28. Pregnancy and Human Development

Early Embryogenesis: Cleavage, Blastulation, Gastrulation, and Neurulation

Embryonic Development

Embryology - Fertilization, Cleavage, Blastulation

 The inner layers of trophoblasts lose their plasma membranes and invade the endometrium. 

 They display L-selectin molecules on their surface after blastocyst hatching. 

 Which of the following does NOT describe a function of trophoblast cells? 

 Gastrulation lays down the basic structural framework of the embryo and sets the stage for the rearrangements that occur during organogenesis. The first major event in organogenesis is neurulation. 

 The first major event in organogenesis is gastrulation. 

 The outermost extraembryonic membrane is the chorion, which is part of the placenta. 

 The outermost extraembryonic membrane is the __________. 

 Urine formation is not a function of the placenta. 

 Which of the following is NOT a function of the placenta? 

Embryonic Development in Humans

 After fertilization, the zygote goes through a rapid period of cell divisions called <i>cleavage</i>, resulting in the blastocyst, which has many smaller cells. 

 After fertilization, the zygote goes through a rapid period of cell divisions called __________. 

Neurulation

 In humans, the allantois is the structural base for the umbilical cord that links the embryo to the placenta. 

 In humans, the extraembryonic membrane that composes the structural base for the umbilical cord is the __________. 

 It takes about 3 to 4 days after fertilization for the egg to travel to the uterus, where it floats for 2 to 3 days before it begins implantation. 

 Implantation of the blastocyst begins __________ after ovulation. 

 hCG levels increase throughout gestation. 

 Estrogen and progesterone levels increase throughout pregnancy. 

 Estrogen levels increase throughout gestation. 

 Estrogen levels decline throughout gestation. 

 hCG levels remain stable throughout gestation. 

 Progesterone levels decline throughout gestation. 

 Which statement about maternal hormones during pregnancy is accurate? 

Organogenesis

Extraembryonic Membranes

 The inner cell mass is not involved in the formation of the placenta. The chronic villi and the decidua basalis form the placenta. 

 The yolk sac is not involved in the formation of the placenta. The chronic villi and the decidua basalis form the placenta. 

 chronic villi and the decidua capsularis 

 The decidua capsularis is not involved in the formation of the placenta. The chronic villi and the decidua basalis form the placenta. 

 The disc-shaped placenta is formed from the __________. 

 The ectoderm develops into many neural structures, including the central nervous system, as well as several integumentary structures. 

 Which of the following structures is/are formed from ectodermal tissues? 

 Most ectopic pregnancies occur in the uterine tubes. 

 An implantation that takes place in a site other than the uterus is called __________. 

 Amnion formation is not the first event in organogenesis. Neurulation is the first event of organogenesis. 

 Sporulation does not take place in humans. Neurulation is the first event of organogenesis. 

 The formation of mesenchyme is not the first event in organogenesis. Neurulation is the first event of organogenesis. 

 The first major event of organogenesis is __________. 

 Relaxin relaxes pelvic ligaments and joints. This increased flexibility eases birth passage. 

 Which hormone produced by the placenta causes the mother’s pubic symphysis to loosen and widen? 

 It causes the uterine lining to slough off or shed to maintain pregnancy. 

 hCG from the fetal trophoblast cells signals the corpus luteum of the ovary to continue producing estrogen and progesterone, which maintains the endometrium and prevents menstruation. 

 It inhibits the production of estrogen and progesterone by the ovary. 

 It increases to high levels near birth, helping initiate the birth process. 

 It signals the corpus luteum to continue producing estrogen and progesterone to maintain the pregnancy. 

 It stimulates the production of FSH by the pituitary. 

 What is the function of the hormone hCG (human chorionic gonadotropin)? 

Fertilization and Implantation

The Placenta - Development and Function

Implantation of Blastocyst

 Ectoderm fashions the structures of the nervous system and the skin epidermis. 

 The ectoderm is the primary germ layer from which the digestive, respiratory, and urogenital systems and the associated glands form. 

Development and Function of Placenta

Embryology - Gastrulation

Early Embryogenesis - Cleavage, Blastulation, Gastrulation, and Neurulation

 Somites are derived from mesoderm and specialize into sclerotome, myotome, and dermatome. 

 The notochord is a rod that provides axial support of the embryo and is derived from mesoderm. 

 During early gastrulation, what structure(s) appear(s) on the dorsal aspect of the embryonic disc and establish(e)s the longitudinal axis of the embryo? 

The Process of Gastrulation

Gastrulation

 Implantation, which takes about a week, is completed after the blastocyst is entirely surrounded by endometrium (typically 12 days after ovulation). 

 blastocyst is entirely surrounded by endometrium 

 Implantation is completed after the __________. 

Implantation

 The development of the primary germs layers is called <i>gastrulation</i>. The three layers that form are the ectoderm, endoderm, and mesoderm. 

 The development of the primary germ layers is called __________. 

Cleavage and Blastulation

 Mesoderm specializes into numerous structures located throughout the body. Nails, hair and the epidermis, however, are derived from ectoderm. 

 All of the following structures are derived from mesoderm EXCEPT __________. 

 the day before ovulation; the third day after ovulation 

 Six to seven days after ovulation, given a properly prepared endometrium, implantation begins. Implantation, when successful, takes about five days; it is usually completed by the twelfth day after ovulation. 

 two to three days after ovulation; the sixth or seventh day after ovulation 

 six to seven days after ovulation; the twelfth day after ovulation 

 the day after ovulation; the third day after ovulation 

 The process of implantation generally begins __________ and is usually completed by __________. 

Germ layer derivatives

 The placenta is usually fully functional as a nutritive, respiratory, excretory, and endocrine organ by the end of the third month of pregnancy. 

 By the end of the third month of pregnancy, the placenta is usually fully functional as a nutritive, respiratory, excretory, and endocrine organ. 

Meet the placenta!

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