Chapter 40 HUMAN REPRODUCTION AND DEVELOPMENT

A. Male Reproductive System Consists of testes, a network of tubules & glandular secretions. Testis Scrotum ] Testes (  gonads) Located outside body cavity in scrotum. Testes contain seminiferous tubules (highly coiled tubules within which sperm are produced). When does sperm production begin? end?

] Epididymis Highly coiled tube in which sperm mature & are stored until ejaculation. Testis Epididymis Vas deferens ] Vas deferens Tube that transports sperm from epididymis into body cavity. Each vas deferens loops over urinary bladder & joins to the urethra. Urethra

] Urethra Tube extending from urinary bladder through penis. Vas deferens Urethra transports urine & sperm, but not at the same time. Pathway of sperm: testis  epididymis  vas deferens  urethra Urethra Bladder

Three sets of glands contribute fluids: ] Seminal vesicles Secrete fluid containing fuctose & prostaglandins into vas deferens. Seminal vesicle Prostate gland Bulbourethral gland ] Bulbourethral glands Secrete an alkaline mucus into urethra. ] Prostate gland Surrounds urethra at point where vasa deferentia enter; secretes milky, alkaline fluid into urethra.

During sexual arousal, penis becomes erect and semen is ejaculated. Semen consists of: ] Sperm ( million) ] Fluid from seminal vesicles, prostate & bulbourethral glands.

B. Female Reproductive System Consists of ovaries, fallopian tubes, uterus & vagina. Ovary Fallopian tube Uterus Vagina ] Ovaries (  gonads) Each ovary contains ~ 1 million follicles at birth. Follicle = developing egg (oocyte) + follicle cells. When does ovulation/menstruation begin? end?

Ovary Fallopian tube Uterus Vagina ] Fallopian tubes (oviducts) Tubes that transport oocyte from ovaries to uterus. Site of fertilization. ] Uterus (womb) Muscular sac that functions to receive, retain & nourish a developing embryo. Lower end of uterus (cervix) opens into vagina. ] Vagina (birth canal) Cervix

Cyclic Changes in the Ovary & Uterus Regulated by hormones. ] GnRH - produced by hypothalamus; regulates release of FSH & LH from anterior pituitary. ] FSH - produced by anterior pituitary; stimulates development of follicles. ] LH - produced by anterior pituitary; triggers ovulation & formation of corpus luteum.

] Estrogen - produced by follicle cells & corpus luteum; causes endometrium (uterine lining) to thicken. ] Progesterone - produced by corpus luteum of ovary; increases thickness of endometrium. Ovarian & menstrual cycles occur about every 28 days (puberty  menopause).

Day 1 of cycle: low levels of estrogen, progesterone, FSH & LH signal hypothalamus...

C. Prenatal Development (gestation) Typically divided into 3 stages: ] Preembryonic stage (first 2 weeks) Includes fertilization, cleavage, implantation & beginning of gastrulation. ] Embryonic stage (3rd - 8th weeks) Completion of gastrulation & organogenesis. ] Fetal period (9th week - birth) Organs begin to function & coordinate to form organ systems.

1. Fertilization Union of a sperm and “egg”, forming a zygote. Female ovulates a secondary oocyte (arrested in metaphase II). Oocyte begins journey down fallopian tube; must be fertilized within hours.

Male deposits sperm in female vagina. Sperm are capacitated (develop fertilizing ability) as they swim toward oocyte. Acrosomal enzymes of sperm digest outer coverings of oocyte. Only 1 sperm enters! Sperm entry signals secondary oocyte to complete meiosis II.

2. Cleavage Period of rapid cell division following fertilization. ] Blastomeres - daughter cells ] Morula - solid ball of ~ 16 cells ] Blastocyst - fluid-filled sphere (~100 cells)

3. Implantation Nestling of blastocyst into endometrium. Blastocyst (5 days post- fertilization) trophoblast inner cell mass blastocyst cavity Trophoblast forms chorion. Trophoblast/chorion produces hCG (human chorionic gonadotropin) hCG prevents degeneration of corpus luteum

4. Gastrulation Process that forms the 3 primary germ layers (ectoderm, mesoderm & endoderm ) ; blastocyst is now a gastrula. 9-day implanted blastocyst amniotic cavity yolk sac epiblast hypoblast embryonic disc chorion 16-day embryo (gastrula) cut edge of amnion epiblast Notochord forms beneath primitive streak.

Derivatives of the primary germ layers: ] Ectoderm - nervous system, sense organs, epidermis of skin, hair, nails, sweat glands & oil glands. ] Endoderm - organs & lining of digestive & respiratory systems. ] Mesoderm - notochord, dermis of skin, bones, muscles, circulatory system, urinary system & reproductive system.

Roles of Extraembryonic Membranes ] Chorion - forms the fetal portion of the placenta. Placenta functions in exchange of materials, and produces estrogen & progesterone. ] Amnion - protects developing embryo. ] Yolk sac - produces blood cells until 6th week; develops into intestines & germ cells. ] Allantois - forms as outpocketing of yolk sac; forms umbilical cord & becomes part of urinary bladder.

5. Organogenesis Formation of body organs & organ systems. First major event in organogenesis is neurulation (formation of the neural tube). ] Notochord induces overlying ectoderm to form neural groove.

Sex Determination Sex is determined at fertilization: ] XY embryos develop into males (SRY gene is activated in week 7). ] XX embryos develop into females

Digestive & respiratory systems are last to mature. 6. Labor and Birth Occurs ~266 days post-fertilization (280 days from last menstrual period). ] Stage 1: dilation stage (6-12 hrs) Initiated by oxytocin, which stimulates: F uterus to contract F placenta to produce prostaglandins Descent of fetus ruptures amniotic sac & dilates cervix to 10 centimeters.

] Stage 2: delivery of infant (~2 hrs) Lasts from full dilation to birth. Usually delivered in head-first orientation. Cesarean section - surgical delivery. ] Stage 3: delivery of placenta (~30 min) Uterine contractions expel placenta & extraembryonic membranes. Of every 100 secondary oocytes exposed to sperm, only 31 will survive to be born.

D. Postnatal Development