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What makes the primitive gonad?

-Intermediate mesoderm of urogenital ridge and primordial cells


What are primordial germ cells?

-Specialised population of cells derived from the yolk sac which migrate along the dorsal mesentery and populate the mesodermal stroma of the gonads and are the 'seed of the next generation'


How does the presence of SRY genes influence development?

-Drives development of the male causing differentiation of the gonads into testis, the duct system and the external genitalia


Describe what happens to mesonephric (wolffian) duct system in a male

-Mesonephric duct makes contact with urogenital sinus and ureteric buds begin to sprout causing development of metanephros
-The urogenital sinus expands as smooth muscle appears in the walls creating independant openings for UBs and MDs as it absorbs the structures
-Presence of androgens causes development of prostate, spongy urethra and vas deferens


Describe what happens to mesonephric (wolffian) duct system in a female

-Mesonephric duct makes contact with urogenital sinus and ureteric buds begin to sprout causing development of metanephros
-The urogenital sinus expands as smooth muscle appears in the walls creating independant openings for UBs
-Lack of adrogens leads to regression of MDs and the development of the female internal and external genitalia


Describe what happens to the paramesonephric (mullarian) ducts in females
Why is this prevented in males?

-PMDs appear as invaginations of urogenital ridge
-As they develop and elongate pulling the peritoneum with it, cranially they open into abdo cavity and caudally they fuse at the midline
-This develops to form the upper 1/3 vagina, cervix, uterus and uterine tubes by regression of the septum which was created by fusion
-Mullarian inhibiting hormone released from the testis prevents development of PDS in males


How does the external genitalia of a fetus begin? Describe how these develop into both the male and femaly external genitalia

-Genital swellings, genital tubercles and genital folds
-Males = GT elongates and GF fuse on the ventral surface. This forms spongy urethra and is influenced by DHT
-Females = lack of DHT causes GT to remain and open into a vestibule instead of elongating


Describe the testicular descent

-Begin on the posterior abdominal wall at urogenital ridge (retroperitoneal)
- Evagination of processes vaginalis derived from parietal peritoneum creates a pathway for the testis to pass through the inguinal canal and into the scrotum


Describe ovarian descent

-Start on posterior abdominal wall at urogenital ridge and are tethered to labioscrotal folds via gubernaculum. Drawn down but do not pass through inguinal canal as they are obstructed by the uterus and uterine tubes


What 3 factors during meiosis ensure genetic variation?

-Crossing over
-Random segregation
-Independent assortment


Briefly describe spermatogenesis How long does it take?

-Germ cells line the seminiferous tubules of the testis and become more differentiated towards the lumen. They are finally released as spermatids and carried to the epididymis by sertoli cell secretions and peristalsis where they become motile ad are now spermatozoa
1)Spermatogonium(2n) undergoes mitosis -> Ad (2n replenishes stock) and ap spermatogonium/1 spermocyte(2n)
2)1spermocyte undergoes meiosis I and forms 2x 2spermatocyte (1n) 3) both 2 spermocytes undergo meiosis II and form 4xspermatid
4) spermatids released and transported to epididymis becoming spermatozoa
-74 days


What is the spermatogenic wave and cycle?

-Spermatogenic wave refers to how spermatogenesis generations spiral around each other within a seminiferous tubule as different germ cells differentiate at different times
-The spermatogenic cycle refers to the time it takes for the same stage of differentiation to appear at the same point in the wave. approxmately 16 days


What are the main constituents of sperm and where do they come from?

-Mostly seminal vesicle secretions (70%) containing a'a, citrate, PGs and fructose
-Prostate secretions (25%) containg proteolytic enzymes
-Sperm - 200-500mill
-Bulbourethral secretions to neutralise and lubricate distal urethra


What is sperm capacitation?

-The final maturation step which occurs in the female genital tract
-Glycoproteins are removed from sperm head which activates signalling pathways and allows the sperm to bind to the zona pellucida of the oocyte to initate the acrosome reaction


Describe oogenesis before birth

-Primordial germ cells in gonads differentiate into oogonia and proliferate by mitosis
-Selected oogonia enter meiosis I whilst others continue in mitosis
-Those which enter meiosis I are primary oocytes and arrest in prophase I and become individually surrounded by follicular cells forming a primordial follicle
-By mid-gestation max number of oogonia are reached and selection occurs. Majority of oogonia undergo atresia
-All surviving oogonia enter meiosis I and halt in prophase I and become primordial follicles


Describe oogenesis when puberty begins, includint the different stages of maturation

-Degeneration of primordial follicles has been occurring since birth
-At puberty approx 15-20 primordial follicles begin to mature passing through preantral, antral and preovulatory stages of maturation. Out of this 20 only 1 will make it to ovulation due to ongoing atresia
-Preantral = primordial follicle grows and granulosa cells form and begin secreting zona pellucida
-Antral = fluid filled spaces appear between granulosa cells and eventually coalesce to form an antrum. Theca interna/externa develop and this is now secondary follice
-Preovulatory = Under influence of FSH and LH meiosis I is completed to produce 2 haploid cells of unequal size. Meiosis II begins but arrests before ovulation and is only completed upon fertilisation. The secondary follicle is now called the graafian follicle.


What induces ovulation and how?

-LH surge causes an increase in collagenase activity inside the ovary-> matrix breakdown in graafian follicle and extrusion of oocyte by PG-induced muscular contraction


What is the corpus luteum? What is its function? What happens to it?

-The granulosa and theca interna of the graafian follicle become vascularised under the influence of LH and begin to secrete progesterone and oestrogen
-The hormones produced from CL stimulate the uterine mucosa to enter the secretory stage and prepare for implantation
-If no fertilisation occurs within 14 days the CL undergoes apoptosis and regresses (corpus albicans) and decreased progesterone levels induce menses, if fertilisation occurs hCG maintains the CL until placenta developed (corpus luteum gravidatis)


What 6 hormones does the anterior pituitary secrete?



How does the ant pituitary communicate with hypothalamas?

-Superior hypophyseal artery


Describe how the hypothalamic releasing hormones are released in to the superior hypophyseal artery? How do they exert their effect at the pituitary?

-There is a basal secretion which is pulsatile in nature and is tied to the biological clock and external stimuli such as light and dark
-Also under negative feedback control from circulating hormones
-Bind to specific cell surface receptors and induce a second messenger which leads to the production of the corresponding hormone


Which hormone controls the secretion of FSH and LH? In what rhythm is it released?

-Gonadotrophin releasing hormone
-Pulsatile every hour


How do LH and FSH exert their effects on a molecular level at the gonad?

-Bind to GPCRs at gonads which are coupled to Gas -> increased in AC activity -> increased cAMP -> Increased PKA -> leads to the production of the corresponding sex steroids


Under which hormonal control is the LH surge? Explain how this works?

-High titres of oestrogen alone
-High titres of oestrogen decrease the threshold level of GnRH needed at the anterior pituitary in order to secrete LH.


How do moderate titres of oestrogen with progesterone modify the GnRH pulses?

-Oestrogen reduces the amplitude of pulses and progesterone reduces frequency


Which cells specifically do FSH and LH target in both the male and female? What do each of the cells produce?

-Male = FSH targets sertoli cells causing ABG and inhibin secretion, LH targets leydig cells causing testosterone secretion
-Females = FSH targets granulosa cells causing inhibin secretion and aromatase production. LH targets theca cells causing androgen production


What is the function of androgen binding globulin?

-binds to testosterone to keep it within the seminiferous tubule


What is the function of inhibin?

-Selectively inhibits FSH production


What will happen to spermatogenesis if testosterone levels increase? how is this prevented?

-Increase rate of spermatogenesis but also increase production of inhibin which will bring the rate back to normal


What is the dominant hormone in the luteal phase? When does production of this hormone begin and why? What phase does this mark the beginning of?

-Begins just after ovulation, granulosa cells develop LH receptors and the remnants of the graafian follice undergoes leutinisation to produce corpus luteum.
-Luteal phase