Classification, Gross Anatomy, and Embryology of Amphibians and Humans

Vocabulary practice cards covering the classification, gross anatomy, anatomical planes and axes, frog embryogenesis, and human prenatal development from Chapters 9 and 10.

Amphibians

Small vertebrates that include frogs, toads, salamanders, and newts. There are more than 7,000 species worldwide, with 112 species found in the Philippines, 94 of which are endemic.

Ferverjarya vittigera

The taxonomic classification of the frog: Phylum Chordata, Subphylum Vertebrata, Class Amphibia, Order Anura, Family Dicroglossidae, Genus Ferverjarya, and Species vittigera.

Rhinella marina

The taxonomic classification of the toad: Phylum Chordata, Subphylum Vertebrata, Class Amphibia, Order Anura, Family Bufonidae, Genus Rhinella, and Species marina.

Dorsal

Descriptive anatomical term that refers to the upper part of the animal or the back.

Ventral

Descriptive anatomical term that refers to the underside or belly of the animal.

Cephalic

Descriptive anatomical term indicating the direction toward the head and neck of the animal.

Caudal

Descriptive anatomical term indicating the direction toward the tail end of the animal.

Lateral

Descriptive anatomical term referring to any part situated along the left and right sides of the body.

Median

Descriptive anatomical term designating the direction toward the middle part or median plane of the body.

Peripheral

Descriptive anatomical term for structures located near the surface of the body or an organ.

Central

Descriptive anatomical term for structures located near the center or middle of the body or an organ.

Proximal

Descriptive anatomical term meaning located close or near to the main body mass or other major points of reference.

Distal

Descriptive anatomical term meaning located far or distant from a major point of reference.

Superficial

Descriptive anatomical term referring to being located near the external surface of an organ or surface of the body.

Deep

Descriptive anatomical term referring to being located in the interior or below the surface of the body or organ.

Superior

Descriptive anatomical term meaning above.

Inferior

Descriptive anatomical term meaning below.

Sagittal plane

An imaginary vertical plane that divides the body into left and right halves which may be unequal.

Median plane

A specific sagittal plane that passes exactly through the midline of the body, creating equal right and left halves.

Transverse or Horizontal plane

An imaginary plane that divides the body into superior (upper) and inferior (lower) sections.

Frontal or Coronal plane

An imaginary vertical plane that divides the body into anterior (front) and posterior (back) sections.

Longitudinal Axis (Vertical axis)

An anatomical axis that runs from superior to inferior (from head to toe).

Transverse Axis (Left-right axis)

An anatomical axis (also termed lateral axis) that runs from left to right.

Sagittal Axis (Anteroposterior axis)

An anatomical axis that runs from front to back.

Embryology

A subfield of biology that studies the growth, development, and formation of an organism from the fertilized egg (zygote) to the embryonic and early larval or fetal stages.

Gray crescent

A region of pigmented molecules formed following a $30^{\circ}$ cortical rotation after sperm entry; it marks the site where the dorsal (back) side of the embryo will form and where gastrulation begins.

Mesolecithal Egg

An egg type characteristic of frogs that contains a moderate amount of yolk, where the vegetal pole contains more yolk than the animal pole.

Holoblastic cleavage

Cleavage pattern in frog eggs where the entire egg divides, but the cell divisions are unequal due to the uneven distribution of yolk.

Blastomeres

The small individual cells produced during the series of rapid mitotic divisions that occur in the cleavage stage.

Morula stage

The embryonic stage resulting from cleavage divisions that forms a solid ball of cells.

Blastula stage

The developmental stage marked by the presence of an internal fluid-filled cavity called the blastocoel, located along the animal pole where yolk concentration is lowest.

Epiboly

The spreading of animal pole cells during early gastrulation by flattening and integrating cells from different layers over the embryo surface.

Bottle cells

Cells on the dorsal side of the embryo that invaginate during early gastrulation to form a crescent-shaped groove, initiating the blastopore.

Archenteron

The central cavity or primitive gut formed during gastrulation as involution occurs around the blastopore lips.

Neurulation

The process of neural tube formation, wherein the neural plate thickens and rolls up over the midline to produce ridges that fuse into the neural tube.

Somites

Segmental blocks of mesodermal tissue formed on each side of the notochord that develop into connective tissues, muscle tissues, and linings of coelomic cavities.

Cutaneous respiration

Respiration through the skin, used by tadpoles immediately after hatching before internal gill systems mature.

Operculum

A fold of skin that appears during the internal gill stage of the tadpole to enclose the opercular chamber as external gills disintegrate and internal gills form.

Pre-embryonic Period

The first 2 weeks of human prenatal development, beginning with fertilization to form a zygote, followed by cleavage, morula formation, blastocyst development, and implantation.

Human Morula

A ball of 12–16 blastomeres formed approximately 72 hours after fertilization as the dividing zygote moves down the fallopian tube toward the uterus.

Blastocyst

The developmental stage formed on the 4th day when the morula enters the uterus and develops a fluid-filled cavity (blastocoele); consists of the embryoblast (inner cell mass) and outer trophoblast.

Embryoblast

The inner cell mass located at the embryonic pole of the blastocyst that differentiates into the epiblast and hypoblast and eventually forms the embryo.

Epiblast

The layer of high columnar cells differentiated from the embryoblast that forms the floor of the amniotic cavity.

Hypoblast

The layer of small cuboidal cells differentiated from the embryoblast that forms the exocoelomic membrane.

Organogenesis

The developmental process occurring from the 4th to the 8th week of human pregnancy by which the three germ layers differentiate into body tissues and organs.

Fetal period

The phase of human prenatal development spanning from the 3rd month until birth, characterized by rapid growth in length from the 3rd to 5th months and rapid weight gain in the final two months.

Breech presentation

A delivery orientation in which the fetus's buttocks, feet, or both present first instead of the head.

Crown-rump length (CRL)

The ultrasonic growth parameter used between the 4th and 8th weeks of gestation to determine fetal size, expressed in millimeters ($\text{mm}$).

Crown-heel length (CHL)

The ultrasonic growth parameter used from the 9th to 40th weeks of gestation to evaluate fetal length, expressed in centimeters ($\text{cm}$).