1. Anatomy and Physiology
Biology 2401
Chapter-29
Development and Inheritance

2. An Introduction to Development and Inheritance
Gradual modification of anatomical structures and physiological characteristics from fertilization to maturity
Inheritance
Transfer of genetic material from generation to generation

3. This chapter on the development includes:
Fertilization – union of an egg and sperm Gestation - fertilization  birth; 38 weeks of pregnancy Prenatal period – time before birth Embryo development (first 8 weeks) Fetal development (week 9 till birth) Neonatal period – first 42 days after birth Labor - events that lead to birthing Parturition - birthing process Obstetrics: branch of medicine that deals with pregnancy, labor and delivery

4. Fertilization Fertilization Capacitation
Occurs in uterine tube within a day after ovulation
Secondary oocyte travels a few centimeters
Spermatozoa must cover distance between vagina and ampulla
Capacitation
Must occur before spermatozoa can fertilize secondary oocyte
Contact with secretions of seminal glands
Exposure to conditions in female reproductive tract

5. Fertilization Sperms:
They have Head – with haploid nucleus (22X or 22Y) and acrosome Midpiece – with mitochondria for producing energy (ATP) Flagella – tail for swiming
About million sperms are deposited in the vagina
They undergo changes and develop the capacity to fertilize (capacitation)
They move through the uterus and uterine tube with the help of their flagella and muscular contractions of the uterus.

6. Fertilization Secondary oocyte:
It is a haploid cell (22X) that is released after meiosis I (ovulation)
It has a glycoprotein layer – zona pellucida
It has multiple layers of follicular/granulosa cells – corona radiata
It moves into the uterine tube with the help of peristalsis and ciliated epithelial cells
It remains active for about hours after ovulation

7. Fertilization Sperms penetrate corona radiata layer
Acrosomal enzymes digest their way through zona pellucida
One sperm fuses with the secondary oocyte (syngamy)
Oocyte membrane depolarizes
Intracellular release of calcium causes zona pellucida to harden (cortical reaction)
Blocks fusion of any other sperm (polyspermy is prevented)
Syngamy triggers secondary oocyte to undergo meiosis II
Ovum and second polar body are formed
Male pronucleus and female pronucleus fuse (fertilization)
Diploid zygote (44XX or 44XY) is formed

8. Gestation First Trimester Second Trimester Third Trimester
Period of embryological and early fetal development
Rudiments of all major organ systems appear
Second Trimester
Development of organs and organ systems
Body shape and proportions change
Third Trimester
Rapid fetal growth and deposition of adipose tissue
Most major organ systems are fully functional

9. The First Trimester First Trimester Includes four major stages
Cleavage
Implantation
Placentation
Embryogenesis

10. Early Embryonic/Cleavage Divisions
Zygote (surrounded by zona pellucida)
 divides by mitosis (cleavage divisions)
2 identical blastomeres are formed
4 blastomeres are formed
by the 4th day, a ball of genetically identical blastomeres is formed – an embryo stage called the morula
blastomeres secrete a fluid in the center
By the 5th day, a hollow ball of cells is formed Blastocyst: - trophoblast cells are the peripheral cells which will form the future embryonic membranes - inner cell mass or embryoblast which will form the future embryo - blastocele is the internal fluid-filled cavity

11. Location of Events
Syngamy takes place in the oviduct
Fertilization takes place in the oviduct
Early embryonic/cleavage divisions take place in the oviduct while the embryo is moving towards the uterus
Blastocyst reaches the uterus by the 5th day
Blastocyst implants in the uterus
Ectopic pregnancy: development of an embryo or fetus outside the uterine cavity : mostly occur in the uterine tube

12. Twins Fraternal twins (dizygotic – from two zygotes)
Release of 2 oocytes  fertilized by 2 sperms  two zygotes are formed  two embryos
genetically as different as any 2 siblings
Identical twins (monozygotic – from one zygote)
Release of 1 oocyte  fertilized by 1 sperm  one zygote is formed  zygote divides to form 2 blastomeres  blastomeres separate to independently develop into 2 embryos
genetically identical & always the same sex
Conjoined twins
If the blastomeres do not completely separate  newborns remain attached to different extents  share some body structures

13. Implantation – Attachment of the Embryo to the Uterus
Trophoblast cells: - Secrete enzymes to digest the uterus wall  the entire embryo slowly becomes embedded into the endometrium of the uterus
- Secrete human chorionic gonadotropin (hCG) that maintains the uterine lining

14. Embryo Development Gastrulation
Cells of embryonic disc produce 3 distinct layers
Endoderm  epithelial lining of GI & respiratory
Mesoderm  muscle, bone & other connective tissues
Ectoderm  epidermis of skin & nervous system

15. The First Trimester Formation of the Extraembryonic Membranes
Support embryological and fetal development
Yolk sac
Amnion
Allantois
Chorion

16. Figure 29-5 Extraembryonic Membranes and Placenta Formation
The embryonic disc bulges into the amniotic cavity at the
head fold. The allantois, an endodermal extension
surrounded by mesoderm, extends toward the trophoblast.
Week 3
Amniotic cavity
(containing
amniotic fluid)
Allantois
Head fold
of embryo
Syncytial
trophoblast
Chorion
Chorionic villi
of placenta
Yolk
sac 16

17. Placenta
Formed during 3rd month
Maternal & fetal blood vessels do not join  blood does not mix
Allows diffusion of O2, nutrients, wastes
Does not allow most microbes (exceptions)
Not a barrier to drugs such as alcohol
Secretes several hormones to support pregnancy
Detaches from the uterus at birth time (afterbirth)
Umbilical cord
2 arteries that carry deoxygenated blood to the maternal vessels
1 umbilical vein that carries oxygenated blood to the fetus
Has embryonic connective tissue
Cut at the time of delivery
Stub drops off in 2 weeks  leaving a scar (umbilicus)

18. The Endocrine Placenta
Synthesized by placenta and released into maternal bloodstream
Human chorionic gonadotropin (hCG)
Human placental lactogen (hPL)
Placental prolactin
Relaxin
Progesterone
Estrogens

19. The First Trimester Embryogenesis
Body of embryo begins to separate from embryonic disc
Body of embryo and internal organs start to form
Folding, differential growth of embryonic disc produces bulge that projects into amniotic cavity
Projections are head fold and tail fold
Organogenesis
Process of organ formation

20. The Second and Third Trimesters
Second Trimester
Fetus grows faster than surrounding placenta
Third Trimester
Most of the organ systems become ready
Growth rate starts to slow
Largest weight gain
Fetus and enlarged uterus displace many of mother’s abdominal organs

21. Fetal Development

22. Labor Parturition: giving birth
Labor: process of expelling the fetus : initiated by a decrease in progesterone levels and elevated levels of estrogens, prostaglandins, oxytocin, and relaxin : Uterine contraction forces fetal head into cervix (stretch)  nerve impulses reach hypothalamus  oxytocin is release  increased contractions  further stretching of cervix
True labor: uterine contractions occur at regular intervals  dilation of the cervix  “show” (discharge of blood-containing mucus from the cervical canal)
False labor: contractions and pain at irregular intervals : no cervical dilation

23. Stages of Labor
1. Dilation to 12 hours regular contractions of the uterus rupture of amniotic sac & dilation of cervix (10cm)
2. Expulsion minutes to several hours baby moves through birth canal
3. Placental minutes placenta (afterbirth) is expelled by uterine contractions constriction of blood vessels that were torn  reduce the possibility of hemorrhage
Cesarean section (C-section): incision through lower abdominal wall and uterus to deliver the baby

24. 29-7 Postnatal Life Duration of Life Stages
Neonatal Period: extends from birth to 1 month
Infancy: 1 month to 2 years of age
Childhood: 2 years until adolescence
Adolescence: period of sexual and physical maturation
Senescence: process of aging that begins at end of development (maturity)

25. Lactation Lactation: production & release of milk
During pregnancy  anterior pituitary secrets increased levels of prolactin  progesterone inhibits the effect of prolactin
After delivery  progesterone levels drop  prolactin stimulates milk production
Suckling  nerve impulses to hypothalamus  increased release of oxytocin  milk ejection reflex
If suckling stops, milk secretion stops
Colostrum: a cloudy fluid released by mammary gland during late pregnancy .
: contain antibodies that protect the infant.

26. Inheritance
Inheritance: passing of traits from one generation to another. Genetics: branch of biology that deals with inheritance. Genetic counselor: health care personnel that offers advice on genetic problems Human somatic cells: - diploid cells - 44 autosomes + 2 sex chromosomes - Males: 44XY - Females: 44XX

27. Determination of Sex

28. Inheritance

29. Inherited Disorders

30. Testing for Genetic Disorders
Ultrasound: - Transducer emits high-frequency sound waves  reflected sound waves are converted to on-screen image called sonogram Amniocentesis: - usually done at weeks gestation - amniotic fluid around the fetus is extracted  fetal cells are examined for genetic defects Chorionic Villus Sampling: - withdrawal of chorionic villi for chromosomal analysis