W3006    Fall 2003     Mini-exam #4         Physiology              Last 5 digits of CU ID #__________________________   

1. Obesity decreases longevity, but are the harmful effects of obesity reversible?  If someone loses weight, will they be healthier?  A recent study by Joyce Harp and colleagues suggests that the answer is yes.  Sixteen people weighing an average of 216 pounds were put on a diet for 5 weeks, during which they lost an average of 15.5 pounds each.  Their blood pressure was lower after weight loss, and blood levels of ACE (angiotensin-converting enzyme) were also changed.  You would expect the decrease in blood pressure to be associated with  (an increase) (a decrease) in ACE.

Circle one and explain the mechanism by which a change in ACE would affect blood pressure in this way.  Your answer should start with ACE and include any hormones and organs involved in the pathway between ACE and the increased blood pressure, including hormonal actions on the cellular level.   (40)

 ACE converts angiotensin I to angiotensin II.   Angiotensin II stimulates the adrenal cortex 5 to secrete aldosterone 5,.  Aldosterone is a steroid hormone, so binds intracellular receptors, which are found in the cells of the collecting duct and distal tubule.  5   Aldosoterone binds to its receptor and acts as a transcription factor stimulating the synthesis of more Na+ channels, which are inserted in the luminal membrane and more Na+/K+ pumps, which are inserted in the basolateral membrane.  As a result, more Na+ is reabsorbed, and water follows by osmosis 5   The more water reabsorbed into the blood, the greater the volume of blood and the greater pressure exerted on the walls of the blood vessels, hence higher blood pressure measured. 5  When weight is loss, blood pressure decreased, suggesting that there was a decrease in ACE.  


Article this is based on:  New study shows weight loss decreases ACE enzyme that controls blood pressure  http://www.eurekalert.org/pub_releases/2002-10/uonc-nss101702.php

2.  Why should weight loss affect blood levels of ACE?   Scientists were recently discovered that ACE is produced not only in the blood vessels in fat tissue, but also in fat cells themselves.  In fact, when pre-adipocytes were grown in cell culture, they were found to produce mRNA for renin, angiotensinogen, and ACE.   This was especially surprising, since it is well-known that renin is made by the ______kidney  (juxtaglomerular cells)  _________

and angiotensinogen is made by the ____liver_________________.    (10)

3. We discussed several reasons why it makes evolutionary sense for cortisol to suppress the immune system during times of stress. However, Stanton Braude, at Washington University, disagrees.  He studied birds like peacocks, that have a very showy appearance to impress and attract females.  They look particularly bright during the mating season, when they have high levels of blood testosterone.   "The whole idea that testosterone and stress suppress the immune system makes absolutely no sense evolutionarily," says Braude. "Why would we have evolved to shut off immunity when that's so important to keep us healthy? I began to search for another mechanism for testosterone."

Braude came across a new body of research -- about a dozen studies in all over the past five years -- that questions the whole idea of immunosuppression and suggests that, instead of suppressing the immune system, testosterone and other steroids play a key role in what's called immunoredistribution.”

What is meant by “immunoredistribution”?  Describe the mechanism by which it would occur, and why it would be beneficial to the birds during the mating season.  (35).

Braude uses "immunoredistribution" to refer to the movement of leukocytes from the blood through the capillaries to the peripheral tissues.  We learned that this process is stimulated by signalling molecules in inflammation, but Braude is saying that testosterone can stimulate the same process.  Leukocytes usually flow in the blood, but when there is inflammation in the tissues, signalling molecules such as TNF and IL-1 can stimulate the endothelial cells of the capillaries  to express certain proteins on their surface (selectins). 5 The leukocytes loosely attach and detach to the selectins via proteins on their surface, and so roll along the inner surface of the blood vessel. 5 They then  begin expressing another surface protein, integrin, which attaches to cell-adhesion molecules on the endothelium.  5 They flatten out and crawl along the epithelium, then squeeze between adjacent endothelial cells 5 as they move through the capillary into the extracellular space (called diapedesis 5).   This might be beneficial because during the mating season, males compete for females, and the fighting between males can lead to injury.  Testosterone may be sending more white blood cells to the areas of potential injury in the skin.  Or the increased white blood cells in the periphery may help fight off parasitic infections, making the male's skin and plumage look better, and so help him attract a mate.   Or birds may aggregate in the mating season, so that each one comes in contact with many more other birds, and so exposed to more pathogens, and leukocytes distributed around the tissues will help fend these off.  5 for explanation of benefit

Based on the article, Lessons from the Birdshttp://record.wustl.edu/archive/1999/10-07-99/articles/birds.html

4.  Compare the neurons of the sympathetic and parasympathetic nervous system.  (15)

                Ganglion location     Neurotransmitter & receptor type in ganglion                NT & R type at target organ

Symp:      near spinal cord  2         Acetylcholine (ACh)  1 nicotinic        1                             Norepinephrine  (NE) 2 adrenergic 2 (alpha/beta)
(-1 for "peripheral nervous system)

Parasymp:  near target organ 2     Acetylcholine (ACh) 1 nicotinic      1                               Acetylcholine (ACh) 1 muscarinic  2
(-1 for "peripheral nervous system)     (-3 for "cholinergic" if no mention of nicotinic and muscarinic)