Line 1: |
Line 1: |
− | <big><center>[[Reproductive System|'''BACK TO REPRODUCTIVE SYSTEM''']]</center></big>
| |
− |
| |
− | <big><center>[[Reproductive_System#Fertilisation.2C_Implantation_and_Early_Embryonic_Development|'''BACK TO FERTILISATION , IMPLANTATION and EARLY EMBRYONIC DEVELOPMENT''']]</center></big>
| |
− |
| |
− |
| |
| | | |
| + | [[Image:Overview of Sexual Differentiation.jpg|thumb|right|150px|Overview of Sexual Differentiation,Copyright RVC 2008]] |
| | | |
| = Genetic Sex = | | = Genetic Sex = |
| * Established at the time of '''fertilisation'''. | | * Established at the time of '''fertilisation'''. |
− | * The foetus receives its genetic endowment in two equal portions from the male gamete ('''Spermatozoon''') and female gamete ('''Oocyte'''). | + | * The foetus receives its genetic endowment in two equal portions from the male gamete ('''spermatozoon''') and female gamete ('''oocyte'''). |
| * The X sex chromosome is larger than the Y sex chromosome. | | * The X sex chromosome is larger than the Y sex chromosome. |
| * '''Females''' have '''XX''' chromosomes. All oocytes contain one X chromosome, they are the '''homogametic''' sex. | | * '''Females''' have '''XX''' chromosomes. All oocytes contain one X chromosome, they are the '''homogametic''' sex. |
Line 15: |
Line 11: |
| | | |
| * The '''Y''' chromosome is required to '''initiate male development'''. | | * The '''Y''' chromosome is required to '''initiate male development'''. |
− | * In absence of the Y chromosome, female gonads (Ovaries) will develop. | + | * In absence of the Y chromosome, female gonads (ovaries) will develop. |
| * The prime male determining gene is '''SRY''' (sex determining region of the Y chromosome). | | * The prime male determining gene is '''SRY''' (sex determining region of the Y chromosome). |
| | | |
| * SRY is a very small piece of DNA that acts as a molecular switch to regulate structural genes and autosomal chromosomes, determining if and when they are to be activated. | | * SRY is a very small piece of DNA that acts as a molecular switch to regulate structural genes and autosomal chromosomes, determining if and when they are to be activated. |
| * SRY encodes the protein '''Testes Determining Factor''' (TDF) | | * SRY encodes the protein '''Testes Determining Factor''' (TDF) |
− | * The presence of SRY alone is sufficient to ensure development of male gonads (Testes). | + | * The presence of SRY alone is sufficient to ensure development of male gonads (testes). |
− | * Female is the default sex, in absence of SRY female gonads (Ovaries) will develop. | + | * Female is the default sex, in absence of SRY female gonads (ovaries) will develop. |
| | | |
| | | |
| * Subsequent gonadal development is dependent on a normal population of '''germ cells'''. | | * Subsequent gonadal development is dependent on a normal population of '''germ cells'''. |
− | * Normal Oocyte growth requires the activity of both X chromosomes. | + | * Normal oocyte growth requires the activity of both X chromosomes. |
− | * Normal Spermatogenesis requires the activity of no more than one X chromosome. | + | * Normal spermatogenesis requires the activity of no more than one X chromosome. |
| | | |
| | | |
Line 43: |
Line 39: |
| | | |
| * Sex cord cells proliferate to form the testes cord. During this period '''SRY''' is expressed for the first time within '''Sertoli cells''' (SRY is NOT expressed in primordial germ cells). | | * Sex cord cells proliferate to form the testes cord. During this period '''SRY''' is expressed for the first time within '''Sertoli cells''' (SRY is NOT expressed in primordial germ cells). |
− | * Sex cords with a basement membrane become '''Semniferous Cords''' which give rise to '''Semniferous Tubules'''. | + | * Sex cords with a basement membrane become '''semniferous cords''' which give rise to '''semniferous tubules'''. |
| * '''Within the semniferous cords''' are two cell populations: | | * '''Within the semniferous cords''' are two cell populations: |
− | ** '''Primordial germ cells''' - Prospermatogonia which give rise to '''Spermatozoa''' | + | ** '''Primordial germ cells''' - Prospermatogonia which give rise to '''spermatozoa''' |
| ** '''Mesodermal cord cells''' which give rise to '''Sertoli cells''' | | ** '''Mesodermal cord cells''' which give rise to '''Sertoli cells''' |
| * '''Between cords''', the loose mesenchyme undergoes '''vascularisation''' and develops as '''stromal tissue'''. | | * '''Between cords''', the loose mesenchyme undergoes '''vascularisation''' and develops as '''stromal tissue'''. |
− | * Within the stromal tissue, cells condense into clusters to form specialized endocrine units - the interstitial '''Leydig Cells''' | + | * Within the stromal tissue, cells condense into clusters to form specialized endocrine units - the interstitial '''Leydig's cells''' |
− | | |
| | | |
| == Female == | | == Female == |
| | | |
| * At the time the male gonad is undergoing marked changes under the direction of SRY, the female gonad continues to appear indifferent and does not express SRY. | | * At the time the male gonad is undergoing marked changes under the direction of SRY, the female gonad continues to appear indifferent and does not express SRY. |
− | * Small clusters of mesenchyme surround the germ cells to initiate formation of '''Primary Follicles''', characteristic of the Ovary. | + | * Small clusters of mesenchyme surround the germ cells to initiate formation of '''primary follicles''', characteristic of the ovary. |
− | * In follicles: | + | * In follicles |
− | ** '''Mesenchymal cells''' give rise to '''Granulosa cells''' | + | ** '''Mesenchymal cells''' give rise to '''granulosa cells''' |
− | ** '''Germ cells''' give rise to '''Oocytes''' | + | ** '''Germ cells''' give rise to '''oocytes''' |
| | | |
| | | |
Line 63: |
Line 58: |
| == Foetal sex differentiation == | | == Foetal sex differentiation == |
| | | |
− | * Endocrine activity of the Ovaries is NOT essential for sex differentiation during foetal life, abnormal ovarian development will have no effect until puberty. | + | * Endocrine activity of the ovaries is NOT essential for sex differentiation during foetal life, abnormal ovarian development will have no effect until puberty. |
| * Testes secrete two essential hormones: | | * Testes secrete two essential hormones: |
− | ** '''Steroidal hormones''' (mainly C19 androgens) from '''Leydig cells''' | + | ** '''Steroidal hormones''' (mainly C19 androgens) from '''leydig's cells''' |
− | ** '''Mullarian Inhibiting Hormone''' (MIH) also known as '''Anti-Mullarian Hormone''' (AMH) from '''Sertoli Cells''' | + | ** '''Mullarian Inhibiting Hormone''' (MIH) also known as '''Anti-Mullarian Hormone''' (AMH) from '''Sertoli cells''' |
| * In absence of these testicular hormones, female differentiation occurs. | | * In absence of these testicular hormones, female differentiation occurs. |
| * Thus, sexual differentiation must be actively diverted down the male route, the female route requires no active intervention. | | * Thus, sexual differentiation must be actively diverted down the male route, the female route requires no active intervention. |
| | | |
− | ----
| |
− |
| |
− | = Internal Genetalia =
| |
− | * Male: '''Wolffian Duct''' developes from the '''Mesonephric Duct'''
| |
− | * Female: '''Mullarian Ducts''' develop from the '''Paramesonephric Duct'''
| |
− | * This is dependent on appropriate hormonal influence.
| |
− |
| |
− |
| |
− |
| |
− | == Male ==
| |
− |
| |
− |
| |
− | * '''MIH''' from '''Sertoli cells''' and '''Androgens''' from '''Leydig cells''' prevent spontaneous development of female internal genetalia.
| |
− | * '''Androgens''' actively maintain '''Wolffian Ducts''', which give rise to male internal genetalia:
| |
− | ** Epididymis
| |
− | ** Vas Deferens
| |
− | ** Vesicular Glands/ Seminal Vesicles
| |
− | * '''MIH''' causes Mullarian Ducts to regress
| |
− |
| |
− |
| |
− | == Female ==
| |
− |
| |
− | * Wolffian Ducts spontaneously regress in absence of Androgens.
| |
− | * '''Mullarian Ducts''' persist to give rise to female internal genetalia:
| |
− | ** Oviducts
| |
− | ** Uterus
| |
− | ** Cervix
| |
− | ** Cranial Vagina
| |
− | * Normal Ovarian activity is NOT essential for the development of normal female internal genetalia.
| |
− | ----
| |
− |
| |
− | = External Genetalia =
| |
− |
| |
− |
| |
− | == Male ==
| |
− |
| |
− | * Potential to develop male of female external genetalia. '''Testosterone''' is required to develop male external genetalia.
| |
− | * Androgen secretion from the Testes induces:
| |
− | ** '''Urethral folds''' to fuse to allow enclosure of the urethral tube. This, together with the cells from the '''genital swelling''', forms the '''shaft of the Penis'''.
| |
− | ** '''Genital swellings''' fuse in the midline to allow formation of the '''Scrotum'''
| |
− | ** '''Genital Tubercle''' expands to give rise to the '''Glans Penis'''
| |
− |
| |
− |
| |
− |
| |
− | == Female ==
| |
− |
| |
− | * Development is ensured by the absence of Testosterone, it is independent of Ovarian endocrine activity.
| |
− | * '''Urethral folds''' and '''Genital Swellings''' remain separate to form the '''Labia Minora and Majora'''.
| |
− | * '''Genital tubercle''' forms the '''Clitoris'''
| |
− |
| |
− |
| |
− |
| |
− | * Exposure of the female tract to Androgens will masculinise external genetalia.
| |
− | * Failure of proper endocrine communication between the gonads, internal and external genitalia can lead to '''dissociation''' of gonadal and genital sex.
| |
− |
| |
− | ----
| |
− |
| |
− | = Sexual Differentiation of the Brain =
| |
− |
| |
− |
| |
− | == Male ==
| |
− |
| |
− | * '''Testosterone''' secreted into the blood reaches the brain.
| |
− | * Converted to Dehydrotestosterone and '''Oestradiol''' by Aromatase enzymes in the Hypothalamus.
| |
− | * Oestradiol masculinises the brain
| |
− |
| |
− |
| |
− | == Female ==
| |
− |
| |
− | * '''Alpha Fetoprotein''' binds Oestradiol, preventing it from crossing the blood-brain barrier.
| |
− | * Oestradiol cannot access the Hypothalamus
| |
− | * Protects female brain from masculising effects of Oestradiol.
| |
− | ----
| |
− |
| |
− | = Associated Disorders =
| |
− |
| |
− |
| |
− | * [[Fertilisation, Implantation and Early Embryonic Development -Turner's Syndrome - Anatomy & Physiology|Turner's Syndrome]]
| |
− |
| |
− | * [[Fertilisation, Implantation and Early Embryonic Development -Kleinfelter's Syndrome - Anatomy & Physiology|Kleinfelter's Syndrome]]
| |
− |
| |
− | * [[Fertilisation, Implantation and Early Embryonic Development -Testicular Feminisation - Anatomy & Physiology|Testicular Feminisation]]
| |
− |
| |
− | * [[Fertilisation, Implantation and Early Embryonic Development -Adrenogenital Syndrome - Anatomy & Physiology|Adrenogenital Syndrome]]
| |
| | | |
− | * [[Fertilisation, Implantation and Early Embryonic Development -Intersex - Anatomy & Physiology|Intersex]]
| |
| | | |
− | * [[Fertilisation, Implantation and Early Embryonic Development -Bovine Freemartinism - Anatomy & Physiology|Bovine Freemartinism]]
| + | [[Category:Pregnancy and Parturition]] |
| + | [[Category:Bullet Points]] |