The Endocrine SystemThe Endocrine System

Sabrena BoboSabrena Bobo

Lawrence YancyLawrence Yancy

Dane TaylorDane Taylor

HORMONES AND THE HORMONES AND THE ENDOCRINE SYSTEMENDOCRINE SYSTEM

A A hormone (from the hormone (from the Greek Greek horman, horman, to excite)to excite) iis a chemical messenger s a chemical messenger secreted by endocrine secreted by endocrine glands into the blood and glands into the blood and transported to specific transported to specific target cells target cells ((H.1.1)H.1.1)

* reaches all parts * reaches all parts of the cell but only of the cell but only target target cells cells respondrespond

-response, -response, eg a change in metabolismeg a change in metabolism

ENDOCRINE SYSTEMENDOCRINE SYSTEM

The The endocrine systemendocrine system consists of a collection consists of a collection of glands, cells and tissues that secrete of glands, cells and tissues that secrete hormones.hormones.Its function is to regulate many aspects of Its function is to regulate many aspects of metabolism, growth and reproduction.metabolism, growth and reproduction.Endocrine glands produce hormones and Endocrine glands produce hormones and secrete them to the surrounding tissues and secrete them to the surrounding tissues and eventually into the capillaries.eventually into the capillaries.EndocrinologyEndocrinology is the study of endocrine gland is the study of endocrine gland function and hormonal effect on target tissues.function and hormonal effect on target tissues.Exocrine glandsExocrine glands release their secretions into release their secretions into ducts.ducts.

OVERLAP BETWEEN ENDOCRINE OVERLAP BETWEEN ENDOCRINE AND NERVOUS REGULATIONAND NERVOUS REGULATION

Some neurons secrete hormones (Some neurons secrete hormones (neurohormonesneurohormones) and are known ) and are known as neurosecretoryas neurosecretory or or neuroendocrine cellsneuroendocrine cells..The regulation of several physiological processes involves structural The regulation of several physiological processes involves structural and functional overlap between the endocrine and nervous systems.and functional overlap between the endocrine and nervous systems.Endocrine hormones regulate growth, development, fluid balance, Endocrine hormones regulate growth, development, fluid balance, metabolism and reproduction.metabolism and reproduction.Hyposecretion: secretion lower than normal.Hyposecretion: secretion lower than normal.Hypersecretion: secretion higher than normal.Hypersecretion: secretion higher than normal.Homeostasis depends on the normal concentrations of hormones.Homeostasis depends on the normal concentrations of hormones.There is a relationship between the endocrine and nervous systems. There is a relationship between the endocrine and nervous systems.

Neurosecretory cellsNeurosecretory cells, specialized nerve cells, release hormones , specialized nerve cells, release hormones through the blood through extra cellular fluid. through the blood through extra cellular fluid.

*eg sustained response such as day/night cycles and *eg sustained response such as day/night cycles and reproductive cycles in many animals, hormones in the endocrine reproductive cycles in many animals, hormones in the endocrine system as well as chemical signals in the nervous systemsystem as well as chemical signals in the nervous system

CONTROL PATHWAYS AND CONTROL PATHWAYS AND FEEDBACK LOOPS FEEDBACK LOOPS

Signaling-Signaling-3 key events3 key events*reception - signal molecule binds to receptor protein in or on the *reception - signal molecule binds to receptor protein in or on the

target celltarget cell*signal transduction - the binding of a signal molecule to a target *signal transduction - the binding of a signal molecule to a target

protein, triggering evens in the target cellprotein, triggering evens in the target cell*response - a change in the cell’s behavior *response - a change in the cell’s behavior

ReceptorsReceptors or sensors throughout the body detect stimuli and send or sensors throughout the body detect stimuli and send information to information to control centercontrol center..E. g. change in CO2 concentration in the blood.E. g. change in CO2 concentration in the blood.The control center compares the signal to a “desired” value and sends out a The control center compares the signal to a “desired” value and sends out a signal to direct an signal to direct an effectoreffector to respond. to respond. E.g. breathing centers in the pons and medulla oblongata; diaphragm and E.g. breathing centers in the pons and medulla oblongata; diaphragm and intercostal muscles receive a message to increase breathing.intercostal muscles receive a message to increase breathing.Target cells have Target cells have receptorsreceptors that combine with a specific hormone. They are that combine with a specific hormone. They are responsible for the specificity of the hormone. The receptors may be in or responsible for the specificity of the hormone. The receptors may be in or out of the cell.out of the cell.

Pathways and Loops (cont.)Pathways and Loops (cont.)Negative and positive feedbackNegative and positive feedback mechanisms control the amount of mechanisms control the amount of hormone and response needed.hormone and response needed.*Negative feedback*Negative feedback- the effector response reduces the initial stimulus, - the effector response reduces the initial stimulus, prevents overreactionprevents overreaction

-maintaining homeostasis-maintaining homeostasis*Positive feedback*Positive feedback- reinforces the stimulus and leads to an even - reinforces the stimulus and leads to an even

greater response, greater response, -suckling-suckling

Simple pathwaySimple pathway: Stimulus → endocrine gland → hormone released into : Stimulus → endocrine gland → hormone released into the blood → target the blood → target effector → responseeffector → responseSimple neurohormones pathwaySimple neurohormones pathway: Stimulus → sensory neuron → : Stimulus → sensory neuron → hypothalamus/pituitary → neurosecretory cell → hormone released into the hypothalamus/pituitary → neurosecretory cell → hormone released into the blood → target effector → responseblood → target effector → responseSimple neuroendocrine pathwaySimple neuroendocrine pathway: Stimulus → sensory neuron → : Stimulus → sensory neuron → hypothalamus/pituitary → neurosecretory cell → hormone released into the hypothalamus/pituitary → neurosecretory cell → hormone released into the blood → endocrine gland → hormone into the blood → target effector → blood → endocrine gland → hormone into the blood → target effector → responseresponse

LOCAL REGULATORSLOCAL REGULATORSPARACRINE SIGNALINGPARACRINE SIGNALING

Local regulators affect neighboring target cells.Local regulators affect neighboring target cells.Some cells release hormones that act on nearby cells. Some cells release hormones that act on nearby cells. This is called This is called paracrine regulationparacrine regulation..Several types of chemical compounds function as local Several types of chemical compounds function as local regulators; many are neurotransmitters.regulators; many are neurotransmitters.Growth factorsGrowth factors are peptides and proteins that stimulate are peptides and proteins that stimulate cell reproduction and differentiation.cell reproduction and differentiation.They must be present in the external environment for They must be present in the external environment for many cells to grow and develop normally.many cells to grow and develop normally.GF may have several kinds of target cells and a variety GF may have several kinds of target cells and a variety of functions.of functions.CytokinesCytokines are local regulators that play a role in the are local regulators that play a role in the immune system. immune system.

Signaling (cont.)Signaling (cont.)Nitric oxideNitric oxide, NO, is a gas produced by many cells., NO, is a gas produced by many cells.It is toxic and causes a fast reaction in cells before it is broken down.It is toxic and causes a fast reaction in cells before it is broken down.It is secreted by neurons and functions as a neurotransmitter.It is secreted by neurons and functions as a neurotransmitter.Secreted by leukocytes, kills bacteria and cancer cells in body fluids.Secreted by leukocytes, kills bacteria and cancer cells in body fluids.Released by endothelial cells, cause the blood vessels to relax and dilate.Released by endothelial cells, cause the blood vessels to relax and dilate.ProstaglandinsProstaglandins are modified fatty acids that have a wide range of activities. are modified fatty acids that have a wide range of activities.Lungs, liver, digestive tract and reproductive organs release prostaglandins. Lungs, liver, digestive tract and reproductive organs release prostaglandins. Affect cells in their immediate vicinity.Affect cells in their immediate vicinity.Mimic cyclic AMP and interact with other hormones that regulate many Mimic cyclic AMP and interact with other hormones that regulate many metabolic activities.metabolic activities.Some are involved in fever and inflammation.Some are involved in fever and inflammation.InterleukinsInterleukins regulate immune responses. regulate immune responses.*Major Human Endocrine Glands and Some of their Hormones (p. 949 of *Major Human Endocrine Glands and Some of their Hormones (p. 949 of text)text)

CHEMICAL SIGNALS TARGET CHEMICAL SIGNALS TARGET CELL RECEPTORSCELL RECEPTORS

Hormones and other chemical signals bind to target cell receptors, initiating Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses. pathways that culminate in specific cell responses. Hormones can be steroids, peptides and tyrosine derivatives Hormones can be steroids, peptides and tyrosine derivatives (H.1.2)(H.1.2)HORMONE TYPESHORMONE TYPESSteroid hormonesSteroid hormones are synthesized from cholesterol, e.g. cortisol, are synthesized from cholesterol, e.g. cortisol, progesterone, testosterone.progesterone, testosterone.Amino acid derivativesAmino acid derivatives called amines, e.g. thyroid, melatonin. called amines, e.g. thyroid, melatonin.Peptide hormonesPeptide hormones are short chains of amino acids, e.g. secretin, ADH, are short chains of amino acids, e.g. secretin, ADH, oxytocin. oxytocin. Modified fatty acidsModified fatty acids, e. g. prostaglandins. , e. g. prostaglandins. Chemical signals produced by secretory cells either bind to a Chemical signals produced by secretory cells either bind to a surface surface receptorreceptor or penetrates the cells and binds to a receptor inside the cell. or penetrates the cells and binds to a receptor inside the cell.Receptor → transduction → responseReceptor → transduction → responseReceptors for Receptors for water-soluble hormoneswater-soluble hormones are embedded in the plasma are embedded in the plasma membrane and project outward from the cell surface. membrane and project outward from the cell surface.

Chemical Signals (cont.)Chemical Signals (cont.)

Intracellular receptorsIntracellular receptors are found either in the are found either in the cytoplasm or in the nucleus of the target cell. cytoplasm or in the nucleus of the target cell. Intracellular receptor proteins usually perform the entire Intracellular receptor proteins usually perform the entire transduction with the cell.transduction with the cell.The chemical signal activates the receptor, which then The chemical signal activates the receptor, which then directly triggers the cell's response.directly triggers the cell's response.The intracellular receptor activated by a hormone acts as The intracellular receptor activated by a hormone acts as a transcription factor.a transcription factor.The active factor, the receptor-hormone complex, The active factor, the receptor-hormone complex, activates or represses the transcription of a gene.activates or represses the transcription of a gene.Epinephrine produces different responses in different Epinephrine produces different responses in different target cells because the target cells have different target cells because the target cells have different transduction pathways. transduction pathways.

Distinguish between the mode of action of Distinguish between the mode of action of steroidsteroid hormones and hormones and peptidepeptide hormones. (H.1.3) hormones. (H.1.3)

Steroid hormone: Steroid hormone: (a) Pass straight through the plasma membrane. (a) Pass straight through the plasma membrane. Directly affects the expression of genes.Directly affects the expression of genes. Peptide hormone:Peptide hormone: (b) Attachment to plasma membrane receptor (b) Attachment to plasma membrane receptor (Glycoprotein) (c) Receptor-Hormone complex (d) Stimulation of (Glycoprotein) (c) Receptor-Hormone complex (d) Stimulation of secondary messenger in cytoplasm which alters the action of the secondary messenger in cytoplasm which alters the action of the cellcell

PITUITARYPITUITARYAt the base of the brain. At the base of the brain. It has two regions that develop from It has two regions that develop from different regions of the embryo and have different regions of the embryo and have different functions.different functions.Posterior lobe of the pituitary or Posterior lobe of the pituitary or neurohypophysis.neurohypophysis.The posterior pituitary gland is an extension The posterior pituitary gland is an extension of the hypothalamus. of the hypothalamus. Produces Produces oxytosinoxytosin..Causes the uterus to contract during birth.Causes the uterus to contract during birth.Causes the mammary glands to eject milk.Causes the mammary glands to eject milk.Produces Produces antidiuretic hormone (ADH)antidiuretic hormone (ADH)..Causes the collecting ducts of the kidneys Causes the collecting ducts of the kidneys to reabsorb water.to reabsorb water.Secretes growth-hormone-releasing Secretes growth-hormone-releasing hormone or hormone or GHRHGHRH and growth-hormone- and growth-hormone-inhibiting hormone or inhibiting hormone or GHIHGHIH also called also called somatostatinsomatostatin..

Pituitary (cont.)Pituitary (cont.)Anterior lobe of the pituitary or adenohypophysis.Anterior lobe of the pituitary or adenohypophysis.The anterior pituitary gland develops from a fold in the roof of the mouth of the The anterior pituitary gland develops from a fold in the roof of the mouth of the embryo, which grows toward the brain and loses its connection with the mouth.embryo, which grows toward the brain and loses its connection with the mouth.Tropic hormonesTropic hormones stimulate other endocrine glands. stimulate other endocrine glands.Thyroid-stimulating hormoneThyroid-stimulating hormone (TSH) causes the thyroid to secrete hormones. (TSH) causes the thyroid to secrete hormones.Adrenocorticotropic hormoneAdrenocorticotropic hormone (ACTH), a peptide, stimulates the secretion of (ACTH), a peptide, stimulates the secretion of hormones by adrenal cortex.hormones by adrenal cortex.Gonadotropic hormonesGonadotropic hormones (follicle-stimulating hormone, FSH, luteinizing hormone, (follicle-stimulating hormone, FSH, luteinizing hormone, LH) stimulate gonad functions.LH) stimulate gonad functions.Nontropic hormonesNontropic hormones are peptide/protein hormones function in simple are peptide/protein hormones function in simple neuroendocrine pathways.neuroendocrine pathways.ProlactinProlactin is a protein that stimulates the mammary glands to produce milk. is a protein that stimulates the mammary glands to produce milk.Melanocyte-stimulating hormoneMelanocyte-stimulating hormone (MSH), a peptide, regulates the activity of (MSH), a peptide, regulates the activity of pigment containing cells in some vertebrates; in mammals probably acts as a pigment containing cells in some vertebrates; in mammals probably acts as a feedback mechanism that targets the neurons of the hypothalamus.feedback mechanism that targets the neurons of the hypothalamus.EndorphinsEndorphins inhibit the perception of pain; increase the threshold of pain. inhibit the perception of pain; increase the threshold of pain.

Nontropic and tropic effects: Nontropic and tropic effects:

Growth hormoneGrowth hormone (GH) stimulates linear body growth and tissue (GH) stimulates linear body growth and tissue and organ growth by promoting protein synthesis.and organ growth by promoting protein synthesis.A protein of about 200 amino acids.A protein of about 200 amino acids.Stimulates the uptake of AA from the blood and their incorporation Stimulates the uptake of AA from the blood and their incorporation into cellular proteins; increase in skeletal muscle mass. into cellular proteins; increase in skeletal muscle mass. Mobilizes fats from fat depots for transport to cells, increasing blood Mobilizes fats from fat depots for transport to cells, increasing blood levels of fatty acids.levels of fatty acids.GH stimulates the liver to produce peptides called GH stimulates the liver to produce peptides called somatomedinssomatomedins including insulin-like growth factor, which stimulate bone and including insulin-like growth factor, which stimulate bone and cartilage growth.cartilage growth.Secretion of GH is regulated by growth-hormone releasing hormone Secretion of GH is regulated by growth-hormone releasing hormone or or GHRHGHRH and growth-hormone-inhibiting hormone or and growth-hormone-inhibiting hormone or GHIHGHIH also also called called somatostatinsomatostatin. Both are released by the hypothalamus.. Both are released by the hypothalamus.It has a diurnal cycle with the highest levels occurring during the It has a diurnal cycle with the highest levels occurring during the night sleep; the total amount secrete peaks during adolescence and night sleep; the total amount secrete peaks during adolescence and then decreases with age. then decreases with age.

Explain the control of ADH secretion by Explain the control of ADH secretion by negative feedback. (H.1.6)negative feedback. (H.1.6)

One important homeostatic function of the body is keeping the blood One important homeostatic function of the body is keeping the blood volume constant. This is accomplished by regulation of the rate at volume constant. This is accomplished by regulation of the rate at which water is removded from the bloodstream by the kidneys. A which water is removded from the bloodstream by the kidneys. A hormone called ADH (anti-diuretic hormone) is produced by the hormone called ADH (anti-diuretic hormone) is produced by the hypothalamus and released from the pituitary gland acts on the hypothalamus and released from the pituitary gland acts on the kidney's tubules to decrease water excretion. The production of kidney's tubules to decrease water excretion. The production of ADH is controlled by sensory receptors in the circulatory system, ADH is controlled by sensory receptors in the circulatory system, particularly in the heart, that measures blood pressure- an indirect particularly in the heart, that measures blood pressure- an indirect measure of blood volume. When bloodpressure goes up, firing of measure of blood volume. When bloodpressure goes up, firing of these receptors inhibits the release of ADH, and more water is these receptors inhibits the release of ADH, and more water is excreted, reducing blood volume. As blood pressure goes down, the excreted, reducing blood volume. As blood pressure goes down, the stimulus from the receptors decreases, ADH production increases, stimulus from the receptors decreases, ADH production increases, water is retained by the kidney, and blood pressure and volume water is retained by the kidney, and blood pressure and volume increase. increase.

VERTEBRATE ENDOCRINE VERTEBRATE ENDOCRINE SYSTEMSYSTEM

Tropic hormonesTropic hormones affect other endocrine affect other endocrine glands.glands.

The hypothalamus and pituitary glands The hypothalamus and pituitary glands integrate many functions of the vertebrate integrate many functions of the vertebrate endocrine system.endocrine system.

Table 45.1 summarizes the activity of Table 45.1 summarizes the activity of major human hormones.major human hormones.

HYPOTHALAMUSHYPOTHALAMUS

Part of the brain.Part of the brain.Links the endocrine system Links the endocrine system with the nervous system.with the nervous system.Most endocrine activity is Most endocrine activity is controlled directly or indirectly controlled directly or indirectly by the hypothalamus.by the hypothalamus.Produces growth releasing and Produces growth releasing and growth inhibiting hormones.growth inhibiting hormones.Anterior lobe of the pituitary is Anterior lobe of the pituitary is the target tissue.the target tissue.Stimulates and inhibits Stimulates and inhibits secretion.secretion.

Outline the relationship between the Outline the relationship between the hypothalamus and the pituitary gland. hypothalamus and the pituitary gland.

((H.1.4)H.1.4) A branch of the hypophyseal artery A branch of the hypophyseal artery ramifies into a capillary bed in the ramifies into a capillary bed in the lower hypothalamus, and hypothalmic lower hypothalamus, and hypothalmic hormones destined for the anterior hormones destined for the anterior pituitary are secreted into that capillary pituitary are secreted into that capillary blood. blood. Blood from those capillaries drains into Blood from those capillaries drains into hypothalamic-hypophyseal portal hypothalamic-hypophyseal portal veinsveins. Portal veins are defined as . Portal veins are defined as veins between two capillary beds; the veins between two capillary beds; the hypothalamic-hypophyseal portal veins hypothalamic-hypophyseal portal veins branch again into another series of branch again into another series of capillaries within the anterior pituitary. capillaries within the anterior pituitary. Capillaries within the anterior pituitary, Capillaries within the anterior pituitary, which carry hormones secreted by that which carry hormones secreted by that gland, coalesce into veins that drain gland, coalesce into veins that drain into the systemic venous blood. Those into the systemic venous blood. Those veins also collect capillary blood from veins also collect capillary blood from the posterior pituitary gland. the posterior pituitary gland.

NONPITUITARY HORMONESNONPITUITARY HORMONES

Nonpituitary hormones help regulate Nonpituitary hormones help regulate metabolism, homeostasis, development metabolism, homeostasis, development and behavior. and behavior.

THYROIDTHYROIDIn humans and other mammals, the thyroid In humans and other mammals, the thyroid is located at the base of the neck, on the is located at the base of the neck, on the ventral surface of the trachea.ventral surface of the trachea.Thyroxine (T4)Thyroxine (T4) and and triiodothyronine (T3)triiodothyronine (T3) contain iodine. They are derivatives of the contain iodine. They are derivatives of the amino acid amino acid tyrosinetyrosine..T4 is converted to T3 in many cases in T4 is converted to T3 in many cases in target cells.target cells.The receptor protein is located in the cell The receptor protein is located in the cell nucleus and has greater affinity for T3.nucleus and has greater affinity for T3.Stimulate general growth and development, Stimulate general growth and development, and the metabolic rate in most tissues by and the metabolic rate in most tissues by stimulating enzymes involved in glucose stimulating enzymes involved in glucose oxidation.oxidation.T4 and T3 help maintain normal blood T4 and T3 help maintain normal blood pressure, heart rate, muscle tone, digestion, pressure, heart rate, muscle tone, digestion, normal hydration and secretory activity of normal hydration and secretory activity of the skin, and reproductive ability and the skin, and reproductive ability and lactation in females. lactation in females. T3 induces or suppresses the synthesis of T3 induces or suppresses the synthesis of enzymes.enzymes.Hypothyroidism in childhood leads to Hypothyroidism in childhood leads to cretinism, retarded mental and physical cretinism, retarded mental and physical development.development.

Thyroid (cont.)Thyroid (cont.)Hypersecretion causes a fast use of nutrients, hunger, excessive sweat, Hypersecretion causes a fast use of nutrients, hunger, excessive sweat, high body temperature, nervousness, irritability and emotional instability.high body temperature, nervousness, irritability and emotional instability.These hormones require iodine. Lack of iodine causes goiter due to an over These hormones require iodine. Lack of iodine causes goiter due to an over production of THS by the anterior pituitary.production of THS by the anterior pituitary.The secretion of thyroid hormones is controlled by the hypothalamus The secretion of thyroid hormones is controlled by the hypothalamus through a negative feedback mechanism. through a negative feedback mechanism. It affects every cell in the body except the adult brain, spleen, testes, uterus It affects every cell in the body except the adult brain, spleen, testes, uterus and the thyroid gland itself.and the thyroid gland itself.Goiter Goiter is a disease caused by hypothyroidism. In the absence of enough is a disease caused by hypothyroidism. In the absence of enough thyroid hormones, the hypothalamus continues to produce TSH, which thyroid hormones, the hypothalamus continues to produce TSH, which leads to an increase in the size of the thyroid.leads to an increase in the size of the thyroid.Produces Produces calcitonincalcitonin, which works antagonistically to the parathyroid , which works antagonistically to the parathyroid hormone.hormone.Lowers the blood calcium level by inhibiting calcium release form bones.Lowers the blood calcium level by inhibiting calcium release form bones.Stimulates calcium incorporation into the bone matrix.Stimulates calcium incorporation into the bone matrix.Calcitonin activity is important in childhood when the skeleton grows quickly Calcitonin activity is important in childhood when the skeleton grows quickly but is weak in adults. but is weak in adults.

Explain the control of thyroxin secretion by Explain the control of thyroxin secretion by negative feedback. (H.1.5)negative feedback. (H.1.5)

The release of thyroxin is regulated by the pituitary gland The release of thyroxin is regulated by the pituitary gland and the hypothalamus. The hypothalamus controls the and the hypothalamus. The hypothalamus controls the pituitary's secretion of tropic hormones, and these, in pituitary's secretion of tropic hormones, and these, in turn, stimulate the secretion of hormones from the turn, stimulate the secretion of hormones from the thyroid, adrenal cortex, and gonads (the testes or thyroid, adrenal cortex, and gonads (the testes or ovaries). As the concentration of the hormones produced ovaries). As the concentration of the hormones produced by these target glands rises in the blood, the by these target glands rises in the blood, the hypothalamus decreases its production of releasing hypothalamus decreases its production of releasing hormones, the pituitary decreases its hormone hormones, the pituitary decreases its hormone production, and production of thyroxin by the target production, and production of thyroxin by the target gland also slows. By way of the hypothalamus, which gland also slows. By way of the hypothalamus, which receives information from many other parts of the brain, receives information from many other parts of the brain, hormone production is also regulated in response to hormone production is also regulated in response to other changes in the external and internal environments. other changes in the external and internal environments.

PARATHYROIDPARATHYROIDThese glands are embedded in the These glands are embedded in the connective tissue surrounding the thyroid.connective tissue surrounding the thyroid.Secrete the Secrete the parathyroid hormoneparathyroid hormone (PTH) (PTH) that regulates calcium level in the blood and that regulates calcium level in the blood and tissue fluid.tissue fluid.Stimulate calcium release from bones. PTH Stimulate calcium release from bones. PTH stimulates the osteoclasts to decompose stimulates the osteoclasts to decompose bone matrix. bone matrix. Stimulates calcium reabsorption from the Stimulates calcium reabsorption from the kidney, and conversion of vitamin D to its kidney, and conversion of vitamin D to its active form.active form.Vitamin D acts together with PTH and Vitamin D acts together with PTH and increases the absorption of calcium in the increases the absorption of calcium in the intestines. Vitamin D binds to receptors in intestines. Vitamin D binds to receptors in the nuclei of target cells and regulates gene the nuclei of target cells and regulates gene transcription. transcription. It increases the concentration of Ca2+ in the It increases the concentration of Ca2+ in the blood and has an effect opposite to that of blood and has an effect opposite to that of the thyroid hormone calcitonin. the thyroid hormone calcitonin. Lack of PTH causes a drop of Ca2+ in the Lack of PTH causes a drop of Ca2+ in the blood leading to convulsion of skeletal blood leading to convulsion of skeletal muscles.muscles.

ISLETS OF THE PANCREAS OR ISLETS OF THE PANCREAS OR OF LANGERHANS OF LANGERHANS

The pancreas is considered a major endocrine gland but only The pancreas is considered a major endocrine gland but only 1 – 2% (by weight) of its cells secrete hormones. The rest of 1 – 2% (by weight) of its cells secrete hormones. The rest of the cells are involved in the production of digestive enzymes. the cells are involved in the production of digestive enzymes. About 1 million little clusters of cells scattered throughout the About 1 million little clusters of cells scattered throughout the pancreas.pancreas.Alpha cellsAlpha cells secrete secrete glucagonglucagon (29-amino-acid polypeptide), (29-amino-acid polypeptide), which increases the concentration of glucose in the blood. Its which increases the concentration of glucose in the blood. Its major target is the liver.major target is the liver.Beta cellsBeta cells secrete secrete insulininsulin (51-amino-acid polypeptide), which (51-amino-acid polypeptide), which lowers the concentration of glucose in the blood.lowers the concentration of glucose in the blood.Insulin stimulates cells to take up glucose, inhibits the release Insulin stimulates cells to take up glucose, inhibits the release of glucose from the liver, stimulates the deposit of fat in the of glucose from the liver, stimulates the deposit of fat in the adipose tissue, and inhibits the use of amino acids.adipose tissue, and inhibits the use of amino acids.Glucose concentration regulates the secretion of glucagon and Glucose concentration regulates the secretion of glucagon and insulin.insulin.The concentration of glucose is maintained in humans near The concentration of glucose is maintained in humans near 90mg/100mL of blood.90mg/100mL of blood.Insulin also inhibits the glycogen break down in the liver and Insulin also inhibits the glycogen break down in the liver and inhibits the conversion of amino acids and glycerol from fats to inhibits the conversion of amino acids and glycerol from fats to sugar.sugar.In general, insulin takes glucose out of the blood, causing it to In general, insulin takes glucose out of the blood, causing it to be used in energy production or converted to other forms be used in energy production or converted to other forms (glycogen and fats), and promotes protein synthesis and fat (glycogen and fats), and promotes protein synthesis and fat storage. storage. Diabetes mellitusDiabetes mellitus is an endocrine disorder. is an endocrine disorder.Type I diabeticsType I diabetics do not produce enough insulin. The immune do not produce enough insulin. The immune system or a virus destroys beta cells.system or a virus destroys beta cells.Type II diabeticsType II diabetics produce enough insulin but the receptors on produce enough insulin but the receptors on target cells cannot bind to it.target cells cannot bind to it.

ADRENAL MEDULLAADRENAL MEDULLA

The The adrenal glandsadrenal glands are located above each kidney. are located above each kidney.Helps the body cope with stress, increases the heart Helps the body cope with stress, increases the heart rate, blood pressure, metabolic rate, reroutes blood, rate, blood pressure, metabolic rate, reroutes blood, mobilize fats and increase glucose level in the blood, mobilize fats and increase glucose level in the blood, dilates bronchioles, decreases digestive system activity dilates bronchioles, decreases digestive system activity and urine output.and urine output.Secretes Secretes epinephrine (adrenaline)epinephrine (adrenaline) and and norepinephrinenorepinephrine. These hormones belong to a group of . These hormones belong to a group of compounds called compounds called catecholaminescatecholamines, and derived from , and derived from the amino acid tyrosine.the amino acid tyrosine.Their secretion is a response to stress. Their secretion is a response to stress. Nervous system can increase their production. Nervous system can increase their production.

ADRENAL CORTEXADRENAL CORTEX

Adrenal secretions do not initiate cellular and enzymatic Adrenal secretions do not initiate cellular and enzymatic activity but permit many biochemical reactions to activity but permit many biochemical reactions to proceed at optimal rates. proceed at optimal rates. Secretes three hormones in significant amounts, but Secretes three hormones in significant amounts, but more than 30 steroids have been isolated.more than 30 steroids have been isolated.The adrenal cortex responds to endocrine stimulus The adrenal cortex responds to endocrine stimulus rather than the nervous system.rather than the nervous system.Hypothalamus → pituitary releases ACTH → adrenal Hypothalamus → pituitary releases ACTH → adrenal cortex secretes cortex secretes corticosteroidscorticosteroids..MineralocorticoidsMineralocorticoids (aldosterone) maintain sodium and (aldosterone) maintain sodium and potassium balance by increasing sodium reabsorption potassium balance by increasing sodium reabsorption and potassium excretion in the kidney tubules; increase and potassium excretion in the kidney tubules; increase in blood pressure and volume.in blood pressure and volume.

The Adrenal GlandsThe Adrenal Glands

Adrenal Cortex (cont.)Adrenal Cortex (cont.)

GlucocorticoidsGlucocorticoids (cortisol) help the body adapt to stress, raise (cortisol) help the body adapt to stress, raise blood glucose level and mobilize fats and proteins for sugar blood glucose level and mobilize fats and proteins for sugar production, and suppress the immune system. production, and suppress the immune system. Cortisone suppresses inflammation. Excessive amount of Cortisone suppresses inflammation. Excessive amount of glucocorticoids suppresses the immune system. glucocorticoids suppresses the immune system. DHEA (dehydroepiandrosterone) is converted in the tissues to DHEA (dehydroepiandrosterone) is converted in the tissues to testosterone.testosterone.Elevated levels of corticosteroids inhibit the secretion of ACTH.Elevated levels of corticosteroids inhibit the secretion of ACTH.There is evidence that corticosteroids help maintain homeostasis There is evidence that corticosteroids help maintain homeostasis when the body experiences stress over an extended period of time. when the body experiences stress over an extended period of time. A third group of corticosteroids are sex hormones, A third group of corticosteroids are sex hormones, androgensandrogens and and small amounts of small amounts of estrogensestrogens. The physiological role of adrenal sex . The physiological role of adrenal sex hormones is not well understood. hormones is not well understood.

GONADSGONADSGonadal steroids regulate growth, development, reproductive cycles, and sexual behavior.Gonadal steroids regulate growth, development, reproductive cycles, and sexual behavior.The gonads, testes and ovaries, produce androgens, estrogens and progestins.The gonads, testes and ovaries, produce androgens, estrogens and progestins.Testes produce mainly Testes produce mainly testosteronetestosterone, an androgen. It is responsible for secondary male , an androgen. It is responsible for secondary male characteristics.characteristics.Ovaries produce estrogens, the most important of which is Ovaries produce estrogens, the most important of which is estradiolestradiol. It is responsible for the . It is responsible for the secondary sexual characteristics of women. secondary sexual characteristics of women. The hypothalamus stimulates the anterior pituitary by releasing GnRH (gonadotropin releasing The hypothalamus stimulates the anterior pituitary by releasing GnRH (gonadotropin releasing hormone). hormone). The gonadotropin hormones LH and FSH, from the anterior pituitary control the synthesis of The gonadotropin hormones LH and FSH, from the anterior pituitary control the synthesis of estrogens and androgens.estrogens and androgens.

PINEAL GLANDPINEAL GLAND

The pineal gland or body is located near the center of The pineal gland or body is located near the center of the mammalian brain. In other animals it is found closer the mammalian brain. In other animals it is found closer to the surface of the brain.to the surface of the brain.Pineal body in the brain releases Pineal body in the brain releases melatoninmelatonin, a modified , a modified amino acid, which influences biological rhythms, sleep amino acid, which influences biological rhythms, sleep and the onset of sexual maturity.and the onset of sexual maturity.Melatonin concentration increases at night and makes us Melatonin concentration increases at night and makes us drowsy.drowsy.Lowest levels occur during daylight hours around noon. Lowest levels occur during daylight hours around noon. Depending on the species, the pineal body has Depending on the species, the pineal body has connections from the eyes, and receives input about the connections from the eyes, and receives input about the intensity of light and length of the dayintensity of light and length of the day

Pineal Gland (cont.)Pineal Gland (cont.)Melatonin secretion is a link between a Melatonin secretion is a link between a biological clock daily or seasonal biological clock daily or seasonal activity. activity. In some animals, mating behavior and In some animals, mating behavior and gonadal size varies with the length of gonadal size varies with the length of daylight and dark periods. Melatonin is daylight and dark periods. Melatonin is involved in these effects.involved in these effects.An area of the hypothalamus called An area of the hypothalamus called the the suprachiasmatic nucleussuprachiasmatic nucleus (SCN) (SCN) is rich in melatonin receptors and is rich in melatonin receptors and functions as a biological clock.functions as a biological clock.Changing melatonin concentration Changing melatonin concentration may also be a means by which the may also be a means by which the day-night cycles influence day-night cycles influence physiological processes that show physiological processes that show rhythmic variations, such as body rhythmic variations, such as body temperature, sleep, appetite, and temperature, sleep, appetite, and hypothalamic activity in general. hypothalamic activity in general. Melatonin seems to decrease the Melatonin seems to decrease the activity of the SCN neurons. Bright activity of the SCN neurons. Bright light suppresses melatonin secretion. light suppresses melatonin secretion.

INVERTEBRATE HORMONESINVERTEBRATE HORMONES

Among insects, hormones are secreted mainly by Among insects, hormones are secreted mainly by neurons. neurons. Hormones regulate regeneration in hydras, flatworms Hormones regulate regeneration in hydras, flatworms and annelids, molting and metamorphosis in insects, and annelids, molting and metamorphosis in insects, color changes in crustaceans, reproductive behavior and color changes in crustaceans, reproductive behavior and other activities.other activities.In hydras, the hormone that stimulates growth and In hydras, the hormone that stimulates growth and budding inhibits sexual reproduction.budding inhibits sexual reproduction.Crustaceans have endocrine glands and neuroendocrine Crustaceans have endocrine glands and neuroendocrine cells.cells.Molting, reproduction, heart rate and metabolism are Molting, reproduction, heart rate and metabolism are influenced by hormones.influenced by hormones.Pigment cells are located beneath the exoskeleton.Pigment cells are located beneath the exoskeleton.

Invertebrates (cont.)Invertebrates (cont.)

Pigment distribution is controlled by the neurosecretory cells.Pigment distribution is controlled by the neurosecretory cells.Dispersed pigments cause color changesDispersed pigments cause color changesInsect development is controlled by the interaction of various Insect development is controlled by the interaction of various hormones.hormones.Generally an environmental factor affects neuroendocrine cells in Generally an environmental factor affects neuroendocrine cells in the brain.the brain.Brain secretes Brain secretes BH hormoneBH hormone (brain hormone) that stimulates the (brain hormone) that stimulates the prothoracic gland to produce MH, molting hormone or prothoracic gland to produce MH, molting hormone or ecdysomeecdysome, , which stimulates growth and molting.which stimulates growth and molting.JH, JH, juvenile hormonejuvenile hormone, maintains the larval stage and prevents , maintains the larval stage and prevents metamorphosis.metamorphosis.When the JH decreases the larva develops into a pupa.When the JH decreases the larva develops into a pupa.In the absence of JH, the pupa molts and becomes an adult.In the absence of JH, the pupa molts and becomes an adult.The amount of JH decreases with each successive molt.The amount of JH decreases with each successive molt.