Biology of Reproduction Summers |
Endocrinology Homeostasis/Feedback Adult Female Steroid Production Ovulation |
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Adult Male Gonadal Axis Regulation Sexual Differentiation Sexual Behavior Puberty |
Reproductive Cycling Estrous Cycles Menstrual Cycle Menopause Fertilization |
Fertilization Systems Gamete Interaction Pregnancy Labor and Parturition Lactation |
Sexual Response & Behavior Pheromones STDs text: Human Reproductive Biology4th Edition- RE Jones & KH Lopez,: pp 159 - 172 Acronyms/Abbreviations end |
XX. Events leading to Fertilization A. Ejaculation 1. Expulsion of Semen = Seminal Fluid a. Sperm + Seminal Plasma b. Ejaculate is made: i. 2/3 from seminal vesicles ii. 1/3 prostate iii. a few drops from the bulbourethral gland 2. three stages a. before orgasm a clear drop or 2 of semen from the bulbourethral gland i. no sensation ii. may contain sperm iii. early withdrawal may be ineffective as contraceptive method b. Orgasm and greatest volume of sperm and semen i. mainly from prostate and seminal vesicle c. clear fluid i. mainly from seminal vesicles 3. Average Volume 2.5 - 3.5 ml a. range 2-6 ml 4. Fertility a. must contain at least 20 million sperm / ml i. 40% must vigorously swim ii. 60% must have normal shape and size b. pH 7.35-7.5 c. sperm must rely on nutrients made by the epididymis and seminal vesicles B. Structure of Spermatozoa 1. Head a. DNA b. Nuclear Membrane i. sub-acrosomal space c. Inner Acrosomal Membrane i. acrosomal space d. Outer Acrosomal Membrane e. Sperm Plasma Membrane i. covers entire cell 11/2. Acrosome = Sharp body (Greek) a. plasma membrane b. outer acrosomal membrane c. inner acrosomal membrane 2. Neck a. centriole 3. Midpiece a. mitochondria i. ATP for energy 4. Tail C. Journey of Spermatozoa 1. Total distance ~15 mm (6 in) a. cervical os to ampullary-isthmic junction 2. Semen coagulates in vagina - then - liquefies after ~20 min a. clotting caused by fibrinogen → fibrin b. liquefying by fibrinolytic enzyme c. vaginal pH goes from 4.2 → 7.2 3. sperm must pass through cervical mucous plug 4. Cervical lining is made up of crypts a. normal sperm life = 48-72h b. in crypts they may live longer (1-2 wks?) 5. Vibration of cervical mucous fibers is the same frequency as the tail motion of sperm which produces forward motion 6. 200-500 million sperm in ejaculate a. 1 million make it to the uterus 7. Sperm is moved through the uterus via uterine contractions a. tail movement doesn't add much to forward movement 8. Coitus causes Oxy release a. neuroendocrine reflex b. increases amplitude of uterine contractions which move sperm up c. cervical os dips into pool of semen 9. Leukocyte Invasion (white blood cells) a. upon sperm entering uterus 10. Cilia enhance sperm movement a. cilia atop Fallopian Tube microvilli move toward uterus b. cilia in troughs/canals move toward ovary c. sperm may travel in canals via ciliary beating i. oocyte travels in the opposite direction also via ciliary beating ii. more mucus in canals during luteal phase iii. E2 intensifies ciliary beating b. ~5-10,000 sperm reach the utero-tubal junction c. 30-60 min for sperm to reach fallopian tubes i. 20 min or less to cervical plug d. ~100-200 sperm make it to the ovum D. Secondary Oocyte 1. ovulated egg = secondary oocyte 2. size of a period in a book 3. barriers to fertilization i. granulosa cells still attached after ovulation (1) cell-cell adhesions b. Vitelline Membrane = Cell Membrane c. sperm capacitation and activation E. Sperm Capacitation and Activation 1. Capacitation a. process by which a sperm acquires the ability to fertilize an egg i. freshly ejaculated sperm are not capable of fertilization b. sperm acquires the ability to undergo the acrosome reaction i. requires the binding fo P to acrosomal membranes (1) membrane bound receptor (a) oocyte also has membranal P-R c. occurs in the uterus or fallopian tubes 2. Activation a. gain the ability to move rapidly b. → ↑ metabolic rate c. → ↑ tail beating d. occurs in the fallopian tubes 3. Fertilization requires capacitation and activation