Human Development, Labour, and Lifespan Physiology

Comprehensive vocabulary flashcards covering human development from embryonic organogenesis, fetal circulation, and labour through neonatal transitions, lactation, and lifespan senescence.

Embryonic Period

The developmental time frame extending from week $1$ to week $8$ of pregnancy, during which primary germ layers differentiate and all body systems are established in rudimentary form.

Fetal Period

The developmental phase extending from week $9$ until birth ($38\text{--}40\text{ weeks}$), recognized as the primary period of organogenesis, growth, and tissue specialization.

Somites

Paired blocks of mesoderm that begin forming in the embryo during week $3$, giving rise to the embryonic musculature and skeleton.

Fetal Week 4 Milestones

The developmental milestone period when the heart begins to pump blood, limb buds first emerge, and the embryo adopts a characteristic $\text{C-shape}$ measuring $4\text{--}5\text{ mm}$ in length.

Week 7 Embryo Structure

The anatomical state of the human conceptus at $7\text{ weeks}$ ($\approx 17\text{ mm}$ length) where the amniotic sac, umbilical cord, yolk sac, and chorionic villi support rapid organ differentiation and the initiation of endocrine function.

Parturition

The culmination of pregnancy resulting in the delivery or birth of the baby, occurring at a gestation period of approximately $280\text{ days}$ calculated from the last menstrual period (LMP).

Labour

A rhythmic series of persistent uterine myometrial contractions resulting in cervical dilation and the physical expulsion of the fetus and placenta.

Dilation Stage

The first stage of labour, initiated by regular uterine contractions and continuing until the cervix reaches full dilation of approximately $10\text{ cm}$, lasting an average of $24\text{ hours}$ in first-time mothers.

Expulsion Stage

The second stage of labour, extending from maximum cervical dilation to the complete vaginal delivery of the infant, lasting between $1\text{ minute}$ and $1\text{ hour}$.

Placental Stage

The third stage of labour, occurring after fetal birth, during which uterine contractions detach and eject the placenta and compress maternal blood vessels to limit postpartum hemorrhage.

Umbilical Vein

A single specialized vessel within the umbilical cord that transports oxygenated, nutrient-rich blood from the placenta into the fetal circulation.

Umbilical Arteries

Two vessels within the umbilical cord that carry deoxygenated blood and metabolic wastes from the fetal internal iliac arteries back to the placenta.

Ductus Venosus

A fetal vascular shunt that directs incoming oxygenated blood from the umbilical vein directly into the inferior vena cava, largely bypassing the liver capillary bed.

Foramen Ovale

A flap-covered interatrial aperture in the fetal heart that diverts blood directly from the right atrium to the left atrium, bypassing the non-functional fetal pulmonary circuit.

Ductus Arteriosus

A fetal arterial conduit connecting the pulmonary trunk directly to the aorta, shunting blood away from the high-resistance fetal pulmonary vascular bed.

Cardiovascular Shunt Remnants

The adult fibrous cords and depressions formed after birth following the occlusion of fetal vessels, including the fossa ovalis, ligamentum arteriosum, ligamentum venosum, ligamentum teres, and median umbilical ligaments.

Neonate

A human infant during the neonatal period, which comprises the initial $4\text{--}6\text{ weeks}$ of life outside the uterus.

Brown Fat

Highly vascularized adipose tissue located in the upper body of neonates, packed with mitochondria that generate metabolic heat via lipolysis to compensate for undeveloped shivering mechanisms.

Vernix Caseosa

A whitish, protective fatty secretion produced by sebaceous glands that coats the fetal epidermis beginning at weeks $17\text{--}20$ to provide lubrication and antibacterial protection against amniotic fluid.

Lanugo

A fine, silklike downy hair covering the fetal body from month $5$ ($17\text{--}20\text{ weeks}$) that is usually shed prior to term and replaced by vellus hair postnatally.

Meconium

The thick, dark-green first stool composed of fetal intestinal secretions and cellular debris, accumulated during intrauterine life and evacuated after birth.

Quickening

The initial maternal sensation of fetal movements in the uterus, typically felt between weeks $17$ and $20$ of gestation.

Lactation

The secretion and ejection of milk by functional mammary glands, stimulated and maintained primarily by prolactin and oxytocin.

Colostrum

A pre-milk fluid secreted during late pregnancy and the first $1\text{--}2\text{ days}$ postpartum, characterized by lower fat content and higher levels of proteins, immunoglobulins, and mucins compared to mature milk.

Milk Let-Down Reflex

A neuroendocrine reflex in which infant suckling triggers nipple mechanoreceptors, signaling the hypothalamus to release oxytocin from the posterior pituitary, prompting myoepithelial cell contraction and milk ejection.

Postpartum Period

The $6\text{--}8\text{ week}$ interval following childbirth during which maternal reproductive organs and physiological systems return to their pre-pregnancy baseline.

Hypertrophy

An increase in tissue or organ size accomplished strictly by an enlargement of preexisting individual cell volumes rather than through cellular division.

Hyperplasia

An increase in tissue mass resulting directly from an elevated rate of mitotic division, yielding an increase in total cell number.

Primary Curvature

The initial anteriorly concave, $\text{C-shaped}$ curvature of the infant vertebral column present at birth.

Secondary Curvatures

The cervical curvature (developed around month $3$ as head control appears) and lumbar curvature (developed around month $12$ with standing and walking) that alter the infant's spinal profile.

Deciduous Teeth

The primary dentition (milk teeth) consisting of $20\text{ teeth}$ ($5$ per quadrant), which typically start erupting at $6\text{ months}$ and finish around $24\text{ months}$.

Permanent Teeth

The secondary set of $32\text{ teeth}$ ($8$ per quadrant) that begin emerging around age $6\text{ years}$ and are usually completely erupted by $17\text{--}25\text{ years}$ of age.

Puberty

The biological milestone initiating adolescence, characterized by gonad maturation, gametogenesis, secondary sex characteristic development, and activation of the hypothalamic-pituitary-gonadal axis.

Adolescence

The transitional developmental period spanning puberty to adulthood, characterized by somatic, psychological, and social maturation.

Menarche

The first occurrence of menstruation in females, which typically occurs between $12$ and $13\text{ years}$ of age.

Senescence

The gradual, progressive deterioration of physiological function and homeostatic reserve capacity occurring across organ systems after the peak reproductive and developmental years.

Photoaging

Premature, degenerative structural alteration of the integumentary system characterized by wrinkling, thinning, and altered elasticity resulting from cumulative ultraviolet (UV) radiation exposure.

Osteoporosis

An age-related skeletal condition characterized by loss of bone calcium and matrix due to osteoclast resorption exceeding osteoblast bone formation, causing an $8\%$ loss of bone mass per decade in women and $3\%$ in men.

Osteoarthritis

A chronic joint disorder characterized by the gradual degeneration of articular cartilage and underlying bone, commonly associated with long-term mechanical wear and tear.

Teratogen

An environmental agent, such as a drug, chemical, or virus, capable of disrupting normal morphogenesis and causing structural abnormalities in an embryo or fetus.