Session 1 Flashcards
Describe the development of the internal and external genitalia of the male
Internal:
Mesonephric duct (Wolffian)
Sertoli cells secrete MIH (mullerian inhibiting hormone), interstitial cells secrete testosterone
Seminiferous tubes join mesonephric duct –> rete testis
Remainder of each duct –> epididymis, vas deferens, seminal vesicles, ejaculatory ducts, prostate, bulbourethral glands
External:
Androgens cause urethral folds to close –> penis shaft
Genital swellings fuse –> scrotum
Genital tubercles expand –> glans penis
Hormonal stimulation from dihydrotestosterone
Describe the development of the internal and external genitalia of the female
Internal:
No androgen therefore mesonephric duct regresses
No MIH therefore paramesonephric duct remains
Paramesonephric duct –> fallopian tubes, uterus, cervix, upper vagina
External:
Urethral folds and genital swelling –> labia minora and majora
Genital tubercle –> clitoris
(Without hormonal stimulation)
What is the urogenital ridge?
A region of intermediate mesoderm giving rise to both embryonic kidney and gonad
Intermediate mesoderm + primordial germ cells
Describe the descent of the gonads
Testes - tethered to labioscrotal folds by gubernaculum, through inguinal canal, behind peritoneum (processes vaginalis). Scrotal ligament is the vestigial remnant of the gubernaculum.
Ovary - tethered to labioscrotal folds by gubernaculum (–> ovarian ligament and round ligament)
Ovarian ligament - ovary –> uterus
Round ligament - uterus –> labia
Round ligament occupies inguinal canal
Describe common abnormalities of genital development
Genotype-phenotype mismatch
Hormone problems (e.g. pituitary adenoma)
Hypospadias
Bicornate uterus
List the main reproductive hormones
Hypothalamus - GnRH, PRH, PIH
Posterior pituitary - oxytocin
Anterior pituitary - FSH, LH, prolactin
Gonads - testosterone, oestrogen, progesterone, inhibin, mullerian inhibiting hormone
Placenta - hCG, hPL, oestrogen, progesterone
Describe the microscopic structure of the testis, including the main compartments and cell types
Surface is covered by visceral layer of tunica vaginalis, adjacent to fascia is parietal layer.
Tough, fibrous outer layer is tunica albuginea
Sertoli cells –> seminiferous tubules, spermatozoa development
Leydig cells –> interstitial tissue, secrete testosterone
Tubules are separated from surrounding tissue by blood testis barrier
Describe the process of spermatogenesis
Germ cells colonise the medulla of sex cords
Proliferate by mitosis –> spermatogonia stem cells (produce testosterone)
At puberty –> sex cords hollow out to form seminiferous tubules
Spermatogonia maintained by mitosis (available up to 70yrs)
A1 spermatogonia arise, divide by mitosis –> type B spermatogonia –> primary spermatocytes
1 spermatocyte –> (meiosis) 4 haploid spermatids (256)
Spermatids remodel as they pass through testis –> spermatozoa
Spermatozoa mature during progress through epididymis
Production is continuous as different sections begin the process at different times
Sperm delivered to female as semen
Describe the constituents of semen
60% seminal vesicle
20% prostate
Bulbourethral secretions
Sperm
Distinguish the spermatogonia cycle and spermatogonia wave
Cycle - development of an A1 spermatogonia –> 256 spermatids. The amount of time it takes for reappearance of the same stage of the cycle within a given segment of the tubule
Wave - different parts of the tube begin the cycle at different times, in a wave, so production of sperm is constant. The distance on the tube between parts that are in the same stage is the spermatogenic wave
Describe the roles of the rete testis, epididymis, vas deferens, seminal vesicles, prostate and bulbourethral glands
Rete testis - network of canals in the mediastinum of the testis that seminiferous tubules drain into
Epididymis - a convoluted duct in which the sperms are stored and continue to mature
Vas deferens - a continuation of the epididymis, the vas deferens has relatively thick, muscular walls and a minute lumen. During copulation these muscular walls contract forcing sperm along the tube to be mixed with the other components of ejaculate
Seminal vesicles - secrete a thick, alkaline fluid that is rich in fructose and a coagulative agent. The duct of the seminal gland joins the ductus deferens to from the ejaculatory duct
Prostate - makes up 20% of the volume in semen and activates sperm
Bulbourethral glands - embedded in the external urethral sphincter, the ducts open into the proximal part of the of the spongy urethra in the bulb of the penis. Their mucus like secretions enters the urethra during sexual arousal
Describe the microscopic structure of the ovary
Almond shaped, where oocytes grow and develop, produce reproductive hormones.
Each ovary is suspended by the suspensory ligament (containing neurovascular).
Medially, the ovary is tethered to the uterus by the ovarian ligament
The tunica albuginea of the ovary is covered by a mesovarium that becomes scarred and distorted because of repeated rupture of a follicle and release of an oocyte.
The broad ligament (peritoneum) can be divided into mesovarium, mesosalpinx and mesometrium.
The ovarian ligament, round ligament of the uterus and suspensory ligament of the ovary are located within the broad ligament.
Describe the process of oogenesis
Germ cells colonise the gonadal cortex –> oogonia
Oogonia proliferate rapidly by mitosis (7 million mid gestation but 2 million by gestation) –> primary oocytes
All oogonia enter meiosis before birth (prophase of 1st division) stimulated by mesonephric/follicular cells and become primordial follicles.
Meiosis stops at the diplotene/resting stage due to oocyte maturation inhibitor (OMI) secreted from follicular cells
Primary oocyte (surrounded by granulosa cells) –> primordial follicle
Describe the ovarian cycle, including the stages of development of follicles
- Pre-antral/primordial follicles:
Primary oocyte grows but meiosis does not restart. Flat follicular cells –> cuboidal granulosa cells.
Granulosa cells secrete glycoprotein to surround cell with zona pellucida.
Surrounding stroma cells form a theca folliculi (inner - vascular, endocrine, outer - fibrous)
Theca and granulosa cells secrete oestrogen - Antral/secondary follicle:
Granulosa cells continue to proliferate and a fluid appears, forming the antrum
More fluid forms, secondary/Graffian follicle expands
Continued development depends on:
FSH - binds to granulosa cells
LH - binds to thecal cells - Pre-ovulatory follicle:
37h before ovulation, oestrogen causes receptors for LH to appear on granulosa
LH surge - follicle restarts meiosis and first mitotic division is completed. Asymmetric division forms one cytoplasm and one condensed polar body.
Secondary follicle enters meiosis II and arrests 3 h prior to ovulation.
LH leads to follicle rupture, ovum is carried out by fluid and gathered into Fallopian tubes by fimbrae.
Unfertilised cells degenerate 24h after ovulation
Describe the corpus luteum
The remains of the follicle reorganise themselves into a corpus luteum, which secretes progesterone and oestrogen under the influence of LH.
The corpus luteum lives for 14 days before regressing spontaneously.
