Anatomy & Physiology: Study Guide for Tissues, Integumentary System, and Skeletal System

Tissues and Cellular Components

Functions of Key Cells and Structures

This section covers the definitions and functions of important cells and structures found in connective, epithelial, and skeletal tissues.

• Elastin: A protein that provides elasticity to tissues such as skin, lungs, and blood vessels.

• Chondroblasts: Cells that produce cartilage matrix.

• Ligaments: Connective tissue bands that connect bones to other bones, providing joint stability.

• Osteoclasts: Cells responsible for bone resorption (breaking down bone tissue).

• Collagen: The main structural protein in connective tissues, providing strength and support.

• Osteoblasts: Cells that synthesize new bone matrix.

• Exocrine glands: Glands that secrete substances onto epithelial surfaces via ducts (e.g., sweat, salivary glands).

• Osteocytes: Mature bone cells that maintain bone tissue.

• Fibroblasts: Cells that produce collagen and other fibers in connective tissue.

• Tendons: Connective tissue structures that attach muscle to bone.

• Endocrine glands: Glands that secrete hormones directly into the bloodstream (e.g., thyroid, adrenal glands).

• Chondrocytes: Mature cartilage cells that maintain cartilage matrix.

• Hemocytoblasts: Stem cells in bone marrow that give rise to all blood cells.

• Adipocytes: Fat cells that store energy as triglycerides.

Exocrine Gland Classification

Exocrine glands are classified based on their structure and mode of secretion.

• Merocrine glands: Secrete products by exocytosis (e.g., sweat glands).

• Apocrine glands: Release part of the cell along with the secretion (e.g., mammary glands).

• Holocrine glands: Entire cell disintegrates to release its product (e.g., sebaceous glands).

Epithelial Tissues

Types and Locations

Epithelial tissues line body surfaces and cavities, and are classified by cell shape and layering.

• Simple squamous: Single layer of flat cells; found in alveoli of lungs, lining of blood vessels.

• Ciliated pseudostratified columnar: Appears layered but all cells touch the basement membrane; found in respiratory tract.

• Stratified squamous: Multiple layers of flat cells; found in skin, mouth, esophagus.

• Simple columnar: Single layer of tall cells; found in digestive tract lining.

• Simple cuboidal: Single layer of cube-shaped cells; found in kidney tubules, glands.

Connective Tissues

Major Categories and Functions

Connective tissues support, bind, and protect organs. They are classified into four major types:

• Connective tissue proper: Includes loose (areolar, adipose) and dense (tendons, ligaments) connective tissues.

• Cartilage: Provides flexible support (hyaline, elastic, fibrocartilage).

• Bone: Rigid support and protection; site of blood cell formation.

• Blood: Transports nutrients, gases, and wastes.

Muscle Tissues

Characteristics of Skeletal, Smooth, and Cardiac Muscle

Muscle tissues are specialized for contraction and movement.

• Skeletal muscle: Voluntary, striated, multinucleated; attached to bones for movement.

• Smooth muscle: Involuntary, non-striated; found in walls of hollow organs (e.g., intestines, blood vessels).

• Cardiac muscle: Involuntary, striated, branched; found only in the heart, with intercalated discs for synchronized contraction.

Integumentary System

Functions and Components

The integumentary system includes the skin and its derivatives, providing protection, sensation, and regulation.

• Protection: Acts as a barrier against pathogens, chemicals, and physical injury.

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

• Thermoregulation: Regulates body temperature via sweat and blood flow.

• Excretion: Removes waste products through sweat.

• Vitamin D synthesis: Initiates production of vitamin D when exposed to sunlight.

Melanin and Keratin

• Melanin: Pigment produced by melanocytes; protects against UV radiation and determines skin color.

• Keratin: Structural protein in skin, hair, and nails; provides strength and waterproofing.

Epidermis, Dermis, and Hypodermis

The skin consists of three main layers:

• Epidermis: Outermost layer; composed of stratified squamous epithelium.

• Dermis: Middle layer; contains connective tissue, blood vessels, nerves, and glands.

• Hypodermis (subcutaneous layer): Deepest layer; composed of adipose tissue for insulation and energy storage.

Layers of the Epidermis

The epidermis is organized into several layers from superficial to deep:

• Stratum corneum (outermost): Dead, keratinized cells.

• Stratum lucidum (only in thick skin): Clear, dead cells.

• Stratum granulosum: Cells with granules of keratin.

• Stratum spinosum: Several layers of living keratinocytes.

• Stratum basale: Deepest layer; site of cell division.

Components of the Epidermis, Dermis, and Hypodermis

• Epidermis: Keratinocytes, melanocytes, Langerhans' cells, Merkel cells.

• Dermis: Collagen fibers, blood vessels, nerves, hair follicles, sweat and sebaceous glands.

• Hypodermis: Adipocytes, larger blood vessels, nerves.

Skin Glands and Cells

Various glands and specialized cells are found in the skin:

• Sudoriferous glands: Sweat glands; regulate temperature.

• Arrector pili muscles: Cause hair to stand up (goosebumps).

• Merkel cells/discs: Sensory receptors for touch.

• Sebaceous glands: Secrete sebum (oil) to lubricate skin and hair.

• Root hair plexus: Nerve endings around hair follicles; sense hair movement.

• Mammary glands: Specialized sweat glands that produce milk.

• Ceruminous glands: Produce earwax in the ear canal.

• Keratinocytes: Main cell type in the epidermis; produce keratin.

• Langerhans' cells: Immune cells in the epidermis.

Skin Cancer Cells

• Basal cell carcinoma: Originates from basal cells in the epidermis.

• Squamous cell carcinoma: Originates from squamous cells in the epidermis.

• Melanoma: Originates from melanocytes; most dangerous type.

Skeletal System

Bone Structure and Terminology

Bones have distinct regions and cell types important for growth and function.

• Diaphysis: Shaft of a long bone.

• Epiphysis: End of a long bone.

• Periosteum: Dense connective tissue covering the bone surface.

• Medullary cavity: Central cavity within the diaphysis; contains bone marrow.

• Osteocytes: Mature bone cells embedded in bone matrix.

• Endosteum: Membrane lining the medullary cavity.

• Central canal: Channel in the center of osteons containing blood vessels and nerves.

• Canaliculi: Small channels connecting osteocytes for nutrient exchange.

• Compact bone: Dense, strong bone tissue forming the outer layer of bones.

• Spongy bone: Porous bone tissue found at the ends of long bones and inside flat bones.

• Epiphyseal plate: Growth plate; site of bone lengthening during development.

• Articular cartilage: Smooth cartilage covering bone ends at joints.

Bone Matrix and Related Terms

• Osteon: Structural unit of compact bone.

• Osteoid: Unmineralized bone matrix produced by osteoblasts.

• Extracellular Matrix: Non-cellular component providing structural and biochemical support.

• Osteoblasts: Cells that build new bone matrix.

Bone Hormones and Actions

Bone formation and resorption are regulated by hormones:

• Calcitonin: Lowers blood calcium by inhibiting osteoclast activity and promoting bone formation.

• Parathyroid hormone (PTH): Raises blood calcium by stimulating osteoclasts to resorb bone.

Bone Ossification

Bones form by two main processes:

• Intramembranous ossification: Bone develops directly from mesenchymal tissue (e.g., flat bones of the skull).

• Endochondral ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Classification of Bones

Bones are grouped into major regions of the skeleton:

• Axial skeleton: Skull, vertebral column, rib cage.

• Pectoral girdle: Clavicle and scapula; connects arms to the trunk.

• Pelvic girdle: Hip bones; connects legs to the trunk.

• Cranium: Bones forming the skull.

• Vertebral column: Series of vertebrae forming the spine.

Table: Comparison of Bone Formation Processes

Process	Origin	Examples
Intramembranous Ossification	Mesenchymal tissue	Flat bones (skull, clavicle)
Endochondral Ossification	Hyaline cartilage	Long bones (femur, humerus)

Table: Layers of the Epidermis (Superficial to Deep)

Layer	Main Features
Stratum corneum	Dead, keratinized cells
Stratum lucidum	Clear, dead cells (only in thick skin)
Stratum granulosum	Cells with keratin granules
Stratum spinosum	Living keratinocytes
Stratum basale	Mitotically active cells

Key Equations

• Bone resorption and formation balance: $\text{Bone Mass} = \text{Bone Formation} - \text{Bone Resorption}$

• Calcium regulation by hormones: $\text{PTH} \uparrow \Rightarrow \text{Blood Ca}^{2+} \uparrow$ $\text{Calcitonin} \uparrow \Rightarrow \text{Blood Ca}^{2+} \downarrow$

Additional info: Academic context and definitions have been expanded for clarity and completeness.