Chapter 16: The Endocrine System

Question 1

Endocrine vs. Exocrine Glands:

Answer 1

o Exocrine glands:
o Secrete non-hormone chem.DUCTS skin, mucous membranes, body cavities.
o Extracellular effects.
o Examples: sweat glands, salivary glands, pancreatic secretions/ducts.
o Endocrine glands:
o Secrete hormones from the endocrine gland/cell into the INTERSTITIAL FLUID, diffuses from IF into capillary.
o Glands have rich vascular supply & lymphatic drainage that receives these hormones from the IF (NO DUCTS!!!).
o Intracellular effect in target tissue.
o Example: thyroid gland = affects metabolism of cells.

Question 2

General Mechanisms of Hormone Actions:

Answer 2

o Cell may then:
o Synthesize new molecules.
o Change permeability of membrane.
o Alter rates of metabolic reactions.
o Secrete stuff.
o Undergo mitosis (divide).
o Each target cell responds to hm differently:
o Liver cells: insulin stimulates glycogen synthesis.
o Adipose: insulin stimulates triglyceride synthesis.

Question 3

Causes of Endocring Gland/Cell Releasing Its Hormone:

Answer 3

o Humoral stimuli:
o A change in the blood level of some nutrient or other chemical triggers the release of hormone.
o Example: cells of parathyroid gland monitor blood levels of calcium, when calcium levels drop, the parathyroid gland release PTH.
o Neural stimuli:
o Neurons release Neurotransmitter onto endocrine glands/cells that cause them to release hormones.
o Example: Sympathetic nervous system neurons stimulate adrenal medulla to release catecholamines into the blood.
o Hormonal stimuli
o An endocrine gland/cell releases its hormone into the blood… travels to a SECOND endocrine gland/cell to cause the release of a different hormone.
o Example: The hypothalamus secretes CRH (corticotropin-releasing hormone), travels to anterior pituitary gland & causes it to release ACTH (adrenocorticotropic hormone, travels to the adrenal cortex & causes it to release cortisol.

Question 4

All Steroid Hormones Come From:

Answer 4

Cholesterol

Question 5

Anatomy of Pituitary Gland:

Answer 5

o Pea-shaped, 1/2 inch gland found in sella turcica of sphenoid bone.
o Anterior lobe = adenohypophysis.
o 75% of weight of pituitary.
o Develops from roof of mouth from ectoderm.
o Glandular tissue that makes many “controlling” hormones.
o Posterior lobe = neurohypophysis.
o 25% of weight of pituitary.
o Composed of ends of axons of 10,000 neurons whose cell bodies are found in hypothalamic nuclei.

Question 6

Hypothalamus:

Answer 6

o Controls Endocrine System!!
o Hypothalamus regulates both the ANS and the Endocrine System. It receives input from the cerebral cortex, thalamus, limbic system, and internal organs.
o Hypothalamus controls the ANTERIOR pituitary gland with many different releasing and inhibiting hormones.
o Hypothalamus controls the POSTERIOR PITUITARY via neuron axons traveling through the INFUNDIBULUM.
o Both the hypothalamus and the pituitary gland are important endocrine glands since their hormones control other endocrine glands.

Question 7

Flow of Blood to Anterior Pituitary Gland:

Answer 7

o Controlling hormones (releasing & inhibiting hormones) enter blood capillaries from hypothalamus.
o Hypophyseal portal system = blood vessels from hypothalsmus to the anterior pituitary gland.

Question 8

Specific Anterior Pituitary Hormones:

Answer 8

o	hGH): Human growth hormone. 
o	(TSH): Thyroid-stimulating hormone. 
o	(ACTH): Adrenocorticotrophic hormone. 
o	(FSH): Follicle stimulating hormone. 
o	(LH): Leutinizing hormone. 
o	(PRL): Prolactin. 
o	(MSH): Melanocyte stimulating hormone.

Question 9

Human Growth Hormone (hGH):

Answer 9

o Secreted by: Anterior Pituitary (released in bursts, especially during deep sleep!).
o Stimulus for release:
o Increased GHRH (growth hormone releasing hormone) from hypothalamus if there is:
o Hypoglycemia.
o Decreased fatty acids in blood.
o Increased amino acids in blood.
o Increased sympathetic activity (stress/exercise).
o Inhibited by GHIH (somatostatin) from hypothalamus (released if hyperglycemia).

Question 10

Imbalances of Human Growth Hormone:

Answer 10

o Hyposecretion of hGH:
o Pituitary Dwarfism: seen in kids before epiphyseal plate closes…short, but proportional
o Hypersecretion of hGH:
o Gigantism: seen in kids before epiphyseal plate closes, very tall, but proportional
o Acromegaly: seen in adults after epiphyseal plate closes soft tissues thicken, increases bone deposition in hands, feet, and facial bones often diabetes.

Question 11

Thyroid Stimulating Hormone (TSH):

Answer 11

o Secreted by: anterior pituitary
o Stimulus for Release: TRH (thyrotropin releasing hormone) from the hypothalamus
o TSH: from anterior pituitary
o Target tissue: thyroid gland
o Stimulates synthesis and secretion of T4 and T3 (thyroid hormones).

Question 12

Adrenocorticotrophic Hormone (ACTH):

Answer 12

o Secreted by: Anterior Pituitary
o Stimulus for Release: increased Corticotropin-releasing hormone (CRH) from hypothalamus because of:
o Stress, trauma, hypoglycemia.
o Target tissue: Adrenal Cortex.
o Effect: Increased release of corticosteroids,especially GLUCOCORTICOIDS (cortisol) from zona fasciculate.

Question 13

Follicle Stimulating Hormone (FSH):

Answer 13

o Secreted by: anterior pituitary.
o Stimulus for Release: GnRH (gonadotropin-releasing hormone) from hypothalamus.
o Target Tissues: gonads.
o Initiates the formation of follicles within ovary.
o Stimulates follicle cells to secrete estrogen.
o Stimulates sperm production in testes (spermatogenesis).

Question 14

Luteinizing Hormone (LH):

Answer 14

o Secreted by: anterior pituitary .
o Stimulus for Release:
o Increased GnRH (gonadotropin-releasing hormone) from hypothalamus.
o Target Tissues: gonads.
o In females, LH stimulates:
o Secretion of estrogen.
o Triggers ovulation.
o Formation of corpus luteum (which is formed from the remaining follicle (ovary) after the egg is released and produces high levels of progesterone to ready the endometrium for pregnancy).
o Secretion of progesterone.
o In males, LH stimulates interstitial cells to secrete testosterone.

Question 15

Prolactin (PRL):

Answer 15

o Secreted by: Anterior pituitary.
o Stimulus for Release:
o Increased PRH (prolactin releasing hormone) from hypothalamus.
o Inhibited by PIH (prolactin inhibiting hormone) from hypothalamus.
o Target Tissue: Mammary Glands.
o Effect:
o Stimulates production of breast milk.
o In males, makes testes more sensitive to LH.

Question 16

Melanocyte-Stimulating Hormone (MSH):

Answer 16

o Secreted by: anterior pituitary.
o Stimulus for Release: increased CRH (cortitropin releasing hormone) from hypothalamus; inhibited by dopamine.
o Target tissue: Skin.
o Effect: function not certain in humans (increase skin pigmentation in frogs) may be involved in appetite regulation pathways?

Question 17

Posterior Pituitary Gland (Neurohypophysis):

Answer 17

o Does not MAKE hormones (just storage)
o Consists of axon terminals of hypothalamic neurons.
o Neurons release two neurotransmitters that enter capillaries as hms.
o Oxytocin.
o ADH (antidiuretic hormone).

Question 18

Oxytocin:

Answer 18

o During delivery:
o Baby’s head stretches cervix.
o Hormone release enhances uterine muscle contraction.
o Baby & placenta are delivered.
o After delivery:
o Suckling & hearing baby’s cry stimulates milk ejection.
o OXYTOCIN causes uterine smooth muscle contraction and milk ejection.
o PITOCIN = synthetic oxytocin used to induce labor.
o Breast-feeding stimulates oxytocin, which ALSO helps uterus contract to pre-pregnancy size.
o Involved in the human response to STRESS… it seems to be a down-regulator of the body’s stress axis system, smaller, briefer stress response.
o Released in men and women during sexual climax.
o In animals, fosters parental caretaking behavior toward young offspring AND monogamous parental behavior, block receptors for oxytocin and prairie voles become promiscuous.

Question 19

Antidiuretic Hormone (ADH):

Answer 19

o Secreted by: posterior pituitary gland
o Stimulus for Release:
o High bl. Osmolarity
o Low blood pressure
o Stress, trauma, pain, anxiety.
o Certain drugs: nicotine, tranquilizers, morphine, some anesthetics.

Question 20

Regulation of ADH:

Answer 20

o	Dehydration:
o	ADH released.
o	Save water/pee less.
o	Overhydration:
o	ADH inhibited.
o	Lose water/pee more.

Question 21

Thyroid Gland:

Answer 21

o Two lateral lobes (isthmus in between lobes).

o Weighs 1 oz and has rich blood supply.

Question 22

Histology of Thyroid Gland:

Answer 22

o Follicle = sac of stored hormone (colloid) surrounded by follicular cells that produced it.
o Produces T4 & some T3 (most T3 is formed inside target tissues).
o Target tissues: almost every cell in body!
o Parafollicular cells are located in between the follicle cells.
o They produce a different hormone (CALCITONIN) which lowers blood calcium levels when they are too high.

Question 23

Control of T3 and T4 Secretion:

Answer 23

o Negative feedback system.
o Low blood levels of T4 and T3 stimulate hypothalamus to release TRH.
o TRH stimulates pituitary to release TSH.
o TSH stimulates gland to increased release T4 and T3.

Question 24

Thyroid Gland Disorders:

Answer 24

o Hyperthyroidism = hypermetabolic state secondary to ↑ thyroid hormone levels.
o Symptoms: HTN, Tachycardia, insomnia, tremor, high body temperature, wt. loss with increased appetite, Increased sweating.
o GRAVE’S DZ = autoimmune dz with weight loss, nervousness, irregular heart beat, sweating, tremor & exophthalmos (edema behind eyes).

Question 25

Goiters:

Answer 25

o A goiter is just an enlarged thyroid gland. It can be from any number of causes:
o Lack of iodine in the diet (endogenous goiter) (in this case, nothing is wrong with the thyroid gland at all…just no building blocks!).
o Hypothyroidism, low levels of T3 & T4 cause an increased secretion of TRH and TSH.
o Grave’s Disease, weird antibody complex formed in this autoimmune disease mimics the effects of TSH.

Question 26

Calcitonin:

Answer 26

o Secreted by: thyroid gland (parafollicular cells).
o Stimulus for Release: high blood calcium levels (must be about 20% above normal).
o Target Tissue: skeleton.
o Inhibits osteoclastic activity, decreases bone resorption.
o Promotes bone deposition.

Question 27

Parathyroid Glands:

Answer 27

o 4 pea-sized glands found on back of thyroid gland.

o Can be as many as 8, rarely even in thorax/neck!

Question 28

Parathyroid Hormone (PTH):

Answer 28

o Secreted by: parathyroid glands.
o Stimulus for Release: low blood calcium levels (release inhibited by hypercalcemia).
o Target Tissues:
o Skeleton: stimulates osteoclasts, Ca++ and phosphate released into blood.
o Kidneys: enhances Ca++ and Mg++ reabsorption and secretion of phosphate. Also activates Vit. D to CALCITRIOL, which promotes absorption of Ca++, Mg++, and phosphates from the digestive tract.

Question 29

Disorders of Parathyroid Hormone:

Answer 29

o Hyperparathyroidism:
o Usually caused from a parathyroid gland tumor.
o Calcium is leached from the bones, bones soften and mineral salts are replaced by fibrous c.t. leads to hypercalcemia.
o HYPERCALCEMIA causes depression of nervous system with abnormal reflexes.
o Calcium deposits form in soft tissues throughout bodyà kidney stones common.
o Hypoparathyroidism:
o Usually caused by trauma to the parathyroid gland, surgical removal, or autoimmune processes.
o Rarely caused by an extreme dietary deficiency of Mg++ (required for secretion). Causes HYPOCALCEMIA, with dental problems, hyperexcitable nervous system, muscle spasm, tetany, convulsion.

Question 30

Adrenal Glands:

Answer 30

o One on top of each kidney…really 2 glands in one!
o Adrenal cortex produces 3 different types of hormones from 3 zones of cortex.
o Adrenal medulla produces epinephrine & norepinephrine.
o Adrenal Cortex produces corticosteroids:
o Zona glomerulosa produces mineralocorticoids (most important = aldosterone).
o Zona fasciculata produces glucocorticoids (most important = cortisol)
o Zona reticularis produces gonadocorticoids (major one = dehydroepiandrosterone = DHEA), precursor to sex hormones androgens/estrogens.
o Adrenal Medulla produces catecholamines:
o 80% epinephrine.
o 20% norepinephrine.
o Trace of dopamine.

Question 31

Mineralcorticoids:

Aldosterone

Answer 31

o 95% of hormonal activity due to aldosterone.
o Secreted by: Adrenal cortex (zona glomerulosa).
o Stimulus for Release:
o High blood potassium (hyperkalemia).
o Low blood sodium (hyponatremia…not as potent).
o Angiotensin II (from renin-angiotensin system responding to low blood pressure or low blood volume).
o Target Tissues: Kidney (principal cells).
o Sodium reabsorption, Potassium excretion.
o Aldosterone also promotes H+ excretion in urine.

Question 32

Glucocorticoids:

Cortisol

Answer 32

o 95% of hormonal activity is due to cortisol.
o Secreted by: Adrenal cortex (zona fasciculata).
o Stimulus for Release:
o Released in bursts driven by patterns of eating and activity…definite pattern throughout day…cortisol peaks just after getting up in the morning.
o This “normal” pattern is overturned if STRESS of any variety: infections physical trauma hemorrhage emotional trauma.
o Stress stimulates sympathetic N.S., triggers release of CRH, triggers release ACTH, triggers release of cortisol. Cortisol = hydrocortisone.

Question 33

Cushing’s Syndrome:

Answer 33

o Hypersecretion of glucocorticoids
o Usually caused by excessive steroid use (meds like prednisone), but can also be caused by a tumor that secretes ACTH (in the pituitary, or ectopically in the lungs, pancreas, kidneys)… could also be a tumor of the adrenal cortex that hypersecretes cortisol.
o Signs and Symptoms: hyperglycemia, loss of muscle tone, redistribution of fat to abdomen, moon face, buffalo hump, osteoporosis, Na+/water retention, edema and HTN, easy bruising, poor wound healing.

Question 34

Addison’s Disease:

Answer 34

o Hyposecretion of glucocorticoids & aldosterone.
o Signs and symptoms:
o Weight loss.
o Hypoglycemia.
o Muscle weakness.
o Major dehydration due to decreased Na+ in blood.
o Low blood pressure (hypotension).
o Hyperkalemia, with potential cardiac arrest.
o Mimics skin darkening effects of MSH.

Question 35

Androgens from Zona Reticularis:

Answer 35

o Small amount of male hormone produced, primarily a precursor to testosterone = DHEA = dehydroepiandrosterone.
o Males: probably insignificant compared to amounts of testosterone made during late puberty/adulthood.
o Females: may contribute to sex drive in females, is converted to estrogen in postmenopausal females.

Question 36

Adrenal Medulla:

Answer 36

o Chromaffin cells receive direct innervation from sympathetic nervous system (splanchnic nerve).
o Develop from same tissue as postganglionic neurons.
o Produce CATECHOLAMINES: epinephrine, norepinephrine, and (trace) of dopamine.
o Catecholamines are sympathomimetic:
o Effects mimic those of sympathetic NS.
o Cause fight-flight behavior.
o Acetylcholine increases catecholamine secretion by adrenal medulla (acts on nicotinic receptors).

Question 37

Hormones Secreted by Small Intestine:

Answer 37

o CCK
o Increased dig. enzyme secretion from panc. acinar cells.
o Increased contraction GB.
o Relaxes Sphincter of Oddi.
o Secretin
o Increased alkaline juices from panc. and liver duct cells.
o Increased bile secretion.
o VIP = decrease motility, decrease HCl…water to pancreatic juices + secretions

Question 38

Melatonin and the Pineal Gland:

Answer 38

o Secreted by: pineal gland.
o Stimulation for Release: darkness (bright light suppresses melatonin secretion).
o Target tissues: Not completely understood
o Melatonin responsible for setting the biological clock of hypothalamus (suprachiasmatic nucleus).

Question 39

Thymus Gland:

Answer 39

o Important role in maturation of T cells
o Hormones produced by gland promote the proliferation & maturation of T cells.
o Thymosin.
o Thymic humoral factor.
o Thymic factor.
o Thymopoietin.