Physiology: Neuroendocrinology and the Pituitary Gland

Question 1

Hypothalamus neurons:

Answer 1

synthesize and secrete hormones which regulate synthesis and secretion of anterior pituitary hormones

Question 2

Hypothalamic Hormones - Tropic

Answer 2

Releasing hormones - stimulate release of anterior pituitary hormone
Inhibitory hormones - inhibit synthesis and release of anterior pituitary hormone

Question 3

Hypothalamic Hormones - Non-Tropic

Answer 3

Neurohormones are synthesized in hypothalamic neurons stored in nerve terminals in the posterior pituitary

Question 4

Tropic Hormones

Answer 4

Synthesized in discrete nuclei, released from the nerve terminals into mediate eminence, reach anterior pituitary via hypophyseal portal circulation

Question 5

Paraventricular Nucleus:

Answer 5

Thyrotropin-Releasing Hormone (TRH) - Thyrotropin (TSH) and Prolactin (PL)
Corticotropin Releasing Hormone (CRH) - Adrenocorticotropin (ACTH)

Question 6

Anterior Periventricular Nucleus:

Answer 6

Somatostatin - inhibits growth hormone (GH)

Question 7

Arcuate Nucleus:

Answer 7

Growth Hormone Releasing Hormone (GHRH) - Growth Hormone

Dopamine - inhibits Prolactin

Question 8

Preoptic Nucleus:

Answer 8

Gonadotropin-releasing hormone (GnRH) - FSH, LH

Question 9

Paraventricular & Supraoptic Nucleus:

Answer 9

ADH, Oxytocin

Question 10

Characteristics of Hypothalamic-Releasing Hormones:

Answer 10

1. Pulsatile Release
2. Act via specific plasma membrane receptors
3. Use cAMP, phospholipids, and Ca2+ as signals
4. Stimulate hyperplasia and hypertrophy of target cells
5. Stimulate synthesis and release of pituitary hormones
6. Regulate their own receptors - modulate own effect

Question 11

Function of hypothalamic nuerohormones:

Answer 11

Synthesis and secretion of anterior pituitary hormones

Question 12

Anterior Pituitary (Adenopophysis)

Answer 12

originates form Rathke’s pouch - outgrowth of roof of oral cavity
TSH, ACTH, FSH, LH, GH,PRL

Question 13

Posterior Pituitary (Neurohypophysis)

Answer 13

originates from the downward outgrowth of the third ventricle
Oxytocin, ADH

Question 14

Feedback Mechanisms: Long-Loop

Answer 14

Target hormones to pituitary or hypothalamus

Question 15

Feedback Mechanisms: Short-Loop

Answer 15

Pituitary hormones to hypothalamus

Question 16

Feedback Mechanisms: Ultra-Short-Loop

Answer 16

Hypothalamus hormones to hypothalamic neurons

Question 17

Pituitary Thyroid Axis: Thyroid Stimulating Hormone

Answer 17

+: Thermal and Caloric Signaling - Thyroid Releasing Hormone (TRH)
-: Dopamine and Somatostatin
Thyroid Stimulating Hormone - (Glycoprotein Hormone)
TSH activates thyroid gland:
1. Synthesis of thyroid hormones (T3)
2. Secretion of thyroid hormones (T4)
T4 deiodinase in target cells to T3, T3 signals more production of T3, T4 negative feed back on TRH

Question 18

Pituitary-Adrenal Axis: Adrenocorticotropic Hormones

Answer 18

Pro-opiomelanocortin protein
binds to receptors on the ZONA FASICULATA
Varies diurnally
+: Feeding, Depression, Anxiety, Stress, Sleep/Wake, Ach, GABA, Serotonin, NE
-: Endorpin
CRH & ADH - ACTH release from pituitary
ACTH: - feedback on CRH; acts on adrenal cortex - Androgen, Aldosterone, Cortisol (- feedback on CRH)

Question 19

Mechanism of ACTH action:

Answer 19

• cAMP mechanism, stimulates cholesterol to enter mitochondria via STAR
• cholesterol modified in mitochondria - to pregnenolone
• cortisol secreted back into blood

Question 20

Pituitary-Liver Axis: Growth Hormone

Answer 20

Single chain protein hormone
Mediated by insulin like growth factor-1 (IGF-1)
+: arginine, dopamine, a-receptor agonists, stress, sleep - release GNRH + feedback on GH
+: B-agonists, glucose, free fatty acids - release of somatostatin - feedback on GH
Ghrelin: + feed back on GH
GH has a biological effect, can go to liver which releases IGF-1, and positive effect on hypothalamic release somatostatin.
IGF-1 + on hypothalamic release of somatostatin, - effect on GH.

Question 21

Growth Hormone Effects

Answer 21

Adipose Tissue: decrease adiposity - decrease glucose uptake, increase lipolysis
Liver: Increase Lean body mass - increase gluconeogensis, IGF-1, IGF-BP
Chondrocyte: increase differentiation

Question 22

IGF-1 Effects

Answer 22

Metabolism: increase plasma glucose and FFA, decrease plasma amino acids and urea
Muscle: decrease glucose uptake, increase amino acid uptake, protein synthesis
Chondrocyte: increase cell size and number (Chondrotin)
Increase organ size and function: Kidney, Pancreas, Parathyroid, Skin, Connective Tissue, Bone, Heart, Lungs: increase cellular hypertrophy and hyperplasia

Question 23

GH Deficiency Causes

Answer 23

Hypothalamic dysfunction
Pituitary tumor
Abnormal synthesis
Receptor disorders
IFG-1 malformation

Question 24

GH Deficiency before Puberty:

Answer 24

Short Stature - laron type dwarfism, pygmies
Delayed ossification and growth
mild obesity

Question 25

GH Deficiency in Adults:

Answer 25

``` High body fat (waist) Anxeity, depression, fatigue High LDLS, trigylcerides Decreased: sexual function and libido Greater sensitivity to heat and cold Less muscle Less strength, stamina, ability to exercise Reduced bone density ```

Question 26

GH Excess before Puberty:

Answer 26

Gigantism

Question 27

GH Excess in Adults: Acromegaly

Answer 27

Excessive Perspiration Headache Skin Tags Carpal Tunnel Joint Pains High Blood Pressure Diabetes Enlarged Heart Kidney Stones Increased risk of colon cancer

Question 28

Pituitary-Mammary Axis: Prolactin

Answer 28

Stimulus: hypoglycemia, exercise, starvation, trauma, surgery, sleep, breast stimulation, TRH Inhibitor: Dopamine PRL: + affects on the breast and liver and dopamine release Ovary has + feedback for PRL release

Question 29

Prolactin effects:

Answer 29

-(with estradiol, progesterone, cortisol, and GH) Proliferation and branching of mammary ducts -(with estradiol and progesterone) Induces alveolar development Induces postpartum milk synthesis

Question 30

Hyperprolactinemia:

Answer 30

impotence, hypothalamic hypogonadism, infertility, galactorrhea

Question 31

Pituitary-Gonadal Axis: Gonadotropic Hormones

Answer 31

FSH and LH are glycoproteins - B chain is hormone specific

Question 32

LH Secretion in Females

Answer 32

pulsatile, periodic, dirunal and cyclic

Question 33

FSH Secretion in Females

Answer 33

periodic and cyclic

Question 34

Gonadotropins act:

Answer 34

Plasma membrane receptors, cyclic AMP or phosphinositols

Question 35

Females - Pituitary-Gonadal Axis

Answer 35

Hypothalamus - release GnRH on pituitary +: Estradiol (high levels), Norepinephrine -: Enorphin, Serotonin, Estradiol, Progesterone Pituitary - Release FSH and LH FSH - granulosa cells - estradiol, inhibins and activin LH - theca cells - progesterone

Question 36

Males - Pituitary-Gonadal Axis

Answer 36

``` Hypothalamus - release GnRH on pituitary +: norepinephrine -: endorphin, serotonin, testosterone Pituitary - Release FSH and LH FSH - sertoli cells - inhibins LH - leydig cells - testosterone ```

Question 37

ADH Synthesis

Answer 37

Synthesized in nerve cell body, transported on neurophysin-2, packaged in herring bodies, released directly on neurohypophysis due to action potential.

Question 38

ADH Function:

Answer 38

Volume regulation by water reabsorption in distal tubules, and collecting tubule

Question 39

ADH Release

Answer 39

Pituitary: Angiotensin 2, Sympathetics, Hyperosmolarity, Hypovolumeia, Hypotension - released ADH

Question 40

ADH - Type 1 Receptor

Answer 40

Works on arteriole Vasoconstricts - increases blood pressure Protein Kinase C

Question 41

ADH - Type 2 Receptor

Answer 41

Works on Kidney Increase renal fluid reabsorption Protein Kinase A, cAMP mechanism

Question 42

Oxytocin Synthesis

Answer 42

Synthesized in nerve cell body, transported on neurophysin-1, packaged in herring bodies, released directly on neurohypophysis due to action potential.

Question 43

Oxytocin

Answer 43

Acts on smooth muscle via CA, in breast and uterus +: suckling and myometrium stretching causes oxytocin -: stress, fear and opioids Oxytocin is essential for milk ejection