2Conception Conception is when sperm and egg meet and fertilization occursConception occurs in the outer third of thefallopian tubeZygote - fertilized egg
3ConceptionThe sperm reaches the caudal epididymis approximately 72 days after the initiation of spermatogenesis.Preservation of optimal sperm function during storage requires adequate testosterone levels and maintenance of a normal scrotal temperature.
4Stages of Fetal Development Preembryonic stage: fertilization through 2nd weekFertilization; cleavage; morulaBlastocyst and trophoblastImplantationEmbryonic stage: end of 2nd week through 8th weekBasic structures of major body organs and main external featuresFetal stage: end of the 8th week until birth
5Embryonic LayersEctoderm: forms the central nervous system, special senses, skin and glandsMesoderm: forms skeletal, urinary, circulatory, and reproductive organsEndoderm: forms respiratory system, liver, pancreas, and digestive system
6Site of sperm formation Seminiferous tubules of Testis
8ConceptionThe alkaline pH of semen provides protection for the sperm from the acid environment of the vagina.Of an average of 200 to 300 million sperm deposited in the vagina, at most only a few hundred achieve proximity to the egg.
9Conception Capacitation is characterized by three accomplishments: The ability to undergo the acrosome reaction.The ability to bind to the zona pellucida.The acquisition of hypermotility.
10SPERMIOGENESIS Spermatids are rounded cells. They modify to assume specific shape of the sperm.This process is called Spermiogenesis. In it they elongate and reorganize internal structure to acquire the particular shape.
11Accomplishing Fertilization The oocyte is viable for 12 to 24 hoursSperm is viable 24 to 72 hoursFor fertilization to occur, coitus must occur no more than:Three days before ovulation24 hours after ovulationFertilization – when a sperm fuses with an egg to form a zygote
12Sperm Transport and Capacitation Fates of ejaculated spermLeak out of the vagina immediately after depositionDestroyed by the acidic vaginal environmentFail to make it through the cervixDispersed in the uterine cavity or destroyed by phagocytic leukocytesReach the uterine tubesSperm must undergo capacitation before they can penetrate the oocyte
13Acrosomal Reaction and Sperm Penetration An ovulated oocyte is encapsulated by:The corona radiata and zona pellucidaExtracellular matrixSperm binds to the zona pellucida and undergoes the acrosomal reactionEnzymes are released near the oocyteHundreds of acrosomes release their enzymes to digest the zona pellucida
14Acrosomal Reaction and Sperm Penetration Once a sperm makes contact with the oocyte’s membrane:Beta protein finds and binds to receptors on the oocyte membraneAlpha protein causes it to insert into the membrane
15Acrosomal Reaction and Sperm Penetration Figure 28.2a
17Blocks to Polyspermy Only one sperm is allowed to penetrate the oocyte Two mechanisms ensure monospermyFast block to polyspermy – membrane depolarization prevents sperm from fusing with the oocyte membraneSlow block to polyspermy – zonal inhibiting proteins (ZIPs):Destroy sperm receptorsCause sperm already bound to receptors to detach
18ImplantationImplantation is defined as the process by which an embryo attaches to the uterine wall and penetrates first the epithelium and then the circulatory system of the mother to form the placenta.The human blastocyst remains in the uterine secretions for approximately 1 to 3 days and then hatches from its zona pellucida in preparation for attachment.
19ImplantationViability of the corpus luteum is maintained by human chorionic gonadotropin (hCG) secreted by the trophoblastshCG prompts the corpus luteum to continue to secrete progesterone and estrogenBetween the second and third month, the placenta:Assumes the role of progesterone and estrogen productionIs providing nutrients and removing wastes
20ImplantationThe blastocyst loosely adheres to the endometrial epithelium, a process called apposition, which most commonly occurs on the endometrium of the upper posterior wall of the uterus.The implantation occur in fundus of the uterus, which is rich blood supply.
22Placental Hormones HUMAN CHORIONIC GONADOTROPIN maintenance of function of the corpus luteumStimulation of the maternal thyroid glandPromotion of relaxin secretionPromote uterine vascular vasodilatation and myometrial smooth muscle relaxation
23Student Practice 2 1. Fates of ejaculated sperm caused by: 2. Explain the process of implantation?