11.4 what to study Flashcards
Insulin vs. Glucagon the functions/response of liver cells (hepatocytes) as the TARGET CELLS!
Insulin and glucagon are hormones that are both produced and secreted by the pancreas. In addition they are both involved in the regulation of blood glucose levels. Cells rely on glucose for the process of cell respiration. Cells never stop cell respiration and thus, are constantly lowering their concentration of glucose in the blood.
In the intestinal villi, the glucose travels through a multitude of capillaries, small venules and veins into the hepatic portion where the two pancreatic hormones- insulin and glucagon are. Alpha cells of the pancreas begin to produce and secrete the hormone glucagon. The glucagon circulates the bloodstream and stimulates hydrolysis.
Insulin- in the pancreas, stimulates the hepatocytes to take the glucose and convert it to glucagon. B (beta cells) produce insulin.
Positive vs. negative feedback- be able to give examples of each!
Negative: The high levels of both estrogen and progesterone at the same time provide a negative feedback signal to the hypothalamus. ▪The hypothalamus does not produce GnRH when the estrogen and progesterone levels are high, so FSH and LH remain at levels that are not conducive to the production of another Graafian follicle during this time.Most feedback mechanisms in physiology are designed to work by negative feedback. Birth is a process that is not a normal part of mammalian homeostasis.
Positive:Another effect of estrogen is to stimulate the pituitary gland to release more FSH and LH. ▪This is the positive feed loop of the menstrual cycle, specifically these two sets of hormones increase because of the increase of the other(s).An example is as birth continues, the uterine contractions become more and more intense, and become more and more frequent. The feedback control that is involved is called positive feedback. In effect, a previous event results in a more forceful and frequent future event. There is no homeostatic factor being controlled, the series of events will only culminate when birth occurs.
Typical location and outline for the process of fertilization
A typical location for fertilization is in one of the fallopian tubes.
As a result of sexual intercourse, millions of spermatozoa are ejaculated. The motile spermatozoa absorb some of the fructose sugar in semen in order to have fuel for the long journey.
At least some of the spermatozoa find their way through the cervical opening (the cervix separates the vagina and the uterus) and gain access to the uterus. They begin swimming up the endometrial lining, and some enter the openings of the two Fallopian tubes.
No single spermatozoon can accomplish the entire act of fertilization because it takes many spermatozoa to penetrate the follicle cell layer and a coating called the zona pellucida surrounding the secondary oocyte. Then an acrosome reaction occurs.
One spermatozoon will reach the plasma membrane of the secondary oocyte first, and will use the hydrolytic enzymes of its acrosome to penetrate the egg. The plasma membranes of the two gametes fuse together. This spermatozoon then donates its paternal set of haploid chromosomes to the maternal set already contained in the ovum. More than one spermatozoon fertilizing an ovum is called polyspermy and results in multiple sets of chromosomes within the ovum. – leads to cortical reaction.
When the first spermatozoa and ovum fuse their plasma membranes, the cortical granules fuse with the ovum’s internal plasma membrane and release their enzymes to the outside. These enzymes result in a chemical change in the zona pellucida, making it impermeable to any more spermatozoa. Many animals prevent polyspermy by reversing an electrical (ion) charge upon first fertilization
Cortical Reaction
Is designed to prevent more than one spermatozoa from fertilizing the ovum. In the cytoplasm, ovum are small vesicles known as cortical granules in the plasma membrane. The first spermatozoa and ovum fuse their plasma membranes, and the cortical granules fuse with the ovum’s internal membrane to release their enzymes outside.This takes place within a few seconds of the first spermatozoon gaining access and ensures that only one actually fertilizes the ovum.
Acrosome reaction
Several spermatozoa gain access to the zona pellucida surrounding the secondary oocyte and release the hydrolytic enzymes continued in their acrosomes. The function of the acrosome reaction is to help the sperm get through the egg’s protective coat and to allow the plasma membranes of the sperm and egg to fuse.
implantation in the endometrium after fertilization
After Division, The early embryo continues to move within the Fallopian tube towards the cavity of the uterus as it divides. The rate of mitotic division continues to increase and, by the time the embryo reaches the uterine cavity, it is approximately 100 cells in size and is ready to implant itself into the endometrium of the uterus. The embryo at this stage is the blastocyst.
When it enters the endometrium, the timing of the menstrual cycle ensures that the endometrium is highly vascular. It then sinks into the endometrial tissue. When the embryo begins implantation, it is rapidly running out of stored nutrients as a result, the embryo and the maternal endometrium begin to form the placenta.
Role of estrogen and progesterone during pregnancy
Progesterone: Helps maintain the highly vascular tissue characteristic of the uterus/placenta. Suppresses contractions of the smooth muscle of the uterus.
Estrogen: Encourages muscle growth of the uterus. Antagonizes the action of progesterone to suppress uterus contractions and stimulates mammary glands development late in pregnancy in preparation for milk production. Induces production of oxytocin receptors in uterine muscles late in pregnancy.
Function of the hormones HCG and oxytocin
Oxytocin is a hormone produced by the hypothalamus and secreted by the posterior pituitary gland. When the time for birth has come, the posterior pituitary will release a small amount of oxytocin in the bloodstream.
The function of HCG is to enter the mother’s bloodstream and ‘maintain’ the corpus luteum of her ovary for a longer period of time compared with a typical menstrual cycle. This hormone is also detected during pregnancy tests.
Hormone Matching to Function
LH: Cases the egg to be released from the ovary by Ovulation. Surge causes ovulation and results in the formation of a corpus luteum. Target tissue= Ovaries
FSH: Stimulates follicular growth in ovaries, stimulates estrogen secretion. Target Tissue=Ovaries
GnRH: produced by the hypothalamus is (GnRH). ▪The target tissue of GnRH is the nearby pituitary gland, and it results in the anterior pituitary producing and secreting two hormones into the bloodstream.
Estrogen:causes an increase in the density of blood vessels of the endometrium, so the endometrium becomes highly vascular. Another effect of estrogen is to stimulate the pituitary gland to release more FSH and LH.
Progesterone: a hormone that maintains the thickened, highly vascular endometrium. As long as progesterone continues to be produced, the endometrium will not break down and an embryo will still be able to implant.
➢Compare and contrast spermatogenesis & oogenesis
Spermatogenesis
Mitosis replaces germinal cells daily
Some cell growth occurs before meiosis I begins
The two divisions of meiosis result in four haploid spermatozoa
Spermatids must remain in seminiferous tubules until differentiation into spermatozoon occurs.
The resulting gamete is extremely small with very little cytoplasm and limited organelles
Millions of spermatozoa are produced every day throughout life (starting at puberty.)
Oogenesis
Mitosis replaces germinal cells only early in a female’s development
A great deal of cell growth occurs before meiosis I begins
The two divisions of meiosis result in one ovum and three possible polar bodies
Differentiation of the oocyte into an ovum occurs partly in the ovary and continues after ovulation
The resulting gamete is extremely large with a great deal of cytoplasm, nutrients and numerous organelles.
Ovulation of one of a total of thousands of oocytes occurs with each menstrual cycle, then stops at menopause.
