Atoms, Elements and Compounds
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
The word atom is derived from an idea first formulated by the ancient Greek philosopher Democritus over 2,000 years ago. Democritus believed that everything was made from indivisible, imperishable and unchanging particles which he called atamos. A remarkable and insightful deduction for someone with no modern scientific equipment at his disposal. Today, atoms are often described as the smallest unit of matter that can exist in a stable form. They are made up of a number of smaller subatomic (literally ‘below’ or ‘less than’ atomic) particles that behave in a much more unpredictable fashion. However, for the purposes of this book, we are only interested in three of these particles: protons, neutrons and electrons. Each atom has a central core called a nucleus which contains varying numbers of protons and neutrons. The nucleus is surrounded by one or more energy layers called a shell which contains the electrons (Figure 1.1). Protons are positively charged particles, neutrons have no charge (they are neutral) and electrons are negatively charged. This is important since, under ‘normal’ circumstances, the number of protons in the atom’s nucleus is equal to the number of electrons in the atom’s outer shell (or shells). This ensures that the atom remains electrically neutral since the positive charge of the proton is cancelled out by the negative charge of the electron. It doesn’t matter how many neutrons there are in the nucleus of the atom (in terms of electrical charge) since they are always neutral.
Radiation Dosimetry
Kwan Hoong Ng, Ngie Min Ung, Robin Hill in Problems and Solutions in Medical Physics, 2023
An ionisation chamber operates based on the principle of measuring the number of ion pairs produced in a volume of air due to radiation. In the simplest arrangement, the ionisation chamber exists as two-electrode plates spaced apart in air. A large potential (100–400 V) is applied to the plates. Radiation dose is delivered by charged particles in excitation and ionisation events. Charged particles are either the radiation of interest themselves (e.g., electron and proton radiotherapy) or indirectly produced by non-charged radiation (e.g., photons and neutrons). When charged particles traverse between the plates, they ionise the air producing free negative electrons and positive ions. The positive- and negative-charged particles are then swept by the electric field between the plates towards the appropriate electrodes, producing a steady current flow in the external circuit, which can be measured by an electrometer. The important premise of an ionisation chamber is that each interaction of the charged particle produces exactly one ion pair and therefore allows for accurate quantification of dose.
Commercial Production of Radioisotopes for Nuclear Medicine
Garimella V. S. Rayudu, Lelio G. Colombetti in Radiotracers for Medical Applications, 2019
Neutrons, being uncharged, behave in a different manner from charged particles. They interact very weakly with atomic electrons through the magnetic moments of the two particles. Thus, the neutron loses energy as it travels through the target almost entirely due to collision with nuclei. A neutron whose kinetic energy is comparable to the thermal agitation energy of the nuclei in the target (thermal neutron) will be as likely to gain energy from a scattering collision as it is to lose it and will therefore continue to diffuse through the target until it is eventually captured through a nuclear reaction. For this reason, thermal neutrons do not have a “range” in the stopping medium (sample). Except for the case of self-shielding, all the nuclei of a sample will be irradiated with the same neutron flux (assuming that the reactor flux is uniform at the irradiation position). In self-shielding, sample nuclei have high reaction cross-sections so that neutrons are absorbed sufficiently to cause a variation in flux as a function of depth within the sample.
Development and in vitro characterization of chitosan-coated polymeric nanoparticles for oral delivery and sustained release of the immunosuppressant drug mycophenolate mofetil
Published in Drug Development and Industrial Pharmacy, 2019
Munawar Mohammed, Holly Mansell, Ahmed Shoker, Kishor M. Wasan, Ellen K. Wasan
The mucoadhesive potential of CS-PNPs was assessed by measuring zeta potential changes upon addition of a mucin solution [35]. Zeta potential is a measurement of the electrical potential difference between the surface of the particle and the bulk phase in which it is suspended. Therefore, it represents indirectly the available charge for binding or repelling oppositely or similarly charged particles, respectively. Likewise, if a particle with a given zeta potential binds another material, such as protein, the surface charge of the particles in suspension would be expected to change. Briefly, 300 µg of CS-PNP were added to mucin (porcine gastric mucus type-II, 5 mg/ml), incubated for 1 h at 37 °C and diluted 100-fold in deionized water before analyzing zeta potential at ambient temperature (23 °C). The zeta potentials of mucin alone and of the CS-PNPs in water without mucin were also measured, serving as controls.
Nanostructured lipid carriers for enhanced in vitro and in vivo schistosomicidal activity of praziquantel: effect of charge
Published in Drug Development and Industrial Pharmacy, 2021
Abdelrahman R. Said, Hager S. Zoghroban, Mona F. Arafa, Soheir S. Mahmoud, Gamal M. El Maghraby
NLCs were able to encapsulate PZQ with high encapsulation and loading efficiencies. The loading capacity depended on the charge with the presence of charging agent replacing some of the entrapped drug. The prepared NLCs retained the drug and showed very slow release pattern. NLCs are promising carriers for oral delivery of PZQ and the delivering efficiency depended on the surface charge of NLCs. Positively charged particles are better than the corresponding negatively charged NLCs. Positively charged particles enhanced both in vitro schistosomicidal activity and improved the pharmacological response of PZQ after oral administration. The in vitro and in vivo activity did not correlate with the recorded slow release pattern suggesting possible invasion of NLCs to the worm surface in vitro and absorption of intact particles in vivo.
The Impact of a Ketogenic Dietary Intervention on the Quality of Life of Stage II and III Cancer Patients: A Randomized Controlled Trial in the Caribbean
Published in Nutrition and Cancer, 2021
Eden Augustus, Isabella Granderson, Kern D. Rocke
The use of extensive surgeries to remove malignant areas from late stage cancer patients is common. However, surgeries are associated with risks including pain, suppressed immunity related to the body’s response to anesthesia, and blood clotting (8,9). Chemotherapy, which is classified as a commonly available cancer treatment, encompasses the use of drugs that work throughout the body (10). It denotes the nonspecific usage of intracellular poisons, which is used to inhibit mitosis (cell division) and excludes more selective agents that block extracellular signals (signal transduction). However, similar to surgeries, there are many side effects associated with chemotherapy, which includes fatigue, overall pain of the body, nausea, vomiting, diarrhea, and blood disorders among others (10). Radiation, yet another traditional treatment, utilizes high-energy to decrease the size of tumors and destroy cancer cells. Examples includes gamma rays and charged particles. Commonly reported side effects include acute skin reddening, loss of hair in initial treatment area, chronic swelling, and rare bone fractures (7).
Related Knowledge Centers
- Atom
- Ionization
- Molecule
- Oxygen
- Solvation
- Salt
- Dissociation
- Dianion
- Zwitterion
- Adenosine Triphosphate