5. Endocrine System

Question 1

In endocrinology, the level of response is dependent on:

Answer 1

1. Dose of hormones
2. Time of exposure

Question 2

What are the two hormones from the hypothalamus that are routed through the pituitary and released into systemic circulation?

Answer 2

1. ADH
2. oxytocin

Question 3

Describe the Pars Distalis

Answer 3

• Makes up two-thirds of the pituitary gland
• Composed of two cell types:
  1. Chromophilic cells (~50%) and include:
• Acidophilic cells (40%): secrete prolactin and growth hormone
• Basophilic cells (10%): secrete TSH, LH, FSH, ACTH, and β-LPH
  2. Chromophobic cells (~50%): thought to be inactive states of acidophilic and basophilic cells

Question 4

Describe the Pars Intermedia

Answer 4

• Makes up less than 5% of the pituitary gland
• Cells from the pars intermedia migrate into the pars distalis to become the ACTH and β-LPH secreting cells
• Secretes melanocyte-stimulating hormone (MSH) and small amounts of ACTH

Question 5

Describe the neurohypophysis

Answer 5

• The posterior lobe
• Composed of pituicytes and unmyelinated nerve fibers
• Nerve fibers contain oxytocin and ADH

Question 6

Describe the hypophyseal portal system

Answer 6

• A system of veins that begins and ends in capillaries
• It consists of:
  1. Primary plexus: located in the ventral part of the hypothalamus
  2. Secondary plexus: located in the anterior adenohypophysis
  3. Portal venules: link the primary and secondary plexuses, carrying blood from the hypothalamus to the pituitary

Question 7

What is the function of the hypophyseal portal system

Answer 7

1. Prevents dilution of hypothalamic hormones that would occur if secreted into the systemic circulation
2. Avoids the need for complex individual wiring for each pituitary cell by hypothalamic axons.

Question 8

List the 4 general classes of hormones

Answer 8

1. Proteins and polypeptides
2. Steroids
3. Fatty acids/eicosanoids
4. Derivatives of the amino acids

Question 9

Describe the production, storage and release of a protein hormone

Answer 9

1. Protein hormones are synthesized as preprohormones on the rough ER.
2. Preprohormones are cleaved to form prohormones.
3. Prohormones are packaged in secretory vesicles in the Golgi.
4. Enzymes in the vesicles convert prohormones to active hormones.
5. Vesicles are stored in the cytoplasm and released by exocytosis.
6. Exocytosis is stimulated by the increase in calcium or cAMP
7. Vesicles fuse with the cell membrane and the inactive fragment (hormone) are extruded into the ICF/bloodstream

Question 10

Production of Steroid Hormones

Answer 10

1. Synthesized from cholesterol esters in cytoplasm vacuoles can be rapidly mobilized for steroid synthesis
2. Never stored
3. Fat-soluble, allowing them to simply diffuse across cell membranes; Can be orally administered due to their fat solubility.

Question 11

Which amino acids are each of the following hormones derived from:
a. thyroid hormone
b. epinephrine and norepinephrine
c. serotonin and melatonin

Answer 11

a. tyrosine
b. tyrosine
c. tryptophan