Module 14: Reproductive System

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How many chromosomes are in each cell?
23 with a pair of sex chromosomes (large X and small Y)
What does every egg carry? What does the sperm carry?
Egg carries an X and sperm carries either X or Y
When is the sex of baby determined?
At fertilization (if sperm carries X, female will develop; if sperm carries Y, male will develop)
How are sex organs developed in the fetus?
- during first 6 weeks of development, male and female embryos contain common gonads
- structures eventually form testes within 6 or 7 weeks for males or ovaries within 9 weeks for females
What two tracts form either the male or female reproductive tract?
- the mesonephric (Wolffman Duct)
- the paramesonephric (Mullerian Duct)
How is the male reproductive tract and external genitalia  developed?
- after 7 weeks, testicular cells produce mullerian inhibiting hormone (MIH) which causes mullerian duct to regress
- at 9 weeks, testicular cells produce testosterone that stimulates wolffian duct to develop into epidymis, vas deferens, seminal vesicles urethra, and external genitalia
How is the female reproductive tract and external genitalia developed?
- requires no hormonal control
- no MIH, so mullerian duct develops into fallopian tubes, uterus, cervix, and part of vagina
- with no testosterone, the wolffian duct regresses and external genitalia develops
What is the function of the male reproductive system?
- produce testosterone and sperm
- deliver sperm to vagina
What are the functions of the female reproductive system?
- producing estrogen and progesterone
- produces eggs, receives sperm, and provides optimal conditions for the development of the fetus
What does the external genitalia of the male consist of?
penis and scrotum
What is the penis made up of?
- urethra
- glans penis
- erectile tissue corpus spongiosum and corpus cavernosum
What does the scrotum contain?
- testes (where sperm and testosterone are produced)
Where is sperm stored after being produced?
- epididymis (coiled tube that is roughly 6 meters)
What occurs during ejaculation?
- sperm travels through vas deferens
- it mixes with fluid from the seminal vesicles 
- it passes through prostate and receives more fluid from the bulbourethral (cowper's) gland
- it enters the urethra and asses out through penis
Where in the testes is sperm produced?
- seminiferous tubues (1000 coiled)
What do the seminiferous tubules contain?
- sertoli cells and developing sperm
What are immediately outside the seminiferous tubules?
- leydig cells (interstitial cells)
- within interstitial space
What is the function of the seminiferous tubules?
- site of spermatogonia
What is the function of sertoli cells?
- regulate spermatogenesis and mantain the developing cells (spermatogonia) 
- produce inhibin, secrete fluid that pushes the immature sperm of the epididymis and form the blood-testis barrier
- BTB isolates developing sperm cells from blood so immune cells don't attach these genetically different cells and lead to sterility
What is the function of leydig cells?
- produce testosterone
What is the function of the epididymis?
- final maturation area and storage site for sperm
What is the function of the vas deferens?
- carries sperm from the epididymis to the ejaculatory duct
What is the function of the ejaculatory duct?
- drains into the urethra
What is the function of the seminal vesicles?
- contrubute to large amount of fluid in semen during ejaculation that maintains and nourishes the sperm
What is the function of the prostate gland?
- secretes enzymes and fluid that help neutralize the acid environment of urethra and vagina
What is the function of the bulbourethral gland?
- secrete fluid that helps to neutralize pH and lubricate the urethra and vagina to create good environment for sperm
What is the function of the urethra?
- transports the sperm during ejaculation and drains bladder during urination
Explain spermatogenesis.
- stermatogonia (germ cells) contain 46 chromosomes located in outer edge of seminiferous tubules and divide into two cells by mitosis
- one cell will still be a spermatogonia and the other will develop into a primary spermatocyte with 46 chromosomes
- primary spermatocyte divides by meiosis into two secondary spermatocyte (during first meiotic division) and then into four spermatid (during second meiotic division)
- dividing cells are surrounded by sertoli cells and they work their way to center of tubule
- spermatids develop into sperm cells and are released by sertoli cells into the lumen of seminiferous tubules
How long does spermatogenesis take?
- 64 days, ends with 4 sperm cells that contain 23 chromosomes each
What is the structure of a sperm cell?
- at stage when not fully mature and able to swim
- sperm cell contains a head with an acrosome and nucleus, a midpiece with mitochondria, and a long tail (flagellum) that will propel sperm when it fully matures
How long does complete maturation of sperm take?
- 12 days
- occurs as sperm are moved to epididymis by fluid that is secreted by sertoli cells
How are testicular function controlled?
- follicle stimulating hormone (FSH) and luteinizing hormone (LH, sometimes called ICSH) released by anterior pituitary gland in response to gonadotropin releasing hormone (GnRH) from hypothalamus
How does FSH control the functions of testes?
- acts on sertoli cells to promote spermatogenesis while producing inhibin
What is the function of inhibin?
- feeds back to the anterior pituitary to decrease the release of LH and FSH
How does LH work to control testes function?
- stimulates leydig cells to produce testosterone which will feed back to both the hypothalamus and anterior pituitary to decrease the production and secretion of LH and FSH
What is testosterone?
- a steriod hormone produced by leydig cells in testes
- formation begins with cholesterol and then several intermediates ending in production of testosterone
*** note: progesterone is one of intermediates
Describe the changes in testosterone levels throughout life.
- there's a rise in testosterone levels during fetal development
- also a brief increase after birth
- remain low until puberty
How do testosterone levels rise during puberty?
- levels of GnRH increase which leads to an increase in LH and FSH which causes testosterone levels to rise
- increase causes final maturation of male reproductive system to the point where mature sperm is produced
- peak levels are reached at age of 16-18
What are the functions of testosterone?
- development of male reproductive tract and external genitalia in embryo
- growth and development of all male reproductive organs
- development of the male secondary sex characteristics at puberty (muscle growth, hair growth, deep voice)
- sex drive at puberty
- spermatogenesis
- bone and skeletal muscle growth
- increased aggressiveness
Describe the decrease in testosterone.
- at 40 years, there is a slow decrease
- at age 50, sperm production decreases
- called andropause because leydig cells no longer respond to LH
What are some side effects of andropause?
- decreased sexual desire and erectile ability
- fatigue and depression
- decreased lean body mass
- increased obesity
- decreased bone density
What is the collective name for the female external genitalia?
- vulva
What makes up the female external genitalia?
- clitoris (small mound of erectile tissue derived from embryonic tissue as the penis)
- also include labium majus (labia majora) that surrounds labia minus (labia minora) which are folds of skin derived from the same embryonic tissue as scrotum and shaft of penis
What does the labium minora enclose?
- vaginal orifice (opening of vagina)
What makes up the female internal genitalia?
- the vagina is the canal that receives the penis
- sperm then travels through the cervix into the uterus (muscular walled, hollow organ)
- sperm continues to fallopian tubes and ends at the fimbria
- the egg, produced in the ovaries, travels through the fimbra to the fallopian tubes to meet the sperm
What is the function of the vagina?
- receives penis and sperm during copulation
- allows for dischage of fluid during menstruation
- birth of baby
What is the function of the cervix?
- secretes mucus from thin (to facilitate sperm entry) to thick (to prevent sperm entry)
What is the function of the uterus?
- site of implantation of fertilized egg
- where developing embryo is nourished and maintained
- during menstrual cycle, the uterine lining undergrows phases undergo hormonal control
What is the function of the fallopian tubes?
- site of fertilization of the egg
- contain cilia that pass egg from fimbria to uterus
What is the function of the fimbrae?
- capture egg after it's expelled from ovaries and funnel it into the infundibulum
What is the function of the ovaries?
- produce eggs (oogenesis) and hormones estrogen and progesterone
What are the steps of oogenesis?
- during development, egg is contained in follicle
- millions of oogonia are developed in embryo which develop into a primary follicle that consists of outer layer of granulosa cells that contain the primary oocyte
- granulosa cells secrete fluid into interior of follicle which forms into the antrum
- primary oocyte and follicle remain in this form until puberty
- at puberty the ovaries are activated by FSH and LH 
- female begins menstrual cycle, when a few primary follicles will begin to grow
- after pubery the primary follicle develops another ring of cells (theca cells) which lie outside the granulosa cells
- primary follicle slowly develops into a mature follicle
- oocyte separates from granulosa cells and floats around freelly in antrum before ovulation
- makes one viable egg (oocyte)
Explain ovulation.
- as follicle grows, estrogen production grows causing granulosa cells to grow and produce more estrogen
- causes a positive feedback, which increases levels of FSH and LH
- LH surge causes granulosa cells to secrete lots of fluid nto antrum, causing it to swll, rupture, and expel egg
- egg gathered by fimbrae goes to fallopian tube
- mature follicle degenerates into hormone releasing corpus luteum and then will continue to generate if pregnancy does not occur
How is estrogen produced?
- estrogen includes estradiol (most potent), estrone, and estriol
- production requires the uptake of cholesterol by the theca cells that are stimulated  to convert cholesterol into androstenedione
- majority of androstenedione is secreted and taken up by adjacent granulosa cells
- FSH stimulates the granulosa cells to convert androstenedione into more estradiole which is then secreted into blood
How is progesterone produced?
- produced in small quantities by granulosa cells and theca cells before ovulation
- LH stimulatees the cells
- after ovulation of oocyte, the follicle degenerates into corpus luteum which will continue to secrete both estrogen and progesterone
- when mature follicle degenerates into corpus luteum, it continues to secrete estrogen and large amounts of progesterone to prepare lining of uterus for implantation of fertilized egg
- if egg isn't fertilized, it becomes scar tissue (corpus albicans)
How do estrogen levels change during the lifetime?
- low until puberty
- puberty brings a dramatic rise in estrogen levels due to increased secretion of GnRH from hypothalamus
- GnRH increases release of LH and FSH from anterior pituitary
- after 40, menstrual cycle becomes irregular and ovulation may not occur during some cycles and will eventually stop altogether 
What happens during menopause?
- decreased number of primary follicles in ovaries
- with fewer follicles, less estrogen is produced
- becuse of low estrogen levels, there is little negative feedback to the anterior pituitary, allowing for LH and FSH to rise
- as a result, ovaries are less responsive to the high levels of LH and FSH, causing estrogen levels to drop
What happens during the proliferative phase (days 7-14)?
- follicle increases production of estrogen, causing LH to surge
- follicle ruptures, egg is expelled
- estrogen and progesterone stimulate growth of uterine lining
What happens during the secretory/luteal phase (days 14-28)?
- follicle develops into corpus luteum and increases production of progesterone that prepares uterus for implantation
- if fertilization and implantation doesn't occur, the corpus luteum degenerates into scar tissue (corpus albicans) and progesterone levels drop
What happens during the menses phase (0-7)?
- levels of LH, FSH, estrogen, and progesterone are low
- lining of uterus can't be maintain, uterine lining is lost
How does the birth control pill work?
- there are two principle hormones (synthetic estrogen and progesterone)
- hormones found in a number of combinations and strengths
- pills with estrogen and progesterone act like the natural hormones and feedback to the hypothalamus to decrease GnRH levels, and to the anterior pituitary to decrease LH and FSH levels
- low FSH suppresses development of follicles
- low LH prevents LH surge which then prevents ovulation
- synthetic progesterone in the pill produces thick cervical mucus that inhibits sperm entering uterus
- also decreases motility of uterus and fallopian tubes which would notmally help transport eggs and sperm to site of fertilization