1. Chapter 18 Lecture Outline
See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 18.1 Fertilization

3. Introduction
Fertilization – penetration of the ovum by one sperm
The zygote is formed when the genetic material of the ovum and sperm unite

4. Sperm and ovum anatomy Sperm Anatomy
Head – contains the nucleus of 23 chromosomes and very little cytoplasm; capped by the acrosome that contains digestive enzymes
Middle piece – contains energy-producing mitochondria
Tail (flagellum) – for swimming

5. Ovum anatomy Ovum contains cytoplasm, organelles , and 23 chromosomes
The plasma membrane is surrounded by the zona pellucida
The corona radiata surrounds the zona pellucida

6. Steps of Fertilization
Several sperm penetrate the corona radiata
Several sperm attempt to penetrate the zona pellucida
One sperm enters the ovum
Acrosome releases digestive enzymes
When a sperm binds to the ovum, their plasma membranes fuse and this sperm enters the ovum
Sperm and ovum nuclei fuse to produce the zygote

7. Prevention of polyspermy
Accidental entry of more than one sperm will halt development of the zygote
When the one sperm fuses to the ovum cell membrane, the membrane depolarizes
Release of cortical oocyte granules with lysosomal enzymes
Zona pellucida becomes impermeable to any other sperm

8. Fertilization

9. 18.2 Development

10. Processes of Development
Cleavage – rapid cell division (mitosis) with no size increase
Growth – size increase
Morphogenesis – shaping of the embryo and movement of cells
Differentiation – groups of cells take on different structures and functions

11. Extraembryonic membranes
Are not part of the embryo and fetus
Functions in humans:
Chorion – develops into the fetal half of the placenta
Yolk sac – first site of blood cell formation
Allantois – contains blood vessels that become the umbilical blood vessels
Amnion – contains fluid to cushion and protect the embryo

12. Extraembryonic membranes

13. Stages of Development
Human gestation of 280 days
Pre-embryonic development
Events of the first week
After fertilization, the zygote divides repeatedly (cleavage)
A morula becomes a blastocyst
Inner cell mass surrounded by the trophoblast; becomes the embryo
The trophoblast will become the chorion
Each cell has the genetic capability of becoming any tissue

14. Pre-embryonic development

15. Embryonic development
Second week
Embryo usually begins the process of implantation
If implantation is successful, the female is clinically pregnant
An ectopic pregnancy occurs if the embryo implants in the uterine tube
The trophoblast begins to secrete HCG
Acts like LH
Stimulates corpus luteum to secrete progesterone and the endometrium is maintained

16. Second week, cont The inner cell mass separates from the trophoblast
The yolk sac and amnion form
Gastrulation occurs
Inner cell mass becomes the embryonic disk
Primary germ layers (ectoderm, mesoderm, and endoderm) form

17. Embryonic germ layers

18. Third week
The nervous system becomes evident
Neural plate
Neural groove
Neural folds
Neural tube forms – later becomes the brain and spinal cord
If the neural tube fails to close completely, a neural tube defect will result – spina bifida or anencephaly

19. Third week, cont Development of the heart begins
Begins with right and left heart tubes
Tubes fuse and begin to pump blood
Arteries and veins grow from the heart tube
Tube twists so that the vessels are all anterior

20. Embryonic development

21. Fourth and fifth weeks
Exchange of gases, nutrients, and wastes can take place across the capillary network within the chorionic villi
Blood vessels of the allantois become the umbilical blood vessels
The umbilical cord completes formation
Limb buds appear
The head enlarges and the sense organs become more prominent

22. Sixth through eight weeks
Embryo is easily recognized as human
The head achieves its normal relationship with the body with the development of the neck
Nervous system has developed enough to allow reflex actions
Embryo is about 1.5 inches long
All organ systems have formed

23. Human embryo at 5 weeks

24. Placenta
Usually fully functional by the end of the embryonic period
Two portions:
Fetal portion composed of chorionic tissue
Maternal portion composed of uterine tissue
Placental membrane – epithelium of embryonic capillary and epithelium of a chorionic villus
Placenta supplies the fetus with its nutritional and excretory needs – digestive system, lungs, and kidneys do not function

25. Placenta, cont
The umbilical cord transports fetal blood to and from the placenta
Two umbilical arteries carry fetal blood to the placenta for gas and waste removal
One umbilical veins carries oxygen and nutrients from the placenta to the fetus
The placenta begins to produce progesterone and estrogen to maintain the pregnancy

26. The placenta

27. Fetal development
Third and fourth months
Head growth slows and the rest of the body increases in length
Epidermal refinements appear – fingernails, nipples, eyelashes, eyebrows, and hair
Cartilage begins to be replaced by bone
Possible to distinguish males from females
During the fourth month, the fetal heartbeat can be auscultated
About 6 inches long and weighs 6 oz.

28. Fetal development, cont
Fifth through seventh months
Fetal movement can be felt by the mother
Lanugo and vernix caseosa
Eyelids are fully open
About 12 inches long and weighs 3 lbs.
Eighth through ninth months
Fetus usually rotates so that the head is pointed towards the cervix
Weight gain due to an accumulation of fat
About 20½ inches long and weighs 7½ lbs.

29. Human Development Summary

30. Five to seven month fetus

31. Development of male and female sex organs
Gender is determined at the moment of fertilization
At six weeks, both males and females have Wolffian and Müllerian ducts
Gonads start developing in the seventh week
Genes on the Y chromosome cause the production of testosterone
Causes testes to develop from indifferent tissue
Stimulates the Wolffian ducts to become male genital ducts and enter the urethra
Testes secrete anti-Müllerian hormone that causes the Müllerian ducts to regress

32. Development of male and female sex organs, cont.
If there is no Y chromosome present
Ovaries develop instead of testes
Müllerian ducts develop into the uterus and uterine tubes and Wolffian ducts regress
At 14 weeks, both ovaries and testes are in the abdominal cavity
During the last trimester, ovaries and testes descend into the pelvic cavity
Testes then descend into the scrotal sacs via the inguinal canal

33. External genitalia
At six weeks – a small bud of indifferent tissue is seen between the legs
At nine weeks – urogenital groove appears
By fourteen weeks
The groove has disappeared in males and the scrotum has formed
In females the groove becomes the vaginal opening and the labia majora and labia minora form

34. Male & female reproductive organs

35. 18.3 Birth

36. Introduction
Labor is marked by regular, long-lasting contractions
A positive feedback mechanism causes the onset and continuation of labor
Stretching of cervix stimulates oxytocin release
Oxytocin stimulates the uterine muscles
Uterine contractions push the fetus forward causing the cervix to stretch more
Expulsion of the mucous plug is usually the first sign that birth is imminent

37. Stages of Birth (parturition)
Effacement
Amniotic membrane will probably ruptured if it has not already
Ends when the cervix has dilated completely (about 10 cm)

38. Stages of Birth, cont
Stage 2
Uterine contractions occur every 1-2 minutes and last about 1 minute each
Baby’s head descends into the vagina
The baby is delivered
Stage 3
The placenta is delivered
About 15 minutes after delivery of the baby, the placenta is dislodged from the uterus and expelled into the vagina

39. Stages of parturition

40. Effects of Pregnancy on the Mother
Early pregnancy
Nausea and vomiting
Loss of appetite and fatigue
Then weight gain due to:
Breast and uterine enlargement
Weight of the fetus
Amount of amniotic fluid
Size of the placenta
Increase in her own body fluid
Storage of proteins, fats, and minerals

41. 3. Physiological changes due to placental hormones
Progesterone
Relax smooth muscle
Reduced uterine motility
Reduced maternal immune response to fetus
Estrogen
Increased uterine blood flow
Increased renin-angiotensin-aldosterone activity
Increased protein biosynthesis by liver
Peptide hormone – increased insulin resistance

42. Other maternal changes
Increase in pulmonary values
Stress incontinence
Edema and varicose veins
Possibility of pregnancy-induced diabetes
Striae gravidarum (stretch marks)