Basics of Human Anatomy and General Embryology

Comprehensive practice flashcards defining core vocabulary terms across Human Anatomy Part I (planes, movements, tissues, skeletal, muscular, vascular, lymphatic, and nervous systems) and Part II General Embryology (gametes, fertilization, implantation, bilaminar/trilaminar germ discs, fetal membranes, and congenital anomalies).

Anatomical Erect Position

The standard reference position where the body is standing upright, the face looks forwards, the upper limbs are stretched beside the body, and the palms are directed forwards.

Coronal Plane

A vertical plane that divides the body into anterior and posterior halves or parts.

Median (Sagittal) Plane

A vertical plane that divides the body into equal right and left halves.

Paramedian Plane (Lateral Sagittal Plane)

A vertical plane that runs parallel to the median plane, dividing the body into two unequal right and left parts.

Horizontal Plane

A transverse plane that divides the body into upper (superior) and lower (inferior) halves or parts.

Abduction

Movement of a body part away from the midline; in fingers, away from the axis of the middle finger, and in toes, away from the axis of the second toe.

Adduction

Movement of a body part towards the trunk; in fingers, towards the axis of the middle finger, and in toes, towards the axis of the second toe.

Opposition

A movement comprising flexion and medial rotation of the thumb so that it comes into contact with the tips of the medial four fingers.

Erectorpili Muscle

A tiny bundle of smooth muscle fibers that connects the side of a hair follicle to the junction between the dermis and epidermis.

Hyaline Cartilage

A translucent, avascular modified connective tissue with minimal collagenous fibers and abundant chondrocytes (single or in cell nests), located in articular cartilage, respiratory cartilages, costal cartilages, and the fetal skeleton.

Yellow Elastic Fibrocartilage

A flexible cartilage containing yellow elastic fibers and abundant chondrocytes in its matrix, found in the ear pinna, external auditory meatus, Eustachian tube, and epiglottis.

White Fibrocartilage

A tough cartilage rich in dense white collagenous fibers with relatively few chondrocytes, found in the intervertebral discs, glenoid and acetabular labra, symphysis pubis, and knee menisci.

Pneumatic Bones

Bones that contain air-filled cavities lined with mucous membrane communicating with the nasal cavity, serving to lighten the skull, condition air, protect the brain, and provide vocal resonance.

Sesamoid Bones

More or less rounded bony nodules embedded within tendons and related to articular surfaces to reduce friction, modify pressure, and alter muscle pull direction (e.g., patella, pisiform, fabella).

Periosteum

A rough fibrous sheath covering the non-articular surfaces of bone, composed of a superficial white fibrous layer and a deep osteogenic layer containing osteoblasts and elastic fibers.

Growing End (Long Bones)

The end of a long bone shaft where the epiphyseal plate ossifies later, continuing to add length for an extra $2$ to $3$ years; its orientation is opposite the direction pointed by the nutrient foramen.

Synergist

A muscle that contracts to eliminate unwanted movements at intermediate crossed joints when a prime mover spans multiple joints, thereby maximizing agonist efficiency at the target joint.

Fixator Muscle

A muscle that stabilizes the origin of an agonist muscle to provide a steady base from which the prime mover can act efficiently.

Gomphosis

A specialized fibrous joint where the collagen fibers of the periodontal ligament anchor a tooth into its bony socket.

Hilton's Law

The anatomical principle stating that the nerve supplying a muscle acting on a specific joint also provides branches to supply both that joint and the overlying skin.

End Arteries

Arteries that lack precapillary arteriolar anastomoses with adjacent arterial channels, such that their occlusion inevitably causes necrosis of the supplied territory (e.g., central artery of the retina, splenic, renal).

Arteriovenous Shunt

A direct vascular communication with a thick muscular wall connecting small arteries to corresponding veins proximal to the capillary bed, regulating body temperature, organ absorption, and erectile tissue tumescence.

Portal Circulation

A specialized vascular circuit that begins and ends in veins, transporting nutrient-rich blood from the digestive viscera through the portal vein into liver sinusoids before reaching the inferior vena cava.

Lacteals

Specialized lymphatic vessels located in the intestinal wall that absorb and transport milky, lipid-rich lymph known as chyle.

Thymosin

An endocrine hormone secreted by the bilobed thymus gland, which grows until puberty and subsequently undergoes age-related involution.

Somatic Extraembryonic Mesoderm

The layer of extraembryonic mesoderm that lines the inner aspect of the cytotrophoblast and covers the outer surface of the amnion, participating in the formation of the chorion.

Splanchnic Extraembryonic Mesoderm

The inner layer of extraembryonic mesoderm that directly surrounds and covers the yolk sac.

Capacitation

The conditioning process occurring within the female reproductive tract (taking approximately $7\,\text{hours}$) that removes the glycoprotein coat and seminal proteins from the sperm acrosome.

Cortical Reaction

The exocytosis of lysosomal enzymes from oocyte cortical granules following fertilizing sperm entry, altering zona pellucida receptors and preventing polyspermy.

Morula

A solid ball of blastomeres ($16$-cell stage, developing into $32$ and $64$ cells) formed by repeated mitotic cleavage of the zygote on the $3\text{rd}$ day post-fertilization.

Blastocyst

The embryonic stage reached when fluid spaces coalesce into a single central cavity (blastocele), bounded by an outer trophoblast layer and an inner embryoblast mass.

Syncytiotrophoblast

The multinucleated outer cellular mass formed by trophoblast proliferation at the embryonic pole that lacks cell boundaries and secretes proteolytic enzymes to erode maternal endometrium during implantation.

Placenta Previa

An abnormal gestational condition where the blastocyst implants in the lower uterine segment, causing the placenta to develop adjacent to, marginating, or completely covering the internal os.

Decidua Basalis

The specialized maternal endometrial region located deep to the implanted conceptus between the blastocyst and the myometrium, forming the decidual plate of the placenta.

Decidua Capsularis

The portion of the maternal decidua that directly arches over and covers the implanted conceptus, separating it from the uterine lumen.

Decidua Parietalis

The remainder of the uterine endometrium lining the internal surface of the uterine cavity away from the implantation site.

Tertiary Chorionic Villi

Chorionic villous projections established at the end of the $3\text{rd}$ week that possess differentiated fetal capillaries and blood vessels within their mesenchymal core.

Gastrulation

The morphogenetic process occurring in the $3\text{rd}$ embryonic week whereby epiblast cells migrate through the primitive streak to convert the bilaminar embryonic disc into a trilaminar disc.

Notochord

A cellular rod acting as the primitive axial skeleton of the embryo, which directs folding limits, induces neurulation, and persists postnatally as the nucleus pulposus of intervertebral discs.

Sclerotome

The ventromedial portion of a paraxial mesodermal somite that migrates around the notochord and neural tube to form the vertebral bodies, neural arches, and intervertebral discs.

Dermomyotome

The dorsolateral region of a paraxial somite that differentiates into the dermatome (forming the dermis) and myotome (forming skeletal musculature).

Placental Barrier

The composite tissue barrier separating fetal blood within chorionic capillaries from maternal blood in intervillous spaces, consisting early of endothelium, mesoderm, cytotrophoblast, and syncytiotrophoblast.

Wharton's Jelly

A protective, gelatinous connective tissue derived from the mesoderm of the connecting stalk that surrounds the umbilical vessels inside the umbilical cord.

Polyhydramnios

An abnormal clinical elevation of amniotic fluid volume exceeding $2\,\text{liters}$ at full term, often secondary to conditions such as maternal diabetes, anencephaly, or esophageal atresia.

Oligohydramnios

A condition characterized by an abnormally low volume of amniotic fluid ($< 400\,\text{ml}$ at full term), commonly resulting from fetal renal agenesis or urinary tract obstructions.

Dizygotic Twins

Fraternal twins produced by the concurrent ovulation and fertilization of two distinct oocytes by two separate spermatozoa, each possessing an independent amnion, chorion, and placenta.

Monozygotic Twins

Identical twins derived from the cleavage of a single fertilized ovum at various developmental stages, having identical gender, genetics, and appearance.

Trisomy 21

A chromosomal condition (Down syndrome, $45 + XX$ or $XY$) caused by meiotic nondisjunction of chromosome 21 in the maternal oocyte, presenting with mental retardation and characteristic facial features.

Cri-du-Chat Syndrome

A genetic disorder caused by a partial structural deletion of the short arm of chromosome $5$, clinically characterized by a high-pitched cat-like cry, microcephaly, mental retardation, and congenital heart disease.