goblet cells).

• Multicellular glands: Composed of many cells (e.g., salivary glands).

Classification of Multicellular Exocrine Glands

• Structural: Simple (unbranched duct) vs. compound (branched duct); tubular, alveolar, or tubuloalveolar shape.

• Functional: Merocrine (secrete by exocytosis), holocrine (entire cell ruptures), apocrine (apical part pinches off).

Connective Tissue: Characteristics and Types

• Common characteristics: Mesenchyme origin, varying vascularity, extracellular matrix (fibers and ground substance).

• Structural elements: Cells (fibroblasts, chondrocytes, osteocytes), fibers (collagen, elastic, reticular), ground substance.

• Types: Loose (areolar, adipose, reticular), dense (regular, irregular, elastic), cartilage, bone, blood.

• Functions: Support, protection, insulation, transport, storage.

The Integumentary System

Layers of the Skin and Subcutaneous Tissue

• Epidermis: Superficial, composed of epithelial tissue.

• Dermis: Deep, composed of connective tissue.

• Subcutaneous tissue (hypodermis): Not part of skin; consists mainly of adipose tissue, anchors skin to underlying structures.

Tissue Types in the Skin

• Epidermis: Stratified squamous epithelium.

• Dermis: Connective tissue (areolar in papillary layer, dense irregular in reticular layer).

Major Layers of the Epidermis

• Stratum basale: Deepest, mitotically active.

• Stratum spinosum: Several layers, provides strength and flexibility.

• Stratum granulosum: Keratinization begins.

• Stratum lucidum: Only in thick skin (palms, soles).

• Stratum corneum: Outermost, dead keratinized cells, protective.

Major Layers of the Dermis

• Papillary layer: Areolar connective tissue, forms dermal papillae.

• Reticular layer: Dense irregular connective tissue, provides strength and elasticity.

Factors Affecting Skin Color

• Melanin: Brown-black pigment produced by melanocytes.

• Carotene: Yellow-orange pigment from diet.

• Hemoglobin: Red pigment in blood, visible in fair skin.

Hair Follicle Structure and Function

• Parts: Bulb (growth zone), root, shaft, follicle wall, dermal papilla, matrix.

• Arrector pili muscle: Smooth muscle that causes hair to stand (goosebumps).

Hair Regions, Color, and Life Cycle

• Regions: Medulla (core), cortex (middle), cuticle (outer layer).

• Color: Determined by melanin type and amount.

• Life cycle: Growth (anagen), regression (catagen), rest (telogen).

• Changes: Hair distribution and color change with age.

Nail Structure

• Nail plate: Visible part.

• Nail bed: Underlying skin.

• Matrix: Growth area.

• Lunula: White crescent at base.

Sweat and Oil Glands

Gland Type	Structure	Location	Secretion	Function
Eccrine (sweat)	Coiled tubular	Most skin	Watery, salt-rich	Thermoregulation
Apocrine (sweat)	Larger, duct to hair follicle	Axilla, groin	Viscous, protein-rich	Activated at puberty, odor
Sebaceous (oil)	Alveolar	All skin except palms/soles	Sebum (oil)	Lubricates skin/hair

Functions of the Skin

• Protection: Barrier against pathogens, chemicals, and physical injury.

• Temperature regulation: Sweat and blood flow control.

• Sensation: Contains sensory receptors for touch, pain, temperature.

• Metabolic functions: Synthesis of vitamin D.

• Excretion: Eliminates wastes via sweat.