Examples of diffusion in the following topics:
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- Absorption of nutrients occurs partially by diffusion through the wall of the small intestine.
- Digested nutrients pass into the blood vessels in the wall of the intestine through a process of diffusion.
- Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions: iron is absorbed in the duodenum; vitamin B12 and bile salts are absorbed in the terminal ileum; water and lipids are absorbed by passive diffusion throughout the small intestine; sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport; and fructose is absorbed by facilitated diffusion.
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- Capillary fluid movement occurs as a result of diffusion (colloid osmotic pressure), transcytosis, and filtration.
- Bulk flow is one of three mechanisms that facilitate capillary exchange, along with diffusion and transcytosis.
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- After carbon dioxide travels through the bloodstream to the capillaries covering the alveoli of the lungs through any of the 3 methods listed above, it must return to dissolved carbon dioxide form in order to diffuse across the capillary into the alveolus.
- Dissolved carbon dioxide is already able to diffuse into the alveolus, while hemoglobin-bound carbon dioxide is unloaded into the plasma.
- Bicarbonate ions dissolved in the plasma enter the red blood cells by diffusing across a chloride ion gradient (replacing chloride inside the cell), and combining with hydrogen to form carbonic acid.
- Next, the action of carbonic anhydrase breaks carbonic acid down into carbon dioxide in water, which leaves the cell by diffusion.
- The dissolved carbon dioxide is then able to diffuse into the alveolus.
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- It describes both the bulk flow of air into and out of the lungs and the transfer of oxygen and carbon dioxide into the bloodstream through diffusion.
- The walls of the alveolar membrane are thin and covered with a fluid, extra-cellular matrix that provides a surface for gas molecules in the air of the lungs to diffuse into, from which they can then diffuse into the capillaries.
- Oxygen has a partial pressure gradient of about 60 mmHg (100 mmHg in alveolar air and 40 mmHg in deoxygenated blood) and diffuses rapidly from the alveolar air into the capillary.
- Based on Henry's law, the greater solubility of carbon dioxide in blood compared to oxygen means that diffusion will still occur very rapidly despite the lower partial pressure gradient.
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- The core concept behind fetal circulation is that fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, which allows a diffusion of oxygen from the mother's circulatory system to the fetus.
- Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen.
- Oxygen then diffuses from the placenta to the chorionic villus, an alveolus-like structure, from which it is carried to the umbilical vein.
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- In the lungs, the relative concentration of gasses determines the rate at which each gas will diffuse across the alveolar membranes.
- These pressure differences explain why oxygen flows into the alveoli and why carbon dioxide flows out of the alveoli through passive diffusion (just as a similar process explains alveolar and arterial gas exchange).
- While inhaled air is similar to atmospheric air due to Dalton's law, exhaled air will have relative concentrations that are in between atmospheric and alveolar air due to the passive diffusion of gasses during gas exchange.
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- Oxygen diffuses into the cells of the tissues, while carbon dioxide diffuses out of the cells of the tissues and into the bloodstream.
- Each of those factors generally increase gas exchange as those factors are increased (i.e., more oxygen diffusion in tissues with more blood perfusion).
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- This allows bidirectional diffusion depending on osmotic gradients.
- Continuous - Endothelial cells provide an uninterrupted lining, only allowing small molecules like water and ions to diffuse through tight junctions.
- They allow small molecules and limited amounts of protein to diffuse.
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- The epidermis does not contain blood vessels; instead, cells in the deepest layers are nourished by diffusion from blood capillaries that are present in the upper layers of the dermis.
- Diffusion provides nourishment and waste removal from the cells of the dermis, as well as for the cells of the epidermis.
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- Dialysis treatments replace some of these functions through diffusion (waste removal) and ultrafiltration (fluid removal).
- Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane.
- Diffusion is a property of substances in water; substances in water tend to move from an area of high concentration to an area of low concentration.
- For another solute, bicarbonate, dialysis solution level is set at a slightly higher level than in normal blood, to encourage diffusion of bicarbonate into the blood, to act as a pH buffer to neutralize the metabolic acidosis that is often present in these patients.