Anatomy Physiology SIXTH EDITION Lecture 29 Development and

Anatomy & Physiology SIXTH EDITION Lecture 29, Development and Inheritance Lecturer: Dr. Barjis Room: P 313 Phone: (718) 260 -5285 E-Mail: ibarjis@citytech. cuny. edu Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings Frederic H. Martini Fundamentals of

Learning Objectives • Explain the relationship between differentiation and development and specify the various stages of development • Describe the process of fertilization • List the three prenatal periods and describe the major events associated with each • Discuss the importance of the placenta as an endocrine organ

Learning Objectives • Discuss the structural and functional changes in the uterus during gestation • List and discuss the events that occur during labor and delivery • Relate basic principles of genetics to the inheritance of human traits

Differentiation and development • Development involves: • 1) Cell division and differentiation • Differentiation is the creation of different types of cells • 2) changes in anatomical structures • Anatomical changes include gradual modification of physical and physiological characteristics • Development begins at fertilization

Stages of development • Development can be divided into: Prenatal and postnatal development • Prenatal development begins at fertilization and ends with birth • Prenatal development includes: • Embryological development • Changes occurring during the first two months after fertilization • Fetal development • Begins at the start of the ninth week and continues until birth • Postnatal development • Commences at birth and continues to maturity

Fertilization (conception) • Fertilization is fusion of two haploid gametes (egg and sperm) each with 23 chromosome to produce a zygote that contains 46 chromosomes • Fertilization occurs in the uterine tubes • Within a day of ovulation • Spermatozoa cannot fertilize an ovum until after capacitation

Fertilization

Fertilization Steps • Step 1 Ovulation • At ovulation the oocyte is in metaphase of meiosis II • Both the occyte and the polar body is surrounded by corona radiate • Step 2 Fertilization • Oocyte is surrounded by the sperms • Acrosomal enzyme from several sperms creates gaps in corona radiata • One sperm makes contact with the oocyte membrane • Sperm and oocyte fused • The process of meiosis will complete

Fertilization

The Oocyte at Ovulation • Ovulation occurs before the oocyte is completely mature i. e. oocyte is ovulated before the process of meiosis is completed • Ovulated oocyte is in metaphase of meiosis II • If the egg is fertilized the process of meiosis will complete • If fertilization does not occur, the oocyte disintegrate without completing the process of meiosis • Oocyte is surrounded by the corona radiate • Spermatozoa release hyaluronidase and acrosin • Enzymes required to penetrate corona radiate • Single spermatozoan contacts oocyte, fertilization begins • Oocyte activation • Polyspermy prevented by membrane depolarization and cortical reaction

The Stages of Prenatal Development Embryonic and Fetal Periods • Induction • During prenatal development differences in cytoplasmic composition trigger changes in genetic activity • Gestation periods • The gestation period is divided into three integrated trimesters

The First Trimester • The first trimester is the period of embryological and early fetal development • Four processes occur during the first trimeter • 1) Cleavage • 2) Implantation • 3) Placentation • 4) Embryogenesis

The First Trimester Cleavage • Cleavage - cleavage is the first cell division • Zygote becomes a preembryo then a blastocyst • Blastocyte includes: • Trophoblast – outer layer of cells • Inner cell mass – cluster of cells at one end of blastocyst

Cleavage and Blastocyst Formation

The First Trimester Implantation and Placentation • Implantation • Attachment of blastocyst into the uterine endometrium • Occurs about 7 days after fertilization • Placentation • Blood vessels form around blastocyst and placenta develops • The placenta is a complex organ that permits exchange between the maternal and embryonic circulatory systems

Stages in Implantation Animation: Location of the Endometrium (see tutorial)

The First Trimester Embryogenesis • Formation of a viable embryo • This process establishes the foundations for all major organ systems • Gastrulation • Embryonic disc composed of germ layers • Endoderm • Mesoderm • Ectoderm

The Inner Cell Mass and Gastrulation

Germ layers • Gastrulation • By day 12 surface cells move toward the primitive streak • A third germ layer forms • The three germ layers are: • Ectoderm – superficial cells that did not migrate • Endoderm – cells facing the blastocoele • Mesoderm – migrating cells between ectoderm and endoderm

Extraembryonic Membranes • Four extraembryonic membranes: • Yolk sac • Amnion • Allantois • Chorion

Extraembryonic Membranes and Placenta Formation

Extraembryonic Membranes and Placenta Formation

Extraembryonic Membranes and Placenta Formation

Embryo Anatomy • Yolk sac • Important site of blood cell formation • Amnion • Encloses fluid that surrounds and cushions developing embryo • Allantois • Eventually becomes bladder • Chorion

A Three-Dimensional View of Placental Structure

Placentation • Chorionic villi extend into maternal tissue • Forms intricate branching network for maternal blood • Umbilical cord connects fetus to placenta

Hormones of the placenta • Trophoblast secretes hormones to maintain pregnancy • HCG • Estrogens • Progesterone • h. PL • Placental prolactin • Relaxin

Second and Third Trimesters • Second trimester • Organ systems increase in complexity • Third trimester • Many organ systems become fully functional • Fetus undergoes largest weight change • At end of gestation fetus and uterus push maternal organs out of position

The Second and Third Trimesters

Growth of the Uterus and Fetus

Growth of the Uterus and Fetus

Developing fetus totally dependent on maternal organs • Maternal adaptations include increased • Respiratory rate • Tidal volume • Blood volume • Nutrient and vitamin uptake • Glomerular filtration rate Animation: Anatomy comparison of pregnant and non-pregnant (see tutorial)

Structural and Functional Changes in the Uterus • Progesterone inhibits uterine muscle contraction • Opposed by estrogens, oxytocin and prostaglandins • Multiple factors interact to produce labor contractions in uterine wall

Factors Involved in the Initiation of Labor and Delivery

Labor and Delivery Goal of labor is parturition • Stages of labor • Dilation • The cervix dilates and fetus moves toward cervical canal • Expulsion • The cervix completes dilation and fetus emerges • Placental • Ejection of the placenta

The Stages of Labor

Other labor and delivery situations • Premature labor • True labor begins before fetus has completed normal development • Difficult deliveries • When the fetus faces the pubis rather than the sacrum • The legs or buttocks enter the vaginal canal first (breech births) • Multiple births • Twins, triplets, etc. • Dizygotic or monozygotic situations

Postnatal Development Postnatal life stages • Neonatal period • Infancy • Childhood • Adolescence • Maturity • Senescence begins at maturity and ends in death

The neonatal period • From birth to one month • Respiratory, circulatory, digestive and urinary systems adjust • Infant must thermoregulate • Maternal mammary glands secrete colostrum first few days • Milk production thereafter • Both secretions are released via the milk letdown reflex • Body proportions change during infancy and childhood

The Milk Let-Down Reflex

Growth and Changes in Body Form

Adolescence • Begins at puberty • The period of sexual maturation • Ends when growth is completed

Puberty marked by • Increased production of Gn. RH • Rapid increase in circulating FSH and LH • Ovaries and testes become sensitive to FSH / LH • Gamete production initiated • Sex hormones produced • Growth rate increases

Hormonal changes at puberty produce gender specific differences in system • Differences are retained throughout life • Adolescence continues until growth completed • Further changes occur when sex hormones decline • Menopause • Male climacteric

Senescence • Aging affects functional capabilities of all system

You should now be familiar with: • The relationship between differentiation and development, and the various stages of development • The process of fertilization • The three prenatal periods and describe the major events associated with each • The importance of the placenta as an endocrine organ

You should now be familiar with: • The structural and functional changes in the uterus during gestation • The events that occur during labor and delivery • The basic principles of genetics as they relate to the inheritance of human traits