Blood–Brain Barrier and Cerebrospinal Fluid (CSF)
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The blood–brain barrier is formed by the capillaries in the brain and prevents the free diffusion of circulating substances into the brain interstitial space. Capillary endothelial cells have the following distinct features: tight junctions (zona occludens) between adjacent cells, absence of fenestrations and a high content of mitochondria. The concentrations of calcium, magnesium and chloride ions in Cerebrospinal Fluid (CSF) are controlled by active transport mechanisms at the blood–brain barrier. Magnesium and chloride ions are present in higher concentrations in CSF than in plasma, suggesting transport of these ions across the blood–brain barrier by both passive and active mechanisms. CSF is formed in the brain by a combination of ultrafiltration and active secretion and circulates through the subarachnoid space and the ventricular system. As the choroid plexus epithelium is relatively impermeable because of the presence of apical tight junctions, ultrafiltration and secretion are important for the transport of selected constituents of the CSF.
Pulsatile Flow
Uri Dinnar in Cardiovascular Fluid Dynamics, 2019
The intermittent action of the heart and aortic valve, results in a highly pulsatile flow that enters the blood circulation system at the root of the aorta. The highly pulsatile nature of the flow that exists in the larger arteries is gradually changing with the branching and tapering of the arterial tree toward the capillary bed. As the venous flow gets closer to the heart, the suction effect of the right atrium is creating a pulsatile pressure gradient, and hence, a pulsatile flow. The mechanism that determines flow, except vessel impedance, is the pressure gradient. The assumption of onedimensional flow must still be included, and the solution is obtained by integration of the characteristics. In the capillaries the flow is steady, and on the route toward the heart the flow in the veins becomes pulsatile again, because of the pumping action of the heart and because of pressure variations in the thoracic cavity due to respiration.
Physical properties of the body fluids and the cell membrane
Ronald L. Fournier in Basic Transport Phenomena in Biomedical Engineering, 2017
This chapter discusses the physical properties of the fluids found in the human body. It focuses on the types and characteristics of the fluids that reside within the body. The body fluids can be classified into three types: extracellular , intracellular , and transcellular fluids. The lymphatic system is an accessory flow or circulatory system in the body that drains excess fluid from the interstitial spaces and returns it to the blood. The chapter looks at that the interstitial fluid composition is very similar to that of plasma. The retention of proteins by the walls of the capillary during filtration of the plasma is readily explained by comparing the molecular sizes of typical plasma protein molecules to the size of the pores within the capillary wall. Retention of proteins in the plasma in comparison to the interstitial fluid creates an osmotic pressure between the plasma and the interstitial fluid.
Multiple Wall In-folds Sub-divide Single Segments During Capillary Regression in Hyperoxic Acute Lung Injury
Published in Ultrastructural Pathology, 2014
Rosemary C. Jones, Diane E. Capen
The present study provides further insight into the structural processes that remodel pulmonary capillaries in the injured adult lung. Early in hyperoxia acute lung injury (HALI), many sub-dividing segments are present throughout the capillary network before segment occlusion and loss predominate and capillary density decreases later in the period. A second segment sub-division triggered in regenerating capillaries after air breathing (post-HALI) demonstrates a similar mechanism of organization at a time of contrasting change in the capillary density. As we have previously reported, the process of segment sub-division includes in-folding of the endothelial-epithelial surface (alveolar–capillary membrane) to form inter-luminal structures (ILSs) and loops, with loop separation increasing segment number. Unexpectedly, the findings support remodeling of the capillary density by wall in-folding in acute lung injury, demonstrating a similar mechanism in capillary regression as well as in regeneration in the adult lung.
Managment of Superficial Infantile Capillary Hemangiomas with Topical Timolol Maleate Solution
Published in Seminars in Ophthalmology, 2015
Syed Ali Raza Rizvi, Faraz Yusuf, Rajeev Sharma, Syed Wajahat Ali Rizvi
Capillary hemangioma is the most common benign tumor of eyelids and orbit in children. Recently, a topical beta blocker has been reported as an effective treatment for superficial capillary hemangiomas. We present a case report of two children having large capillary hemangiomas who responded well to topical treatment by 0.5% timolol maleate solution. After 12 months of treatment, the lesion has significantly reduced in size, thickness, and color in both cases. Thus, we conclude that long-term use of topical 0.5% timolol maleate solution is safe and effective in treating superficial capillary hemangiomas.
Carbon dioxide alters the Hoffmann reflex independent of hydrogen ions
Published in International Journal of Neuroscience, 2014
The purpose of this study was to examine the effect of changes in capillary blood pH on the resting soleus Hoffmann (H) reflex in the intact human. H-max size, H-wave at 20% of H-max, M-max and H-reflex latency were recorded in 10 subjects (apparently healthy, ages 19–36) before and after exposure to 3 hours of NaHCO3, CaCO3, NH4Cl (all at 0.3 g/kg) or 10 minutes 7% Carbon dioxide (CO2) administration. NaHCO3 increased capillary blood pH, CaCO3 did not change capillary blood pH, and NH4Cl and 7% CO2 decreased capillary blood pH. H-max and H-wave at 20% of M-max size were significantly decreased with no change in M-max, and H-reflex latency significantly increased during 7% CO2 administration only. No other changes in H-maximum size or H-reflex latency in response to dry chemical administration were observed. Seven percent CO2 administration reduces the size and increases the latency of the H-maximum size as previously found, but other chemicals which alter capillary blood pH do not. CO2 modulates afferent nerve function, and does so, it appears, independent of changes in capillary blood pH.