Comparative Anatomy and Physiology of the Mammalian Eye
David W. Hobson in Dermal and Ocular Toxicology, 2020
The vascular system of the retina varies greatly between species (Table 6). In those animals possessing retinal blood vessels, the arterial supply enters as either a central retinal vessel (human, primate) or via the short posterior ciliary arteries which give rise to the cilioretinal arteries.3 The number of larger arterioles and venules varies with the species, but all large vessels are contained in the nerve fiber layer. The arterioles are, in general, internal to the venules and are surrounded by a very large capillary-free zone.4 The smaller vessels extend deeper into the retina and the capillaries can extend as far as the middle limiting membrane. All structures external to this, the photoreceptor cell bodies, inner and outer segments, and the RPE are supplied by the choroid via the choriocapillaris.4 The capillaries have a single layer of endothelial cells surrounded by a basement membrane and an interrupted layer of pericytes which are, in turn, surrounded by their own basement membrane.4 The capillary endothelial cells are attached to each other by terminal bars and are, like the RPE, part of the blood-retinal barrier.
Microcirculation
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
There are an estimated 25,000 million capillaries in the body, and they perform the essential cardiovascular system function of nutrient and metabolite exchange between blood and tissues. Normally, 6% of the total blood volume is in the systemic capillaries and 3% in the pulmonary capillaries. Capillaries are thin-walled vessels made up of tubes of endothelial cells lying on a basement membrane. The capillary wall has channels connecting the inside and outside of the vessel. (Note: This is not present in the brain where endothelial cells of the blood–brain barrier are joined by tight junctions.) There are narrow intercellular clefts between adjacent endothelial cells, and also there are fused-vesicle channels formed by amalgamation of some of the many endocytotic and exocytotic vesicles present. Fluids and solutes move across the capillary wall by diffusion, by filtration and by pinocytotic transport of vesicles (carrier-mediated transport is also important in the capillaries of the brain). Capillary wall permeability varies between tissues (high in the liver, low in the brain) and is higher at the venous than at the arterial end of the vessel.
Muscle Fiber Types
Charles Paul Lambert in Physiology and Nutrition for Amateur Wrestling, 2020
Capillaries are the small vessels in between arterioles and venules (i.e., in between the arterial side of the body and venous side of the body). Capillaries are the blood delivery apparatus of the circulatory system. They deliver blood and remove metabolic by-products from the muscle. With training, the number of capillaries per muscle fiber goes up. Clearly, this is a good thing from both a metabolic by-product removal perspective and from a nutrient and oxygen delivery perspective. This means that the greater number of capillaries the greater perfusion of the muscle tissue in question. This results in better oxygen and nutrient delivery and the removal of hydrogen ions and lactic acid. This means that from the middle of the muscle fiber to the capillaries, the distance is decreased which allows for oxygen and nutrient delivery and the removal of metabolic by-products, to occur faster. This is a good thing for a wrestler as this means his physiology has improved. Interestingly, strength training with heavy weights without any other type of training will actually decrease capillary density relative to muscle fiber size as the distance from capillary to the middle of the muscle cell will become greater. This makes it more difficult to deliver oxygen-rich blood and nutrients (glucose, fatty acids, amino acids) and remove metabolic waste products (hydrogen ions and lactic acid) (Hudlicka 2011).
Nanonization techniques to overcome poor water-solubility with drugs
Published in Expert Opinion on Drug Discovery, 2020
Flávia Lidiane Oliveira Da Silva, Maria Betânia De Freitas Marques, Kelly Cristina Kato, Guilherme Carneiro
Therefore, the size limit is usually established in function of the proposed application or to avoid capillary obstruction. In the organism, the smallest blood vessels are the lung capillaries with diameter in the range of 2–13 µm, which is the constraint limit for the particles to avoid clogging. Thus, particles with diameter >10 μm remain retained; microparticles with a size of 3–6 μm may be caught in lung capillaries, but eventually are released into the systemic circulation, and nanoparticles (<3 μm) escape pulmonary retention [50,51]. Other limits can also be considered if the nanoparticles are utilized for specific features. For instance, in tumor applications, the fenestrations found in the vasculature are in the range of 200–600 nm and thus nanoparticles should be within or below this range in order to efficiently accumulate in the tumor [52]. These particulate nanomaterials should have the ability to overcome the cell barriers and deliver the drug into the cell. In fact, non-phagocytic eukaryotic cells can internalize particles with size <1 µm [53,54].
Evolutionary life history theory as an organising framework for cohort studies: insights from the Cebu Longitudinal Health and Nutrition Survey
Published in Annals of Human Biology, 2020
Christopher W. Kuzawa, Linda Adair, Sonny A. Bechayda, Judith Rafaelita B. Borja, Delia B. Carba, Paulita L. Duazo, Dan T. A. Eisenberg, Alexander V. Georgiev, Lee T. Gettler, Nanette R. Lee, Elizabeth A. Quinn, Stacy Rosenbaum, Julienne N. Rutherford, Calen P. Ryan, Thomas W. McDade
The scaling of an organism’s energy expenditure on body size, as reflected in the classic “three-quarter” scaling of a species’ energy expenditure on body mass (Kleiber 1932), provides a useful starting point for considering the factors that constrain the evolution of life histories. One model to explain this regularity, proposed by West et al. (1999), posits that an organism’s metabolic expenditure is limited by its ability to distribute resources. Animal circulatory systems are organised to deliver blood, enriched with oxygen, energy and other nutrients, from a single, large vessel (the aorta) to capillaries that service individual cells throughout the body. West and colleagues note that the strategy for distributing resources within a given mass that minimises hydrodynamic resistance within the system is a fractal network in which large vessels branch into smaller vessels, with nested vascular branching continuing until individual cells are reached. The authors show that such a fractal distribution network leads to 0.75 scaling of energy expenditure on mass, irrespective of the size of the organism or system (West et al. 2002), thus, potentially helping explain metabolic scaling from first principles of physics.
Kinetic studies on oxygen releasing of HBOC and red blood cells as fluids and factors affecting the process
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Baojuan Zhao, Shengkang Zhang, Zhengyan Meng, Dan Wang, Qian Li, Yan Guo, Fengjuan Li, Xiang Wang, Chengmin Yang
As can be seen from oxygen-releasing curves of Hb in different concentrations of PHY in Figure 4, in the absence of PHY, pO2 of oxygen releasing of Hb plummeted in the range of 160–70 mm Hg firstly and about 200 s was needed. Then, pO2 decreased gradually from 70 mm Hg to the bottom of 20 mm Hg and about 1300 s was consumed. And both segments of the oxygen-releasing curves of Hb in the presence of PHY showed linear in the range of 160–40 and 40–20 mm Hg. It was indicated from oxygen-releasing rate curves in Figure 5 that the oxygen-releasing rate for each sample in different concentration of PHY was comparable when pO2 was >40 mm Hg. This was in accordance with the oxygen-releasing course of artery and arteriole in the human body. However, the oxygen-releasing rate for each sample improved as the concentration of PHY increased when pO2 was <40 mm Hg. It was corresponding to the oxygen-releasing process of capillaries in the human body.