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Transcellular transport
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<h2 id="active-transport">Active Transport</h2> <p class="note">Main article: <a href="/facts/Active_transport/7EAcsfb2">Active transport</a></p> <p>Active transport is the process of moving <a href="/facts/Molecule/N9ljSfFq">molecules</a> from an area of low <a href="/facts/Concentration/wqBmz5od">concentrations</a> to an area of high concentration. There are two types of active transport, <a href="/facts/Primary_active_transport/7EAcsfb2">primary active transport</a> and <a href="/facts/Secondary_active_transport/7EAcsfb2">secondary active transport</a>. Primary active transport uses <a href="/facts/Adenosine_triphosphate/nB9bwgcU">adenosine triphosphate</a> (ATP) to move specific molecules and solutes against its concentration gradient. Examples of molecules that follow this process are <a href="/facts/Potassium/FWPwS7Rj">potassium</a> K+, <a href="/facts/Sodium/eYuSPu2V">sodium</a> Na+, and <a href="/facts/Calcium/hf252CC0">calcium</a> Ca2+. A place in the human body where this occurs is in the intestines with the uptake of <a href="/facts/Glucose/oUSkoLCD">glucose</a>. Secondary active transport is when one solute moves down the <a href="/facts/Electrochemical_gradient/IEfjjoIL">electrochemical gradient</a> to produce enough energy to force the transport of another solute from low concentration to high concentration. An example of where this occurs is in the movement of glucose within the proximal convoluted tubule (PCT). </p> <h2 id="passive-transport">Passive Transport</h2> <p class="note">Main article: <a href="/facts/Passive_transport/pH9lfpaW">Passive transport</a></p> <p>Passive transport is the process of moving molecules from an area of high concentration to an area of low concentration without expelling any energy. There are two types of passive transport, passive diffusion and <a href="/facts/Facilitated_diffusion/CxHhRHKa">facilitated diffusion</a>. Passive diffusion is the unassisted movement of molecules from high concentration to low concentration across a <a href="/facts/Semipermeable_membrane/YxENKzn5">permeable membrane</a>.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> One example of passive diffusion is the <a href="/facts/Gas_exchange/3vUewPNH">gas exchange</a> that occurs between the <a href="/facts/Oxygen/acyn6o8r">oxygen</a> in the <a href="/facts/Blood/03zEulkj">blood</a> and the <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> present in the lungs.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> Facilitated diffusion is the movement of polar molecules down the concentration gradient with the assistance of <a href="/facts/Membrane_protein/FboTeM8Q">membrane proteins</a>. Since the molecules associated with facilitated diffusion are polar, they are repelled by the hydrophobic sections of permeable membrane, therefore they need to be assisted by the membrane proteins. Both types of passive transport will continue until the system reaches equilibrium.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> One example of facilitated diffusion is the movement glucose from small intestine <a href="/facts/Epithelium/ecKHcHC3">epithelial</a> cells into the <a href="/facts/Extracellular_matrix/kaHC5Ez8">extracellular matrix</a> of the blood capillaries.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <h2 id="transcytosis">Transcytosis</h2> <p class="note">Main article: <a href="/facts/Transcytosis/Racr1uMg">Transcytosis</a></p> <p>Transcytosis is the movement of large molecules across the interior of a cell. This process occurs by engulfing the molecule as it moves across the interior of the cell and then releasing the molecule on the other side. There are two types of transcytosis are receptor-mediated transcytosis (RMT) and adsorptive-mediated transcytosis (AMT). An example where both types of transcytosis occur is the movement of macromolecules across the blood-brain barrier (BBB) into the central nervous system (CNS). </p> <h2 id="paracellular-transport">Paracellular Transport</h2> <p>In contrast, <a href="/facts/Paracellular_transport/64ImkGCg">paracellular transport</a> is the transfer of substances across an epithelium by passing through an intercellular space between the cells. </p> <ol><li>It differs from transcellular transport, where the substances travel through the cell passing through both the apical membrane and basolateral membrane</li> <li><a href="/facts/Renal_physiology/4S4JajIw">Renal physiology</a>. Transcellular transport is more likely to involve energy expenditure than paracellular transport.</li> <li><a href="/facts/Capillaries/4BIzKJAe">Capillaries</a> of the <a href="/facts/Blood%E2%80%93brain_barrier/xYzvVwdu">blood–brain barrier</a> have only transcellular transport, in contrast with normal capillaries, which have both transcellular and paracellular transport.</li></ol> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Rhoades, Rodney A.; Bell, David R. (2012). "Plasma membrane. membrane transport, and resting membrane potential". Medical physiology : principles for clinical medicine (4th ed., International ed.). Philadelphia, Pa.: Lippincott Williams & Wilkins. p. 36. ISBN 978-1451110395. <a href="978-1451110395" target="_blank">978-1451110395</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"5.2A: The Role of Passive Transport". Biology LibreTexts. 2018-07-10. Retrieved 2021-11-29. <a href="https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/5%3A_Structure_and_Function_of_Plasma_Membranes/5.2%3A_Passive_Transport/5.2A%3A_The_Role_of_Passive_Transport" target="_blank">https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/5%3A_Structure_and_Function_of_Plasma_Membranes/5.2%3A_Passive_Transport/5.2A%3A_The_Role_of_Passive_Transport</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Wagner, Peter D. (2015-01-01). "The physiological basis of pulmonary gas exchange: implications for clinical interpretation of arterial blood gases". European Respiratory Journal. 45 (1): 227–243. doi:10.1183/09031936.00039214. ISSN 0903-1936. PMID 25323225. S2CID 14808756. <a href="https://erj.ersjournals.com/content/45/1/227" target="_blank">https://erj.ersjournals.com/content/45/1/227</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"5.2 Passive Transport - Biology 2e | OpenStax". openstax.org. Retrieved 2021-11-29. <a href="https://openstax.org/books/biology-2e/pages/5-2-passive-transport" target="_blank">https://openstax.org/books/biology-2e/pages/5-2-passive-transport</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Chen, Lihong; Tuo, Biguang; Dong, Hui (2016-01-14). "Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters". Nutrients. 8 (1): 43. doi:10.3390/nu8010043. ISSN 2072-6643. PMC 4728656. PMID 26784222. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728656" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728656</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> </ol>