Endocrine System. Chapter 18

Transcription

1 Endocrine System Chapter 18

2 Learning Outcomes Explain the importance of intercellular communication, describe the mechanisms involved, and compare the modes of intercellular communication that occur in the endocrine and nervous systems. Compare the cellular components of the endocrine system with those of other systems, contrast the major structural classes of hormones, and explain the general mechanisms of hormonal action on target organs. Describe the location, hormones, and functions of the pituitary gland, and discuss the effects of abnormal pituitary hormone production. Describe the location, hormones, and functions of the thyroid gland, and discuss the effects of abnormal thyroid hormone production. Describe the location, hormone, and functions of the parathyroid glands, and discuss the effects of abnormal parathyroid hormone production.

3 Learning Outcomes (contd) Describe the location, structure, hormones, and general functions of the adrenal glands, and discuss the effects of abnormal adrenal hormone production. Describe the location of the pineal gland, and discuss the functions of the hormone it produces. Describe the location, structure, hormones, and functions of the pancreas, and discuss the effects of abnormal pancreatic hormone production. Describe the functions of the hormones produced by the kidneys, heart, thymus, testes, ovaries, and adipose tissue. Explain how hormones interact to produce coordinated physiological responses and influence behavior.

4 Two systems that directly/indirectly control most body functions Nervous System Endocrine System

5 How do these systems work? Nervous System Example: Foot steps on a nail impulse is generated impulse travels to the spinal cord impulses travel to the thigh muscle thigh muscles contract foot is lifted Endocrine System Example: Eat a candy bar blood sugar level goes up pancreas are stimulated to release hormone insulin in blood insulin helps liver and skeletal muscle in taking out access blood sugar and storing as glycogen blood sugar level goes down

6 How do these systems work? Nervous System Sensory system Transmits impulses Impulses go directly to the specific target cells Impulses cause contraction of muscles or secretion from glands Takes a fraction of a second to respond faster system Affect wears off within seconds Endocrine System Chemical system Releases hormones into blood Hormones are sent everywhere but act on specific target cells Hormones affect metabolism, membrane permeability, growth or development Takes minutes, hours, or days to respond.slower system Affect last days, hours or months

7 Endocrine and nervous systems work together and affect each other: Impulses may affect the release of certain hormones. Hormones may affect generation/conduction of impulses.

8 How Cells Communicate with one another Direct communication: is seen between cells of the same type which are in direct contact with one another via gap junctions. Paracrines: Local regulators, Released by body cells Act on neighboring cells Example: Nitric oxide (NO) secreted by endothelial cells lining blood vessels causes vasodilation of the blood vessels Endocrines: True hormones Made by endocrine cells or glands Diffuse into blood Travel to their specific target cells or organs Example: Insulin released by pancreas and act on liver and other cells as target cell. Synaptic communication: Neurons release chemicals called neurotransmitters at junctions close to target cells with specific receptors.

9 Components of the Endocrine System Some endocrine glands secrete hormone as their primary function: Pituitary gland Pineal gland Thyroid gland Parathyroid Adrenal gland Other endocrine glands secrete hormones as their secondary function: Hypothalamus Thymus Pancreas Ovaries Testis Stomach Kidneys Small intestine

10 Functions of Hormones Help maintain homeostasis (water, ph, blood sugar, temperature, minerals). Help regulate metabolism (making/breaking organic chemicals, energy production). Help regulate growth, development and reproduction.

11 Review Time!!! Labeling Activity: Endocrine glands of the body. Answer the following questions to review the material covered so far. What is Hoemostasis? Which two systems of the body maintain homeostasis? What is their mechanism of action? What is the difference between primary and secondary endocrine organs? Give examples of each. Write down the functions of hormones in the body?

12 Characteristics of hormones Over 50 types of hormones produced by human body Hormones are made by endocrine glands Hormones are made in very small amounts Hormones diffuse into blood and are transported by blood to all body parts Only specific target cells or organs recognize and respond to each hormone Target cells have specific receptor proteins

13 Classification of Hormones Based on their chemical structure, hormones can be divided into three groups: Amino acid derivatives: also known as biogenic amines, are derived from amino acids, e.g. thyroid hormones, epinephrine, norepinephrine and melatonin. Peptide hormones: are chains of amino acids, e.g. TSH, LH, FSH, ADH, Oxytocin, GH and PRL. Lipid derivatives: are divided into two classes eicosanoids (signaling molecules, e.g. prostaglandins) and steroid hormones (derived from cholesterol, e.g. estrogen and androgens).

14 Measurement of Hormones Hormones are released in blood and transported by blood. Most hormones are measured by taking a blood sample Some hormones are produced in excess and excreted in urine.measured in urine sample

15 Secretion and Distribution of Hormones Hormones are released in blood and transported by blood Some hormones circulate freely in the blood, e.g peptide hormones. These hormones remain functional for a short period of time, minutes to hours. Taken as shots/injections. Examples insulin, growth hormone. Thyroid hormones and steroid hormones travel in the blood bound to a special transport proteins and therefore remain in circulation much longer. Can be administered orally.

16 Hormone Action Hormones are made by an endocrine gland they travel through blood they are recognized by specific receptors present on the target cells a new protein is made or an inactive protein is activated protein could be an enzyme, a transport protein, or a protein hormone There are 2 basic mechanisms of hormone action: Water insoluble/lipid soluble hormone action Water soluble/lipid insoluble hormone action

17 Hormones and Intracellular receptors Hormone diffuses out of the blood capillary to go to its target cell --> Lipid soluble hormone diffuses through the phospholipid bilayer of the plasma membrane --> Hormone binds to the specific cytoplasmic receptor --> OR --> Hormone diffuses through the nuclear membrane to enter the nucleus and bind to nuclear receptor --> Hormone-receptor (HR) complex is formed --> HR complex binds to specific locations on DNA --> Specific genes are activated --> new mrna and proteins are made --> These proteins could be enzymes or transport proteins needed for specific hormone action

18 Hormones and Plasma Membrane Receptors Hormone diffuses out of the blood capillary to go to its target cell --> Peptide hormones cannot pass phospholipid bilayer of the plasma membrane --> Hormone binds to specific receptor present on plasma membrane --> Hormone receptor (HR) complex is formed on the outer surface of the plasma membrane --> G protein on the inside of the membrane is activated --> leads to the appearance of a second messenger (camp/cgmp/ca) -- > second messenger acts as an enzyme activator, inhibitor, or cofactor --> results in a change in the rate of metabolic reactions

19 Down Regulation: Presence of a hormone triggers decrease in number of hormone receptors. When levels of particular hormone are high, cells become less sensitive to it. Up Regulation: Absence of a hormone triggers increase in number of hormone receptors. When levels of particular hormone are low, cells become more sensitive to it.

20 Stimulation of an Endocrine Gland There are 3 types of signals that stimulate endocrine glands: Nerve impulse stimulation A nerve impulse stimulates an endocrine gland Example: Stress or anxiety generation of nerve impulses impulses travel to adrenal cortex release of epinephrine and norepinepherine increased blood sugar, heart rate, breathing help the body cope with stress Hormonal stimulation A hormone stimulates another endocrine gland to make its hormones Example: Hypothalamus makes thyrotropin releasing hormone (TRH*) TRH stimulates anterior pituitary to make thyrotropin thyrotropin* stimulates thyroid gland to make thyroid hormones * TRH and thyrotropin are called tropic hormones Non-hormonal or other chemical stimulation A chemical other than a hormone stimulates an endocrine gland Example: When blood sugar goes up pancreas are stimulated to produce insulin; when blood sugar level goes down insulin secretion goes down

21 Hormone Interaction Most body functions are regulated by two or more hormones hormones often have to interact with each other Permissive interaction When one hormone is required before the target cell can respond to another hormone Example: Estrogen is required for the development of the uterus lining then progesterone maintains this lining during pregnancy Synergistic interaction When two or more hormones complement each other to produce a greater response Example: Estrogen, progesterone, prolactin affect the growth of the mammary gland Antagonistic interaction When two hormones oppose the action of each other Example: Insulin decreases blood sugar while glucagon increases blood sugar

22 Control of Hormone Concentration Hormones are released in short bursts Feedback control mechanism A sequence of events where the end response regulates the secretion of the hormone Negative feedback control most common Where the body s response has an opposite affect on secretion of hormone Positive feedback control not as common Where the body s response has the same affect on the secretion of hormone

23 Review Time!!!! Labeling Activity: three mechanisms of hypothalamic control over endocrine function. Answer the following questions to review the material covered so far. Name the types of hormones based on their structure. Differentiate between the types of hormones based on their solubility, transportation in blood and administration in the body? Discuss the two mechanism of hormone action. Differentiate between up and down regulation. Differentiate between the three types of hormone interaction. Describe the three types of signals that stimulate endocrine secretions. Which hormone diffuses through the plasma membrane and binds to its receptors in the cytoplasm?

24 Things to learn for each gland Location and Anatomy Hormone/s secreted For each hormone, know Its target tissue and the response of the tissue to the hormone Regulation of the hormone i.e. what controls its release (chemical, neurons, or hormone) Effects of Hyposecretion/Hypersecretion

25 Hypothalamus Pituitary Gland Hypothalamus Links nervous system with endocrine system Is anatomically and physiologically connected to pituitary gland by infundibulum

26 Pituitary Gland Made of two lobes: Anterior pituitary An endocrine tissue Makes a variety of hormones Regulated by releasing and inhibitory tropic hormones made by hypothalamus Posterior pituitary A nervous tissue Does not make hormones Houses axon terminals of neurosecretory cells located in hypothalamus Stores and releases hypothalamic hormones in response to nerve impulses

27 Anterior Pituitary Hormones Hypothalamus secretes specific releasing hormones (RH) and inhibiting hormones (IH) Hormones travel via circulatory system hypothalamo hypophyseal portal system. anterior pituitary is stimulated or inhibited to release its hormones hormones are circulated throughout the body.

28 Anterior Pituitary Hormones Human Growth Hormone (hgh) Secretion: - Most actively secreted in early childhood years - Its secretion goes down during puberty Stimulates: Growth of body cells, especially bone, cartilage and muscle cells Protein synthesis, fat metabolism, blood sugar level, ATP production Regulation: chemical control Decreased blood sugar level (hypoglycemia) stimulates GHRH secretion by hypothalamus stimulates anterior pituitary increased hgh secretion Increased blood sugar level (hyperglycemia) stimulates GHIH secretion by hypothalamus inhibits anterior pituitary decreased hgh secretion

29 Growth Hormone (contd) Clinical application: Dwarfism: hyposecretion of hgh during early childhood years Giantism: hypersecretion of hgh during early childhood years Acromegaly: hypersecretion of hgh in an adult after most long bones have sealed thicker jaw bone and forehead, larger hands, feet, tongue, lips Diabetogenic effect of hgh: hypersecretion of hgh symptoms similar to diabetes mellitus (increased blood sugar)

30 Anterior Pituitary Hormones Thyroid Stimulating Hormone (TSH) Thyrotropin Tropic hormone Stimulates: Thyroid gland increased secretion of thyroid hormones, T3 and T4 increased metabolism Regulation: Decreased metabolism stimulates Thyrotropin Releasing Hormone (TRH) secretion by hypothalamus increased TSH secretion by anterior pituitary Increased metabolism decreased TRH secretion by hypothalamus decreased TSH secretion by anterior pituitary Clinical application: Causes metabolic disorders due to its affect on thyroid hormone secretion

31 Anterior Pituitary Hormones Gonadotropins Tropic hormones: Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH) Stimulate: Ovaries increased secretion of female hormones (estrogen, progesterone) stimulate follicular development and ovulation Testis increased secretion of male hormones (testosterone, inhibin) stimulate sperm formation Regulation: Decreased sex hormones increased Gonadotropin Releasing Hormone (GnRH) secretion by hypothalamus increased FSH and LH secretion by anterior pituitary increased sex hormones by ovaries and testis Increased sex hormones decreased (GnRH) secretion by hypothalamus decreased FSH and LH secretion by anterior pituitary decreased sex hormones by ovaries and testis Clinical application: Cause reproductive disorders due to their affect on secretion of sex hormones

32 Anterior Pituitary Hormones Adrenocorticotropic Hormone (ACTH) Tropic hormone Stimulates: Cortex of adrenal gland Secretion of cortisol Regulation: Corticotropin Releasing Hormone (CRH) secretion by hypothalamus increased ACTH secretion by anteriorpituitary increased cortisol secretion by adrenal cortex

33 Anterior Pituitary Hormones Prolactin (PRL) Stimulates: mammary gland milk production Melanocyte Stimulating Hormone (MSH) Stimulates: melanin synthesis by melanocytes Darkening of color in the skin

34 Posterior Pituitary Hormones Hypothalamus has neurosecretory cells make two hormones (ADH and OT) hormones are transported through the axons that from the hypothalamic hypophyseal tract hormones are stored in axon terminals hormones are released when a nerve impulse is transmitted by hypothalamus to the axon terminals

35 Posterior Pituitary Hormones Oxytocin (OT) Secretion: - Stimulated by nerve impulses Stimulates: Smooth muscle contraction in mammary duct release of milk Smooth muscle contraction in the wall of the uterus delivery of the baby Regulation: Positive feedback system Clinical application: Low OT during delivery Pitocin (commercial form of OT) shot is given to induce labor

36 Posterior Pituitary Hormones Antidiuretic Hormone (ADH) Secretion: Stimulated by water levels in blood Stimulates: Water reabsorption at the distal convoluted tubule and collecting duct Regulation: Low water intake hypothalamus detects osmolarity of blood neurosecretory cells in hypothalamus generate impulses stimulates release of ADH from axon terminals located in posterior pituitary ADH stimulates water reabsorption in kidneys less urine formed water is conserved High water intake hypothalamus detects osmolarity of blood neurosecretory cells in hypothalamus do not generate impulses less ADH released from axon terminals located in posterior pituitary less water reabsorption in kidneys more urine formed Clinical application: Diabetes insipidus: hyposecretion of ADH symptoms similar to diabetes mellitus (large amounts of urine formed, dehydration, thirst)

37 Summary of Pituitary Hormones

38 Review Time!!!! We have covered a lot of important information in the last few sections. Make sure you spend enough time reviewing this material. Assess your understanding by attempting these questions: Name the two lobes of the pituitary gland? Describe the relationship between hypothalamus and anterior vs posterior pituitary gland. Name the hormones made by the hypothalamus and released by posterior pituitary gland. What is the effect of these hormones in the body. Name the hormones of anterior pituitary gland and their target tissues. What is diabetogenic effect of growth hormone? What are tropic hormones? Give examples.

39 Thyroid Gland Located anterior to trachea and inferior to larynx Made of two lobes connected by isthmus Each lobe consists of numerous sacs called follicles Follicles store large amounts of hormones Has a rich blood supply for quick delivery of hormones in the blood stream Secretes: Thyroid hormones - T3 and T4 for maintaining metabolism Calcitonin (CT) for maintaining blood calcium level

40 Thyroid Gland Hormones Thyroid Hormones T3 Triiodothyroxine: tyrosine with 3 iodines T4 Thyroxine: tyrosine with 4 iodines Made by follicular cells Modified and stored inside the follicles with the help of thyroglubulin (TGB) Function: - Regulate carbohydrate and lipid metabolism - Affect growth and development - Increase blood pressure, heart beat, body temperature, and GI tract movement

41 Clinical application Cretinism: hyposecretion of T3 and T4 in infants physical and mental retardation, yellow skin, fat pads, protruding tongue, enlarged belly; hormone therapy Myxedema: hyposecretion of T3 and T4 in adults low metabolism, lethargy, increased weight, decreased body temperature and heart rate, enlarged heart Exophthalmic goiter/graves disease: hypersecretion of T3 and T4 in adults high metabolism, decreased weight, increased body temperature and heart rate, bulging eyes

42 Thyroid Gland Hormones Calcitonin(CT) Calcitonin (CT) Made by parafollicular cells (C Cells) located between the follicles Function: - Decreases blood calcium - Increases bone calcium

43 Parathyroid Gland Four tiny glands on the posterior surface of thyroid gland Made of two types of cells: Chief cells secrete parathyroid hormone (PTH) Oxyphil cells function unknown PTH - Increases blood calcium - Decreases bone calcium

44 Calcium Regulation Calcitonin and PTH are antagonistic hormones High blood levels of Ca+2 stimulate Calcitonin Low blood levels of Ca+2 stimulate PTHPTH

45 Review time Assess your understanding of the Thyroid and Parathroid hormones by attempting these questions: Name the hormones of thyroid gland? Which trace element plays an important role in the structure of thyroid hormones? Which thyroid hormone/s are under the regulation of anterior pituitary? Name the hormone/s secreted by the follicular cells and their function in the body. Describe the location of parathyroid glands? Increased blood calcium levels will stimulate the secretion of hormone by the gland.

46 Adrenal Gland Located above the kidneys Consists of: Capsule Adrenal cortex Adrenal medulla

47 Adrenal Gland Capsule Connective tissue protective layer Adrenal cortex Made up of three zones, secrete three types of hormones Adrenal medulla Secretes two types of hormones

48 Adrenal Cortex Hormones Secreted by zona glomerulosa Mineralocorticoids: Mostly aldosterone Regulate minerals Reabsorption of Na+, Cl-, HCO3- and water Excretion of K+ and H+ Affects water level in the body Clinical application: Hypersecretion causes Na+ and water retention hypertension

49 Adrenal Cortex Hormones Secreted by zona fasciculata Glucocorticoids: Mostly cortisol Functions: - Increases blood glucose level - Causes vasoconstriction increases BP - Has anti-inflammatory effects Clinical application: Addison s disease: hyposecretion of aldosterone and cortisol hypoglycemia, lower BP, dehydration Cushing s disease: hypersecretion of cortisol redistribution of fat, spindle legs, moon face, pendulous abdomen

50 Adrenal Cortex Hormones Secreted by zona reticularis Androgens: Insignificant in males (main source is testis) Main source in females Clinical application: Hirsuitism: hypersecretion of androgens excessive hair growth

51 Adrenal Medulla Hormones Epinephrine and norepinephrine: Similar structure and function Released in response to sympathetic nerve Involved in Fight or flight response Increase heart rate, BP, breathing rate, blood sugar, metabolism, and muscle contraction

52 Pancreas Located inferiorly and posteriorly to stomach Consists of Head, Body and Tail Endocrine 1% of the tissue produces hormones that diffuse into blood Exocrine 99% of the tissue produces digestive enzymes that are released through a pancreatic duct into small intestine

53 Pancreas Islet of Langerhans/Pancreatic Islets are the endocrine portion of the pancreas. This region is made up of 3 types of cells: Alpha cells secrete glucagon, which stimulates liver cells to release glucose > causes blood glucose to rise. Beta cells secrete insulin, which stimulates glucose uptake by body cells and increased conversion of glucose to glycogen in liver. Delta cells secrete peptide hormone similar to GHIH, which regulates the secretion of insulin and glucagon.

54 Pancreas Insulin and Glucagon Regulation Low blood glucose stimulates release of glucagon High blood glucose stimulates secretion of insulin Diabetes mellitus Type I childhood diabetes - decrease in beta cells decrease in insulin secretion high blood glucose (hyperglycemia) excretion of glucose (glucosuria) and large amounts of water (polyuria) low blood glucose (hypoglycemia) and dehydration excessive thirst. - Treatment insulin shots Type II Non-insulin dependent diabetes - Obese or older adults fewer insulin receptors on target cells lesser response symptoms as above - Treatment diet, exercise, insulin shots Hyperinsulinism - Overdoze of insulin sudden drop in glucose coma and death

55 Role of Insulin in blood Sugar Homeostasis

56 Role of Glucagon in blood Sugar Homeostasis

57 Review time!!! Assess your understanding of the Thyroid and Parathroid hormones by attempting these questions: Describe the location of adrenal gland. Identify the two regions of an adrenal gland? List the three zones of adrenal cortex. What effect will elevated cortisol levels have on blood glucose levels? Which hormone/s are responsible for the fight or flight response of the body? Identify the types of cells in the pancreatic islet and the hormones produced by each. The secretion of which hormone lowers blood glucose concentration. Describe diabetes mellitus. Identify the two types of diabetes mellitus.

58 Ovaries and Testis Primary function: Gamete formation eggs and sperms Secondary function: Hormone production - Ovaries produce estrogen, progesterone, relaxin, inhibin - Testis produce testosterone, inhibin Regulation: Hypothalamus secretes GnRH anterior pituitary secretes gonadotropins (FSH and LH) stimulate ovaries (follicular and oocyte development, hormone production) and testis (sperm and hormone production)

59 Pineal Gland Located posterior to thalamus Has neuroglial cells and secretory cells Secretes hormone, melatonin secretion is regulated by light impulses affects secretion of gonadotropins regulates internal cycle

60 Thymus Large organ in infants but atrophied as adult 2 lobed organ located in mediastinum superior to the heart Primary function maturation of T lymphocytes Secondary function secretion of hormone thymosin to aid maturation process

61 Other Endocrine Glands Stomach: secretes gastrin to regulate secretion of gastric juices Small intestine: secretes secretin, cholecystokinin that stimulate pancreas and gall bladder but inhibit stomach Placenta: secretes several hormones to support pregnancy Kidneys: secrete erythropoietin to stimulate RBC production by red bone marrow