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.

• Blastulation: Formation of the blastula, a hollow ball of cells.

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

• Organogenesis: Formation of organs from the germ layers.

Fertilization and Events in the First Week

During the first week, the zygote undergoes cleavage and forms a blastocyst, which implants in the uterine wall.

• Zygote: Single cell formed after fertilization.

• Morula: Solid ball of cells resulting from cleavage.

• Blastocyst: Structure with an inner cell mass (embryoblast) and outer layer (trophoblast).

• Implantation: Blastocyst embeds into the endometrium.

Three-Layered Embryo and Its Origin

The three germ layers are established during gastrulation and give rise to all tissues and organs.

• Ectoderm: Forms skin, nervous system.

• Mesoderm: Forms muscles, bones, cardiovascular system.

• Endoderm: Forms lining of 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 various regions that will form specific tissues.

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

• Intermediate mesoderm: Forms urogenital structures.

• Lateral plate mesoderm: Forms body wall and circulatory system.

Major Derivatives of the Embryonic Germ Layer

Each germ layer gives rise to specific tissues and organs.

• Ectoderm: Epidermis, nervous system.

• Mesoderm: Muscles, bones, blood vessels.

• Endoderm: Gut lining, lungs.

Key Developmental Events of the Fetal Period

The fetal period involves growth and maturation of tissues and organs established during embryogenesis.

• 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 lies beneath the epidermis and provides structural support and nourishment.

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

• Reticular layer: Dense irregular 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, secrete sebum (oil).

Histology and Types of Hair

Hair is a keratinized structure produced by hair follicles in the dermis.

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

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

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, severe pain.

• Third-degree: Destroys epidermis and dermis; may affect underlying tissues, no pain due to nerve damage.

Chapter 6. Bones and Skeletal Tissues

Histology of Bone

Bones are composed of specialized connective tissue with cells embedded in a mineralized 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 a complex structure that supports movement and protects organs.

• Diaphysis: Shaft of long bone.

• Epiphysis: Ends of long bone.

• Medullary cavity: Central cavity containing bone marrow.

• Periosteum: Outer fibrous covering.

Compact vs. Spongy Bone

Bone tissue is classified based on density and structure.

• Compact bone: Dense, forms outer layer; contains osteons (Haversian systems).

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

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 Skeletal Structures

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

• Male pelvis: Narrower, deeper, more robust.

• 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 genetically unique haploid gametes for sexual reproduction.

Key equations:

• 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

Genotypic ratio: 1 AA : 2 Aa : 1 aa

Phenotypic ratio (if A is dominant): 3 dominant : 1 recessive

Variation During Sexual Reproduction

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

• 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 organism carries two alleles, which separate during gamete formation.

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