WEEK 6: Hormonal Control and Reproduction - OBJECTIVES

Explain how the structures of the human female reproductive system are adapted to produce ova, receive sperm, and nourish a developing embryo.

The human female reproductive system includes the vagina, uterus, fallopian tubes, and ovaries. During oogenesis, immature diploid cells called oogonia develop into mature ova in one of the ovaries. A primary oocyte undergoes meiosis I to produce a secondary oocyte and a polar body. The secondary oocyte undergoes meiosis II to produce a second polar body and a haploid ovum, or egg.

What conditions must be met for fertilization to occur in animals?

- Individuals must produce sperm and eggs. - Individuals must deliver sperm and eggs to the same location. - Environmental conditions must be suitable for fertilization.

What are a function(s) of the uterus?

- support the developing embryo - provide an environment for embryo implantation - support the fetus and placenta - deliver the fetus via muscular contractions

Which of the following scenarios is true of the condition known as sexual ambiguity?

A child can be born with genitalia opposite from what would be expected based on its chromosomal makeup.

What is the Red Queen hypothesis?

A host must continually evolve new defences to fight off potential disease-causing agents, while these agents are also developing new tactics for infecting the host.

Distinguish negative and positive feedback loops and give examples of each.

A negative feedback loop is a series of steps in which the final product of the loop decreases or eliminates the stimulus that initiated the loop. A positive feedback loop is the reverse, a series of steps in which the final product of the series increases or augments the stimulus with which the loop began.

Describe hormonal control of events in the human female reproductive life cycle, including puberty, pregnancy, and menopause.

A precise timing of hormone-controlled events is required in the reproductive life cycle, leading to puberty, pregnancy, and menopause.

What hormone does the pituitary gland produce during the fight-or-flight response?

ACTH

After vigorous exercise, a person becomes dehydrated. Which hormone would the body begin to produce as a result of this condition?

ADH

Which of the following statements best describes ovulation?

An ovum is released from the ovary.

Give examples of fertilization strategies in the animal kingdom.

Animal species have many physical and behavioral adaptations to accomplish fertilization. These include the use of environmental cues to synchronize mating behaviors, pheromones to attract mates for spawning or copulation, courtship behaviors that allow individuals to judge the fitness of prospective mates, and structural adaptations, such as the penis, for delivery of sperm.

Human sperm and ova are similar in which way(s)?

Both are haploid.

How do neuroendocrine signaling pathways combine features of both endocrine and synaptic signaling?

Both neuroendocrine and synaptic signaling types release chemical signals from neurons, and signals of both neuroendocrine and endocrine pathways travel through the bloodstream.

Compare and contrast five types of chemical signal pathway mechanisms.

Chemical signaling pathways allow all of an organism's cells to coordinate their operations, maintaining the organism in homeostasis. There are five main types of chemical signaling pathway mechanisms: endocrine, paracrine, autocrine, neuroendocrine, and synaptic. The latter two involve transmission of signals via neurons. All signaling pathways involve signal transmission, signal reception, and cellular response. Endocrine signals are called hormones and act via the bloodstream; paracrine and autocrine chemical signals are local regulators and diffuse locally; neurons release neurotransmitters into synaptic junctions between themselves and other cells; and neuroendocrine signals are called neurohormones, discharged directly into the bloodstream.

Explain how cyclical fluctuations in hormones govern human female reproductive cycles.

Cyclical fluctuations in hormones govern human female reproductive cycles. Release of GnRH from the hypothalamus into the blood supply of the anterior pituitary causes the synthesis and release of LH and FSH. FSH and LH act on the gonads (ovaries or testes) to activate sex hormone production and gamete formation.

All of the following are consequences of a "World Without Hormones" except one. Which is that one?

Everyone would be afflicted with goiter.

Distinguish between internal fertilization and external fertilization.

External fertilization occurs outside of the mother's body and is found mainly among aquatic species. Internal fertilization occurs inside the mother's body and predominates among land-dwelling species. Internal fertilization increases the chances of fertilization and prevents the desiccation of the zygote.

Which of the following is true of the pituitary hormone FSH?

FSH stimulates the development of gametes.

Which of the following is true of the pituitary hormone FSH?

FSH stimulates the development of the egg and sperm cells.

Describe how an organism's size or activity level can influence metabolism.

Factors that affect basal metabolic rate include sex, age, body surface area, external temperature, and genetic factors. Two of the greatest influences on BMR are an animal's size and level of activity. In general, a greater body mass corresponds to a higher basal metabolic rate. BMR also increases in direct proportion to the level of an animal's activity; the more active an animal, the greater its metabolic rate. This relationship is observed during periods of activity, but an animal's BMR does not remain significantly altered after its exercise has been completed.

Identify the conditions that must be met for fertilization and zygote survival to occur.

For fertilization to occur, individuals must produce haploid gametes (sperm and eggs). Both gametes must be brought into the same location so that they can meet and fuse to form a zygote (fertilization). Certain environmental conditions, such as temperature, salinity, and pH, must be optimized to ensure zygote survival. Parents may also provide extensive parental care, during which they protect offspring from predation and provide them with nourishment. Internal fertilization and parental care increase the offspring's chances of survival.

Distinguish between torpor and true hibernation and relate these conditions to metabolic changes.

Hibernation is a state of inactivity in animals, characterized by a reduced metabolic rate, lower body temperature, and reduced respiration. Many species of animals hibernate during times when food is not readily available or when environmental conditions are too severe for their survival. Torpor is a physical state that lies somewhere between a deep sleep and hibernation. During torpor, an organism's metabolic rate drops, its temperature and respiration rate decreases, but these changes are not nearly as profound as during hibernation.

Describe how a basic hormone triggers a response in a target tissue.

Hormonal pathways tend to have common characteristics. A hormone is produced at a particular gland in the body, after which it travels through the bloodstream to some target tissue. There it either docks at receptor sites on cells or enters the cell (depending on whether it is water — or lipid — soluble), and initiates signal transduction within those cells, which produces some type of specific output from the cells.

Describe and give examples of hormonal regulation of reproductive cycles and behaviors in the animal kingdom.

Hormonal regulation of reproductive cycles and behaviors is a common theme in the animal kingdom. Several hormones control the male and female reproductive systems.

Differentiate among the three major groups of hormones in terms of chemical structure and solubility.

Hormones are chemicals produced in one part of the body that then travel to target cells in other parts of the body. Hormones can be classified on the basis of their chemical structures as amines, polypeptides, or steroids. They can also be classified on the basis of their solubility as hydrophilic (soluble in water) or lipophilic (soluble in organic solvents).

Explain the role of hormones in maintaining homeostasis.

Hormones play a significant role in maintaining homeostasis in the human body. Internal (i.e., low blood sugar, too much water) and external (exposure to sunlight, smoke from a fire) stimuli trigger the release of hormones allowing an organism to either to respond in survival mode or to balance critical life functions. If a hormonal cycle is disrupted, the body can experience disorders such as hypothyroidism and goiter. In hypothyroidism, the thyroid gland grows abnormally large in an effort to produce sufficient quantities of thyroid hormones to maintain necessary levels of the hormones in the bloodstream.

Delineate the various hypothalamic-pituitary-target tissue axes, including thyroid, adrenal, and gonadal, and the various hormones and target tissues involved in each step.

In the hypothalamic-pituitary-endocrine axes, hormones flow from the hypothalamus to the anterior or posterior pituitary, which then releases hormones to other glands or target tissue. Oxytocin and antidiuretic hormone (ADH) move along the hypothalamic-posterior pituitary axis. Oxytocin is involved in a number of maternal functions, while ADH regulates the absorption of water in the kidneys. The hypothalamic-anterior pituitary axis includes several hormones, including follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and prolactin.

What is the primary purpose of an animal adopting a promiscuous mating strategy?

It increases the likelihood of mating with the fittest partners.

Describe the relationship between estradiol levels and GnRH production during a female's reproductive cycle?

Low estradiol levels inhibit GnRH release, whereas high estradiol levels stimulate GnRH release.

Explain how fertilization strategies are adaptive to particular environments.

Many of the fertilization strategies employed by different animals are adaptive to specific environmental conditions. External fertilization is advantageous when it occurs at a time and/or location that will provide protection or important resources to offspring. For example, spawning is usually advantageous in aquatic environments because the eggs and sperm are able to float and drift through the water to one another. Internal fertilization tends to protect gametes, zygotes, and embryos of land animals from harsh conditions in the external environment. For example, internal fertilization allows for the maintenance of optimum temperature and pH for fertilization events, and internal gestation results in the birth of more developed offspring.

List some of the key hypotheses that have been proposed to explain the evolutionary advantages of sexual reproduction, and describe the process of sexual selection.

Many viable hypotheses have been proposed explaining the evolutionary advantages of sexual reproduction including DNA Repair, Muller's Ratchet, and the Red Queen Hypothesis. Scientists gather evidence and use models to study the validity of these hypotheses. Sexual selection is a form of natural selection in which one sex prefers certain traits in the opposite sex. These can include traits that allow one individual to outcompete other members of the same sex and thus gain access to the opposite sex. Individuals possessing the preferred traits will mate more frequently and leave more offspring in the next generation, thereby driving evolution.

Explain what metabolism is and how we measure it.

Metabolism is the sum total of all chemical reactions that occur within an organism that keep it alive, allow it to grow, and make reproduction possible. The metabolic rate quantifies the pace at which these reactions occur. Metabolic rate can be measured several ways, including gauging the amount of heat produced by an organism over a given period of time or determining the amount of oxygen consumed or carbon dioxide produced during a given time period.

What is the advantage of being monogamous?

Monogamy ensures that the energy involved in reproduction and offspring rearing is only invested in rearing the parents' own offspring.

What is the main difference between pheromones and other types of chemical signals?

Most chemical signals remain within an organism; pheromones leave organism boundaries to signal others of the same species.

Researchers discover a previously unknown species that reproduces both sexually and asexually. The offspring produced through sexual reproduction have fewer harmful genetic mutations than offspring produced through asexual reproduction. Which hypothesis regarding the advantages of sexual reproduction does this data support?

Muller's Ratchet hypothesis

Explain how negative feedback mechanisms control sex hormone concentration in human males.

Negative feedback is commonly used to regulate hormone levels. The sex steroid hormones estradiol and testosterone negatively feed back upon neurons in the brain, slowing hypothalamic release of GnRH in most cases. Negative feedback mechanisms control sex hormone concentration in both human males and females.

Give a specific example of how the endocrine system regulates homeostasis.

One important function of the endocrine system is to maintain homeostasis. It often does so by means of negative feedback loops, in which the final outcome of a series of reactions acts to moderate or terminate the initial stage of those reactions. Conversely, the final outcome of a series of reactions may act on the initial stage by enhancing it instead, a process called a positive feedback loop. Negative feedback loops ensure that these concentrations are maintained at the appropriate levels, while positive feedback loops ensure that once a process begins, it increases in intensity or proceeds to completion. Improper function of a feedback system may result in disease. One example of the endocrine system regulating homeostasis is the release of corticoids from the adrenal cortex, which regulates the production of blood sugar, salt and water levels, and blood volume and pressure.

If the adrenal medulla were removed, which of the following statements would be true?

Organisms would be less able to survive sudden attacks and emergencies.

Explain how pheromones function between individuals.

Pheromones are chemical signals released into the environment for the purpose of communicating with other members of the same species.

Which of the following hormones is a nontropic hormone?

Prolactin

Which of the following statements about releasing hormones is true?

Releasing hormones are released by the hypothalamus.

What is the overall advantage of hormone-controlled reproductive cycles?

Reproduction can be timed with variable environmental conditions.

Distinguish between sexual and asexual reproduction.

Sexual reproduction involves joining two haploid gametes to form a diploid offspring with a unique genetic combination. Asexual reproduction is the production of offspring from only one parent. Asexually-produced offspring are genetic clones of the parent.

Biological signals can be amplified through chains of events. Which of the following describes a multi-step chain of events in which final signal is larger than the starting signal?

T3 and T4 are released from the thyroid after being stimulated by TSH, which was itself stimulated by TRH.

Which of the following conclusions can be drawn from experiments by Alfred Jost, in which he removed the gonads (ovaries and testes) from rabbit embryos in order to study their role in sexual differentiation?

Testosterone is responsible for the development of male gender in rabbits.

Distinguish the hormones, target tissues, and signals from the adrenal cortex and adrenal medulla

The adrenal cortex and adrenal medulla both play important roles in responding to stress. The adrenal medulla initiates a short-term immediate response mediated by the nervous system, while the adrenal cortex initiates a long-term extended response mediated by the endocrine system. In the adrenal medulla, the nerve signals stimulate modified neurons called chromaffin cells to release epinephrine and norepinephrine into the bloodstream. These two hormones travel throughout the circulatory system of the body and initiate a series of responses to the emergency, including increasing blood pressure, blood sugar levels, and respiratory, metabolic and heart rates. The adrenal cortex releases glucocorticoids (most notably cortisol) and mineralocorticoids (most notably aldosterone) in response to stress. Mineralocorticoids stimulate retention of sodium ions and water by the kidneys, increasing blood pressure and blood volume, while glucocorticoids shift metabolism from fats to glucose in order to increase blood sugar levels.

Give examples of diverse reproductive strategies in the animal kingdom.

The animal kingdom contains a great diversity of reproductive strategies, both sexual and asexual. Asexual strategies include fission, budding, fragmentation and regeneration, and parthenogenesis. Sexual strategies include monogamy, polygamy, polyandry, promiscuity, hermaphroditism, and sex-role reversal. These strategies evolve largely by sexual selection.

Describe how sex steroids govern development of sex characteristics, reproductive readiness, and reproductive behavior.

The endocrine system also regulates the growth and development of an organism. Both male and female sexual development begins when the hypothalamus releases gonadotropin-releasing hormone to the anterior pituitary, which, in turn, releases luteinizing hormone and follicle-stimulating hormone to the gonads. Feedback loops control the continuing functioning of this process in both males and females.

Describe the primary role of the pituitary in vertebrate endocrine signaling and distinguish tropic vs. non-tropic effects of hormones.

The endocrine system consists of eight major glands and tissues in other organs that produce hormones that travel to other endocrine cells or target cells throughout the body. The hypothalamus produces thyrotropin-releasing hormones (TRH), growth-hormone-releasing hormones (GHRH), gonadotropin-releasing hormones (GnRH), and corticotropin-releasing hormone (CRH). In addition, the hypothalamus produces oxytocin and the antidiuretic hormone (ADH), which are transported to and released from the posterior pituitary. The anterior pituitary produces thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), growth hormone (GH), and prolactin, among other hormones. Tropic hormones stimulate other endocrine cells, while non-tropic hormones only stimulate target cells.

Compare the levels of estradiol and progesterone seven days after ovulation to the respective levels immediately before ovulation.

The estradiol level is slightly lower than it was before ovulation, but the progesterone level is much higher.

Explain how the structures of the human male reproductive system are adapted to produce and deliver sperm.

The human male reproductive system includes the testes, a series of ducts to carry the sperm and semen, and several glands that add components such as nutrients and enzymes to the semen. A diploid spermatogonium divides mitotically to produce two diploid spermatocytes. Each spermatocyte undergoes meiosis to produce four haploid spermatids, which mature into spermatozoa.

Describe the primary role of the hypothalamus in vertebrate endocrine signaling and how the hormones it secretes move to the pituitary.

The hypothalamus is a complex portion of the brain located between the thalamus and the brain stem. One of its most important functions is the production of releasing and inhibiting hormones to the pituitary gland, which then produces other hormones in response to the hypothalamic hormones. The endocrine system often makes use of feedback loops. In a negative feedback loop, the outcome of a series of reactions inhibits the continued operation of that loop. In a positive feedback loop, the outcome augments the continued operation of that loop

Describe and give examples of the diversity and unity of reproductive structures.

The male and female reproductive organs are designed to manufacture and store the gametes, as well as to allow the act of mating. The processes of spermatogenesis and oogenesis produce haploid sperm and ova in the gonads, the testes and ovaries.

Describe basal metabolism rate and how researchers apply this information.

The minimum metabolic rate needed to keep an organism alive is called its basal metabolic rate (BMR). Physicians use basal metabolic rate to determine whether a person's body is functioning normally and, if not, what potential problems may be present. Appropriate caloric intake can also be calculated using basal metabolic rate.

Which of the statements is true about a hormone's relationship to water?

The terms hydrophobic, lipophilic, and water-insoluble, refer to hormones that are not soluble in water, but do dissolve in non-aqueous solvents such as alcohol.

Which is the correct general purpose of pheromones?

They let organisms signal to others of their own species.

What is the function of spermathecae in the female reproductive system?

They store sperm for long periods until conditions are suitable for fertilizations.

Which of the following reproductive strategies requires fertilization?

monogamy

Compare and contrast water-soluble hormone and lipid-soluble hormone signal mechanisms.

Water-soluble hormones are proteins and derivatives of amino acids. Water-soluble hormones leave the signaling cell by exocytosis and travel through the bloodstream. When they reach their target cells, they dock on membrane spanning signal transductor proteins, which carry their signal to the interior of the cell. There, the signal transductor proteins set off a range of reactions, which ultimately amplify the hormone's signal and switch cell processes on or off. Lipid-soluble, or steroid hormones, pass freely through signaling cell membranes without the need for signal transductor proteins. They are escorted by carrier proteins in the blood stream to the target cells, and pass directly into a target cell's cytosol. There they are met by hormone receptors, which form complexes with the receptors that pass into the nucleus. The hormone-receptor complex stimulates the transcription of particular genes.

In humans, the absence of any specific signal during embryonic development leads to the degeneration of ___ and the preservation of ___.

Wolffian ducts, Müllerian ducts

Which structure must a target cell have in order for a hormone to initiate a response?

a receptor

Chemical castration is most often accomplished by which of the following procedures?

administration of medroxyprogesterone acetate, a progesterone-like chemical that causes a decrease in testosterone production

What is the appropriate treatment for a person with Addison's disease?

administration of supplemental steroids on a long-term basis

Based on their chemical structure, most hormones can be classified into which of the following three groups?

amines, peptides, and steroids

In which type of animals would hermaphroditism most likely confer the greatest selective advantage?

animals that remain in one location for their entire lives

In which of the following glands would you expect the abnormality responsible for the exaggerated height achieved by Charles Byrne, the so-called Irish Giant?

anterior pituitary

Which fertilization strategy is specifically adapted to land environments?

copulation

Which of the following pairs of hormones are released by the adrenal cortex?

cortisol and aldosterone

All animals that rely on sexual reproduction produce ___(s). The male ___ is the sperm and the female ___ is an ovum.

gamete

The hormone tyrosine is an amino acid. Based on this information, which choice correctly describes the solubility of tyrosine?

hydrophilic

Between which glands of the hypothalamic-pituitary axis do hormones directly pass through neurosecretory cells?

hypothalamus and posterior pituitary

Which of the following correctly describes the function and target tissue of luteinizing hormone (LH)?

in the gonads, stimulates sex steroidogenisis

Scientists discover a new chemical that is similar in structure to estrogen. What might be the consequences of excessive exposure to this drug?

irregular menstrual cycles in women; premature onset of puberty in girls; and abnormal prostate gland development in males

Which reproductive strategy results in offspring with the greatest genetic diversity?

mating

A primary spermatocyte undergoes ___ to produce two secondary spermatocytes.

meiosis I

The cessation of ovulation after about 500 cycles is called ___.

menopause

The entire process of oogenesis produces which of the following?

one ovum and two polar bodies

Which organ produces eggs in many animal species?

ovaries

A cell releases chemical signals that diffuse to receptors on different cell types nearby. What type of signal pathway mechanism is the cell using?

paracrine

Which signal pathways use local regulators as signals?

paracrine and autocrine

The period during which a sexually immature individual becomes sexually mature is called ___.

puberty

Human spermatogenesis occurs in which structure?

seminiferous tubules

Female peacocks prefer to mate with males with large and colorful tails. What is this process of choosing a mate called?

sexual selection

Which reproductive strategy is almost exclusively found among aquatic animal species?

spawning

An Apatosaurus must suddenly run from a speeding lava flow. What chemical signal pathway would you expect it to use to make its leg muscles contract?

synaptic signaling

What stimulus initiates the positive feedback loop that takes place during childbirth?

tactile signals produced by the newborn's head against the mother's cervix

Which organ produces sperm in many animal species?

testes

In males, which of the following hormones exhibits negative feedback on GnRH secretion?

testosterone

What is fertilization?

the joining of male and female gametes

Which two glands regulate the level of calcium in the blood?

thyroid and parathyroid

A cell produces a lipid-soluble hormone. What molecule can help the hormone reach its target cell?

transport protein, also called a carrier protein