Solute Translocations
Lelio G. Colombetti in Biological Transport of Radiotracers, 2020
The consequences of placing an impermeable solute on only one side of a semipermeable membrane extend beyond those described above. Water will move from the side without added solute (where the chemical activity of water is high) to the side containing the impermeable molecule (where the activity of water is low). In a completely open system, this process — called osmosis — results in dilution of the solute. In a system where the solute-containing compartment is closed, the process results in a pressure in the closed compartment. The osmotic pressure is defined practically as the pressure on the compartment containing the impermeable molecule required to prevent the flow of water. It is the semipermeable nature of biological membranes which results in the osmotic activity of cells. As the osmotic pressure depends on the concentration of the dissolved solute (and not on its chemical nature), the pressure can be maintained or modified by molecules as diverse as proteins, amino acids, and inorganic ions.
The abdomen
Peter Kopelman, Dame Jane Dacre in Handbook of Clinical Skills, 2019
Although no glandular secretion occurs in the small and large intestines, there is a rapid exchange of water and electrolytes across parts of the mucosa. Water moves in response to osmotic gradients, a hypertonic solution being rapidly diluted by the movement of water from blood to lumen, and a hypotonic solution being rapidly concentrated by the absorption of water. Sodium is actively absorbed in both the small and large intestine, while potassium is absorbed by the small intestine but secreted by the large intestine. In normal circumstances, albumin leaks into the gut lumen in various secretions such as saliva, gastric juice, succus entericus and bile. The exuded albumin is digested and the nitrogen subsequently absorbed as amino acids. This intestinal loss accounts for approximately 10% of the total albumin catabolism in the normal subject.
The microcirculation and solute exchange
Neil Herring, David J. Paterson in Levick's Introduction to Cardiovascular Physiology, 2018
In the previous account, there was no solvent flow across the membrane, so solute transport was purely diffusive. If there is also pressure-driven fluid filtration across the membrane, solute transport is partly by filtration and partly by diffusion, and we need a new membrane parameter to deal with this, namely the reflection coefficient, a (sigma). The reflection coefficient is the fraction of solute molecules reflected by the membrane during filtration at a high rate; it is an index of the difficulty a solute experiences in passing through a pore, relative to water. When a small solute (radius a) is washed into a large pore (radius r), steric exclusion is negligible, so the solute passes through the pore as freely as water. Its reflection is zero (a = 0; Figure 10.7c) and the solute exerts no osmotic pressure across the membrane. At the other extreme, if the solute is wider than the pore (a > r), steric exclusion is total, so all the solute molecules are reflected (a = 1.0) and the ultrafiltrate contains no solute (Figure 10.7a). The solute exerts its full osmotic potential in these circumstances. In the intermediate state, where a/r is >0.1 but <1, the solute is partially excluded from the pore (Figure 10.6a), so a fraction is reflected (a is >0 but <1) and the ultrafiltrate has a reduced solute concentration, 1 - a (Figure 10.7b). The solution exerts a fraction of its osmotic pressure in these circumstances (Section 11.1).
Evaluation of antifungal activity, mechanisms of action and toxicological profile of the synthetic amide 2-chloro-N-phenylacetamide
Published in Drug and Chemical Toxicology, 2023
Elba dos Santos Ferreira, Laísa Vilar Cordeiro, Daniele de Figuerêdo Silva, Hermes Diniz Neto, Aleson Pereira de Sousa, Helivaldo Diógenes da Silva Souza, Petrônio Filgueiras de Athayde-Filho, Felipe Queiroga Sarmento Guerra, José Maria Barbosa-Filho, Abrahão Alves de Oliveira Filho, Edeltrudes de Oliveira Lima, Ricardo Dias de Castro
Cordeiro et al. (2020), also tested the protective potential of a synthetic amide against erythrocytes of the ABO system, and reported similar results. It was observed that the molecule presents moderate hemolysis and moderate protective effect in certain concentrations, despite variations in cell lysis according to blood group, this makes it necessary to increase the concentrations used for the effect to be potentiated. Low osmotic pressure in the extracellular medium causes erythrocytes to absorb water to achieve osmotic equilibrium, and in extreme conditions, hypotonic hemolysis occurs when excess extracellular water causes significant swelling and disruption of the erythrocyte, which releases its intracellular contents. In hypotonic conditions, reducing erythrocyte membrane fluidity can reduce hemolysis (Zhang et al.2019).
Biomechanical response of lumbar intervertebral disc in daily sitting postures: a poroelastic finite element analysis
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Liang-dong Zheng, Yu-ting Cao, Yi-ting Yang, Meng-lei Xu, Hui-zi Zeng, Shi-jie Zhu, Antonio Candito, Yuhang Chen, Rui Zhu, Li-ming Cheng
There were some simplifications in the current study. First, no experimental data of the permeability parameters of ILM has been reported. Therefore, their material parameters were assumed to be the same as those of fibrous lamellae. Second, the muscle was not modelled in the established FE model. The spinal ligaments pretension was neglected, but the previous research showed that this simplification had little effect on predicted disc stress (Hortin and Bowden 2016). In studies where ligament stress is the primary output, the role of ligament pretension must be considered. Using CT taken at supine posture will affect the curvature of the model and the load in standing and upright sitting to some degree. However, the establishment of a single-segment model and the application of follower load could alleviate the influence. Applying simplified loads to define sitting postures may not be realistic enough, but the combination of follower load and rotation could achieve a certain degree of mechanical effect. Fixed pore pressure to simulate osmotic pressure was another limitation. Although this approach has been successfully adopted in previous studies (Schmidt et al. 2010; Galbusera et al. 2011; Fan et al. 2018), a more realistic description of osmotic pressure is still necessary. A model describing the osmotic potential with a three-phase fully coupled approach is needed in further study. Above simplifications were involved, but to a certain extent, the validation tests illustrated the accuracy of established FE model.
Piperine fast disintegrating tablets comprising sustained-release matrix pellets with enhanced bioavailability: formulation, in vitro and in vivo evaluation
Published in Pharmaceutical Development and Technology, 2020
Yuan Zhu, Jianyin Yu, Guanghui Zhou, Zhengqing Gu, Michael Adu-Frimpong, Wenwen Deng, Jiangnan Yu, Ximing Xu
To date, a variety of novel industrialized techniques (pro-drugs, inclusion complex, co-crystals and osmotic pump) are available to improve the solubility and dissolution of poorly water-soluble drugs (Rao et al. 2009; Yadav et al. 2009; Nechipadappu et al. 2017; Feng et al. 2018). Owing to its ability to transform drugs from crystalline to the amorphous state or the molecular form, solid dispersion stands out as one of the most effective strategies (Mohammadi et al. 2014). The major methods for the preparation of solid dispersions are the fusion and solvent methods which are easy to perform (Eloy and Marchetti 2014). Although the solubility of lipophilic drugs can be significantly enhanced by solid dispersion, some clinical challenges such flexible dosage regimen, initial burst reaction and fluctuating plasma concentration of drug usually ensue (Madhuri et al. 2007). Therefore, researchers have developed various approaches such as coated pellets and matrix pellets to control the release and prolong the half-life of some drugs (Hu et al. 2006; Zhang et al. 2010). The multi-particulate system (pellets) with sustained-release effects has attracted much attention due to less irritation of the gastro-intestinal tract and a lowered risk of side effects attributable to dose dumping (Muley et al. 2016). Compared with the coated pellets, matrix pellets can be prepared simply and conveniently with better reproducibility (Hamdani et al. 2002).
Related Knowledge Centers
- Diffusion
- Osmotic Pressure
- Polysaccharide
- Protein
- Semipermeable Membrane
- Solution
- Colligative Properties
- Biological Membrane
- Chemical Polarity
- Ion