Microcirculation and Starling forces

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Microcirculation and Starling forces

Cardiovascular system


Microcirculation and Starling forces


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Microcirculation and Starling forces

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A 32-year-old man presents to his outpatient provider due to periorbital edema and lower extremity swelling. He has also experienced weight gain despite making no changes to his diet or exercise routine. Laboratory testing demonstrates proteinuria. An additional workup is performed and the patient is diagnosed with nephrotic syndrome. A change in which of the following factors is primarily responsible for this patient’s symptoms?  


With microcirculation and Starling forces, microcirculation refers to the blood that flows through the smallest vessels in the circulatory system called capillaries.

And Starling forces, named after British physiologist Ernest Starling, sometimes called Starling pressures, are the forces that drive the exchange of fluid through the walls of the capillaries.

The capillaries have a single layer of endothelial cells lining their walls with clefts between these cells.

Normally, blood flows into smaller and smaller arteries, eventually reaching the arterioles, the metarterioles, and then the capillaries. In the capillary bed, due to the capillary’s thin walls and clefts, substances like nutrients or waste products can move from the blood into surrounding tissues and vice-versa.

After the capillaries, blood moves into venules, and then finally into veins. Intertwined with these capillaries are the lymphatic capillaries, which return interstitial fluid and proteins to the vascular system.

Lymphatic capillaries can also empty into larger lymphatic vessels and eventually into the thoracic duct, which empties lymphatic fluid directly into the large veins.

So, arterioles, metarterioles, capillaries, venules, and lymphatic vessels together make up the microcirculation.

Now, the arterioles that come before the capillaries act as floodgates, regulating blood flow into the capillaries.


The microcirculation refers to the network of small blood vessels that deliver oxygen and nutrients to individual cells and remove waste products. Starling forces are the physical forces that determine the movement of fluid between capillaries and tissue fluid.

The two major starling forces are hydrostatic pressure and oncotic pressure. Hydrostatic pressure is the force exerted by blood inside the capillary or in the interstitial space. It is generated by the contraction of the heart muscle, which squeezes blood through the arteries and pushes it into the capillaries. On the other hand, the oncotic pressure is created by proteins (mainly albumin) in the blood, which pulls water out of tissue fluid into capillaries.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2017)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Microvascular fluid exchange and the revised Starling principle" Cardiovascular Research (2010)
  6. "Revised Starling equation and the glycocalyx model of transvascular fluid exchange: an improved paradigm for prescribing intravenous fluid therapy" British Journal of Anaesthesia (2012)

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