Study Guide 5 - (MCAT) Reproduction (professors) PDF

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Lecture notes uploaded by a professor from a previous student, taken from the MCAT Biology book review, material was needed to be known for the exam...

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Anatomy Study Guide 5 MCAT – Reproduction 

TYPES OF REPRODUCTION o Sexual reproduction in hermaphrodites  Used when the chance of finding a mate is really, really low  Happens in sea slugs and worms o Asexual reproduction  Budding  Cloning itself  Happens in sea anemone  Pros  Don’t need another participant  All your DNA goes into your offspring… this makes you supremely fit because you are passing on 100% of your genes (One definition of fitness = ability to pass on your genes)  If your environment is stable, then you are the perfect thing for living in that environment  Cons  As soon as your environment changes, the whole population may not fit anymore and it can get wiped out completely o Parthenogenesis  Ex: Parthenogenetic lizards  Entire species is female  A female will act as a male to induce the other female to stimulate oogenesis…. Some sort of compression mechanism  This is also asexual, but it goes through the normal reproductive route because there are still ova produced, just no fertilization  Offspring are complete clones  Have normal hormone patterns from mammals  Can switch between acting male like and acting female…. Depends on hormones and times o External fertilization  Ex: Frogs  Cons o Any local frog that’s releasing sperm may be the father of the female’s eggs (which have been laid outside of the body already) o Not 100% guarantee that the mate that the female chose (for ultimate fitness) is actually the father

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GENDER o Sequential hermaphroditism  Ex: Black sea bass  All black sea bass are born female  Then around 2-3 years old, the female will turn into a male

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For every male, you can fertilize a ton of eggs…. So only need a few males to fertilize the whole population  maximum reproduction

STRUCTURES OF REPRODUCTIVE SYSTEM

o Pelvis  Ox caxa… made of 3 individual parts  Ileum (the bone on the top)  Ischeum (on the back)  Pubis (most anterior surface)  Sacrum  Cocyx bone  Tail bone, loosely attached to the sacrum  Pubic symphysis  Joint between the two pubic bones of ox caxa = amphiarthrotic joint o Pelvic angles  Sub-pubic angle  Indicative of gender  Angle of the ileum (flare)  Indicative of female or male  Angles in relation to childbirth o Changes with pregnancy  Sometime in 2nd trimester, body starts to release relaxin, which acts on the ligaments in the body to lower the cross linking and allow the ligaments (specifically in the pubic symphysis) to stretch more, which is one of the reason why pregnant women waddle a little bit (joints are a little looser than normal)

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Reason for that is because during childbirth, the 2 pubic bones are going to open up even more so that the baby can pass through Bottom left = normal spacing (1/2 – 1mm under normal conditions) Right picture = spacing is 15mm (15x what it normally is) … this is after birth.. If it doesn’t come back, then have to go in for surgery maybe So ft

tissue in females  Urethra, vagina, anus  Levator ani  Around the urethra, you have these circular muscles that are basically sphincters…. Keeps things together o Soft tissue in males  Everything is the same except no vagina o Female reproductive organs  Ovary and fallopian tubes  THERE IS AN OPEN SPACE between the ovary and the fallopian tube  This is how ectopic pregnancies occur!  You can also get a bacterial infections in this space, meaning an abdominal infection can spread to ovaries and fallopian tubes  Cervix

 Rectum  Uterus  Vagina  Urethra o Male reproductive organs  Clitoris = same thing as glens penis on the male  Prepuce = foreskin (females = clitoral hood)  Shaft of the penis (analogous to the external labia of a female)  Tissue that engorges during ejection  Three groups of erectile tissues  Corpus cavernosum penis  Corpus spongiosum penis  Pars longa glandis 

MALE REPRODUCTION o Sperm  Develop in the seminiferous tubules in the testes  Nourished by Sertoli cells  Testes are located in the scrotum  Hangs outside the abdominal cavity and has a temperature 2-4 degrees C lower than the rest of the body  Once formed, sperm gain motility in the epididymis and are stored there until ejaculation o Ejaculation  Sperm travel through the vas deferens  ejaculatory duct  urethra  penis  Seminal vesicles contribute fructose to nourish sperm and produce alkaline fluid  Prostate gland produces alkaline fluid  Bulbourethral glands produce a clear, viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal  Fluid from seminal vesicles, prostate, and bulbourethral glands = semen

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Composed of sperm and seminal fluid o Interstitial cells of Leydig secrete testosterone and other male sex hormones  Androgens o Spermatogenesis  Four haploid sperm are produce from a spermatogonium  After S stage, the germ cells are called primary spermatocytes  After meiosis I, the germ cells are called secondary spermatocytes  After meiosis II, the germ cells are called spermatids  After maturation, the germ cells are called spermatozoa  Negative feedback loop  Decrease the production of something  FSH goes to sertoli cells which will start spermatogenesis so that you’re not producing more and more sperm throughout your life  Don’t want this to be increasing constantly  Sperm  The head contains the genetic material o Covered with an acrosome  Modified golgi apparatus that contains enzymes that help the sperm fuse to and penetrate the ovum  Midpiece generates ATP from fructose and contains many mitochondria  Flagellum promotes motility

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FEMALE REPRODUCTION

o Anatomy  Ova (eggs) are produced in follicles in the ovaries  Once each month, an egg is ovulated into the peritoneal sac and is drawn into the fallopian tube (oviduct)  Fallopian tubes are connected to the uterus, the lower end of which is the cervix  The vaginal canal lies below the cervix and is the site where sperm are deposited during intercourse  Birth also occurs through the vaginal canal  External female anatomy = vulva o Oogenesis  One haploid ovum and a variable number of polar bodies are formed from an oogonium  At birth, all oogonia have already undergone replication and are considered primary oocytes  Arrested in prophase I  Follicle growing  Oocytes are surrounded by the zona pellucida o Secreted by oocyte and follicular cells o Acellular mixture of glycoproteins that protect the oocyte and contain the compounds necessary for sperm binding  The ovulated egg each month is a secondary oocyte  Arrested in metaphase II  Mature follicle ruptures, and secondary oocyte is released  Oocyte is surrounded by the corona radiata o Layer of cells that adhered to the oocyte during ovulation  Cytokinesis is uneven in oogenesis  The cell receiving very little cytoplasm and organelles is called a polar body  If the oocyte is fertilized, it will complete meiosis II to become a true ovum o Menstrual cycle  Periodic growth and shedding of the endometrial lining  Follicular phase  GnRH secretion stimulates FSH and LH secretion  This promotes follicle development

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Estrogen is released  stimulates vascularization and glandularization of the decidua Ovulation  Stimulated by a sudden surge in LH  Surge occurs because estrogen stops having negative feedback effects at a certain threshold and begins to have positive feedback effects Luteal phase  LH promotes the ruptured follicle to become the corpus luteum  Corpus luteum secretes progesterone that maintains the uterine lining  High estrogen and progesterone cause negative feedback on GnRH, LH, and FSH Menstruation  Occurs if there is no fertilization  Estrogen and progesterone levels drop  Endometrial lining is sloughed off  Block on GnRH is removed Fertilization… if it happens  Blastula produces human chorionic gonadotropin (hCG) o LH analog o Maintains the corpus luteum  At end of first trimester, hCG levels drop as the placenta takes over progesterone production Implantation  Implantation takes about 1 week  Trophoblast cells secrete human hCG to maintain the viability of the corpus luteum  estrogen and progesterone  Trophoblast literally chew a hole th  Eventually, uterine lining re-heals around it  Fertilized egg eventually becomes a meshy network with holes that are called lacuna o Where the mother’s blood starts to pool into and vascularize from her side  Then, embryo on its side sends out its own chorionic villi to vascularize and pair up in between those holes

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Birth 

Hopefully this starts to look like what the placenta would be Now you have a fetus! o Mothers blood is coming in o Fetal blood in those chorionic villi going out (only oxygen, nutrients, and Abs cross through mother’s blood)

Positive feedback loop = amplification  In childbirth, once uterine contractions start, you want them to get stronger and stronger to actually give birth  Estradiol is the first step o Pressure on the cervix triggers this o Estradiol from ovaries will activate oxytocin receptors in the myometrium  starts contractions  Oxytocin causes contraction in smooth muscle of the breast for lactation too  Consequences of childbirth: o Sometimes tear one of the muscles in levator ani… this may cause problems later on, mostly with urinary incontinence o Pregnancy can change the orientation of the urethra so the sphincters don’t work so well  Ex: Sometimes after childbirth if jumping on trampoline or laugh really hard, there’s some incontinence Menopause  Ovaries stop producing estrogen and progesterone between the ages of 45 and 55  FSH and LH levels rise  Physical and physiological changes occur o Flushing, hot flashes, bloating, headaches, irritability...