Assigned readings:Chapters 1-3 in Griffin & Ojeda; Chapter 1 in

Bentley• Lecture: Tuesdays 6-8:45 PM• Professor: Dr. Frank V. Paladino• Office: SB G-56• Phone: 481-6304 or 6305

• Lecture 2

Thus there are 2 general patterns of hormone effects on cells

1. Protein – amine effect on membrane receptors:

Second messenger cAMP causes responses in cytoplasm

Specific Example Antidiuretic (argenine vasopressin or ADH) hormone a nonapeptide (9 aa): regulates water levels in body by action on nephron distal tubule: very close relationship of the nonapetides secreted from the Posterior Pituitary or neurohypophysis.

2. Steroid hormones act directly on nuclear DNA, chromosomes puff shows areas of DNA where steroid hormone has induced new mRNA production

Cholesterol is a 17 ketosteroid and an important precursor for all steroid hormones.

Ca also an important cell regulator and Ca – Calmodulin system for cellular control:

• Hormone control: Usually done by feedback loops but other general patterns;

• Pattern 1 – On/off --- For this pattern hormone secretion is initiated by some factor (may be neural)

For this case the hormone us usually not found in the general circulation – some factor turns on the secretion i.e.

Ext stim>neural signalGland> hormone secreted>H in blood>Target organ> response> Stimulus removed>

• Example: Food bolus in duodenum> neural receptors Intestinal plexus> Endocrine cells in intestinal mucosa >Secretin Hormone dumped into blood> Receptors in pancreas> secretin cause release of digestive enzymes from pancreas> Food digested and absorbed> bolus gone> Stimulus gone> Neural signal off> secretin gone from blood

• This is an example of On/off

• Persistent secretion pattern: There is always a certain level of the hormone in the blood and feedback control regulates the amount and level. Usually there are hormone pairs that work in concert to maintain a constant level (homeostasis) of some chemical in system.

• SIMPLE feedback control: steady state hormone levels control some variable

• Specific example: Regulation of blood Ca levels

Parathormone (PTH) produced by Parathyroid glands regulates blood Ca levels in concert with Thyrocalcitonin (TCT) secreted from the thyroid

Levels of Ca are relatively constant in blood. PTH cells monitor [Ca] > when [Ca]^ PTH secretion is reduced and blood [Ca]v

PTH causes Bone cells to reabsorb Ca from bone matrix and deposit free Ca in Blood , Stimulates gut to absorb Ca and reduces Ca secretion in Kidney tubules

A. Thyrocalcitonin (TCT) produced by cells in thyroid nodules has an opposite effect and opposes the action of PTH

As [Ca]^ > TCT cells in thyroid [TCT]^

TCT causes bone cells to deposit Ca in bone matrix, Kidney tubules secrete Ca, and gut cells reduce absorption of Ca from food.

Thus these 2 hormones are persistently secreted at low levels in the blood and regulate very closely the levels of free Ca in the blood. They are known as a simple negative feedback hormone pair Feedback loop is negative because the hormone removes the stimulus [Ca] change and thus the system comes into steady state or homeostasis

3. Multistep feedback loops: more complex and now have feedback at more than 1 level

a. It was thought that the Pituitary gland located at the base of the brain was the “Master Gland”

b. Embryologically derived from neural tissue and a pouch from the oral tube (Rathke’s pouch)

Special circulation between Pituitary and Hypothalamus called Hypothalmo-hypophoseal portal system. Capillary’s in hypothalamus go to adenohypophysis

Tropic hormones from the Anterior Pituitary (Adenohypophysis) and Regulating Factors (RF’s) from the Hypothalamus put multiple levels of control and feedback in the feedback loops

1. Study and know all the Pituitary hormones and actions

2. Know the hypothalmus nuclei and regulating factors

3. Know the unique anatomy of these 2 structures

4. Understand now the multiple levels of control and feedback

i.e. control of gonad function –

Hypothalamus produces GnRF (gonadotropin reg Factor – goes via special circulation to Ant. Pit. Effects release of Gonadotropin (like FTH foliculotropin AKA FSH) FSH effects ovary – ovary produces estrogen (Female sex hormone) estrogen effects uterus, breasts etc… and can now feed back to hypothalamus as well as Pituitary, and the ovary at multiple levels

Hypersecretion of thyroid causes enlarged goiter

Exopthalmus (Bug eyes) and Graves Disease

Hyposecretion as a child can cause cretin as an adult Myxedema