Biology of Reproduction

XIX.  Gamete Interaction                          back to XVIII. Fertilization Systems

	A. Sperm competition

	B. One spermatozoon fertilizes

		1. after capacitation and activation

		2. Hyaluronic Acid

			a. cements together cells of the Cumulus Oophorus

				i. sperm must penetrate between these cemented cells

					(1) Acrosome Reaction necessary for this

		3. Acrosome Reaction

			a. sperm plasma membrane and outer acrosomal membrane
			   fuse at distinct points

				i. now called composite membrane

			b. openings formed in composite membrane

			c. enzymes are released through these openings

				i. hyaluronidase

			d. hyaluronidase dissolves the hyaluronic acid cement
			   and allows the activated sperm through

			e. shedding of the composite membrane

			f. Corona penetrating enzyme also in acrosome

			g. Inner acrosomal membrane attaches to Zona Pellucida

				i. protein receptors on zona pellucida
				   for inner acrosomal membrane

			h. Other enzymes from acrosome left on the outer margin
			   of inner acrosomal membrane

				i. Acrosin

					(1) protease that digests
					    part of the zona pellucida

				ii. Neuramidase

					(1) dissolves Neuramininc acid a component
					    of the zona pellucida

			i. inner acrosomal membrane fuses with the
			   Vitelline Membrane

					(1) Cortical Vesicles:
					    contain Cortical Granules
	
			j. an opening forms at the point of fusion

			k. Chromosomes and Centriole enter into Ooplasm

			l. Cortical Granules expelled into the Perivitelline Space

				i. membranes of cortical vesicles and vitelline
				    membrane fuse releasing granules

			m. Cortical Granules contain:

				i. factors which chemically/structurally change zona
				    pellucida to block sperm penetration

				ii. acrosin inhibitor

				iii. cortical granule protease

					(1) keeps inner acrosomal membrane from binding
					    to  vitelline membrane

				iv. i-iii  prevent multiple fertilizations
				    = polyspermy

	C. Ovum Activation

		1. Sperm penetration causes Ovum Activation

		2. Ends 2nd Meiotic Arrest

		3. 2nd polar body formed

			a. 2o Oocyte ® Ootid + Polar Body

	D. Nuclear Membranes Dissolve

		1. Sperm + Ootid

		2. ® Pronuclei

	E. Fusion of Pronuclei = Conception

		1. ® Zygote (2N)

		2. 12 h from Ovum Activation to fusion of Pronuclei

			a. all happens in the fallopian tubes

			b. mitosis begins immediately

XX. Pregnancy