Endocrine

Question 1

What three types of hormones exist?

Answer 1

1. Proteins and polypeptides: secreted by anterior/posterior pituitary gland, pancreas, parathyroid, and many others. Water soluble.
2. Steroids: secreted by adrenal cortex (cortisol and aldosterone), the ovaries (estrogens/progesterones) and testes (testosterone), and the placenta (estrogen and progesterone)
3. Derivatives of the amino acid tyrosine: thyroid hormones, and adrenal medulla hormones (catecholamines)

Question 2

Describe protein/polypeptide hormone synthesis, storage and release

Answer 2

Synthesized in the rough ER as large, non-active proteins called pre-hormones.

Pre-hormones are cleaved to form smaller pro-hormones, that will be transferred to the Golgi apparatus.

In the Golgi, they will be packed into small vesicles, and enzymes in the vesicles will cleave the pro-hormones to smaller biologically active hormones and inactive fragments.

Vesicles are stored in the cytoplasm until their secretion is needed then leave via exocytosis

In many situations, the stimulus for exocytosis is increased cytosolic calcium level; in other cases the stimulus will be increased cAMP which will active protein kinases

Question 3

Explain steroid hormone synthesis

Answer 3

Chemical structure is similar to cholesterol and in many cases derived from cholesterol.

Most of the cholesterol comes from plasma, but also de-novo synthesis in steroid-producing cells

Highly lipid soluble- once synthesized can readily diffuse across the cell membrane, into interstitium then into the blood.

Question 4

What is the most common mechanism of hormone secretion regulation?

Answer 4

Negative feedback

A hormone has biologic actions that in direct or indirect ways, inhibits additional secretion of itself.

Question 5

How can hormones regulate the sensitivity of target tissues?

Answer 5

By up- or down-regulating the target receptors.

Question 6

Where are different types of hormone receptors located on/in the cell?

Answer 6

Peptide/protein hormones and catecholamine hormones receptors are in or on the surface of the cell membrane.

Steroid hormone receptors are in the target cell cytoplasm.

Thyroid hormone receptors are located in the target cell nucleus.

Question 7

What ways does thyroid hormone contribute to an increased cardiac output?

Answer 7

Unregulated expression of beta receptors on the myocardium (increased responsiveness to catecholamines).

Positive inotropic and chronotropic effects (due to alterations in ion channel activities and enhanced activities of cardiac myosin enzymes).

Causes shorter AV nodal conduction time.

Question 8

True/False: thyroid hormone increases the synthesis of Na/K/ATP-ase and consequently increases oxygen consumption related to Na/K pump activity

Answer 8

True

Question 9

The anterior lobe of the pituitary gland is linked to the hypothalamus by the _______

Answer 9

The hypothalamic-hypophyseal portal system

Blood from the hypothalamus that contains high concentrations of hypothalamic hormones is delivered directly to the anterior pituitary (adenohypophysis).

Question 10

Where in the pituitary is ADH created?

Answer 10

The supraoptic and paraventricular nuclei of the posterior pituitary (AKA neurohypophysis)

Question 11

What are the four main actions of ADH?

Answer 11

1. Attaches to V2 receptors on the basolateral membranes of the principal cells of the cortical and medullary collecting ducts. Increases water permeability by insertion of aquaporins into the luminal membranes of the principal cells.
2. Constriction of vascular smooth muscle (via a V1 receptor and IP3/Ca2+ mechanism)
3. Increased Na-2Cl-K cotransport in thick ascending limb, leading to increased countercurrent multiplication and osmotic gradient development.
4. Increases urea recycling in inner medullary collecting ducts –> osmotic gradient.