BMS206 Final Exam Q1 - The Physiological Concept of Flow Down Gradient PDF

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BMS206 Final Examination 1. Explain the physiological concept of flow down gradient and illustrate your understanding by presenting three examples from at least two different body systems. In your answer include the terms gradient and resistance The physiological concept of flow down gradient is one of the principal concepts in the physiology world. Flow down gradient is defined as the movement of a substance going from one location to another location in the system, it also can be called “concentration gradient”, since it is the concentration difference between two locations. Substances can be molecules, cells, ions, or even chime or blood that is going on in the human body. It is important to also note that the larger the flow of gradient is, the more significant the difference in energy is, creating a higher flow gradient which entails that substances flow from an area of high concentration to an area of lower concentration. In this essay, three different examples will be presented to illustrate the physiological concept of flow down gradient from skeletal muscles, cardiovascular system, and respiratory system. It is important to first understand the foundation of cellular gradient within cells. With cells being able to communicate with each other electrically, they can create electrical gradients across cell membranes, hence the flow down gradient. The sodium-potassium ATPase is used to move K+ ions inside the muscle cell while Na+ ions are outside, giving a small electrical charge but a huge concentration gradient since there is a lot of K + ions in the cell while there is a lot of Na+ ions outside the cell. K + ions and Na+ ions can create a resting membrane potential due to the negative charge left behind when entering or leaving the cell. Cells are polarized, meaning there is an electrical voltage across the cell membrane. In a resting cell, the voltage is negative and known as the resting membrane potential. This means the cell is more negative in the inside than the outside of the cell. This resting state will have concentration gradients of several ions across the cell membrane: there is more sodium and calcium outside the cell and more potassium inside the cell. These gradients are maintained by several pumps to bring sodium and calcium out and potassium in. While an action potential is a brief reversal of electric polarity of the cell membrane and is produced by voltage gated ion channels, they are regulated by membrane voltage and open and close at certain values of membrane potential. When membrane voltage increases, it becomes more positive and the cell becomes less polarized, known as depolarization. But when the membrane potential becomes more negative, the cell is repolarized. For an action potential to be generated, the membrane voltage must be depolarized to the threshold. Excitation-contraction coupling in the skeletal muscle has the physiological concept of flow down gradient. Excitation is when the nervous system stimulates action potential in the muscle fibres sarcolemma. Skeletal muscles must contract to function, meaning it will get shorter, and when a muscle gets shorter, the skeleton that the joint crosses moves. The events that link these two phases together is known as excitation contraction coupling. Firstly, a wave of action potential will spread across the motor end plate from various directions. When the action potential wave, also can be called the wave of excitation reaches to the transverse “T” tubules, it continues down the sarcoplasm of the muscle fibre. Secondly, when reached to the sarcoplasm, the action potential stimulates the opening of the voltage-gated Na+ and K+ ion channels in the Ttubules. These channels are linked to Ca2+ channels in the terminal cisternae of the sarcoplasmic

reticulum. Due to the wave of action potential, Ca 2+ channels open and since Ca2+ ions are higher in concentration in the sarcoplasmic reticulum than in the sarcoplasm, it causes them to diffuse out and into the cytosol from an area of high concentration to low concentration. Lastly, the Ca2+ ions will then bind to the troponin of the sarcomere’s thin filaments. This binding causes the troponin tropomyosin complex to change shape and move into the actin. This exposes active sites on the actin filament, and the active sites are now available for binding to myosin heads, which are the main protein for thick filaments. Heart: maintains pressure; from high pressure to low pressure. Maintaining pressure gradient by generating high hydrostatic pressure to pump blood out of the heart while creating low pressure to bring it back in. Blood pressure: the amount of strain arteries feels as the heart moves the blood around. Fluids like to move from areas of high pressure to low pressure. The heart is divided laterally into two sides by a thin inner partition called the septum. There are 4 chambers, two superior atria which are the lower pressure areas and two interior ventricles which produced the high pressures. Each chamber has its corresponding valve which halts blood from backflow. When a valve opens, blood flows from one direction into the next chamber. Atria is the receiving chambers back to the heart after circulating through the body, the ventricles are the discharging chambers that push the blood back out of the heart. The heart’s lub sound is made by the mitral and tricuspid valves closing and they do that because the ventricles contract to build up pressure and pump blood out of the heart. The high pressure caused by the ventricular contraction is called systole. The “dub” sound is from the aortic and pulmonary semilunar valves closing at the start of diastole. This is when the ventricles relax to receive the next volume of blood from the atria. When the valves close, the high-pressure blood that is leaving the heart tries to rush back in but runs into the valves. The smaller the diameter of the blood vessel, the harder it is for blood to move through it. Respiratory system: When breathing in, the diaphragm contracts and pulling itself flat, and the external intercostal muscles between the ribs contract. They lift the ribs up and out, causing the chest cavity to expand. This creates the pressure inside the lungs lower than the air outside of the body, since fluids like gases travel from high pressure to low pressure, the lungs fill up with outside air. The diaphragm then relaxes, and the weight of the ribs settles in, the pressure inside the lungs because higher than the outside air and the air rushes out. Molecules also diffuse from areas of high concentration to areas of low concentration. Pulmonary ventilation is the movement of air into and out of the lungs, which can lead to lung compliance or airway resistance. Airway resistance is a property that change gas flow in the lungs. When resistance is decreased, the flow increases and vice versa. The bronchiole smooth muscle is responsible for contracting and relaxing. When it contracts, it restricts the bronchi and if it relaxes, it dilates the bronchi. Sympathetic and parasympathetic nervous system relates to the constriction and dilation, when SNS releases NE, it triggers a dilation of the bronchioles and more air to come in. Parasympathetic NS, releasing acetylcholine into different types of muscarinic receptors and will trigger constriction on the bronchiole. When dilating, the bronchi will increase while when constricting, the bronchi will decrease. Decrease in diameter will increase the friction and increase the resistance, while flow decreases. Certain cases such as people will asthma or allergies can trigger a powerful constriction on the bronchiole smooth muscles, creating a high resistance and blocking gas flow....