Anatomy & Physiology Study Guide: Embryology, Integumentary System, Bones & Skeletal Tissues, Genetics

Chapter 3. Embryology

Stages of Prenatal Development

Embryology is the study of the development of an organism from fertilization to birth. Understanding the stages of prenatal development is essential for recognizing how complex structures arise from a single cell.

• Fertilization: The union of sperm and egg to form a zygote.

• Cleavage: Rapid mitotic divisions of the zygote, forming a multicellular embryo.

• Gastrulation: Formation of three germ layers: ectoderm, mesoderm, and endoderm.

• Organogenesis: Development of organs from the germ layers.

Fertilization and Events in the First Week

During the first week, the zygote undergoes several changes, including cell division and differentiation.

• Zygote: The single cell formed after fertilization.

• Morula: A solid ball of cells resulting from cleavage.

• Blastocyst: A hollow ball of cells that implants into the uterine wall.

• Key cell types: Trophoblast (forms placenta), inner cell mass (forms embryo).

Three-Layered Embryo and Its Origin

The three germ layers give rise to all tissues and organs in the body.

• Ectoderm: Forms skin and nervous system.

• Mesoderm: Forms muscles, bones, and circulatory system.

• Endoderm: Forms digestive and respiratory tracts.

Neurulation and Its Sequence

Neurulation is the process by which the neural tube forms, eventually developing into the central nervous system.

• Neural plate formation

• Neural groove and folds

• Neural tube closure

Differentiation of Mesoderm in Week 3

During the third week, the mesoderm differentiates into several regions, each giving rise to specific tissues.

• Paraxial mesoderm: Forms somites (muscle, vertebrae).

• Intermediate mesoderm: Forms urogenital structures.

• Lateral plate mesoderm: Forms body wall and limbs.

Major Derivatives of the Embryonic Germ Layer

Each germ layer produces distinct tissues and organs.

• Ectoderm: Epidermis, nervous system.

• Mesoderm: Muscles, bones, blood vessels.

• Endoderm: Lining of gut, lungs.

Key Developmental Events of the Fetal Period

The fetal period is characterized by growth and maturation of tissues and organs.

• Organ maturation

• Rapid growth

• Functional development

Chapter 5. The Integumentary System

Layers of the Epidermis and Key Features

The epidermis is the outermost layer of the skin, composed of several distinct layers.

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

• Stratum spinosum: Provides strength and flexibility.

• Stratum granulosum: Contains granules for waterproofing.

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

• Stratum corneum: Outermost layer, dead keratinized cells.

Layers of the Dermis and Key Features

The dermis supports and nourishes the epidermis and contains important structures.

• Papillary layer: Loose connective tissue, contains capillaries and sensory neurons.

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

Types of Glands, Their Location, and What They Produce

Skin contains several types of glands with distinct functions.

• Sudoriferous (sweat) glands: Eccrine (all over body, produce watery sweat), apocrine (armpits, groin, produce thicker secretion).

• Sebaceous glands: Associated with hair follicles, produce sebum (oil).

Histology and Types of Hair

Hair is a keratinized structure produced by hair follicles.

• Vellus hair: Fine, unpigmented hair covering most of the body.

• Terminal hair: Coarse, pigmented hair (scalp, eyebrows, etc.).

Levels of Severity in Burns

Burns are classified by depth and extent of tissue damage.

• First-degree: Affects only the epidermis (redness, pain).

• Second-degree: Involves epidermis and part of dermis (blisters).

• Third-degree: Destroys both epidermis and dermis (may affect deeper tissues).

Chapter 6. Bones and Skeletal Tissues

Histology of Bone

Bones are composed of specialized cells and a mineralized extracellular matrix.

• Osteocytes: Mature bone cells.

• Osteoblasts: Bone-forming cells.

• Osteoclasts: Bone-resorbing cells.

• Matrix: Collagen fibers and hydroxyapatite (calcium phosphate).

Anatomical Structure of Bone

Bones have distinct regions and structures that support their function.

• Diaphysis: Shaft of long bone.

• Epiphysis: Ends of long bone.

• Medullary cavity: Central cavity containing bone marrow.

• Periosteum: Outer covering of bone.

Compact vs. Spongy Bone

Bone tissue is classified based on density and structure.

• Compact bone: Dense, forms outer layer, contains osteons.

• Spongy bone: Porous, contains trabeculae, found at ends of long bones.

Shapes of Bones

Bones are classified by shape, which relates to their function.

• Long bones: Femur, humerus.

• Short bones: Carpals, tarsals.

• Flat bones: Skull, ribs.

• Irregular bones: Vertebrae.

• Sesamoid bones: Patella.

Factors Affecting Bone Growth

Bone growth is influenced by genetic, nutritional, and hormonal factors.

• Growth hormone

• Calcium and vitamin D intake

• Physical activity

Types of Fractures

Fractures are breaks in bone, classified by pattern and severity.

• Simple (closed) fracture: Bone breaks but does not pierce skin.

• Compound (open) fracture: Bone pierces skin.

• Comminuted fracture: Bone shatters into multiple pieces.

• Greenstick fracture: Incomplete break, common in children.

Sex Differences in Bone Structure

Male and female skeletons differ in several ways, especially in the pelvis.

• Male pelvis: Narrower, deeper.

• Female pelvis: Wider, shallower (adapted for childbirth).

Function of the Arches of the Foot

The arches of the foot provide support and flexibility for movement.

• Medial longitudinal arch

• Lateral longitudinal arch

• Transverse arch

Common Bone Diseases

Several diseases affect bone health and structure.

• Osteoporosis: Decreased bone density, increased fracture risk.

• Osteomalacia: Softening of bones due to vitamin D deficiency.

• Paget's disease: Abnormal bone remodeling.

Genetics

Haploid and Diploid

Cells are classified by the number of chromosome sets they contain.

• Haploid (n): One set of chromosomes (gametes).

• Diploid (2n): Two sets of chromosomes (somatic cells).

Heterozygous and Homozygous

These terms describe the genetic makeup at a specific gene locus.

• Homozygous: Two identical alleles for a gene.

• Heterozygous: Two different alleles for a gene.

Meiosis and Mitosis

Cell division occurs by two main processes, each with distinct outcomes.

• Mitosis: Produces two identical diploid cells for growth and repair.

• Meiosis: Produces four non-identical haploid gametes for sexual reproduction.

Equation:

• Mitosis: $2n \rightarrow 2n$

• Meiosis: $2n \rightarrow n$

Dominant and Recessive; Phenotype and Genotype

Genes can be dominant or recessive, affecting the traits (phenotype) expressed.

• Dominant allele: Expressed if present.

• Recessive allele: Expressed only if both alleles are recessive.

• Genotype: Genetic makeup (e.g., AA, Aa, aa).

• Phenotype: Observable traits (e.g., brown eyes).

Punnett Square and Application

The Punnett square is a tool for predicting genetic outcomes of crosses.

• Example: Crossing Aa x Aa for a trait.

	A	a
A	AA	Aa
a	Aa	aa

Variation During Sexual Reproduction

Sexual reproduction increases genetic diversity through independent assortment and crossing over.

• Independent assortment: Random distribution of chromosomes.

• Crossing over: Exchange of genetic material between homologous chromosomes.

Mendelian Genetics Principles

Mendel's laws describe inheritance patterns of traits.

• Law of Segregation: Each individual has two alleles for each gene, which separate during gamete formation.

• Law of Independent Assortment: Genes for different traits are inherited independently.