Hormones and Metabolism: The light version of signalling

Hormones and Metabolism: The light version of signalling D5

D.5 Human Endocrine System

Understandings 1. Endocrine glands secrete hormones directly into the bloodstream. 2. Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a receptor-hormone complex. 3. The receptor-hormone complex promotes the transcription of specific genes. 4. Peptide hormones bind to receptors in the plasma membrane of the target cell. 5. Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside the cell. 6. The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland. 7. Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis.

Applications and Skills A1 Some athletes take growth hormones to build muscles. A2 Control of milk secretion by oxytocin and prolactin.

Syllabus Statements 1. Define hormone. Describe the 2 general types of hormones with 2 examples of each type. 2. Differentiate between the actions of peptide hormones and steroid hormones. 3. Describe the structural and functional relationship between the hypothalamus and the anterior and posterior pituitary glands. 4. Outline the functions of the pituitary hormones giving an example of each function. 5. Describe the control of the secretion of ADH from the posterior pituitary gland. 6. Describe the control of production and secretion of prolactin. 7. Discuss the use by some athletes of Growth Hormone. Be sure to include the type of hormone GH is, its source, its effects, the reasons that some athletes take it along with its side effects.

Retro (New SL) Syllabus 1. Describe the source and effects of the hormone, thyroxin. 2. Describe the effects of the hormone, leptin, and its testing on patients with clinical obesity along with the reasons for the failure to control the disease. 3. Describe the source and effects of the hormone, melatonin and how it may be used to counter jet lag. 4. Describe the hormonal control of blood glucose levels.

Example of Homeostasis and Negative Feedback: Regulation of Body Temperature The thermostat function of the hypothalamus and feedback mechanisms in human homeostasis

Glucose Homeostasis (Retro) Glucose homeostasis: maintained by insulin and glucagon. A rise in blood glucose above the set point (about 90mg/100mL in humans) stimulates the pancreas to secrete insulin, which triggers its target organs to take up excess glucose from the blood. Once the excess is removed and blood glucose concentration dips below the set point, the pancreas responds by secreting glucagon, which acts on the liver to raise the blood glucose levels.

Hormone: Chemical messengers secreted by endocrine glands into the blood and transported by the blood to specific target cells. Long distance signaling molecules Two major types of hormones: A. Lipid soluble hormones: e.g. steroid hormones come from gonads (testosterone, estradiol (estrogen), and progesterone (progestin)) and the adrenal cortex (cortisol and aldosterone). B. Water soluble hormones: e.g. peptide hormones include Oxytocin (posterior pituitary) and ADH (posterior pituitary), calcitonin (thyroid gland); tyrosine derivatives (epinephrine and norepinephrine, thyroxin also known as T4 and Triiodothyronine).

Catecholamines (Tyrosine Derivatives)

Steroid Hormones

Some Hormones of the Endocrine System

General Mechanisms of Chemical signaling A chemical signal secreted by a cell either A. Binds to a receptor protein on the surface of a target cell, triggering a signaltransduction pathway or B. Penetrates the target cell s plasma membrane and binds to a receptor inside the cell.

Chemical Signaling Mechanism

Peptide Hormones: act through signal transduction pathways. A signal transduction pathway is a series of molecular changes that convert an extracellular chemical signal to a specific intracellular response. Components of signal-transduction pathway include: 1. Reception of signal: signal receptor located in the plasma membrane. 2. Transduction: might involve phosphorylation by a kinase, the generation of a second signal using cyclic AMP (camp) or Ca++. In any case a 2 nd signal or 2 nd message is generated. 3. Third event is a cellular response

Signal-Transduction Pathway

Signal That Binds to a Surface Receptor That Activates a Gene

Enzyme Cascade: NB ATP is used to create unstable phosphorylated intermediates

camp as a second messenger

Cyclic AMP

G Protein Receptor

G Protein Receptor

Specific example of cellular response to epinephrine by liver cells

Specific Mechanism of Action: Steroid Hormones Steroids hormones:are able to pass through the plasma membrane. 1. Hormones such as estrogen and testosterone bind to a receptor protein in the cytosol, activating it. 2. Receptor-hormone complex enters the nucleus and binds to specific genes. 3. The bound protein stimulates the transcription of the gene into mrna. 4. The mrna is translated into specific protein.

Another way to say this: When the signal is bound to an intracellular receptor, the receptor acts as a transcription factor, causing a change in gene expression. The binding of signal to a surface receptor, it can lead to either a change in gene expression or a change in cytoplasmic activity.

Hormones of the hypothalamus and pituitary glands. The pituitary gland is located at the base of the brain and is surrounded by bone. It consists of the posterior pituitary (neurohypophysis) and the anterior pituitary (adenohypophysis). The posterior pituitary is actually an extension of the hypothalamus. Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis.

Pituitary Gland Secretions Growth: Growth Hormone (GH) which stimulates mitosis and organism growth. Targets liver to release insulin-like growth factor which stimulates bone and cartilage growth. Reproduction: LH (luteinizing hormone) and FSH (follicle stimulating hormone). Prepares ovarian cells for ovulation in females, and needed for sperm production in males. Developmental Changes: GH, LH and FSH. GH is necessary for all developmental growth throughout adulthood. LH and FSH secretions increase during puberty, leading to ovulation and sperm production, among other functions. Homeostasis: ADH (antidiuretic hormone): Secretion of ADH is needed for the reabsorption of water from the collecting ducts in the kidneys. Involved in osmoregulation.

Neurosecretory cells: many endocrine organs and tissues contain specialized nerve cells that secrete hormones. Animals have neurosecretory cells in their brain that secrete hormones into the blood. The hypothalamus plays an important role in integrating the vertebrate endocrine and nervous system.

Posterior Pituitary

a) The Posterior Pituitary Neurosecretory cells in the hypothalamus synthesize antidiuretic hormone (ADH) and oxytocin. These hormones are transported down the axons to the posterior pituitary, where they are stored. The posterior pituitary releases them upon stimulation into the blood circulation. ADH binds to target cells in the kidneys (collecting duct). Increases water retention, thus decreasing urine volume. Oxytocin binds to target cells in the mammary glands (regulates milk release during nursing) and uterus (induces muscular contraction). Also functions in regulating mood and sexual arousal in both males and females.

Hormonal Control of the Kidney by Negative feedback circuits. ADH enhances fluid retention by making the kidneys permeable to water. a. Neurosecretory cells in the supra-optic nucleus of the hypothalamus synthesize ADH, transport it down axons and store it in nerve endings in the posterior pituitary gland. b. The release of ADH is triggered by osmoreceptor cells in the hypothalamus that detect an increase in osmolarity of blood. c. If plasma becomes too concentrated. Impulses are passed to ADH-secreting neurosecretory cells, which convey the impulses to their nerve endings in the posterior pituitary.

ADH continued d. Impulses stimulate release of ADH into the blood from the stores in nerve endings. e. ADH causes reduction in the concentration of blood plasma by stimulating the kidney to produce hypertonic urine. f. Osmoreceptor cells also promote thirst. Drinking reduces osmolarity of blood, which inhibits secretion of ADH, completing circuit. If detectors sense low concentration of blood plasma, neurosecretory cells are not stimulated to release ADH and blood levels of ADH levels rapidly drop.

Anterior Pituitary

b) The Anterior Pituitary The release of hormones from the anterior pituitary gland is controlled by the hypothalamus. Neurosecretory cells in the hypothalamus secrete releasing hormones and inhibiting hormones into a capillary network located above the stalk of the pituitary. The capillaries drain into the portal vessels (short blood vessels that subdivide into a second capillary bed within the anterior pituitary). In this way, hypothalamic hormones have direct access to the gland they control.

Prolactin: Diversity of effects among vertebrates 1. Stimulates mammary gland growth and milk synthesis in mammals. 2. Regulates fat metabolism and reproduction in birds. 3. Delays metamorphosis in amphibians. 4. Regulates salt and water balance in freshwater fishes. Suggests that prolactin is an ancient hormone with functions that have diversified during the evolution of vertebrate groups.

Control of milk secretion: regulated by pituitary hormones 1. Prolactin is secreted by anterior pituitary which stimulates mammary glands to grow and to produce milk. 2. During pregnancy, high estrogen levels increase prolactin production but inhibit its effects. 3. Abrupt decline in estrogen following birth ends this inhibition and milk production begins.

Involvement of oxytocin 4. Milk is produced in small spherical chambers (alveoli) distributed throughout gland. 5. Oxytocin stimulates the letdown of milk to a central chamber where it is accessible to the baby. 6. Physical stimulus of sucking (nursing) by a baby (or breast pump) stimulates oxytocin secretion by posterior pituitary gland.

Regulation of milk release: mediated by a simple neurohormone pathway. 1. Stimulus is received by a sensory neuron which stimulates a neurosecretory cell. 2. The neurosecretory cell then secretes a neurohormone, which diffuses into the blood stream and travels to target cells. 3. In the case of oxytocin pathway, the initial stimulus is the infant s sucking (could also be the sight/sound/thought of the baby). 4. Stimulation of sensory nerve cells in the nipples generates signals in the nervous system that reach the hypothalamus. 5. A nerve impulse from the hypothalamus then triggers the release of oxytocin from the posterior pituitary gland. 6. In response to circulating oxytocin, the mammary gland secretes milk.

Have you ever wondered how breast milk production keeps up with the growth of the infant? The answer involves positive feedback.

An example of positive-feedback mechanisms. Oxytocin stimulates milk release which leads to more suckling and therefore more stimulation. Sustained until the baby stops suckling. Increased sucking also leads to increased prolactin secretion which leads to increased milk production.

Growth hormone (GH): Peptide 1. Secreted by the anterior pituitary. 2. Major target: liver which responds by releasing insulin-like growth factors (IGFs), which circulate in the blood and directly stimulate bone and cartilage growth. hormone 3. Also exerts diverse metabolic effects that tend to raise blood glucose levels (opposing insulin).

Metabolic Effects of Growth Hormone Stimulates the synthesis of protein. Stimulates the breakdown of fat. Increases mitosis of cartilage cells and the mineralization of bone. Stimulates increases in muscle mass and growth of all organs apart from the brain. GH has been used by athletes since the 1960s to help build muscles. Some evidence that it does enhance performance in events depending on muscle mass: homerun hitting, weightlifting.

Human Growth Hormone production decreases with age Hypersecretion during childhood can result in Gigantism (growth as tall as 8 feet). In adulthood, excessive GH production stimulates bony growth in the few tissues that are still responsive to the hormone: face, hands and feet. Hyposecretion: pituitary dwarfism (less than 4 ft.) Genetic engineering of bacteria allows HGH to be made and is used in treatment.

Adverse Effects of taking HGH Increased cholesterol levels. Increased risk of diabetes. Carpal tunnel syndrome Acromegaly (growth of bones of face) Bloated guts

Thyroid and Thyroxin Thyroid gland is a butterfly shaped gland located in your neck. The major hormone produced, thyroxin, is formed from the amino acid, tyrosine, and iodine and exists in 2 forms, T4 and T3 based on number of iodine atoms. T4 converted to T3. T3 acts as a transcription regulator.

Thyroxin leads to increase in metabolism of the cell. Thyroxin also helps to regulate internal body temperature. An increase in metabolic rate produces more heat from the increased chemical reactions. So an increase in thyroxin will lead to an increase in body temperature and vice-versa.

Disorders of the thyroid Hyperthyroidism: Over production of thyroid hormones leads to high body temperature, profuse sweating, weight loss, irritability, and high blood pressure. Graves disease is leading cause. Hypothyroidism: Under production of thyroid hormone which can lead to lethargy and weight gain. Can be caused by an inadequate supply of iodine, or an autoimmune disease that attacks the thyroid. (Hashimoto s thyroiditis).

Graves disease

Pineal Gland and Melatonin Melatonin is a hormone made by the pineal gland, a small gland in the brain. It is a modified amino acid. Melatonin helps control your sleep and wake cycles. Circadian rhythms: rhythms of behavior/ biochemistry that fit a 24 hour cycle.

Production of melatonin under the control of the hypothalamus. Sequence of events leading to release: 1. Ganglion cells in the retina detect whether it is light or dark and send impulses to the supra-chiasmatic nuclei (SCN) in the hypothalamus. 2. Supra-chiasmatic nucleus functions as a biological clock. 3. Neurons in the SCN control secretion of melatonin by the pineal gland. 4. Regulates functions related to light and to seasons marked by changes in day length. 5. Primary functions relates to biological rhythms associated with reproduction.

Normally, melatonin levels begin to rise in the mid-to-late evening, remain high for most of the night, and then drop in the early morning hours. Light affects how much melatonin the body produces. During the shorter days of winter, the body may produce melatonin either earlier or later in the day than usual. This change can lead to symptoms of seasonal affective disorder (SAD) or winter depression.

Melatonin secretion decreases with age which explains how sleep patterns become more irregular as we grow older. Circadian rhythms are disrupted by travelling rapidly between time zones. Symptoms include: sleep disturbance, fatigue, headaches, irritability. This pattern = jet lag. SCN and pineal set rhythm to the timing of day and night at point of departure. Only lasts a few days. Exposure to light at destination resynchronizes circadian rhythm. Melatonin can be used to prevent or reduce jet lag. Taken orally at the time when sleep should ideally start. Works best when travelling East, crossing 5 or more time zones.

Appetite-regulating hormones include Leptin which suppresses appetite Appetite regulating hormones are secreted by various organs and tissues and act on the hypothalamus that, in turn, controls the satiety center. Understanding this satiety pathway came about from the discovery of mutants (ob and db genes) in mice that caused them to be chronically obese.

Sooo Leptin: hormone secreted by fat storage cells (adipose cells) As levels increase, leptin suppresses appetite. When body fat decreases, leptin levels fall, and appetite increases. Helps to regulate body weight. ob+ allele produces the satiety factor, now understood to be the hormone, leptin, in fat cells. db+ allele encodes the leptin receptor in membranes of cells in the hypothalamus.

The difficulties associated with moving from animal to human studies When ob/ob mice injected with leptin, appetite declined, energy expenditure increased and body mass dropped by 30% in a month. Leptin is also made in humans. Moved to clinical trials of 73 obese volunteers, only 47 of which finished the trial. Double blind study (neither researchers nor volunteers knew what the subjects were injecting). Results in humans showed varied results although on average, humans on highest dose lost the greatest amount of weight which quickly found them again when the trial was over. Only small fraction of human obesity due to lack of leptin. Most due to lack of response by target cells. So, increasing leptin levels have no effect on levels of obesity. Route of administration: injections. These were not well tolerated by the subjects (35% drop out rate).

R.1. Describe the source and effects of the hormone thyroxine Thyroid gland is a butterfly shaped gland located in your neck. The major hormone produced, thyroxin, is formed from the amino acid, tyrosine, and iodine and exists in 2 forms, T4 and T3 based on number of iodine atoms. T4 converted to T3. T3 acts as a transcription regulator. Thyroxin leads to an increase in metabolism by targeting all cells but mainly liver, muscles and brain. Thyroxin also helps to regulate internal body temperature. An increase in metabolic rate produces more heat from the increased chemical reactions. So an increase in thyroxin will lead to an increase in body temperature and vice-versa.

See page 82 in review guide: In response to body temperature changes, hypothalamus causes thyroid gland to either increase of decrease thyroid gland secretions. Raised body temperature causes reduced metabolic rate (less thyroxin) and reduced respiration in brown adipose tissue (BAT). Also vasodilation in skin arterioles. Lowered body temperature causes increased metabolic rate and increased respiration in BAT. Also shivering and vasoconstriction in skin arterioles.

Disorders of thyroid Hyperthyroidism: Over production of thyroid hormones leads to high body temperature, profuse sweating, weight loss, irritability, and high blood pressure. Graves disease is leading cause. Hypothyroidism: Under production of thyroid hormone which can lead to lethargy and weight gain. Can be caused by an inadequate supply of iodine, or an autoimmune disease that attacks the thyroid. (Hashimoto s thyroiditis).

R.2 Describe the effects of the hormone, leptin, and its testing on patients with clinical obesity along with the reasons for the failure to control the disease. Leptin is an appetite regulating hormone Appetite regulating hormones are secreted by various organs and tissues and act on the hypothalamus that, in turn, controls the satiety center. Understanding this satiety pathway came about from the discovery of mutants (ob and db genes) in mice that caused them to be chronically obese. Leptin is a hormone produced by fat storage cells (adipocytes) As levels increase, leptin suppresses appetite. When body fat decreases, leptin levels fall, and appetite increases. Helps to regulate body weight. ob+ allele produces the satiety factor, now understood to be the hormone, leptin, in fat cells. db+ allele encodes the leptin receptor in membranes of cells in the hypothalamus.

Difficulties in moving to clinical trials from animal studies p.82 When ob/ob mice injected with leptin, appetite declined, energy expenditure increased and body mass dropped by 30% in a month. Leptin is also made in humans. Moved to clinical trials of 73 obese volunteers, only 47 of which finished the trial. Double blind study (neither researchers nor volunteers knew what the subjects were injecting). Results in humans showed varied results although on average, 8 humans on highest dose lost the greatest amount of weight. (7.1 kg) which quickly found them again when the trial was over. Control lost 1.3 kg (12 volunteers) Only small fraction of human obesity due to lack of leptin. Most due to lack of response by target cells. So, increasing leptin levels have no effect on levels of obesity. Route of administration: injections. These were not well tolerated by the subjects (35% drop out rate).

R.3 Describe the source and effects of the hormone, melatonin, and how it may be used to counter jet lag. Melatonin is a hormone made by the pineal gland, a small gland in the brain. It is a modified amino acid. Melatonin helps control your sleep and wake cycles. Circadian rhythms: rhythms of behavior/ biochemistry that fit a 24 hour cycle. Under control of hypothalamus. Sequence of events leading to release: 1. Ganglion cells in the retina detect whether it is light or dark and send impulses to the supra-chiasmatic nuclei (SCN) in the hypothalamus. 2. Supra-chiasmatic nucleus functions as a biological clock. 3. Neurons in the SCN control secretion of melatonin by the pineal gland. 4. Regulates functions related to light and to seasons marked by changes in day length. 5. Primary functions relates to biological rhythms associated with reproduction.

Sequence of events leading to release: 1. Ganglion cells in the retina detect whether it is light or dark and send impulses to the suprachiasmatic nuclei (SCN) in the hypothalamus. 2. Supra-chiasmatic nucleus functions as a biological clock. 3. Neurons in the SCN control secretion of melatonin by the pineal gland. 4. Regulates functions related to light and to seasons marked by changes in day length. 5. Primary functions relates to biological rhythms associated with reproduction.

Melatonin secretion decreases with age which explains how sleep patterns become more irregular as we grow older. Circadian rhythms are disrupted by travelling rapidly between time zones. Symptoms include: sleep disturbance, fatigue, headaches, irritability. This pattern = jet lag. SCN and pineal set rhythm to the timing of day and night at point of departure. Only lasts a few days. Exposure to light at destination resynchronizes circadian rhythm. Melatonin can be used to prevent or reduce jet lag. Taken orally at the time when sleep should ideally start. Works best when travelling East, crossing 5 or more time zones.

R.4 Describe the hormonal control of blood glucose levels Glucose homeostasis: maintained by insulin and glucagon. A rise in blood glucose above the set point (about 90mg/100mL in humans) stimulates the pancreas to secrete insulin, which triggers its target organs to take up excess glucose from the blood. Once the excess is removed and blood glucose concentration dips below the set point, the pancreas responds by secreting glucagon, which acts on the liver to raise the blood glucose levels.

D.5.1 Define hormone. Describe 2 general types with 2 examples of each Hormone: Chemical messenger secreted by endocrine glands into the blood and transported by the blood to specific target cells. Major types: Lipid soluble: (gonads) testosterone, estradiol, progesterone, (adrenal cortex) cortisol, aldosterone Water soluble: peptide hormones (ADH, Oxytocin, calcitonin, Growth hormone) and tyrosine derivatives (epinephrine and norepinephrine, thyroxin, LH and FSH)

D.5.2 Differentiate between the actions of peptide hormones and steroid hormones

Lipid soluble vs. water soluble Steroids are lipids/lipid soluble They can pass through the plasma membrane. 1. Bind to receptor protein in the cytosol, activating it. 2. Receptor-hormone complex enters the nucleus and binds to specific genes. 3. The bound protein stimulates the transcription of the gene into mrna. 4. The mrna is translated into specific protein. hormone action A signal transduction pathway is a series of molecular changes that convert an extracellular chemical signal to a specific intracellular response. Water soluble. 1. Reception of signal: signal receptor located in the plasma membrane. 2. Transduction: might involve phosphorylation by a kinase or the generation of a second signal using cyclic AMP (camp). 2 nd signal or 2 nd message is generated. 3. Cellular response

D.5.3 Describe the structural and functional relationship between the hypothalamus and the: posterior pituitary (neurosecretory cells: specialized nerve cells that secrete hormones) extension of hypothalamus Neurosecretory cells in the hypothalamus synthesize antidiuretic hormone (ADH) and oxytocin. These hormones are transported down the axons to the posterior pituitary, where they are stored. The posterior pituitary releases them upon stimulation into the blood circulation. ADH binds to target cells in the kidneys (collecting duct). Increases water retention, thus decreasing urine volume. Oxytocin binds to target cells in the mammary glands (regulates milk release during nursing) and uterus (induces muscular contraction). Also functions in regulating mood and sexual arousal in both males and

D.5.3 Describe the structural and functional relationship between the hypothalamus and the: anterior pituitary. Not an extension of the hypothalamus but controlled by it. The release of hormones from the anterior pituitary gland is controlled by the hypothalamus. Neurosecretory cells in the hypothalamus secrete releasing hormones and inhibiting hormones into a capillary network located above the stalk of the pituitary. The capillaries drain into the portal vessels (short blood vessels that subdivide into a second capillary bed within the anterior pituitary). In this way, hypothalamic hormones have direct access to the gland they control. Give examples of hormones controlled this way.

D.5.4 Outline the functions of the pituitary hormones giving an example of each function Growth: Growth Hormone (GH) which stimulates mitosis and organism growth. Targets liver to release insulin-like growth factor which stimulates bone and cartilage growth. Reproduction: LH (luteinizing hormone) and FSH (follicle stimulating hormone). Prepares ovarian cells for ovulation in females, and needed for sperm production in males. Developmental Changes: GH, LH and FSH. GH is necessary for all developmental growth throughout adulthood. LH and FSH secretions increase during puberty, leading to ovulation and sperm production, among other functions. Homeostasis: ADH (antidiuretic hormone): Secretion of ADH is needed for the reabsorption of water from the collecting ducts in the kidneys. Involved in osmoregulation. Or thyroid stimulating hormone that adjusts metabolic rate and temp.

D.5.5 Describe the control of the secretion of ADH from the posterior pituitary gland ADH enhances fluid retention by making the kidneys permeable to water. a. Neurosecretory cells in the supra-optic nucleus of the hypothalamus synthesize ADH, transport it down axons and store it in nerve endings in the posterior pituitary gland. b. The release of ADH is triggered by osmoreceptor cells in the hypothalamus that detect an increase in osmolarity of blood. c. If plasma becomes too concentrated. Impulses are passed to ADH-secreting neurosecretory cells, which convey the impulses to their nerve endings in the posterior pituitary. d. Impulses stimulate release of ADH into the blood from the stores in nerve endings. e. ADH causes reduction in the concentration of blood plasma by stimulating the kidney to produce hypertonic urine. f. Osmoreceptor cells also promote thirst. Drinking reduces osmolarity of blood, which inhibits secretion of ADH, completing circuit. If detectors sense low concentration of blood plasma, neurosecretory cells are not stimulated to release ADH and blood levels of ADH levels rapidly drop.

D.5.6 Describe the control of production and secretion of prolactin 1. Prolactin is secreted by anterior pituitary which stimulates mammary glands to grow and to produce milk. 2. During pregnancy, high estrogen levels increase prolactin production but inhibit its effects. 3. Abrupt decline in estrogen following birth ends this inhibition and milk production begins. 4. Milk is produced in small spherical chambers (alveoli) distributed throughout gland. 5. Oxytocin stimulates the letdown of milk to a central chamber where it is accessible to the baby. 6. Physical stimulus of sucking (nursing) by a baby (or breast pump) stimulates oxytocin secretion by posterior pituitary gland.

Regulation of milk release: mediated by a simple neurohormone pathway. 1. Stimulus is received by a sensory neuron which stimulates a neurosecretory cell. 2. The neurosecretory cell then secretes a neurohormone (releasing factor), which diffuses into the blood stream and travels to target cells. 3. In the case of oxytocin pathway, the initial stimulus is the infant s sucking (could also be the sight/sound/thought of the baby). 4. Stimulation of sensory nerve cells in the nipples generates signals in the nervous system that reach the hypothalamus. 5. A nerve impulse from the hypothalamus then triggers the release of oxytocin from the posterior pituitary gland. 6. In response to circulating oxytocin, the mammary gland secretes milk.

How milk production keeps up with baby s needs An example of positive-feedback mechanisms. Oxytocin stimulates milk release which leads to more suckling and therefore more stimulation. Sustained until the baby stops suckling. Increased sucking also leads to increased prolactin secretion which leads to increased milk production.

D.5.7 Discuss the use of some athletes of Growth Hormone. What type? Peptide Source: Anterior pituitary Effects: Targets liver to produce insulin-like growth factor that causes bones and cartilage to increase mitosis. Also exerts diverse metabolic effects that tend to raise blood glucose levels (opposing insulin).

Stimulates the synthesis of protein. Stimulates the breakdown of fat. Increases mitosis of cartilage cells and the mineralization of bone. Stimulates increases in muscle mass and growth of all organs apart from the brain. GH has been used by athletes since the 1960s to help build muscles. Some evidence that it does enhance performance in events depending on muscle mass: home-run hitting, weightlifting. GH decreases with age. Hypersecretion during childhood can result in Gigantism (growth as tall as 8 feet). In adulthood, excessive GH production stimulates bony growth in the few tissues that are still responsive to the hormone: face, hands and feet. Hyposecretion: pituitary dwarfism (less than 4 ft.) Genetic engineering of bacteria allows HGH to be made and is used in treatment.

Adverse effects of athletes taking GH to enhance performance Increased cholesterol levels. Increased risk of diabetes. Carpal tunnel syndrome Acromegaly (growth of bones of face) Bloated guts

Hormonal Control of Blood Calcium Levels

Chemical Signaling Effectors

Adrenal Gland and Stress

Calcium signal pathway