Reproductive system

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Reproductive system

• Males
• Production of sperm cells
• Sustaining and transfer of sperm to female
• Production of male sex hormones
• Females
• Production of female sex cells
• Reception of sperm from male
• Nurturing development and nourishment of new
  individual
• Production of female sex hormones

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Formation of sex cells

• Testes in males, ovaries in females produce sex
  cells called gametes
• Occurs by meiosis

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Fig. 19.2
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Scrotum

• Saclike structure containing testes
• Divided into compartments by septum
• Smooth muscle (dartos muscle), connective tissue
  covered by skin
• Cold temperatures- dartos and cremaster muscles
  contract
• Reduces size of scrotum and pulls testes towards
  body for warmth
• Vice versa- extremely important

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Testes

• Capsule of thick, white connective tissue
• Extensions project into testes, divide it into
  250 cone shaped lobules
• Lobules contain seminiferous tubules- develop
  sperm cells
• Interstital cells surround tubules- secrete
  testosterone

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Spermatogenesis

• Formation of sperm cells
• Before puberty- interstitial cells not prominent,
  non-functional seminiferous tubules
• Puberty- large interstitial cells and tubules
• Sertoli cells- in tubules, nourish germ cells and
  produce number of hormones
• Numerous meiotic divisions produce sperm cells
• Sperm cell- head, midpiece and flagellum
• Acrosome on head contains enzymes

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Epididymis

• Seminiferous tubules empty into rete testis
  (network), into efferent ductules, into
  epididymis
• Comma-shaped structure on posterior surface of
  testes
• Sperm cells mature, learn how to swim and
  penetrate oocyte
• Capacitation- final changes occurring after
  ejaculation, prior to fertilization

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Vas deferens

• Ductus deferens
• Leaves epididymis, becomes part of spermatic cord
• Penetrates into body
• Swells before reaching prostate gland
• Contains smooth muscle
• Rhythmic contractions propel sperm

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Seminal vesicle/ ejaculatory duct

• Seminal vesicle- sac-shaped gland
• Seminal vesicle- duct connects to vas deferens at
  prostate gland- ejaculatory duct
• Ejaculatory duct extends into prostate and joins
  urethra

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Urethra

• 3 parts
• Prostatic urethra- passes through prostate
• Membranous urethra- surrounded by external
  sphincter
• Spongy urethra- extends length of penis
• Common passageway
• Fluids do not mix- Internal sphincter

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Penis

• 3 columns of erectile tissue
• Erection- tissue becomes engorged with blood
• Organ of copulation and sperm transfer
• Corpus cavernosa dorsal and side portions
• Corpus spongiosum- smaller ventral portion, forms
  glans penis (head)
• Covered by skin, lots of nerves and prepuce

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Glands

• Prostate- size of walnut, produces prostatic
  fluids
• Bulbourethral glands- pair of small mucus
  secreting glands, duct connects to urethra

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Secretions

• Semen- mixture of sperm and glandular secretions
• 60 seminal fluid, 30 prostatic fluid, 5
  testes, 5 bulbourethral
• Mucus- lubricates and neutralizes acidity
• Testicular- sperm and fluid
• Seminal fluid- fructose, nutrients,
  prostaglandins
• Prostatitc- pH balance and fluidity

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Hormonal Regulation

• Gonadotropin-releasing hormone (GnRH) is released
  from hypothalamus and stimulates anterior
  pituitary to release leutinizing hormone (LH) and
  follicle stimulating hormone (FSH)
• LH and FSH named for functions in female
• LH causes interstitial cells to secrete
  testosterone
• FSH causes seminiferous tubules to produce sperm,
  and promotes secretion of inhibin

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Hormonal Regulation

• Testosterone has a negative feedback on GnRH, LH,
  and FSH secretion
• Inhibin has a negative feedback on FSH secretion

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Puberty

• Development of sexual maturity
• Before- small amounts of testosterone inhibit
  GnRH, LH, FSH
• During- hypothalamus and anterior pituitary
  become less sensitive to testosterone

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Testosterone

• Major sex hormone secreted by testes
• Puberty- enlargement, differentiation of male
  genitals, spermatogenesis
• Secondary sexual characteristics
• Sex drive

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Male Sexual Act

• Series of reflexes- erection, secretion of
  mucous, emission, ejaculation
• Emission- movement of sperm and secretions into
  urethra
• Ejaculation- forceful expulsion
• - sensation of pleasure- orgasm/climax
• Resolution/refractory- flaccid penis, feeling
  of satisfaction, male is unable to achieve
  erection and ejaculation

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Ovaries

• Suspended in pelvic cavity by suspensory and
  ovarian ligaments
• Outer part is covered by connective tissue
• Contains ovarian follicles
• Each follicle contains an oocyte

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Oocyte Development

• Formation of sex cells starts in fetus
• 4 months- 5 million oogonia
• Meiotic divisions end prematurely- primary oocyte
• Ovulation is the release of the oocyte from the
  ovaries
• Meiotic divisions commence and finish just before
  ovulation- secondary oocyte

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Follicle Development

• Primordial follicle- primary oocyte surrounded by
  single layer of cells- ganulosa cells
• Puberty- some primordials are converted to
  primary follicles
• Primary follicle- enlarged oocyte, enlarged
  ganulosa cells
• As granulosa cells divide, a clear material is
  deposited around oocyte called zona pellucida

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Follicle Development

• Every 28 days- hormones stimulate some primary
  follicles to develop into secondary follicles
• Secondary follicles- fluid-filled vesicles formed
  among granulosa cells, and a capsule
• Theca- capsule that forms around follicle
• Follicle enlarges, vesicles fuse to form the
  antrum

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Follicle Development

• Mature/ graafian follicle- primary oocyte is
  encased in ganulosa cells called cumulus cells
• Mature follicle forms a lump on the surface of
  the ovary

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Fig. 19.11
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Ovulation

• Mature follicle ruptures- sends secondary oocyte
  into peritoneal cavity, fallopian tubes
• Cells of ruptured follicle transform into a
  glandular structure called the corpus luteum-
  secretes hormones
• If pregnancy- corpus luteum enlarges in response
  to HCG secreted by placenta

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Fig. 19.11
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Uterine tubes

• Fallopian tubes/ oviduct
• Extend from ovaries to uterus
• Not connected to ovary, but open near it
• Fimbriae surround the openings
• Cilia on the surface pull egg into tube
• Fertilization usually occurs near the opening of
  the oviduct

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Uterus

• Fundus- part superior to the opening of the
  oviduct
• Body- main part
• Cervix- inferior opening to vagina
• Uterine cavity continues through cervix as the
  cervical canal
• 3 layers of the uterine wall

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Uterus

• Outer layer- serous or perimetrium
• Middle- muscular or myometrium
• Inner- endometrium, simple cuboidal cells,
  superficial part is sloughed off during
  menstruation

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Vagina

• Organ of copulation
• Functions to receive penis, allow menstrual flow
  and childbirth
• Wall- outer muscular layer, inner mucosal layer
• Allows for an increase in size to accommodate
  penis, stretch during childbirth
• Hymen cover opening in young females
• Hymen is not accurate indicator of virginity

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Puberty

• Marked by the first menstrual bleeding called the
  menarche
• Development of secondary sexual characteristics
  and sexual drive
• Result of increasing estrogen and progesterone
  secreted by ovaries
• Cyclical pattern of hormones is gradually
  established

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Puberty

• Prior- GnRH, LH, FSH secretion is very low
• Estrogen and progesterone have strong negative
  feedback on hypo, and pituitary
• Puberty- large amounts of GnRH, LH, and FSH
• Estrogen has a positive feedback effect

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Menstrual cycle

• 2 cycles- ovarian, uterine
• ovarian cycle drives uterine cycle

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Ovarian cycle

• under control of gonadotropic hormones
• FSH and LH
• Secreted at different times of cycle
• 2 phases follicular phase, luteal phase

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Follicular phase

• FSH promotes development of follicle in ovary
• Follicle secretes estrogen and progesterone
• Estrogen exerts negative feedback on FSH
• High levels of estrogen cause a sudden secretion
  of GnRH
• Leads to a LH surge
• LH surge responsible for ovulation on day 14 of
  cycle

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Luteal phase

• LH promotes development of corpus luteum
• Corpus luteum secretes progesterone and estrogen
• Progesterone causes build up of endometrium
• Progesterone exerts negative feedback over
  anterior pituitary
• Menstruation after luteal phase

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Uterine cycle

• estrogen and progesterone cause 28 day cycle
• menstrual period days 1-5 low level of
  hormones cause endometrium to disintegrate, blood
  vessels rupture, menstruation
• proliferative phase days 6-13 increased
  production of estrogen by new follicle in ovary
  causes thickening of endometrium

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Uterine cycle

• OVULATION
• Secretory phase days 15-28 thickening of
  uterus due to progesterone, uterine glands mature
  and produce thick mucus
• Uterus is ready to receive embryo, if not,
  hormone levels fall, endometrium breaks down
• Repeat cycle

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Pregnancy

• embryo imbeds in endometrial lining
• placenta originates from maternal and fetal
  tissue
• no mixing of fluids
• placenta produces HCG (human chorionic
  gonadotropin)
• HCG maintains the corpus luteum until placenta
  produces its own estrogen and progesterone
• Progesterone and estrogen have 2 effects
• Shut down anterior pituitary so no new follicle
  develops
• Maintain endometrium

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Orgasm

• upon sexual stimulation, labia minora, vaginal
  wall and clitoris become engorged with blood
• breasts swell and nipples become erect
• labis majora enlarge, redden and spread away from
  vaginal opening
• vagina expands and elongates
• blood vessels in vaginal wall release fluid to
  lubricate vagina
• mucus-secreting glands beneath labia minora
• vagina is organ of sexual intercourse

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Orgasm

• clitoris plays a significant role in female
  response
• clitoris swells to 3-4 times its normal size
• stimulation via thrusting of penis and pressure
  of pubic symphases
• orgasm occurs at height of sexual response
• blood pressure and pulse rate rise
• breathing quickens
• walls of uterus and oviducts contract
  rhythmically
• sensation of intense pleasure
• NO refractory period
• MULTIPLE orgasm during a single sexual experience