Preamble
Sunday, January 3rd, 2010
What follows is the original preamble (more or less the same as those from M2M, etc). A few notes on LC:
1) People tend to be split on Life Cycle. About a third of the class tends to think it’s great, intuitive, and interesting. The other two-thirds think it’s a mishmash of mumbo-jumbo haphazardly sewn together into something that looks like a course. While not willing to admit my fealty to one or the other camp, I will say that I frequently found it difficult to know what to focus on in LC (thus the title of this collection). The emphasis I place in these LOs, therefore, should serve as a starting point only for figuring out how to concentrate studying.
2) Dr. Ericksson, who you may have met in DEMS and who is one of the block directors for LC, is tough, concise, and a very good lecturer as long as you keep paying attention so you don’t get lost. I recommend attending her classes.
3) As far as the boards go, this information is sometimes useful, sometimes not—better as background knowledge to be able to link a question’s answer together than primary knowledge to link up symptoms and pathology. Qbank and First Aid are going to help you on step 1 much more than this course.
4) Test questions in LC have a tendency to be either imprecise or focus on minutiae.. again, not always, but often enough. This is one reason why you should probably go to class if you want to honor the block—LOs are well and good, but it’s frequently the tangential thing that the professor mentioned in passing that shows up on exams.
5) That said, many people skip out on going to LC altogether to study for boards. I don’t endorse it myself, but if you’re going to skip one block at the end here, in the name of all that’s holy don’t skip ID, which is information you just have to slog and slog and slog through and which, unless you’ve a brain like a steel trap, can’t be crammed.
–jcr
PS- if you find these useful and can go without a latte for a couple of days, I’d like you to give another $5 to charity.
Hey, everybody. These are my compiled learning objectives for Life Cycle when I took it in the spring of 2009. I hope you find them useful. A few notes:
1. These aren't to be taken as everything-you-need-to-know material, or anything close to it. They can be, however, extremely useful, if only to look at the material a second time in a different format.
2. Learning objectives change. Granted, in our vaunted institution, they often don't change a lot. But it's worth figuring out where these overlap with what you're studying and where they don't to avoid any unnecessary learning (God forbid).
3. They can be incorrect. I hope this is infrequent, but I'm sure there are things in here that aren't accurate. I've tried to curate them reasonably well; I hope one of your classmates will do likewise. If you find an error, kindly let him or her know.
4. They are nothing more or less than my personal take on what we happened to be learning on a given day. Sometimes they're very detailed, sometimes they're uncomprehending, frequently they're irreverent. I occasionally call babies vampires and things like that (dude, they are). Internet lesson: free trumps tasteful. In any case you are free to disagree with me.
5. To anyone who's wondering: I honored this block and all the rest in my first two years. That's not supposed to impress you, but it is supposed to give you some kind of confidence that I have a reasonably good handle on what's going on.
6. To the many of you who are thinking, "How can I repay this wonderful, wonderful man?" I would reply that I never turn down free beer if I can help it. The problem with that is that I suspect I will never meet most of your class, and beer-buying in absentia is a cold and heartless thing. So if you find these useful and would like to do something for me, I would prefer it if you donated $5 to the charity of your choice; if you're stumped, I suggest browsing www.charitynavigator.com for some good options. Kindly do not donate money to armed insurrectionist groups.
i. Addendum on donating to charity: always always ALWAYS have an email account that you set aside purely to sign up for or donate to things (thus ducking all the spam associated therewith). I think I have 1,200 emails in mine, mostly from a donation I made to the SPCA a couple of years ago. Gmail and Hotmail work well. I also recommend using a false street address to avoid direct-mail campaigns.
ii. "That seems like a lot of trouble to go through to donate five bucks"-- yeah, well, welcome to the world, sonny Jim. Doing things for other people frequently is a pain in the ass. Doesn't make it less worth doing.
Regional Anatomy of the Pelvis and Perineum
Monday, January 05, 2009
8:06 AM
Regional Anatomy of the Pelvis and Perineum, 1/5/08:
Note that these aren't on the exam. A few notes (haven't been vetted or reviewed so take with a grain of salt):
· 2 important ligaments: sacrospinal (from sacrum to ischial spine) and sacrotuberous ligament (from sacrum to ischial tuberosity). These form part of the wall of the pelvis and form foramina out of the greater and lesser notches. Note, relevant to boards, that the ischial spine is where you place pudendal nerve blocks.
· Pelvic diaphragm: levator ani and coccygeus muscles contained within two layers of fascia. Supports viscera; vagina (and thus baby) passes through it. Kegel exercises postpartum help tighten this back up afterwards.
· Urogenital diaphragm: covers the anterior half of the pelvic diaphragm; contains deep tranverse perineal and sphincter urethrae muscles, plus the bulbourethral glands in the male, within two more layers of fascia. Erectile muscles of the penis attach here (on the inferior fascia).
· Perineum: where the urogenital diaphragm attaches to the pelvic diaphragm.
· Anal triangle: the other half of the pelvic diaphragm (posterior to the urogenital diaphragm). Note that there are recesses (ischiorectal fossae) above the urogenital diaphragm into which prolapse or infection can occur (no hard boundaries). Note also that there is no supportive diaphragm for the rectal structures.
· Embryology:
o Y gene has SRY gene (sex-determining region of Y)-- encodes a factor that causes the gonad cells to differentiate into Sertoli and Leydig cells (produces androgens). Mullerian inhibitory factor (MIF, or MIS with 'substance') is also produced by the gonad cells (specifically the Sertoli cells).
o Recall that there are two sets of internal tubing: Mullerian ducts for women (aka paramesonephric ducts), Wolffian ducts for men (aka mesonephric ducts). MIF/MIS, then, causes resorption of the Mullerian ducts to make sure males don't develop internal female genitalia.
· Note there's no comparable factor for women; the mesonephric ducts are automatically resorbed unless acted on by testicular factors.
o Note that resorption of internal female reproductive systems is MIF (Sertoli cell)-dependent; development of internal male reproductive systems is testosterone (Leydig cell)-dependent. Thus if you have no Sertoli cells but functioning Leydig cells you wind up with both sets of internal genitalia (I got this as a USMLE prep question).
· Remnants of the gubernaculum: round ligament anchors uterus to the abdominal wall, ovarian ligament anchors ovaries to uterus.
· From medial to anterior: rectum, [uterus in women], bladder.
· Rectouterine pouch (pouch of Douglas): lowest-lying part of female pelvis (between uterus and rectum). Note there's also a vesiculouterine pouch more anteriorly.
· Broad ligament: hold ovaries to fallopian tubes.
· Suspensory ligaments: contain ovarian artery and vein.
· Cardinal ligaments: hold the cervix in position. Contain uterine artery and vein.
· Note that, during ovulation, the egg is secreted into the peritoneal sac before it's picked up by the fimbriae.
· Blood supply: ovarian vessels, uterine vessels, vaginal vessels. Vaginal and uterine vessels arise from the internal iliac artery, ovarian vessels arise from the abdominal* aorta.
· Note urethra is longer in men than women.
· Note that most external genitalia is ectoderm-derived; the big exception is the urethra, which mostly (at least as it courses through the inside of the pelvis) is derived from the urogenital sinus (endoderm).
o The seminal vesicles are mesoderm-derived.
o The prostate gland is endoderm-derived (it develops from the bladder).
o Bulbourethral glands: lubricating glands that are also endoderm-derived.
· Note that testes and ovaries drain to the para-aortic lymph nodes.
· Urogenital folds: form labia minora in women, seal of shaft of penis in men. Labioscrotal folds: form labia majora in women, seal of scrotum in men.
Sexual Medicine: Embryology
Tuesday, January 06, 2009
3:26 PM
Sexual Medicine: Embryology, 1/7/08:
[All the things I could say about Sexual Medicine. I'll leave them to your sweet imagination.]
[Suffice to say the notes and slides are a little scattered and not always on speaking terms. Best guess follows.]
[General notes:]
· No oogonia form postnatally; most degenerate before birth.
· Why sperm come out a tube while eggs have to be released from the ovaries before being taken up by the fimbriae: the primitive gonads are connected to the mesonephric ducts; the paramesonephric ducts are just sort of hanging out nearby.
· Testes and ovaries have lymphatic drainage to the para-aortic nodes because that's where they start out. While descending, the coelom they drag with them develops into the tunica vaginalis. Recall that they follow the gubernaculum (the kind of lead-line descending to the base of the abdomen) down; the vas deferens comes down over the ureter. Recall also that the ovary follows the gubernaculum down a touch, but not nearly as far; the gubernaculum forms the suspensory ligament.
· Sperm are stored at the distal (scrotal) end of the deferens, in the epididymis.
· A genital tubercle, a labio-scrotal swelling, and a urogenital fold are present in all normal fetuses; genital tubercle develops into the penis/clitoris, urogenital fold develops into the shaft of the penis or labia minora, labioscrotal swelling develops into the scrotum or labia majora. Note that the inferior urethra develops from the urogenital sinus.
· This differentiation is largely determined by the presence or absence of androgens (or the responsiveness or lack thereof to androgens).
· Re boards: Hypospadias is the urethra opening out in the ventral (underside) shaft of the penis due to a failure of the urethral folds to close. Epispadias is the urethra opening out in the dorsal (topside) shaft of the penis due to faulty positioning of the genital tubercle. Hypo- is more common.
· Cloaca has three openings in females: urethra, vagina, and anus.
· Female sexual development does NOT depend on the presence of sex hormones or functioning ovaries-- it depends on the absence of androgens and MIF.
· Note the lower portion of the vagina is derived from the allantois (endoderm), not the Mullerian duct (mesoderm)-- so if the Mullerian duct doesn't develop properly, a fair part of the vagina will still develop and end in a blind pouch.
· Note that parts of the mesonephric ducts may persist and form cysts.
· Note that my wife informs me that calling female "the default gender" is out of vogue. Can we go back to "the fairer sex?" (although, having watched our Powderpuff ladies throw down, maybe we better not-- I distinctly saw a thrown elbow or two in there, though I'm not naming names. Lauren.)
1. Describe the normal development of the male and female reproductive systems/organs.
· 5th week: gonad development begins; primordial germ cells migrate in from the yolk sac up to the gonadal ridge (near the mesonephric and paramesonephric ducts).
· 6th week: migration of germ cells is complete. The gonads, at this point, are bipotential.
· 7th week: testicular development begins in the presence of SRY gene (see below).
· 9th week: ovarian development begins in the absence of SRY gene (see below).
· Note that the dates in his notes and the dates in his slides are different.
· See above for more notes.
2. Describe the roles of SRY on the development of the gonads and of Mullerian Inhibitory Substance, Testosterone and Dihydrotestosterone on the development of the internal and external genitalia. Indicate the outcome which occurs in the presence vs. the absence of these factors.
· SRY: gene on Y chromosome that produces H-Y, a product which causes testicular differentiation (Leydig and Sertoli cells, plus spermatogenic cords and seminiferous tubules). The Leydig and Sertoli cells, in turn, secrete testosterone and MIF respectively to further influence gender fate.
· Note human chorionic gonadotropin (hCG) secreted by the placenta promotes testosterone formation early in development before FSH/LH take over.
· Note the SOX9 gene is also essential for testicular development.
· There's a SRY-cofactor called SF-1 that is involves in activating testosterone and MIF secretion from Sertoli and Leydig cells.
· Testosterone (and derivatives): determine the fate of external genitalia (male with, female without) and the Wolffian ducts (causes them to develop into epididymis, vas deferens, and seminal vesicles).