1. Chapter 17 Development and Aging
Mader, Sylvia S. Human Biology. 13th Edition. McGraw-Hill, 2014.

2. Points to Ponder What is fertilization?
Describe the steps in fertilization.
What is cleavage? Growth? Morphogenesis? Differentiation?
What are the 4 extraembryonic membranes?
Be familiar with what happens during pre-embryonic development, fetal development and development after birth.
Follow the path of fetal circulation.
What determines the sex of an individual? Be sure to understand the 3 hormones involved and the SRY gene.
What are two conditions in which sex determination is ambiguous and 2 conditions in which there are abnormal development of the sex organs?
What are the 3 stages of birth?
What can you do to help prevent birth defects?
What are the 3 hypotheses of aging?
What is the effect of aging on the body?

3. 17.1 Fertilization
Fertilization
Fertilization is the union of the sperm and egg to form zygote
Egg is surrounded by an outer matrix called the zona of pellucida
Outside this matrix has a few layers of follicular cells collectively called the corona radiata
These cells had nourished oocyte within the ovarian follicle

4. Steps of Fertilization
1. Several sperm penetrate the corona radiata
2. Acrosomal enzymes digests a portion of the zona pellucida
3. The sperm binds to and fuses with the egg’s plasma membrane
4. Sperm nucleus enters the egg
5. Sperm and egg nucleus will fuse

5. 17.1 Fertilization
Fertilization

6. What prevents more than one sperm from entering?
17.1 Fertilization
What prevents more than one sperm from entering?
The egg’s plasma membrane changes to prevent other sperm from binding
depolarizes
Vesicles within the egg
release enzymes that cause the zona pellucida to become impenetrable and sperm cannot bind

7. What are the main processes of development?
17.2 Pre-embryonic and embryonic development
What are the main processes of development?
Cleavage
cells undergo division (2, 4, 8 etc) without the embryo increasing in size
Growth
cells undergo division as well as increase in size
Morphogenesis
the embryo begins to take shape as cells migrate
Differentiation
when cells take on specific structure and function (the nervous system is the first visible system)

8. Functions of the extraembryonic membranes (Outside of the embryo)
Chorion: Gas Exchange
fetal half of the placenta, the organ that provides the embryo with nourishment and gets rid of wastes
Allantois: Collects Nitrogenous Wastes
gives rise to the bladder
blood vessels of umbilical cord carry blood to/from the fetus
Yolk sac: Provides Nourishment
contains many blood vessels
blood cells first form
Amnion: Provides Protection
contains amniotic fluid that cushions and protects the embryo

9. Extraembryonic membranes
17.2 Pre-embryonic and embryonic development
Extraembryonic membranes

10. What are the stages of development?
Pre-embryonic development
- 1st week of development after fertilization
Embryonic development
- 2nd week after fertilization until the end of the 2nd month
Fetal development
- the 3rd through the 9th months of development
Development after birth
- stages of life including infancy, childhood, adolescence and adulthood

11. 1. Pre-embryonic development
Cleavage
cell division that increases the number of cells
Morula
compact ball of embryonic cells that becomes a blastocyte
Early blastocyst
inner cell mass  becomes the embryo
All inner cells have capabilty to become any cell type
Inner mass covered by layer of cells  becomes chorion
Implantation
embryo embeds into the uterus around day 6

13. 2. Embryonic development: week 2
Pregnancy begins after implantation
Human chorionic gonadotropin (HCG) secreted
maintain corpus luteum and endometrium
HCG is the basis for a pregnancy test
The inner cell mass detaches itself and becomes the embryonic disk
goes through gastrulation to become 3 primary germ layers

15. 3 Primary Germ Layers Ectoderm: outer layer Mesoderm: middle layer
Epidermis of skin
Epithelial lining of oral cavity and rectum
Nervous system
Mesoderm: middle layer
Skeleton, muscular system, dermis of skin
Cardiovascular system, urinary system
Reproductive system, out layers of respiratory and digestive system
Endoderm: inner layer
Epithelial lining of digestive tract and respiratory tract and associated glands
Epithelial lining of urinary bladder

16. 2. Embryonic development: week 3
17.2 Pre-embryonic and embryonic development
2. Embryonic development: week 3
Nervous system begins to develop
The posterior neural tube will become the spinal cord and brain
Development of the heart begins

17. 2. Embryonic development: weeks 4 & 5
17.2 Pre-embryonic and embryonic development
2. Embryonic development: weeks 4 & 5
4th week:
Chorionic villi form
Umbilical cord forms
Limb buds form (later develop into legs and arms)
Hands and feet are apparent
5th week:
Head enlarges
Eyes, ears and nose become prominent

18. 2. Embryonic development: weeks 4 & 5

19. 17.2 Pre-embryonic and embryonic development
The embryo at week 5

20. 2. Embryonic development: weeks 6-8
17.2 Pre-embryonic and embryonic development
2. Embryonic development: weeks 6-8
Embryo begins to look like a human being
Reflex actions occur
Startle response to touch
All organ systems have been established
38mm by the end of this period and weight ~ the same as an aspirin tablet

21. 3. Fetal development Placenta
Source of progesterone and estrogen during pregnancy
Functions of hormones:
Negative feedback on hypothalamus and anterior pituitary prevent new follicles from maturing
Maintain endometrium so menstruation does not occur
Gasses and wastes are exchanged between the maternal and fetal sides of the placenta via diffusion

22. Fetal circulation Umbilical artery Umbilical vein
Carries O2-poor blood to the placenta towards the maternal side
Umbilical vein
Carries O2-rich blood, rich in nutrients from the placenta to the fetus
O2-rich and O2-poor blood mix in the heart of the fetus
Path of O2-rich blood
Umbilical vein Liver  join venous duct  merge with inferior vena cava  return blood to right atrium  enter the heart  shunted to left atrium via oval opening  left ventricle pump blood into the aorta
Path of O2-poor blood
Enter right atrium  pumped into pulmonary trunk  joins aorta via arterial duct

23. Fetal circulation
Note: Fetal and maternal blood do not mix because exchange of materials between
the two occurs at the chorionic villi.

24. 3. Fetal development: months 3 & 4
Hair develops
The head slows in growth so that the body size can catch up
Cartilage begins to be replaced by bone
Fontanels “soft spots” remain in the skull for birthing and brain growth
Able to distinguish female from male (month 3)
Presence of SRY gene on Y chromosome leads to the development of testes and male genital
Lack of SYR gene allows ovaries and female genital to form
Can hear heartbeat with the stethoscope (month 4)
By the end of this period the fetus is ~6 inches and ~6 ounces

25. 3. Fetal development: months 5-7
Fetal movement can be felt by the mother
Fetus is in fetal position
Eyelids are fully open
Fetus size has increased to ~12 inches and ~3 pounds

26. 3. Fetal development: months 8 & 9
Weight gain is about a pound per week
Fetus rotates so that the head is pointed towards the cervix
At the end of fetal development the fetus weighs ~7.5 pounds and ~20.5 inches

27. Development of the sex organs
Sex of an individual is determined at conception
(XX is female and XY is male)
- Six weeks: both male and females have the same types of ducts
If the SRY (the sex determining region on the Y
chromosome) gene is present
at ~ week 6 testes develop and testosterone is produced
1. Testosterone stimulates Wolffian ducts to become male genital ducts
2. Wolffian ducts enter the urethra, which belongs to both the urinary and reproductive systems in male
3. Anti-mullerian hormone causes Mullerian ducts to regress

28. Development of the sex organs
If the SRY (the sex determining region on
the Y chromosome) gene is absent
1. Ovaries develop instead of testes
2. Wolffian ducts regress
3. Estrogen from ovaries causes Mullerian ducts to develop into the uterus and oviducts

29. Development of the sex organs

30. Development of the sex organs
17.3 Fetal development
Development of the sex organs
At 14 weeks primitive testes and ovaries with gametes are already developing
The development of the external organs is dependent on the presence or absence of dihydrotestosterone (DHT) produced by the testes

31. Hormones produce by the Testes
Testosterone:
Stimulate development of epididymides, vasa deferentia, seminal vesicles, etc
Anti-Mullerian hormone:
prevents development of female structures
Dihydrotestosterone:
directs development of the urethra, prostate gland, penis and scrotum

32. Abnormal development of the sex organs
XY female syndrome
an individual develops into a female
piece of Y chromosome containing the SRY gene is missing
XX male syndrome
an individual develops into a male
same small piece of the Y containing the SRY gene is present on an X chromosome
SRY gene allows formation of the testes
Testes produce 3 important hormones involved in the development of the male genital

33. Ambiguous sex determination
17.3 Fetal development
Ambiguous sex determination
Results from the absence of testosterone, Anti-Mullerian hormone and/or DHT
Androgen insensitivity syndrome:
all hormones are made
testosterone receptors on cells are ineffective
individual has testes that do not descend and outwardly appear to be female
Male pseudo-hermaphroditism:
an individual appears female until puberty when anti-Mullerian hormone is produced but the testes never produce testosterone or DTH

34. What are the good and bad changes in the mother’s body?
Nausea and vomiting are common symptoms early on (morning sickness)
Some mothers report an overall increase in energy levels and sense of well-being
Acid reflux and constipation are common problems
There is an increase in vital capacity
Incontinence is not uncommon
The placenta produces peptide hormones that makes cells resistant to insulin so diabetes can result
Melanocyte activity increases in some areas

35. Pregnancy: Uterus Relaxes
Placenta produce progesterone which:
Decrease uterine motility by relaxing smooth muscle
Arteries Dilate  leads to low blood pressure
Stimulate renin-angiotension-aldosterone results in sodium and water retention
Increase in blood cells
Gastrointestinal effects of pregnancy
Heartburn: relaxation of esophageal sphincter
Constipation: caused by a decrease in intestinal tract motility

36. Pregnancy: Pulmonary Values Increase
Bronchial tubes relax
Increase vital capacity and tidal volume
Maternal oxygen level changes little, but blood carbon dioxide levels fall by 20%
creates concentration gradient favorable to flow of carbon dioxide from fetal blood to maternal blood at the placenta

37. Birth
True labor is characterized by uterine contraction that occur every minutes and last for at least 40 seconds
3 stages:
1st: Effacement occurs; Cervical Dilation
cervical canal slowly disappears
babies head acts as a wedge to cause cervical dilation
2nd: Uterine contractions; Birthing
uterine contractions every 1-2 minutes lasting for ~1 minute e
an incision is made to the opening to help the baby as its head reaches the exterior
once the baby is born the umbilical cord is cut and tied
3rd: Afterbirth; release of placenta
Afterbirth is delivered about 15 minutes after birth of baby

38. 17.4 Pregnancy and birth
Birth

39. Health focus: preventing birth defects
17.4 Pregnancy and birth
Health focus: preventing birth defects
Get physical exams by a trained doctor
Have good health habits:
proper nutrition and adequate sleep and exercise
Avoid smoking, alcohol and drug abuse
Avoid having x-rays
Avoid certain medications and supplements
Avoid sexually transmitted diseases or know if you have one

40. Aging Stages of life: infancy, childhood, adolescence and adulthood
17.5 Development after birth
Aging
Stages of life: infancy, childhood, adolescence and adulthood
3 hypotheses of aging:
Genetic origin:
suggests mitochondrial activity is involved with aging
Whole body processes
suggests aging may be a result from body systems or type of tissue
such as loss of hormonal activities or cross-linking in support tissues
Extrinsic factors:
suggests that aging may be due to years of poor health habits such as a poor diet and lack of exercise

41. What are the effects of age on body systems?
17.5 Development after birth
What are the effects of age on body systems?
Skin becomes thinner, less elastic and dry
Less adipose in the skin so one feels colder more easily
Decrease in melanocytes leading to gray hair while some of the remaining cells are larger leaving “age spots” (dark spots on the skin)
Heart shrinks and arteries become more rigid
Reaction time slows and senses are muted

42. What are the effects of age on body systems?
Lens in the eye loses ability to accommodate
Blood pressure usually increases
Bone density declines
Muscle mass decreases
Weight gain results from a decrease in metabolism and an increase in inactivity
Females undergo menopause and males andropause