1. BIO 211 Lecture Instructor: Dr. Gollwitzer
Chapter 29: Development
BIO 211 Lecture
Instructor: Dr. Gollwitzer

2. Today in class we will: Define and describe development
Trace the general processes from ovulation through fertilization and formation of a zygote
List the stages of development
List the 3 stages of gestation and briefly describe the major events associated with each
Distinguish between embryo and fetus
Discuss the two major roles of the placenta
Discuss the basic structural and functional changes in the uterus during gestation
Briefly describe the events that occur during labor and delivery
Describe lactation and milk let-down reflex

3. Development Begins with fertilization (conception) =
When male and female gametes (sperm and egg) unite to form single-cell zygote
Occurs in uterine tube hr after ovulation
Is the gradual modification from fertilization to maturity of:
Anatomical structures
Physiological characteristics

4. Fertilization
Figure 29–1a, b

5. Amphimixis Fusion of female and male pronuclei Moment of conception
Cell becomes zygote (46 chromosomes)
Fertilization complete

6. Stages of Development Prenatal – before birth Postnatal – after birth
Embryological development
Occurs during first 2 mo after fertilization
Organs established
Fetal development
Begins at 9th wk and continues to birth
Organs develop
Postnatal – after birth
Neonate = newborn

7. Gestation Time spent in prenatal development
Consists of 3 trimesters, each 3 months long
First trimester
Second trimester
Third trimester

8. First Trimester Cell cleavage (division) and blastocyst formation
Blastocyst implantation = burrowing into uterine wall
Placentation = formation of placenta
Temporary structure in uterine wall
Permits diffusion between fetal and maternal circulatory systems
Embryogenesis – all organ systems begin to be established; but nonfunctional
Embryo = organism in the developmental stage beginning at fertilization and ending at the start of the third developmental month (weeks 1 – 8)

9. First Trimester Most dangerous period in prenatal life
Only 40% of conceptions produce embryos that survive past first trimester

10. Cleavage and Blastocyst Formation
Figure 29–2

11. Stages in Implantation
Figure 29–3

12. Placenta
Complex organ that permits exchange between maternal and embryonic circulatory systems
Supports fetus in second and third trimesters
Stops functioning and is ejected from uterus after birth

13. Extraembryonic Membranes and Placenta Formation
Figure 29–5 (1, 2 of 5)

14. Extraembryonic Membranes and Placenta Formation
Figure 29–5 (3, 4 of 5)

15. Extraembryonic Membranes and Placenta Formation
Figure 29–5 (5 of 5)

16. First Trimester
Figure 29–7a, b

17. First Trimester
Figure 29–7c, d

18. First Trimester: hCG hCG = human chorionic gonadotropin
Produced by placenta
Appears in maternal bloodstream soon after implantation
Used as pregnancy test/kit
Maintains CL for 3-4 months
So CL  P (until placenta takes over P production)

19. Second Trimester
Fetal stage = development of all organ systems (organogenesis)
Rapid growth of fetus
Fetus = organism in the developmental stage lasting from the start of the third developmental month to delivery (week 9 through delivery)
Body proportions change
Progesterone levels increase

20. Third Trimester Organ systems fully functional Fetal growth rate slows
Largest weight gain

21. Growth of Fetus and Uterus
Figure 29–9a, b

22. Growth of Fetus and Uterus
Figure 29–9c, d

23. Overview of Prenatal Development
Table 29–2 (1 of 4)

24. Overview of Prenatal Development
Table 29–2 (3 of 4)

25. Overview of Prenatal Development
Table 29–2 (2 of 4)

26. Overview of Prenatal Development
Table 29–2 (4 of 4)

27. Third Trimester Hormones
P (placental)
Until 3rd trimester, “calms” myometrium so no contractions
E (placental)
Increases  myometrial contractions
Sensitizes uterus to oxytocin (maternal and fetal)  prostaglandins (PGs)  initiate labor

28. Third Trimester Hormones
Human placental lactogen (hPL)
Helps prepare mammary glands for milk production
Effects on other tissues comparable to GH
Prolactin (placental)
Helps convert mammary glands to active status
Relaxin (CL and placental) 
Increased flexibility of pubic symphysis  pelvis expands
 Dilation of uterine cervix  so fetus can enter vagina

29. Factors Involved in Initiation of Labor and Delivery
Figure 29–10

30. Labor False True Premature Occasional spasms in uterine musculature
Contractions not regular or persistent
True
Results from biochemical and mechanical factors
Continues due to positive feedback
Premature
When labor begins before fetal development complete; survival related to BW

31. Labor and Delivery Goal: parturition = forcible expulsion of fetus
Stages of labor
Dilation
Explusion
Placental

32. Labor and Delivery Dilation stage Begins with onset of true labor
Cervix dilates
Fetus moves toward cervical canal
Frequency of contractions increases
Amniochorionic membrane ruptures (“water breaks”)

33. Stages of Labor
Figure 29–11 (1,2 of 4)

34. Labor and Delivery Expulsion stage Cervix completely dilated
Maximum intensity of contractions
Continues until fetus emerges from vagina = delivery/birth

35. Labor and Delivery Placental stage
Uterine contractions tear connection between endometrium and placenta
Placenta (afterbirth) ejected
Accompanied by loss of blood, usually tolerated without difficulty

36. Stages of Labor
Figure 29–11 (3,4 of 4)

37. Milk Let-Down Reflex
Figure 29–12