Human Body Plan Development, Cell Biology, and Chemistry

Comprehensive vocabulary flashcards covering early human embryology, germ layer differentiation, tissues, cellular chemistry, biomolecules, membrane transport, neurulation, and mesodermal development.

Zygote

The single-cell organism created when a sperm fertilizes an oocyte (egg), containing a complete set of $46$ chromosomes.

Zona Pellucida

The protective membrane surrounding the zygote and early embryo that prevents the entry of additional sperm and is shed during blastocyst hatching prior to implantation.

Cleavage

A series of rapid holoblastic cell divisions following fertilization where cells divide equally and increase in number while decreasing in individual size, keeping the overall embryonic volume constant.

Morula

A solid sphere of approximately $32$ cells formed through cleavage that maintains the same overall size as the original zygote.

Blastocoele

The fluid-filled central cavity formed within the blastocyst as cells migrate to the outer edge, facilitating efficient diffusion of substances.

Trophoblast

The superficial layer of cells in the blastocyst that assists the embryo in evading the maternal immune system and merges with the endometrium during implantation.

Embryoblast (Inner Cell Mass)

The inner cluster of cells within the blastocyst that imbeds first into the uterine lining and subsequently differentiates into the bilaminar and trilaminar embryo.

Implantation

The process occurring after blastocyst hatching wherein the trophoblast layer attaches to and merges with the endometrial lining of the uterus, with an estimated failure rate of approximately $45\%$.

Epiblast

The dorsal cell layer of the bilaminar embryo facing the endometrium that forms the amniotic cavity and gives rise to all three primary germ layers during gastrulation.

Hypoblast

The ventral cell layer of the bilaminar embryo facing the hollow uterine cavity that gives rise to the yolk sac.

Amniotic Cavity

A protective, fluid-filled space formed on the dorsal side of the embryo by migrating epiblast cells that ultimately surrounds the embryo and fetus.

Yolk Sac

A nutrient-supplying sac on the ventral side of the embryo formed by hypoblast cells that functions before placental development and later becomes the allantois for waste storage and removal.

Gastrulation

The embryonic process during week $3$ in which epiblast cells migrate medially and ventrally through the primitive streak/groove to form a trilaminar embryo with three germ layers.

Primitive Streak

A narrow median groove formed on the dorsal surface of the epiblast during gastrulation through which cells invaginate in a caudal-to-cranial progression.

Endoderm

The primary germ layer formed first during gastrulation by epiblast cells displacing the hypoblast on the ventral surface; it gives rise to the epithelial linings of the digestive, respiratory, urinary, and reproductive systems.

Mesoderm

The middle primary germ layer formed second during gastrulation between the ectoderm and endoderm; it gives rise to muscles, dermis of skin, heart, kidneys, and connective tissue.

Ectoderm

The dorsal primary germ layer remaining on the outer embryo surface after gastrulation; it gives rise to the epidermis of the skin and the nervous system.

Epithelial Tissue

An adult tissue type characterized by tightly packed, polarized cells with distinct top (apical) and bottom (basal) surfaces that is avascular, innervated, covers body surfaces, lines cavities, forms glands, and regenerates easily.

Connective Tissue

The most abundant adult tissue group, derived entirely from mesoderm, featuring loosely arranged cells embedded within an extracellular matrix (ECM) of ground substance and protein fibers.

Chemistry

The branch of science that studies the structure, properties, composition, and interactions of matter.

Matter

Anything that occupies space and has mass, making up all physical substances in the universe including human bodies.

Atom

The fundamental unit of matter and chemical elements, consisting of a central nucleus of protons and neutrons surrounded by electrons.

Ion

An atom or molecule that carries an electrical charge due to the gain or loss of electrons, such as sodium ($\text{Na}^+$), potassium ($\text{K}^+$), or calcium ($\text{Ca}^{2+}$).

Hydrophilic

Describes charged or polar molecules ("water-loving") that dissolve or dissociate readily in water.

Hydrophobic

Describes uncharged or nonpolar molecules ("water-hating") that do not mix well or dissolve in water.

Solute

A substance dissolved within a liquid medium (solvent) to produce a chemical solution.

Solvent

The liquid substance, predominantly water in biological systems, that dissolves solutes.

Carbohydrates

Organic compounds made of $5\text{--}6$ carbon rings that function in short-term energy storage and cell structures, encompassing monosaccharides, disaccharides, and complex forms like starch and glycogen.

Nucleic Acids

Polymers composed of nucleotide monomers that serve as information storage and transfer molecules (DNA and RNA) as well as energy carriers like $\text{ATP}$.

Proteins

Polymers of amino acid monomers that provide tissue structure, act as enzymatic catalysts, enable cellular movement, and mediate membrane transport.

Lipids

Diverse hydrophobic biomolecules lacking a repeating subunit, including phospholipids, triglycerides, and cholesterol, utilized for long-term energy storage and plasma membrane architecture.

Selectively Permeable

The functional characteristic of the plasma membrane that allows nonpolar hydrophobic molecules to pass freely while restricting the unassisted passage of polar hydrophilic molecules.

Passive Transport

The movement of substances across a cell membrane down their concentration gradient (from high to low concentration) without requiring cellular energy expenditure ($\text{ATP}$).

Active Transport

The movement of substances across a cell membrane against their concentration gradient (from low to high concentration) requiring cellular energy input in the form of $\text{ATP}$.

Isotonic Solution

A solution having an equal solute concentration compared to intracellular fluid, administered clinically to rapidly increase blood volume without altering cell size.

Hypertonic Solution

A solution with a higher solute concentration than intracellular fluid, causing water to leave cells by osmosis; administered clinically to treat swollen (edematous) patients.

Hypotonic Solution

A solution with a lower solute concentration than intracellular fluid, causing water to move into cells by osmosis, requiring cautious clinical administration to prevent cell lysis.

Mitosis

The process of nuclear and cellular division that produces two genetically identical daughter cells from a single parent cell through interphase, prophase, metaphase, anaphase, telophase, and cytokinesis.

Trans-segmental Structures

Anatomical structures that extend continuously along the length of the embryo without interruption, appearing in virtually all transverse cross-sections (e.g., notochord, dorsal hollow nerve tube, gut tube).

Segmental Structures

Anatomical structures organized as a repeating series of distinct, individual blocks that appear in some cross-sections but not all (e.g., somites, spinal nerves).

Notochord

A trans-segmental midline structure derived from mesoderm that induces neurulation and later degenerates to persist as the nucleus pulposus of intervertebral discs.

Neurulation

The embryonic process forming the dorsal hollow nerve tube (future brain and spinal cord) from neural ectoderm, initiating in the middle of the embryo and proceeding cranially and caudally simultaneously.

Neural Crest

A specialized population of ectodermal cells from the elevating neural folds that detaches and migrates ventrally and laterally to form most of the peripheral nervous system and ganglia.

Epidermal Ectoderm

The outer surface layer of ectoderm that remains intact following closure of the neural tube, forming the epidermis of the skin.

Spina Bifida

A congenital birth defect caused by incomplete closure of the neural tube during embryonic development, most frequently occurring in the lumbar or sacral regions.

Somite

A segmental block of mesoderm situated lateral to the dorsal hollow nerve tube and notochord that differentiates into dermatome, myotome, and sclerotome.

Dermatome

The division of a somite that develops into the dermis of the dorsal body region, supplying sensory innervation along a specific segmental spinal nerve map.

Myotome

The division of a somite that gives rise to trunk and limb musculature, differentiating into epaxial and hypaxial muscle groups.

Sclerotome

The medial division of a somite that differentiates into the vertebrae and ribs.

Intermediate Mesoderm

The segmental mesoderm region located lateral to the somites that differentiates into the kidneys and gonads.

Lateral Plate Mesoderm

The unsegmented mesoderm located lateral to the intermediate mesoderm that splits into somatic and splanchnic layers surrounding the coelom cavity.

Somatic Mesoderm

The outer layer of lateral plate mesoderm that forms body wall linings (parietal serosa) and limb connective tissues and bones.

Splanchnic Mesoderm

The inner layer of lateral plate mesoderm that coats internal organs (visceral serosa) and forms the heart, dorsal aorta, and smooth muscle/connective tissue of digestive/respiratory walls.

Coelom

The fluid-filled internal body cavity formed between the somatic mesoderm and splanchnic mesoderm layers of the lateral plate mesoderm.

Gut Tube

A trans-segmental, closed cylindrical structure formed when endoderm rolls ventrally, giving rise to the epithelial lining and secretory glands of the digestive and respiratory systems.

Mesenteries

Double layers of peritoneum (dorsal and ventral) formed by splanchnic mesoderm that suspend and anchor the gut tube within the coelomic cavity.