Movement of substances across the cell membrane - Assignment Example

Movement of substances across the cell membrane a. Osmosis In any organism, there is a need for the transfer of substances across the different cells that make up the organism. One of the processes through which substances move across the cells in the organism is through osmosis, which is a process in which substances move across the cell membrane in the opposite direction from the concentration of the solutions in the cells (Sperelakis, 2001). The best definition of osmosis is that it is the cumulative process by which water moves across a cell membrane as a result of the differences in the concentrations of the solutions in the two sides of the cell membrane. The main characteristic of the cell membrane that allows for osmosis to occur is that the cell membrane is selectively permeable, meaning that it only allows water molecules to pass through and not the molecules of any other substance. This leads to the term semi-permeable membrane when the cell membrane is being referred to in biological terms. An analysis of the process of osmosis reveals that it is similar to simple diffusion, with the main difference being the presence of the semi permeable membrane that only allows the passage of water through to the different concentrations (Sperelakis, 2001). Before the process is explained, it is important to note that the water in the cells will always move from the side with a low solute concentration to the area with a high solute concentration. Logically, it should be noted that as the concentration of the solute increase, so does the concentration of the solution, and across different cells, this causes an imbalance and equilibrium must be restored. Osmosis then occurs to move the water molecules from the highly concentrated side (with low solvent content) to the lower concentrated side (with high solvent content) until the two sides are equally concentrated. Biologically, the side with a high solvent concentration is called the hypertonic solution, the side with the low solute concentration is called the hypotonic solution and equilibrium solutions are called isotonic solutions. In the hypertonic and hypotonic solutions, more water molecules repeatedly strike the cell membrane from the side with a high solute concentration, meaning that more water molecules will be forced to pass through the pores of the semi-permeable membrane (Sperelakis, 2001). As a result of this, the water molecules move from the side with high water concentration to the side with a low water concentration until the two sides are equally concentrated. The final solution is called an isotonic solution. Looking at the cell membrane itself, it can be seen that its composition allows for the selective movement of only certain substances. The osmotic pressure in the different cells ensures that the process of osmosis is continued until all the cells in the organism are of equal concentrations. As already mentioned, the semi permeability of the cell membrane allows only for the passage of certain particles, and in the case of the organism, it only allows for the passage of water molecules. This means that the process of osmosis is used to equalize the concentration of solutions in the body cells and their environment. b. Phagocytosis One of the other process by which cell movement is achieved is through phagocytosis, which is the process by which cells engulf foreign particles and ingest them by virtue of their power of amoeboid movement (Sperelakis, 2001). The movement due to phagocytosis is two way, from the point at which the cell moves towards the invading organism to the point when the organism is engulfed into the cell. In most organisms, this process was used for nutrition, but higher organisms have developed it to be used for other functions like fighting disease in the body. In the process, the cell is attracted towards the microbe that needs to be ingested through a process of chemotaxia, which means that the microbe is identified through a chemical signature that attracts the cell. This process is called activation of the phagocyte, where the phagocyte increases its metabolic activity in response to the activation. Through positive chemotaxia, the phagocyte then moves towards the increased concentration that caused the attraction, after which the phagocyte attaches itself to the attractant. After the attraction process, the cells then engulf the organism through a process of polarization and depolarization, which is basically done by sending out pseudopods to engulf the foreign organism. Once this is passed, the cell then forms a vacuole that keeps the organism either for ingestion or discarding. 2. Component parts of the Synovial Joint In medical terms, a synovial joint is also referred to as freely moving joints and make up most of the parts of the appendicular skeleton (Tortora and Derickson, 2012). The synovial joints in the body are the ones that enable free movement since they can move in almost any direction in the skeleton. The main components of the synovial joint are the ones that help the joint perform the functions that it is supposed to perform. The parts of the synovial joints in the body are divided into bones and the other components parts like the cartilage and fluid that enables lubrication and movement. The first bones in synovial joints are the articulating bones that form the joint itself. In every synovial joint, there are usually at least two bones that make up the articulating parts, and they are used to ensure that the joint remains firm. In other synovial joints, there exists a periosteum that is used to cover the outer surface of the synovial joint (Tortora and Derickson, 2012). The periosteum is usually a white fibrous membrane that serves to protect the outer surface of the articulating bones that make up the synovial joint. Apart from the periosteum that serves to protect the articulating bones, another important bone in the synovial joint is the articular cartilage, which is basically a hyaline cartilage that supports and protects the articulating bones in the joint. The articular cartilage in the synovial joint is usually coated with synovial fluid, meaning that its main function is to reduce friction in the joint during movement. As the movement in the joint increases, which also increases the pressure on the joint, the spongy articular cartilage absorbs more water from the fluid, which serves to increase the lubricating fluid in the lubricating fluid. One of the other main functions of the articular cartilage in the synovial joint is absorption of shocks that occur as movement is effected in the joint. The other part of the synovial joint is the articular or fibrous capsule that is formed from dense connective tissue in the bone (Tortora and Derickson, 2012). This capsule is attached to the periosteum in the synovial joint, and the flexibility of the fibrous capsule helps in movement in the joint. The other function of the articular capsule is for increasing the tensile strength of the bone, which helps in ensuring that the muscle is not dislocated. This is mainly done through the function of the collagen fibers in the capsule. The synovial cavity of the synovial joint contains two main components, which are the synovial membrane and synovial fluid. The synovial membrane is made of connective tissue that includes elastin fiber and adipose tissue that helps in the secretion of synovial fluid to the membrane. The synovial fluid is also an important part of the synovial joint, since it helps in the many functions of the membrane (Tortora and Derickson, 2012). The functions of the synovial fluid include lubrication and reduction of friction in the membrane, supply of nutrients to the components of the membrane, removal of metabolic waste, and phagocytic process that help in removal damaged cells in the joint. 3. Structure of joints a. Synovial Joint There are three main classes of joints in the human body as indicated by their function and designation in the body. One of these joints is the synovial joints, whose structure ensures that it is freely movable in the skeleton (Ellis and Mahadevan, 2010). The basic structure of the synovial joint is the presence of two or more articulating bones on either side of a synovial cavity filled with synovial fluid that helps in lubrication of the joint. The articulating bones on the synovial joint are usually covered by the periosteum in the parts where the bone is not covered by the articular cartilage. The articular capsule is also a part of the synovial joint that covers the synovial cavity. Between the two articulating bones is the synovial cavity that contains the synovial fluid and is covered by the articular cartilage to reduce friction and absorb shocks that result from movement. The synovial fluid helps in the lubrication of the whole joint. b. Cartilaginous joint The second structural classification of joints is cartilaginous joints, which are different from synovial joints in that they are slightly movable or allow little or no movement, as opposed to synovial joints that are freely movable (Ellis and Mahadevan, 2010). The use of cartilage tissue that holds the bones of the joints together ensure that the bones are immovable. The two types of cartilage used to hold cartilaginous together are the either the hyaline cartilage or the fibro-cartilage, both of which perform the same function. The two types of cartilages define the type of cartilaginous joint that is present in the skeleton, for example, a joint with a hyaline cartilage forms a synchondrosis joint, as opposed to symphysis joint formed from a fibro-cartilage. In the fibro-cartilage, the bones are attached together through a layer called a disc of fibro-cartilage. c. Fibrous joint The last structural class of joints in the body is fibrous joints, which, from definition are immovable joints and are usually present in the skull or other places that require immovable joints (Ellis and Mahadevan, 2010). The three main examples of fibrous joints are the sutures in the skull, the syndesmoses between long bones and gomphoses in the human jaw. Fibrous joints are made up of fibrous connective tissue that connects the bones in the skeleton. The structure of the fibrous joint is defined by the type of fibrous joint, which is usually divided into three main parts. The first fibrous joint is a suture, which is an immovable joint made up of a thin layer of fibrous tissue that attaches the bone to the skull. These bones are usually strong as a result of interlocking cranial bones that make up the joint. The second type of fibrous joints is syndesmoses, which are usually found at the articulation of the fibula and tibia. The third and last type of fibrous joints is the gomphoses, which are in the shape of sockets. In these sockets, solid bones in the body are attached to other solid bones through fibrous joints. Reference Ellis, H and Mahadevan, V 2010. Clinical Anatomy. New York, Wiley-Blackwell. Sperelakis, N 2001. Cell Physiology Source Book. Boston, Academic Press. Tortora, G and Derickson, B. 2012. Principles of Anatomy and Physiology. Boston, Wiley and Sons. Read More