Calcium in the diet of a teenager is actively absorbed in the small intestine and transferred into the intestinal capillaries. Describe the route this calcium would follow to end up in the upper arm. Describe in detail the role of calcium at the neuromuscular junction as well as its role in the mechanism of muscle contraction and relaxation of the triceps. Considering the function of calcium in bone growth, explain in detail how the humerus would grow in length.
Calcium in the diet of a teenager is absorbed in the small intestine and transferred to the intestinal capillaries. It diffuses into the bloodstream through the gastric vein into the hepatic vein and then through the common iliac vein into the superior/inferior vena cava that brings the blood into the right atrium of the heart. The sinoatrial node which is located in the right atrial wall, would send an electrical impulse through the heart, causing it to contract. This would then trigger the AV node (which is located between the septum between two atria) to contract as well. When the AV node contracts it sends an impulse through the AV bundle and into the purkinje fibers (which in return causes the entire heart to contract). After going through the right atrium, when the heart contracts it opens up the tricuspid valve, therefore pushing the calcium into the right ventricle.
When the heart contracts again (SA node contracts again through AV bundle and purkinje fibers) it causes the pulmonary semilunar valve to open and enters the pulmonary trunk and pulmonary arteries which then brings the blood into the lungs. Then it goes through a systemic loop (the tissue capillaries of the lungs) , which takes the now oxygenated blood and returns to the heart via the pulmonary veins from the lungs. Then from the pulmonary veins the blood enters the left atrium (SA node will contract, causing AV node to contract, sending impulse through the AV bundle, ending at the purkinje fibers) and calcium forces through the bicuspid valve, and into the left ventricle. Then the heart contracts, and (SA node/AV node/AV bundle/purkinje fibers) causing contraction and blood travels through the aortic valve and then into the aorta. From the aorta, the calcium in the blood goes into the right and left subclavian artery and branches down to the axillary artery, and then towards the brachial artery. From the brachial
artery, the oxygenated blood containing calcium in it, goes to the muscles of the upper arm (the brachii muscles) and gives nutrients to the tissue cells.
Calcium plays an important role in muscle contraction. Firstly, an action potential arriving at the acon triggers the release of the neurotransmitter called acetylcholine (ACH) at the neuromuscular junction. The acetylcholine (ACH) binds with the muscle receptor and sodium ions (Na+) are released, which triggers the action potential in the muscle cell. The action potential transmits through the sarcolemma. The calcium (Ca+) ions are then released from the sarcoplasmic reticulum. The calcium ions bind with troponin (making it change shape) which makes the troponin release tropomyosin. The myosin then binds to the actin. With the hydrolysis of ATP the myosin head changes shape and a cross-bridge is formed causing the muscle cell to contract. This cycle repeats itself until the contraction is done, or when there is nor more calcium or ATP energy. Once the triceps muscle is relaxed then the calcium gets back into the sarcoplasmic reticulum.
During relaxation of muscle cells, the level of calcium in sarcoplasm is low and the troponin holds the tropomyosin in position to block myosin-binding sites on actin. During contraction of the muscle cells, a muscle action potential opens calcium channels in the sarcoplasmic reticulum and the calcium flows into the cytosol.
The growth of bones can happen through two different types of ossification which include: intramembranous ossification and endochondral ossification. The process for the growth of a long bone like the humerus, the process of endochondral ossification is used. This takes place on the epiphyseal plate (made from remaining hyaline cartilage) in the metaphysis area of the bone. There are four zones on the epiphyseal plate: a) the resting zone which contains the chondrocytes, b) the zone of proliferation where the chondrocytes divide and push the resting cartilage outwards, c) the zone of hypertrophic cartilage where the chondrocytes enlarge and lengthen the diaphysis, d) Zone of calcification- where dead chondrocytes and new one matrix is created. At the end of the growth period, the epiphyseal plates are completely ossified and the epiphyseal plates close around the age from 18-25. The epiphyseal plates then become the epiphyseal lines. The calcium is a necessary dietary requirement for proper bone growth, development in the body, and to prevent bone deterioration or an example of a disease called osteoporosis.