1. The Endocrine System
chemical messages (hormones) that are released into the blood
Hormones control several major processes
Reproduction - gametogenesis, sexual desire
Growth and development
Maintenance of homeostasis - salts, water, blood pressure, RBCs
Regulation of metabolism - digestion, stress responses
Messenger system of the body
Slower communication system than nervous system. Effects also often longer lasting.
Hormones are produced by specialized cells
Cells secrete hormones into extracellular fluids
Blood transfers hormones to target sites
These hormones regulate the activity of other cells

2. Endocrine System Characteristics
Access to every cell
Each hormone acts only on specific cells (target cells) that have matching receptors
Endocrine control slower than nervous system
Endocrine and nervous systems interact
Access to every cell - since every cell gets nutrients from blood. Exception is central nervous system, which is partly exempted by blood/brain barrier. contrast w/ nervous system, which requires hard wiring to reach a cell..
Each hormone acts only on specific cells (target cells) - although signal is sent everywhere, only certain cells have correct receptor and can “hear” the signal. Allows precise sending of messages.
Only specific cells have receptors for specific hormones - each cell can “hear” one or more hormones but will ignore all other signals.
Endocrine control slower than nervous system - takes time to excrete hormone, travel via bloodstream and react with target cells. Minimum 20 sec. Effects can be longer-lasting. Slower control can be suited for homeostasis to avoid pushing pendulum too far in effort to correct condition.
Endocrine and nervous systems interact - some hormones are released only in response to nervous signals. Development of sexual maturity involves both systems, signals btw them.
Def of hormone - chemical secreted by cells into the extracellular fluids that regulate the metabolic activity of other cells.

3. Classification of Hormones: Steroid
Steroid Hormones:
Lipid soluble, derived from cholesterol
Enter target cells
Activate specific genes to produce proteins
Slower acting: minutes to hours
Def of hormone - chemical secreted by cells into the extracellular fluids that regulate the metabolic activity of other cells.
Steroids actually enter cells, go into nucleus and turns on certain genes, which then are used to produce proteins. Entire process has more steps than with non steroids, takes a bit longer.

4. Steroid Hormones: How does a steroid hormone cause changes in cells?
Note solubility differences among classes of hormones. Linked to mechanism of action.

5. Hormones: Nonsteroid Amino acid-based hormones
proteins, peptides, amines
Water soluble
Bind to receptors on target cell surface
Work via second messengers to activate existing enzymes
Faster action: seconds to minutes
Mechanism of action of hormones:
Changes in plasma membrane permeability or electrical state. These hormones never enter the cell.
Can stimulate Synthesis of proteins, such as enzymes
Often causes Activation or inactivation of enzymes
Ex. Stimulation of mitosis

6. Non-Steroid Hormones:
How does a non-steroid hormone cause changes in cells?

7. Control of Hormone Release
Hormone levels are maintained by negative feedback
Low hormone levels or a stimulus triggers the release of more hormone
Hormone release stops once an appropriate level in the blood is reached
Analogy with furnace thermostat. Oven temperature.
Slower mechanism of action of hormones (compared to nervous system) leads to smaller adjustments, less swing; closer to desired level of activity of cells, organs.
Hormone release into blood stops as result of negative feedback, even before effects on other cells are achieved. So, negative feedback works before consequences of increased hormone are effective.
Ex. Ca++ levels, K+ levels.
Positive feedback is rare - contraction of uterus during childbirth is one example.
NEXT: 3 ways that hormone release is triggered.

8. 1. Hormonal Stimulus Endocrine glands are activated by other hormones
Most common signal- coordinates response of several glands
Most common signal for hormone release.
Hormone levels tend to be rhythmic, rising and falling repeatedly.
Reason for this type of stimulation:
1. Amplification of signal; impt b/c
2.target groups of glands needed for overall response.
3. Coordinated response to maintain homeostasis.
Figure 9.2a

9. 2. Humoral Stimulus
Changing blood levels of certain ions stimulate hormone release
PTH - to raise Ca++
Calcitonin - to decrease Ca++
Insulin - to decrease glucose
HUMORAL refers to factors in blood that are NOT hormonal.
Ex. Ca++ in blood. As per diagram.
Other examples: calcitonin released by thyroid, insulin, produced by pancreas.
Figure 9.2b

10. 3. Neural Stimulus Nerve impulses stimulate hormone release
Usually by sympathetic nervous system
Release of epinephrine and norepinephrine released during periods of stress.
Some exceptions to these 3 means of stimulating hormone release. Most done by one of these 3 methods.
Figure 9.2c

11. Location of Major Endocrine Organs
Total mass is only about 4 ounces.
Hypothalamus - part of nervous system, but also a gland b/c it produces hormones
Some glands are only endocrine (ductless): anterior pituitary, thyroid, adrenals
Some are both endocrine and exocrine: pancreas, gonads.
Difference: ductless, well vascularized (product released into the blood)
Ducts, products released externally (surface) or into cavity open to the surface (digestive system).
Figure 9.3

12. Pituitary - Hypothalamus Relationship
Release of anterior pituitary hormones is controlled by hormones from hypothalamus
Hypothalamus produces two hormones that are stored in the posterior pituitary
posterior pituitary releases hormones when neurally stimulated by hypothalamus
Release of hormones is controlled by releasing and inhibiting hormones produced by the hypothalamus. So, endocrine stimulation.
Hypothalamus produces two hormones that are transported to neurosecretory cells of the posterior pituitary. So, neural stimulation of posterior pit’y.
Portal circulation - veins from hypothalamus dump into vessels which drain into capillaries of pituitary.
The posterior pituitary is not strictly an endocrine gland, but does release hormones when stimulated neurally by hypothalamus.

13. Hormones of the Posterior Pituitary
Oxytocin
Stimulates contractions of the uterus during labor
Causes milk ejection
Antidiuretic hormone (ADH)
Can inhibit urine production
In large amounts, causes vasoconstriction
Oxytocin - positive feedback. So, as labor begins, oxytocin released, causing stronger contractions of uterus, leads to more oxytocin released. Positive, rather than negative feedback.
Oxytocin (Pitocin) most often used to induce uterine contractions and speed up delivery of baby. Also to induce faster contraction and shrinkage of uterus AFTER delivery, to limit blood loss of mother.
ADH - In large amounts, causes vasoconstriction leading to increased blood pressure (vasopressin)
Alcohol depresses ADH (anti diuretic hormone) secretion, which allows more urine to be made. Result is dehydration. So, cure for hangover usually involves fluid replacement.
Diuretics cause more urine to be flushed from body. Help to avoid edema, fluid retention.

14. Hormones of the Anterior Pituitary
Six anterior pituitary hormones; common characteristics:
Proteins (or peptides)
Act through second-messenger systems
Regulated by hormonal stimuli, mostly negative feedback
Six anterior pituitary hormones
Two affect non-endocrine targets
Four stimulate other endocrine glands (tropic hormones)
Characteristics of all anterior pituitary hormones
Proteins (or peptides)
Act through second-messenger systems
Regulated by hormonal stimuli, mostly negative feedback

15. Growth Hormone (GH) General metabolic hormone
Major effects are directed to growth of skeletal muscles and long bones
Causes amino acids to be built into proteins
Causes fats to be broken down for a source of energy
Fats broken down for energy, rather than glucose. Helps to maintain blood sugar level.
Reputation as being the fountain of youth. Does help to reverse decline in elderly patients, AIDS patients with wasting away. Builds muscle mass, reduces fat tissues.
Lots of WEB scams on this drug. Oral version is not effective, must be injected.

16. Functions of Other Anterior Pituitary Hormones
Prolactin (PRL)
Stimulates milk production following childbirth
Function in males is unknown
Adrenocorticotropic hormone (ACTH)
Regulates the adrenal cortex (affects salt, glucose levels)
Thyroid-stimulating hormone (TSH)
Influences thyroid gland
ACTH - effects alter glucose, salt concentrations of blood.

17. Functions of Other Anterior Pituitary Hormones
Gonadotropic hormones - appear at puberty
Follicle-stimulating hormone (FSH)
Stimulates follicle development (ovaries) and sperm development (testes)
Luteinizing hormone (LH)
Triggers ovulation
Stimulates testosterone production in males
Interaction of FSH, LH on lining of uterus results in monthly menses. Interaction w/ estrogen, progesterone to maintain lining, maintain pregnancy.
Testosterone produced mostly by testes.
Estrogen, progesterone produced mainly by ovaries, uness pregnancy.

18. Thyroid Gland Found at the base of the throat Produces two hormones
Thyroid hormone - controls metabolism
Calcitonin - affects Ca++ levels in blood
Thyroid hormone - Major metabolic hormone
Composed of two active iodine-containing hormones
Thyroxine (T4) – secreted by thyroid follicles
Triiodothyronine (T3) – conversion of T4 at target tissues
Both hormone components contain iodine, as indicated by T4 and T3. Target tissue cells convert T4 to T3.
If there is insufficient iodine in one’s diet, then low levels of thyroid hormone in blood, and more TSH released by pituitary. This constant stimulation by high levels of TSH results in enlargement of the thyroid gland = goiter. This is the reason that salt is iodized. Can also get iodine from seafood, which usually has high levels.
Thyroid hormone controls metabolic rate of cells, ALL cells.
Hence, hypothyroidism can cause symptoms of obesity, tiredness, mental sluggishness in adults.
Thyroid hormone also needed for normal growth and development of reproductive and nervous systems.
In children, hypothyroidism can lead to cretinism, with altered proportions of body such that legs are shorter than is usual, and mental retardation. Preventable with early diagnosis and replacement therapy.
Hyperthyroidism has opposite effects: high metabolic rate of cells, weight loss, hyper behavior - not relaxed.
Knock out the thyroid gland with radioactive iodine - iodine absorbed by thyroid, radiation kills cells that take it up.

19. Calcitonin
Decreases blood calcium levels by causing calcium deposition in bone (in children)
Antagonistic to PTH, parathyroid hormone
Second hormone secreted by thyroid gland, by a different group of cells than those that secrete thyroxine.
Good example of how 2 glands function together to maintain homeostasis within the body. Opposite effect of two hormones = antagonistic. Helps to maintain Ca++ levels within narrow range.
Calcitonin is released as a direct response to high levels of Ca++ in the blood.
Causes Ca++ to be deposited in bone, only in children. Mech. rarely used in adults.
Parathyroid gland = 4 tiny masses on the posterior of the thyroid
Secrete parathyroid hormone - PTH in response to lowered blood calcium levels, nonsteroidal
Stimulate osteoclasts to remove calcium from bone
Stimulate the kidneys: (retention of calcium and excretion of phosphate) and intestine to absorb more calcium. Via PTH role in final activation of Vit D in kidneys.
Overall effect: Raise calcium levels in the blood
Why? Recall that Ca++ is needed in large quantities for muscle contraction. If Ca++ levels get too low, neurons misfire, continually stimulate muscles, which contract in spasms. Lethal.
Figure 9.9

20. Adrenal Glands Two glands
Cortex – outer glandular region in three layers
Medulla – inner neural tissue region
Sits on top of the kidneys
Functionally and structurally, the adrenals are two glands. Similar to pituitary gland.
Adrenal cortex makes 3 groups of hormones, all called corticosteroids.
Adrenal Medulla is neural tissue (as is posterior pituitary).

21. Hormones of the Adrenal Cortex
Mineralocorticoids (mainly aldosterone)
Regulate mineral content in blood, water, and electrolyte balance via kidney action
Glucocorticoids (cortisone, cortisol)
Promote normal cell metabolism
Help resist long-term stressors
depress inflammatory response
Androgen, estrogen
Mineralocorticoids (mainly aldosterone)
Mineralocorticoids, because they regulate level of minerals in blood
Produced in outer adrenal cortex
Regulate mineral content in blood, water, and electrolyte balance; esp Na+ and K+ ions.
Target organ is the kidney. Aldosterone causes more Na to be reabsorbed, more K+ secreted. Water retained AND balance of ions is changed. Affects BP and blood volume.
Glucocorticoids - 95% of these are cortisol. Released in response to increased blood levels of ACTH A. Promotes normal cell metabolism by increasing use of fats, proteins to maintain glucose levels in blood. B. resist long term stressors by raising blood glucose levels. C. causes depression of immune system, long term. D. also reduce pain of inflammation, inhibit pain-causing prostaglandins.
Levels of glucocorticoids that are too low are fatal. Too much gives variety of symptoms, including moon face, hump of fat on upper back, high BP
Also releases Sex hormones - produced on low amounts by inner layer of the adrenal cortex
Androgens (male) and some estrogen (female). Both hormones produced in both sexes. If over production, leads to masculine features, such as body and facial hair of male pattern.

22. Hormones of the Adrenal Medulla
Produces two similar hormones (catecholamines)
Epinephrine
Norepinephrine
prepare the body to deal with short-term stress
= adrenaline. Causes increased blood flow to heart, brain, muscles. Raises glucose level in blood.
Responds to stimulus of nervous system. Fast response.
Ask students: what type of hormones are these likely to be? (non-steroid)
Compare that with role of adrenal cortex. Diag on next slide

23. Roles of the Hypothalamus and Adrenal Glands in the Stress Response
Hypothalamus controls trigger for both levels of response.
Neural stimulus in adrenal medulla leads to rapid response of epinephrine, norepinephrine.
Hormonal stimulus of hypothalamus on anterior pit’y on adrenal cortex. Longer term response.
Figure 9.12

24. Pancreatic Islets pancreas is a mixed gland
islet cells produce hormones:
Insulin – allows glucose to cross plasma membranes into cells
Glucagon – allows glucose to enter the blood
Somatostatin
MIXED = both endocrine and exocrine gland. Exocrine secretions are digestive enzymes. Later.
Endocrine portion is the pancreatic islets, groups of cells within the pancreas.
Islets spread throughout pancreas, interspersed among exocrine cells
Islets consist of 3 cell types ; alpha and beta, delta, all interspersed within islet. Well supplied with capillaries.
3 important hormones,:insulin, glucagon, somatostatin. First two are antagonists that maintain blood sugar homeostasis
Insulin produced by beta cells when blood sugar levels are high. Essential compound for uptake of glucose and utilization of it by ALL cells of the body. Th4, called the hypoglycemic hormone. the only hormone that causes drop in blood sugar. Q. which hormones cause INCREASE in blood glucose?
Lack of insulin = diabetes mellitus. Glucose levels are very high in blood, excess gets excreted in urine “sweet siphon”. Body must use fats, proteins for energy. Wasting, weak immune system. Ketones build up, causing acidosis of blood. Result is coma and death. TYPE I, juvenile.
Mild diabetes mellitus (type II, adult onset) produce insulin but are resistant to its effects. Careful diet, drugs to increase sensitivity to insulin needed.
GLUCAGON secreted by alpha cells. Stimulates liver to break apart glycogen, release glucose into blood.
Triggered by low glucose levels in blood.
Somatostatin - from delta cells. Complete function not clear. Seems to inhibit secretion of both insulin and glucagon. Not unique to pancreas, also made by hypothalamus (inhibits GH secretion) and digestive system (controls digestive secretions). Effect depends on target cells.
Homeostasis. Antagonistic effect of hormones. Shows importance of glucose level. Brain uses ONLY glucose as energy source.
Other hormones that affect glucose level:
Glucocorticoids, epinephrine
Figure 9.13

25. Diabetes Diabetes mellitus - “sweet siphon” Type I - lack of insulin
juvenile
Type II - resistant to effects of insulin
Adult onset
Lack of insulin = diabetes mellitus. Glucose levels are very high in blood, excess gets excreted in urine “sweet siphon”. Body must use fats, proteins for energy. Wasting, weak immune system. Ketones build up, causing acidosis of blood. Result is coma and death. TYPE I, juvenile.
Mild diabetes mellitus (type II, adult onset) produce insulin but are resistant to its effects. Careful diet, drugs to increase sensitivity to insulin needed.
GLUCAGON secreted by alpha cells. Stimulates liver to break apart glycogen, release glucose into blood.
Triggered by low glucose levels in blood.
Somatostatin - from delta cells. Complete function not clear. Seems to inhibit secretion of both insulin and glucagon. Not unique to pancreas, also made by hypothalamus (inhibits GH secretion) and digestive system (controls digestive secretions). Effect depends on target cells.
Homeostasis. Antagonistic effect of hormones. Shows importance of glucose level. Others that affect glucose level: Glucocorticoids, epinephrine

26. Other Hormone Sources
Thymus: thymosin and thymopoietin, assist maturation of T lymphocytes
Pineal gland: melatonin
Heart: atrial natriuretic hormone (ANH)
Digestive system: gastrin, secretin, cholecystokinin
Kidney: erythropoietin, renin
Other tissues in body use hormone signals.
Melatonin - regulates sleep cycle. Reset clock when traveling across time zones.
ANH from heart - helps to lower blood pressure by causing kidney to excrete more Na+, dilate blood vessels
Gastrin,secretin, cholecystokinin - stimulate action of stomach, pancreas, gallbladder.
Leptin - produced by fat tissue when fats are eaten; depresses appetite.
Ghrelin - counteracts leptin, increases appetite.
Erythropoietin stimulate production of RBC
Renin - stim adrenal cortex to produce aldosterone, constricts blood vessels.