The Endocrine System

Hormone =

Types:

• peptide or protein = at least 3 amino acids

• steroid = derived from cholesterol

• amine = derived from single amino acids (tryptophan, tyrosine)

Peptide Hormones

Synthesis/transport/half-life =

Storage?

Multiple processing patterns for protein hormones

Because peptides are impermeable, they must use membrane receptors and second messenger signal transduction mechanisms to produce the desired effects.

Most use g-protein coupled receptors, but some use tyrosine kinase type receptors (i.e. insulin)

Steroid Hormones

Steroid hormone synthesis/storage/half-life

Mechanism of cellular activation?

Amine hormones

Neurohormones =

Three major groups

1. Posterior pituitary/hypothalamus

• Vasopressin (ADH)

• Oxytocin

2. Anterior pituitary/hypothalamus

3. Catecholamines of the adrenal medulla

2. Anterior pituitary –hypothalamus

• Prolactin

• Thyroid stimulating hormone (TSH)

• Adrenocorticotropic hormone (ACTH)

• Growth hormone (GH)

• Follicle stimulating hormone (FSH)

• Leutinizing hormone (LH)

Most target other endocrine glands or cells

Tissues can be targeted by multiple hormones

Hormones can act synergistically, permissively, or antagonistically

Synergistic effects of hormones on blood glucose concentration

Example of Hormone Regulation – Vasopressin (ADH)

• Regulation of body water is a response to ECF volume changes (in particular, blood volume)

• When blood volume changes, volume receptors in the blood vessels and atria respond

• Carotid sinus and aortic baroreceptors

• Afferent nerves from these receptors go to the cardiovascular center in the brainstem

• Increased pressure would signal the center to

• Decreased pressure would signal the center to

• When blood volume changes, stretch receptors in the atria also respond

• Increased pressure also signals the cardiovascular center to

• Increased pressure signals the hypothalamus (this is where ADH release is controlled)

• When blood volume increases, filtration in the kidney is adjusted so that more fluid is filtered per minute

• Typically, under normal situations, the kidneys are not under the influence of ADH and water follows ions as they pass through the kidney tubules

• There are few aquaporin molecules in the cell membranes of the kidney collecting ducts in the absence of ADH. They are stored inside the cells.

Influence of ADH on the Collecting Ducts

Feedback Loop for ADH

Negative feedback

What regulates NaCl?

Regulation of Na+

• Increasing osmolarity of the blood stimulates thirst behaviors, and increases ADH secretion. Drinking and preventing water loss from the kidneys, decreases blood osmolarity

How would this graph change if an individual had hypertension (high blood pressure)?

Long-term regulation of Na+

• Under the control of aldosterone; it increases Na+ reabsorption into the blood from the kidney filtrate

What will happen to plasma [K+]?

What will be the overall effect on plasma osmolarity?

The hormone leutininzing hormone (LH) stimulates ovarian cells to produce the hormone progesterone by way of a second messenger system. When an antagonist is used to activate adenylyl cyclase in the ovarian cells, the level of progesterone produced is not as great as when LH stimulates the cells. It has also been observed that the intracellular levels of free calcium increase when LH stimulates the cells. What does this information imply about the mode of action of LH? Explain.