KIN 268: Reproductive Systems

Reproduction

Reproduction

producing new individuals; fertilization of an ovum by a sperm to form a zygote, followed by repeated cell division and differentiation; also forming new cell for tissue repair, growth, replacement

Scrotum

sac of loose skin and underlying subcutaneous tissue containing testes; separated into two compartments by the dartos muscle and a subcutaneous layer

Testes

paired, oval glands in the scrotum approximately 5 cm long and 2.5 cm diameter and partially covered by the tunica vaginalis

Tunica albuginea (male)

connective tissue capsule internal to the tunica vaginalis; extends inward to form septa that create lobules

Seminiferous tubules

1-3 coiled tubules in each of the 200-300 lobule compartments in testes; where sperm is produced; carry sperm out of the testes

Interstitial/Leydig cells

secrete testosterone

Spermatogonia

form cells; spermatogenic stem cells (2n) that arise from primordial germ cells (embryonically) and remain dormant until puberty; layers of varying maturity sperm cells within the spermatogenic cells beginning with spermatogonia and ending as mature sperm (n)

Sustentacular (Sertoli) cells

support sperm; embedded among spermatogenic cells that are scattered from the basement membrane to seminiferous tubule lumen; nourish sperm and developing sperm cells and control release of sperm; produce fluid, inhibin; regulate testosterone and FSH

Blood testis barrier

formed by tight junctions of sustentacular cells and spermatogonia; isolate developing gametes from immune responses to spermatogenic cells; prevents surface antigens being identified as foreign

Spermatogenesis

begins with spermatogonia (2n) that differentiate into a primary spermatocyte (2n) and a precursor stem cell (continues mitosis); toward lumen are layers progressively more mature cells; takes 65-75 days; sperm cell is formed → released in lumen

Spermiogenesis

final stage of development into sperm

Spermiation

spermatids are released from their connections to nurse cells; can’t swim yet

Sperm

designed to reach and penetrate the secondary oocyte to achieve fertilization and create a zygote; 300 million/day complete spermatogenesis; produced throughout adulthood

Sperm head

contains nucleus with 23 chromosomes; covered by acrosome which contains enzymes to assist penetration

Sperm neck

contains centrioles that form the microtubules that make up the rest of the tail

Sperm middle piece

contains mitochondria that make ATP for locomotion of the sperm

Sperm principal and end piece

make up tail used for movement

Gonadotropic releasing hormone

stimulates cells in anterior pituitary gland to produce luteinizing and follicle stimulating hormone

Luteinizing hormone

stimulates interstitial cells between seminiferous tubules to produce testosterone (synthesized from cholesterol); lipid soluble; diffuses from the interstitial cells to interstitial fluid to the blood

Follicle stimulating hormone

synergistic with testosterone; stimulates spermatogenesis

Testosterone

suppresses secretion of LH and GnRH through negative feedback; synergistic with FSH; stimulates spermatogenesis

Dihydrotestosterone

with testosterone, give rise to prenatal development of external genitals and brain development, development and enlargement of male sex organs and secondary sex characteristic development, development of sexual function (spermatogenesis and behaviour), stimulation of anabolism (protein synthesis)

Inhibin

secreted by sustentacular cells once degree of spermatogenesis has been achieved; inhibits FSH

Epididymis

where sperm mature for 14 days; degenerated sperm are reabsorbed; propels sperm into ductus deferens; tightly coiled; connects to efferent ducts at head, body, tail of epididymis; 6 m; store sperm for months; lined with stereocillia (microvilli)

Ductus deferens

conveys sperm from epididymis towards the urethra by peristaltic contractions; exits the tail of the epididymis and ascends through the spermatic cord into the pelvis; terminal (dilated) portion is the ampulla; store sperm for months

Spermatic cord

ascends out of the scrotum and surrounds the ductus deferens, testicular artery, veins draining the testes, autonomic nerves, lymphatic vessels and the cremaster muscle; with ilioinguinal nerve, passes through the inguinal canal which originates at the deep inguinal ring and ends at the superficial inguinal ring

Ejaculatory duct

arise from junction of seminal vesicle and ductus deferens ampulla; eject seminal vesicle secretions, sperm, and semen

Urethra

shared by reproductive and urinary systems; semen and urine pass; passes through the prostate gland (prostatic), deep muscles of the perineum (intermediate/membranous), and penis (spongy)

Accessory glands

secrete liquid portion of semen

Prostate gland

single, donut-shaped gland that secretes a milky, slightly acidic fluid containing citric acid, proteolytic enzymes, acid phosphatase, and seminalplasmin; contributes to sperm motility and viability; 25% of liquid portion of semen

Seminal vesicles/glands

secrete an alkaline, viscous fluid containing fructose, prostaglandins and clotting proteins; 60% of liquid portion of semen

Bulbourethral (Cowper’s) glands

secrete an alkaline fluid during sexual arousal that neutralizes acids from urine and mucus for lubrication; decreases sperm damage; 15% of liquid portion of semen

Semen

mixture of sperm and seminal fluid; average volume: 2.5-5 mL (150 million sperm/mL); pH 7.2-7.7; fluid provides sperm with a transportation medium, nutrients and protection from hostile acid environments; once ejaculated, liquid coagulates in 5 min and reliquefies after 10-20 min

Penis

contains urethra; passageway for semen and urine; supported by two ligaments continuous with fascia; body is composed of 3 cylinders: 2 corpora cavernosa (dorsolateral masses) and 1 corpus spongiosum (contains urethra)

Glans penis

head of penis covered by the prepuce (foreskin)

Crura

part of the root; separate, tapered portions of the corpora cavernosa penis

Bulb

part of the root; attached on the inferior surface to deep muscles of the perineum

Erection

parasympathetic; nitric oxide vasodilates arterioles in erectile tissue and large amounts of blood enter widened sinuses; veins are compressed to slow blood flow away from penis; mechanoreceptor stimulation contributes

Ejaculation

sympathetic; muscles contract to force the semen out; arterioles supplying erectile tissues constrict, blood sinuses relax, pressures on veins is alleviated, blood drains from them

Ovaries

paired glands; produce gametes that mature into ova and progesterone, estrogens, inhibin, relaxin; contain hila

Broad, ovarian, and suspensory ligaments

respectively, fold of parietal peritoneum, anchors ovaries to uterus, attaches ovaries to pelvic wall

Ovarian/surface mesothelium

covers ovary surface

Tunica albuginea (female)

capsule of dense irregular connective tissue below germinal epithelium

Ovarian cortex

below tunica albuginea; consists of ovarian follicles and stromal cells; indistinct border with medulla

Ovarian medulla

connective tissue, blood vessels, lymphatic vessels, nerves; indistinct border with cortex

Ovarian follicles

contain oocytes in various stages of development and the surrounding cells (follicular and granulosa cells)

Follicular cells

single layer of surrounding cells; early development

Granulosa cells

several layers of surrounding cells; late development

Graafian follicle

mature follicle ready to rupture and expel secondary oocyte

Corpus luteum

develops after ovulation; empty follicle produces progesterone, estrogens, inhibin, relaxin; eventually degenerates into corpus albicans

Oogenesis

begins before birth with meiosis; primordial germ cells migrate from yolk sac to ovaries and differentiate into oogonia → oogonia (2n stem cells) divide by mitosis to produce germ cells → germ cells become primary oocytes which enter prophase (meiosis I) until puberty

Primordial follicles

primary oocyte + surrounding single layer of flat follicular cells

Corona radiata

innermost layer of granulosa cells of secondary follicle surrounding secondary oocyte

Phase 3: Ovulation

rupture of graafian follicle and release of secondary oocyte; cells and corona radiata are expelled in pelvic cavity into uterine tube; day 14 (variable timing); caused by high levels of estrogen at end of preovulatory which exert positive feedback on FSH and LH production

Uterine tubes

extend from uterus to ovaries; site of fertilization; pathway for sperm to reach ovum and secondary oocyte and fertilized ova to travel to uterus; 3 layers: mucosa, muscularis, serosa

Uterine tube: mucosa

simple ciliated columnar epithelium

Uterine tube: muscularis

has inner circular and outer longitudinal smooth muscle; peristaltic contractions and cilia of mucosa help move fertilized ovum or secondary oocyte towards the uterus

Infundibulum

end of uterine tubes; close to ovary but open to pelvic cavity; fimbriae project from it and sweep oocyte into uterine tubes

Ampulla

widest and longest portion of uterine tubes where ferilization usually takes place

Isthmus

part of the uterine tubes that joins the uterus

Peg cells

non-ciliated mucosa cells in uterine tube; secrete a fluid providing nourishment for ovum

Uterus

part of pathway for sperm deposited in the vagina to reach the uterine tube; where fertilized ovum implants; top is the fundus, central portion is body, inferior extension into vagina is cervix, isthmus is between body and cervix

Uterine cavity

interior of the body of the uterus

Cervical canal

interior of the cervix

Internal os

opening of the canal into the uterus

External os

opening of the canal into the vagina

Ligaments of the uterus

extensions of the parietal peritoneum or fibromuscular cords; maintain position of uterus but allow some movement; broad ligaments attach uterus to sides of pelvic cavity; uterosacral ligaments attach uterus to sacrum; cardinal and round ligaments further anchor

Uterine layers: perimetrium (serosa)

outermost layer; laterally, becomes broad ligament

Uterine layers: myometrium

thick middle layer; 3 layers of smooth muscle; circular while inner and outer layers are longitudinal or oblique

Uterine layers: endometrium

inner layer; stratum functionalis layer is shed monthly during menstruation; permanent stratum basalis layer gives rise to new stratum functionalis after each menstruation

Uterine arteries

branches of the internal iliac artery that supply blood to the uterus; give rise to arcuate arteries that feed the myometrium and branch into radial arteries that go deep into the myometrium

Straight arterioles

supply the stratum basalis with materials to regenerate the stratum functionalis

Spiral arterioles

supply the stratum functionalis and change markedly during the menstrual cycle

Uterine and iliac veins

where blood exits uterus

Cervical mucus

secretory cells of cervix; chemically more hospitable to sperm during ovulation i.e. less viscous, more alkaline; nourish sperm; can form a cervical plug; may aid capacitation

Capacitation

series of functional changes a sperm undergoes in the female reproductive tract before they are able to fertilize a secondary oocyte; increased tail movement and ability for fusion with oocyte

Vagina

fibromuscular canal lined with mucous that extends from the body’s exterior to the cervix; mucosa continuous with uterus’s; epithelium and areolar connective tissue lie in a series of transverse folds called rugae

Vagina: mucosa

stores glycogen which breaks down to produce acids and create antimicrobial environment

Vagina: muscularis

composed of an inner circular layer and outer longitudinal layer of smooth muscle; allows stretching during intercourse and childbirth

Hymen

thin fold of vascularized mucous membrane that partially closes the inferior end of the vagina

Vulva (pudendum)

female external genitalia; mons pubis, labia minora, labia majora, clitoris, vestibule (hymen, vaginal orifice, external urethral orifice, openings of ducts of several glands)

Paraurethral (Skene’s) glands

secrete mucous and are embedded in the wall of the urethra

Greater vestibular (Bartholins’s) glands

produce mucous during sexual arousal to provide lubrication

Bulb of the vestibule

2 masses of erectile tissue that engorges during sexual arousal to narrow the vaginal orifice applying pressure to the penis during intercourse

Female reproductive cycle

24-36 days; ovarian and uterine cycles as well as hormonal changes that regulate them; non-pregnant females experience changes in the ovaries and uterus lasting approx. one month; involves oogenesis and preparation by the uterus to receive a fertilized ovum

Phase 1: Menstrual

first 5 days; uterine lining is shed; hormone levels decline except for FSH which causes secondary follicle to develop; happens as a result of decreased estrogen and progesterone (no corpus luteum)

Phase 2: Preovulatory

day 6-13; endometrium repairs; secondary follicles begin to produce estrogen and inhibin which decreases FSH → dominant follicle outgrows others → graafian follicle increases production of estrogen

Phase 4: Postovulatory

time between ovulation and onset of next menses; constant: 14 days; low levels of progesterone and estrogens cause secretion of GnRH, FSH, and LH

Progesterone

maintain endometrium temporarily (while corpus luteum is around); if fertilization takes place, endometrium begin to produce and levels stay high; stimulates endometrial glands to secrete glycogen and lipids which serve as an initial nutrient source for implanted fertilized egg; high levels inhibit release of GnRH, FSH, and LH

Estrogens

promote development/maintenance of reproductive structures and secondary sex characteristics; increase protein anabolism; lower blood cholesterol; stimulate proliferation of stratum basalis to form stratum functionalis after menstruation; moderate levels inhibit release of GnRH, FSH, and LH; high levels trigger positive feedback

Relaxin

inhibits contractions of uterine smooth muscle; during labour, increases flexibility of pubic symphysis and dilates uterine cervix

Mammary glands

modified sudoriferous glands that produce milk; in breasts; contain 15-30 lobes with lobules containing milk secreting glands (alveoli); breast has a nipple containing lactiferous ducts where milk emerges; skin around the nipple is the areola

Ovarian cycle

changes that occur during and after maturation of the oocyte

Uterine cycle

changes in the endometrium that prepare it for implantation of the developing embryo