Lecture Outline - Chapter 17

17.1 Fertilization (p. 358, Figs. 17.2, 17.3)
	1.	Fertilization normally occurs in the upper third of the oviduct. Uterine and oviduct contractions may help transport the sperm.
	2.	Fertilization occurs when a sperm and egg interact. The sperm must pass through the several layers of follicular cells surrounding the egg, called the corona radiata. The egg cell also has its own plasma membrane, a vitelline membrane, and the zona pellucida.
	3.	Sperm gain entry through a species-specific mechanism of contacting the vitelline membrane, then fusing with the egg plasma membrane before the sperm nucleus enters the cell. Once the sperm and egg nuclei fuse, fertilization is accomplished.
	4.	The zygote travels down the oviduct and eventually implants in the endometrium. It then secretes human chorionic gonadotropin, the presence of which is the basis for pregnancy tests.
17.2 Human Development Before Birth (p. 360)
	1.	Processes of Development (p. 360, Fig. 17.4)
		a.	Embryonic development of humans and all other animals includes the following processes:
			i.	Cleavage begins right after fertilization as the zygote divides and divides again. The size of the cell does not increase during this stage. 
			ii.	Morphogenesis is the reshaping of the embryo as cells migrate to different areas.
			iii.	Differentiation occurs as cells take on specific structures and then functions.
			iv.	Growth accompanies cell division during embryonic development.
		b.	Morula (p. 360)
			During cleavage, the mass of cells is referred to as a morula.
		c.	Blastula (p. 360)
			The blastula stage begins once the morula transforms into a hollow ball with an inner cell mass off to one side.
		d.	Gastrula (p. 360, Table 17.1)
			i.	The inner cell mass becomes an embryonic disk composed of two germ layers: an upper ectoderm and a lower endoderm.
			ii.	The bilayered disk elongates, and a primitive streak is seen at the midline of the embryo. Some of the cells within the primitive streak invaginate, giving rise to a third germ layer, the mesoderm.
			iii.	As differentiation continues throughout development, the three germ layers give rise to all other tissues and organs of the body.
		e.	Neurula (p. 361, Fig. 17.5)
			i.	Mesoderm cells along the main axis give rise to a notochord, which is eventually replaced by the vertebral column. Neural folds fuse to form a neural tube, which gives rise to the spinal cord and brain.
			ii.	During neurulation, induction occurs, a process in which one tissue influences the development of another. Induction probably requires the presence of certain chemicals that turn genes on.
			iii.	Somites arise from the mesoderm. These become the muscles of the body and the vertebrae. A body cavity called the coelom forms and is lined by mesoderm. The coelom becomes the thoracic and abdominal cavities.
	2.	Extraembryonic Membranes (p. 362, Fig. 17.6)
		a.	Extraembryonic membranes extend out beyond the embryo.
		b.	The amnion envelops the fetus in protective fluid.
		c.	The yolk sac is the first site of red blood cell formation, and part of this membrane eventually becomes a portion of the umbilical cord.
		d.	The allantois contributes to the circulatory system, and its vessels become the umbilical blood vessels.
		e.	The chorion, the outermost membrane, contributes to the placenta.
	3.	Placenta: For Exchange (p. 362)
		a.	Fingerlike extensions of the chorion (chorionic villi) project into the maternal tissue as the placenta develops.
		b.	The chorion contributes the placenta on the fetal side, while uterine tissues supply the placenta on the maternal side.
		c.	Fetal and maternal blood do not mix. Instead, carbon dioxide and wastes diffuse from the fetal side of the placenta, and oxygen and nutrients move from the maternal side to the fetal side.
		d.	The umbilical cord carries gases and nutrients to the fetus from the placenta.
		e.	Harmful molecules can cross the placenta; this is especially damaging during the embryonic period.
		f.	Fetal Circulation (p. 362, Fig. 17.7)
			i.	Fetal circulation is different from adult circulation because the fetus does not breathe air.
			ii.	Blood passes between the atria of the heart through an oval opening because not as much blood needs to travel to the lungs. An arterial duct shunts blood between the pulmonary trunk and aorta for the same reason.
			iii.	Two umbilical arteries lead to the placenta; one umbilical vein takes nutrients to the baby. The umbilical vein joins a venous duct entering the vena cava.
			iv. 	The persistence of the oval opening at birth is the most common heart defect in newborns.
				HEALTH FOCUS: Preventing Birth Defects (p. 364, Fig. 17A)
				i.	Birth defects can be detected before birth by amniocentesis, chorionic villi sampling, and screening eggs for defects before conception.
				ii.	Birth defects have a number of causes, many of which can be prevented by the mother having a nutritious diet and healthy personal habits.
				iii. 	Toxic chemicals, illegal drugs, alcohol, some medications, tobacco smoke, X- ray treatment, and STDs all contribute to birth defects and should be avoided.
	4.	Timing of Embryonic Development (p. 366, Fig. 17.8, Table 17.2)
		a.	Embryonic development lasts from fertilization to the end of the second month of gestation, at which time all organ systems have formed.
		b.	First Month (p. 366, Fig. 17.9)
			i.	The zygote undergoes the morula stage, and the blastocyst implants in the uterine lining by the end of the second week. The inner cell mass is present, and extraembryonic membranes are forming.
			ii.	At the end of the first month, organs are developed and the placenta is forming. Limb buds are present, and eyes, ears, and a nose appear.
		c.	Second Month (p. 367, Fig. 17.10, Table 17.2)
			i.	Legs, arms, and digits are better formed, the head is large, and all internal organs have appeared.
			ii.	During the first two months, the mother may experience nausea, breast tenderness, fatigue, and other symptoms.
			iii.	At the end of two months, the embryonic stage is over.
	5.	Timing of Fetal Development (p. 368)
		a.	Third and Fourth Months (p. 368, Fig. 17.11)
			i.	Fetal development extends from the third to the ninth month. 
			ii.	During the third and fourth months, the body increases in size, and epidermal refinements (eyelashes, nipples) become apparent. Bone is replacing cartilage.
			iii.	During this time, it becomes possible to distinguish males from females.
		b.	Fifth through Seventh Months (p. 369, Fig. 17.12)
			i.	The mother can feel fetal movement. The fetus's thin skin is covered with lanugo, and the eyelids open fully.
			ii.	At the end of seven months, the fetus can survive if born prematurely. Its lungs may lack surfactant, however, putting the baby at risk.
		c.	Eighth and Ninth Months (p. 369)
			During the last two months, the fetus grows greatly in size. It rotates its head down toward the cervix.
17.3 Birth (p. 370, Fig. 17.13)
	1.	Estrogen, prostaglandins, and oxytocin cause the uterus to contact and expel the fetus.
	2.	Stage 1 (p. 370)
		Stage 1 labor involves contractions that move the baby's head downward, enhancing effacement and dilation of the cervix. The amnion breaks, releasing amniotic fluid. This stage ends when the cervix is completely dilated.
	3.	Stage 2 (p. 371)
		Stage 2 labor has frequent contractions of longer duration. The mother experiences a desire to push. An episiotomy is often performed to prevent tearing. The baby is pushed out during this stage.
	4.	Stage 3 (p. 371)
		Stage 3 is the delivery of the afterbirth.
	5.	Female Breast and Lactation (p. 371, Fig. 17.14)
		a.	No milk is produced during pregnancy, but milk ducts and alveoli proliferate during that time, and the breasts enlarge.
		b.	Once the baby is delivered, the pituitary secretes prolactin, and milk is produced. Suckling of the baby at the breast enhances milk production.
17.4 Human Development After Birth (p. 372)
	1.	Development is a lifelong process into adulthood. After that period, aging occurs. Gerontology is the study of aging.
	2.	Why We Age (p. 372, Fig. 17.15)
		a.	Genetic in Origin (p. 372)
			One theory of aging suggests that aging has a genetic basis. Cells can divide only so many times. As we grow older, it may be that more cells age and die. Also, some cell lines may die before that maximum number of cell divisions has been reached. In addition, offspring of long-lived people also tend to be long-lived. Some people may have genes that code for efficient enzymes that remove free radicals, causing the individuals to live longer.
		b.	Whole-Body Process (p. 372)
			A second theory of aging suggests that a hormonal decline can affect many different organ systems. The immune system no longer performs as well, which is perhaps why cancer is more prevalent in the elderly. Aging may be due to the failure of a particular tissue type found throughout the body.
		c.	Extrinsic Factors (p. 373)
			A third theory on aging suggests that years of poor health habits contribute most to aging. Osteoporosis is a good example.
	3.	How Aging Affects Body Systems (p. 373)
		a.	Skin (p. 373)
			i.	Skin loses elasticity and becomes thinner with age, resulting in sagging and wrinkling.
			ii.	Fewer sweat glands are present, so temperature regulation is less efficient.
		b.	Processing and Transporting (p. 373)
			i.	Deterioration of the cardiovascular system is the leading cause of death among the elderly. The heart shrinks with age, and fatty deposits clog arteries. Low-cholesterol, low-fat diets slow degenerative changes.
			ii.	Lungs lose some elasticity, so ventilation is reduced.
			iii.	A reduced blood supply to the kidneys results in the kidneys becoming smaller and less efficient.
			iv.	The digestive tract may lose muscle tone but still absorbs nutrients efficiently.
		c.	Integration and Coordination (p. 374)
			i.	Normal aging results in the loss of few nerve cells. Short- term memory may decline, but overall cognitive skills remain.
			ii.	After age 50, there is a slow decline in the ability to hear higher frequencies, and the lens of the eye does not accommodate as well.
			iii.	Loss of skeletal muscle mass is common but can be controlled through exercise. Bone density declines, which can be slowed by adequate calcium intake and exercise.
		d.	The Reproductive System (p. 374)
			Females undergo menopause and are no longer reproductive. In males, sperm production continues until death.
		e.	How to Age Well (p. 374, Fig. 17.16)
			Good health habits started when young slow the aging process and contribute to a long, healthy life span.