Genetic Differentiation 1. H-Y Antigen- Histocompatability Y antigen 1. Male specific antigen present on the surfaces of cells XY = H-Y antigen XX = Not present 2. NOT the sex determining gene in males. 2. Sry Gene - Sex determining region of Y chromosome a. Gene for sexual development on the Y chromosome b. Responsible for TDF- Testis determining factor production c. Transcription factor which activates other “male” genes d. Stimulates male development

XY chromosomal pair  TDF production Testes Formation A) Anti Mullerian Hormone (Sertoli cells) Blocks development of the Mullerain duct B) Androgens from testis promote Wolffian Duct development Hormones: testosterone and 5a dihydrotestosterone Testosterone - stimulates development of Wolffian duct 5a Dihydrotestosterone - stimulates external development of genitalia (scrotum, glands, penis)

Figure 4-5

Descent of the Testis Cont. Phases of testicular descent 1) growth of body away from testes. 2) growth of distal gubernaculum. Descendin, produced by fetal testes may regulated growth of the gubernaculum. 3) regression of gubernaculum.

Brain Sexual Differentiation Masculinization of the Brain in the male: testosterone from the fetal testis reaches the brain testosterone is converted to estradiol by aromatase enzyme in the hypothalamus Regression of Hypothalamic GnRH surge center by estradiol Defeminization of the hypothalamus

Testosterone (T) Brain Hypotalamus T Estradiol aromatase enz. Regression of GnRH Surge center Fetal testis Surge center is responsible for the follicular ovulation

The Key to Initiation of Puberty GnRH secretion in high frequency and high amplitude The Key to Initiation of Puberty Enough LH secretion to initiate follicular growth and/or spermatogenesis

High LH pulses and amplitudes and thus LH surge do not occur Unless Hypothalamic sensitivity to gonadal estradiol increases Hypothalamus Sensitivity to E2 changes with age

Factors Impacting the Development of Hypothalamic GnRH neurons 1) Genetic and Breeds 2) Body Size and Composition Degree of fatness and body weight Metabolic signals 3) Environmental factors Season Photoperiod Presence of the opposite sex

Hormone Receptor Classification 1) Plasma membrane receptor 2) Nuclear Receptors

Nuclear Receptors                                         

Hormone Receptor Classification Cont. Plasma membrane receptor Nuclear Receptors Protein hormones Steroid hormones Protein hormones Receptors Intracellular receptors

Stages of the Estrous Cycle Subdivision of the Follicular and Luteal Phases Proestrus Estrus Metestrus Diestrus Follicular Phase Luteal Phase

Follicular phase Luteal Phase

CL Follicle

Four Major Events Gonadotropin (LH & FSH) release from the anterior pituitary Follicular growth and maturation for ovulation Sexual receptivity Ovulation

What does LH Surge Do?? 1) Weakening of the follicular wall and ovulation 2) Reconstruction and remodeling of the theca cells and granulosa cells Preparation for progesterone synthesis 3) Oocyte (egg) maturation and completion of Oogenesis (egg division)

Mitotic Step 1-3 Meiotic LH Surge