Autoregulation

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Autoregulation is a process within many biological systems, resulting from an internal adaptive mechanism that works to adjust (or mitigate) that system's response to stimuli. While most systems of the body show some degree of autoregulation, it is most clearly observed in the kidney, the heart, and the brain.[1] Perfusion of these organs is essential for life, and through autoregulation the body can divert blood (and thus, oxygen) where it is most needed.

Cerebral autoregulation[edit]

More so than most other organs, the brain is very sensitive to overperfusion, and cerebral autoregulation plays an important role in maintaining an appropriate blood pressure to that region.[2] Brain blood flow autoregulation is abolished when abnormally high CO2 levels persist. More detail is available at Cerebral perfusion pressure.

Homeometric autoregulation[edit]

Homeometric autoregulation, in the context of the circulatory system, is the heart's ability to increase contractility and restore stroke volume when afterload increases.[3] This is in contrast to heterometric regulation.

Coronary circulatory autoregulation[edit]

Since the heart is a very aerobic organ, needing oxygen for the efficient production of ATP & Creatine Phosphate from fatty acids (and to a smaller extent, glucose & very little lactate), the coronary circulation is auto regulated so that the heart receives the right flow of blood & hence sufficient supply of oxygen. If a sufficient flow of oxygen is met and the resistance in the coronary circulation rises (perhaps due to vasoconstriction), then the coronary perfusion pressure (CPP) increases proportionally, to maintain the same flow. In this way, the same flow through the coronary circulation is maintained over a range of pressures. This part of coronary circulatory regulation is known as auto regulation and it occurs over a plateau, reflecting the constant blood flow at varying CPP & resistance. The slope of a CBF (coronary blood flow) vs. CPP graph gives 1/Resistance.

Renal autoregulation[edit]

There is "autoregulation" of renal blood flow and glomerular filtration rate in isolated kidneys. However it is likely that both these parameters change to some extent in vivo, e.g. hypotension, during exercise. Autoregulation is the relative independence, from systemic blood pressure, of glomerular filtration rate and renal blood flow over the physiological range of mean arterial pressure (c.80-180 mmHg)

Autoregulation of genes[edit]

This is so-called "steady-state system". An example is a system in which a protein a that is a product of gene A "positively regulates its own production by binding to a regulatory element of the gene coding for it"[4] , and the protein gets used or lost at a rate that increases as its concentration increases. This feedback loop creates two possible states "on" and "off". If an outside factor makes the concentration of a increase to some threshold level, the production of protein a is "on", i.e. a will maintain its own concentration at a certain level, until some other stimulus will lower it down below the threshold level, when concentration of a will be insufficient to make gene A express at the rate that would overcome the loss or use of the protein a. This state ("on" or "off") gets inherited after cell division, since the concentration of protein a usually remains the same after mitosis. However, the state can be easily disrupted by outside factors. [4]

See also[edit]

References[edit]

  1. ^ Autoregulation
  2. ^ K. P. Budohoski, M. Czosnyka, P. J. Kirkpatrick, P. Smielewski, L. a Steiner, and J. D. Pickard, “Clinical relevance of cerebral autoregulation following subarachnoid haemorrhage.,” Nat. Rev. Neurol., vol. 9, no. 3, pp. 152–63, Mar. 2013.
  3. ^ Sarnoff SJ, Mitchell JH, Gilmore JP, Remensnyder JP (1960). "Homeometric autoregulation in the heart". Circulation Research 8 (5): 1077–1091. PMID 13746560. 
  4. ^ a b Jablonka E., Lachmann M., Lamb M.J. (1992). "Evidence, Mechanisms and Models for the Inheritance of Acquired Characters". Journal of Theoretical Biology: 245–268.