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Reproductive Systems

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Survival of genes  

	Despite what you've heard, the prime importance is not survival of the individual or species
	In The Selfish Gene, biologist Richard Dawkins explains the theory that reproduction, indeed all the mechanisms of life in general, can be explained in terms of the continued survival of genes (brief video of Dawkins)
	Genes are information --NOT strands of nucleotides (any more than the information contained in these notes is a string of letters; the information in the notes can be copied [multiplied] and even changed to another form such as speech or digital code or Swahili)
	Thus genes build organisms to live in just as humans build houses to live in Likewise, organisms have homeostatic control mechanisms to maintain constancy just as homes have automatic control systems such as heating/cooling systems to maintain constancy Organisms provide a vehicle for the genes and the apparatus to  make copies (children) that outlive the organism Thus, genes can be almost "immortal"
	Individuals come and go; species come and go; genes remain [theoretically] forever

Sexual mode of reproduction     

Sexual / two-parent (rather than asexual/one-parent) reproduction allows more variation among offspring

	Individual genes want to survive and through sexual reproduction can form coalitions with different genes to improve their chances that at least some gene copies will survive (those genes that end up in combinations that turn out to be successful)
	It's more fun that way

Functional anatomy

	Testes (sing. testis) The male gonads (paired) Spermatogenesis - making of sperm (gamete) cells Secrete testosterone Originate near kidneys Descend through inguinal canal Gubernaculum (literally, "governor") is a ligament that guides the way Temperature is lower outside the body cavity (low temp req'd for spermatogenesis) Cryptorchidism (crypt- "hidden" -orchid- "testis" -ism "condition") occurs when one or both testes fail to descend completely into scrotum Structure Within scrotum  Scrotum is fold of skin into which testes descend, stretching it into a pouch     GA Dartos muscle in wall of scrotum & cremaster muscle around each testis regulate position of testes relative to body      GA Temperature regulation Fibrous capsule (tunica albuginea) Surrounded by serous membranes forming the fluid-filled tunica vaginalis     GA  GA Lobules     GA About 250 lobules per testis Contain seminiferous tubules  (semin- "seed" -ifer- "carry" -ous "pertaining to")     GA  FIG Semiferous tubules are made of germinal epithelium  (70 cm each) Site of spermatogenesis Interstitial cells (of Leydig) Found between the seminiferous tubules Endocrine cells that secrete androgens (primarily testosterone) Rete testis (literally "network of the testis") Network of tubules into which the seminiferous tubules carry the sperm Forms a sort of "exit lobby" Efferent ductules lead from rete testis to the epididymis
	Reproductive tract Epididymis  Within scrotum; coiled tubule alongside testis (6 m) Storage and conduction of semen (sperm and spermatic fluid)     GA Where sperm learn to swim Secretes <5% of seminal fluid Contains glycogen (to nourish sperm) Ductus (vas) deferens  (vas "duct" or "vessel" deferens "detour") Muscular tube Last part widens to form ampulla     GA Conducts semen from epididymis through inguinal canal into pelvic cavity, where it turns back down to behind the bladder to join the urethra (during emission)     GA Left and right ductus deferens each join with a duct from a seminal vesicle (exocrine gland) to form an ejaculatory duct The left and right ejaculatory duct extend through the prostate gland and to the urethra Urethra Shared by reproductive & urinary systems Extends through penis, delivering semen (potentially) to the female's vagina  Two main parts: prostatic urethra, penile urethra
	Accessory glands Produce seminal fluid Seminal vesicles     GA Paired exocrine glands Duct joins ductus deferens behind bladder, just before the ductus deferens joins its partner to form the ejaculatory duct Contributes about 60% of seminal fluid at ejaculation Contains prostaglandins, fructose, etc. Prostate     GA Unpaired (single) exocrine gland Surrounds first part of urethra (under bladder) like a donut Prostatitis or benign prostatic hypertrophy (BPH) can constrict urethra, interfering with urination BPH occurs in about 3 of every 4 men over 50 yrs old Has many ducts leading into prostatic urethra Contributes about 30% of seminal fluid at ejaculation High pH to neutralize male urethra and female reproductive tract Highly viscous and slippery to aid swimming of sperm Bulbourethral (Cowper's) glands     GA Tiny, paired exocrine glands Located near base of penis Duct leads into penile urethra Secrete <5% of seminal fluid Secretion released just before the rest of the semen arrives Therefore, called "pre-ejaculate" Lubricates penis/vagina Neutralizes pH Pre-ejaculate MAY contain sperm (thus fertilization may occur even if "ejaculate" never enters female body)
	Penis     GA Urethra extends through penis     GA Erectile columns     GA Vascular reservoirs: arteries dilate, veins constrict during sexual arousal     GA  GA Corpora cavernosa (two) and corpus spongiosum Insertion into female tract: delivery of semen/sperm     FIG Coitus (sexual intercourse; copulation) Glans penis Distal enlargement of corpus spongiosum Highly sensitive skin on surface - sexual stimulation Foreskin (prepuce) is collar of skin over the glans  Often removed by circumcision  MGM=male genital mutilation     FIG

Functional anatomy

	Ovary Located in pelvic cavity (paired organs)     GA  GA Descend from position near kidney during fetal development (as do the testes, but don't drop as far) Suspended by ligaments Structure     GA Medulla (inner region) Cortex (outer region) Ovarian follicles are pockets in which eggs (pl. ova, sing. ovum) develop     GA All follicles are "started" before birth, but during each adult reproductive cycle a group of follicles resume their development Some studies now challenge the idea that new egg cells are not produced during adulthood Only one [usually] follicle/ovum per cycle reaches point of development where follicle bursts open, releasing the egg (ovulation) Some studies now challenge the idea that ovulation only occurs once per cycle.  It may occur more often.
	Fallopian (uterine) tubes Paired muscular tubes lined with folded, ciliated mucosa Fimbriae form a fringe of fingerlike processes at distal end of tube Help pull ovum into tube Conduct ovum toward uterus via action of cilia (& peristalsis & fimbriae) Site of gamete fusion (fertilization) Takes 3 days for egg to travel down fallopian tube, but egg can only be fertilized during first 24 hours after ovulation so fertilization must take place in first one-third of fallopian tube
	Uterus Unpaired (single) organ Wall Endometrium     GA Mucous lining Sensitive to sex hormones estrogen(s), progesterone Highly vascular Uterine glands (exocrine) Hormones cause endometrium to thicken and change through reproductive (menstrual) cycle, then when hormones drop off so do the new, outer layers of the endometrium Menses, menstruation from Latin menses meaning "month" after the 28-day lunar month which seems to be used as a time keeping signal by the pineal gland, which in turn influences reproductive hormone levels Endometriosis occurs when membranes outside the uterus (for example, in the vagina or peritoneum) also respond to hormonal changes, thickening then dropping off     FIG Myometrium Middle, muscular coat Smooth muscle contracts when stretched, which is a problem during pregnancy  hormones inhibit uterine contraction during pregnancy, then at end of gestation [time of pregnancy] hormones change and labor contractions begin Contracts during menstruation