Editing Capillary (section)

=== Types ===
[[File:Different Types of Capillaries.jpg|thumb|upright=1.2|Types of capillaries: (left) continuous with no big gaps, (center) fenestrated with small pores, and (right) sinusoidal (or 'discontinuous') with intercellular gaps]]

Blood capillaries are categorized into three types: continuous, fenestrated, and sinusoidal (also known as discontinuous).

==== Continuous ====
Continuous capillaries are continuous in the sense that the endothelial cells provide an uninterrupted lining, and they only allow smaller [[molecule]]s, such as water and [[ion]]s, to pass through their [[intercellular cleft]]s.<ref name="keep">{{cite journal |pmc=4836471|year=2016|last1=Stamatovic|first1=S. M.|title=Junctional proteins of the blood-brain barrier: New insights into function and dysfunction|journal=Tissue Barriers|volume=4|issue=1|pages=e1154641|last2=Johnson|first2=A. M.|last3=Keep|first3=R. F.|last4=Andjelkovic|first4=A. V.|pmid=27141427|doi=10.1080/21688370.2016.1154641}}</ref><ref name="wilhelm">{{cite journal|pmc=4836475|year= 2016|last1=Wilhelm|first1=I.|title=Heterogeneity of the blood-brain barrier|journal=Tissue Barriers|volume=4|issue=1|pages=e1143544|last2=Suciu|first2=M.|last3=Hermenean|first3=A.|last4=Krizbai|first4=I. A.|pmid=27141424|doi= 10.1080/21688370.2016.1143544}}</ref> Lipid-soluble molecules can passively diffuse through the endothelial cell membranes along concentration gradients.<ref name="sarin">{{cite journal |pmc=3234205|year=2010|last1=Sarin|first1= H.|title=Overcoming the challenges in the effective delivery of chemotherapies to CNS solid tumors|journal=Therapeutic Delivery|volume=1|issue=2|pages=289–305|doi=10.4155/tde.10.22|pmid=22163071}}</ref> Continuous capillaries can be further divided into two subtypes:
:# Those with numerous transport vesicles, which are found primarily in [[skeletal muscle]]s, fingers, [[gonad]]s, and skin.<ref>{{cite journal |pmid=22574942|year=2012|last1=Michel|first1=C. C.|title=Electron tomography of vesicles|journal=Microcirculation |volume=19|issue=6|pages=473–6|doi=10.1111/j.1549-8719.2012.00191.x|s2cid=205759387|doi-access=free}}</ref>
:# Those with few vesicles, which are primarily found in the [[central nervous system]]. These capillaries are a constituent of the [[blood–brain barrier]].<ref name=wilhelm/>

==== Fenestrated ====
Fenestrated capillaries have pores known as [[fenestra (histology)|''fenestrae'']] ([[Latin]] for "windows") in the endothelial cells that are 60–80&nbsp;[[nanometre]]s (nm) in diameter. They are spanned by a diaphragm of radially oriented [[fibril]]s that allows small molecules and limited amounts of protein to diffuse.<ref>{{BUHistology|22401lba|inline=1}}</ref><ref>{{cite book |last1=Pavelka |first1=Margit |last2=Roth |first2=Jürgen |title= Functional Ultrastructure: An Atlas of Tissue Biology and Pathology |date=2005 |publisher=Springer |location=Vienna |isbn=978-3-211-26392-1 |page=232 |url=https://doi.org/10.1007/3-211-26392-6_120 |language=en |chapter=Fenestrated Capillary|doi=10.1007/3-211-26392-6_120 }}</ref> In the [[renal glomerulus]] the capillaries are wrapped in [[podocyte foot processes]] or pedicels, which have slit pores with a function analogous to the diaphragm of the capillaries. Both of these types of blood vessels have continuous [[basal lamina]]e and are primarily located in the [[endocrine gland]]s, [[intestines]], [[pancreas]], and the [[renal glomerulus|glomeruli]] of the [[kidney]].

==== Sinusoidal ====
[[File:Sinusoid.jpeg|alt=Scanning electron micrograph of a liver sinusoid with fenestrated endothelial cells.|thumb|[[Scanning electron micrograph]] of a [[liver sinusoid]] with fenestrated endothelial cells. Fenestrae are approximately 100&nbsp;nm in diameter.]]

Sinusoidal capillaries or discontinuous capillaries are a special type of open-pore capillary, also known as a ''sinusoid'',<ref name="HLM">{{cite web |title=Histology Laboratory Manual |url= http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab07_micrograph.html |website=www.columbia.edu}}</ref> that have wider fenestrations that are 30–40&nbsp;[[micrometre]]s (μm) in diameter, with wider openings in the endothelium.<ref name="Saladin">{{Cite book| isbn=9780071222075|title=Human Anatomy|last1=Saladin|first1=Kenneth S.|year=2011|pages=568–569|publisher=McGraw-Hill }}</ref> Fenestrated capillaries have diaphragms that cover the pores whereas sinusoids lack a diaphragm and just have an open pore. These types of blood vessels allow [[red blood cell|red]] and [[white blood cell]]s (7.5&nbsp;μm – 25&nbsp;μm diameter) and various [[Blood plasma|serum]] proteins to pass, aided by a discontinuous basal lamina. These capillaries lack [[pinocytotic vesicles]], and therefore use gaps present in cell junctions to permit transfer between endothelial cells, and hence across the membrane. Sinusoids are irregular spaces filled with blood and are mainly found in the [[liver]], [[bone marrow]], [[spleen]], and brain [[circumventricular organs]].<ref name="Saladin"/><ref name="gross1">{{cite book|pmid=1410407|year=1992|last1=Gross|first1=P. M|chapter=Chapter 31: Circumventricular organ capillaries |title=Circumventricular Organs and Brain Fluid Environment - Molecular and Functional Aspects|series=Progress in Brain Research|volume=91|pages=219–33|doi=10.1016/S0079-6123(08)62338-9|isbn=9780444814197}}</ref>