Chapter 13 Endocrine System Endocrine glands are ductless

Chapter 13 Endocrine System • Endocrine glands are ductless • Exocrine glands have ducts 1

Major Endocrine Glands 2

General Characteristics • Includes the cells, tissues, and organs that secrete hormones into body fluids • The exocrine system secretes into tubes or ducts which lead to internal or external body surfaces Ex: sweat and sebaceous glands 3

• Endocrine glands and their hormones help regulate metabolic processes: control the rates of some chemical reactions, aid in transporting substances through cell membranes, and help regulate water balance, electrolyte balance, and blood pressure. • Play vital roles in reproduction, development, and growth 4

Comparison of Nervous System and Endocrine System • Neurons release neurotransmitters into a synapse, affecting postsynaptic cells • Glands release hormones into the bloodstream • Only target cells of hormone responds 5

Comparison of Nervous System and Endocrine System 6

Hormone Types • A hormone is a biochemical secreted by a cell that affects the function of another cell. • Five general types: steroids, amines, peptides, protein hormones, glycoproteins (last four are also called nonsteroidal) 7

Steroids • lipids that include complex rings of carbon and hydrogen atoms • derived from cholesterol • ex: estrogen and testosterone 8

Amines • • Derived from amino acids Produced by neurons Ex: epinephrine and norepinephrine Also synthesized from the adrenal medulla from tyrosine 9

Peptides • • Short chains of amino acids Ex: oxytocin and antidiuretic hormone 10

Protein hormones • • Long chains of amino acids Ex: growth hormone and parathyroid homone 11

Glycoprotiens • • A protein joined to a carbohydrate Ex: follicle-stimulating hormone 12

Types of Hormones 13

Prostoglandins • Paracrine substances that regulate only neighboring cells (local action) • Lipids that are made from a type of fatty acid • Found in the liver, kidneys, heart, lungs, thymus, pancreas, brain, and reproductive organs • Regulates the formation of c. AMP (2 nd messenger) 14

Actions of hormones • Hormones bind to specific receptors on target cells • Each hormone receptor is a protein or glycoprotein that has a binding site for a specific hormone • The more receptors a hormone binds, the greater the cellular response 15

Steroid hormones • • • Soluble in cell membranes Can diffuse easily into target cells Once inside they bind to receptors (usually in the nucleus) 16

• Specific genes are activated which are transcribed into m. RNA • m. RNA goes to the cytoplasm and directs the synthesis of specific proteins • Proteins then cause the cellular changes associated with the hormone 17

Actions of Steroid Hormones • hormone crosses membranes • hormone combines with receptor in nucleus • synthesis of m. RNA activated • m. RNA enters cytoplasm to direct synthesis of protein 18

Nonsteroid hormones • • • Combines with specific receptors on the target cell membrane Receptor binding alters the function of enzymes or membrane transport mechanisms which changes the concentration of other cellular components The first messenger is the hormone that triggers the activity 19

• Second messengers are the biochemicals that cause the changes in response to the hormones • Many hormones use cyclic AMP as a second messenger • Many second messenger molecules can be activated in response to just a few hormonereceptor complexes • Cells are highly sensitive to changes in the concentration of nonsteroid hormones 20

Actions of Nonsteroid Hormones • hormone binds to receptor on cell membrane • ATP converted to c. AMP • c. AMP acts as a 2 nd messenger • c. AMP promotes a series of reactions leading to cellular changes • Takes place in cytoplasm 21

Actions of Nonsteroid Hormones 22

Control of Hormonal Secretions • primarily controlled by negative feedback mechanism 23

Negative Feedback 24

Major Endocrine Glands 25

Pituitary Gland • About 1 cm in diameter • Attached to the hypothalmus by the pituitary stalk (infundibulum) and lies in the stella turcica of the sphenoid bone • Consists of an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis) • Anterior lobe secretes GH, TSH, ACTH, FSH LH, and PRL 26

• Posterior lobe cells (pituicytes) do not synthesize any hormones • ADH and OT are secreted by the nerve endings of special neurons into the bloodstream in posterior lobe • Cell bodies of neurosecretory cells are in the hypothalmus 27

• Substances secreted by the hypothalmus are carried directly to the anterior lobe • hypothalmus is an endocrine gland it also controls other endocrine glands • Anterior pituitary also controls other endocrine glands 28

• Most hypothalmic releasing hormones act on specific cells of the anterior pituitary(AP) • some actions are inhibitory • most stimulate the AP to release hormones that then stimulate other endocrine gland secretions • negative feedback regulates hormone levels in the bloodstream – fig 13. 8 page 496 29

Pituitary Gland Two distinct portions • anterior pituitary (adenohypophysis) • posterior pituitary (neurohypophysis) 30

Pituitary Gland Control • Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones • Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release hormones 31

Anterior Pituitary Hormones • AP lobe is enclosed in a dense capsule of connective tissue and consists of epithelial tissue arranged around • thin blood vessels • Five types of secretory cells within the epithelial tissue • Table 13. 6 page 503 32

Posterior Pituitary Hormones • • • Posterior lobe consists mainly of nerve fibers and neuroglial cells (pituicytes) Pituicytes support nerve fibers that originate in the hypothalmus Table 13. 6 page 503 33

Hormones of the Pituitary Gland 34

Hypothalamic Hormones 35

Thyroid Gland • Very vascular • Made of 2 large lateral lobes connected by a broad isthmus • Located just below the larynx on either side and anterior to the trachea • Removes iodine from the blood 36

Structure of the thyroid gland • It is covered by connective tissue made of follicles (secretory parts) • Follicles produce and secrete hormones • Extrafollicular cells(C cells) lie outside the follicles • Center filled with a clear viscous glycoprotein called colloid 37

Thyroid Gland 38

Thyroid Hormones • Follicular cells synthesize thyroxine (T 4)and triiodothyronine (T 3) which affect the metabolic rates of cells • Follicular cells need iodine salts to produce T 3 and T 4 • thyroid enlarges (goiter) if not enough iodine • C cells produce calcitonin 39

Thyroid Gland Hormones 40

Disorders of the Thyroid Gland 41

Disorders of the Thyroid Gland Graves Disease • Hyperthyroidism Cretinism • Infantile hypothyroidism 42

Parathyroid Gland • Located on the posterior surface of the thyroid gland • Usually 4 of them • Each gland is a small, yellowish brown structure covered by a thin capsule of connective tissue • Body consists of many tightly packed secretory cells associated with capillary networks 43

Parathyroid Glands 44

Parathyroid Hormone • PTH increases blood calcium ion concentration and decreases blood phosphate ion concentration through actions in the bones, kidneys, and intestines • PTH stimulates bone resorption by osteocytes and osteoclasts • Ca and PO 4 ions are released into blood 45

• PTH causes kidneys to conserve blood Ca ions and excrete more PO 4 ions in the urine • PTH helps kidneys convert Vitamin D into an active form which controls the absorption of Ca ions from the intestines 46

Parathyroid Hormone 47

Parathyroid Hormone Mechanism by which PTH promotes calcium absorption in the intestine 48

Disorders of the Parathyroid Glands 49

Adrenal Glands • Sits atop each kidney • Embedded in adipose tissue that encloses each kidney 50

Structure of the Adrenal Glands • • • Shaped like pyramids Very vascular Consists of a central portion (adrenal medulla) and an outer portion (adrenal cortex) 51

Adrenal Glands 52

Hormones of the Adrenal Medulla • Impulses arriving on the sympathetic nerve fibers stimulate the adrenal medulla to release its hormones • These impulses originate in the hypothalamus in response to stress • Hormones work with the sympathetic division of the autonomic NS to prepare for energy expending action (fight or flight) 53

• Two closely related hormones, epinephrine (adrenalin) and norepinephrine (noradrenalin) • Ratio of the 2 is usually about 80% epinephrine secreted and 20% norepinephrine • Effects of the two are similar, but certain effectors respond differently to them • Table 13. 10 page 510 – functions 54

Hormones of the Adrenal Medulla 55

Hormones of the Adrenal Cortex • Cells of the adrenal cortex produce more than 30 steroids, including several hormones (corticosteroids) • Some are vital for survival • The 3 most important adrenal cortical hormones are aldosterone, cortisol, and adrenal androgens 56

Hormones of the Adrenal Cortex • Table 13. 11 page 512 – functions - Aldosterone helps maintain Na ion concentration and blood volume - Cortisol helps keep blood glucose concentration normal between meals • ACE inhibitors treat high blood pressure – page 511 • Cortisol (hydrocortisone) and related compounds are used to reduce inflammation – page 513 57

Hormones of the Adrenal Cortex 58

Hormones of the Adrenal Cortex 59

Hormones of the Adrenal Cortex 60

Pancreas • Functions as an exocrine gland that secretes digestive fluid through a duct • Functions as an endocrine gland that releases hormones into body fluids 61

Structure of the Pancreas • • • Elongated and somewhat flattened Posterior to the stomach and behind the parietal peritoneum Attached to the first section of the small intestine 62

• Endocrine portion consists of groups of cells called islets of Langerhans that have 3 types of hormone secreting cells • alpha cells – secrete glucagons • beta cells – secrete insulin • delta cells – secrete somatostatin 63

Pancreas 64

Hormones of the Islets of Langerhans • Table 13. 11 Page 515 • Insulin and glucagon function together to help maintain a relatively stable blood glucose concentration • Negative feedback controls both hormones Fig 13. 36 Page 514 • Diabetes Mellitus – clinical application page 516 65

Hormones of the Pancreatic Islets 66

Insulin and Glucagon Insulin and glucagon function together to stabilize blood glucose concentrations 67

The Pancreas • Endocrine portion consists of groups of cells called islets of Langerhans • Insulin is produce by beta cells • Insulin is needed in order for glucose to enter cells (it lowers blood glucose concentration) • Glucagon is produced by alpha cells • Glucagon increases blood glucose concentration

Diabetes • Characterized by hyperglycemia (high blood sugar) • Type I caused when the beta cells do not produce enough insulin • Type II is caused by body cell receptors that do not respond to insulin (insulin resistance)

Type I Diabetes • Can be controlled by insulin injections or pump • Is an autoimmune disease – body’s own immune system attacks and destroys beta cells • Less than 10% of diabetics have this type • Often develops in children or young adults but can develop in people of any age

Type II Diabetes • Controlled by diet (medication also possible) • 90% of diabetics have this type • Often associated with genetic history, obesity, lack of exercise, advanced age, or certain ethnic groups (ex. Native Americans)

Uncontrolled Diabetes • Can cause damage to the retina leading to blindness • Can cause kidney failure • Can cause nerve damage • Increases the risk of cardiovascular disease • Can cause poor wound healing • Can damage blood vessels and lead to poor circulation

Pineal Gland • Small oval structure • Located deep between the cerebral hemispheres where it is attached to thalamus 73

• Secretes melatonin which regulates circadian rhythms (repeated cycles of day and night) • sleep/wake cycles • seasonal cycles of fertility in many mammals • helps regulate human female menstrual cycle • may control the onset of puberty 74

Thymus Gland • Located posterior to the sternum between the lungs • Large in children but gets smaller with age • Secretes thymosins that affect production and differentiation of certain white blood cells (T lymphocytes) • Important role in immunity 75

Reproductive Glands • • • Ovaries secrete estrogen and progesterone Placenta produces estrogens, progesterone, and a gonadotropin Testes produce testosterone 76

• Digestive Glands - Secrete hormones associated with the linings of the stomach and small intestines Other Hormone Producing Organs • Heart • Kidneys 77

Stress and Its Effects • Stressors are factors that cause increased activity of the sympathetic NS in an attempt to maintain homeostasis • Stress is the condition stressors produce in the body 78

Types of Stress 1. Physical – threatens tissues Ex: extreme heat or cold, decreased O 2 concentration, injuries, infections, prolonged heavy exercise, loud sounds 79

2. Psychological – results from thoughts about real or imagined dangers, personal losses, unpleasant social interactions, or any factors that threaten a person • may also stem from pleasant stimuli • factors vary from person to person 3. Combination of physical and psychological 80

Response to Stress • • Controlled by the hypothalamus Called the general stress (adaptation) syndrome Attempts to maintain homeostasis Fight or flight response is activated 81

Fight or Flight and General Stress Syndrome • Fig 13. 37 Page 518 • Table 13. 13 Page 519 – major events 82

Responses to Stress 83

Stress 84

Life-Span Changes • endocrine glands decrease in size • muscular strength decreases as GH levels decrease • ADH levels increase due to slower break down in liver and kidneys • calcitonin levels decrease; increase risk of osteoporosis • PTH level changes contribute to risk of osteoporosis • insulin resistance may develop • changes in melatonin secretion affect the body clock • thymosin production declines increasing risk of infections 85

Clinical Application Growth Hormone Ups and Downs • Gigantism - hypersecretion of GH in children • Acromegaly – hypersecretion of GH in adults • Dwarfism – hyposecretion of GH in children Figure shows oversecretion of GH in adulthood as changes occur in the same person at ages (a) nine, (b) sixteen, (c) thirty-three, and (4) fifty-two 86