1. Anatomy & Physiology Chapter 16
Endocrine System
Anatomy & Physiology
Chapter 16

3. Endocrine vs. Nervous System
See Table 16-1

4. Classification of hormones by chemical structure

5. Steroid hormones Derived from cholesterol Lipid-soluble
Pass through plasma membranes easily

6. Nonsteroid hormones Synthesized primarily from amino acids
Protein hormones: long chains of amino acids ex: insulin, PTH
Glycoproteins: protein hormones with a carbohydrate group attached ex: FSH, LH
Peptide hormones: short chain of amino acids ex: oxytocin, ADH
Amino acid derivatives: derived from a single amino acid
Amine hormones: derived from tyrosine ex:epinephrine
Iodine added to tyrosine ex: thyroid hormones

7. General Principles of Hormone Action
Bind to a specific receptor on cell by “lock-and-key” mechanism
Some hormones are attached to plasma proteins in bloodstream
Since blood carries hormones most everywhere lots more produced than makes it to its target

8. Mechanism of steroid hormone action (Mobile-receptor hypothesis)
Attach to soluble plasma proteins in blood
Receptors usually found within the cell
Regulate cells by regulating production of certain critical proteins
Amount of steroid hormone present determines magnitude of target cell’s response
Response to steroid hormones often slow

9. Mechanisms of Nonsteroid Hormones
Second messenger mechanism: also called fixed-membrane-receptor hypothesis
Nuclear receptor mechanism

10. Second messenger mechanism
Binds to receptors on target cell’s plasma membrane
Then second messenger within cell triggers appropriate cellular changes
Most use cAMP as second messenger
Operates more quickly than steroid mechanism

11. Nuclear receptor mechanism
Small iodinated amino acids (T3 & T4)
Enter target cell & bind to receptors associated with DNA which triggers transcription of mRNA

12. Regulation of hormone secretion
Usually part of a negative feedback loop and is called endocrine reflexes
Endocrine cells often sensitive to changes produced by its target cells
May be regulated by hormone produced by another gland, esp pituitary gland
May be influenced by nervous system input

13. Prostaglandins Lipid molecules
Tissue hormones: secretion produced in tissues & diffuse short distance only to other cells in same tissue
Tissues known to secrete prostaglandins: kidneys, lungs, iris, brain, thymus

14. Vocabulary Words Hormone Synergism Permissiveness Antagonism
Tropic hormones
Sex hormones
Anabolic hormones

15. Pituitary Gland

16. Pituitary gland (Hypophysis)
Lies within sella turcica of skull
Connected to the hypothalamus by a stalk, infundibulum
Consists of 2 different glands
Adenohypohysis or anterior pituitary
Neurohypophysis or posterior pituitary

17. Anterior Pituitary Two parts 5 types of secretions
pars anterior: major part
pars intermedia
5 types of secretions
Somatrophs-secrete GH
Corticotrophs-secrete ACTH
Thyrotrophs: secrete TSH
Lactotrophs: secrete prolactin
Gondatrophs: secrete LH and FSH

18. Growth Hormone (GH)
Promotes protein anabolism thus promotes growth of bones, muscles
Promotes lipid mobilization & catabolism
Indirectly inhibits glucose metabolism
Indirectly increases blood glucose levels

19. Prolactin (PRL) During pregnancy promotes breast development
After birth stimulates mammary gland to begin milk secretion

20. Tropic hormones Have stimulating effect on other endocrine glands
Thyroid stimulating hormone: TSH
Adrenocorticotropic hormone: ACTH
Follicle stimulating hormone: FSH
Luteinizing hormone: LH

21. TSH
Maintains growth & development of thyroid gland & causes it to secrete its hormones

22. ACTH
Promotes & maintains normal growth of cortex of adrenal gland & stimulates it to secrete some of its hormones

23. Gonadotropins Stimulate growth & development of gonads
FSH: stimulates follicles (with ovum) to maturity, also stimulates follicle to secrete estrogen; in male: stimulates development of seminiferous tubules
LH: stimulates formation of corpus luteum; in males: stimulates interstitial cells in testes to develop & secrete testosterone

24. Control of secretion of anterior pituitary
Hypophyseal portal system: complex of small blood vessels between hypothalamus & anterior pituitary
Hypothalamus secretes releasing hormones through this system
During times of stress cerebral cortex can send impulses to hypothalamus to secrete releasing hormones thus mind-body link

25. Posterior pituitary Storage & release site for:
ADH (antidiuretic hormone)
Oxytocin
Hormones are not made within the pituitary but within the supraoptic or paraventricular nuclei of hypothalamus
Release of these hormones thus controlled by nervous stimulation

26. Antidiuretic hormone Prevents formation of a large volume of urine
Release triggered by osmoreceptors near supraoptic nucleus

27. Oxytocin Stimulates contraction of uterine muslces
Causes ejection of milk from breasts
Regulated by a positive feedback mechanism

29. Pineal gland Located on dorsal surface of brain’s diencephalon
Member of both nervous system & endocrine system
Produces melatonin, functions to support biological clock

30. Thyroid gland
In neck, on anterior & lateral surface of trachea just below the larynx
Composed of structural units called follicles
Hormones:
Thyroid hormones
Calcitonin

31. Thyroid hormones T3: principal thyroid hormone
T4: most abundant, precursor of T3
Thyroid gland stores thyroid hormone as thyroglobulins
Regulate metabolic rate of all cells

32. Calcitonin Produced by parafollicular cells of thyroid
Influences processing of calcium by bone cells by decreasing blood calcium levels
Antagonist to parathyroid hormone

33. Parathyroid gland
4-5 of them embedded on posterior surface of thryoid’s lateral lobes
Hormone: PTH (parathryroid hormone)

34. PTH Antagonist to calcitonin
Acts on bones & kidneys to increase blood calcium
Bones: calcium & phosphate released from bones
Kidneys: calcium reabsorbed, phosphate secreted, activates Vitamin D in kidney which permits Ca to be absorbed in intestine

35. Adrenal glands On top of kidneys Adrenal cortex: outer part
Zona glomerulosa: mineralocorticoids
Zona fasiculata: glucocorticoids
Zona reticularis: gonadocorticoids
Adrenal medulla: inner portion

36. Mineralocorticoids Aldosterone: important mineralocorticoid
Primary function is maintenance of sodium homeostasis by increasing sodium reabsorption in kidneys
Increase water retention & promotes loss of potassium
Secretion controlled by renin-angiotensin & blood potassium concentration

37. Glucocorticoids Cortisol most significant Affect every cell in body
Protein mobilizing, lipid catabolism as energy source, secretion increase in times of stress, essential for maintaining normal blood pressure, decrease in number of WBCs

38. Gonadocorticoids Secretes small amounts of male hormones
Released from zona fasiculata & zona glomerulosa
Influences appearance of pubic & axillary hair

39. Adrenal medulla Composed of neurosecretory tissue
Produce epinephrine & norepinephrine
Prolong & enhance effects of sympathetic stimulation (fight or flight response)

40. Pancreas
Endocrine portion: pancreatic islets (or islets of Langerhans)
Alpha cells: secrete glucagon
Beta cells: secrete insulin
Delta cells: secrete somatostatin
Pancreatic polypeptide cells: secrete pancreatic polypeptide

41. Glucagon
Increase blood glucose levels by stimulating conversion of glycogen to glucose in liver cells
Also stimulates gluconeogenesis in liver
Hyperglycemic effect

42. Insulin
Promotes movement of glucose, amino acids, fatty acids into tissue cells
Lowers blood glucose

43. Somatostatin
Regulates other endocrine cells of pancreatic islets by inhibiting secretion

44. Gonads
Primary sex organs
Males: testes
Females: ovaries

45. Testes Interstitial cells within testes produce testosterone
Responsible for growth & maintenance of male sexual characteristics & for sperm production

46. Ovaries
Estrogens: secreted by follicles, promote development & maintenance of female sexual characteristics, breast development, menstrual cycle
Progesterone: secreted by corpus luteum, maintains lining of uterus necessary for pregnancy

47. Placenta
Produces human chorionic gonadotropin (hCG), serves as a signal to maintain uterine lining for pregnancy
Temporary endocrine gland

48. Thymus Atrophies at puberty Produces thymosin & thymopoietin
Stimulate production of T cells

49. Gastric & Intestinal Mucosa
Secretin: reduce acid secretion, triggers pancreas to produce bicarbonate
CCK: trigger pancreas to release digestive enzymes, gall bladder contraction
Ghrelin: stimulates hypothalamus to boost appetite

50. Heart
Atrial natriuretic hormone (ANH): promotes loss of sodium in urine thus it opposes increase in blood volume or blood pressure
Antagonistic to ADH & aldosterone