USMLE - Reproduction Part 1
Produced at the base of limbs in the zone of polarizing activity (ZPA), Shh patterns the anterior-posterior axis and is crucial for central nervous system (CNS) development. Mutations can result in holoprosencephaly, a failure of forebrain division.
Sonic Hedgehog Gene
Where is it produced?
What axis does it pattern?
Involved with the development of what system??
Mutations lead to
Produced at base of limbs in zones of polarizing activity
Anterior Posterior Axis
Involved in CNS development
Mutations –> holoprosencephaly
Key Terms
Sonic Hedgehog Gene
Where is it produced?
What axis does it pattern?
Involved with the development of what system??
Mutations lead to
Produced at base of limbs in zones of polarizing activity
Anterior Posterior Axis
Involved in CNS development
Mutations –> hol...
Wnt 7 gene
Where is it produced?
What axis does it pattern?
Produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb)
Dorsal Ventral Axis
FGF Gene
Where is it produced?
What does it do?
Produced at apical ectodermal ridge
Stimulates mitosis of underlying mesoderm, providing for lengthening limbs
Homeobox (Hox) Genes
What dos it do?
What axis?
Mutations result in
Involved in segmental organization of embryo in craniocaudal direction
Hox mutations –> appendages in wrong location
Day 0
Fertilization by sperm forms zygote initiating embryogenesis
Week 1
hCG secretion begins after implantation of blastocyst
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| Term | Definition |
|---|---|
Sonic Hedgehog Gene Where is it produced? What axis does it pattern? Involved with the development of what system?? Mutations lead to | Produced at base of limbs in zones of polarizing activity Anterior Posterior Axis Involved in CNS development Mutations –> holoprosencephaly |
Wnt 7 gene Where is it produced? What axis does it pattern? | Produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb) Dorsal Ventral Axis |
FGF Gene Where is it produced? What does it do? | Produced at apical ectodermal ridge Stimulates mitosis of underlying mesoderm, providing for lengthening limbs |
Homeobox (Hox) Genes What dos it do? What axis? Mutations result in | Involved in segmental organization of embryo in craniocaudal direction Hox mutations –> appendages in wrong location |
Day 0 | Fertilization by sperm forms zygote initiating embryogenesis |
Week 1 | hCG secretion begins after implantation of blastocyst |
Week 2 | “2 weeks = 2 layers” Bilaminar disc with epiblast and hypoblast |
Week 3 | 3 weeks = 3 layers Trilaminar disc Gastrulation Primitive streak, notochord, mesoderm and its organization, and neural plate begins to form |
Week 3 - week 8 By week 4 Danger? | Embryonic Period Neural tube formed by neuroectoderm and closes by week 4 Heart begins to beat at week 4 upper and lower limb buds begin to form Organogenesis Extremely susceptible to teratogens |
Week 8 | Start of fetal period Fetal movement and fetus looks like a baby |
Week 10 | Genitalia have male/female characteristics |
Gastrulation What is established? Starts with… | Process that forms the trilaminar disc Establishes ectoderm, endoderm and mesoderm Starts with epiblast invaginating to form primitive streak |
What comes from Surface Ectoderm? | Adenohypophysis (Ant Pituitary from Rathke’s Pouch), Lens, Epithelial lining of oral cavity, Sensory organ of ear, Anal canal below pectinate line, Parotid, Sweat, and Mammary glands |
What comes from Neuroectoderm? | Brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland) Retina, Optic Nerve, Spinal Cord |
What comes from Neural Crest Cells? | PNS (DRG, CN, Celiac ganglion, Schwann cells, ANS) Melanocytes, Chromaffin Cells of adrenal medulla, Parafollicular (C) cells of thyroid, Schwann cells, Pia and Arachnoid, Bones of skull, Odontoblasts, Aorticopulmonary septum |
Craniopharyngioma Origin Histo | Benign Rathke’s pouch rumor with cholesterol crystals and calcification |
What comes from Mesoderm? | Muscle, Bone, Connective Tissue, Serous Lining of Body Cavities (Peritoneum), Spleen, CV Structures, Lymphatics, Blood, Wall of Gut Tube, Wall of Bladder, Urethra, Vagina, Kidneys, Adrenal Cortex, Dermis, Testes, Ovaries |
Mesodermal Defects | "VACTERL" Vertebral defects Anal atresia Cardiac defects Tracheo-Esophageal fistula Renal defects Limb defects (bone and muscle) |
What comes from Endoderm? | Gut tube epithelium (including anal canal above pectinate line) Luminal epithelium derivatives (Liver, Lung, Gallbladder, Pancreas, Eustachian Tube, Thymus, Parathyroid, Thyroid follicular cells |
Agenesis | Absent organ due to absent primordial tissue |
Aplasia | Absent organ despite presence of primordial tissue |
Deformation | Extrinsic disruption Occurs after embryonic period |
Hypoplasia | Incomplete organ development Primordial tissue present |
Malformation | Intrinsic disruption Occurs during embryonic period (3-8 weeks) |
Teratogenic Effects of ACEI | Renal damage |
Teratogenic Effects of Alkylating Agents | Absence of digits | Multiple abnormalities |
Teratogenic Effects of Aminoglycosides | "A mean guy hit the baby in the ear" | CN VIII toxicity |
Teratogenic Effects of Carbamazepine | Neural tube defects Craniofacial defects Fingernail hypoplasia Developmental delay IUGR (IntraUterine Growth Restriction ) |
Teratogenic Effects of Diethylstilbestrol (DES) | Vaginal clear cell carcinoma | Congenital Mullerian anomalies |
Teratogenic Effects of Folate Antagonists | Neural Tube Defects |
Teratogenic Effects of Li | Ebstein's Anomaly (Atrialized RV) |
Teratogenic Effects of Phenytoin | Fetal hydantoin syndrome: microcephaly, dysmorphic craniofacial features, hypoplastic nails and distal phalanges, cardiac defects, IUGR (IntraUterine Growth Restriction ), mental retardation |
Teratogenic Effects of Tetracyclines | Discolored Teeth |
Teratogenic Effects of Valproate | Inhibition of maternal folate absorption --> neural tube defects |
Teratogenic Effects of Warfarin | "Do not wage Warfare on the baby, keep in Heppy with Heparin (does not cross the placenta)" Bone deformities, fetal hemorrhage, abortion, ophthalmologic abnormalities |
Teratogenic Effects of Thalidomide | "Limb Defects with tha-LIMB-domide" Limb defects (flipper limbs) |
Teratogenic Effects of EtOH | Leading cause of birth defects and mental retardation | Fetal Alcohol Syndrome |
Teratogenic Effects of Cocaine | Abnormal fetal development and fetal addiction; Placenta abruption |
Teratogenic Effects of Smoking (nicotine, CO) | Preterm labor, Placental problems, IUGR (IntraUterine Growth Restriction ), ADHD |
Teratogenic Effects of Iodide (Lack or Excess) | Congenital Goiter or Hypothyroidism (cretinism) |
Teratogenic Effects of Maternal Diabetes | Caudal regression syndrome (anal atresia to sirenomelia), Congenital Heart Defects (Transposition of the Great Vessels), Neural Tube Defects |
Teratogenic Effects of Excess Vit A | Extremely high risk for spontaneous abortions and birth defects (cleft palate, cardiac abnormalities) |
Teratogenic Effects of X Rays | Microcephaly, Mental Retardation |
Fetal Alcohol Syndrome | Mental Retardation, Pre and Post Natal Developmental Retardation, Microcephaly, Holoprosencephaly, Facial Abnormalities, Limb Dislocation, Heart and Lung Fistulas |
Source of Estrogen | Ovary --> 17β-estradiol Placenta --> estriol Adipose tissue --> estrone via aromatization |
Potency of different kinds of estrogens | Estradiol > Estrone > Estiol |
Estrogen Function Development In menstrual cycle Receptors Blood | Development of genitalia, breast, and female fat distribution Growth of follicle, endometrial proliferation, and ↑ myometrial excitability Feedback inhibition of LH and FSH and then LH surge Stimulation of prolactin secretion (but blocks it's action at the breast) Upregulates estrogen, LH, and progesterone receptors ↑ Transport proteins, SHBG, HDL, ↓LDL |
How does pregnancy change estrogen levels | 50x ↑ in estradiol and estrone | 1000x ↑ in estiol (indicator of fetal well being |
Mechanism of estrogen receptor | Expressed in cytoplasm | When bound with ligand, translocates to the nucleus |
Molecular cascade in Theca Cells | Pulsatile GnRH --> LH --> Desmolase | D turns cholesterol in to androstenedione |
Molecular cascade in Granulosa Cells | Pulsatile GnRH --> FSH --> Aromatase | A turns androstenedione into estrogen |
Source of Progesterone | Corpus Luteum, Placenta, Adrenal Cortex, Testes |
Elevation of Progesterone indicates… | Ovulation |
Function of Progesterone Menstural cycle Receptors Pregnancy | Stimulation of endometrial glandular secretions and spiral artery development Maintains endometrium to support implantation --/ LH and FSH ↓ myometrial excitability ↓ estrogen receptor expressivity Maintain pregnancy Production of thick cervical mucus (inhibits sperm entry into uterus) ↑ Body Temp Uterine smooth muscle relaxation (prevents contractions) |
Tanner Stages of Sexual Development | I: Childhood II: Pubic hair appears (Pubarche), Breast bud forms (Thelarche) III: Pubic hair darkens and becomes curly. Penis size/length and breasts enlarge IV: Penis width ↑, Darker scrotal skin, Development of glans, raised areolae V: Adult. Areolae are no longer raised |
Follicular Phase Estrogen FSH LH Progesterone | Estrogen: Stead rise FSH: Rises slightly then decreases slightly LH: Rises slightly then decreases slightly Progesterone: Low |
Luteal Phase Estrogen FSH LH Progesterone | Estrogen: decreases, then spikes briefly before decreasing again FSH low LH low Progesterone: increases then decreases |
Ovulation Estrogen FSH LH Progesterone GnRH Temp | Estrogen: just past peak FSH: low surge LH: high surge Progesterone: beginning to rise ↑ in GnRH receptors on ant pituitary ↑ Temp (due to progesterone) |
Basic schematic of menstrual cycle | ↑ estrogen --> LH surge --> Ovulation --> Progesterone (from corpus luteum) --> Progesterone levels fall --> menstruation (apoptosis of endometrial cells) |
Length of Follicular phase | Variable |
Length of Luteal phase | Constant 14 days |
When is follicular growth fastest? | 2nd week of proliferative phase (follicular phase) |
Oligomenorrhea | Cycle > 35 days |
Polymenorrhea | Cycle < 21 days |
Menometrorrhagia | Heavy, irregular menstruation at irregular intervals |
Mittelschmerz | Blood from ruptured follicle or follicular enlargement causes peritoneal irritation that can mimic appendicitis |
Primary Oocytes N C When do they enter and complete meiosis I | 2N 4C | Begin meiosis I during fetal life and complete meiosis I just prior to ovulation |
When is meiosis II arrested? | Until when? | "Arrested until egg MET sperm" | Meiosis II arrested at Metaphase II until fertilization |
If fertilization does not occur within 1 day what happens to secondary oocytes? | Degenerate |
Oogenesis | Names of cells with N and C | Oogonium (2N 2C) --> Primary Oocyte (2N 4C) --> Secondary Oocyte (1N 2C) --> Ovum (1N 1C) |
Where and When does fertilization most commonly occur? | Upper end of fallopian tube (ampulla) within 1 day of ovulation |
When does implantation within the wall of the uterus occur? | Within 6 days after fertilization |
What secretes hCG? | When is hCG first detectable in blood and urine? | Trophoblast secretes hCG Detectable in blood 1 week after conception Detectable in urine 2 weeks after conception |
Lactation When does it occur? What has changed chemically that allows it to happen? What is required to maintain lactation? | Occurs after labor because progesterone ↓ and this allows lactation to occur Suckling is required to maintain lactation: ↑ nerve stimulation --> ↑ oxytocin and prolactin |
Prolactin | What does it do? | Induces and maintains lactation and ↓ reproductive function |
Oxytocin | What does it do? | Helps with milk letdown and involved with uterine contraction |
hCG Source Function Uses | Syncytiotrophoblast of placenta Maintains corpus luteum (and thus progesterone) for 1st trimester by acting like LH Used to detect pregnancy |
Why is hCG not needed in 2nd and 3rd trimesters? | Placenta synthesizes its own estriol and progesterone |
Elevated hCG in pathological states | Hydatidiform moles, choriocarcinoma |
Average age of menopause? | What makes it earlier? | Average age at onset is 51 | Earlier in smokers |
What is happening hormonally in menopause? | ↓ estrogen production becuse of ↓ # of follicles ↑↑FSH, ↑LH (no surge), ↑GnRH Ovaries continue to produce androgens under LH stimulation |
What usually precedes menopause? | 4-5 years of abnormal menstrual cycles |
Source of estrogen after menopause? | Peripheral conversion of androgens |
Best test to confirm menopause? | ↑↑ FSH |
What does Menopause produce? | "HHAVOC" | Hirsutism, Hot flashes, Atrophy of the Vagina, Osteoporosis, Coronary artery disease |
Menopause before age 40 indicates… | Premature ovarian failure |
Menorrhagia | Heavy and/or prolonged menses |
Average length of menses | 3-5 days |
Average blood loss during menses | 35mL (10-80) |
Metrorrhagia | Irregular menses |
Dysmenorrhea | Painful menses |
As women approach menopause, how does their cycle change | Follicular part becomes shorter. Failure of ovaries to produce follicles and estrogen --> ↑↑ FSH and earlier LH/FSH surge |
Perimenopause What is it? How long does it last? | Irregular/skipped menses and beginning of vasomotor symptoms | Can last 5-10 years before menopause |
Menopause definition | 12 months of amenorrhea |
Mechanisms of osteoporosis in menopause | Estrogen --/ bone resorption by osteoclasts |
Leuprolide Mechanism Uses Toxicity | GnRH analog Pulsatile --> Agonist Continuous --> Antagonist (downregulation of GnRH receptors in pituitary --> ↓ FSH/LH Pulsatile: treats infertility Continuous: Endometriosis, Prostate cancer (w/ Flutamide), Uterine fibroids, Precocious puberty Tox: Antiandrogen, Nausea, Vomiting |
Testosterone, Methyltestosterone Mechanism Use Toxicity | Agonist for androgen receptors Treats: hypogonadism, Promotes development of secondary sex characteristics, Stimulation of anabolism to promote recovery after burn injury Tox: Masculinization in females, Reduces intratresticular testosterone in males by inhibiting release of LH which leads to gonadal atrophy, Premature closure of epiphyseal plate, ↑LDL, ↓HDL |
Names of antiandrogens | Finasteride, Flutamide, Ketoconazole, Spironolactone |
Finasteride Kind of drug MoA Uses Tox | Antiandrogen --/ 5α Reductase which turns T into DHT Treats BPH and hair loss Breast growth |
Flutamide Kind of drug MoA Uses | Antiandrogen Nonsteroidal competitive inhibitor of androgens at the testosterone receptor Treats prostate carcinoma |