Reproduction Flashcards
Define gonad
Protective structure in which gametes can be produced
What is the indifferent gonad derived from?
Intermediate mesoderm and primordial germ cells
Where do primordial germ cells originate and migrate?
Originate - yolk sac, migrate - retroperitoneum (along the dorsal mesentery)
Explain the embryological formation of testis
Male gametes have the Y chromosome (which has the SRY gene). Indifferent gonad therefore has medullary cord development (to form the definitive testis cordis), no cortical cords and a thick tunica albuginea
Explain the embryological development of the ovaries
Absence of a Y chromosome leads to the indifferent gonad having cortical cords with degeneration of medullary cords and no tunica albuginea
State how different cell types in the male embryo develop
Germ cells enter the definitive testis cordis (formed by medullary cords) and give rise to seminiferous tubules. Mesodermal cells give rise to Sertoli cells (which express SRY and MIS). Interstitial cells secrete testosterone.
State how different cell types in the female embryo develop
Germ cells are surrounded by mesenchymal cells which form primordial follicles. These oogonia are surrounded by a single layer of granulosa cells. No expression of the SRY gene
Describe the contents and function of internal male genitalia
Male internal genitalia consists of: duct system (epididymis, vas deferens and urethra), seminal vesicles, prostate gland and bulbo-urethral glands. Function - collect and mature sperm (continuous sperm production), production of other components of semen
Describe the contents and function of the external male genitalia
Consists of: penis, scrotum and testes. Function - delivers semen which is ejaculated during intercourse
Describe the contents and function of the internal female genitalia
Consists of: ovaries and duct system (fallopian tube, uterus, cervix and vagina). Function - provides an environment within which sperm can travel and fertilise the ova; conceptus can then implant, form a placenta and go on to develop into an embryo
Describe the contents and function of the external female genitalia
Consists of: vagina, vestibule, labia minora, labia majora and clitoris. Functions - provides a means for introducing sperm to the female reproductive tract. Also means the birth canal can be formed
Describe the development of the male external genitalia
The wolffian duct remains patent in males due to the presence of testosterone. Then goes on to produce the epididymis, vas deferens and seminal vesicles. Testis produces MIS which causes regression of the Mullerian duct
Describe the development of the female external genitalia
Wolffian duct regresses due to lack of testosterone. Mullerian ducts develop due to lack of MIS; the two Mullerian ducts fuse due to an inductive event where they touch the UGS. Eventually the septum regresses and the UGS grows (majority of vagina is formed by hindgut)
State what the three basic components of the indifferent gonad form in the male
Genital tubercule - glans penis
Genital folds - urethral folds and the shaft of the penis
Genital swellings - scrotum
State what the three basic components of the indifferent gonad form in the female
Genital tubercule - clitoris
Genital folds - labia minora and urethra
Genital swellings - labia majora
Describe the descent of the testis
Descends retroperitoneally. It arises in the upper lumbar regions and is tethered to the labioscrotal folds. Between 25 and 28 weeks the testis migrates over the pubic bone, behind the processus vaginalis. Above the testis the fascial layers become closely apposed. Evagination of the processus vaginalis occurs for the passage of the scrotum. Scrotal ligament is the vestigal remnant of the gubernaculum
Describe the movement of the ovaries in the embryo
Dont pass through the inguinal canal due to growth of uterus and uterine tube. Gubernaculum attaches the ovary inferiorly to the scrotal folds and becomes the ovarian ligament and round ligament of the uterus. Only thing in the inguinal canal in females is the round ligament of the uterus
Describe some common abnormalities of genital development
XY embryo with tissue that is unresponsive to testosterone can have female genitalia
XXY embryos have testes due to the presence of the Y
XO embryos might not have secondary female characteristics
PGC tumours can develop retroperitoneally
Hypospadias
List the main reproductive hormones and where they are produced
Hypothalamus - peptide releasing factors, GnRH, PRH and PIH
Posterior pituitary gland - oxytocin
Anterior pituitary gland - gonadotrophins (e.g. FSH/LH) and prolactin
Gonads - testosterone, oestrogens and inhibin
Placenta - hCG, hPL, oestrogens and progesterones
Describe the macroscopic structure of the testis
Ovoid reproductive organs that are suspended superiorly by the spermatic cord. Inferiorly the scrotal ligament holds them in place. Tunica vaginalis testis envelopes the testis in a double layer (except the superior and posterior borders where the spermatic cord and epididymis adhere to the testis)
Briefly describe the microscopic appearance of the testis
Composed of lobules of glandular tubules which are highly convoluted and held together by loose connective tissue with interspersed groups of interstitial tissue. Each tubule consists of: basement membrane (laminated connective tissue with numerous elastic fibres), flattened cells, external layer of flattened epitheloid cells and Sertoli cells.
Describe the process of spermatogenesis
Spermatogonia divide into Ap and Ad spermatogonium. Primary spermatocytes divide by giving rise to secondary spermatocytes and then spermatids. Each primary spermatocytes forms 4 haploid spermatids
Distinguish between the spermatogenic cycle and the spermatogenic wave
Cycle - time taken for reappearance of the same stage within a given segment of the tubule
Wave - distance between the same stage along the length of the tubule
Describe spermiogenesis
When spermatids mature into motile spermatozoa. Spermiation occurs, removing any unnecessary cytoplasm and organelles. Spermatids are remodelled as they pass through the rete testis, ductuli efferentes and the epididymis
When do sperm become motile?
When they reach the epididymis
Describe the role of the rete testis
Removes fluid and concentrates the sperm. Carries sperm from the seminiferous tubules to the efferent ducts
Describe the role of the epididymis
Stores sperm (for up to two days) and delivers it to the vas deferens. Walls are lined by pseudostratified epithelia (looks like two layers when there is only one). Head - stores sperm until it’s ready to undergo maturation. Body - maturation of sperm occurs here (takes about 1 week). Tail - connects to vas deferens; upon arousal contractions cause sperm to move into the vas deferens)
Describe the role of the vas deferens
Transports mature sperm to the urethra in preparation for ejaculation
Describe the role of seminal vesicles
Produce a sugar-rich fluid (fructose) that provides substrate for the sperm for energy production. Also produce amino acids, citrate and prostaglandins. Fluid from seminal vesicle makes up most of the ejaculatory fluid
Describe the role of the prostate gland
Contributes additional fluid to the ejaculate which helps nourish the sperm. Secretes proteolytic enzymes and zinc. Urethra also runs through the prostate (potential pathological consequences)
Describe the role of the bulbourethral glands in males
Located on the sides of the urethra. Produce a clear, slippery fluid that enters directly into the urethra - fluid lubricates and neutralises the urethra
Describe sperm capacitation
Final step of sperm maturation. Occurs in the female genital tract because conditions there stimulate: removal of glycoproteins and cholesterol from the sperm membrane, activation of sperm signalling pathways and it allows sperm to bind to the zona pellucida of the oocyte and initiate the acrosome reaction
Briefly describe the histological appearance of the ovaries
Outer cortex and inner medulla. Germinal layer made of cuboidal cells that coats the ovaries. Cortex - follicles and oocytes and is made of connective tissue that is tightly packed. Stroma of this CT is composed of fibroblasts. Medulla - ovarian vasculature and is composed of loose stromal tissue
What is a follicle?
An oocyte surrounded by granulosa cells
Describe the stages of follicular development
Primordial follicle - primary oocyte enters meiosis I and surrounded by follicular cells
Preantral - follicular cells become cuboidal and stratified (granulosa) with formation of zona pellucida
Antral - formation of antrum, several follicles develop
Preovulatory - one cell, one polar body with the cell entering metaphase II
What is the corpus luteum?
Hormone secreting structure that appears after ovulation. Made when theca interna cells and granulosa cells become vascularised - develop a yellowish tint and change into lutein cells. Hormones it secretes are: oestrogen and progesterone
Describe the hormones involved process of ovulation and their effects
FSH - triggers cumulus expansion in the preovulatory stage. Also trigger an increase in prostaglandins which then cause muscular contractions of the ovarian wall
LH - triggers signal transduction cascade which causes proteolytic enzymes (collagenase) to be secreted. These degrade the follicular tissue and form the stigma through which the ovum will leave
Describe the mechanical features that stimulate ovulation
Fimbriae sweep over the surface of the ovary, uterine tube contracts rhythmically and the oocyte is carried into the tube by sweeping movements of fimbriae and cilia. Peristaltic muscular contractions of the tube then occur.
If an oocyte is fertilised then explain what happens post-ovulation
Degeneration of corpus luteum is prevented by hCG production, therefore the corpus luteum continues to grow to become the corpus luteum of pregnancy (corpus luteum graviditatis). Cells continue to secrete progesterone until the fourth month, after which the placenta takes over
Describe what occurs post-ovulation if fertilisation does not occur
The corpus luteum degenerates and becomes the corpus albicans. Progesterone production falls thus precipitating menstrual bleeding
State some differences between spermatogenesis and oogenesis
Around 200M sperm/day vs 1 ovum every 28 days, 4 spermatids no polar bodies vs one ovum with two polar bodies, starts at puberty vs starts as a foetus, continues throughout adult life vs ends at menopause, motile gametes vs non-motile gametes, all stages complete in the testes vs last stage of meiosis II only occurs in the oviduct
State the hormones involved in reproduction produced by the hypothalamus, anterior pituitary gland and gonads
Hypothalamus - GnRH
Anterior pituitary - FSH and LH
Gonads - progesterone, oestrogen, testosterone and inhibin
List which cell types in the anterior pituitary gland produce which hormones
Prolactin cells - prolactin Somatotropic cells - growth hormone Thyrotrophs - TSH Corticotrophs - ACTH Gonadotrophs - LH and FSH
Describe the control of gonadotrophin secretion by the hypothalamus in males
Negative feedback by testosterone
Describe the control of gonadotrophin secretion in females
Moderate titres of oestrogen reduce GnRH secretion whereas high titres promote GnRH secretion. Progesterone increases the inhibitory effects of moderate oestrogen and prevents positive feedback of high oestrogen. Oestrogen reduces GnRH per pulse whereas progesterone reduces the frequency of pulses
Describe the effect of gonadotrophins on testes and ovaries
Trigger Gs subunit. Target cells - ovarian granulose cells, theca interna cells, testicular Sertoli cells and Leydig cells. Stimulate synthesis of sex hormones and control gamete production
List the actions of LH and FSH in males
FSH - stimulates Sertoli cells to produce ABG and inhibin. ABG binds to testosterone and keeps it in the seminiferous tubules. Inhibin supports spermatogenesis and inhibits production of GnRH, LH and FSH
LH - stimulates Leydig cells in testicles to produce testosterone, promotes spermatogenesis and maintains the reproductive system
Describe the effects of testosterone
Determinative - non-reversible and development of secondary sexual characteristics
Regulatory - maintenance of adult reproductive system
List the actions of LH and FSH in females
LH - binds to thecal cells which secrete androgens which are converted by granulosa cells to oestrogen (under the influence of FSH)
FSH - stimulates production of inhibin which inhibits activin
What are the three phases of menstruation?
Preparation of the gamete (ovarian cycle) and endometrium (uterine cycle)
Ovulation - release of the gamete
Waiting - pause in which the endometrium is maintained until a signal is received to indicate fertilisation has occurred
