Microcirculation Structure and Function

The microcirculation is comprised of arterioles, capillaries, venules, and terminal lymphatic vessels.

Arterioles
Small precapillary resistance vessels (10-50 μ) composed of an endothelium surrounded by one or more layers of smooth muscle cells.
Richly innervated by sympathetic adrenergic fibers and highly responsive to sympathetic vasoconstriction via both α 1 and α 2 postjunctional receptors.
Represent a major site for regulating systemic vascular resistance.
Rhythmical contraction and relaxation of arterioles sometimes occurs (i.e., spontaneous vasomotion).
Primary function within an organ is flow regulation, thereby determining oxygen delivery and the washout of metabolic by-products.
Regulate, in part, capillary hydrostatic pressure and therefore influence capillary fluid exchange.
Capillaries
Small exchange vessels (6-10 μ) composed of highly attenuated (very thin) endothelial cells surrounded by basement membrane ? no smooth muscle.
Three structural classifications: Continuous (found in muscle, skin, lung, central nervous system) ? basement membrane is continuous and intercellular clefts are tight (i.e., have tight junctions); these capillaries have the lowest permeability.;

Fenestrated (found in exocrine glands, renal glomeruli, intestinal mucosa) ? perforations (fenestrae) in endothelium result in relatively high permeability.

Discontinuous (found in liver, spleen, bone marrow) ? large intercellular gaps and gaps in basement membrane result in extremely high permeability.

Large surface area and relatively high permeability (especially at intercellular clefts) to fluid and macromolecules make capillaries the primary site of exchange for fluid, electrolytes, gases, and macromolecules.
In some organs, precapillary sphincters (a circular band of smooth muscle at entrance to capillary) can regulate the number of perfused capillaries.
Venules
Small exchange vessels (10-50 μ) composed of endothelial cells surrounded by basement membrane (smallest postcapillary venules) and smooth muscle (larger venules).
Fluid and macromolecular exchange occur most prominently at venular junctions.
Sympathetic innervation of larger venules can alter venular tone which plays a role in regulating capillary hydrostatic pressure.
Terminal Lymphatics
Composed of endothelium with intercellular gaps surrounded by highly permeable basement membrane and are similar in size to venules ? terminal lymphatics end as blind sacs.
Larger lymphatics also have smooth muscle cells.
Spontaneous and stretch-activated vasomotion is present which serves to "pump" lymph.
Sympathetic nerves can modulate vasomotion and cause contraction.
One-way valves direct lymph away from the tissue and eventually back into the systemic circulation via the thoracic duct and subclavian veins (2-4 liters/day returned).
This article comes from: http://www.cvphysiology.com/Microcirculation/M014.htm
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Microcirculation
Edited by:
Professor Jefferson C Frisbee

ISI Journal Citation Reports? Ranking: Haematology (29/62), Peripheral Vascular Disease (27/56)
Impact Factor: 2.464

Microcirculation features original contributions that are the result of investigations contributing significant new information relating to the vascular and lymphatic microcirculation addressed at the intact animal, organ, cellular, or molecular level. Papers describe applications of the methods of physiology, biophysics, bioengineering, genetics, cell biology, biochemistry, and molecular biology to problems in microcirculation.

The journal also publishes state-of-the-art reviews that address frontier areas or new advances in technology in the fields of microcirculatory disease and function. Specific areas of interest include: Angiogenesis, growth and remodeling; Transport and exchange of gasses and solutes; Rheology and biorheology; Endothelial cell biology and metabolism; Interactions between endothelium, smooth muscle, parenchymal cells, leukocytes and platelets; Regulation of vasomotor tone; and Microvascular structures, imaging and morphometry. Papers also describe innovations in experimental techniques and instrumentation for studying all aspects of microcirculatory structure and function.
This article comes from: http://www.wiley.com/bw/journal.asp?ref=1073-9688
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Hepatic microcirculatory dysfunction during cholestatic liver injury in rats.

Ito Y, Bethea NW, Baker GL, McCuskey MK, Urbaschek R, McCuskey RS.

Department of Cell Biology Anatomy, College of Medicine, University of Arizona, Tucson, AZ 85724, USA.

Abstract
OBJECTIVE:: The present study was conducted to elucidate the sequential alterations in the hepatic microvascular inflammatory response to extrahepatic biliary obstruction. METHODS:: The hepatic microvasculature in anesthetized Sprague-Dawley rats was studied by in vivo microscopy 3, 7, and 14 days after bile duct ligation (BDL) or sham operation. RESULTS:: The numbers of adhering leukocytes and swollen sinusoidal endothelial cells were significantly increased at 3, 7, and 14 days after BDL when compared with sham-operated controls. Concomitantly, the numbers of sinusoids containing blood flow were significantly and progressively decreased by up to 30%. The phagocytic activity of hepatic macrophages was significantly elevated during the development of biliary cholestasis. In particular, centrilobular phagocytosis at 14 days after BDL was significantly increased 1.4- to 2.0-fold when compared with that at 3 and 7 days after BDL. Electron microscopy also revealed evidence of activated Kupffer cells reflected by numerous filopodia and ruffles. CONCLUSIONS:: These results suggest that hepatic microcirculatory dysfunction subsequent to BDL contributes to cholestatic liver injury
This article comes from:http://www.ncbi.nlm.nih.gov/pubmed/14557825
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Microcirculation

– The Circle of Life:
Heart disease is a killer. In fact, it is the number one killer in North America taking another life every 33 seconds!
Thousands of people with great cholesterol readings continue to die every year from heart disease. Women need to also pay close attention, as heart disease should not be considered just a “man’s disease”. In 1996, 52.7% of all female deaths were due to heart disease, compared to 47.3% for men. That is more deaths due to compromised circulation than the next 16 causes of death combined.
An alarming 800,000 North Americans die each year from heart disease. And people don’t die due to high cholesterol ‘numbers’. They die from the disease process that prevents your trillions of cells from getting sufficiently nourished and cleansed.
Ensuring proper circulation is essential. Your life is literally dependent upon your circulation. The vast majority of the vital functions of circulation are done in the microcirculation network of capillaries; where some of these are so small; it takes 10 of them to equal the width of a single human hair. This is where the oxygen and nutrition is transferred to vital organs and tissues, and where CO2 (carbon dioxide) and other waste toxins are removed. This is possible because the membrane walls are so thin, this exchange can easily occur in a healthy system.
Basically your cardiovascular health is totally dependent upon how efficient the arteries to your heart are at delivering oxygen and nutrient enriched blood through the arteries, into the capillaries and then returning this to start the cycle over and over again.

Hypertension (High Blood Pressure)
One in four North Americans suffer from overt diagnosed cardiovascular disease, and that does not include all the individuals yet to be diagnosed. Over 50 million suffer from increased resistance within their circulatory system, particularly the arteries and microcirculation, with the result being the risks associated with increased blood pressure.
It is important to note that a disproportionately large amount of blood pressure resistance arises from within your microcirculation. The overall health of your cardiovascular system is greatly impacted by even the smallest capillary. It can become blocked and affect the blood flow to all parts of the human body. This is just one example of the cascading affect of high blood pressure.
Complacency is dangerous when it comes to heart disease for virtually all of us have elevated blood pressure readings throughout the day depending on our stress levels. So, as your heart pumps 100,000 times day, any improvement that can be accomplished in lowering blood pressure by increasing the diameter within the arteries and capillaries can pay big dividends in decreasing wear and tear on the heart and the entire cardiovascular system.


Diabetes mellitus (Sugar diabetes)
We all know someone with diabetes, which is not surprising since it is the fastest rising cause of death in America. New cases of diabetes pile up at a rate of 798,000 annually and contribute to the cause of many deaths indirectly as well; including heart disease, high blood pressure, stroke, blindness, kidney disease, amputations, dental disease, nervous system disease, infections, and others.
Improved microcirculation can help mitigate some of the short and long term side effects of diabetes, since this disease is directly linked to decreased efficiency of microcirculation. This can arise in some diabetics simply from an increase in capillary resistance early on in the disease process, further damaging local tissues and vital organs such as the kidneys, which are all dependent upon capillary blood flow to function.
Diabetes cases are projected to surge in the next few years. The University of Maryland, School of Medicine states that more than 258,000 residents are estimated to have diabetes, yet only 129,000 have been diagnosed with it. The impact of early intervention can’t be over-emphasized, educating a friend or family member can be a life saving pursuit that rewards you and them for a lifetime.

Glaucoma
As was stated before, the cardiovascular system reaches and affects all areas and functions of the body, your eyes are no exception. Glaucoma is a common condition that arises from increased pressure within the eye which has now also been linked to vascular changes in microcirculation.
It is important to remember the eye is the only readily assessable window to view circulatory and neurological health. When a physician examines your eye with an ophthalmoscope the life sustaining arteries and veins can be clearly observed along with actual nerves, providing vital information to gauge vascular health.

Microcirculation and Smokers:
Individuals that have become addicted to nicotine require more help to protect and offset the detrimental effects on their microcirculation. Nicotine stimulates the sympathetic nervous system, which can lead to vasoconstriction (narrowing) of arteries and increased resistance in arteries and capillaries. The sum effect is more work for the heart from increased blood pressure, at the same time that the body has less oxygen and more waste products to cope with as a direct effect of smoking.
Stopping smoking is a challenge even for those with strong wills, but until success is achieved, offsetting side effects by improving micro-circulation is a good investment in yourself or someone you love. It should be noted that smoking increases the risk of dying from heart disease by 140% to 240% even in those that smoke lightly and an incredible 350% for heavy smokers.
Part of the challenge of successfully kicking this life threatening habit comes down to brain chemistry and proper brain circulation is essential for optimal production of neurotransmitter messengers linked to the addictive cycle that smokers find themselves.

Microcirculation and Alcohol
When drinking alcohol, a certain degree of free radical damage occurs. The classic signs of changes in circulatory health in consumers of alcohol are clear with the overt redness of the cheeks and nose, and frequently the visible appearance of blood vessels on the surface of the face. Numerous chemical processes are required to detoxify the body from the metabolism (breakdown) of alcohol. Therefore as with all forms of the clearing of waste products from the body, optimal circulation and microcirculation should be actively sought and enhanced.

Microcirculation and Stress:
The effects of this constant exposure to stress are numerous and include lowered immune function and diminished blood flow. Thus, with increased stress, the tissues of your body are asked to cope with a heightened level of alertness or readiness, commonly known as the “fight or flight response”. As a result, your micro-circulation particular to vital organs is detrimentally altered.
Millions of us exist in this state of high demand for abundant delivery of nutrients and oxygen to sustain our rapid lifestyle, yet our body must deal with drought-like conditions when it comes to proper circulation.
When pursuing peak performance nourishing the body with sufficient nutrients and oxygen is key, yet without the highways and by-ways that take the form of arteries within your body, the supply center may be full, yet your tissues can literally starve awaiting life-sustaining circulation.

Microcirculation Facts:
There are some 18,000 miles of capillaries within the body.
Peripheral vascular disease is the leading cause of amputation in this country.
Colds hand and feet can be a warning sign of poor circulation.
Numbness and tingling in the arms and legs can point to a lack of microcirculation.
Raynaud’s phenomenon results from too much contraction within the circulation network.
Healthy capillaries are so small that red blood cells must pass through single file.
Capillaries are how your body nourishes the trillions of cells (that equal you).

Steps to Improve Your Circulation:
Eating a proper and healthy diet can be essential in providing your body and microcirculation with vitamins, nutrients and antioxidants. Regular exercise can also greatly improve blood flow and increase the immune response to stress. In addition to regular exercise and proper diet, the additional steps you can take to help improve your microcirculation can be relatively simple.
Traditional Chinese Medicine (TCM) herbals like LingZhi Medicinal Mushrooms, plus Cordyceps have all been clinically shown to help strengthen and enhance microcirculation. They also support immune function, acting as antioxidants and helping to fuel the body with oxygen and nutrition.
LingZhi studies have reported positive blood thinning effects, antioxidant properties with cardiac protective potential, blood pressure lowering, cholesterol lowering, and clot protective properties. Each of these findings supports the inclusion of Lingzhi into a microcirculation promoting protocol.
Similarly, ongoing Cordyceps research has demonstrated blood pressure lowering, vasodilating (blood vessel expanding), protection against heart ischemia (lack of oxygen) and blood clot formation. These study findings strongly support the role of Cordyceps as a tool in the arsenal to augment and support healthier microcirculation. These properties are in addition to Cordyceps anti-fatigue and anti-stress effects that have also been noted in the medical literature.

This article comes from: http://www.ihealthcast.com/Conditions/Microcirculation/tabid/462/Default.aspx
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The Hepatic Microcirculation: Mechanistic Contributions and Therapeutic Targets in Liver Injury and Repair

Brigitte Vollmar and Michael D. Menger

Institute for Experimental Surgery, University of Rostock, Rostock; and Institute for Clinical and Experimental Surgery, University of Saarland, Homburg-Saar, Germany

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.
This article comes from: http://physrev.physiology.org/cgi/content/abstract/89/4/1269
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From British Journal of Anaesthesia
Effects of Propofol on Human Microcirculation

M. Koch; D. De Backer; J. L. Vincent; L. Barvais; D. Hennart; D. Schmartz

Authors and Disclosures

Posted: 11/06/2008; Br J Anaesth. 2008;101(4):473-478. ? 2008 Oxford University Press

Abstract and Introduction
Abstract
Background: It is increasingly believed that acute microvascular alterations may be involved in the development of organ dysfunction in critically ill patients. Propofol significantly decreases vascular tone and venous return, which can induce arterial hypotension. However, little is known about the microcirculatory effects of propofol in healthy humans.
Methods: We conducted a prospective, open-labelled trial in 15 patients anaesthetized by propofol for transvaginal oocyte retrieval. The sublingual microcirculatory network was studied before, during, and after propofol infusion using orthogonal polarization spectral imaging.
Results: Mean (SD) calculated propofol effect-site concentration was 6.5 (1.8) μg ml-1. During propofol administration, systemic haemodynamic and oxygenation variables were unchanged, but total microvascular density decreased by 9.1% (P<0.05). The venular density remained unchanged, but the density of perfused capillaries was significantly reduced by 16.7% (P<0.05). Microcirculatory alterations resolved 3 h after discontinuation of the propofol infusion.
Conclusions: Propofol infusion for anaesthesia in man reduces capillary blood flow.

Introduction
Propofol administration, at clinical doses, has significant haemodynamic effects.[1,2] It has limited effects on the contractility of the heart,[3,4] but induces arterial hypotension primarily by decreasing vascular tone and venous return.[5-9] These effects are usually easily compensated by fluid administration, vasopressor agents, or both. In contrast to its systemic haemodynamic effects, little is known about the effects of propofol on the microcirculation. Acute microvascular alterations have been observed in patients with severe sepsis[10,11] and in patients with severe cardiac failure,[12] and these alterations are more severe in patients with a poor outcome.[10-13] Experimental data suggest that an impaired microcirculation may lead to organ dysfunction;[14] although this is difficult to prove in man, it may be justified to avoid the agents that could further worsen microvascular perfusion. Some anaesthetic agents have been shown to alter the microcirculation in experimental conditions,[15-17] leading to impaired oxygen extraction capabilities.[18] However, these effects may be specific to the anaesthetic agent, its dosage, and its route of administration. We hypothesized that anaesthesia with propofol may be associated with microvascular alterations.

We used the orthogonal polarization spectral (OPS) imaging technique (Figure 1),[19] a non-invasive method for assessing the microcirculatory blood flow in vivo in humans,[10-13] to study the effects of propofol on the human microcirculation in patients undergoing transvaginal oocyte retrieval for assisted reproductive techniques.

This article comes from:http://www.medscape.com/viewarticle/581346
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