Regulation of pH
1.1. Explain the pH in simple terms.
Felicetti (2019), states that pH is an abbreviation for potentiometric hydrogen ion concentration. This is a scale which represents whether a solution is acidic, neutral or alkaline. The more acidic a solution, the greater the hydrogen ion concentration would be. A pH of 7.0 indicates neutrality, a pH less than 7 indicates acidity and a pH of more than 7 indicates alkalinity. An acceptable pH level within the body is between 7.1 and 7.5 (Allen, 2017).
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A common use of acid in the body is gastric acid within the stomach. This consists mostly of hydrochloric acid combined with potassium chloride and sodium chloride. Its pH level is 1 to 2. When digested food enters the stomach, the acid begin to break down the protein structure and then its bonds. Antacid tablets can be used to neutralize excess stomach acid if it exceeds its natural pH levels (NHS 2016).
Once the human body contains too much acid problems can occur such as acidosis. This arises when the lungs and kidneys have difficulty keeping the balance of the bodies’ pH at a level. These organs can usually compensate with slight imbalances although, problems can proceed leading to excess acid collecting in the body. There are two types of acidosis, respiratory acidosis and metabolic acidosis which are characterised by different causes. Respiratory acidosis takes place when too much CO2 accumulates within the body. Ordinarily the lungs would remove CO2 while breathing. however, due to chronic airway conditions, injury to chest, sedative misuse or even a deformation with the chest structure the Body can find it difficult to remove adequate CO2 (Boskey, 2017).
1.2. Explain how the tubule cells of the kidney nephron collecting duct work to maintain the pH of the blood.
The distal convoluted tubule has a function of maintaining the pH of the blood. The cells of the tubule contains an enzyme called carbonic anhydrase. This merges water and carbon dioxide to create carbonic acid (H2CO3). The acid then splits inside the cell into hydrogen ions and hydrogen carbonate ions. Cells then pump the hydrogen ions into the lumen within the second tubule. Hydrogen phosphate ions (HPO42) in the lumen combines with hydrogen ions to form dihydrogen phosphate (H2PO4). When the hydrogen ion mixes, a sodium ion is released within the lumen and sodium dihydrogen phosphate (NaH2PO4) is created. This molecule is then eliminated in the urine, removing the hydrogen. The hydrogen carbonate ions (HCO3–) then moves from the tubule cells into the blood. This is where they encounter the sodium ions which were found in the lumen within the tubule (wiseGEEK, 2017). Bicarbonate will also form to counterbalance the metabolic acids.
A.C 6.3. Briefly describe the three main buffer systems found in the blood.
Three main buffer systems found within the blood are protein buffer systems, phosphate buffer system and the bicarbonate buffer system. The protein buffer system is a fundamental component of the pH controlling mechanism for blood Hydrogen (H+) ion homeostasis. Both intracellular and extracellular proteins have negative charges which serve as buffers for changes within hydrogen ion concentration.
The phosphate buffer system consists of two ions, hydrogen phosphate ions and dihydrogen phosphate ions. The pH level of the blood falls below 7.4 if the H+ ions in the blood increase. Hydrogen phosphate ions accept all added H+ ions to restore the stability between the hydroxide and hydrogen ions within the blood. When the pH level of the blood increases above 7.4 the dihydrogen phosphate ions deliver further hydrogen ions to restore the pH level of the blood to its foremost 7.
The bicarbonate buffer system is an acid-base homeostatic mechanism involving the balance of carbonic acid (H2CO3), bicarbonate ion (HCO−3), and carbon dioxide (CO2) in order to maintain pH in the blood and duodenum to support proper metabolic function. Produced by carbonic anhydrase, carbon dioxide (CO2) reacts with water (H2O) to form carbonic acid (H2CO3), which quickly dissociates to form a bicarbonate ion (HCO−3) and a hydrogen ion (H+).
The pH is balanced by the occurrence of a weak acid (for example, H2CO3) and its base (for example, HCO−3) so that any excess acid or base introduced to the system is neutralized (Physiol, 2010).
A.C 6.1. The respiratory centre in the medulla oblongata in the brain controls the blood pH by regulating breathing. Explain how the centre is stimulated by changes in blood CO2, and how it responds to those changes to help regulate blood pH.
According to normalbreathimg.com (2018) the respiratory centre located in the medulla oblongata regulates the concentration of H+ y controlling the rate and depth of respiration. Chemoreceptors within the body work by sending the pH of their environment through the concentration of hydrogen ions due to carbon dioxide eing converted to carbonic acid in the bloodstream. This making chemoreceptor able to use the bloods pH as a way of measure carbon dioxide levels of the blood. Main chemoreceptors used in the respiratory feedback are the central chemoreceptors which are located on the ventrolateral surface of the medulla and detects changes of the pH in the spinal fluid, another being peripheral chemoreceptors which includes the aortic body and carotid body. The aortic body detects changes within the bloods oxygen and carbon dioxide but not pH, whereas, the carotid body detects changes in all three. There are three main components in the respiratory feedback response. One being sensor, in this case the sensor would be the chemoreceptors detecting the changes in the bloods pH, the medulla and the pons from the integrated centre and the respiratory muscles as the effector.
Giving thought to a case in which a person is hyperventilating from anxiety. Their increased ventilation rate will remove too much carbon dioxide, leading to less carbonic acid within the blood. This meaning the concentration of hydrogen ions decreases allowing the pH of the blood to increase. In response to this the peripheral chemoreceptors detect these changes leading to the transport of signals to the respirator centre of the medulla. After receiving these messages more signals will be sent through the nerves to the respiratory muscles to decrease the ventilation rate so the carbon dioxide levels and pH can return to its normal levels. Three types of important respiratory nerves are the phrenic nerves which stimulate the activity of the diaphragm, the vagus nerve which encourages the diaphragm movement but also helps the larynx and pharynx and lastly the posterior thoracic nerves which enables the movement of the intercostal muscle located around the pleura. These types of nerves lead to signals of the escalating respiratory pathway from the spinal cord to stimulate the muscles that perform the needed movements for respiration (Lumen, 2017).
The Nervous System
A.C 5.1. Briefly describe the main functions of the nervous system.
The nervous system is formed by two parts, the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord whereas the peripheral nervous system contains the nerves which branches off from the spinal cord to all other parts of the body. The nervous system transmits signals between the brain and to the rest of the human body, this includes the internal organs. The functions of the nervous system is to process input form sensory receptors, transfer and interpret impulses and to control the bodily functions. The nerves within the nervous system are made up of specialised cells known as neurons.
The autonomic nervous system regulates many of the body’s processes which takes place without conscious effort. This nervous system controls a variety of internal processes including digestion, circulation, heart rate, body temperature, sexual response and metabolism.
A.C 5.2. Use diagrams and tables to explain the differences in structure between sensory, relay and motor neurons. The functions of each of the three types of neurons.
Overall functions of the neurone, position and function of the cell body, dendrite or dendron structure and function, axon structure and function.
Found in receptors such as eyes, ears, tongue and skin. They carry nerve impulses to the spinal cord and brain. When these nerve impulses reach the brain, they will be translated into sensations such as visions, hearing and taste. They have long dendrites and short axons (PsychologyHub 2018). The axons divide into two branches, the peripheral which extends from the soma into the receptor cells present on the peripheral sensory organs through the spinal nerve, and the central branch, this extends from the soma into the posterior horn of the spinal cord forming a synaptic junction (Ray, 2017).
Found in the visual system, the spinal cord and the brain. They receive messages from the sensory neurons and pass messages to either other interconnecting neurons or to motor neurons. They have short dendrites and short or long axons (PsychologyHub 2018).
Carry electrical impulses away from the brain and spinal cords central nervous system to the organs and muscles in the body. They have short dendrites and long axons (PsychologyHub 2018).
A.C 5.3. Describe the structure of the knee jerk reflex arc with the aid of a diagram.
The knee jerk reflex is also known as the patellar reflex. It is a sudden kicking movement of the lower leg showing a response of a sharp knock of the patella tendon. Pressure on the stimulus, in this case the ligament joining the patella to the tibia pulls the patella downwards. This downwards motion of the patella pulls on the tendon attached to the thigh muscle and stretches it. The stretch rector at the end of the sensory neuron is stimulated, and an impulse then travels up the sensory neuron to the spinal cord. Intermediate neurones will then be stimulated by chemical neurotransmitters from the sensory neuron. Intermediate neuron may stimulate neutrons running up the spinal cord to the brain, this will also stimulate the motor neuron leading to one of the thigh muscles rectus femoris. The motor neuron is stimulated by a chemical neurotransmitter from the intermediate neurone which sends impulses to the motor end plates attached to the rectus femoris. This encouraging the release of the neurotransmitter and stimulates the contraction of the rectus femoris. Contraction of this muscle will then pull on the patella which in turn pulls on the tibia. Meaning this motion will pull the lower leg in an upwards movement (Augustyn, 2019).
A.C 5.4. Write short notes with appropriate diagrams on the roles of the sodium/potassium pump and the sodium and potassium channels in creating resting and action potentials across the membrane.
According to Zeidan, (2017) the resting potential is the axon membrane paralysed. For example, electrically excitable neurons. It is negative on the inside about -70mV due to the being more positive sodium ions (Na+) and potassium ions (K+) on the outside of the membrane than the inside. This forming an electrochemical gradient between the outside and the inside of the membrane. Active transport by the sodium/potassium pump forces Na+ out of the axon and pulls K+ into the axon. This does not create a resting potential because K+ can also leak out. The membrane is considered to be excitable and ready to create an electrical impulse along the axon.
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Depolarisation is caused a stimulus reaching the neuron. This causes the Na+ channels to open in a patch of the axon membrane. Some Na+ moves into the axon which reduces the electrochemical to about -50mV. Then more Na+ that flows into the axon which changes polarity to +40Mv (Wong, 2009). The action potential is the depolarisation which creates a flow of electric currents in the membrane. This stimulates next to the membrane which opens up the next group of Na+ channels. Leading to the action potential moving down the axon (Yelle, 2009).
- Allen, S. (2017). Acidosis. Available at: https://www.healthline.com/health/acidosis. (Accessed: 1 March 2019).
- Augustyn, A. (2019). Knee-jerk reflex. Available at: https://www.britannica.com/science/knee-jerk-reflex (Accessed: 6 March 2019).
- Boskey, E. (2017). Acidosis. Available at: https://www.healthline.com/health/acidosis#causes. (Accessed: 2 March 2019).
- Felicetti, M. (2019). How to Balance Your Ph. Available at: https://www.mindbodygreen.com/0-6243/How-to-Balance-Your-pH-to-Heal-Your-Body.html. (Accessed: 1 March 2019).
- Lumen. (2017). Respiration control. Available at: https://courses.lumenlearning.com/boundless-ap/chapter/respiration-control/ (Accessed: 1 March 2019).
- NHS, (2016). Available at: https://www.nhs.uk/conditions/antacids/. (Accessed: 15 March 2019).
- Physiol, J. (2010). Hydrogen ion dynamics in human red blood cells. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3036193/ (Accessed: 2 March 2019).
- PsychologyHub. (2018). The structure and function of sensory, relay and motor neurons. Available at: https://psychologyhub.co.uk/the-structure-and-function-of-sensory-relay-and-motor-neurons/ (Accessed: 19 March 2019).
- Ray, A. (2017). Location, Structure, and Functions of Sensory Neurons with Diagrams. Available at: https://bodytomy.com/sensory-neurons-location-structure-function (Accessed: 19 March 2019).
- WiseGEEK. (2017). Roles of the tubule cells in the kidney. Available at: https://www.wisegeek.com/what-is-the-distal-convoluted-tubule.htm. (Accessed: 2 March 2019).
- Wong, E. (2009). Physiology of cardiac conduction and contractility. Available at: http://www.pathophys.org/physiology-of-cardiac-conduction-and-contractility/ (Accessed:19 March 2019).
- Yelle, D. (2009). Physiology of cardiac conduction and contractility. Available at: http://www.pathophys.org/physiology-of-cardiac-conduction-and-contractility/ (Accessed: 15 March 2019).
- Zeidan, A. (2017). Resting potential. Available at: https://www.britannica.com/science/resting-potential (Accessed: 2 March 2019).
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