17 Aging and Development

Question 1

Fertilization

Answer 1

The union of egg and sperm (ovum, ova) to form a zygote

Question 2

Zona Pellucida

Answer 2

outer matrix surrounding the egg

Question 3

Corona Radiata

Answer 3

outside the zona pellucida are few residual follicular cells from the ovarian follicle, called the corona radiata

Question 4

Steps of Fertilization

Answer 4

1. several sperm penetrate the corona radiata (but not the zona pellucida. First sperm to penetrate the zona pellucida triggers changes in the zona so others cant get in
2. Sperm’s acrosomal enzymes digest a portion of the zona pellucida
3. one sperm binds to and fuses with the egg’s plasma membrane
4. sperm nucleus enters the egg

Question 5

What prevents more than one sperm from entering the egg?

Answer 5

1. The egg’s plasma membrane depolarizes from 265mv to 10mv, which helps prevent more sperm from attaching to the egg.
2. Vesicles (cortical granule) within the egg releases enzymes that causes the zona pellucida to become impenetrable to other sperm

Question 6

Development of embroyo after sperm and egg nuclei fuse

Answer 6

• Cleavage: cells undergo division (2,4,8, etc) without the embryo increasing in size
• Growth: cells continue to undergo division and size of embryo increases
• Morphogenesis: the embryo begins to take shape as cells migrate to specific locations
• Differentiation: cells take on specific structure and function (the nervous system is the first visible system fomed)

Question 7

Extra-embryonic Membranes

Answer 7

• Chorion: forms the placenta, the organ that provides the embryo with nourishment and oxygen and rids it of waste
• Allantois: give rise to the urinary bladder, and the blood vessels of the umbilical cord that carry blood between the fetus and placenta
• Yolk sac: contains many blood vessels and where blood cells first form (there is a little yolk in humans, in contrast to eggs of other animals)
• Amnion: contains amniotic fluid that surrounds, cushions, and protects the embryo

Question 8

Stages of Development

Answer 8

1. pre-embryonic development - from moment of egg fertilization until end of 1st week
2. embryonic development - from begin of 2nd week after fertilization until the end of the 2nd month
3. fetal development - the 3rd throught the 9th month of development
4. development after birth - stages of life including infancy, childhood, adolescence and adulthood

Question 9

Pre-embyonic development

(1st week of development after fertilization)

Answer 9

• Cleavage: cell division that incrases the number of cells
• Morula: compact ball of embryonic cells
• Early blastocyst: inner cell mass that becomes the embryo covered by a layer of cell that becomes the chorion
• Implantation: embyo embeds into the uterine endometrial lining on approximately day 6 after fertilization

Question 10

Embyonic Development: Week 2

Answer 10

• Pregnancy begins after implantation of fertilized egg
• Human Chorionic Gonadotropin (HCG) secreted by chorion. LIke LH, HCG maintains the corpus luteum in the ovary, which secretes progesterone to maintain the thick endometrium of the uterus - HCG is measured by the pregnancy test
• Inner cell mass becomes the embryonic disk that will go through gastrulation to become 3 primary germ cell layers of the embyo (endoderm, mesoderm, and ectoderm)

Question 11

Ectoderm

(outer layer)

Answer 11

epidermis of skin, epithelial lining of oral cavity and rectum, nervous system

Question 12

Mesoderm

(middle layer)

Answer 12

skeleton, muscular system, dermis of skin, cardiovascular system, urinary system, reproductive system, outer layers of respiratory system and digestive system

Question 13

Endoderm

(inner layer)

Answer 13

epithelial lining of digestive tract and respiratory tract; associated glands of these sytems, epithelial lining of urinary bladder

Question 14

Embryonic Development: Week 3

Answer 14

Nervous system begins to develop from ectoderm - is first system to be seen

The posterior neural tube will become the spinal cord and brain

Development of the hear begins from mesoderm

Question 15

Embryonic Development: Weeks 4 & 5

Answer 15

4th week: embryo is appx 1/16 inch long. Chorionic villi and umbilical cord form. Limb buds form (later develop into legs and arms)

5th week: head enlarges. Eyes, ears and nose become prominent

Question 16

Embryonic Development: 6-8 weeks

Answer 16

Embryo begins to look human

Movement begins

All organ systems are established

1.5” long and weigh about the same as an aspirin tablet

Question 17

Fetal Development: month 3 and 4

Answer 17

hair develops, head slows in growth, body size catches up.

Cartilage begins to be replaced by bone

Able to distinguish female from male

Stethoscope will detect heartbeat

By the end of the month 4, the fetus is about 6 inches long and weighs roughly 6 ounces

Question 18

Fetal Development: month 5-7

Answer 18

Fetal movement can be felt by the mother

Fetus in “fetal” poition

Eyelids are fully open

Fetal size increased to about 12 inches and roughly 3 pounds

Question 19

Fetal Development: months 8 and 9

Answer 19

Weight gain is about a pound per week

Fetus usually rotates upside down so the head is pointed towards the uterine cervix

At the end of fetal development just prior to birth, the fetus weighs about 7.5 lbs and roughly 20 inches long

Question 20

Preventing Birth Defects

Answer 20

• Get periodic physical exams during pregnancy
• Maintain good health habits: proper nutrition,
adequate sleep and exercise
• Avoid smoking, alcohol, drug abuse
• Avoid having x-rays
• Avoid certain medications and supplements (many drugs cross the placenta from mother into the fetus)
• Avoid sexually transmitted diseases or know if you have one so it can be treated

Question 21

Placenta

Answer 21

Secretes estrogen and progesterone - maintain thick endometrium and prevent new follicles in ovary from maturing

Question 22

Fetal Circulation

Answer 22

• The placenta functions as the fetal respiratory center for CO2 and O2exchange (as well as exchange of nutrients and wastes)

Mother’s uterine arteries carry oxygenated blood to the uterine endometrium.

• Fetal hemoglobin has a higher attraction for O2 than adult hemoglobin, so O2 diffuses from the mother’s blood across the chorionic villus of the placenta, into fetal blood vessels (no blood connection between fetus and mother).

• Oxygen-rich fetal blood from placenta into umbilical vein fetal liver ductus venosus inferior vena cava fetal right atrium.

• Most of this oxygenated blood is “shunted” through the foramen ovale of the atrial septum. Right atrium left atrium left ventricle aorta.

• Most of the oxygen-poor fetal blood entering the right atria (that did not go to the placenta) enters the pulmonary artery, but is “shunted” back into the aorta through the ductus arteriosus. Most blood entering the right atria is shunted away from the fetal lungs (which are not working!).

Question 23

Movement of O2

Answer 23

Umbilical vein takes O2 rich blood from placenta

Imbillical arteries take O2 low blood to placenta

Question 24

Fetal Ciculation: changes at birth

Answer 24

• Lungs suddenly inflate with air and begin to work for breathing, increasing blood flow into pulmonary artery. Gas exchange in lungs begins, O2 rich blood from lungs enters left side of heart via pulmonary veins

• This increased flow and pressure in left atria closes the foramen ovale – which stops shunting O2 - poor blood from right atria into left atria

• Ductus arteriosus between pulmonary artery and aorta closes, stopping that shunt

• Ductus venosus at liver, as well as umbilical arteries and veins close. Umbilical cord vessels stop working. Cord is cut.

Question 25

Development of the Sex Organs

Answer 25

Sex of an individual is determined by chromosomes at fertilization (XX is female and XY is male) If the SRY (the sex determining region on the Y chromosome) gene is present at week 6, then the embryo develops into a male Anti-Mullerian hormone secreted by the testes prevents the development of female sex organs At 14 weeks primitive testes and ovaries with eggs are already developing The development of the external sex organs is dependent on the presence or absence of dihydrotestosterone (DHT) produced by the testes

Question 26

Abnormal Development of Sex Organs

Answer 26

* XY female syndrome - an individual develops into a female because a piece of the Y chromosome containing the SRY gene (that determines “maleness”) is missing * XX male syndrome – an individual develops into a male because the same small piece of the Y chromosome containing the SRY gene is present on an X chromosome

Question 27

Mother Changes During Pregnancy

Answer 27

* Nausea and vomiting common early on (morning sickness), related to estrogen levels * Some mothers report overall increase in energy and sense of well-being * Acid reflux and constipation * 40% increase in lung vital capacity * Edema (swelling) and varicose veins in legs * Urinary incontinence * The placenta produces peptide hormones that makes cells resistant to insulin - diabetes in mother can result * Stretch marks from increased steroid hormones * Melanocyte activity increases in some areas

Question 28

Birth

Answer 28

True labor is characterized by uterine muscle contractions every 15-20 minutes that lasts for at least 40 seconds ## Footnote 3 stages: – 1st: effacement occurs in which the cervical canal of uterus slowly disappears and the baby’s head acts as a wedge to cause cervical dilation – 2nd: uterine contractions every 1-2 minutes lasting 1 minute each • An incision is sometimes made to the perineum (episiotomy) to help the baby exit • Once baby is born the umbilical cord is tied off and cut. The end attached to the baby later falls off. – 3rd: • The “afterbirth” (placenta) is passed out of the uterus about 15 minutes after the birth of the baby

Question 29

Aging: Stages of Life

Answer 29

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 of declines in hormonal systems – Extrinsic factors: suggests that aging may be due to years of poor health habits such as a poor diet and lack of exercise

Question 30

Affects of age on body systems

Answer 30

Skin becomes thinner, less elastic and dry • Less adipose (fat) in the skin so one feels colder more easily • Decrease in melanocytes leading to gray hair while some of the remaining cells enlarge, leaving “age spots” (dark spots on the skin) • Heart shrinks and arteries become more rigid • Reaction time slows and senses are muted • Lens in the eye loses ability to accommodate rapidly • Blood pressure usually increases • Bone density declines • Muscle mass decreases • Weight gain results from a decrease in metabolism and a decrease in activity • Females undergo menopause and males andropause, when ovaries and testis lose function