6.6: Hormones, Homeostasis and Reproduction

Outline the role of medical insulin the treatment of diabetes. Application: Causes and treatment of Type I and Type II diabetes.

Before the availability of medical insulin, the life expectancy of children with type 1 diabetes was short and the prognosis for the adult onset type 2 diabetes was very poor. The discovery of insulin in 1922 marked a major breakthrough in medicine for treatment of patients with diabetes. Medical insulin was initially isolated from animal pancreas but the potency varied and the supply fell short of the demand. In the early 1980's, recombinant DNA human insulin was prepared by adding the human insulin genes for expression in Escherichia coli. Insulin continues to be the primary therapy used in diabetes treatment.

Explain the role of pancreas beta cells in the control of blood glucose concentration. Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

Beta (β) cells are endocrine cells of the pancreas that produce and secrete the hormone insulin when blood glucose levels are high. Insulin promotes the storage of glucose as glycogen by liver cells and the uptake of glucose from the bloodstream of muscle and fat cells, thereby lowering the blood glucose levels.

Distinguish between treatment of type I and type II diabetes.​ Application: Causes and treatment of Type I and Type II diabetes.

Controlling blood glucose levels is the major goal of diabetes treatment. Type 1 diabetes is managed with insulin injections and diet management. Type 2 diabetes is first managed with dietary changes, weight reduction and exercise. Diabetes medications are prescribed when these measures fail to control the elevated blood sugars of type 2 diabetes. If other medications become ineffective treatment with insulin may be initiated.

Explain the role of insulin in the control of blood glucose concentration. Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

Insulin is a protein hormone secreted from β cells of the pancreas in response to high blood glucose levels. Insulin moves through the blood and binds to receptor proteins located in the membrane of target cells, major ones being liver, skeletal muscle and fat. Insulin helps reduce blood glucose levels by signaling the liver to convert glucose to the storage molecule glycogen. Insulin causes muscle and fat cells to take in glucose from the blood.

Describe the action of melatonin. Understanding: Melatonin is secreted by the pineal gland to control circadian rhythms.

Melatonin is a hormone secreted into the bloodstream by the pineal gland. Melatonin regulates the sleep-wake circadian rhythm in mammals. Melatonin is a protein hormone that binds to melatonin receptor proteins embedded in target cell membranes. Melatonin receptors are found throughout the body in places such as brain, retina, cardiovascular system, liver and gallbladder, colon, skin, and kidney.

Describe use of melatonin in treatment for jet lag.​ Application: Causes of jet lag and use of melatonin to alleviate it.

Melatonin pills are a commonly accepted jet lag treatment. Melatonin aids sleep during times when the body would not normally be resting, making it beneficial for people with jet lag.

State the source and location of action of progesterone in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Progesterone is a steroid hormone produced by the corpus luteum of the ovary during the luteal phase of the menstrual cycle. In the menstrual cycle, the target tissue for progesterone action is the uterus, where it prepares the endometrium for pregnancy in the event that the released egg is fertilized. Progesterone penetrates the cell surface and binds to a progesterone receptor protein in the cytoplasm of the cells. The progesterone-receptor complexes enter the cell nucleus, where it binds to DNA and influences the rate at which particular genes are transcribed.

Outline Harvey's methods of studying reproduction. Application: William Harvey’s investigation of sexual reproduction in deer.

Renowned physician and scientist William Harvey is best known for his accurate description of how blood circulates through the body. However, he also studied chicken embryos developing in eggs, carefully documenting differentiation and the stages of embryonic development. Through his work, Harvey (1651) was able to support the idea of development through epigenesis. Harvey thought that omne vivum ex ovum, or ‘every living thing comes from an egg’. In order to support his hypothesis, Harvey thought it would be easier to observe eggs in the uterus of large mammals. He slaughtered deer that had recently mated, opened the uterus, and searched for eggs or other early signs of embryonic development. However, he was not able to observe anything in the initial stages. He did not know that the eggs were microscopic in size (strong enough microscopes were not developed for almost another 200 years)!

Outline the function of the ovary in female reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The ovaries have two main reproductive functions in the body. They produce oocytes (eggs) for fertilization and they produce the reproductive hormones, estrogen and progesterone.

Outline the function of the penis in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The penis is the male organ used in sexual intercourse. The opening of the urethra, the tube that transports semen and urine, is at the tip of the penis. The glans of the penis also contains a number of sensitive nerve endings. The penis contains erectile tissue that fill with blood when the man is sexually aroused. The skin of the penis is loose and elastic to accommodate changes in penis size during an erection.

Outline the function of the scrotum in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The scrotum is a suspended sack of skin and smooth muscle that is present in most terrestrial male mammals and located under the penis. The scrotum contains the testes, epididymis, and vas deferens.

Outline the function of the seminal vesicles in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The seminal vesicles are a pair of exocrine glands that secrete a significant proportion of the fluid that ultimately becomes semen. The secretions from the seminal vesicles contain fructose (provide nutrient energy for the sperm), mucus (for lubrication and immune protection), and prostaglandins (triggers uterine contractions).

Outline the process of "embryo transfer" in vitro fertilization. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

After 2-6 days of development in an incubator, healthy fertilized eggs will have gone through multiple rounds of cell division and will have developed into an embryo. 1-2 embryos are transferred to the uterus for implantation. Prior to embryo transfer, the recipient woman is given artificial doses of estrogen and progesterone. These hormones prepare the endometrium lining of the uterus so that it becomes receptive to the embryo.

Outline the process of "fertilization" in vitro fertilization. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

After retrieval, eggs that appear healthy and mature will be mixed with sperm in a dish under a dissecting microscope. The sperm may then fertilize some of the eggs. Any resulting embryos are kept in the incubator to develop for up to 6 days before they are placed into the woman's uterus.

Explain the role of pancreas alpha cells in the control of blood glucose concentration. Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

Alpha (α) cells are endocrine cells of the pancreas that produce and secrete the hormone glucagon when blood glucose levels are low. Glucagon promotes the breakdown of glycogen by liver cells and the subsequent release of glucose into the bloodstream, thereby raising the blood glucose levels.

Outline the process of "down-regulation" in vitro fertilization. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

Down-regulation is a term to describe the process of reducing or suppressing the body's response to specific stimuli. When used with regard to in vitro fertilization (IVF), down-regulation uses drugs to suppress the natural action of FSH and LH on the ovaries so that doctors can better control ovulation and egg maturation during treatment. Down-regulation is the first step of IVF.

List characteristics triggered by testosterone at puberty. Understanding: Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.

During human puberty, there is an approximate 30X increase in testosterone production in boys. Testosterone is linked to many of the changes seen in boys during puberty, including: -sperm and semen production -increase in height and muscle mass -increase in body and pubic hair growth -deepening of the voice -enlargement of the penis, testes and prostate gland -development and maintenance of a sex drive

List characteristics triggered by estrogen at puberty. Understanding: Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty.

During human puberty, there is an increase in estrogen in females. Estrogen is secreted by the ovaries and is linked to many of the changes seen in girls during puberty, including: -breast growth -widening of pelvis -fat deposits in the breast, buttocks, thighs, and hips -growth of the uterus -commencement of menstruation. -growth of underarm and pubic hair

Outline the role of progesterone in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

During the luteal phase, the remnants of the ruptured ovarian follicle form the corpus luteum. The corpus luteum releases progesterone, which prepares the body for pregnancy in the event that the ovulated egg is fertilized. If the egg is not fertilized, the corpus luteum breaks down. Along with estrogen, the drop in progesterone levels signals the endometrium layer to shed, resulting in menstrual bleeding. If the egg is fertilized, progesterone stimulates the growth of blood vessels that supply the endometrium and stimulates glands in the endometrium to secrete nutrients that nourish the early embryo. Progesterone helps to maintain the endometrium throughout pregnancy.

Outline the function of endocrine glands. Understanding: Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.

Endocrine glands are glands of the endocrine system that secrete hormones directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid, parathyroid, hypothalamus and adrenal.

Name the two ovarian hormones that control the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Estrogen and progesterone are the two hormones that are released from the ovary and control the menstrual cycle. Estrogen and progesterone are steroid hormones.

Define in vitro fertilization. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

In vitro fertilization (IVF) is a complex series of procedures used to help with fertility or prevent genetic problems and assist with the conception of a child. During IVF , mature eggs are collected from ovaries and fertilized by sperm in a lab.

State symptoms of jet lag. Application: Causes of jet lag and use of melatonin to alleviate it.

Jet lag is a temporary sleep problem that can affect anyone who quickly travels across multiple time zones. Jet lag can cause daytime fatigue, difficulty concentrating, a generalized unwell feeling, and gastrointestinal problems.

Outline role of leptin resistance in human obesity. Application: Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease.

Leptin is a hormone that is secreted from adipocytes that acts on target cells in the hypothalamus and functions to suppress appetite and increase energy expenditure. Most obese people produce plenty of leptin, but their bodies fail to respond to it. The leptin is secreted but the receptor proteins in the hypothalamus fail to respond to it. When the hypothalamus doesn't receive the leptin signal, it erroneously thinks that the body is starving. The brain then encourages more eating and reduced energy expenditure.

State the source and location of action of LH (luteinising hormone) in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Luteinising hormone (LH) is a protein hormone produced and released by cells in the anterior pituitary gland. In females, LH moves through the blood and binds to receptor proteins found on ovary cells.

Outline how thyroxine regulates metabolic rate and body temperature based on negative feedback mechanisms. Understanding: Thyroxine is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.

Negative feedback is a situation in which a change in a given direction causes change in the opposite direction. An example of a negative feedback is seen in control of thyroid hormone secretion. Neurons in the brain (hypothalamus) sense circulating levels of thyroid hormone. If blood concentrations of thyroid hormones increase above a certain threshold, the thyroid stops thyroxine secretion until the levels in the blood return to normal. If thyroid hormone levels drop below the threshold, the thyroid is stimulated to produce and secrete thyroxine until levels in the blood return to normal.

Define "ovulation." Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Ovulation is the release of a mature egg from the surface of the ovary. This usually occurs mid-cycle, around day 14 of the average 28 day cycle. Ovulation is triggered by high levels of luteinizing hormone.

Discuss the ethical issues surrounding IVF. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

Positive considerations: -chance for infertile couples to have children -decision to have children is clearly a conscious one -genetic screening of embryos could decrease suffering from genetic diseases -spare embryos can safely be frozen and used for future pregnancies or for stem cell research Negative considerations: -IVF is expensive and not equally accessible to all people -success rate is relatively low -ethical or religious objections -could lead to eugenic choices -could lead to pregnancies with multiple fetuses, with associated risks -ethical dilemma of what to do with unused embryos

Define "positive feedback loop." Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Positive feedback is a situation in which a change in a given direction causes additional change in the same direction. For example, an increase in the concentration of a substance causes a response that causes continued increase in concentration of the substance.

Define "secondary sexual characteristic." Understanding: Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.

Secondary sex characteristics are features that appear during sexual maturity (puberty in humans). They are characteristics that distinguish the sexes of the species but are not directly part of the reproductive system (for example, deeper voice of male).

Outline the function of the cervix in female reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The cervix is the lowermost part of the uterus and is made up of strong muscles. The function of the cervix is to allow flow of menstrual blood from the uterus into the vagina, and direct the sperms into the uterus during intercourse.

Define "circadian rhythm." Understanding: Melatonin is secreted by the pineal gland to control circadian rhythms.

The circadian rhythm is the physical, mental, and behavioral changes that follow a daily cycle. The circadian rhythm responds primarily to light and darkness in an organism's environment. Sleeping at night and being awake during the day is an example of a light-related circadian rhythm. Circadian rhythms are found in most living things, including animals, plants, and microbes.

Outline the function of the endometrium in female reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The endometrium is the inner layer of the mammalian uterus. It thickens and then is shed during menstruation in humans and some other mammals (in most other mammals, the endometrium is reabsorbed). After fertilization, the embryo implants into the endometrium. During pregnancy, the glands and blood vessels in the endometrium further increase in size and number to support the placenta and developing fetus.

Outline the function of the prostate gland in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The prostate is a exocrine gland located between the bladder and the penis. The urethra runs through the center of the prostate, from the bladder to the penis. During ejaculation, the secretes an alkaline fluid, which helps protect sperm and prolong their life after they are deposited in the acidic environment of the vagina. The muscles of the prostate gland help propel this seminal fluid into the urethra during ejaculation .

Outline the function of the uterus in female reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The uterus is the hollow organ in the female reproductive system that holds a fetus during pregnancy. During pregnancy, the uterus grows and the muscles become stretched and thinner. Without the ability to expand, the human body would be unable to tolerate the rapid growth of a fetus.

Outline the function of the vagina in female reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The vagina is a muscular canal lined with nerves and mucus membranes. It connects the uterus and cervix to the outside of the body, allowing for menstruation, intercourse, and childbirth.

Outline the function of the vas deferens (sperm duct) in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The vas deferens is a long tube through which sperm move during ejaculation. Smooth muscle in the walls of the vas deferens contracts reflexively, propelling the sperm from the epididymis to the urethra.

Describe the function of thyroxine. Understanding: Thyroxine is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.

Thyroxine is a hormone secreted into the bloodstream by the thyroid gland. All cells in the body are likely targets for thyroid hormones. Thyroid hormones play vital roles in regulating the body’s metabolic rate and are essential for normal development, growth, and neural differentiation.

List symptoms of thyroxine deficiency. Understanding: Thyroxine is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.

Too little production of thyroxine by the thyroid gland is known as hypothyroidism. It may be caused by autoimmune diseases, low iodine intake or by the use of certain drugs. Thyroid hormones are essential for physical and mental development so untreated hypothyroidism before birth or during childhood can cause mental impairment and reduced growth. Hypothyroidism in adults causes reduced metabolism. It can result in symptoms such as fatigue, decreased body temperature, weight gain, poor memory, depression, stiffness of the muscles and reduced fertility.

Outline the cause of Type I diabetes. Application: Causes and treatment of Type I and Type II diabetes.

Type 1 diabetes occurs when the pancreatic beta cells are destroyed by an autoimmune process due to a genetic disorder. Because the pancreatic beta cells sense plasma glucose levels and respond by releasing insulin, individuals with type 1 diabetes have a reduced or complete lack of insulin. Type 1 diabetes is often diagnosed in childhood. With this disease, daily injections of insulin are needed.

Outline the cause of Type II diabetes. Application: Causes and treatment of Type I and Type II diabetes.

Type 2 diabetes occurs when the pancreas does not produce enough insulin for the amount of circulating glucose in the blood and/or the target cells do not respond effectively to normal levels of insulin, a condition termed insulin resistance. Type 2 diabetes is due to a combination of genetic and lifestyle factors. Type 2 diabetes is far more common than type 1. Type 2 diabetes is becoming more common due to increasing obesity and failure to exercise, both of which contribute to insulin resistance.

Describe the role and discovery of the ob allele in obese mice. Understanding: Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.

Leptin is a protein that is coded for by the "obese gene" (OB). The dominant allele (OB) leads to the production of leptin. The recessive allele (ob) is the mutated version of the gene. The OB gene was discovered by chance in a laboratory mouse colony in 1949. Homozygous recessive (ob/ob) mice were discovered that ate excessively and gained weight rapidly throughout their lives, reaching a weight three times that of unaffected mice. The ob/ob mice were not making functional leptin, and therefore there was no hormone to signal that the animal had had enough to eat.

State testosterone's role in stimulating the primary sexual characteristic of males. Understanding: Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.

Soon after the formation of the testis, the Leydig cells within the testes begin to secrete testosterone. Testosterone can influence tissues to become the male primary sexual characteristics during fetal development. Male primary sexual characteristics are the external and internal reproductive structures present at birth: the penis, the epididymis, the seminal vesicles, the prostate and the duct systems.

Define "gonad." Understanding: A gene on the Y chromosomes causes embryonic gonads to develop as testes and secrete testosterone.

A gonad is a gland that produces the gametes and sex hormones of an organism. The gonads are testis in males and ovaries in females. No difference can be observed in the gonads until the 6th week of embryonic life in humans. Undifferentiated gonads of XX or XY individuals are identical and can form either ovaries or testes. This period is called the bipotential stage of gonadal development. Presence of the SRY gene on the Y chromosome drives the bipotential gonad to differentiate into a testis. If there is no SRY gene, the gonad will develop into an ovary. As part of this SRY-prompted cascade, germ cells in the bipotential gonads differentiate into spermatogonia. Without SRY, different genes are expressed, oogonia form, and primordial follicles develop in the primitive ovary. Soon after the formation of the testis, the Leydig cells begin to secrete testosterone. Testosterone can influence tissues that are bipotential to become male reproductive structures.

Define "hormone." Essential Idea: Hormones are used when signals need to be widely distributed.

A hormone is a molecule released by a cell in a multicellular organism that influences the behavior of another cell within the same organism. Hormones are secreted from one cell and bind to a specific receptor on (or in) the target cell. Hormones are used to coordinate and control everything from metabolism to behavior.

Define "adipose tissue." Understanding: Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.

Adipose tissue is a loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body.

Outline the process of "superovulation" in vitro fertilization. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

Administration of high doses of artificial FSH induces "superovulation", or the stimulation of the development of more than the usual number of mature follicles and hence, an increased number of mature eggs. Multiple eggs are needed because some eggs won't fertilize or develop normally after fertilization.

Outline the role of follicle stimulating hormone (FSH) in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

During the follicular phase, FSH stimulates follicle development. With their growth, the cells of the follicles produce and secrete increasing amounts of estrogens.

Outline the role of luteinising hormone (LH) in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

During the follicular phase, LH is stimulates the follicles in the ovary to produce estrogen. Around day 14 of the cycle, a surge in LH levels causes the ovarian follicle to release a mature oocyte (egg), a process called ovulation. During the luteal phase, LH promotes the change of the follicle to the corpus luteum. The corpus luteum produces progesterone, which is required to support the early stages of pregnancy.

Outline the role of estrogen in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

During the follicular phase, estrogens are released from the developing follicle of the ovary. The estrogens stimulate the building of the endometrium lining of the uterus. Additionally, as more and more estrogen is produced from the follicles, it simulates a surge in luteinising hormone which in turn triggers the release of an egg from a mature follicle (ovulation). During the luteal phase, estrogens are released from the corpus luteum of the ovary. The estrogen, along with progesterone, cause the endometrium to thicken. If there is is no pregnancy, estrogen levels fall after day 21–24. The drop in estrogen levels signals the endometrium layer to shed, resulting in menstrual bleeding.

State the source and location of action of estrogen in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Estrogens are steroid hormones produced by the ovaries (follicle and corpus luteum). In the menstrual cycle, the target tissue for estrogen action is the uterus, where it causes growth of the endometrial lining. Estrogen penetrates the cell surface and binds to an estrogen receptor protein in the cytoplasm of the cells. The estrogen-receptor complexes enter the cell nucleus, where it binds to DNA and influences the rate at which particular genes are transcribed.

Summarize the action of hormones used to control the human menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Follicle stimulating hormone (FSH) stimulates the development of follicles. Follicles produce estrogen. Estrogen stimulates the growth of the endometrium lining of the the uterus and stimulates luteinizing hormone (LH) secretion. LH surge causes ovulation. LH stimulates the development of the corpus luteum. The corpus luteum secretes progesterone and estrogen. Progesterone and estrogen cause thickening of the endometrium lining and prepares the uterus for implantation. Progesterone and estrogen inhibit the secretion of FSH and LH (so that new follicles aren't developed and/or ovulated in the case of a pregnancy). Without pregnancy, aging corpus luteum secretes less estrogen and progesterone. Decreasing levels of estrogen and progesterone trigger menstruation. Additionally, with less estrogen and progesterone the inhibition on FSH and LH secretion is lifted. FSH levels begin to rise again, and the cycle repeats.

Name the two pituitary hormones that control the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are the two hormones that are released from the anterior pituitary and control the menstrual cycle. FSH and LH are protein hormones.

State the source and location of action of FSH (follicle stimulating hormone) in the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Follicle stimulating hormone (FSH) is a protein hormone produced and released by cells in the anterior pituitary gland. In females, FSH moves through the blood and binds to receptor proteins found on ovary cells, where it stimulates the growth of follicles (and resulting increased estrogen production) during the follicular phase of the menstrual cycle.

Outline early beliefs about the process of human reproduction. Application: William Harvey’s investigation of sexual reproduction in deer.

Generally, there were two historical ideas about the process of human reproduction. Preformationism Preformationism is the idea that that organisms develop from preformed, miniature versions of themselves that have existed since the beginning of creation. The new animal developed from these tiny particles that were fully formed, but smaller versions of the adult animals. Epigenesis Epigenesis proposed that the new animal develops progressively through a series of steps in which structures differentiate from each other. Aristotle was the first to propose this (correct) philosophy, however the idea was controversial until the 18th century. While Aristotle was correct in proposing epigenesis, his mechanism was incorrect! He believed that fathers contribute the essential characteristics of their offspring while mothers contribute only a material substrate, the menstrual blood. This 'soil and seed' idea was that males provide a "seed" which forms an egg when mixed with menstrual blood (the "soil"). The ‘egg’ then develops into a fetus inside the mother according to the information contained within the male 'seed’ alone.

Explain the role of glucagon in the control of blood glucose concentration. Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

Glucagon is a protein hormone secreted from α cells of the pancreas in response to low blood glucose levels. Glucagon moves through the blood and binds to receptor proteins located in the membrane of liver cells (hepatocytes). When glucagon binds to the glucagon receptors, the liver cells convert the storage polysaccharide glycogen into individual glucose molecules and release them into the bloodstream, thereby increasing blood glucose levels.

State Harvey's discoveries about reproduction. Application: William Harvey’s investigation of sexual reproduction in deer.

Harvey's (1651) observations of developing chicken embryos provided support for the idea of epigenesis (development progresses through a series of steps in which structures differentiate from each other). However, Harvey contradicted many of Aristotle's fundamental ideas on the matter. He correctly came to the conclusion that menstrual blood did not contribute to the formation of a fetus and that the fetus does not develop strictly from a male ‘seed.’ Harvey was also the first to speculate that humans and other mammals reproduce through the an egg. While he was incorrect in his proposed mechanism (suggesting that an egg found inside a female becomes fertilized by a kind of infection set in motion by the sexual act), Harvey's doctrine of omne vivum ex ovo (all life comes from the egg) was the first definite statement against the idea of spontaneous generation and was made nearly 200 years before a mammalian egg was observed in a microscope.

Outline how the human body regulates blood glucose levels. Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

High blood glucose levels are detected by beta cells in the pancreas. The cells secrete insulin in response. Insulin circulates in the bloodstream until it finds and binds to its receptor protein located on the target cell membranes (primarily liver, muscle and fat cells). Insulin stimulates the target cells to absorb glucose, thereby reducing the blood glucose levels. Within the target cells, the glucose is used in cell respiration, converted to glycogen (in liver and muscle) and/or converted to fat. Low blood glucose levels are detected by alpha cells in the pancreas. The cells secrete glucagon in response. Glucagon circulates in the bloodstream until it finds and binds to its receptor protein located on the target cell membranes (primarily liver cells). Glucagon stimulates the target cells to digest glycogen and release glucose, thereby increasing the blood glucose levels.

Define "homeostasis." Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

Homeostasis refers to stability, balance, or equilibrium. Physiologically, homeostasis is the body’s attempt to maintain a constant and balanced internal environment, which requires persistent monitoring and adjustments as conditions change.

Outline the prenatal development of female reproductive organs. Understanding: Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty.

In a chromosomal XX embryo, the the sex-determining region Y (SRY) gene is absent since there is no Y chromosome. Without the SRY gene, the bipotential gonads will differentiate to become the ovaries.

State the sources of estrogen and progesterone used in prenatal development. Understanding: Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty.

In placental mammals, both female and male fetuses are bathed in estrogens and progesterone of maternal origin (hormones from the mom and the placenta). Development of female reproductive structures is independent of maternal estrogen and progesterone (rather, female sex determination is based on absence of SRY gene). Once developed, the fetal ovary does not contribute significantly to circulating estrogens. The female fetus ovary has no documented role in differentiation of the female genital tract.

Outline a positive feedback mechanism that regulates the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

In positive feedback, rising levels of hormones feedback to increase hormone production. Positive feedback mechanisms regulate ovulation. During days 12–14, there is a dramatic increase in estrogen produced by the preovulatory follicle. The very high levels of estrogen (along with the absence of progesterone) provides positive feedback to the pituitary gland, initiating a rapid rise in the production of follicle stimulating and luteinizing hormones. This "LH surge" is what triggers ovulation.

Outline the biological cause of jet lag. Application: Causes of jet lag and use of melatonin to alleviate it.

Jet lag results from the desynchronization of the body's natural circadian rhythm and environmental cues for day and night. Jet lab is caused by traveling to different time zones. Melatonin concentration is key to the body's circadian rhythm synchronizing with daylight and darkness cycles. When jet lag happens, melatonin secretion is out of sync with the environmental cues of nightime.

Outline the mechanism of action of leptin. Understanding: Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.

Leptin is a hormone secreted into the bloodstream by adipose cells. If the amount of adipose tissue increases, blood leptin concentration rises. Leptin acts on cell receptors in the hypothalamus. Leptin helps to regulate energy balance by causing the hypothalamus to inhibit appetite, which in turn diminishes fat storage in adipocytes.

Discuss the use of leptin to treat human obesity. Application: Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease.

Leptin is a hormone that is secreted from adipocytes that acts on target cells in the hypothalamus and functions to suppress appetite and increase energy expenditure. Inheriting mutations of the OB gene (ob/ob; homozygous recessive) can lead to obesity because the leptin protein is not made. Leptin has been successfully used in the treatment of leptin-deficient obese patients. However... … injections of leptin must occur multiple times a day. … leptin injection affect the development and functioning of the reproductive systems. … weight loss with leptin treatment was immediately regained when treatment stopped. ...injections irritated the skin and caused swelling. … and, giving leptin to people who are obese due to leptin resistance (as opposed to having the leptin mutation) has no effect on weight loss.

Outline role of testosterone in prenatal development of male genitalia. Understanding: Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.

Male phenotypic differentiation of the bipotential gonad depends on the presence of the SRY gene on the Y chromosome. The gene codes for a protein called the sex-determining region Y protein (also called testis-determining factor, TDF). The protein acts as a transcription factor and initiates processes that cause the bipotential gonad to develop into testes. The fetal testes then begin to produce testosterone. Testosterone stimulates the development of the male reproductive structures during fetal development; the penis, the epididymis, the seminal vesicles, the prostate and the duct systems.

Outline the mechanism that regulates melatonin secretion in response to the day-night cycle. Understanding: Melatonin is secreted by the pineal gland to control circadian rhythms.

Melatonin production is controlled by the amount of light detected by the retina in the eyes. When the retina detects light, the pineal gland's production of melatonin is inhibited and the mammal is awake. When the retina does not depict light, melatonin is produced in the pineal gland and the mammal becomes tired.

Outline events occurring the menstruation phase of the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Menstruation is the elimination of the thickened lining of the uterus (endometrium) from the body through the vagina. Menstrual fluid contains blood, cells from the lining of the uterus (endometrial cells) and mucus.

Outline how leptin regulates hunger based on negative feedback mechanisms. Understanding: Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.

Negative feedback is a situation in which a change in a given direction causes change in the opposite direction. Adipose tissue produces leptin in amounts proportional to the amount of fat stored in the body. When a person eats less and their fat tissue decreases, their leptin levels also decrease. This change signals an area of the brain called the hypothalamus, which increases the person’s appetite. When a person eats more and their fat tissue increases, leptin levels increase and reduce appetite.

Outline how blood glucose homeostasis depends negative feedback mechanisms. Understanding: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations.

Negative feedback is a situation in which a change in a given direction causes change in the opposite direction. Negative feedback involving insulin and glucagon keep blood glucose levels within a narrow concentration range. After a meal, the small intestine absorbs glucose from digested food. If glucose levels get too high, the body releases insulin into the bloodstream. Insulin causes the body’s cells to take in and store glucose, lowering the blood glucose concentration. If blood glucose gets too low, the body releases glucagon, which causes the release of glucose from some of the body’s cells.

Define "negative feedback." Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Negative feedback is a situation in which a change in a given direction causes change in the opposite direction. For example, an increase in the concentration of a substance causes a response that ultimately causes the concentration of the substance to decrease. Negative feedback typically produces a condition in which a variable oscillates around a set point.

Outline a negative feedback mechanism that regulates the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

Negative feedback is a situation in which a change in a given direction causes change in the opposite direction. With the exception of events of ovulation, negative feedback mechanisms regulate the menstrual cycle, for example: Increasing FSH leads to increasing estrogen production by ovarian follicles. Increasing estrogen then inhibits the production of FSH, decreasing FSH which in turn causes ovaries to make less estrogen. Decreasing estrogen will again lead to increasing FSH... and the cycle repeats. The negative feedback loop outlined above ensures that only one dominant follicle can continue to maturity and complete each menstrual cycle. As estrogen levels rise, negative feedback reduces FSH levels, and only one follicle can survive.

Define "obesity." Application: Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease.

Obesity is defined by excessive fat accumulation that presents a risk to health. A crude measure of obesity is the body mass index (BMI). A person with a BMI of 30 or more is generally considered obese. Obesity is a major risk factors for a number of chronic diseases, including diabetes, cardiovascular diseases and cancer.

List symptoms of thyroxine over production. Understanding: Thyroxine is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.

Overproduction of thyroxine by the thyroid gland is known as hyperthyroidism. It may be caused by overactivity of the thyroid gland, autoimmune diseases, inflammation of the thyroid or a benign tumour. Hyperthyroidism is often recognised by a goitre, which is a swelling of the neck due to enlargement of the thyroid gland. Common symptoms of hyperthyroidism include increased body temperature, nervousness, insomnia, high heart rate, eye disease and anxiety.

Outline the cause and consequence of leptin resistance. Understanding: Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.

People with leptin resistance make high levels of leptin, but the leptin receptor protein doesn't function and as a result the hypothalamus doesn't receive the signal to reduce appetite and limit food-intake. Leptin resistance is caused by mutations in the LEPR gene. This gene provides instructions for making the leptin receptor protein, which is found on the surface of cells in the hypothalamus. LEPR gene mutations that cause leptin receptor deficiency prevent the receptor from responding to leptin, leading to the excessive hunger and weight gain associated with the disorder.

Outline the function of the epididymis in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The epididymis is a narrow, tightly coiled tube that connects a testicle to a vas deferens in the male reproductive system. It is present in all male reptiles, birds, and mammals. The epididymis is where sperm matures and develop the ability to be motile (swim). Mature sperm is stored in the epididymis until ejaculation

Outline the function of the fallopian tubes (oviducts) in female reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The fallopian tubes (oviducts), are of a pair of long, narrow tubes that transport the egg from the ovary towards the uterus, transport male sperm cells to the egg and are the location of fertilization. If fertilization occurs, the zygote will continue through the fallopian tube for implantation in the uterus.

Outline events occurring during the follicular phase of the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

The follicular phase starts on the first day of menstruation and ends with ovulation (typically day 14). Prompted by the hypothalamus, the pituitary gland releases follicle stimulating hormone (FSH). This hormone stimulates the ovary to produce 5 to 20 follicles (tiny nodules or cysts), which bead on the surface of the ovary. Each follicle contains an immature egg and secretes estrogen. As the follicular phase progresses, one follicle in one ovary becomes dominant and continues to mature. This dominant follicle suppresses all of the other follicles in the group. As a result, they stop growing and die (around day 10). The dominant follicle continues to produce estrogen. Estrogen stimulates the lining of the uterus (endometrium) to thicken in preparation for possible pregnancy.

Label a diagram of the female reproductive system. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The following structures should be included on a diagram of the female reproductive system: Ovary – two, shown adjacent to but not joined to the fallopian tube. Fallopian tube (oviduct) – drawn as a pair of arched tubes leading from just outside the ovary into the uterus. Uterus – drawn as an ovular pyramid with a thicker wall than the fallopian tube. Endometrium – drawn as a line on the inner lining of uterus. Cervix – shown as a constriction between the vagina and uterus. Vagina – drawn as a wide tube leading from the uterus

Label a diagram of the male reproductive system. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The following structures should be included on a diagram of the male reproductive system: Scrotum – shown around testes Testis/testicle - shown inside scrotum Epididymis - shown on top of the testis and connected to the vas deferens Vas deferens (sperm duct) - drawn as a double line connecting the epididymis to the urethra Seminal vesicle - sac shown branched off sperm duct Prostate gland - shown positioned where sperm duct connects with urethra Urethra - shown as double line linking bladder to end of penis, connecting to the vas deferens at the prostate gland Penis – shown with erectile tissue inside and with the urethra passing through it

Outline events occurring during the luteal phase of the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

The luteal phase begins at ovulation and ends with the start of menstruation (days 14-28). After ovulation, the pituitary hormones FSH and LH released from the anterior pituitary cause the remaining parts of the dominant follicle to transform into a structure known as the corpus luteum. This structure starts releasing progesterone, along with small amounts of estrogen. This combination of hormones maintains the thickened endometrium lining of the uterus, waiting for a blastocyst to implant. If a blastocyst implants in the lining of the uterus, it produces the hormones that are necessary to maintain the corpus luteum. The corpus luteum keeps producing the raised levels of progesterone that are needed to maintain the thickened lining of the uterus during the pregnancy. If implantation of a does not occur, the corpus luteum withers and dies, usually around day 22. The resulting drop in progesterone level causes the endometrium lining of the uterus to fall away (menstruation).

Outline the function of the urethra in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The male urethra is a narrow tube that conducts urine and semen from the bladder and vas deferens, respectively, to the exterior of the body via the penis.

Define "menstrual cycle." Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

The menstrual cycle is the pattern of changes in the ovary and uterus that occurs in the human female reproductive system and which makes pregnancy possible. The cycle starts on the first day of a menstrual period and averages 28 days long.

Describe the mechanism by which the SRY gene regulates prenatal gonad development.​​ ​ Understanding: A gene on the Y chromosomes causes embryonic gonads to develop as testes and secretes testosterone.

The sex-determining region Y (SRY) gene is found on the Y chromosome. The SRY gene provides instructions for making a protein called the sex-determining region Y protein (also called testis-determining factor, TDF). The protein acts as a transcription factor, which means it attaches to specific regions of DNA and helps control the activity of particular genes. The protein initiates processes that cause a fetus to develop male gonads (testes) and suppresses genes that are important in female development .of female reproductive structures (uterus and fallopian tubes).

Outline the function of the testis in male reproduction. Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

The testicle or testis (plural testes) is the male gonad. The functions of the testes are to produce sperm and testosterone.

Outline the role of thyroxine in body temperature regulation. Understanding: Thyroxine is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.

Thyroid hormones stimulate diverse metabolic activities in most tissues, leading to an increase in basal metabolic rate. One consequence of this increase in metabolic activity is an increase in body heat production. Heat generated by metabolism plays an important role in keeping the bodies of endothermic animals warm. Endotherms, primarily birds and mammals, are animals that are able to regulate their own body temperature using the energy generated by metabolism.

Outline the process of "egg retrieval" in vitro fertilization. Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.

When the follicles are large enough, the woman is given a dose of a hormone that is similar to LH. This hormone stimulates ovulation. The eggs must be retrieved before they are released from the ovary. 34-36 hours after the drug is given, an ultrasound probe is inserted into the vagina to identify follicles. Then a thin needle is inserted through the vagina and into the follicles to retrieve the eggs. The eggs are removed from the follicles through a connected suction device. Because of superovulation, multiple eggs will be removed, typically up to 12. Not all of the eggs will be viable.

Out the effects of diabetes on the body. Application: Causes and treatment of Type I and Type II diabetes.

With diabetes, the pancreas either produces no insulin, too little insulin or the cells become resistant to the insulin. All of these causes allows blood glucose levels to rise while depriving the body cells of the much-needed glucose energy source. This can lead to a wide variety of problems affecting nearly every major body system. The most common long-term diabetes-related health effects are: -damage to the large blood vessels of the heart, brain and legs -damage to the small blood vessels, causing problems in the eyes, kidneys, feet and nerves

Describe how Harvey was limited in his reproduction research given the tools available at the time.​ Nature of Science: Developments in scientific research follow improvements in apparatus- William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented 17 years after his death.

Working in the mid 1600's, William Harvey did not have the tools required for visualizing mammalian egg cells. The microscope was invented 17 years after his death, and a compound microscope with the magnification required for visualizing mammalian egg cells would not be developed for about 200 more years! So, Harvey used a simple hand lens while observing deer reproductive structures. Given the technology available, Harvey was unable to observe direct evidence of his omne vivum ex ovo (all life comes from the egg) hypothesis.

Annotate a graph of progesterone hormone levels during the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

X axis = day of menstrual cycle (0-28) Y axis = relative hormone level Day 0-14: low levels of progesterone (since there is no corpus luteum to produce it). Day 15-25: increase in progesterone as the corpus luteum secretes the hormone to prepare the uterus for a pregnancy. Day 25-28: without a pregnancy, progesterone levels drop as the corpus luteum degrades.

Annotate a graph of estrogen hormone levels during the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

X axis = day of menstrual cycle (0-28) Y axis = relative hormone level Day 0-8: gradual increase in estrogen as FSH stimulates follicles to grow and secrete estrogen. Day 9-11: steeper increase to the estrogen peak as the dominant follicle grows (this increase activates positive feedback on FSH and LH which leads to ovulation). Day 12-19: drop in estrogen levels as follicle ruptures and develops in to the corpus luteum. Day 20-25: increase in estrogen as the corpus luteum secretes the hormone to prepare the uterus for a pregnancy. Day 25-28: without a pregnancy, estrogen levels drop as the corpus luteum degrades (eventually triggering menstruation).

Annotate a graph of luteinizing hormone levels during the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

X axis = day of menstrual cycle (0-28) Y axis = relative hormone level Day 0-9: LH levels remain low (estrogen negative feedback on pituitary hormones). Day 10-14: LH surges to peak level (due to high estrogen positive feedback) and triggers ovulation. Day 15-18: LH drops (due to loss of high estrogen positive feedback after ovulation). Day 19-28: LH levels remain low (estrogen negative feedback on pituitary hormones).

Annotate a graph of follicle stimulating hormone levels during the menstrual cycle. Understanding: The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.

X axis = day of menstrual cycle (0-28) Y axis = relative hormone level FSH has the lowest levels relative to the other hormones. Day 0-5: (low estrogen negative feedback causes) gradual increase in FSH leads to follicle growth. Day 6-11: gradual decrease in FSH due to dominant follicle secreting estrogen (estrogen negative feedback on FSH). Day 12-14: increase in FSH to peak at ovulation (due to high estrogen positive feedback). Day 14-19: decrease in FSH to lowest level (due to loss of high estrogen positive feedback after ovulation). Days 20-28: FSH remains at lowest level (as estrogen from the corpus luteum provides negative feedback).