Search This Blog

Microcirculation Structure and Function


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

Arterioles
· Small precapillary resistance vessels (10-50 ) 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 a 1 and a 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 ) 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 ) 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).


Vessel Sizes

Vessel Diameter in Microns
Arterioles 20-50
Capillaries 5-10
Sinusoids 30-40
Venules 30-40

5 comments:

  1. Thank you for posting this, it was very interesting to read, and would be a fun little thing for a main character in a story to figure out and play with. Can you imagine it? Oh how fun! Thanks for the inspiration!


    Cardiovascular Company CA

    ReplyDelete
  2. The Emilio Aguinaldo College School of Medicine was founded and established by Dr. Paulo C. Campos, a National Scientist in Nuclear Medicine. It was formally opened on July 23, 2001 with 24 enrollees. Dr. Salvador R. Salceda, an ophthalmologist, became the first Dean (2001-2003), followed by a gastroenterologist, Dr. Esteban P. Pineda (2003-2010), and a surgical oncologist, Dr. Conrado C. Cajucom (2010-2013). The fourth and present Dean is Dr. Asuncion L. Abaya-Morido, a general surgeon and the former Hospital Director of Medical Center Manila, now known as the Manila Med.

    ReplyDelete

  3. Our Lady of Fatima University ever since the seven years. The lady of fatima University, formerly known as Fatima Medical Science Foundation is the private university in the Philippines. The popularity of the college is recognized by its expansion to the three campuses. The university offers 5 years duration course of the MBBS comprises 1 year of BS+ 4 years of MD, the first three year course is balanced between medical theories and practices, whereas the fourth year course focus on the medical rotations to bestow the best of the medical practices to the students. After completing the study from the Our Lady of Fatima University, you need to pass the screening test of the respective country and then you are eligible to work as doctor in any of the country in the World. The MD degree of the Our Lady of Fatima University is recognized as equivalent to the UK, Singapore, India, Australia, USA and other gulf countries.

    ReplyDelete
  4. Wisdom Overseasis authorized India's Exclusive Partner of Southwestern University PHINMA, the Philippines established its strong trust in the minds of all the Indian medical aspirants and their parents. Under the excellent leadership of the founder Director Mr. Thummala Ravikanth, Wisdom meritoriously won the hearts of thousands of future doctors and was praised as the “Top Medical Career Growth Specialists" among Overseas Medical Education Consultants in India.

    Southwestern University PHINMAglobally recognized university in Cebu City, the Philippines facilitating educational service from 1946. With the sole aim of serving the world by providing an accessible, affordable, and high-quality education to all the local and foreign students. SWU PHINMA is undergoing continuous changes and shaping itself as the best leader with major improvements in academics, technology, and infrastructure also in improving the quality of student life.

    ReplyDelete