Intro to Endocrine Hormones - Trachte

Question 1

What is Endocrinology?

Answer 1

the study of the endocrine glands and tissues that secrete hormones which impact homeostasis and reproduction

Question 2

What does virtually all physiology emphasize?

Answer 2

HOMEOSTASIS

Question 3

What is the basic model of the hierarchy of the endocrine system?

Answer 3

Hypothalamus => Pituitary => End organ

When the Anterior pituitary is involved, the hierarchy involves the hypothalamus and usually a tertiary endocrine gland in the periphery that produces a final hormone. This is called an hypothalamic-pituitary endocrine axis.

Question 4

What are the three types of hormones?

Answer 4

protein, steroid, and amine

Question 5

What hormone controls/regulates Na or K?

Answer 5

Aldosterone

Question 6

What hormone controls/regulates Ca or Phosp.?

Answer 6

PTH

Question 7

What hormone controls/regulates H2O?

Answer 7

ADH

Question 8

In what two ways do hormones alter target cells?

Answer 8

Activate secondary messenger systems

and/or

Transcription in target cells

Question 9

What body systems and functions are hormones critical in?

Answer 9

Growth and development
Respiration, excretion, metabolism
Reproduction
Electrolyte balance

Question 10

What are the three portal systems in the body?

Answer 10

1. Hepatic portal system
2. Pituitary
3. Renal portal system

Question 11

If you disrupt the pituitary portal system, what is the only hormone that would increase instead of decrease? Why?

Answer 11

Prolactin

it is under inhibitory control

Question 12

How does the hypothalamus regulate hormonal production and secretion in the pituitary?

Answer 12

Secretion of its hormones regulates anterior pituitary hormone production and secretion.

Some of hypothalamic neurons extend into the posterior pituitary from which hormones can be released.

Question 13

What stimulates the release of ADH?

Answer 13

High osmolarity

Question 14

How does the hypothalamus interact with the posterior pituitary?

Answer 14

Hypothalamic neurons which produce the hormones oxytocin and vasopressin project into the posterior pituitary.

With appropriate signals, hormones are released from these hypothalamic neurons in the posterior pituitary and immediately enter the general circulation.

Question 15

How does the hypothalamus interact with the anterior pituitary?

Answer 15

Hypothalamic neurons secrete “releasing” or “inhibitory” hormone into the hypothalamo-hypophyseal portal system.

Portal system bathes anterior pituitary cells.

Hypothalamic hormone binds to receptors on anterior pituitary cells.

Anterior pituitary cells release their hormone into the general circulation and produce more hormone.

Target cells (+/- with a third endocrine gland) are exposed to the anterior pituitary hormone.

This process is relatively slow (compared to posterior pituitary hormones response times).

Question 16

How is hormone secretion regulated?

Answer 16

Negative feedback:

• Most common mechanism
• Limits the amount of hormone release
  e. g., thyroid hormone curtails release of thyroid releasing hormone and thyroid stimulating hormone

Positive feedback:

• Rare
• Reinforcing “snow ball effect” resulting in more of the hormone secretion
  e. g., ovarian estrogen effects on ovulation

Question 17

How are protein/peptide hormones synthesized?

Answer 17

Preprohormone synthesized and cleaved into prohormone in rough endoplasmic reticulum (RER)

Prohormone moves into Golgi apparatus where further enzymatic cleavage occurs to produce mature hormone

Mature hormone packaged into secretory granules

Question 18

How are protein/peptide hormones secreted?

Answer 18

Upon appropriate signals, secretory granules fuse with plasma membrane, releasing the hormone.

Protein hormones are soluble in water

Protein hormones may be transported by carrier proteins which protect from metabolic breakdown

Question 19

What are the inactive forms of peptide hormones called?

Answer 19

Preprohormones

Question 20

What glands synthesize steroid hormones?

Answer 20

Gonads and Adrenal Glands

Question 21

How are amine tyrosine-based hormones produced?

Answer 21

Phenylalanine => Tyrosine => DOPA => Dopamine => NE => EPI

Produced in neurons, and packaged in vesicles for intermittent release upon demand.

Question 22

How do hormones regulate receptors on target cells?

Answer 22

Hormones can down-regulate receptor signaling by:

• Decreasing receptor number
• Decreasing affinity of receptors for the hormone
• Example: In the breast, increased estrogen concentration reduces the number of estrogen receptors

Hormones can up-regulate receptor signaling by:

• Increasing receptor number
• Increasing affinity of receptors for the hormone
• Example: In the breast, increased estrogen concentration increases the number of progesterone receptors.

Question 23

How do protein/peptide hormones act on target cells?

Answer 23

Hormone binds to receptor located in target cell membrane

Hormone bound receptor may be a tyrosine kinase (example: insulin and insulin-like growth factors)

Hormone-bound receptor may activate one or more second messenger signaling network including:
-Guanosine triphosphate binding-proteins (G-Protein) (Adenylate cyclases (AC), Inositol triphosphate (IP3), Calcium-calmodulin (Ca++))

Question 24

What are the five steroid hormone receptor ligands?

Answer 24

Estrogens (receptor: ER)

Progesterones (receptor: PGR)

Androgens (receptor: AR)

Glucocorticoids (receptor: GR)

Mineralocorticoids (receptor: MR)

Question 25

How do steroid and thyroid hormones act on target cells?

Answer 25

Hormone diffuses across cell membranes and binds to cytoplasmic receptors (steroids).

Hormone-bound receptor enters the nucleus and forms hormone-receptor dimers .

These dimers are transcription factors that bind to specific DNA sequences (“steroid responsive elements”) on DNA and initiate transcription.

Question 26

What is the result of steroid and thyroid hormones acting on target cells?

Answer 26

Result: production of proteins that have physiologic functions.

Question 27

What are the 6 steps in nuclear receptor signaling?

Answer 27

1. Free Hormone dissociates from carrier protein and enters the cell.
2. Hormone binds to cytoplasmic receptor and translocates to the nucleus.
3. Dimers form and sit down on specific steroid hormone response element contained on a subset of genes.
4. Transcription of mRNA.
5. Translation to protein.
6. Hormone cellular response.

Question 28

What is the fate of hormones?

Hint: 3 things

Answer 28

1. Liver/Kidney metabolic degradation of circulating hormone
   - e.g., steroid hormones undergo oxidation by liver cytochrome P450s (Phase I metabolism)
   - Carrier proteins protect extend half life of hormones by protecting them from liver/kidney metabolism
2. Urinary and/or biliary excretion
3. Cell uptake and degradation following receptor signaling

Question 29

What is the pattern of release hypothalamic hormones?

Answer 29

***PULSATILE secretion of the hypothalamic and pituitary hormones is required to prevent desensitization of downstream hormone receptors.

Continuous administration of hormones down regulates hormone receptors and therefore, after a few days, a general reduction in hormone signaling ensues.

Question 30

What are the four possible responses to multiple hormones?

Answer 30

additive, synergistic, permissive, antagonistic