The Gonads; Sexual differentiation, Development & Hormones Flashcards
(30 cards)
Name the respective gonads and what they do.
Testis (males)
Ovaries (females)
Gonads (pair) are reproductive glands that maintain a species; producing gametes (cells that contain genetic information that is transferred) and providing sex hormones.
What is the function of the reproductive tract?
- Provides passage and supportive secretions for gametes (enabling cells to be delivered and fertilise/be fertilised)
- Consists of ducts and associated glands
What cells do the male foetal gonads comprise of?
Primordial germ cell: Spermatozoa
Mesenchymal tissue: Sertoli and Leydig cells
What cells do the female foetal gonads comprise of?
Primordial germ cell: Oocytes
Mesenchymal tissue: Granulosa and Theca cells
What are primordial germ cells responsible of?
Produces gamete and carries genetic information (spermatozoa/oocytes)
What is mesenchymal tissue and the two main different functions associated?
- Forms the matrix of the gonads surrounding the primordial germ cell
- Sertoli (male) and granulosa (female) cells nurse/foster germ cells during maturation and movement into the genital duct system, whilst also producing oestrogens and androgen binding protein (ABP)
- Leydig (male) and theca (female) cells produce androgenic hormones
Describe the genetic basis of sexual differentiation.
- Parents have 46 chromosomes (22 paired autosomes; 23rd is sex chromosome (XY - male, XX - female) (diploid)
- Meiotic cell division leads to formation of ovum or spermatozoa possessing 23 chromosomes - primordial germ cell formation (haploid)
- Fertilisation of ovum with ‘Y’ spermatozoa yields male, fertilisation with ‘X’ yields female (Y is more important determinant of ‘maleness’ but X also contributes)
- Embryro develops via mitotic cell division, with each cell containing 46 chromosomes (23 pairs) (diploid)
Describe the stages of the development of male foetal gonads and genitalia.
Weeks 3 - 7: both Wolffian and Mullerian genital duct develop either side of gonads; embryo is sexuallly indeterminate at this point
Week 7:
- Anti-Mullerian hormone (AMH; Sertoli cells) cause atrophy of Mullerian duct and initiates descent of testes
- FSH production terminates action of AMH
Week 9: Testosterone (Leydig cells) stimulates Wolffian duct to differentiate into epididymis, vas deferens, seminal vesicles and ejaculatory duct.
What is the main difference regarding the development of male foetal gonads/genitalia rather than female?
Positive hormone influence (testosterone from leydig cells) is required to produce a masculine format.
What is noteworthy regarding Weeks 3 to 7 of foetal gonad/genitalia development?
- Genetically sex has already been determined but cannot distinguish distinguish physically at this point which sex it is
- Sexual differentiation is not dependent upon fetal pituitary gonadotropins (not LH/FSH, but androgen dependent (testosterone/AMH)
Describe the stages of the development of female foetal gonads and genitalia.
Weeks 3 - 7: Both Wolffian and Mullerian genital ducts develop either side of gonads (embryo is sexually indeterminate)
Weeks 10 - 11:
- Absence of testosterone leads to regression of Wolffian duct
- Absence of AMH (anti-Mullerian hormone) leads to growth and differentiation of Mullerian Duct into fallopian tubes, uterus, cervix, and vagina
Weeks 18-20:
- Process completed; development of female genitalia does not require gonad hormones
What determines the gonadotropin pattern secretion and how does it differ between males and females?
- Determined by testosterone; constant = males, cyclical = females (pre-set neural wiring)
- Once female pattern is established, testosterone cannot influence organs
What enzyme is testosterone converted into once secreted into circulation and what is the product called?
- Intracellular 5-alpha-reductase
- Testosterone is converted to dihydrotestosterone
What components of the external male sex organ develop as a result of testosterone?
- Glans penis
- Scrotum
- Penile urethra
- Prostate glands
What may a genetic abnormality in the enzyme intracellular 5-alpha-reductase result in?
- Intracellular 5-alpha-reductase is responsible for conversion of testosterone to dihydrotestosterone
- Genetic abnormality in enzyme may mean poorly developed penis/prostate/testes
Are any hormones responsible for the development of the female external sex organs?
- No overt hormonal influence
- Lower vagina, clitoris, labia majora, labia minora
How does exposure to high levels of androgens affect external female sex organs after differentiation?
It causes an enlargement of the clitoris (due to its relation to the glans penis)
What are the hormones LH/FSH and how do they differ?
- Gonadotropins from the anterior pituitary
- Luteinizing Hormone (LH) = 28,000 dalton glycoprotein
- Follicle Stimulating Hormone = 33,000 dalton glycoprotein
(they are large glycoproteins) - Consist of identical α subunit (14,000 dalton) but differing β subunits
How do the subunits of LH/FSH work together?
- Physiological activity lies in the β subunit
- But is inactive with the α subunit
What do gonadotropins do?
- Produce steroidogenesis via plasma membrane receptors (unlike steroid hormones; intracellular receptors), bringing about changes in cAMP and activation of protein kinase C (second messenger signalling)
Where are LH receptors found and what occurs upon activation?
- Present on Leydig (male) and theca (Female) cells (of mesenchymal tissue)
- LH increases uptake of HDL and LDL
- LH activates 20, 22 desmolase enzyme (CYP11A1)
- Activates granulosa cells (other cell type in mesenchymal tissue) to produce progesterone
What is the enzyme CYP11A1 (20, 22 desmolase enzyme) responsible for and how is it activated?
- Converts cholesterol to pregnanolone, and then to androsterone
- Activated by LH
What enzyme is responsible for the conversion of testosterone to estradiol?
Aromatase enzyme (CYP17)
What does FSH activation do?
- Activates ovarian granulosa cells and leydig cell aromatase enzyme (CYP17; converting androsterone previously made from cholesterol in leydig/theca cells to testosterone to estradiol)
