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NORMAL GAMETOGENESIS Spermatogonium AG.XY ‘SPERMATOGENESIS: Testis Primary spermatocyte 48xXY — ‘ Vey \ 23, 23,¥ Spermatids SPERMIOGENESIS Normal sperms 23,X 23x 23Y 23,¥ OOGENESIS Ovary Primary oocyte 46,XX in primary follicle { Primary oocyte 46,XX in Follicular cells growing follicle Primary oocyte 46,XX in larger follicle mature follicle Zona pellucida’ Corona radiata Sas Fertilized oocyte Second polar body Figure 2-5 Normal gametogenesis: conversion of germ cells into gametes. The illustrations compare spermatogenesis and oogenesis. Oogonia are not shown in this figure because they differentiate into primary oocytes before birth. The chromosome complement of the germ cells is shown at each stage. The number designates the total number of chromosomes, including sex chromosome(s) (shown after the comma). Note: (1) After the two meiotic divisions, the diploid number of chromosomes, 46, is reduced to the haploid number, 23; (2) four sperms form from one primary spermatocyte, whereas only one secondary oocyte results from matura- tion of a primary oocyte; (3) the cytoplasm is conserved during oogenesis to form one large cell, the oocyte. 02 CHAPTER S& THIRD WEEK OF DEVELOPMENT Amniotic cavity Cut edge of amnion Connecting Notochordal process stalk Plane of }--- sections Allantois B,C, and E Connecting stalk . Umbili eX. ilical sees lt ae) Abies. vesicle Primitive streak Prechordal plate Primitive pit A Neural plate Neurenteric canal (arrow) e ‘ ( Embryonic Neural groove —_Intraembryonic ectoderm mesoderm Primitive streak Umbilical vesicle Notochordal plate intercalated in the Oropharyngeal : Embryonic membrane Levarot endoderm D embryonic endoderm en 5 Neural groove section Cc Notochordal plate infolding Notochord Neurenteric canal Cloacal . membrane Neural groove Neural fold Intermediate mesoderm Paraxial mesoderm Lateral mesoderm y endoderm G Notochord Figure 5-6 Development of the notochord by transformation of the notochordal process A, Dorsal view of the embryonic disc (at approximately 18 days), exposed by removing the amnion. B, Three-dimensional median section of the embryo. C and E, Similar sections of slightly older embryos. D, F, and G, Transverse sections of the trilaminar embryonic disc shown inCandE. Decidua parietalis Umbilical vein Umbilical arteries (O,-tich blood) (O,-poor blood) ‘Smooth chorion Amniochorionic membrane Fetal circulation Intervillous space Chorionic plate Stump of main stem villus Main stem villus Placental septum Anchoring villus Decidua basalis Spiral artery Cytotrophoblastic shell Myometrium Endometrial Endometrial veins arteries Maternal circulation Figure 8-5 |llustration of a transverse section through a full-term placenta, showing (1) the relation of the villous chorion (fetal part of placenta) to the decidua basalis (maternal part of placenta); (2) the fetal placental circulation; and (3) the maternal-placental circulation. Maternal blood flows into the intervillous spaces in funnel-shaped spurts from the spiral arteries, and exchanges occur with the fetal blood as the maternal blood flows around the branch villi. The inflowing arterial blood pushes venous blood out of the intervillous space and into the endo- metrial veins. Note that the umbilical arteries carry poorly oxygenated fetal blood (shown in blue) to the placenta and that the umbilical vein carries oxygenated blood (shown in red) to the fetus, Only one stem villus is shown in each cotyledon, but the stumps of those that have been removed are indicated. Arrows indicate direction of maternal (red and blue) and fetal (black) blood flow. ‘Second polar body Zona pellucida Blastomere A 2-cell stage Zona pellucida c B-cell stage Embryoblast (inner cell mass) Degenerating zona pellucida Blastocystic cavity Trophoblast e Early blastocyst F Later blastocyst Figure 3-3 Illustrations showing cleavage of the zygote and formation of the blastocyst. A to D show various stages of cleavage. The period of the morula begins at the 12- to 32-cell stage and ends when the blastocyst forms. E and F show sections of blastocysts. The zona pellucida disappears by the late blastocyst stage (5 days). Although cleavage increases the number of blastomeres, nate that each of the daughter cells is smaller than the parent cells. As a result, there is no increase in the size of the developing embryo until the zona pellucida degenerates. The blastocyst then enlarges considerably (D). Amnion Embryonic disc Connecting stalk Embryonic Notochordal Connecting stalk. Umbilical vesicle pal See eee Primitive pit Notochordal process under ectoderm — plane of sections Cranial end Gloacal membrane Cardiogenic Embryonic Allantois Pease eM, g (heartfarming) area endoderm A Prechordal piate primitive node Primitive pit’ Primitive Cloacal membrane Notochordal Neural Primitive pit Primitive streak streak process plate Intraembryonic mesoderm Allantois Notochordal Embryonic Notochordal canal Figure 5-5 Illustrations of the development of the notochordal process. The small sketch at the upper left is for orientation. A, Dorsal view of the embryonic disc (at approximately 16 days), exposed by removal of the amnion, The notochordal process is shown as if it were visible through the embryonic ectoderm. B, C, and D, Median sections, at the same plane as shown in A, illustrating successive stages in the development of the notochordal process and canal. The stages shown in € and © occur at approximately 18 days. endoderm | Prechordal plate canal Pharyngeal 8 Lateral lingual arches: swelling Median lingual swelling Foramen cecum of tongue Copula Hypopharyngeal eminence A Esophagus _Laryngotracheal groove Migration of third arch mesoderm Hypopharyngeal eminence Rima glottidis (opening to vocal apparatus) Midline groove Oral part of tongue : Circumvallate papillae Terminal sulcus Pharyngeal part of tongu Foramen cecum Cc Epiglottis Stomach 1 Bile duct Dorsal Ventral D pancreatic mesogastrium —— Dorsal mesogastrium bud < / Primordial Primodial liver Dorsal liver Level of _-—~ pancreatic bud section E Gallbladder Gallbladder Duodenum Foregut part Ventral pancreatic we of duodenum Dorsal bud (ventral pancreas) mesentery ~, Midgut part of A duodenum = B Dorsal mesentery / Fusion of dorsal and ventral pancreatic buds Duodenum _—Level of _-- section G fe} D Head of pancreas Tail of pancreas 
