34 4 FERTILIZATION AND DEVELOPMENT SC 912 L

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34. 4 FERTILIZATION AND DEVELOPMENT SC. 912. L. 16. 1 Describe the process of

34. 4 FERTILIZATION AND DEVELOPMENT SC. 912. L. 16. 1 Describe the process of human development from fertilization to birth and major changes that occur in each trimester of pregnancy. Copyright © 2010 Pearson Education, Inc.

Pregnancy • Pregnancy: events that occur from fertilization until the infant is born •

Pregnancy • Pregnancy: events that occur from fertilization until the infant is born • Gestation period: time from the last menstrual period until birth (~280 days) • Embryo: from fertilization through week 8 • Fetus: from week 9 through birth Copyright © 2010 Pearson Education, Inc.

1 -week conceptus Fertilization Embryo 3 -week embryo (3 mm) 5 -week embryo (10

1 -week conceptus Fertilization Embryo 3 -week embryo (3 mm) 5 -week embryo (10 mm) 8 -week embryo (22 mm) After 8 weeks the embryo is called a fetus 12 -week fetus (90 mm) Copyright © 2010 Pearson Education, Inc. Figure 28. 1

From Egg to Zygote • The oocyte is viable for 12 to 24 hours

From Egg to Zygote • The oocyte is viable for 12 to 24 hours • Sperm is viable 24 to 48 hours after ejaculation Copyright © 2010 Pearson Education, Inc.

From Egg to Zygote • For fertilization to occur, coitus must occur no more

From Egg to Zygote • For fertilization to occur, coitus must occur no more than • Two days before ovulation • 24 hours after ovulation • Fertilization: when the sperm’s chromosomes combine with those of a secondary oocyte to form a fertilized egg (zygote) Copyright © 2010 Pearson Education, Inc.

Fertilization Copyright © 2010 Pearson Education, Inc.

Fertilization Copyright © 2010 Pearson Education, Inc.

Embryonic Development • Cleavage • Mitotic divisions of zygote • First cleavage at 36

Embryonic Development • Cleavage • Mitotic divisions of zygote • First cleavage at 36 hours two daughter cells (blastomeres) • At 72 hours morula (16 or more cells) • At day 3 or 4, the embryo of ~100 cells (blastocyst) has reached the uterus Copyright © 2010 Pearson Education, Inc.

Embryonic Development • Blastocyst: fluid-filled hollow sphere • Inner cell mass • Becomes the

Embryonic Development • Blastocyst: fluid-filled hollow sphere • Inner cell mass • Becomes the embryonic disc ( embryo and three of the embryonic membranes) Copyright © 2010 Pearson Education, Inc.

(a) Zygote (b) 4 -cell stage (fertilized egg) 2 days Zona pellucida (c) Morula

(a) Zygote (b) 4 -cell stage (fertilized egg) 2 days Zona pellucida (c) Morula (a solid ball of blastomeres). 3 days Degenerating zona pellucida Blastocyst cavity Sperm Uterine tube Fertilization (sperm meets and enters egg) Oocyte (egg) (e) Implanting blastocyst (Consists of a sphere of trophoblast cells and an eccentric cell cluster called the inner cell mass). 7 days Ovary Ovulation Uterus Endometrium Cavity of uterus Copyright © 2010 Pearson Education, Inc. (d) Early blastocyst (Morula hollows out, fills with fluid, and “hatches” from the zona pellucida). 4 days Blastocyst cavity Trophoblast Inner cell mass Figure 28. 4

Implantation • Blastocyst floats for 2– 3 days • Implantation begins 6– 7 days

Implantation • Blastocyst floats for 2– 3 days • Implantation begins 6– 7 days after ovulation Copyright © 2010 Pearson Education, Inc.

Placentation • Formation of the placenta from embryonic and maternal tissues • Placenta is

Placentation • Formation of the placenta from embryonic and maternal tissues • Placenta is fully formed and functional by the end of the third month Copyright © 2010 Pearson Education, Inc.

Placenta • Organ that connection between mother and embryo • Act‘s as embryo’s organ

Placenta • Organ that connection between mother and embryo • Act‘s as embryo’s organ of respiration, nourishment, and excretion. • Oxygen and nutrients diffuse from the mother to the embryo. • Carbon dioxide and metabolic waste diffuse from the embryo to the mother. • Maternal and embryonic blood supplies do not intermix Copyright © 2010 Pearson Education, Inc.

Placenta Decidua basalis Chorionic villi Yolk sac Amnion Amniotic cavity Umbilical cord Decidua capsularis

Placenta Decidua basalis Chorionic villi Yolk sac Amnion Amniotic cavity Umbilical cord Decidua capsularis Uterus Extraembryonic coelom Lumen of uterus (e) 13 -week fetus. Copyright © 2010 Pearson Education, Inc. Figure 28. 7 e

Embryonic Development: Gastrula to Fetus • Germ Layers • During implantation, the blastocyst starts

Embryonic Development: Gastrula to Fetus • Germ Layers • During implantation, the blastocyst starts to convert to a gastrula • Inner cell mass develops into the embryonic disc (subdivides into epiblast and hypoblast) • The three primary germ layers and the extraembryonic membranes develop Copyright © 2010 Pearson Education, Inc.

Extraembryonic Membranes 1. Amnion: transparent sac filled with amniotic fluid • Provides a buoyant

Extraembryonic Membranes 1. Amnion: transparent sac filled with amniotic fluid • Provides a buoyant environment that protects the embryo • Helps maintain a constant homeostatic temperature • Allows freedom of movement and prevents parts from fusing together • Amniotic fluid comes from maternal blood, and later, fetal urine Copyright © 2010 Pearson Education, Inc.

Extraembryonic Membranes 2. Yolk sac: a sac that hangs from the ventral surface of

Extraembryonic Membranes 2. Yolk sac: a sac that hangs from the ventral surface of the embryo • Forms part of the digestive tube • Source of the earliest blood cells and blood vessels Copyright © 2010 Pearson Education, Inc.

Gastrulation • Occurs in week 3, in which the embryonic disc becomes a three-layered

Gastrulation • Occurs in week 3, in which the embryonic disc becomes a three-layered embryo with ectoderm, mesoderm, and endoderm • Begins with appearance of primitive streak, a raised dorsal groove that establishes the longitudinal axis of the embryo Copyright © 2010 Pearson Education, Inc.

Amnion Bilayered embryonic disc Yolk sac (a) Head end of bilayered embryonic disc (b)

Amnion Bilayered embryonic disc Yolk sac (a) Head end of bilayered embryonic disc (b) Frontal section (c) 3 -D view (d) Section view in (e) Head end Cut edge of amnion Primitive streak Epiblast Yolk sac (cut edge) Right (f) 14 -15 days Endoderm Hypoblast Left Ectoderm Primitive streak Tail end (e) Bilayered embryonic disc, superior view Copyright © 2010 Pearson Education, Inc. (g) 16 days Mesoderm Endoderm Figure 28. 9

Gastrulation • Cells begin to migrate into the groove • The first cells form

Gastrulation • Cells begin to migrate into the groove • The first cells form the endoderm • Cells that follow push laterally, forming the mesoderm • Cells that remain on the embryo’s dorsal surface form the ectoderm • Notochord: rod of mesodermal cells that serves as axial support Copyright © 2010 Pearson Education, Inc.

Primary Germ Layers • The primitive tissues from which all body organs derive •

Primary Germ Layers • The primitive tissues from which all body organs derive • Ectoderm nervous system and skin epidermis • Mesoderm forms all other tissues • Endoderm epithelial linings of the digestive, respiratory, and urogenital systems Copyright © 2010 Pearson Education, Inc.

Building Vocabulary • Prefix and their meaning: • Ecto- “outer” • Meso- “middle” •

Building Vocabulary • Prefix and their meaning: • Ecto- “outer” • Meso- “middle” • Endo- “inner” Copyright © 2010 Pearson Education, Inc.

Specialization of Ectoderm • Neurulation • First major event of organogenesis • Gives rise

Specialization of Ectoderm • Neurulation • First major event of organogenesis • Gives rise to brain and spinal cord • Ectoderm over the notochord forms the neural plate • Neural plate folds inward as a neural groove with neural folds Copyright © 2010 Pearson Education, Inc.

Specialization of Endoderm • Forms the lining of organs of the • GI tract

Specialization of Endoderm • Forms the lining of organs of the • GI tract (gastro intestinal) • Respiratory tract • Excretory system Copyright © 2010 Pearson Education, Inc.

Specialization of the Mesoderm • Dermis of the skin in the ventral region •

Specialization of the Mesoderm • Dermis of the skin in the ventral region • Parietal serosa of the ventral body cavity • Bones, ligaments, and dermis of limbs • The heart and blood vessels • Most connective tissues of the body Copyright © 2010 Pearson Education, Inc.

Epiblast ECTODERM MESODERM Notochord • Epidermis, hair, nails, glands of skin • Brain and

Epiblast ECTODERM MESODERM Notochord • Epidermis, hair, nails, glands of skin • Brain and spinal cord • Neural crest and derivatives (sensory nerve cells, pigment cells, bones and blood vessels of the head) Copyright © 2010 Pearson Education, Inc. Nucleus pulposus of intervertebral discs Somite • Sclerotome: vertebrae and ribs • Dermatome: dermis of dorsal body region • Myotome: trunk and limb musculature Intermediate mesoderm • Kidneys • Gonads ENDODERM Lateral plate mesoderm Somatic mesoderm Splanchnic mesoderm • Parietal serosa • Dermis of ventral body region • Connective tissues of limbs (bones, joints, and ligaments) • Wall of digestive and respiratory tracts (except epithelial lining) • Visceral serosa • Heart • Blood vessels Epithelial lining and glands of digestive and respiratory tracts Figure 28. 13

Neurulation • First step in the development of the nervous system • If the

Neurulation • First step in the development of the nervous system • If the neural tube doesn’t close completely a serious birth defect known as spina bifida can result. • Folic Acid (Vitamin B 9) can prevent spina bifida • The neural tube forms before a woman knows she is pregnant. • So, folic acid should be part of any woman's diet. Copyright © 2010 Pearson Education, Inc.

Pharynx Parathyroid glands and thymus Thyroid gland Esophagus Trachea Connection to yolk sac Right

Pharynx Parathyroid glands and thymus Thyroid gland Esophagus Trachea Connection to yolk sac Right and left lungs Stomach Liver Umbilical cord Pancreas Gallbladder Small intestine Allantois Copyright © 2010 Pearson Education, Inc. 5 -week embryo Large intestine Figure 28. 12

Events of Fetal Development • Fetal period: weeks 9 through 38 • Time of

Events of Fetal Development • Fetal period: weeks 9 through 38 • Time of rapid growth of body structures established in the embryo Copyright © 2010 Pearson Education, Inc.

Umbilical cord Chorionic villi Umbilical vein Amniotic sac Yolk sac (a) Embryo at week

Umbilical cord Chorionic villi Umbilical vein Amniotic sac Yolk sac (a) Embryo at week 7, about 17 mm long. Copyright © 2010 Pearson Education, Inc. Cut edge of chorion Figure 28. 15

Copyright © 2010 Pearson Education, Inc. Table 28. 1 (1 of 3)

Copyright © 2010 Pearson Education, Inc. Table 28. 1 (1 of 3)

Copyright © 2010 Pearson Education, Inc. Table 28. 1 (2 of 3)

Copyright © 2010 Pearson Education, Inc. Table 28. 1 (2 of 3)

Copyright © 2010 Pearson Education, Inc. Table 28. 1 (3 of 3)

Copyright © 2010 Pearson Education, Inc. Table 28. 1 (3 of 3)

Parturition • Parturition giving birth to the baby • Labor events that expel the

Parturition • Parturition giving birth to the baby • Labor events that expel the infant from the uterus Copyright © 2010 Pearson Education, Inc.

Initiation of Labor • During the last few weeks of pregnancy • Fetal secretion

Initiation of Labor • During the last few weeks of pregnancy • Fetal secretion of cortisol stimulates the placenta to secrete more estrogen • Causes production of oxytocin receptors by myometrium • Antagonizes calming effects of progesterone, leading to Braxton Hicks contractions in uterus Copyright © 2010 Pearson Education, Inc.

Initiation of Labor • Surfactant protein A (SP-A) from fetal lungs causes softening of

Initiation of Labor • Surfactant protein A (SP-A) from fetal lungs causes softening of the cervix • Fetal oxytocin causes the placenta to produce prostaglandins • Oxytocin and prostaglandins: powerful uterine muscle stimulants Copyright © 2010 Pearson Education, Inc.

Initiation of Labor • Maternal emotional and physical stress • Activates the hypothalamus, causing

Initiation of Labor • Maternal emotional and physical stress • Activates the hypothalamus, causing oxytocin release from posterior pituitary • Positive feedback mechanism occurs Copyright © 2010 Pearson Education, Inc.

Estrogen from placenta Oxytocin (+) from fetus and mother’s posterior pituitary Induces oxytocin receptors

Estrogen from placenta Oxytocin (+) from fetus and mother’s posterior pituitary Induces oxytocin receptors on uterus Stimulates uterus to contract Stimulates placenta to make (+) Prostaglandins Stimulate more vigorous contractions of uterus Copyright © 2010 Pearson Education, Inc. Figure 28. 17

Stages of Labor: Dilation Stage • Longest stage of labor: 6– 12 hours or

Stages of Labor: Dilation Stage • Longest stage of labor: 6– 12 hours or more • Initial weak contractions: • 15– 30 minutes apart, 10– 30 seconds long • Become more vigorous and rapid • Cervix effaces and dilates fully to 10 cm • Amnion ruptures, releasing amniotic fluid • Engagement occurs: head enters the true pelvis Copyright © 2010 Pearson Education, Inc.

Umbilical cord Placenta Uterus Cervix Vagina (a) Dilation (early) Copyright © 2010 Pearson Education,

Umbilical cord Placenta Uterus Cervix Vagina (a) Dilation (early) Copyright © 2010 Pearson Education, Inc. Figure 28. 18 a

Pubic symphysis Sacrum (b) Dilation (late) Copyright © 2010 Pearson Education, Inc. Figure 28.

Pubic symphysis Sacrum (b) Dilation (late) Copyright © 2010 Pearson Education, Inc. Figure 28. 18 b

Stages of Labor: Expulsion Stage • Strong contractions every 2– 3 minutes, about 1

Stages of Labor: Expulsion Stage • Strong contractions every 2– 3 minutes, about 1 minute long • Urge to push increases (in absence of local anesthesia) • Crowning occurs when the largest dimension of the head distends vulva • Delivery of infant Copyright © 2010 Pearson Education, Inc.

Stages of Labor: Expulsion Stage • Strong contractions every 2– 3 minutes, about 1

Stages of Labor: Expulsion Stage • Strong contractions every 2– 3 minutes, about 1 minute long • Urge to push increases (in absence of local anesthesia) • Crowning occurs when the largest dimension of the head distends vulva • Delivery of infant Copyright © 2010 Pearson Education, Inc.

Perineum (c) Expulsion Copyright © 2010 Pearson Education, Inc. Figure 28. 18 c

Perineum (c) Expulsion Copyright © 2010 Pearson Education, Inc. Figure 28. 18 c

Stages of Labor: Placental Stage • Strong contractions continue, causing detachment of the placenta

Stages of Labor: Placental Stage • Strong contractions continue, causing detachment of the placenta and compression of uterine blood vessels • Delivery of the afterbirth (placenta and membranes) occurs ~30 minutes after birth • All placenta fragments must be removed to prevent postpartum bleeding Copyright © 2010 Pearson Education, Inc.

Uterus Placenta (detaching) Umbilical cord (d) Placental Copyright © 2010 Pearson Education, Inc. Figure

Uterus Placenta (detaching) Umbilical cord (d) Placental Copyright © 2010 Pearson Education, Inc. Figure 28. 18 d