1. Biology, 9th ed,Sylvia Mader
Chapter 09
The Cell Cycle

2. 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

3. 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

4. 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

5. 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

6. Fertilization

7. 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

8. The First Trimester Cleavage
Cleavage - cleavage is the first cell division
The first cleavage occurs at 32 hours
Second cleavage occurs at 60 hour
Third cleavage occurs at 72 hours
Several divisions later the embryo becomes a solid mass of cells known as morula
Molurla becomes a blastocyst (also known as blastula)
Blastocyte includes:
Trophoblast – outer layer of cells that give rise to the chorion and placenta
Inner cell mass – cluster of cells at one end of blastocyst
Blastocoel – hallow fluid-filled inner cavity

9. Cleavage and Blastocyst Formation

10. The First Trimester Implantation and Placentation Implantation
Attachment of blastocyst into the uterine endometrium
The uterus is prepared for implantation by the hormone progesterone (see reproductive and endocrine lectures)
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

11. The First Trimester Gastrulation
After implantation, cell migration transforms blastula (single cell layer) to gastrula (3 layered structure)
Gastrulation is the generation of 3 distinct germ (cell) layers
Endoderm
Mesoderm
Ectoderm

12. The Inner Cell Mass and Gastrulation

13. Germ layers Gastrulation The three germ layers are:
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
Will become integument (epidermis, hair, nail, epithelium, nose, mouth and anal canal), lense of eye, ear and nervous system
Endoderm – cells facing the blastocoele
Will become liver, pancreas, thyroid, bladder, lungs, epithelium of digestive and respiratory systems.
Mesoderm – migrating cells between ectoderm and endoderm
Will become musculskeletal system, circulatory system, excretory system, gonads, connective tissue of digestive and respiratory systems, smooth and cardiac muscle.

14. Germ layers

15. Germ layers
Organs and glands are consist of or include more than one germ layer
Adrenal cortex is derived from mesoderm
Adrenal medulla is derived from ectoderm

16. Neurulation
By the end of gastrulation, regions of the germ layers begin to develop into a rudimentary nervous system
Neurulation is the process of rudimentary nervous system formation
Notochord – a rod of mesodermal cells that develop along the axis.
Notochord cause ectoderm to bend inward and form a groove
Ectoderms grow on either side of the groove and then fuse together to form a neural tube
Neural tube becomes central nervous system (Brain and spinal cord)

17. Fetal Respiration
Growing fetus receives oxygen and eliminates carbon dioxide through a specialized circulatory system
The two components of this system are:
Placenta
Umbilical cord
Placenta and umbilical cord are outgrowths of the 4 extra-embryonic membrane (Amnion, Chorion, Allantois and yolk sac) that are formed during the development
Chorion extends villi into uterine wall and these villi become closely associated with endometrial cells
Chorionic villi forms intricate branching network for maternal blood
Umbilical cord connects fetus to placenta

18. Extraembryonic Membranes
Four extraembryonic membranes:
Yolk sac
Amnion
Allantois
Chorion

19. Extraembryonic Membranes and Placenta Formation

20. Extraembryonic Membranes and Placenta Formation

21. Extraembryonic Membranes and Placenta Formation

22. Embryo Anatomy Yolk sac Amnion Allantois Chorion
Important site of blood cell formation
Amnion
Encloses fluid that surrounds and cushions developing embryo
Allantois
Eventually becomes bladder
Chorion
Placenta formation begins for chorion
Chorion is a membrane that completely surrounds amnion

23. A Three-Dimensional View of Placental Structure

24. Hormones of the placenta
Trophoblast secretes hormones to maintain pregnancy
Human chorionic gonadotropin (hCG) – Prevents disintegration of corpus luteum
At the ovaries corpus luteum produce progesterone
Estrogens – in addition to having role in secondary sexual characteristics it is involved in the thickening of the endometrium
Progesterone - enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus
Human Placental Lactogen (hPL) - decreases maternal insulin sensitivity, and therefore raises maternal blood glucose levels, whilst decreasing maternal glucose utilization, which helps ensure adequate fetal nutrition
Placental prolactin- stimulates the mammary glands to produce milk
Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands of the breasts and increases the production of milk. However, the high levels of progesterone during pregnancy stop ejection of milk.
After childbirth progesterone decreases and milk ejection initiates.
Relaxin

25. 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

26. The Second and Third Trimesters

27. Growth of the Uterus and Fetus

28. Growth of the Uterus and Fetus

29. Developing fetus totally dependent on maternal organs
Maternal adaptations include increased
Respiratory rate
Tidal volume
Blood volume
Nutrient and vitamin uptake
Glomerular filtration rate

30. 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

31. Factors Involved in the Initiation of Labor and Delivery

32. 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