Human Development Flashcards
What does meiosis achieve
- chromosome # stays consistent b/wn generations by producing haploid gametes
- random assortment in gametes
- crossing over, which allows for recombination of genetic material= genetic diversity
What is the source of GRH, the target cell, and its effects
Hypothalamus; anterior pituitary; release of FSH and LH
What is karyogamy
fusion of two nuclei b/wn sex cells
What is the source of LH, the target cell, and its effects
Anterior pituitary; thecal and follicle cells in ovary; permits hormone synthesis from acetate –> cholesterol –> progesterone –> testosterone
What is the source of FSH, the target cell, and its effects
Anterior pituitary; follicle cells in ovary; stimulates initiation of follicle growth; converts testosterone and estrogen
What is the source of Progesterone, the target cell, and its effects
placenta, thecal cells, follicle cells; endometrial layer; prepare and maintain the endometrium for implantation and pregnancy
What is the source of Inhibin, the target cell, and its effects
follicle cells; pituitary and hypothalamus; suppress production of FSH inhibits GRH secretion
What is the source of hCG, the target cell, and its effects
placenta; corpus luteum; functions as LH-like gonadotropin to maintain corpus luteum during early parts of pregnancy
What part of the early embryo secretes hCG to maintain the corpus luteum
syncytiotrophoblast layer
What events occur during the first embryonic week (3rd wk GA)
Fertilization occurs at the beginning of the week
Implantation at the end of the week
Separation into identical twins
What events occur during the second embryonic week (4th wk GA)
Holoprosencephaly (cleavage of the forebrain at FOUR weeks)
All or none period ends
What events occur during the third embryonic week (5th wk GA)
Heart starts beating
Arms/legs begin to form
What events occur during the fourth embryonic week (6th wk GA)
Neural tube closes
eyes/ears begin to form
What events occur during the tenth embryonic week (12th wk GA)
genitalia starts to form
When is the umbilical cord formed
Between 13-38dys (2-5ish wks) embryonic age
What is the umbilical cord made of
two umbilical arteries and one umbilical vein
What do the umbilical arteries and veins do (what is their function)
The arteries return deoxygenated blood to the mother, while the vein takes oxygenated blood to the fetus
What are the four defects associated with Tetralogy of Fallot
- pulmonary valve stenosis
- VSD
- shifted aorta
- right ventricular hypertrophy
In what part of human development can disorders of sexual development occur
bipotential gonads differentiate based on the sex chromosomes present
SRY will cause development in males by 6wks
Testes will produce Mullerian inhibiting substance, causing the Mullerian ducts to regress (testosterone produced from testes at 12wks develop the spermatic ducts from Wolffian ducts)
If the Wolffian ducts atrophy and the Mullerian ducts grow, female gonadal development will occur
What is spina bifida occulta
failure of the caudal (posterior) neuropore to close. Spinal cord, meninges, and overlying skin remains intact
often found incidentally; small gap in the spine but there is no protruding sac; can have a possible hair tuft (sacral tuft of hair, sacral dimple)
What is spina bifida cystica
meningocele (herniation of the meninges only; protruding sac of fluid that does NOT contain spinal cord, little to no nerve damage) and myelomeningocele (herniation of meninges and neural tissue; protruding sac containing part of the spinal cord and nerves; exposure to the amniotic fluid causes damage; symptoms: loss of feeling/movement in legs/feet, incontinence)
What is myeloschisis
exposed neural tissue w/out skin or meninges covering
What is anencephaly
Failure of rostral (anterior) neuropore to close; changes the brain and cranial vault are grossly malformed with normal hindbrain development
micky mouse u/s sign; low survival
What is the most severe and common form of spina bifida
Myelomeningocele; it involves the spinal cord, unlike meningocele
What is the incidence of NTDs? Anencephaly? Spina bifida?
1 in 3000
1 in 1000
1 in 1500
What prevents NTDs in a pregnancy and how much should be taken? What is the success rate? What is the risk if there was a previously affected pregnancy?
Folate (vitamin B9) at 0.4mg (400ug) prevents 75% of pregnancies from being affected with an NTD
If there is a previous pregnancy with a NTD, the carrier of the pregnancy should take 4mg in the next. 2-3% increased risk in this second pregnancy if the first was affected
What are some causes of NTDs
folate deficiency, FH of NTDs (2-3% increased risk), mat diabetes/obesity, mat fever in early pregnancy, antiseizure meds (valproate/carbamazepine)
What is considered a screen positive for NTDs and when is this measurement taken
AFP> 2.50 MoM
Done between 15-22wks
What is a chondroma
around 4wks embryonic age (6wks GA) the vertebrae develop
sometimes small portions of the notochord remain at the base of the skull, forming a slow-growing malignant tumor called a chondroma
What is the diaphysis
short region of the bone
What is the epiphyseal plate? What influences its’ growth
site of long bone lengthening
growth is influenced by growth and sex hormones
very high levels of GH/sex hormones at the end of puberty stops growth at the epiphyseal plate
Why does osteoporosis occur
typically occurs in menopause but is a common feature in genetic conditions
bone reabsorption is > than bone deposition due to decreased estrogen
What occurs at 6wks embryonic age (8wks GA)
teeth and palate begin to develop
Generally, what are the pharyngeal arch complexes
produce cartilage, bone, nerves, muscles, glands, and connective tissue of the face and neck
What is PAC#1, what is it involved in, and what is it innervated by
innervated by cranial nerve #5 (trigeminal nerve)
involved in development of maxillary process (palate) and mandibular process
auditory meatus also comes from here (External ear canal, ear drum, eustachian tube)
What is PAC#2, what is it involved in, and what is it innervated by
innervated by cranial nerve #7 (facial nerve)
involved in external ear development
What are the first arch syndromes, what causes them, and briefly describe them
failure of the neural crest cells to properly migrate, proliferate, and differentiate
- Treacher Collins: AD (TCOF1 gene): underdevelopment of the jaw, eyelid defects
- Pierre Robin sequence: AD- rarely inherited, typically de novo; hypoplasia of the jaw, cleft palate, eye and ear defects
- DiGeorge syndrome: born without thymus and parathyroid glands (derived from 3rd and 4th PACs); defects of cardiac outflow: separation between the systemic and pulmonary sections of the heart; micro del in 22q11.2 (contains 30-40 genes)
What are endocardial cushions
column of tissue between the early ventricle and atrium
NOT a wall; will later fuse with the interventricular septum to separate chambers
What is ductus arteriosus
shunts blood AWAY from the lungs, only receives blood from the RV; closes at birth, only present in fetal life
What is patent ductus arteriosus? What is it associated with and which gender is it more associated with? What can be done to tx it?
ductus arteriosus stays open after birth
2-3x more common in females
associated with failure of TGF-b induction signaling after birth
can be caused by congenital rubella infection
get more blood flow to body, less to lungs, and mixing of the deO2 + O2 within and outside the heart
if left untx, pulmonary HTN can develop which will lead to premature death; can tx w ibuprofen to close although sx may be necessary (~3d if responsive); rare for it to spontaneously close after first 3mo of birth
What is the truncus arteriosus
important in separating the pulmonary and systemic aorta. Typically closes around 8wks GA
What is patent truncus arteriosus? What is it associated with? What can be done to tx it?
failure of a normal bulbar ridge formation and aortopulmonary septum causing incomplete separation of the pulmonary artery and aorta to the body
caused by failure of the neural crest cells to migrate and proliferate in the heart
often associated with VSDs
frequently associated with 22q11.2 del (12-35% of pts)
leads to mixing of deO2 and O2 in the body
without sx correction, pts die before 2mo; after sx, 80% survival rate over 20yrs but reoperation rate remains high
What is left heart syndrome? What is it associated with? What can be done to tx it?
occurs when the shunt between the RA–>LA does NOT function properly, causing less blood to be diverted to the L side of the heart. The LV does not develop musculature properly, causing a weak pump
involves under development of the mitral valve, LV, aortic valve, ascending aorta and aortic arch
2/3 will survive until 5yo; 1/3 will die before palliative sx can take place
heart transplant possible but typically reserved for those who cannot undergo palliative sx
gene mutations cause sporadic cases, typically de novo and not inherited
What are VSDs/ASDs? What is it associated with? What can be done to tx it?
failure of the foramen ovale and foramen secondum to close the area between the RA + LA; opening still exists after birth (corrected during sx)
failure of the intraventricular septum to fuse with the endocardial cushions (one of the more common CHDs, 25% of cases corrected during sx)
When do the fetal kidneys develop
4th-8th week of fetal development
functional kidney formed at wk 9
when does gonadal development begin? how do the male and female cells come to be?
at wk 5
sertoli cells will make antimullerian duct hormone, testosterone increases are stimulated by hCG reaching peak levels between 8-12wks
follicle cells will secrete estrogen, NO antimullerian duct hormone; histology of the ovary is recognizable by 10wks
Describe (briefly) the features of Androgen Insensitivity syndrome
XLR
In males, the sertoli cells make AMDH; the leydig cells which make testosterone but there is no response so no derivatives of the male duct system are produced
will develop 2/3 of the lower vagina and therefore, genitalia may look more “female”; testes are internal and nonfunctional
Describe (briefly) the features of 5 alpha reductase deficiency
typically converts testosterone to dihydrotestosterone (the more potent androgen)
AR
in males, external genitalia may be somewhat ambiguous at birth
puberty is typically when testosterone increases, causing increased vivilization of external genitalia at puberty
Describe (briefly) the features of CAH
Caused by PVs in any of the enzymes involved in cortisol production
XY: precocious puberty (develop 2ndary sex characteristics much younger than usual)
XX: virilization of the external genitalia
What is situs solitus
normal or typical asymmetrical positioning of the organs
What is situs inversus
mirror image to the typical positions of the internal organs in the body
1 in 8500 births; no health problems
What is heterotaxia
positional mixture of internal organs
linked to primary ciliary dyskinesia
also associated with malformations of the pulmonary venous drainage system
What is right/left isomerism
1 in 10,000 births, CHDs (ASD + VSD in 60%)
5yr survival rate for L atrial isomerism is ~64%; for R atrial isomerism is down to 29% (lack of oxygenated blood and venous malformations)
What is triad syndrome
bronchiectasis (wide/damaged airway)
sinusitis
situs inversus totalis
What is an encephalocele
sac containing part of brain protrudes through the skull
most involve the occipital area of the brain (back of the head)
can occur anywhere on midline from nose to back of head; better prognosis if in the front of the head and less likely to contain brain matter
What is a lemon/banana sign consistent w on u/s
lemon: front of skull looks pinched
banana: banana shaped cerebellum
suggest Chiari II malformation and/or spina bifida
