BIO 259 Exam 2 Study Guide: Embryogenesis, Tissues, Bone, and Joints

Embryogenesis

Coelom and Serosa

The coelom is a fluid-filled body cavity completely lined by mesoderm. It is crucial for organ function because it allows organs to move, grow, and develop independently of the body wall.

• Parietal serosa: Lines the internal body wall.

• Visceral serosa: Covers the organs within the cavity.

• Retroperitoneal: Organs (e.g., kidneys) located behind the peritoneum, not surrounded by the peritoneal cavity.

Fertilization and Cleavage

• Fertilization: The fusion of sperm and egg, typically occurring in the ampulla of the uterine tube.

• Cleavage: Series of rapid mitotic divisions of the zygote without growth, resulting in smaller cells called blastomeres.

• Characteristics of cleavage: rapid cell division, no cell growth, formation of blastomeres.

• Occurs in the uterine tube.

Early Embryonic Structures

• Zygote: Single fertilized cell.

• Morula: Solid ball of cells.

• Blastocyst: Hollow ball with an inner cell mass and trophoblast.

• Components of blastocyst: trophoblast (forms placenta), inner cell mass (forms embryo).

• Trophoblast roles: implantation, secreting enzymes, forming part of the placenta.

Germ Layers

Formation and Function

• Three germ layers: Ectoderm (nervous system, skin), Mesoderm (muscle, bone, blood), Endoderm (lining of digestive and respiratory tracts).

• Embryonic disk: Flat group of cells that gives rise to the germ layers.

• Gastrulation: Process where cells migrate to form the three germ layers.

• Ingression: Migration of individual cells from the surface into the embryo.

• Mesenchyme: Loosely organized embryonic connective tissue.

• Neurulation: Formation of the neural tube from ectoderm; germ layers undergo folding and differentiation.

• Formation of gut tube, body tube, and coelom: Folding of germ layers creates these structures.

Epithelial Tissue

Overview and Classification

• Four primary tissues: Epithelial, Connective, Muscle, Nervous.

• Tissue: Group of similar cells performing a common function.

• Functions of epithelial tissue: protection (skin), absorption (intestines), filtration (kidneys), secretion (glands).

• Simple epithelium: single layer, specialized for absorption/secretion.

• Stratified epithelium: multiple layers, specialized for protection.

Types of Epithelial Tissue

Type	Function	Location
Simple squamous	Diffusion, filtration	Alveoli, blood vessels
Simple cuboidal	Secretion, absorption	Kidney tubules
Simple columnar	Absorption, secretion	Digestive tract
Pseudostratified columnar	Secretion, propulsion	Trachea
Stratified squamous	Protection	Skin, esophagus

• Microvilli: Increase surface area for absorption.

• Cilia: Move substances across the surface.

• Goblet cell: Secretes mucus.

• Exocrine glands: Secrete products into ducts (e.g., sweat glands).

• Endocrine glands: Secrete hormones into blood.

• Exocrine glands form by invagination of epithelial sheets; endocrine glands lose their ducts during development.

Integumentary System

Functions and Structure

• Chemical defense: Antimicrobial peptides, acidic secretions.

• Glycolipids: Waterproofing, barrier to pathogens.

• Functions of sweat glands: Thermoregulation, excretion, protection.

• Metabolic function: Synthesis of vitamin D.

• Three layers: Epidermis (epithelial), Dermis (connective), Hypodermis (adipose).

• Four basic layers of epidermis: Stratum basale, spinosum, granulosum, corneum.

• New epidermal cells are made in the stratum basale and move upward, becoming keratinized and eventually shed.

• Melanocytes: Produce melanin for UV protection.

• Dendritic cells: Immune defense.

• Optional 5th layer: Stratum lucidum, found in thick skin (palms, soles).

• Eccrine glands: Widely distributed, secrete watery sweat.

• Apocrine glands: Axillary/genital areas, secrete milky sweat.

• Sebaceous glands: Secrete sebum (oil), lubricate skin/hair.

Connective Tissue

General Features

• Found throughout the body; supports, binds, and protects tissues.

• Extracellular matrix: Non-living material between cells, composed of ground substance and fibers.

• All connective tissues have: cells, fibers, ground substance.

• Ground substance: Gel-like material; supports cells, binds them, stores water.

• Cell adhesion proteins: Glue cells to matrix.

• Proteoglycans: Trap water, affect matrix viscosity.

• Three fiber types:

  • Collagen: Strength

  • Elastic: Stretch and recoil

  • Reticular: Support

• Fibroblast: Produces fibers in connective tissue proper.

• Chondroblast: Produces cartilage matrix.

• Osteoblast: Produces bone matrix.

• Other cells: adipocytes, white blood cells, mast cells, macrophages.

Connective Tissue Proper

• Loose connective tissue: More ground substance, fewer fibers (e.g., areolar, adipose, reticular).

• Dense connective tissue: More fibers, less ground substance (e.g., dense regular, dense irregular, elastic).

Function	Connective Tissue Type
Water/salt reservoir	Areolar
Energy storage	Adipose
Support network	Reticular
Strong in one direction	Dense regular
Strong in multiple directions	Dense irregular
Stretch and recoil	Elastic

Cartilage Types

Type	Function	Location
Hyaline	Support, flexibility	Nose, trachea, ends of long bones
Elastic	Maintains shape, flexibility	Ear, epiglottis
Fibrocartilage	Strong, resists compression	Intervertebral discs, menisci

Bone Anatomy

Structure and Cells

• Terms: Spongy bone (trabeculae), compact bone, diaphysis (shaft), epiphyses (ends), articular cartilage, epiphyseal plate (growth), epiphyseal line (adult remnant).

• Medullary cavity: Contains bone marrow.

• Periosteum: Outer fibrous membrane; endosteum: inner lining, both contain osteogenic cells.

• Osteoprogenitor cells: Stem cells; osteoblasts: build bone; osteocytes: mature bone cells, maintain matrix.

• Osteoclasts: Break down bone, derived from macrophages.

• Osteon: Structural unit of compact bone, made of concentric lamellae.

• Osteons resist twisting due to alternating collagen fiber orientation.

• Osteocytes communicate via canaliculi.

• Organic components: collagen, resist tension.

• Inorganic components: hydroxyapatite (calcium phosphate), resist compression.

Bone Growth and Development

Ossification Processes

• Endochondral ossification: Most bones, replaces hyaline cartilage with bone.

• Intramembranous ossification: Flat bones (skull, clavicle), develops from fibrous membrane.

• Endochondral ossification steps:

  1. Bone collar forms around cartilage model.

  2. Cavitation of cartilage in center.

  3. Invasion of internal cavities by periosteal bud; spongy bone forms.

  4. Formation of medullary cavity; secondary ossification centers in epiphyses.

  5. Ossification of epiphyses; hyaline cartilage remains at growth plate and articular surfaces.

• Bone collar: Provides support for developing bone.

• Secondary ossification: Occurs in epiphyses after birth.

• Hyaline cartilage at growth plate allows lengthening; at ends, provides smooth surface for joints.

• Osteoblasts become osteocytes when surrounded by matrix.

• Long bone growth: Occurs at epiphyseal plate through proliferation, hypertrophy, calcification, and ossification zones.

Zone	Description
Proliferation	Chondrocytes divide rapidly
Hypertrophic	Chondrocytes enlarge
Calcification	Matrix calcifies, chondrocytes die
Ossification	New bone forms

• Bone remodeling: Continuous bone resorption and deposition.

• Bone healing: Hematoma forms, fibrocartilaginous callus, bony callus, bone remodeling.

• Wolff’s law: Bone grows/remodels in response to stress.

• Low blood calcium: Parathyroid hormone stimulates osteoclasts to release calcium.

• Osteoporosis: Bone resorption exceeds formation; imbalance between osteoclasts and osteoblasts.

Joints

Classification and Structure

• Fibrous joints: Bones joined by dense connective tissue; immovable or slightly movable.

• Cartilaginous joints: Bones joined by cartilage; slight movement.

• Synovial joints: Bones separated by fluid-filled cavity; freely movable.

Fibrous Joint Type	Location
Sutures	Skull
Syndesmoses	Between tibia and fibula
Gomphoses	Teeth in sockets

Cartilaginous Joint Type	Cartilage Type
Synchondroses	Hyaline cartilage
Symphyses	Fibrocartilage

• Synovial joint components: articular cartilage, joint cavity, synovial fluid, articular capsule, ligaments, nerves, blood vessels.

• Bursae: Fluid-filled sacs, reduce friction between tissues.

• Tendon sheath: Elongated bursa wrapping around a tendon.

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard anatomy and physiology textbooks.