Study Questions #10
Explain genetic, environmental, and maternal sex determination and describe how each of these systems work in a specific animal.
-genenetic - sex determined by sex chomosome at the time of fertilization (snakes) -env determines sex - (turtles/crocodiles) depends on temp -extreme temps male predominates -Female default sex
Define each of the following and explain where in the female reproductive system and when, relative to fertilization, each occurs:Zygote, cleavage, blastocyst, trophoblast, gastrulation 4 steps
1. Formation of Zygote(fusedmale and female games = diploid) IS fertilization 2. Zygote begins cleavage (series of cell division) for about 24 hrs 3. after 4 days it produces a Blastocyst (sphere of cells surrounding the central cavity) 4. during the first 2-4 weeks of development, the embryo obtains nutrients directly from the endometrium. Meanwhile, the outer layer of the blastocyst, which is called the trophoblast, grows outward and mingles with the endometrium, eventually helping form the placenta. Formation of these three primary germ layers is the process known as gastrulation.
Diagram the negative feedback regulating sperm production and testosterone production in men ( 2 circuits). Indicate the roles of Testosterone, GNRH, FSH, and LH, in this regulatory pathway. What are the roles of Leydig cells and Sertoli cells?
1. Testosterone regulates blood levels of GnRH, FSH, and LH through inhibitory effects on the hypothalamus and anterior pituitary. 2. inhibin, a hormone that in males is produced by Sertoli cells, acts on the anterior pituitary gland to reduce FSH secretion. -GnRH causes the Anterior pituitary to release FSH to Sertoli cells, and LH to Leydig cells -Sertiocells produces Inhibin which reduce anterior pituitary secretion of FSH -Leydig cells produce testosterone and secrete small quantities of many other hormones and local regulators, including oxytocin, renin, angiotensin, corticotropin-releasing factor, growth factors, and prostaglandins. These signals coordinate the activity of reproduction with growth, metabolism, homeostasis, and behavior. -Testosterone promotes sperm production and prevents the secretion of LH and FSH via anterior pituitary by inhibiting hypothalamus release of GnRH.
How do the hormones in birth control pills affect the hypothalamus, anterior pituitary, and ovary? How do they prevent pregnancy? Why is it not accurate to say that they hormonally mimic pregnancy?
Birth control pills combine a synthetic estrogen and synthetic progesterone - like hormone (progestin) This mimics negative feedback in the ovarian cycle: -stops the release of GnRH in the hypothalamus ->stops release of LH and FSH by the pituitary -->this prevention of LH release blocks ovulation Also, the prevention of FSH release by the low dose of estrogens in the pills prevents follicles from developing. Because they don't.
Graph the changes in concentration of each of the following during a woman's monthly ovarian(1-8)/uterine(9-10) cycle (10 steps total): luetenizing hormone (LH), follicle stimulating hormone (FSH), estrogen, progesterone. For each of those hormones, which endocrine gland is responsible for its production?
FSH and LH - Anterior pituitary Estrogen and Progesterone - gonads (ovaries)
What is the hormonal cue for ovulation in female mammals?
Initiated in hypothalamus when it releases gonadotropin-releasing hormone (GnRH)
Define male and female with a definition that works for all animals. Define hermaphrodite and gonochoristic. Provide an example of a gonochoristic invertebrate, a sequential hermaphrodite (invertebrate or vertebrate), and a simultaneous hermaphrodite (invertebrate or vertebrate).
Male - sex chromosomes (XY) Female - sex chromosomes (XX) Hermaphrodite - organism with both male and female sex characteristics Gonochorisitic or unisexualism or gonochory describes the state of having just one of at least two distinct sexes in any one individual organism. -zebrafish -seastars/wrasse -
Define parthenogenesis. Describe an animal that reproduces through parthenogenesis (I talked about 2 examples in class). What is the other common form of asexual reproduction in animals?
Parthenogenesis - production of diploid eggs identical to mother resulting in an all female species. -Whip tail lizards that hange behavior from female like to male like after ovulation -Aphids - have parthenogenetic and sexual reproduction Fission
Why does testing for human chorionic gonadotropin work as a pregnancy test early in pregnancy but not late in pregnancy?
Placenta secretes: -Early pregnancy: hCG - nourishes the egg after it has been fertilized and becomes attached to the uterine wall -Late pregnancy: estrogen and progesterone
What hormones are produced by the follicle/corpus luteum during the pre-ovululation, post-ovulation, and menstrual phases of the human female reproductive cycle? What effects do these hormones have on the hypothalamus, anterior pituitary, and uterine lining?
Pre-ovulation: -follicle secretes estridiol --low levels inhibit secretion of pituitary hormones, keeping levels of FSH and LH releatively low --high levels promotes secretion of GnRH --high lvls also ingreases the gonadotropin releasing hormone sensitivity of LH-releasing cells in the pituitary Post-ovulation: -corpus leteum secretes progesterone and estridiol --In combination exert negatie feedback on the hypothalamus and pituitary. This greatly reduces LH and FSH secretion. --If pregnancy does not occur, low GnRH lvls cause the corpus luteum to disintegrate, triggering a sharp decline in estradiol and progesterone con. The decline releases the hypothalamus and pituitary from the negative feedback loop. Menstrual phases: -after ovulation the estrogen and progesterone secreted by the corpus luteum stimulate maintanance and further development of the uterine lining (enlargement of arteries and growth of endometrial glands) --If pregnancy does not occur, low GnRH lvls causes the arteries and endometrial glands to constrict. Deprived of circulation, the uterine lining largely disintegrates, releasing blood that is shed along with endometrial tissue and fluid --> menstration
Which portion of the ovarine/uterine cycle is regulated by a positive feedback loop, and which portion is regulated by a negative feedback loop?
Prior to ovulation there is a positive feedback loop between estrogen secreted by follicle and the hypothalamus secreting gonadotropin-releasing hormone (GnRH) After ovulation there is a negative feedback loop. The Corpus luteum secretes estrogen and progesterone stimulating endometrial lining. Combination of estrogen and progesterone inhibit hypothalamus production of GnRH
Where and when is human chorionic gonadotropin produced? What is its direct function in pregnancy?
Produced during pregnancy. Made by cells formed in the placenta. It nourishes the egg after it has been fertilized and becomes attached to the uterine wall.
Describe the purpose and structure of the placenta. When during pregnancy does it form? What hormones are secreted?
The Placenta is the composite structure of embryonic and maternal tissues that supplies nutrients to the developing embryo. The placenta is a unique organ, found only in mammals, that allows the mother to provide a very large amount of nutrients to her offspring for an extended period of time before they are even born. The placenta serves as an interface between the mother and the developing fetus and has three main jobs: -Attach the fetus to the uterine wall -Provide nutrients to the fetus -Allow the fetus to transfer waste products to the mother's blood 8 weeks Placenta secretes Human Chornic Gondatropin in early pregnancy, and estrogen and progesterone later.
How are the functions of LH and FSH in men and women similar and different?
Women: -LH and FSH stimulate follicle growth -LH surge triggers ovulation Men: -FSH stimulates Sertoli cells to produce inhibin -LH Stimulates Leydig cells to produce testosterone -They both support gametogenesis, in part by stimulating sex hormone production by the gonads
What 3 tissue layers are formed during gastrulation? What parts of the animal do each of these layers develop into?
ectoderm- neuronal tissue and epidermis mesoderm- somites that differentiate into skeletal muscle tissues, the notochord, blood vessels, dermis, and connetive tissues endoderm- epithellium of digestive and respiratory systems and the organs associated with the digestive system, such as the liver and pancreas.
Define pregnancy. Define pregnancy rate in terms of evaluating effectiveness of contraceptives.
the period in which a fetus develops inside a woman's womb or uterus.
What is the major fitness cost of sexual reproduction compared to asexual reproduction for females? Describe at least 2 other costs of sexual reproduction. Describe 3 hypotheses for why almost all animal species have sexual reproduction as part of their life cycles despite this cost.
-Expensive in terms of fitness. sex is a work out Mating process 2-fold cost of sex: in man y species, males do not provide any resource to the next generation, yet sexual females typically invest half of their resources into the production of males. Breaking favorable genetic combinations
Define asexual and sexual reproduction. What are the two most common types of asexual reproduction in animals?
-Sexual reproduction-fusion of haploid gametes to form genetically distinct diploid individual (zygote)-expensive in terms of fitness! -Asexual reproduction- new individuals are generated without the fusion of egg and sperm. Usually mitotic cell division. 1. Budding - new individuals arise from outgrowths of existing ones 2. fission - the separation of a parent organism into two individuals of approximately equal size
Describe at least 2 strategies that animals use to reduce the costs of sexual reproduction.
Alternation of sexual and asexual reproduction (aphids) Investment by both parents in offspring
No successful hormonal birth control for men has yet been developed. Why might hormonal birth control for men be more difficult than hormonal birth control for women? Recent efforts at hormonal birth control for men have included supplemental testosterone as part of the formulation. Why might this be helpful?
in women, you just have to stop one feedback loop, but in men there are 2. inhibition of one process would not be significantly effective. Unlike inhibin, testosterone targets the hypothalamus. Where it all begins. If the hypothalamus doesn't release GnRH the anterior pituitary can't release FSH to the Sertoli cells in the testis.
Briefly explain the point in the reproductive process when each of the following birth control methods act to prevent pregnancy: oral birth control pills, vasectomy, tubal ligation, morning after pill, intrauterine device.
oral birth control pills inhibit follicle growth and prevent ovulation vasectomy disconnect tubes of male, tubal ligation, morning after pill, intrauterine device. *****
