BSCI342-test3notes

BSCI342-test3notes - Gastrulation is the beginning of...

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Gastrulation is the beginning of Organogenesis 3 Germ Layers 1. Ectoderm – external germ layer differentiates into nervous system and epidermis 2. Mesoderm – middle germ layer differentiates into epithelial lining of body’s tracts (digestive tracts, reproductive tract, respiratory tract, urinary tract) 3. Endoderm – internal germ layer differentiates into all the internal organs not derived from ectoderm and endoderm skeletal system, muscular system, connective tissue (derived from mesoderm) These 3 layers differentiate into the tissues and organs of the body, which is called organogenesis Sexual Differentiation - Genital Ridge Primordia forms in a 4 week old differentiated embryo, located below thoracic cavity - Male gametes are heterogametic (XY, 2 chromosomes), Female are homogametic (XX, 1 chromosome type) SRY Gene - is located on Y chromosome and is required to express “maleness” - directs synthesis of proteins that stimulate genital ridge primordia to develop into tests XX Males - present phenotypically as males with testes - 1 of the 2 X chromosomes had SRY gene translocated onto it XXmale = XXsry specified formation of testes from genital ridge primordial XY Females - presented phenotypically as females and lack testes - Y chromosome has mutation on SRY gene ( making it non-functional), or it was deleted Lack of SRY gene genital ridge primordial develops into ovaries Experimental Evidence SRY Specifies Testes Formation XX mice zygote injected with SRY gene on Y chromosome Result: - XX zygote that incorporated gene into X chromosomes developed into males - XX zygote that failed to incorporate SRY gene into X chromosome developed into female
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- XX female develop ovaries from absence of SRY gene around 7 th week of embryonic life - testes in XY male differentiate under influence of SRY by 6 th week of embryonic life after differentiation of testes, SRY gene becomes dormant and maleness is taken over by testes which produce 2 hormones 1. Androgens - testosterone produced by interstitial cells (Leydig) 2. Mullerian Inhibiting Hormone (MIH) - produced by sustentacular (sertoli) cells * these 2 hormones bind to the receptors located on 2 types of ducts 1. Wolffian (mesonephric) ducts - androgen receptors are located here - androgens bind to Wolffian ducts to stimulate them to differentiate into the internal male reproductive system 2. Mullerian (paramesonephric) ducts - MIH produced in sustentacular cells bind to MIH receptors to stimulate regression and degeneration Ovaries do not produce hormones in XX females (androgens and MIH are NOT present) - Wolffien ducts regress/ degenerate due to absence of androgen - Mullerian ducts persist and differentiate into female reproductive duct system - fallopian tubes, uterus, vagina XXsry Male - Wolffien ducts differentiate in male structure - Mullerian ducts regress/degenerate XY Female - ovaries in Mullerian ducts persist External Genitalia Differentiation - the 3 structures on the external surface of the perineum differentiate into the external
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This note was uploaded on 04/07/2008 for the course BSCI 412 taught by Professor Lee during the Spring '08 term at Maryland.

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BSCI342-test3notes - Gastrulation is the beginning of...

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