Chapter 11: Endocrine System Textbook - PDF

Because learning changes everything.® Chapter 11 Endocrine System HOLE’S ESSENTIALS OF HUMAN ANATOMY & PHYSIOLOGY Fifteenth Edition Charles J. Welsh and Cynthia Prentice-Craver © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent...

Because learning changes everything.® Chapter 11 Endocrine System HOLE’S ESSENTIALS OF HUMAN ANATOMY & PHYSIOLOGY Fifteenth Edition Charles J. Welsh and Cynthia Prentice-Craver © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.  11.1: Introduction to the Endocrine System The endocrine system works with the nervous system to maintain homeostasis The endocrine system is made up of cells, tissues, and organs called endocrine glands, that secrete hormones into body fluids Organs are not anatomically adjacent to each other Hormones diffuse into the bloodstream to act on specific target cells some distance away Certain glands secrete messenger molecules that never reach the bloodstream, so they are not true hormones; they are called “local hormones,” and include paracrine secretions (affect neighboring cells) and autocrine secretions (affect only the secretory cells) The body has 2 major types of glands, exocrine (secretes products into ducts, outside the internal environment) and endocrine (secrete hormones into body fluids to affect target cells) © McGraw Hill, LLC 2  Figure 11.1: Figure Locations of Major Endocrine Glands Access the text alternative for these images © McGraw Hill, LLC 3  Endocrine Glands of the Body Major endocrine glands include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, pineal gland, reproductive glands (ovaries and testes), kidneys, and thymus gland There are specialized cells in various other organs that produce hormones, but are mainly part of other systems: liver, heart, and gastrointestinal tract © McGraw Hill, LLC 4  The Nervous and Endocrine Systems There are similarities and differences in how the nervous and endocrine systems communicate with cells Both the nervous and endocrine systems are precise in their action on specific target cells The endocrine system communicates with various target cells using chemical messengers called hormones; the nervous system uses neurotransmitters Endocrine glands and their hormones regulate a number of metabolic processes within cells, and the whole body © McGraw Hill, LLC 5  Other Chemical Messengers Paracrine secretions (local hormones): Substances secreted into the interstitial fluid by certain glands Broken down rapidly, so they do not reach the bloodstream Function in a similar manner to hormones, but act only on nearby cells Example: Histamine released from white blood cells dilates local blood vessels Autocrine secretions: Act only on the cell that secretes them Example: Substance secreted by liver cells that cause them to release iron © McGraw Hill, LLC 6  A Comparison Between Nervous & Endocrine Systems TABLE 11.1 A Comparison Between the Nervous System and the Endocrine System Nervous System Endocrine System Cells Neurons Epithelial and others Chemical signal Neurotransmitter Hormone Specificity of response Receptors on Receptors on target cell postsynaptic cell Speed of onset Seconds Seconds to hours Duration of action Very brief unless May be brief or may last neuronal activity for days even if secretion continues ceases © McGraw Hill, LLC 7  Figure 11.2: Chemical Communication in the Nervous & Endocrine Systems Access the text alternative for these images © McGraw Hill, LLC 8  11.2: Hormone Action Structurally, there are 2 types of hormones: Steroids or steroid-like substances, which are derived from cholesterol Nonsteroids: amines, peptides, proteins, or glycoproteins, which are produced from amino acids © McGraw Hill, LLC 9  Types of Hormones TABLE 11.2 Types of Hormones Type of Compound Formed From Examples Steroids Cholesterol Estrogen, testosterone, aldosterone, cortisol Amines Amino acids Norepinephrine, epinephrine, thyroid hormones Peptides Amino acids Antidiuretic hormone, oxytocin, thyrotropin-releasing hormone Polypeptides and Amino acids Parathyroid hormone, growth proteins hormone, prolactin Glycoproteins Protein and Follicle-stimulating hormone, carbohydrate luteinizing hormone, thyroid- stimulating hormone © McGraw Hill, LLC 10  Steroid Hormones Characteristics of steroid hormones: Lipid-soluble, so they can pass through cell membranes Carried in the bloodstream weakly bound to plasma proteins, which prevents rapid degradation Protein receptors for steroid hormones are located inside the target cell The hormone-receptor complex binds with the DNA and activates specific genes that, in turn, direct the synthesis of specific proteins The new protein may function as an enzyme, transport protein, or hormone receptor; it carries out the effects of the steroid hormone © McGraw Hill, LLC 11  Figure 11.3: Steroid Hormone Action Access the text alternative for these images © McGraw Hill, LLC 12  Nonsteroid Hormones Characteristics of nonsteroid hormones: Water-soluble; cannot penetrate the phospholipid bilayer of cell membranes Nonsteroid hormones combine with receptors in target cell membranes; the receptors have a binding site and an activity site The hormone is called the first messenger The chemicals in the cell that respond to binding of the hormone, and cause changes in the cell, are called second messengers The cascade of biological activity through the cell membrane to the inside, beginning with the binding of the hormone, is called signal transduction The hormone-receptor complex generally activates a G protein, which then activates the enzyme adenylate cyclase that is bound to the inside of the cell membrane Adenylate cyclase breaks down ATP to cAMP, which activates protein kinases Protein kinases phosphorylate other proteins, activating them; this carries out the effects of the hormone © McGraw Hill, LLC 13  Figure 11.4: Nonsteroid Hormone Action Access the text alternative for these images © McGraw Hill, LLC 14  Prostaglandins Prostaglandins are lipids produced from the fatty acid, arachidonic acid, in cell membranes Cells in many organs produce prostaglandins Potent in small amounts Act locally, usually affecting the organ in which they are produced They are not stored; rather they are produced when needed, and inactivated after exerting their effects Prostaglandins produce a variety of regulatory effects: some relax smooth muscle, others contract smooth muscle, some stimulate secretion of other hormones or chemicals, some influence blood pressure, and others affect reproductive physiology © McGraw Hill, LLC 15  11.3: Control of Hormonal Secretions Hormone levels are very precisely regulated Negative feedback control mechanisms: Release of hormones from the hypothalamus controls secretions of the anterior pituitary, and anterior pituitary hormones affect the activity of peripheral endocrine glands The nervous system influences certain endocrine glands directly via nerve impulses Other glands respond directly to changes in the internal fluid composition, such as the level of glucose or a particular ion © McGraw Hill, LLC 16  Figure 11.5: Methods of Control of the Endocrine System Access the text alternative for these images © McGraw Hill, LLC 17  Negative Feedback Systems Commonly, negative feedback mechanisms control hormone release In a negative feedback system, a gland is sensitive to the concentration of the substance it regulates As hormone level rises, the hormone exerts its effects; further secretion is inhibited by negative feedback, and then hormone secretion decreases When the concentration of the hormone then drops below its normal level, the inhibition is removed, and the gland begins secreting more hormone again By this mechanism, hormone levels remain fairly constant, fluctuating within a normal average range © McGraw Hill, LLC 18  Figure 11.6: Effects of Negative Feedback Access the text alternative for these images © McGraw Hill, LLC 19  11.4: Pituitary Gland The pituitary gland (hypophysis) is attached to the hypothalamus by a stalk called the infundibulum: Anterior pituitary (anterior lobe): Consists mostly of glandular epithelial tissue Arranged around blood vessels and enclosed in a capsule of collagenous connective tissue Posterior pituitary (posterior lobe): Part of the nervous system Consists of axons of neurons of the hypothalamus © McGraw Hill, LLC 20  Figure 11.7: The Pituitary Gland and Hypothalamus Access the text alternative for these images © McGraw Hill, LLC 21  Control of the Pituitary Gland by the Hypothalamus The hypothalamus controls the activity of the pituitary gland. Anterior pituitary control: Releasing and inhibiting hormones from the hypothalamus control the secretion from the anterior pituitary These hormones are carried in the bloodstream along the pituitary stalk directly to the anterior pituitary by hypophyseal portal veins Specific anterior pituitary cells are then stimulated to release or stop releasing their hormone Posterior pituitary control: The posterior pituitary stores hormones made by the hypothalamus The posterior pituitary releases these hormones into the blood in response to nerve impulses from the hypothalamus © McGraw Hill, LLC 22  Figure 11.8: Secretion of Pituitary Hormones Access the text alternative for these images © McGraw Hill, LLC 23  Anterior Pituitary Hormones 1 Growth Hormone (GH): Stimulates body cells to grow and reproduce Speeds the rate at which cells use carbohydrates and fats Growth hormone-releasing hormone (GHRH) from the hypothalamus increases the amount of GH secreted, GH inhibiting hormone (GHIH, somatostatin) inhibits its secretion Nutritional status also affects the release of GH; more is released when glucose is low, or when certain amino acids increase GH imbalances: Pituitary dwarfism: Due to GH deficiency during childhood Gigantism: Due to GH oversecretion during childhood Acromegaly: Due to GH oversecretion in adulthood © McGraw Hill, LLC 24  Anterior Pituitary Hormones 2 Prolactin (PRL): Promotes milk production following the birth of an infant Controlled by prolactin releasing factor (PRF) and prolactin inhibiting hormone (PIH) from the hypothalamus There is no known normal physiological role in males Thyroid-stimulating hormone (Thyrotropin or TSH): Controls the secretion of hormones from the thyroid gland Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the release of TSH As blood concentration of thyroid hormones increases, secretions of TRH and TSH decrease © McGraw Hill, LLC 25  Figure 11.9: The TRH-TSH-Thyroid Hormone Pathway Access the text alternative for these images © McGraw Hill, LLC 26  Anterior Pituitary Hormones 3 Adrenocorticotropic hormone (ACTH): Controls the secretion of certain hormones from the adrenal cortex Regulated by corticotropin-releasing hormone (CRH) from the hypothalamus Stress can also increase release of CRH, which increases ACTH secretion Gonadotropins (FSH and LH): Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) affect the gonads: testes in the male and ovaries in the female In males, LH is also known as interstitial-cell stimulating hormone (ICSH). © McGraw Hill, LLC 27  Posterior Pituitary Hormones 1 Neurons in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin (OT), which are stored in the posterior pituitary Impulses from the hypothalamus release the hormones from the posterior pituitary gland These hormones travel down the axons of the hypothalamus to their storage area in the posterior pituitary gland Even though these 2 hormones are synthesized in the hypothalamus, they are called posterior pituitary hormones, because they are released into the blood there © McGraw Hill, LLC 28  Figure 11.10: Histology of the Anterior and Posterior Pituitary (all): Jose Luis Calvo/Shutterstock © McGraw Hill, LLC 29  Posterior Pituitary Hormones 2 Antidiuretic hormone (ADH or vasopressin): Causes the kidneys to conserve water, and reduces amount of water excreted in the urine The hypothalamus regulates the secretion of ADH, based on the amount of water in body fluids Osmoreceptors detect changes in osmotic pressure in body fluids, and adjust amount of ADH secretion At high level, also causes vasoconstriction of blood vessels, which helps to maintain blood pressure in conditions of dehydration Diabetes insipidus is a condition resulting from insufficient ADH © McGraw Hill, LLC 30  Posterior Pituitary Hormones 3 Oxytocin (OT): Plays a role in childbirth by contracting muscles in the uterine wall, and in milk ejection by forcing milk into ducts from the milk glands during breastfeeding Stretching of the uterine and vaginal tissues in the latter stages of pregnancy stimulates release of oxytocin Suckling of an infant at the breast stimulates release of oxytocin after childbirth Release is controlled through positive feedback © McGraw Hill, LLC 31  Hormones of the Pituitary Gland 1 TABLE 11.3 Hormones of the Pituitary Gland Hormone Action Source of Control Anterior Lobe Growth hormone Stimulates an increase in the Secretion stimulated by growth (GH) size and division rate of body hormone-releasing hormone from the cells; enhances movement of hypothalamus. Secretion inhibited by amino acids across membranes growth hormone inhibiting hormone from hypothalamus Prolactin (PRL) Sustains milk production after Secretion inhibited by prolactin- birth inhibiting hormone (dopamine) from the hypothalamus. Secretion stimulated by numerous prolactin-releasing factors, including thyrotropin-releasing hormone (TRH) from the hypothalamus Thyroid-stimulating Controls secretion of hormones Thyrotropin-releasing hormone (TRH) hormone (TSH) from thyroid gland from hypothalamus Adrenocorticotropic Controls secretion of certain Corticotropin-releasing hormone (CRH) hormone (ACTH) hormones from adrenal cortex from hypothalamus © McGraw Hill, LLC 32  Hormones of the Pituitary Gland 2 TABLE 11.3 Hormones of the Pituitary Gland Hormone Action Source of Control Follicle-stimulating In females, responsible for the Gonadotropin-releasing hormone (FSH) development of egg-containing follicles in hormone from hypothalamus ovaries and stimulates follicular cells to secrete estrogen; in males, stimulates production of sperm cells Luteinizing Promotes secretion of sex hormones; plays Gonadotropin-releasing hormone (LH) a role in releasing an egg cell in females hormone from hypothalamus Posterior Lobe* Antidiuretic Causes kidneys to conserve water; in high Hypothalamus in response to hormone (ADH) concentration constricts blood vessels changes in water concentration in body fluids Oxytocin (OT) Contracts smooth muscle in the uterine Hypothalamus in response to wall; contracts myoepithelial cells stretching of uterine and associated with milk-secreting glands vaginal walls and stimulation of breasts *These hormones are synthesized in the hypothalamus, as explained in the text. © McGraw Hill, LLC 33  11.5: Thyroid Gland The thyroid gland is located below the larynx and consists of two broad lobes connected by an isthmus Two hormones of the thyroid gland help control caloric intake, and one helps regulate blood calcium level and bone growth Structure of the thyroid gland: The thyroid consists of secretory units called follicles, filled with hormone-storing colloid Follicular cells secrete hormones that can be stored in the colloid or released into the blood © McGraw Hill, LLC 34  Figure 11.11: Structure of the Thyroid Gland (c) Jose Luis Calvo/Shutterstock Access the text alternative for these images © McGraw Hill, LLC 35  Hormones of the Thyroid Gland 1 Follicular cells produce 2 iodine-containing hormones, thyroxine (T4 or tetraiodothyronine), and triiodothyronine (T4 ) T3 is the more potent hormone These two hormones have similar actions; they regulate metabolism of carbohydrates, lipids and proteins They also increase the rate at which cells release energy from carbohydrates, enhance protein synthesis, and stimulate the breakdown and mobilization of lipids Thyroid hormone level is the major factor in determining the basal metabolic rate (BMR), the caloric intake necessary to maintain life These hormones are essential for normal growth and development and nervous system maturation The hypothalamus and pituitary gland control release of thyroid hormones Iodine is needed by the follicular cells to make thyroid hormones © McGraw Hill, LLC 36  Hormones of the Thyroid Gland 2 Extrafollicular (parafollicular) cells of the thyroid secrete calcitonin, a hormone which lowers blood levels of calcium and phosphate ions when they are too high Calcitonin increases calcium deposition in bones, by inhibiting the bone-resorbing activity of osteoclasts It also increases calcium and phosphate excretion by the kidneys into urine Calcitonin secretion is regulated by the blood concentration of calcium; when calcium is high, calcitonin is secreted © McGraw Hill, LLC 37  Thyroid Disorders Hypothyroidism: Underactivity of the thyroid gland Causes low metabolic rate, fatigue and weight gain in adults In infants, causes cretinism: poor growth and bone formation, abnormal mental development, sluggishness Hyperthyroidism: Overactivity of the thyroid gland Causes high metabolic rate, restlessness, overeating in adults May lead to eye protrusion (exophthalmia) Depending on cause of disease, either hypothyroidism or hyperthyroidism may lead to formation of a goiter, an enlarged thyroid that appears as a bulge in the neck © McGraw Hill, LLC 38  Hormones of the Thyroid Gland 3 TABLE 11.4 Hormones of the Thyroid Gland Hormone Action Source of Control Thyroxine (T4 ) Increases rate of energy release Thyroid-stimulating hormone from carbohydrates; increases from the anterior pituitary rate of protein synthesis; gland accelerates growth; necessary for normal nervous system maturation Triiodothyronine (T3 ) Same as above, but five times Thyroid-stimulating hormone more potent than thyroxine from the anterior pituitary gland Calcitonin Lowers blood calcium and Blood calcium concentration phosphate ion concentrations by inhibiting release of these ions from bones and by increasing excretion of these ions by kidneys © McGraw Hill, LLC 39  11.6: Parathyroid Glands 4 tiny parathyroid glands are located on posterior of thyroid gland Structure of the Glands: Parathyroid glands consist of tightly packed secretory cells covered by a thin capsule of connective tissue; secretory cells are associated with capillaries Parathyroid Hormone (PTH): PTH increases blood calcium ion concentration and decreases phosphate ion concentration PTH stimulates bone resorption by osteoclasts, which releases calcium into the blood PTH also stimulates the kidneys to conserve calcium PTH causes activation of vitamin D by kidneys, which causes increased absorption of calcium in the intestines A negative feedback mechanism involving blood calcium level regulates release of PTH © McGraw Hill, LLC 40  Figure 11.12: The Parathyroid Glands Access the text alternative for these images © McGraw Hill, LLC 41  Figure 11.13: Effects of Parathyroid Hormone Access the text alternative for these images © McGraw Hill, LLC 42  Calcium Regulation and Parathyroid Disorders Calcitonin and PTH maintain proper blood calcium concentration Calcitonin and PTH exert opposite effects in regulating calcium ion levels in the blood Calcitonin decreases blood calcium when it is too high PTH increases blood calcium when it is too low Parathyroid hormone disorders: Hypoparathyroidism: deficiency of PTH, due to surgical removal or injury to glands, which results in a decrease in blood calcium Hyperparathyroidism: excess of PTH, perhaps due to parathyroid tumor, which results in an increase in blood calcium © McGraw Hill, LLC 43  11.7: Adrenal Glands The adrenal glands sit on top of the kidneys, enclosed in a layer of adipose and connective tissues Structure of the Glands: The pyramid-shaped glands consist of an inner adrenal medulla and an outer adrenal cortex The adrenal medulla consists of modified postganglionic neurons that are connected to the sympathetic nervous system The adrenal cortex comprises most of the adrenal glands, and consists of epithelial cells in three layers: an outer layer (zona glomerulosa), middle layer (zona fasciculata), and an inner layer (zona reticularis) © McGraw Hill, LLC 44  Figure 11.14: Structure of the Adrenal Glands Access the text alternative for these images © McGraw Hill, LLC 45  Hormones of the Adrenal Medulla The adrenal medulla secretes epinephrine and norepinephrine into the bloodstream These two hormones are similar in structure and function Adrenal medulla secretes 80% epinephrine and 20% norepinephrine Effects resemble those of the sympathetic neurotransmitters of the same name, except that they last up to 10 times longer when they are secreted as hormones They are used in times of stress and for “fight-or-flight” responses Effects: increase heart rate, blood pressure and blood glucose, dilate airways, decrease digestive activities Release of medullary hormones is regulated by nerve impulses from the central nervous system through the sympathetic division of the autonomic nervous system © McGraw Hill, LLC 46  Effects of Epinephrine & Norepinephrine TABLE 11.5 Comparative Effects of Epinephrine and Norepinephrine Structure or function affected Epinephrine Norepinephrine Heart Increases rate Increases rate Increases force of contraction Increases force of contraction Blood vessels Vasodilation, especially Vasoconstriction in skin and viscera shifts important in skeletal muscle at blood flow to other areas, such as exercising onset of fight-or-flight response skeletal muscle Systemic blood pressure Some increase due to increased Some increase due to increased cardiac cardiac output output and vasoconstriction (offset in some areas, such as exercising skeletal muscle, by local vasodilation due to other factors) Airways Dilation Some dilation Reticular formation of brainstem Activated Little effect Liver Promotes breakdown of glycogen Little effect on blood glucose level to glucose, increasing blood sugar concentration Metabolic rate Increases Increases © McGraw Hill, LLC 47  Hormones of the Adrenal Cortex 1 The cells of the adrenal cortex produce over 30 steroids, some of which are hormones that are vital to survival Most important hormones are aldosterone, cortisol, and the sex hormones Aldosterone: Aldosterone, a mineralocorticoid, is secreted by cells of the outer zone; helps regulate mineral/electrolyte balance Causes the kidneys to conserve sodium ions and thus water, and to excrete potassium ions in the urine Aldosterone is secreted in response to decreasing blood volume and blood pressure; these changes are detected by the kidney © McGraw Hill, LLC 48  Cortisol Characteristics of Cortisol: Cortisol is a glucocorticoid; regulates glucose metabolism Produced by cells of the middle layer of the adrenal cortex Functions of cortisol: Inhibits protein synthesis, which increases blood amino acids Promotes fatty acid release from adipose tissue, increasing use of fatty acids for energy and decreasing use of glucose Causes liver cells to produce glucose from noncarbohydrates, to increase blood glucose A negative feedback mechanism involving CRH from the hypothalamus and ACTH from the anterior pituitary controls the release of cortisol Stress, injury, or disease can also trigger increased release of cortisol © McGraw Hill, LLC 49  Figure 11.15: Negative Feedback and Cortisol Secretion Access the text alternative for these images © McGraw Hill, LLC 50  Adrenal Sex Hormones and Disorders of the Adrenal Cortex Adrenal sex hormones: Sex hormones, produced in the inner zone, are mostly male hormones (adrenal androgens), but can be converted to female hormones in the skin, liver, and adipose tissues These hormones supplement those released by the gonads and may stimulate early development of reproductive organs Disorders of hormones of the adrenal cortex: Addison disease: hyposecretion of glucocorticoids and mineralocorticoids Cushing syndrome: hypersecretion of adrenal cortical hormones © McGraw Hill, LLC 51  Hormones of the Adrenal Cortex 2 TABLE 11.6 Hormones of the Adrenal Cortex Hormone Action Factor Regulating Secretion Aldosterone Helps regulate concentration of Blood sodium and potassium extracellular electrolytes by concentrations conserving sodium ions and excreting potassium ions Cortisol Decreases protein synthesis, Corticotropin-releasing increases fatty acid release, and hormone from the stimulates glucose synthesis from hypothalamus and noncarbohydrates adrenocorticotropic hormone (ACTH) from the anterior pituitary Adrenal androgens Supplement sex hormones from Adrenocorticotropic hormone the gonads; may be converted to (ACTH) from the anterior estrogens in females pituitary plus unknown factors © McGraw Hill, LLC 52  11.8: Pancreas The pancreas secretes hormones as an endocrine gland, and digestive juice into the digestive tract as an exocrine gland Pancreatic hormones control level of blood glucose Structure of the gland: The pancreas is an elongated organ posterior to the stomach Its endocrine portions are the pancreatic islets (islets of Langerhans), that include 2 cell types: alpha cells that secrete glucagon, and beta cells that secrete insulin Pancreatic duct joins the pancreas to the duodenum, for digestive juice to enter duodenum of the small intestine © McGraw Hill, LLC 53  Figure 11.16: Structure of the Pancreas Access the text alternative for these images © McGraw Hill, LLC 54  Figure 11.17: Light Micrograph of a Pancreatic Islet Victor P. Eroschenko Access the text alternative for these images © McGraw Hill, LLC 55  Hormones of the Pancreatic Islets Glucagon: Increases the blood level of glucose, by stimulating the breakdown of glycogen and the conversion of noncarbohydrates into glucose by the liver The release of glucagon is controlled by negative feedback Low blood glucose level stimulates the secretion of glucagon Insulin: Decreases the blood level of glucose by stimulating the liver to form glycogen, promotes facilitated diffusion of glucose into cells, increases protein synthesis, and stimulates adipose cells to store fat The release of insulin is controlled by negative feedback High blood glucose stimulates the release of insulin Insulin and glucagon coordinate to maintain a relatively stable blood glucose concentration © McGraw Hill, LLC 56  Figure 11.18: Control of Blood Glucose by Insulin and Glucagon Access the text alternative for these images © McGraw Hill, LLC 57  Diabetes Mellitus A metabolic disease due to lack of insulin or the inability of cells to recognize insulin High blood glucose harms eyes, heart, kidneys, peripheral nerves Causes disturbances in metabolism of carbohydrates, fats, proteins Glucose entry into body cells is impaired Symptoms: hyperglycemia, glycosuria, polydipsia, polyphagia, acidosis Type 1 diabetes mellitus (insulin-dependent diabetes mellitus, IDDM) is an autoimmune disorder, in which beta cells are destroyed, so insulin production decreases or stops Type 2 diabetes mellitus (noninsulin-dependent diabetes mellitus, NIDDM) occurs when insulin is produced but is not recognized by cells © McGraw Hill, LLC 58  11.9: Pineal, Thymus, and Other Endocrine Tissues and Organs Pineal Gland: Located near the upper portion of the thalamus Secretes melatonin, which is involved in the regulation of circadian rhythms of the body It is released at night, but is suppressed during the day Thymus Gland: Lies between the lungs, behind the sternum Secretes thymosins, that affect production and differentiation of T lymphocytes (which are important in immunity) The gland is largest in children, and shrinks with age © McGraw Hill, LLC 59  Other Endocrine Tissues and Organs Reproductive Organs: The ovaries produce estrogen and progesterone The placenta produces estrogen, progesterone, and gonadotropin The testes produce testosterone Digestive Organs: The digestive glands secrete hormones associated with the stomach and small intestine for the processes of digestion Fat Cells of Adipose Tissue: Secrete leptin, a hormone that helps regulate food intake and energy balance When fat stores increase, leptin level increases and appetite is suppressed Heart: Secretes atrial natriuretic peptide, which affects sodium and water excretion by the kidneys Kidneys: Secrete erythropoietin for blood cell production © McGraw Hill, LLC 60  11.10: Stress and Health Factors that serve as stressors to the body can threaten homeostasis Stressors increase the activity of the sympathetic nervous system Types of Stress: Stress may be physical, psychological, or some combination of the two Physical stress threatens the survival of tissues, such as extreme cold, prolonged exercise, oxygen deficiency, or infections Psychological stress results from real or perceived dangers, and includes feelings of anger, depression, fear, and grief; sometimes even pleasant stimuli cause stress © McGraw Hill, LLC 61  Responses to Stress 1 Responses to stress are designed to maintain homeostasis Responses to stress involve a set of reactions called the stress response or general adaptation syndrome The stress response has 2 stages: the “alarm” stage and the “resistance” stage: The alarm stage involves the immediate "fight or flight" responses of the sympathetic nervous system; it is activated by the hypothalamus: Increases blood glucose and fatty acids Increases heart rate, breathing rate, blood pressure Increases epinephrine secretion from adrenal medulla Dilates air passages Sends more blood to skeletal muscles, and less to skin and digestive organs © McGraw Hill, LLC 62  Responses to Stress 2 In the longer-lasting resistance stage, CRH from the hypothalamus travels to the anterior pituitary, and increases ACTH secretion, which increases cortisol secretion from the adrenal cortex Actions of cortisol from the adrenal cortex: Increases blood amino acids, fatty acid release, and glucose formation from noncarbohydrates Long term stress can be harmful: Decreases lymphocytes, which lowers resistance to infections and some cancers Increases risk of high blood pressure, atherosclerosis, and GI ulcers © McGraw Hill, LLC 63  Figure 11.19: The Stress Response Access the text alternative for these images © McGraw Hill, LLC 64  Because learning changes everything. ® www.mheducation.com © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.