Key questions: NOTE: IF YOU MAKE A CHANGE TO A QUESTION, WRITE THE WORD "CHANGE" AT THE BEGINNING OF THE QUESTION, RIGHT AFTER THE NUMBER. DO NOT DELETE MY COMMENTS UNLESS YOU ARE DIRECTED TO DO SO.
1. Describe how sperm are produced and transported throughout the male body. (And ova throughout the female body.) DONE
Sperm, consisting of an acrosome, head, middle piece, and tail, are produced in coiled tubes in the testes, seminiferous tubules. As the sperm mature they are stored in the epididymis. Sperm is then transported through the male through a pathway that begins at the testes. From one testis sperm travel through the epididymis, a long coiled tube. Next the sperms are shot through the epididymis to a tunnel called the vas deferens. The vas deferens then joins to another duct where three glands each add elements to create semen (the secretions by the glands and the traveling sperms): the seminal vesicles add sugar (provides energy used by the sperm's tail to propel), the prostate gland adds alkaline fluid, and the bulbourethral gland adds mucous. The sperm then is emptied into the urethra which empties the body of both urine and sperm (not concurrently) and the sperm ends its travels through the male reproductive system by being ejaculated during an orgasm.
In the female reproductive system the maturation of an ovum (egg cell) takes place in the ovary. Eggs develop from primary oocytes and one primary oocyte results in one ovum and three "polar bodies". However, the second oocyte is actually the larger daughter cell and receive almost all of the cytoplasm that is divided during Meiosis I. This second oocyte is released by the ovary during ovulation, a process that takes place roughly 14 days before menstruation. Then the ovum is fertilized in oviducts and moved along by oviduct-lining cilia. After several days in the oviduct the embryo needs nutrients and implants on the wall of the uterus, also known as the endometrium. If the ovum is not fertilized it cannot stick onto the endometrium and at the end of the cycle will be sloughed away through bleeding with the lining of the uterus.
2. Compare and contrast the nervous system and endocrine system as options for controlling body functions. DONE
The nervous system is used when you need a very fast response. For example, when you touch a hot stove the nerves in your hand shoot a message back to the brain, which then sends a message back to your hand telling you to take your hand off of the stove immediately. These messages are called neurotransmitters. Neurotransmitters are called “local regulators” because they travel short distances and are usually produced right where they act. The only issue with using the nervous system is that it is energy demanding. It needs a lot of ATP to function properly. However, when time is not important you would use the endocrine system. With the endocrine system, hormones are used and get a free pass down the blood stream. They flow slowly and do not use as much ATP as the nervous system does. With both systems the neurotransmitter and the hormone travel all throughout the body, but only effect cells that have the matching receptor protein through the process called signal transduction. This makes them specific because the signal molecule (the hormone or neutrotransmitter) must match the receptor protein. If it does, it will release a relay protein, which then goes on to turning on genes by triggering the synthesis of transcription factors.
3. How do hormones regulate the ovarian and menstrual cycles? DONE
The hypothalamus produces the hormone called gonadotropic releasing hormone (GnRH) to the anterior pituitary, which produces follicle stimulating hormone (FSH) and leutenizing hormone (LH). The FSH goes to the ovarian follicle and stimulates the growth of the ovarian follicle, which starts the ovarian cycle. The ovarian follicle secretes estrogen that initially, when at low levels, tells the hyptholamaus to stop making GnRH. Estrogen also triggers the hypothalamus to make an increase in LH which eventually causes the rupturing of the ovarian follicle. It also builds up the endometrium to provide nutrients if the ovum were to implant in the uterus wall.
The hormone LH, that is produced in the anterior pituitary, goes to the ovarian follicle and causes it to rupture at mid-cycle. The secretion of estrogen from the ovarian follicle triggers the spike in LH before it ruptures. This rupturing of the ovarian follicle (aka ovulation) then releases an ovum that travels down the oviduct where it either gets fertilized or not.
The ruptured ovarian follicle becomes the corpus luteum and secretes progesterone and estrogen. If the ovum is fertilized, the embryo implants in the walls of the uterus, or the endometrium, that has been built up due to high estrogen levels. The developing embryo produces human chorionic gonadotropin (HCG) that keeps the corpus luteum intact and remains secreting high levels of estrogen and progesterone. However, if the ovum is not fertilized, the corpus luteum degenerates due to the falling levels of LH and the absence of HCG.
With the loss of the corpus luteum, estrogen and progesterone levels go down. With the falling levels of LH and no HCG being made, the corpus luteum degenerates, which also triggers the loss of the endometrial lining (aka menstruation) and the start of a new cycle. The new cycle begins because the hypothalamus is turned on by the low levels of estrogen and protesterone and signals the anterior pituitary to release FSH and LH to start the process all over.
4. What role do extraembryonic membranes play in supporting pregnancy? DONE
The chorion completely surrounds the embryo and the other extraembryonic membranes, and becomes part of the placenta where it plays a significant role in gas exchange. Cells in the chorion secrete the human chorionic gonadotropin hormone which maintains production of estrogen and progesterone by the corpus luteum of the ovary during the first months of pregnancy. Without the secretion of these hormones, the embryo would abort because the brain would proceed with menstruation.
The placenta is formed from the mother's uterine lining and chorion of the embryo, and once the chorionic villi grow from the placenta, the placenta development is complete. The villi absorb nutrients and oxygen from the mother's blood, and pass them to the embryo through the chorionic blood vessels. Other chorionic vessels carry the embryo's waste and deposit them into the mother's bloodstream, where it becomes part of her own bodily processes. The placenta is responsible for supplying nutrients and carrying out gas exchange, but is unable to protect the embryo from harmful viruses in the mother's blood. The embryo is still vulnerable to chemicals in alcohol, drugs, smoke, and even STD's.
About a month after fertilization, the amnion is filled with fluid and encloses the embryo in order to protect it. When the mother goes into labor, the amnion breaks and the fluid leaves the mother's body.
In mammals, the yolk sac produces the embryo's first blood cells and first germ cells, which will give rise to the gamete-forming cells in the gonads. In a bird or reptile egg, the yolk sac contains a large mass of yolk, which provides nourishment to the developing bird instead of a placenta.
In birds and reptiles, the allantois expands around the embryo and functions in waste disposal. The allantois becomes part of the umbilical cord in mammals, and part of the embryo's urinary bladder.
5. What is the difference between reproductive and therapeutic cloning? DONE
Reproductive cloning is taking a cell from the animal to be cloned, placing the cell in an egg with its DNA removed, and de-methylating it so that is its like a zygote. The goal of reproductive cloning is to make a copy of an animal, where as on the other hand, theraputic cloning aims to take the zygote, and grow it into a mass of stem cells that can be used to repair damaged tissue. Instead of letting nature take its course and create a fetus, theraputic cloning is controlled to produce a certain type of cell, for example a spinal cord cells to go onto a spinal cord and grow where the old cells were broken.
