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Biology 221 Anatomy & Physiology II. TOPIC 13 Survey of Development. Chapter 29 and others. E. Lathrop-Davis / E. Gorski / S. Kabrhel. Pregnancy. Events from fertilization to birth Results from union of sperm and egg
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Biology 221 Anatomy & Physiology II TOPIC 13Survey of Development Chapter 29 and others E. Lathrop-Davis / E. Gorski / S. Kabrhel
Pregnancy • Events from fertilization to birth • Results from union of sperm and egg • Sperm must swim from vagina upstream to meet secondary oocyte – normally meet in fallopian tubes • Sperm must overcome: • acidity of male urethra and female vagina • mucus plug • uterine contractions during orgasm Fig. 28.14, p. 1089
Fertilization • union of haploid gametes (egg & sperm) produces diploid zygote • occurs in 2 stages: • Stage 1: penetration of egg • Stage 2: union of sperm & egg membranes and nuclei
Fertilization: Stage 1 - Penetration • Acrosomal enzymes from many, many sperm must be released to break through corona radiata and zona pellucida • When one sperm finally makes it through, conditions in the oocyte change so that no more sperm can enter Fig. 29.2, p. 1121
Fertilization: Stage 2 Union • Oocyte undergoes meiosis II and ejects the 2nd polar body • Sperm nucleus migrates to center of oocyte, rest of sperm degenerates • Sperm and egg nuclei unite to form diploid zygote Fig. 29.3, p. 1122
Characteristics of Living Things • Maintenance of boundaries (cell membrane) • Movement (cellular and organismal) • Respond to stimuli (recognize changes in environment and creates responses) • Digest (provides nutrients in usable form) • Metabolism (chemical reactions) • Excretion (removal of wastes) • Reproduction (cellular) • Growth (increase in size)
Pre-embryonic Development1st Through 2nd Weeks Overview • Cleavage • Blastocyst foramtion • Implantation • Placentation
Cleavage &Blastocyst Formation • Cleavage – rapid replication of DNA and mitotic cell divisions produce ever smaller cells resulting in a solid ball called a morula • Continued division produces blastocyst • inner cell mass becomes future embryo • trophoblast cells form fetal part of placenta Fig. 29.4, p. 1123
Implantation • blastocyst implants itself into endometrium of uterine wall • ectopic pregnancy – implantation occurs in some other location (e.g., fallopian tube) • trophoblast cells (outer cells of blastocyst) secrete human chorionic gonadotropin (hCG) that maintains corpus luteum through 1st four months Fig. 29.5, p. 1124
Placentation • development of placenta • originates from chorion (trophoblast cells) of embryo/fetus and endometrial tissue of mother • begins to produce estrogens and progestins Fig. 29.7a-c, p. 1126
Embryonic DevelopmentWeeks 3-8 Overview • Development of extra-embryonic membranes • Gastrulation (formation of primary germ layers) • Organogenesis (formation of rudiments of organ systems)
Development of Extra-Embryonic Membranes • chorion – forms part of placenta • anmion • becomes filled with amniotic fluid: • cushions embryo • maintains temperature • allows freedom of movement • yolk sac • forms part of the primitive gut • 1st site of blood cell formation • allantois • contributes to the umbilical cord • becomes part of urinary bladder Fig. 29.7d, p. 1126
Gastrulation • development of Primary Germ Layers • ectoderm – outmost – forms epidermis and nervous system • endoderm – inner layer – forms epithelial linings of digestive tract, respiratory tract, urogenital system and associated glands • mesoderm – middle layer – forms connective tissues and muscle See also Table 29.1, p. 1135 Fig. 29.8, p. 1131
Specialization of Ectoderm • over most of body, forms epidermis • over middle back, forms neural plate neural groove & neural folds neural tube brain & spinal cord Fig. 29.9, p. 1132
Specialization of Endoderm • gives rise to lining of gut • structures that come from gut arise as “outpocketings” • lungs and respiratory tree (epithelial linings) • thyroid, parathyroid glands • liver and gall bladder • pancreas Fig. 29.10, p. 1133
Specialization of Mesoderm • gives rise to muscle, connective tissues, serous membranes • limb buds form and move laterally in what will become shoulder and hip areas Fig. 29.11, p. 1134
Embryonic developmentWeeks 3-8: Organogenesis • heart beats by week 4 • all systems present in some form by week 8 • all major regions of brain present by week 8 • liver produces blood cells by week 8
Fetal Development: 12 - 16 Weeks By 12 weeks: • blood cell formation in bone marrow • ossification begins By 16 weeks: • kidneys have typical shape • joint (synovial) cavities present • cerebellum becomes large • sensory organs differentiated See Table 29.2, p. 1138
Fetal Development: 20-30 Weeks • by 20 weeks • skin covered by lanugo (silky hair) • activity can be felt by mother (“quickening”) • by 30 weeks • myelination of spinal cord begins • finger and toe nails present • bone marrow becomes only site of blood cell formation • testes descend (7th month) in males • surfactant production begins at ~ 24 weeks See Table 29.2, p. 1138
Fetal Development:8 Months - Birth • 8th to 9th months • continued development of organ systems • significant weight gain • weeks 38-42 – birth • before 38 weeks, less fat, organ systems not as well developed • after 42 weeks, placenta begins to degenerate See Table 29.2, p. 1138
Development of Integumentary System (Ch. 5) • Pp. 165-168 • epidermis and dermis developed by 4th month • epidermal derivatives grow down into dermis • lanugo present from 20 weeks • vellus hairs present by 7th month http://www.uoguelph.ca/zoology/devobio/210labs/ecto5.html
Development of Skeletal System • Ch. 6; P. 181 • begins by 8th week • primary ossification completed by birth • secondary ossification continues to early adulthood http://www.uoguelph.ca/zoology/devobio/210labs/meso2.html#osteo
Development of Skeletal System • endochondral ossification – in hyaline cartilage models of most bones other than cranial bones and clavicles • intramembranous ossification – in flat bones of cranium and clavicles http://www.uoguelph.ca/zoology/devobio/210labs/meso2.html#osteo
Development of Skeletal System • fontanels – unossified membranes in skull at birth; allow head to change shape slightly for easier birth http://www.bio.psu.edu/faculty/strauss/anatomy/skel/fetal.htm
Development of Spinal Curvatures • primary curvatures – thoracic and sacral – present at birth • secondary curvatures – cervical and lumbar – develop as infant lifts head and stands, respectively http://www.csu.edu.au/faculty/arts/humss/bioethic/abort1.htm
Development of Nervous System • Ch. 11; pp. 429-430, 463-464 • develops from “neural ectoderm” • neural crest cells (adjacent to tube) give rise to sensory neurons • neural tube cells give rise to interneurons and motor neurons http://www.angelfire.com/mb/jessicasjourney/info.html Fig. 12.2, p. 430
Development of Nervous System • eyes develop as outgrowth of diencephalon • brain and spinal cord develop from neural tube • brain regions represent enlargements of anterior tube • ventricles develop from openings in neural tube • anencephaly – failure of cerebrum and part of brain stem to develop Fig. 12.4, p. 431
Development of Nervous System • spinal cord develops from middle and posterior portions of tube • spina bifida • incomplete fusion of vertebral arches, usually in lumbrosacral region • up to 70% of cases associated with inadequate folate levels in mother • some cases associated with mother’s exposure to high levels of UV radiation [DISCOVER Vol. 22 No. 2 (February 2001)] http://www.abbottdiagnostics.com/medical_conditions/fertility_pregnancy/afp.htm
Development of Endocrine System • complex development including all three germ layers • two glands in particular develop from two different layers • pituitary • adrenal http://anatomy.med.unsw.edu.au/cbl/embryo/Notes/endocrine9.htm
Development of Pituitary Gland • adenohypophysis (anterior) develops from endoderm (roof of primitive mouth) • neurohypophysis (posterior) develops from neural ectoderm as extension of diencephalon (hypothalamus) http://www.teaching-biomed.man.ac.uk/histology/T270.HTML See also http://anatomy.med.unsw.edu.au/cbl/embryo/Notes/endocrine7.htm
Development of Adrenal Gland • cortex develops from mesoderm • medulla develops from neural ectoderm http://sprojects.mmi.mcgill.ca/embryology/ug/Adrenal_Stuff/Normal/zones.html
Development of Circulatory System • Blood – bone marrow, yolk sac • Heart – thoracic cavity • Blood vessels – start in yolk sac
Development of Blood • develops in yolk sac, liver, spleen, bone marrow of fetus • fetal hemoglobin (HbF) has a greater affinity for O2 than adult hemoglobin does http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Blood/Images/bma10he.jpg http://www.smbs.buffalo.edu/bch/faculty/garrett_sinha.html
Development of Heart • begins as 2 tubes that fuse by 4th week • begins pumping in 1st month (4th week) • foramen ovale allows blood to flow from right to left atrium • moves oxygenated blood more quickly into general circulation • partially by-passes developing lungs Fig. 19.24, p. 709
Fetal Circulation • umbilical arteries – carry partially oxygenated blood to placenta • umbilical vein – returns oxygenated blood from placenta to fetal liver • ductus venosus – shunt through liver connecting umbilical vein to inferior vena cava • ductus arteriosus – connects pulmonary trunk to aorta Fig. 29.13, p. 1136
Development of Respiratory System • develops as buds from throat • surfactant production begins in week 24 • not produced in sufficient quantities until about weeks 32-35 • infant respiratory distress syndrome Fig. 23.28, p. 877
Development of Digestive System • epithelium develops from endoderm; muscle develops from mesoderm • glands develop as buds from tube Fig. 24.37, p. 938
Development of Urinary System • kidneys development begins in 4th week, completed by week 9 Fig. 26.21, p. 1035
Development of Reproductive System • ovaries & testes develop in abdominal cavity • first 6 weeks embryonic reproductive organs are “bipotential” • differentiation begins during week 7-8 under influence of testosterone • testes descend into scrotum during 7th month Fig. 28.24, p. 1106; Fig. 28.25, p. 1108
Parturition (Birth): Stages of Labor • dilation stage – cervix dilates to ~ 10 cm (4”) • expulsion stage – delivery of fetus • placental stage – delivery of placenta Fig. 29.17, p. 1142
Hormonal Control of Labor • Estrogen from ovaries induces myometrium to make more oxytocin receptors • Oxytocin from posterior pituitary (made by hypothalamus) stimulates: • Contraction of uterus • Production of prostaglandins • Stimulates contraction of uterus • Stimulates oxytocin secretion • Positive feedback cycle continues until delivery of placenta (breast feeding causes stimulation of oxytocin secretion and helps return uterus to prepregnancy size) Fig. 29.16, p. 1141
Hormonal Control of Lactation • Stimulation of pressure receptors (pressoceptors) in breast sends sensory impulses to hypothalamus • Hypothalamus stimulates posterior pituitary to release oxytocin • Oxytocin stimulates release of milk from breast • Baby continues sucking until he/she is full • After baby stops sucking, hypothalamus is no longer stimulated. Fig. 29.18, p. 1144