Renal System: Anatomy and Histology - Research Paper Example

Renal system: Anatomy and Histology Introduction The renal system also referred to as the urinary or the excretory system is used to remove the waste materials that are formed within the body in form of a liquid waste product (Field, Pollock, Harris & Britton, 2010). The renal system therefore refers to the group of organs that are functionally combined to for m a system that is used to produce, to store and then to release urine out of the body (Mirzaii-Dizgah & Salmanyan, 2013). The whole system comprises of several organs which are well interconnected and coordinated within the body, so that they communicate through the whole process of converting wastes into a liquid substance which is eventually released from the body. The renal system is arranged in a systematic order depending on what function the organ plays within the system. Thus, the renal system comprises of the kidneys, the ureters, the bladder and the urethra, all combined and connected so that the function starts from one organ and is then directly connected to the other organ which continues the process until the whole formation of the urine as the waste product is formed and eventually excreted from the body (Drexel, et al., 2014). Nevertheless, while the excretion of the urine from the body is the major function of the renal system, the renal system also plays other vital functions in the body, most especially the maintenance of the balance and homeostasis of water, blood pressure, minerals such as calcium and ions, PH and blood pressure (Kornakova, 2010). The maintenance of homeostasis by the renal system comprises of the control of how such substances are excreted from the body, to ensure that the body is not deprived of important functional components or congested with excessive retaining of such components. Therefore, this discussion seeks to analyze the renal system, with a view to establishing its histology, anatomy and functionality. Renal system Anatomy The renal system comprises of four main organs, namely the kidney, ureters, bladder and the urethra (Drexel, et al., 2014). Kidneys Anatomy of the kidneys First, the renal system comprises of the kidney. The kidney refers to two bean-shaped organs that form a pair, which are embedded on the walls of the abdominal cavity along the posterior wall (O'Callaghan, 2009). However, the positioning of the kidneys is different, with the left kidney being positioned slightly higher compared to the right kidney. This is because, the liver, which occupies the space above the kidney has the right hand side bigger than the left side, thus pushing the right kidney slightly lower (O'Callaghan, 2009). Contrary to all the other body organs which are positioned on the interior of the peritoneum, the kidneys are located on the posterior side of the peritoneum, making them touch the muscles of the back directly. Therefore, being exteriorly exposed, the kidneys are easily exposed to damage, and thus they are surrounded by a layer of adipose tissue, which helps to hold the kidneys in place and to protect them from being damaged (Baeumler, Haszprunar, & Ruthensteiner, 2012). The major function of the kidneys is to filter the wastes, excess ions and also chemicals from the blood, and form the wastes filtered into urine. Kidneys are especially concerned with two major ion components; sodium and chlorine, which are the essential elements that the kidney filters from the blood and combines them with water to form urine, which is eventually excreted out of the body (Kornakova, 2010). Additionally, kidneys regulate the amount of water within the body, through ensuring that when there is excessive water within the body, the water is filtered and excreted through urine, while also ensuring to retain as much water as possible when the body has little water or is dehydrated. In addition to the excretory function of the kidneys, they are also responsible for the production of certain hormones, which are essential for regulating certain functions within the body. The kidneys produce hormone rennin which is very essential for the regulation of blood pressure within the body (Mirzaii-Dizgah & Salmanyan, 2013). The kidneys also produce erythropoietin, which is a protein component that is essential for producing the red blood cells (Field, Pollock, Harris & Britton, 2010). Kidneys have a reddish brown color, taking the shape of a bean and being 2.5 cm thick, while their length is approximately 10 centimeters and their width approximately 5 centimeters (Field, Pollock, Harris & Britton, 2010). The kidney has opening on the side with the small curve which is called Hilum, where the blood vessels, the ureters and the nerves enters the kidney to connect it with the rest of the body system (Baeumler, Haszprunar, & Ruthensteiner, 2012). When the ureters enters the kidney, they form an open ended funnels-shaped structure, where the water, chemicals and other ions that are filtered by the kidney from the blood collects as urine, and are then transported to the bladder. The kidney comprises of muscular tissues within, which helps to push the collected urine down the ureter (O'Callaghan, 2009). Histology of the kidneys The histology of the kidneys mainly comprises of the glands, which are highly modified to comprise of other secretory units as well as other specialized ducts (Field, Pollock, Harris & Britton, 2010). The secretory units consists of secretory epithelial cells, which are combined together to form acini, which are the units responsible for draining the urine into branching units of the surrounding ducts that are responsible for collecting the urine and talking it to the ureters (Deshmukh & Wong, 2009). Kidneys can mainly be divided into two major parts namely the cortex and the medulla. The cortex is the outer red-brown part of the kidney, which is made up of corpulscles and nephrons, as well asa system of curvy and straight collecting tubules that are supplied by the blood vessels, to act as the collecting units for the waste products produced (Mirzaii-Dizgah & Salmanyan, 2013).The renal tubules combined forms the filtering unit of the kidney referred to as the nephrons. The nephrons located on the outer part of the kidneys are the kidney components that are responsible for the filtering. In turn, each unit of the nephrons comprises of a ball of small blood vessels that are referred o as the glomeruli (Kornakova, 2010). The glomeruli empty the blood plasma filtrate into the Bowman's space from where the process of re-absorption of the essential blood elements continues. On the other hand, the inner part of the kidney, referred to as the medulla comprises the continuation of a series of highly specialized nephrons. The medulla is supplied by a network of small vessels known as the vasa recta, these networked vessels connects to the renal arteries which supplies the kidney and branches to form many units that surround all the parts of the kidneys (O'Callaghan, 2009). The renal veins are the ones responsible for draining the kidney, through taking away the reabsorbed blood elements back into the blood. The straight segments of the tubules are known as loops of Henle, while the curvy ones are known as the convoluted tubules (O'Callaghan, 2009). Each of these highly modified tubules plays the role of reabsorbing different components of the blood which are not considered wastes back into the body. The Kidney corpuscle comprises of highly specialized unit of acinus, responsible for secreting the filtrate plasma into the associated renal tubules. After the secreted filtrate reaches the renal tubules, the tubules reabsorbs back every component of the blood plasma that is not waste back into the blood, leaving only a fluid of water, ions and any other chemical or cellular waste, forming the urine (Deshmukh & Wong, 2009). The renal tubules in turn comprises of the highly striated ducts, which are the actual unit of the tubules that reabsorbs the nutrients and the blood cells back. Therefore, the first step of kidney filtering entails the filtering of essential blood components at the nephrons, and then allowing the rest of the semi-blood fluid which is a precursor of the urine to pass through the ball of the small blood vessels. Here, the semi-blood fluid is now filtered further, with the small tubules then reabsorbing water, salts and nutrients back into the body, and leaving the rest of the urine component to pass forward for excretion (Baeumler, Haszprunar, & Ruthensteiner, 2012). Ureters Anatomy of the Ureters Ureters are a pair of the tubules that carries the urine that has been formed in the kidneys from the kidneys to the bladder for storage and subsequent excretion from the body (Drexel, et al., 2014). The ureters are aligned along the vertebral column running both on the left and the right side of the body for each of the tubules. The ureters comprises of thin but long tubules, which are approximately 12 inches long (Drexel, et al., 2014). The ureters are formed of smooth tissue muscles. It is the smooth tissue muscle on the walls of the ureters as well as gravity forces and the peristalsis that pushes the urine down the ureter towards the urinary bladder (Kornakova, 2010). The smooth muscles in the ureters continuously contracts and relaxes, giving the force that is accompanied by the force of gravity and the peristalsis to push the urine down to the bladder. If urine is allowed to stand still within the ureters, or if it is allowed to flow back into the ureters from the bladder, there are high chances of developing a kidney infection (Drexel, et al., 2014). Therefore, ureters extend slightly into the inside of the bladder. Histology of the ureters The ureters consist of the endings that extend through to the inside of the bladder. The ends that enter the bladder are then sealed by the ureterovesical valves at the point of entry into the balder. It is these valves that ensure that once urine has entered into the bladder from the ureters, the urine cannot flow back through the ureters into the kidney. To ensure that there is no accumulation of urine within the ureters, the process of emptying the ureters into the bladder occurs every 10 t0 15seconds (Deshmukh & Wong, 2009). The upper end of the ureter forms the renal pelvis, where the urine filtered inside the kidney is collected, and then allowed to run down the ureters towards the bladder (Kornakova, 2010). The renal pelvis forms a cup shaped funnel that catches the urine as it is being filtered from the blood plasma, and then drains it directly into the ureter. The renal cavity consists of numerous openings referred to as the ducts, each of which drains a specific nephron off the filtered urine components. The ureters are formed of a thick fibroelastic mucosa that is found underneath the epithelium of the ureters, which acts as the protective measure against the damage of the ureters (O'Callaghan, 2009). The fibroelastic mucosa is also where the connective tissue, the lymphatics, the blood vessels and the nerves are connected to the ureter system (Mirzaii-Dizgah & Salmanyan, 2013). The smooth muscles aligning along the ureters are both circularly and longitudinally developed, a combination of forces which helps the folds of mucosa to protect against the reflex of the urine, once the bladder is full (Deshmukh & Wong, 2009). Bladder Anatomy of the bladder The bladder is a sac-like hollow membrane structure that is used for the storage of urine from the ureters, before the urine is finally excreted from the body (Kornakova, 2010). The bladder holds urine as it is being formed from the kidney, and at the appropriate signal, the bladder releases the urine through the urethra so that the urine can leave the body (Drexel, et al., 2014). The bladder is located at the tail end of the ureters and along the midline of the body, just below the pelvis. The bladder consists of elastic walls, and urine from the ureters enters slowly into the bladder every 10 to 15 seconds, until the bladder is full, when the reflex action for the emptying of the bladder is developed (Field, Pollock, Harris & Britton, 2010). The walls of the bladder can keep on expanding until the bladder has held between 600 to 800 millimeters of urine, when the bladder is unable to contain any more of the urine. The bladder has two openings on the upper side and one opening on the lower side. The two openings on the lower side forms the points of entry of the two ureters that brings in the urine from the kidney for storage in the bladder, while the single opening on the lower side is used as the exit point for emptying the urine through connecting to the urethra (Baeumler, Haszprunar, & Ruthensteiner, 2012). Histology of the bladder The bladder consists of a series of smooth muscles, and the main muscle that is applied for pushing the urine stored in the bladder out through the urethra is called the detrusor muscle (Field, Pollock, Harris & Britton, 2010). The muscles on the lower end of the bladder that connects the bladder to the urethra is formed in a ring-like shape, which is used to control the movement of the urine out of the body (Mirzaii-Dizgah & Salmanyan, 2013). The bladder is also connected to the nervous system in the brain and the spinal cord through a series of receptors and nerve endings that are connected through the wall of the bladder. When the bladder is full and it is time to empty the bladder, the stretch receptors in the bladder are activated, which then sends a signal to the brain to the effect that the bladder is full (Kornakova, 2010). The brain initiates the process of relieving the urine, with the brain causing the reflex action that causes the detrusor muscle to contract while at the same time causing the ring-like muscle at the base of the bladder to relax, allowing the urine to flow (Field, Pollock, Harris & Britton, 2010). The bladder is also supplied by many blood vessels, which ensure the functioning of the bladder is efficient, through a supply of requisite oxygen that is essential for the proper functioning of the reflex action that works towards the initiation of the bladder emptying process. Urethra Anatomy of the Urethra The urethra is the tubal connection of the bladder and the exterior of the body, through which the urine is emptied from the bladder to the outside (Deshmukh & Wong, 2009). There is a difference in the length of the urethra between the female and the male, with the female only having a urethra that is approximately 2 centimeters long, while the male have a urethra length of approximately 8 to 10 centimeters (Drexel, et al., 2014). Additionally, the functions of the urethra vary with gender, with the urethra in females being only an organ of the renal system, since it is only used to excrete urine. In the males, the urethra doubles as a renal organ and also a reproductive organ, used to carry sperm out of the body to the pennies (O'Callaghan, 2009). Histology of the Urethra The urethra consists of the urethral sphincter muscles, which are found both internally and externally. The internal urethral sphincter muscle is comprised of smooth muscles, which opens involuntarily, when the bladder has extended to a certain level (Drexel, et al., 2014). This opening of these muscles is what causes the reflex action that creates the sensation to urinate. On the other hand, the external urethral muscles are comprised of skeletal muscles, which are capable of opening or closing at will, to allow urine to flow out (O'Callaghan, 2009). Thus, even after the sensation to urinate is formed by the opening of the inner smooth muscles, the outer skeletal muscles can still hold the urethra closed, until an individual is in a position to urinate (Deshmukh & Wong, 2009). References Baeumler, N., Haszprunar, G., & Ruthensteiner, B. (2012). Development of the excretory system: stages in metanephridial system development. Frontiers In Zoology, 9(1), 23-39. Deshmukh, S. R., & Wong, N. W. K. (2009). The renal system explained: An illustrated core text. Nottingham: Nottingham University Press. Drexel, T. et al. (2014). Renal denervation. Anatolian Journal Of Cardiology, 14(2), 186-191. Field, M. J., Pollock, C. A., Harris, D. C., & Britton, R. (2010). The renal system: Basic science and clinical conditions. Edinburgh: Churchill Livingstone. Kornakova, E. E. (2010). Ultrastructure of excretory system in Bothrioplana semperi (Platyhelminthes, Turbellaria). Journal Of Evolutionary Biochemistry & Physiology, 46(4), 407-413. Mirzaii-Dizgah, I., & Salmanyan, B. (2013). Renal function in a rat model of neurogenic bladder, effect of statins and phosphodiesterase-5 inhibitors. European Spine Journal, 22(12), 2766-2769. O'Callaghan, C. A. (2009). The renal system at a glance. Chichester, West Sussex: Wiley-Blackwell. Read More