The Endocrine System

1. The Endocrine System Chapter 15

2. Introduction • Nervous system and endocrine system share responsibility for control and coordination of entire body. • Homeostasis- balance of the body. • Systems have similarities and differences: • Both systems use chemicals to transmit their messages. • Endocrine system produces hormones • Nervous system produces neurotransmitters • Endocrine system reacts more slowly to changes but can sustain response longer. • Nervous system reacts more quickly to changes but cannot sustain prolonged responses.

3. Basics • Endocrine glands- basic units of the endocrine system. • Secrete hormones directly into the bloodstream. • Circulate throughout body and produce effects when attach to receptors in or outside of cells. • Ductless glands. • Exocrine glands- units that secrete their products onto epithelial surfaces through tiny tubes called ducts.

4. Endocrine vs. Exocrine Glands

5. Endocrine Glands

6. Major Endocrine Glands Gland Hormone Target Effect • Anterior pituitary Growth Hormone all body cells growth, metabolic (master endocrine gland)Prolactin mammary tissue (f) lactation Thyroid StimHor Thyroid gland Thy horm prod ACTH Adrenal cortex gluco-, mineralo- FSH follicles, semi tub egg, sperm prod LH follicles, inter cells CL, testosterone • Posterior pituitary ADH kidney water reabsorption (Storage only)oxytocin uterus, mamgl contract, milk • Thyroid Thyroid Hormone all body cells growth, metabolic Calcitonin bones Ca+ deposition • Parathyroid PTH bones, kid, intest ↑ blood Ca+ • Adrenal cortex glucocorticoids whole body ↑glu, ↓immunity mineralocorticoids kidneys Na+ retention sex hormones whole body minimal effects • Adrenal medulla epi, NE whole body fight/flight resp • Pancreas (islets) insulin all body cells ↓ blood glu glucagon whole body ↑ blood glu • Testis androgens whole body masculinization • Ovary estrogen whole body feminize, heat progesterone uterus maintain preg • Kidney erythropoietin bone marrow RBC production

7. Hormones • Chemical messengers produced by endocrine glands and secreted directly into blood vessels. • Produce effects when find their receptors in or on cells. • Each body cell has specific receptors to certain hormones (target). • If body does not have receptor, hormone will pass by. • Only certain hormones can fit to receptors and when it occurs, then it changes the activity of the cell.

9. Control of Hormone Secretion • “Negative Feedback System” • Endocrine glands will be stimulated to produce more hormone when it drops below a certain amount in the body. • If hormone is of adequate levels, gland will either slow or stop production of the hormone. • Direct Stimulation of Nervous System • Secretion of some hormones is stimulated by sympathetic nerve impulses when an animal feels threatened. • Fight or flight response from sympathetic nervous system

10. Negative Feedback Loop

11. Negative Feedback Loop

12. Fight or Flight Response

13. The Hypothalamus • Part of diencephalon of brain. • Has control of pituitary gland. • Portal system of blood vessels links hypothalamus with anterior portion of pituitary gland

14. Hypothalamus and anterior pituitary gland • Portal system of blood vessels links hypothalamus with anterior portion of pituitary gland. • Modified neurons in hypothalamus secrete releasing and inhibiting hormonesinto portal blood vessels • Specific for a particular anterior pituitary hormone • Either promote or inhibit the production of a specific hormone.

16. Hypothalamus and Posterior Pituitary • Hypothalamus produces antidiuretic hormone (ADH) and Oxytocin • Are transported to posterior pituitary where they are stored. • Released into bloodstream by nerve impulses from hypothalamus.

17. The Pituitary Gland • Also referred to as the “hypophysis”. • Master endocrine gland. • Many hormones direct activity of other endocrine glands. • Very small • Housed in pituitary fossa of skull. • Actually two separate glands: • Anterior- adenohypophysis • Produces seven known hormones • Posterior-neurohypophysis. • Does not produce any hormones but stores and releases ADH and Oxytocin.

18. Anterior Pituitary Gland • Hormones: • 1. Growth Hormone (GH) • 2. Prolactin • 3. Thyroid-stimulating Hormone (TSH) • 4. Adrenocorticotropic Hormone (ACTH) • 5. Follicle-stimulating Hormone (FSH) • 6. Luteinizing Hormone (LH) • 7. Melanocyte-stimulating Hormone (MSH).

19. Growth Hormone (GH) • Also known as somatotropin and somatotropic hormone. • Promotes growth in young animals. • Helps regulate metabolism of proteins, carbohydrates, and lipids in body’s cells. • GH breaks down lipids for energy while discouraging use of carbs for energy. • Can cause hyperglycemic effect.

20. Dwarfism Rare now since GH is commercially available

21. Giantism Body proportions normal

22. Acromegaly Excessive GH after epiphyseal plates close Responsive tissues: bones of hands, feet, face thickened facial features/tongue

23. Dairy Cows • Synthetic GH may be used to increase milk production of dairy cows. • Bovine Somatotropin (BST) • Enhances milk production by mammary glands. • Can elevate body temperature. • Reduce conception rates • Increases risk of mammary gland infections • Increases risk of digestive disorders.

24. Prolactin • Helps to trigger and maintain lactation • Continues as long stimulation of nipple continues. • Mammary glands will shrink to normal size once stimulation stops. • Has no known effect in male.

25. Thyroid-Stimulating Hormone (TSH) • Also referred to as thyrotropic hormone. • Stimulates growth and development of thyroid gland and causes it to produce hormones. • TSH production is regulated by feedback from Thyroid gland.

26. Adrenocorticotropic Hormone (ACTH) • Stimulates growth and development of the cortex of adrenal gland. • Stimulates release of some of adrenal gland’s hormones • Can be released in two ways: • First by feedback system from adrenal glands • Second during stress, can be released by stimulation of hypothalamus by other parts of brain. • This sends releasing factor to anterior pituitary through blood vessels.

27. ACTH stimulation test • Test used to check for hyperadrenocorticism or hypoadrenocorticism. • What are these also called? • ACTH stimulates production of cortisol.

28. Follicle-Stimulating Hormone (FSH). • Stimulates growth and development of follicles in ovaries to create ovum. • Helps produce estrogens as well. • Can be used to produce “superovulation” • Can then be harvested for Artificial Insemination.

29. Luteinizing (LH) • Completes process of follicle development that was started by FSH. • Surge in LH is what causes ovulation to occur. • High LH is maintained to produce corpus luteum which produces its own hormones. • In male, LH stimulates interstitial cells to produce testosterone. • Sometimes LH and FSH are called gonadotropins.

30. Melanocyte-Stimulating Hormone (MSH) • Associated with color changes in the melanocytes (pigment cells) of reptiles, fish, and amphibians. • Can cause pigment to darken when administered artificially. • Other effects are unknown.

31. Posterior Pituitary Gland • Does not produce, but stores and releases ADH and Oxytocin when stimulated. • ADH • Where does it act? • What does it do? • Lack of can cause what disease? • Oxytocin • Two targets are uterus and mammary glands. • What does it do in uterus? • What does it do in mammary glands?

32. The Thyroid Gland • Consists of two parts called lobes located on either side of the larynx. • Connected by narrow band called isthmus in some species. • Composed of tiny follicles, where thyroid hormone is produced. • Each follicle consists of globule surrounding thyroid precursor called a colloid. • Only endocrine gland that stores large amounts of hormone precursor for use later. • Produces two hormones: • Thyroid hormone • Calcitonin

33. Thyroid Hormone • T3(Triiodothyronine)- contains three iodine atoms per molecule. • T4(Tetriodothyronine, thyroxine)-contains four iodine atoms per molecule. • Production can be inhibited by stress on animal. • These hormones are produced when TSH from anterior pituitary gland reaches the thyroid gland. • T4 produced in greater abundance than T3 but is mostly converted to T3 before producing effects on target cells • T3 more potent • Necessary for normal growth and development in young animals. • Influences development and maturation of the central nervous system, muscles and bones.

34. Calorigenic Effect • Helps to heat the body and regulates the metabolic rate of all the body’s cells. • Allows an animal to generate heat and maintain a constant internal body temperature, when outside temperature changes. • Production of thyroid hormone increases with exposure to cold temperatures. • Increases body’s metabolic rate, which generates more heat.

35. Effect on Protein, Carbohydrate and Lipid Metabolism by Thyroid Hormone • Proteins: • Encourages synthesis of proteins if diet is adequate in energy sources. • If energy sources are not adequate in diet, then can actually catabolize proteins. • Carbohydrates: • Hyperglycemic effect. • Helps to maintain homeostasis of the blood glucose level by helping to prevent it from dropping too low. • Lipids: • Encourages their catabolism.

36. Thyroid Dysfunction:Hypothyroidism • Too little thyroid hormone produced. • Occurs commonly in dogs. • Symptoms include: • Alopecia • Dry skin • Lethargy • Reluctance to exercise • Weight gain • Seeking out sources of heat. • Easily treated with thyroid supplementation • Usually occur in middle age.

38. Thyroid Dysfunction: Hyperthryoidism • Too much thyroid hormone production. • Commonly seen in cats. • Symptoms include: • Nervousness • Excitability • Weight loss • Increased appetite, but no weight gain • Tachycardia • Vomiting • Diarrhea • Polyuria • Polydipsia • Treated surgically by removing the thyroid gland, radioactive treatment, or drugs to suppress thyroid production.

40. Thyroid Dysfunction: Goiter • Non-cancerous, non-inflammatory enlargement of the thyroid gland. • Results from iodine deficiency which is a component of thyroid hormone. • Not enough iodine produced, less hormone that can be produced. • Causes hyperplasia of the gland • Can be treated and prevented with iodine supplements. • Iodized salt.

41. Calcitonin • Produced by C cells located between the thyroid follicles. • Involved with maintaining homeostasis of the blood calcium levels. • Will prevent hypercalcemia by decreasing blood calcium levels if they go too high. • Encourages excess calcium to deposit in bones

42. Parathyroid Glands • Small nodules located near, in or on thyroid glands. • Produce: • Parathyroid Hormone (PTH)

43. Parathyroid Hormone (PTH) • Also called parathormone. • Opposite effect of calcitonin. • Prevents hypocalcemia by increasing blood calcium if gets too low. • Causes kidneys to retain calcium and intestines to absorb calcium from food. • Can take calcium out of storage from the bones.

44. Calcitonin/Parathormone Ca++ to bone Ca++ from bone Ca++ from kidneys Ca++ from GI tract

45. Parathyroid Dysfunction: Hypocalcemia • Milk fever- when parathormone is overwhelmed in lactating animals. • Can cause muscle weakness and tremors. • Can progress to seizures and spasms if left untreated. • “Downer cows” • Called Eclampsia in dogs and cats • Treated by supplementing calcium rapidly into system

47. Adrenal Glands • Located on cranial aspect of kidneys. • Composed of two glands wrapped around one another. • Outer Adrenal Cortex • Classic endocrine gland tissue • Produce under direction of ACTH: • Glucocorticoid hormones • Mineralcorticoid hormones • Sex hormones • Inner Adrenal Medulla • Resembles nervous tissue • Controlled by sympathetic portion of nervous system • Produces: • Epinephrine • Norepinephrine

49. Glucocorticoid Hormones • Hormones produced are: • Cortisone • Cortisol • Corticosterone • General hyperglycemic effect by causing blood glucose levels to rise. • Cause catabolism of proteins and lipids • Products are ultimately converted back to glucose through gluconeogenesis. • Also may help to maintain blood pressure and help body to resist stress.

50. Glucocorticoid-Related Diseases • Too much of cortisol in system-Hyperadrenocorticism=Cushing’s Disease. (Iatrogenic Cushings) • Symptoms include: • Polyuria • Polydipsia • Polyphagia • Hair loss • Muscle wasting • Slow wound healing • Too little of cortison in the system- Hypoadrenocorticism=Addison’s Disease. • Symptoms include: • Weakness • Lethargy • Vomiting • Diarrhea • Can lead to circulatory and kidney failure.