Reproductive System & Embryology - VOCABULARY Flashcards
Overview: Reproductive System and Embryology
Reproductive systems in both sexes share core concepts: gonads (primary reproductive organs) and accessory reproductive organs (ducts and structures that transport gametes and support fertilization).
Gonads: ovaries in females; testes in males. Functions:
Produce gametes (ova/sperm) that unite at fertilization to form a new individual.
Produce large amounts of sex hormones that regulate maturation, development, and activity of reproductive organs.
Accessory reproductive organs: ducts and related structures that carry gametes toward fertilization site (female) or outside the body (male).
Core endocrine basis of puberty and reproduction: hypothalamus secretes GnRH → stimulates anterior pituitary to release FSH and LH → gonads produce sex hormones and regulate gamete maturation.
Puberty and Endocrine Basis
Puberty: onset during adolescence; external sex characteristics develop (e.g., breast enlargement in females; pubic hair growth in both sexes) and gonads begin secreting sex hormones, initiating gamete maturation.
Hormones initiating puberty:
Hypothalamus secretes gonadotropin-releasing hormone (GnRH).
GnRH stimulates anterior pituitary to release two hormones:
ext{FSH}, ext{LH}Gonads begin producing significant levels of sex hormones, starting gamete maturation and sexual maturation.
Gametogenesis: Meiosis and Germ Cells
Gametogenesis: formation of human sex cells (gametes).
Female gametes: secondary oocytes (eggs).
Male gametes: sperm.
Gametogenesis begins with cell division, meiosis; otherwise, somatic cell division is mitosis.
Haploid vs diploid concepts:
Diploid cell: 2n = 46 chromosomes; n=23 refers to haploid number (unpaired chromosomes).
In humans, meiosis ensures offspring do not receive a 4n chromosome complement and introduce genetic variation via crossing over.
Gamete production:
Female: typically produces and releases a single gamete monthly (the oocyte).
Male: produces large numbers of gametes; about
ext{~}100 imes 10^{6} ext{ sperm/day}; stored briefly and often resorbed if not used.
Meiosis: Key Stages and Features
Meiosis vs Mitosis:
Meiosis starts from a diploid parent cell and produces four haploid gametes; includes crossing over (genetic material exchanged between homologous chromosomes).
Mitosis produces two identical diploid daughter cells with no crossing over.
Interphase (before meiosis): DNA replication; replicated chromosomes consist of two sister chromatids attached at the centromere.
Meiosis I: homologous chromosomes separate; reductional division, producing two haploid cells.
Meiosis II: sister chromatids separate, producing four haploid gametes.
Nondisjunction and Chromosomal Abnormalities
Nondisjunction: failure of homologous chromosomes or sister chromatids to separate properly during meiosis.
Resulting gametes may have 22 or 24 chromosomes (monosomy or trisomy).
Fertilization with such a gamete can produce embryos with 45 or 47 chromosomes.
Clinical correlations:
Most trisomies and monosomies are lethal; some survivable examples include trisomy 21 (Down syndrome).
Down syndrome features: intellectual disability, slanting eye folds, congenital heart defects, low muscle tone, short stature.
Incidence increases with maternal age; nondisjunction can originate from either the oocyte or sperm.
Ovarian Cycle: Hormonal Regulation and Follicular Milestones
General hormonal orchestration:
GnRH from hypothalamus → stimulates FSH and LH from anterior pituitary.
FSH/LH promote maturation of ovarian follicles and hormone secretion (estrogen, inhibin, etc.).
Follicles in the ovary:
Primordial follicles (most primitive type) with a primary oocyte and single flattened layer of follicle cells.
Primary follicles: granulosa cells secrete estrogen; thecal cells secrete androgens converted to estrogen by granulosa cells.
Secondary follicles: more granulosa layers, fluid-filled space (antrum); zona pellucida and corona radiata form around the oocyte.
Vesicular (Graafian) follicle: large with secondary oocyte; completed meiosis I; arrested at metaphase II until fertilization; ovulates one oocyte per month.
Corpus luteum: forms from remnants after ovulation; secretes progesterone and estrogen to maintain the uterine lining; life span ~10–13 days if no fertilization.
Corpus albicans: scar tissue formed from regressed corpus luteum.
Hormonal regulation details:
Negative feedback: gonadal hormones (estrogen, inhibin) inhibit GnRH and FSH/LH release as levels rise.
Positive feedback: large estrogen surge from a mature follicle triggers LH surge and ovulation.
If fertilization occurs: human chorionic gonadotropin (hCG) from the embryo mimics LH to maintain the corpus luteum, which continues to secrete estrogen and progesterone to support the uterine lining until placental hormones take over.
Follicular phase ( ovarian cycle, days 1–13):
Primordial follicles stimulated to mature by LH/FSH; typically one becomes a vesicular follicle.
Follicular cells secrete inhibin; helps inhibit further FSH production; prevents excessive follicle development.
As the follicle matures, fluid accumulates in the antrum; oocyte is pushed to one side; zona pellucida and corona radiata form.
Primary oocyte completes meiosis I to form a secondary oocyte and a polar body; metaphase II arrest occurs until fertilization.
Ovulation (day ~14 in a 28-day cycle):
Release of the secondary oocyte from the mature follicle.
Triggered by peak LH secretion; usually one ovary ovulates per cycle.
Antrum enlarges and follicle ruptures to expel the oocyte.
Luteal phase (days 15–28):
Remaining follicle cells become corpus luteum; secretes progesterone and estrogen.
Builds up uterine lining to prepare for implantation; if oocyte not fertilized, corpus luteum degenerates to corpus albicans; hormone levels fall; menses begin.
Fertilization and implantation affect cycle:
If secondary oocyte fertilized and implants, hCG maintains corpus luteum early in pregnancy; placenta later assumes progesterone and estrogen production.
If not fertilized, corpus luteum degenerates; progesterone falls; endometrium shed.
Ovarian Follicles: Morphology and Developmental Sequence
Follicle types and progression:
1) Primordial follicle – primary oocyte + single flattened follicle cell layer; arrested in prophase I; ~1.5 million present at birth.
2) Primary follicle – primary oocyte + cuboidal granulosa cells; granulosa cells secrete estrogen; thecal cells on periphery secrete androgens; follicle growth begins.
3) Secondary follicle – multiple granulosa layers; fluid-filled space; formation of the antrum; cumulus oophorus surrounds the oocyte.
4) Vesicular (Graafian) follicle – large antrum; secondary oocyte; completes meiosis I; oocyte arrested at metaphase II until fertilization; one follicle usually matures per cycle.
5) Corpus luteum – forms after ovulation; secretes progesterone and estrogen to support the uterine lining.
6) Corpus albicans – white scar formed from regressed corpus luteum.Oogenesis: maturation of a primary oocyte to a secondary oocyte occurs in stages over a female’s life; details include hormonal control (FSH/LH, estrogen, inhibin) and timing before birth and after puberty.
Key developmental statistics:
At birth: ~1.5 million primordial follicles.
At puberty: ~400,000 follicles remain in the ovaries.
Ovarian and Uterine Cycles: Phases and Events
Ovarian cycle phases (28-day pattern):
Follicular phase: days 1–13; recruitment of several primordial follicles; one typically becomes vesicular follicle.
Ovulation: day 14; LH surge triggers release of secondary oocyte.
Luteal phase: days 15–28; corpus luteum secretes estrogen and progesterone; if fertilization occurs, hCG maintains CL; otherwise, CL regresses.
Uterine (menstrual) cycle phases (28-day model):
Menstrual phase (days 1–5): functional layer sheds; bleeding occurs.
Proliferative (follicular) phase (days 6–14): endometrium rebuilds under estrogen from growing follicles.
Secretory phase (days 15–28): progesterone from corpus luteum promotes endometrial gland development and vascularization for implantation.
Interplay of cycles:
Ovulation (ovarian cycle) is coordinated with the proliferative/secretory phases of the uterine cycle.
Hormonal regulation includes GnRH → FSH/LH; gonadal hormones influence endometrial development; feedback loops switch from negative to positive depending on follicle maturation and luteal phase.
Hormonal Interactions in the Ovarian Cycle
Hypothalamus→GnRH stimulates anterior pituitary to release:
FSH and LH (FSH drives follicle growth; LH triggers ovulation and stimulates theca/interstitial cells).
Follicular development and hormone production:
Early follicles secrete estrogen; estrogen exerts negative feedback on GnRH and FSH/LH, keeping follicle growth in check.
As estrogen from the mature follicle rises, it switches to positive feedback, triggering an LH surge and ovulation.
Post-ovulation: corpus luteum secretes progesterone and estrogen; inhibin provides negative feedback to FSH; endometrium maintained for implantation.
If fertilization occurs: hCG from the embryo maintains the corpus luteum, enabling continued production of estrogen and progesterone until placental hormones take over.
Female Reproductive System: Anatomy and Pathways
Ovaries:
Primary ovarian structure is the site of oocyte production and hormone release; divided into an outer cortex (follicles) and inner medulla (vessels, nerves).
Germinal epithelium (simple cuboidal) covers the ovary; tunica albuginea (dense connective tissue capsule) lies beneath.
Ovarian follicles (structures around oocytes): ~thousands in the cortex; include primordial, primary, secondary, vesicular; eventually form corpus luteum after ovulation.
Internal reproductive organs: ovary, uterus, oviducts (uterine tubes), vagina.
Oogenesis and the Ovarian Cycle: Timeline and Key Events
Before birth:
Primordial germ cells (oogonia) divide by mitosis to produce primary oocytes; meiotic divisions start but arrest in prophase I.
At birth, about 1.5 million follicles in the ovarian cortex.
From puberty to menopause:
FSH and LH regulate monthly cycles; a cohort of follicles begins to mature, but typically only one reaches maturation per cycle.
Primary oocytes complete meiosis I to yield a secondary oocyte and a first polar body; meiosis II is completed only if fertilization occurs.
Primary reproductive events:
Follicular growth, estrogen production (and inhibin), LH surge, ovulation, corpus luteum formation, secretory endometrium, potential implantation.
Fertilization, Zygote Formation, and Early Cleavage
Fertilization window:
Oocyte viability: ~24 hours after ovulation.
Sperm viability: ~3–4 days in female reproductive tract.
Fertilization steps:
Capacitation: capacitation of sperm in the female tract removes glycoprotein coat and prepares for acrosome reaction.
Corona radiata penetration and zona pellucida penetration via acrosome reaction; sperm entry prevents polyspermy via zona hardening.
Fusion of sperm and oocyte plasma membranes; second meiotic division completes in the oocyte; zygote forms with paternal and maternal haploid pronuclei fuse to create a diploid nucleus.
Cleavage and early embryo development:
Cleavage: rapid mitotic divisions that increase cell number without growth in overall size; embryo becomes a morula (16-cell stage) and then a blastocyst with trophoblast and embryoblast.
Trophoblast forms the chorion; embryoblast forms the embryo proper; blastocyst implants into the uterine lining.
Implantation and placentation:
Implantation occurs as the blastocyst attaches to the endometrium; syncytiotrophoblast produces hCG to maintain corpus luteum; placenta eventually takes over estrogen and progesterone production.
Extraembryonic Membranes and Placental Development
Bilaminar germinal disc (by day 8):
Hypoblast and epiblast layers form a bilaminar disc.
Extraembryonic membranes: amnion, chorion, yolk sac arise from interactions between the bilaminar disc and trophoblast.
Amnion: encloses embryo in amniotic cavity; produces amniotic fluid.
Chorion: outer membrane; formed from cytotrophoblast and syncytiotrophoblast; contributes to placenta.
Yolk sac: first to develop; site of early blood cell formation and primordial germ cell development; not a food source in humans.
Placenta: a highly vascular organ that exchanges nutrients, wastes, and respiratory gases between mother and fetus; produces estrogen and progesterone to maintain pregnancy; placenta forms from chorionic villi and endometrial tissue; maternal and fetal blood do not mix directly but exchange occurs at the villi.
Placental components: chorionic villi, endometrium (functional layer), maternal blood spaces (intervillous spaces).
Maternal-fetal interface characteristics: selective permeability; some substances cross (viruses, drugs, toxins) depending on timing and dose.
Gastrulation and the Primary Germ Layers
Gastrulation: occurs during the third week; establishes three primary germ layers from the epiblast via the primitive streak and primitive node.
Endoderm: displaces hypoblast; forms inner linings of GI, respiratory, urinary, and reproductive tracts, among other structures.
Mesoderm: forms several subgroups (notochord; paraxial; intermediate; lateral plate; head mesenchyme) that give rise to axis, muscles, skeleton, kidneys, genitalia, circulatory and other systems.
Ectoderm: remaining cells of the epiblast; gives rise to epidermis, nervous system, sensory organs, pituitary gland, and more.
Neurulation: differentiation of ectoderm into neural tissue and related structures; forms CNS, neural crest derivatives, etc.
Organogenesis and Teratogens
Organogenesis: organ development that begins after folding is complete; by week 8, limbs have their basic shape and most organ systems have rudimentary forms.
Teratogens: substances that cause birth defects or embryonic death; critical windows of vulnerability exist during peak development of specific organs (e.g., limbs, neural tube).
Examples of teratogens: alcohol, tobacco, drugs, certain viruses.
Embryonic period is particularly sensitive to teratogens; fetal period involves growth and maturation of already formed organs.
Pregnancy: Hormonal Regulation and Maternal Changes
Hormonal milieu during pregnancy:
Estrogen and progesterone: produced by corpus luteum early, primarily by placenta later; high levels promote uterine expansion, mammary gland development, fetal growth, and suppression of ovulation.
Relaxin: promotes vascular remodeling in uterus.
CRH (placental): influences timing of pregnancy and birth; contributes to aldosterone rise and fluid retention.
hCG: produced by trophoblast; sustains corpus luteum early in pregnancy (detectable in urine by end of second week).
Human placental lactogen (HPL): modifies maternal metabolism to favor fetal glucose availability.
Prolactin: supports lactation readiness; levels rise later in pregnancy.
Oxytocin: supports uterine contractions and milk ejection during lactation.
Maternal physiological changes during pregnancy:
Uterine expansion due to muscular growth, placental growth, and amniotic fluid; effects on bladder and GI system.
Cardiovascular: plasma volume increases ~50%; cardiac output rises 30–50%; heart rate rises; blood pressure later drops due to reduced resistance.
Respiratory: increased demand for gas exchange; respiratory rate and tidal volume may adjust.
Digestive and metabolic: insulin resistance increases; increased nutrient demand; risk of gestational diabetes in some cases; morning sickness common in the first trimester.
Mammary changes: glandular tissue growth in preparation for lactation; areola darkening (linea nigra) due to MSH.
Gestational diabetes: screening and management via diet, monitoring, and sometimes medication; can lead to larger baby and delivery complications.
Labor, Delivery, and Postnatal Changes
Labor and delivery:
Labor is the physical expulsion of the fetus and placenta at term (around 38 weeks in humans).
Estrogen increases uterine sensitivity to oxytocin; oxytocin receptor density on the uterus increases; prostaglandins contribute to contractions and cervix dilation.
True labor involves a positive feedback loop: contractions cause cervical dilation, which triggers more oxytocin release and prostaglandin production, amplifying contractions until birth.
Labor induction methods (when indicated) may include prostaglandin gel and synthetic oxytocin (Pitocin).
Postnatal newborn changes:
Respiratory: first breath initiates lung inflation; surfactant helps keep alveoli open; preterm infants (<28 weeks) may require assistance due to insufficient surfactant.
Circulatory: closure of fetal shunts (ductus arteriosus, foramen ovale) with first breaths and changes in pressures.
Thermoregulation, nutrition, and excretory systems adapt postnatally; placental hormones decline, and maternal hormones drop rapidly after birth.
Lactation after birth:
Prolactin stimulates milk production in the mammary glands; oxytocin stimulates milk ejection (letdown).
Colostrum is produced in late pregnancy and the first days after birth; rich in IgA and provides passive immunity.
Mature breast milk contains fats, sugars, proteins, enzymes, and antibodies; optimal infant nutrition.
Breastfeeding can suppress ovulation via GnRH inhibition, though it is not a reliable contraception method.
Male Reproductive System: Testes, Spermatogenesis, and Accessory Glands
Testes: housed in the scrotum; produce sperm and androgens; covered by a serous membrane (tunica vaginalis).
Seminiferous tubules: highly convoluted, contained in lobules; house germ cells and sustentacular (Sertoli) cells; Sertoli cells nourish developing sperm and secrete inhibin to regulate FSH.
Interstitial (Leydig) cells: reside in interstitial spaces; stimulated by LH to secrete testosterone.
Blood-testis barrier: protects developing sperm from blood-borne substances; formed by tight junctions between Sertoli cells.
Hormonal regulation of spermatogenesis and androgen production:
GnRH from hypothalamus stimulates FSH and LH release.
LH stimulates Leydig cells to secrete testosterone; FSH stimulates Sertoli cells to produce sperm-supporting factors and ABP (androgen-binding protein).
Testosterone exerts negative feedback on GnRH and pituitary sensitivity; also supports spermatogenesis and secondary sexual characteristics.
Inhibin from Sertoli cells provides negative feedback on FSH.
Spermatogenesis and spermiogenesis:
Spermatogonia (primordial germ cells) divide by mitosis to produce spermatogonium and primary spermatocytes.
Primary spermatocytes undergo meiosis I to form secondary spermatocytes; meiosis II yields spermatids.
Spermiogenesis converts spermatids into mature spermatozoa with a head (nucleus), midpiece (mitochondria), and tail; acrosome cap forms to assist fertilization.
Duct system and accessory glands:
Epididymis: site of sperm maturation and storage.
Ductus (vas) deferens: transports sperm during ejaculation.
Seminal vesicles: secrete alkaline fluid rich in fructose and prostaglandins to nourish sperm and aid sperm mobility.
Prostate gland: secretes milky fluid rich in nutrients and enzymes (PSA); contributes to semen viscosity and pH balance.
Bulbourethral (Cowper's) glands: produce mucus to lubricate the urethra.
Semen composition: sperm plus seminal fluid from accessory glands; seminal fluid provides nutrients, protection, and mobility support for sperm.
Paternal age risks and genetic considerations:
Advancing paternal age increases risk of genetic mutations and several neurodevelopmental disorders in offspring; risk rises in men over 45.
Sexually Transmitted Infections (STIs) and Cervical Cancer
STIs are infections transmitted via sexual contact; many are asymptomatic.
HPV is a major risk factor for cervical cancer; vaccines exist for the most common types.
Pap smear: detects cervical cancer by sampling epithelial cells at the cervical edge for abnormal development; if cancerous cells are detected, part or all of the cervix/ uterus may be removed.
Other infections discussed: chlamydia, gonorrhea, genital herpes, syphilis (treated with antibiotics when detected).
Breast Anatomy, Lactation, and Breast Cancer Risk
Mammary glands: subdivided into lobes and lobules with secretory units (alveoli); lactiferous ducts drain milk to the nipple; lactation occurs after birth.
Milk production and release:
Prolactin drives milk production; oxytocin drives milk ejection (let-down).
Prolactin is highest during lactation; dopamine inhibits prolactin in nonpregnant states.
Colostrum vs mature milk:
Colostrum: produced in late pregnancy and first days after birth; rich in immunoglobulins (IgA) and has a laxative effect for newborn elimination.
Mature breast milk: higher fat content and rich in nutrients and antibodies for infant nutrition.
Breast cancer:
Most common cancer in women; risk factors include family history, obesity, nulliparity, late first pregnancy, and BRCA1/BRCA2 gene mutations.
Arises primarily from duct epithelium; mammography used for early detection.
Pregnancy, Labor, and Postnatal Physiology: Summary of Hormones and Changes
Key pregnancy hormones and roles:
Estrogen and progesterone: major roles in maintaining pregnancy and stimulating maternal tissues; estrogen supports growth and blood vessel expansion; progesterone maintains uterine lining.
hCG: sustains corpus luteum in early pregnancy; supports estrogen and progesterone production until placenta takes over.
Prolactin and oxytocin: lactation-related hormones; prolactin stimulates milk production; oxytocin triggers milk ejection and supports uterine contractions during labor.
Relaxin, CRH, HPL, and placental thyroid-stimulating hormones contribute to maternal adaptation and fetal development.
Labor physiology:
Labor is activated by a combination of maternal and fetal signals that increase oxytocin release and prostaglandin production, leading to progressively stronger contractions and cervical dilation.
Positive feedback mechanism drives labor to completion; afterbirth occurs with placental expulsion.
Postnatal transitions:
Neonate transition involves respiratory initiation, circulatory changes (closure of fetal shunts), thermoregulation, fluid clearance from lungs, and initiation of feeding.
Hormonal shifts after birth include rapid declines in placental hormones; hormonal balance shifts to support lactation and maternal recovery.
Key Quantitative and Conceptual Points (Recap with Formulas)
Chromosome numbers and cell types:
Diploid number: 2n = 46
Haploid number: n = 23
Gametes are haploid; zygote is diploid after fertilization.
Gamete production rates:
Sperm production: roughly ext{100 million/day}
Fertilization biology:
Oocyte viability: up to 24 ext{ h} post-ovulation.
Sperm viability: 3-4 ext{ days} in the female tract.
Ovarian cycle timing (classic model):
Follicular phase: days 1-13
Ovulation: day 14 (in a 28-day cycle)
Luteal phase: days 15-28
Uterine cycle timing (classic model):
Menstrual phase: days 1-5
Proliferative phase: days 6-14
Secretory phase: days 15-28
Developmental timelines:
Prenatal period: starts at fertilization; ends at birth; subperiods include pre-embryonic (0–2 weeks), embryonic (3–8 weeks), and fetal (9–38 weeks).
Primary germ layers formed during gastrulation (weeks 3–4) and give rise to ectoderm, mesoderm, and endoderm.
Placental physiology:
Placenta is a selective barrier with maternal and fetal blood streams not directly mixing; chorionic villi facilitate exchange.
Hormonal support shifts from corpus luteum to placenta around the end of the first trimester.
Labor and delivery:
True labor involves a positive feedback loop with oxytocin and prostaglandins driving contractions and cervical dilation; labor can be medically induced with prostaglandins or oxytocin.
Neonatal circulation changes:
Postnatal heart shifts: closure of foramen ovale and ductus arteriosus as pulmonary circulation becomes predominant; first breaths cause dramatic changes in pressures.
Key terms to know for exam:
GnRH, FSH, LH, inhibin, ABP, estrogen, progesterone, testosterone, hCG, hPL, CRH, relaxin, oxytocin, prolactin, amnion, chorion, yolk sac, placenta, gastrulation, neurulation, teratogens, diapause-like concepts, and the three germ layers.
Review Questions (as study prompts)
What are the three phases of the ovarian cycle, and what major events occur in each phase?
How do FSH and LH regulate the ovarian cycle?
Describe spermatogenesis and spermiogenesis; how do they differ from oogenesis?
What is the function of each component of the male reproductive ducts and accessory glands?
Trace the journey of a sperm from the testes to fertilization.
Compare and contrast sperm, seminal fluid, and semen.
What are the stages of embryonic development from fertilization to implantation?
What are the extraembryonic membranes, and what are their roles?
What is the role of hCG in early pregnancy?
How does the placenta form, and what are its main functions?
What are the main hormonal changes during pregnancy, and what are their effects on maternal physiology and fetal development?
What is endometriosis, and how is it diagnosed and treated (clinical correlation)?
What are the signs, risk factors, and screening methods for cervical cancer?
How does lactation influence ovulation and female reproductive cycling?