Ex phys endocrine Flashcards
Describe the mechanisms by which hormones act of their target cells
Hormones can act on their target cells in numerous ways. They can induce
secretions, activate or inactive an enzyme and induce an action. There are normally done by the hormone binding to its receptor and initiating a cascade of events. Polypeptide derived hormones bind to receptors on the cell membrane whereas steroid derived hormones can bind to the promoter region within the nucleus on DNA. Recall hormones are usually stimulated in many ways meaning hormone to hormone, neural to hormone and humoral to hormone (see below). Hormones primarily act using negative feedback mechanisms to keep in check.
What are humoral and neural stimuli
Humoral stimuli that cause a hormone release is one that is an ion that is monitored
and when that deviates from the norm, the hormone is released. The best examples of humoral stimuli are glucose and calcium. Neural stimuli are factors from the nervous system that stimulate the release of hormones. Norepinephrine and epinephrine can act as both a neurotransmitter and hormone. They both stimulate the regulation of substrate metabolism, fat and glucose in particular
How does the intensity and duration of exercise affect the hormonal response
The short answer is that intensity and duration will influence the substrates required for exercise, e.g. fats versus CHO. In addition, water retention will need to be addressed as exercise persists particularly in the presence of hot and humid environments. Details below.
Describe the mechanisms of control the breakdown of muscle glycogen during exercise.
Exercise requires CHO usage starting at 50% of VO2 max! We recall this from sport
nutrition lectures. As such, CHO metabolism is critical at all phases of exercise. We do know however, that CHO becomes a primary fuel at HIGH intensity exercise. Low and moderate intensity you will find glucose release being suppressed in order to support fatty acid oxidation. However, as exercise rises, particularly at and above LT/VT we see many changes. We see an increased in the release on EPI. EPI acts directly on the pancreas to control the hormones on glucose balance. In particular there is release of glucagon and insulin at higher intensities. Glucagon will need to help facilitate gluconeogenesis from glycerol, amino acids, and lactate. Insulin will help promote GLUT-4 receptors to translocated to the muscle cell membrane so that glucose can be taken up into the cell to undergo glycolysis to make ATP for muscular work.
Describe the hormonal mechanisms for fluid and sodium balance during exercise
The two main hormones responsible for fluid and sodium are anti-diuretic
hormone/vasopressin and aldosterone respectively. ADH and aldosterone work to monitor the distal convoluted tubule in the nephron. ADH monitors the descending look of Henle also since that area is only permeable to water and aldosterone keeps tabs on the ascending loop since that
side is only permeable to sodium. Aldosterone is a steroid derived hormone so it can work to increased sodium transporters in the kidney also. BOTH hormones also regulate blood pressure, specifically by increasing it because of the retention of water and sodium.
Understand the way that cortisol, growth hormone and the catecholamines affect substrate utilization during exercise
These hormones act as helpers to other primary hormones, particularly cortisol and
GH. GH acts to help promote lipid metabolism and suppress CHO metabolism up until LT/VT
when fat metabolism is suppressed.
Cortisol is a stress hormone and we recall that stress when exercising is normal. However, extra cortisol is released during other times of stress too, especially our exceptions to the rule when it
comes to when our body uses protein to actually make ATP… starvation and prolonged, intense exercise. Cortisol can cause fat, CHO AND PROTEIN to be liberated for energy and the use of fat and protein for gluconeogenesis.
Catecholamines are used to enhance both the CV system (heart rate and vasoconstriction) but also promote fat and CHO metabolism. NOREPI promotes fat metabolism and is typically released at approx. 50% VO2 max to ensure this happens. It is such a strong stimulus of fat metabolism when the receptors for NOREPI are blocked, fat oxidation does not really occur. Keep in mind NOREPI will continue to be released up to 100% VO2 max because of its CV effects. EPI will promote CHO oxidation… see above!
What are the effects of insulin and glucagon on glucose and fatty acid metabolism
Insulin promotes uptake of glucose into the cell during high intensity exercise to be
used for ATP production. It also suppresses fat metabolism universally. Glucagon promotes fatty acid oxidation by needing to use the glycerol for gluconeogenesis.
