General Physiology

• Negative feedback is a mechanism used by the body to maintain homeostasis by reversing any deviations from the set point.
• The main components of cells are the cell membrane, cytoplasm, and nucleus.
• The cell membrane, also known as the plasmalemma, is a lipoproteic molecular complex separating the cell from the extracellular environment.
• The main function of the cell membrane is to act as a barrier with selective and dynamic permeability, controlling the exchanges between the cell and the extracellular environment.
• The cell membrane has a structure known as the fluid lipoprotein mosaic model, with lipid components including phospholipids, cholesterol, and glycolipids, and protein components including peripheral proteins and integral proteins.
• Hemoglobin level is 4.6 g/dl, indicating anemia due to blood loss.
• Reticulocyte count is 0.1%, indicating bone marrow failure.
• Leukocyte count is 4000/mm3, indicating leukemia.
• Platelet count is 14,000/mm3, indicating thrombocytopenia.
• Membrane lipids have a structural and functional role, forming a phospholipid matrix composed of two monolayer membranes, each with a hydrophilic extremity towards the peripheral part of the membrane and a hydrophobic extremity towards the middle part of the membrane, creating a hydrophobic core which prevents free movement of substances.
• Cholesterol, on the inner part of the phospholipid matrix, provides flexibility and membrane stability, contributes to selective characteristics of cellular membrane, and is partly responsible for the permeability of the cell membrane.
• ATP hydrolysis products cause a change in myosin head conformation that results in the power stroke and generation of increased tension.
• The power stroke is the result of the release of myosin from actin filament.
• Rapid hydrolysis of ATP causes changes in myosin head conformation to return to high actin affinity state.
• Ca2+ ions are necessary for binding of myosin head to actin filament.
• Myosin head binding to actin filament allows muscle contraction.
• The power stroke is the result of the tilting of myosin head.
• Ca2+ ions are necessary for the power stroke.
• The cycle stops in relaxed living muscle due to removal of myoplasmic calcium.
• The cycle stops in absence of ATP (rigor mortis).
• ATP binds to myosin head, stimulating the release of myosin from actin filament.
• Ca2+ ions are necessary for the release of myosin from actin filament.
• Sickle cell anemia is a pathological hemoglobin due to the replacement of glutamic acid with valine in position 6 of β chain from hemoglobin A1.
• Affinity of hemoglobin for oxygen (HbO2) is the main form of oxygen transport in blood.
• MetHb is produced in large amounts in the presence of oxidant agents such as nitrites and drugs, leading to "blue disease" in neonates.
• Thalassemia is a pathological hemoglobin due to a disorder in the synthesis of α or β globin chains.
• Substitution or lack of one or more amino acids of globin chains can lead to a structural anomaly of hemoglobin, generating changes in erythrocytes morphology, properties, and functions.
• MetHb is an oxidation of ferric to ferrous iron (Fe3+ to Fe2+) continuously produced in a decreased amount due to the glutathione reducing system.
• Oxyhemoglobin formation is a reversible chemical reaction.
• Carboxyhemoglobin is a stable compound of hemoglobin with carbon dioxide (250 times more increased affinity for hemoglobin than oxygen).
• Glycolipids are part of the cellular layer called glycocalix or pericellular atmosphere, establishing contacts with structures from extracellular environment.
• The cell membrane is permeable for small liposoluble uncharged molecules such as respiratory gases (O2, CO2), fatty acids, glycerol, steroid hormones, urea, and ethanol, and is impermeable for water-soluble substances, large uncharged molecules (glucose, amino acids), and small charged molecules (ions).
• The cell membrane is the source of intracellular messengers such as Phosphatidyl inositol- 4,5 - biphosphate (PIP2) and Membrane C phospholipase.
• The cell membrane is also the source of extracellular messengers such as Prostacyclin (PGI2) and TxA2.
• Membrane proteins represent half of the membrane mass and are the active element which induces the membrane properties and specific functions.
• Diffusion is the transport of substances through a semipermeable membrane based on electrochemical gradient.
• Osmotic pressure (Posm) is the force opposing water passage (osmosis) through a semipermeable membrane, with Posm gradient determining the direction and size of water transfer.
• Chemical gradient in diffusion is from higher concentration (C1) to lower concentration (C2).
• Hydrostatic pressure (Ph) is the pressure exerted by a fluid column on the exchange surface.
• Simple diffusion is the transport of substances through a semipermeable membrane based on chemical gradient.