head+injury+HW-+rebecca

Human Life Cycle 16.1 p. 320 INSERTING FIGURES IS ALWAYS A GOOD THING.

(1) How many chromosomes does a mother contribute to a new individual? A father?
 * Mother(egg) contributes 23 chromosomes and the father(sperm) contributes 23 chromosomes.

(2) Where does meiosis occur in males? in females?
 * Meiosis only take place in the testes of males during the production of sperm and in the ovaries of females during the production of eggs.

(3) Compare and egg cell to a sperm cell.
 * Sperm is quite small compared to the egg. It carries only chromosomes as it swims to the egg. The egg is specialized to await the arrival of a sperm and to provide the new individual with cytoplasm in addition to chromosomes. Both the egg and the sperm have 23 chromosomes.

(4) What is the difference between meiosis and mitosis.
 * Meiosis is cell division, which is reduction division. Chromosomes are reduced from 46, to 23 chromosomes. Meiosis has two divisions, meiosis I and II. Mitosis is duplication division and cells are copied exactly.

Development Chapter 17 17.1

(5) Describe in detail how fertilization occurs.
 * The sperm is a flagellum, which allows it to swim towards the egg.Several sperm penetrate the corona radiata, several sperm attempt to penetrate the zona pellucide, but only one sperm enters the egg. After the sperm head binds tightly to the zona pellucida, the acrosome releases digestive enzymes that gorge a pathway for the sperm through the zona pellucida. When the sperm binds to the egg, their plasma membranes fuse, and this sperm enters the egg. Once the sperm touches an egg, the eggs plasma membrane depolarizes and this prevents the binding of any other sperm. Then vesicles called cortical granules releases enzymes that cause they zona pellucida to become an impenetrable fertilization membrane. Now sperm cannot bind to teh zona pellucida either.

(6) What is polyspermy and how is prevented during fertilization?
 * Polyspermy is when one or more sperm enters into an egg. When the sperm touches the egg, the egg's plasma membrane depolarizes, and therefore the binding of sperm is prevented.

17.2 (7) Describe the processes involved in development.
 * Cleavage: the zygote begin to divide. Increase in size does not accompany these divisions. Cell division during ceavage is mitotic and each cell recives a full complement of chromosomes and genes.
 * Growth: cell division is accompanied by an increase in size of the daughter cells.
 * Morphogenesis: Morphogenesis refers to the shaping of the embryo and is first evident when certain cells are seen to move or migrate in relation to other cells. By these movements the embryo begins to assume various shapes.
 * Differentiation: When cells take shaoe and function, differentiation occurs. Teh first system to become visibly differentaited in the nervous system.

(8) What are the extraembryonic membranes and what is their role?
 * They are not part of the embryo and fetus, instead as implied by their name, the are outside the embryo.
 * 1. chorion- develops into the fetal half or the placenta, teh organ that provides the embryo/ fetus with nourishment and oxygen and takes away its waste. Blood vessels.
 * 2. Allantois- it accumulates the small amount of urine priduced by teh fetal kidney and later gives rise to the urinary bladder. Blood vessels take blood to and away from the fetus.
 * 3- Yolk sac- The first embryonic membrane to appear, the yolk sac contains yolk- which is food for the embryo. The yolk sac contains blood vessels. It is the first sign of blood cells formation.
 * 4- Amnion- enlarges the embryo and then the fetus enlarges. It contains fluids to cushion and protect the embryo, which develops into a fetus.

(9) What happens during pre-emrbyonic development?
 * Pre- embryonic development encompases the events of the first week. A morula is a compact ball of embryonic cells that become blastocyst. The many cells of the blastocyst arrange themselves so that there is an inner cell mass surrounded by an outer layer of cells. The layer of cells will become the chorion. Each cell within the inner cell mas has the genetic capability of becoming any type of tissue. Sometimes during development the cell of the morula separate or the inner cell mass splits and two pre embryos are present rather than one. These pre embryos will be identical twins because they have inherited exactly the same chromosomes.

(10) What happens during embryonic development? (11) What are the primary germ layers and what body structures come from each layer?
 * Begins the second week and lasts until the end of the second month of development.
 * Implantation: the embryo implants itself in a location other than the uterus- most likely the oviduct. Ectopic pregnancy cannot succeed because an oviduct is unable to support it. Human chorionic gonadotropin(HCG)- the hormone that is the basis of the pregnancy test. HCG acts like luteinizing hormone(LH) in that it serves to maintain the corpus luteum past the time it normally disintegrates. Also during the second week embryoonic disk, gastrulation and primary germ layers takes place.
 * 3rd week: The nervous system starts to develop. The heart begins to take shape.
 * 4th and 5th week: Blood vessels become visible. The chorion's villi ad the umbilical cord develop. The head enlarges. You can make out the head, eyes, and ears and the nose.
 * 6th-8th week: Embryo changes into a human. Normal development begins. Reflexes form.
 * The primary germ layers are the ectoderm(outer layer)- Epidermis of skin, epithelial lining of oral cavity and rectum, nervous system., mesoderm( midle layer)- Skeleton, muscular system, dermis of skin, cardiovascular system, urinary system, reproductive system, outer layers of respiratory and digestive system, and endoderm( inner layer)- Epithelial lining of digestive tract and respiratory tract, associated glands of these systems, epithelial lining of urinary bladder.