reproductive systems Flashcards
what is reproduction
- biological process by which new individual organisms (offspring) are produced from their parents, two types (asexual and sexual)
what are the types of asexual reproduction and the advantages / disadvantages
- asexual: offspring originates from a single organism and inherits the parents’ genes
- gemmation: formation of small buds on the surface of progenitor which develops into a new individual
- fragmentation: new organism growing from fragments of progenitor
- parthenogenesis: offspring develops from unfertilised eggs (arthropods, amphibians)
- advantages: very quick, no gamete formation necessary, advantage for small populations, not very complex, less energy, survival in a stable environment
- disadvantages: offspring is clone of parent (little genetic diversity), environment usually not stable long term (adaptation / evolution), often struggle for existence as well as overcrowding
what is sexual reproduction and the advantages / disadvantages
- gametes: haploid chromosome set
- gonads: primary sex organs, male testes (spermatozoa), female ovaries (ova)
- sex hormones: males (androgens) and females (oestrogen and progesterone)
- fertilisation: leads to a diploid zygote (humans 2n)
- advantages: introduces genetic diversity, survival in a changing environment
- disadvantages: cost intensive (energy), only 50% of genome contribute to offspring, few offspring
describe the male reproductive tract
- penis: copulatory organ, root, shaft, glans penis (tip), foreskin (prepuce), corpus spongiosum (surrounds urethra) and corpus cavernosa (paired dorsal erectile bodies)
- erection: vascular event, sexual arousal, nerves release nitric oxide, vasodilation, BF to corpora cavernosa
- semen: milky white mixture of sperm / accessory gland secretions, 2-5 mL ejaculation
- scrotum: sac of skin and superficial fascia, hangs outside abdominopelvic cavity, contains testes, midline septum divides scrotum in two
what are the testes
- testes: within the scrotum, surrounded by two tunics
- tunica vaginalis (outer layer derived from peritoneum)
- tunica albuginea (inner layer forms fibrous capsule)
- septa: divides the testis into ~250 lobules
- seminiferous tubules: each lobule contains 1-4 tubules, these produce sperm (gametes)
- spermatogonium: sperm ripens from this into mature sperm
- interstitial tissue: produce hormones (androgens)
- cryptorchidism: undescended testes, treated at 6 months with special operation, if not treated risk of infertility, testicular torsion, cancers
describe temperature control of the testes
- kept constantly 3ºC lower than core body temperature
- necessary for sperm production, two sets of muscles contract scrotum towards abdominal cavity when cold
- dartos muscle: smooth, wrinkles scrotal skin, pulls close to body
- cremaster muscles: bands of skeletal that elevate testes
- pampiniform plexus: testicular artery from abdomen and testicular vein entering abdomen from scrotum lie in torturous plexus
- countercurrent heat exchange: heat exchange in the plexus decreases temp of blood entering testes, blood leaving testes is warmed by contraction
- spermatogenesis: greatly affected by temperature of testicle
describe the male duct system
- seminiferous tubules: produce, maintain and store sperm
- straight tubules: form due to converging of seminiferous tubules, convey sperm into rete testis
- rete testis: tubular network on inner seminiferous tubules
- efferent ductules: sperm leave the testis to enter the head of epididymis
- epididymis: single highly coiled tube, about 6m long, maturation of sperm, passage of sperm 2-6 days, microvilli absorb testicular fluid and pass nutrients to stored sperm (head, body, tail)
- vas / ductus deferens: sperm transport, smooth muscle in walls propels sperm from epididymis to urethra, sperm storage, palpable, about 45cm long
- ejaculatory duct: enters prostate, and there it empties into the urethra
- urethra: terminal portion of the male duct system, conveys both urine and semen
what are the accessory glands of male reproductive system
prostate gland:
- encircles urethra inferior to bladder, size of peach pit
- single gland, contributes ~30% of seminal fluid
- contains enzymes, secretes milky, slightly acid fluid
seminal vesicles:
- paired glands, on posterior bladder surface, contribute ~65% of seminal fluid, alkaline, prostaglandins, clotting proteins and fructose
- smooth muscle that contracts during ejaculation, duct of seminal gland joins ductus deferens to form ejaculatory duct
bulbourethral gland:
- cowper’s gland, pea-sized glands inferior to prostate, paired glands, contribute <5% of seminal fluid, lubricate glans penis (tip)
- alkalinity neutralises acidic urine in urethra, pre-ejaculatory fluid, produce thick, clear mucus during sexual arousal
describe female internal genitalia
- located in pelvic cavity; include ovaries and duct system (uterine tubes, uterus, cervix and vagina)
describe female external genitalia
- mons pubis: fatty area overlying pubic symphysis
- labia majora: sebaceous glands, protection
- labia minora: erectile connective tissue
- clitoris: highly sensitive to touch / temp, nerves, BV, erectile tissue
- perineum: muscle between vaginal opening and anal canal, abundance of nerve endings, sensitive to touch
- vaginal opening: vestibule, inferior to urethral opening, may be covered by hymen
- urethral opening: vestibule, urination
- bartholin’s glands: major vestibular / paravaginal glands, alkalinity promotes sperm survival, lubrication during coitus
- skene’s glands: minor vestibular / paraurethral glands, lubrication during coitus
describe the female duct system
- uterine tube system does not have direct contact with ovaries
- includes two uterine tubes (fallopian tubes), one uterus and one vagina
what are the uterine tubes
- F: receive ovulated oocyte, site of fertilisation, early nourishment of embryo, transports oocyte to the uterus (smooth muscle peristalsis and ciliary action)
- peg cells: non-ciliated cells, nourish oocyte and sperm
- S: isthmus, ampulla and infundibulum with fimbriae, ~10cm long and extends from area of ovary to superolateral region of uterus
- externally: covered by peritoneum and supported by a short mesentery
what is the uterus / uterine blood supply
- structure: body, fundus, isthmus, uterine wall ~1.5cm thick (endometrium, myometrium, perimetrium), cervix (inferior), cervical canal
blood supply: - abdominal aorta
- uterine arteries: ascend sides of uterus and send branches in the myometrium
- radial branches: descend into the endometrium and give rise to straight arteries (to stratum basalis) and spiral arteries (to stratum functionalis)
what is the vagina
- S: elastic muscular tube, extends from cervix to exterior of the body, vaginal discharge (mucous secretions from the cervix and vagina)
- F: receives the penis during coitus, acidic environment (protection)
what are the ovaries
- F: produce gametes (ova), secrete female steroids, estradiol / oestrogen and progesterone
- S: no connection between fimbriae and ovaries
- ovary held in place by ovarian, suspensory and mesovarium ligaments
- flattened oval surrounded by fibrous tunica albuginea, covered by germinal cuboidal epithelial outer layer
- blood supply: ovarian arteries and ovarian branch of the uterine arteries
- inner medulla: large BV and nerves
- outer cortex: ovarian follicle (oocyte surrounded by follicle and granulosa cells)
what is oogenesis
- aim: production of ova (oocytes) with haploid (single) chromosome set
- generation: begins during foetal development, no new ova formed after birth, ovary contains at birth ~2 million primordial follicles each containing and immature oocyte (not all develop)
- female meiosis: begins at foetal stages and completes at time for fertilisation
- process:
1. oogonia (diploid) undergo mitosis and become develop to primary oocytes (diploid) which rest in prophase 1
2. at puberty FSH stimulates one primary oocyte (diploid) a month to complete meiosis 1
3. meitotic division to produce secondary oocyte (haploid) and polar body
4. secondary oocyte (haploid) develops to metaphase II, rests till after ovulation
5. if fertilised completion of meiosis II, if not fertilised the secondary oocyte dies - summary: primordial germ cells - oogonium (2n) - primary oocyte (2n) - secondary oocyte (n) + polar body - ovulation - fertilised (zygote) / not fertilised (dies) - ovum (n) + second polar body
what is the female HPG axis
- female HPG axis: oestrogen and progesterone levels feedback to hypothalamus and anterior pituitary
- follicular phase: vascular growth before ovulation, FSH + granulosa cells (androgens + aromatase to oestrogen) , LH + theca cells (secrete androgens), oestrogen (-ve to hyp and AP), inhibin (-ve to AP)
- ovulation: rising levels of LH because ovary wall is about to rupture and secondary oocyte
- luteal phase: period of corpus luteum activity
what is spermatogenesis
- diploid chromosome set reduced to achieve haploid chromosome set
- formation of haploid spermatids from diploid spermatogonia during meiosis
- stem cells enter into spermatogenesis approximately every 16 days 3
- process
1. spermatogonium (diploid) undergo mitosis to produce primary spermatocyte (diploid) during prophase of meiosis 1
2. first meiotic division to produce two secondary spermatocytes (haploid)
3. second meiotic division to produce four spermatids (haploid)
4. undergo spermiogenesis and develop into sperm cells (haploid)
5. once mobile, sperm travel from seminiferous tubules to rete testis
6. from rete testis to efferent ductules to epididymis (coiled)
7. from the epididymis to vas deferens (uncoiled)
what is spermiogenesis
- remodelling and maturation of spermatids into mature spermatozoa (sperm), in epididymis, takes ~74 days
- haploid spermatids change their shape and content to become sperm
describe hormone effects on the testes
- seminiferous tubules: germ cells (form sperm) and sertoli cells (support, protection, maturation)
- interstitial space: leydig cells (secrete testosterone), peritubular myoid cells (peristaltic movement) and capillary cells of BV
- pathway 1: LH - leydig cells - testosterone synthesis - bind androgen receptors - spermatogenesis
- pathway 2: FSH - sertoli cells - secretion of inhibin and ABP (binds to testosterone) - spermatogenesis
- testosterone: development of male genitalia during foetal development, maintenance of spermatogenesis, accessory glands and ducts, development of male secondary sexual characteristics, anabolic effects, growth and fusion of epiphysis of long bones
describe the difference between meiosis 1 and 2
- meiosis 1: reduction division, separation of homologous chromosomes (diploid to haploid)
- meiosis 2: equational division, separation of sister chromatids (haploid to haploid), producing for spermatids (haploid n)
what is the ovarian cycle
- F: maturation / growth of follicle / oocyte and initiation of meiosis for dominant follicle
- secretion: follicle (oestrogen) and corpus luteum (progesterone, some oestrogen, inhibin which inhibits release of FSH and LH)
- follicular phase: days 1-14, FSH initiates antral follicle growth, varies in length
- ovulation: days 12-14, oestrogen levels peak, LH and FSH surge from AP which stimulates secondary oocyte formation and ovulation
- luteal phase: days 14-28, corpus luteum becomes gland and secretes hormones
- folliculogenesis: maturation of ovarian follicles, each month one dominant follicle (pre-ovulatory follicle / graafian follicle) ruptures at LH surge (due to LH receptors)
- causing release of oocyte, takes longer than a month, several develop at the same time
- atresia: follicles which do not proceed to ovulation degenerate and are re-absorbed
describe the summary of steps in the ovarian cycle
- primordial follicle (single layer of granulosa surrounding primary oocyte)
- late primary follicle (antral follicle), layers of granulosa cells and outer layer of thecae cells, fluid forms (antrum)
- secondary follicle (one will become dominant follicle)
- graafian follicle (ruptures and releases oocyte during ovulation)
what is the menstrual cycle
- F: cyclical growth, loss and repair of endometrial lining in uterus, on average 28 days
- menses: menstruation, cyclic changes in endometrium occur in response to ovarian hormones in blood (oestrogen and progesterone)
- absence: before puberty, during pregnancy, during lactation and permanently stops at menopause
- menarche: first ovarian controlled uterine bleed
- menopause: reproductive capacity stops