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A patient is admitted to the ward with dehydration as shown by their low urinary output dry mouth and dry skin which has poor elasticity. Describe how homeostasis is normally maintained, regarding fluid balance, within the body and how giving oral fluid to this patient can correct this imbalance.
According to Watson’s anatomy and physiology for nurses, the notion of homeostasis is fundamental in determining good health and physiology (Watson, 2018). The word ‘homeostasis’ stems from a Greek expression meaning ‘staying the same’. Throughout this assignment, I will be describing how nurses can maintain homeostasis with close regards to fluid balance. I will explain in detail my knowledge and understanding of the normal functioning of the urinary system, which will also include relevant issues and concepts around it. From there I will identify the relevant homeostatic mechanism’s and its associated anatomical and physiological components.
The urinary system is a group of organs within the body that’s key functions are filtering out substances and other excess fluid from the bloodstream (Marieb, 2009). The system consists of; two bean-shaped organs called the kidneys, which are located in the superior dorsal abdominal cavity, two tubes called ‘ureters’ that help carry the urine from each one of the kidneys to the urinary bladder located in the inferior ventral pelvic cavity and finally the urethra, a tube that runs from the bladder to the outside of the body, ranging in length depending on gender. For males, it can be as long as 20cm and for females, it can range from approximately 4.8cm to 5.1cm (Kohler et al, 2008). The main purpose of the urinary system is to control the body’s fluid and electrolyte balance and remove waste products in the form of urine.
There are three major regions of the kidney; the renal cortex, the renal medulla and renal pelvis (Watson, 2018). The renal cortex is made from the space between the outer capsule and the medulla. It is a rough tissue, and this is due to the presence of nephrons deeper within the renal pyramids of the medulla, that help the kidneys perform their main function. The cortex provides space for arterioles and venules from the renal artery and veins, as well as space for glomerular capillaries to help perfuse the nephrons of the kidney (Watson, 2018).
The renal medulla contains a large number of nephrons and is the main functional component of the kidney that helps filter water, electrolytes and waste from the blood (Watson, 2018) It is located within the inner region of the ‘parenchyma’, the functional tissue of the organ. The medulla is made of up multiple pyramidal tissue masses, called the renal pyramids, which are triangular structures that contain a dense network of nephrons (Lumen, 2014).
The renal pelvis connects the kidneys with the nervous and circulatory systems from other parts of the body. It contains the hilum, a concave part of the kidney that allows blood vessels and nerves to exit and enter the body. It is also a point of exit for the ureters that help empty the waste fluid into the bladder (Mitchell and Stephenson, 2019). The kidneys are supplied with blood through arteries that branch off from the abdominal aorta. The supply of blood from the arteries can vary from person to person, which results in some people having one or more arterial supplies to each kidney (Mitchell and Stephenson, 2019).
The renal blood supply starts with renal arteries branching off from the abdominal aorta, each renal artery having their own name based on what region it enters the kidney (Watson, 2018). The renal arteries can carry up to a third of the total cardiac output, for the blood to be filtered by the kidneys. Which all ends by the blood exiting through the renal veins to enter the inferior vena cava (Gross Anatomy of the Kidney, 2018).
When the blood enters the kidneys through the renal artery they split up into several different segmental arteries, which then splits into several different arterioles that branch into the glomerular capillaries. These glomerular capillaries enable fluid to transfer to the nephrons within the Bowman’s capsule and help take blood away from the glomerulus into the interlobular capillaries to provide oxygen to the functional tissue of the kidney (Watson, 2018). The renal veins drain blood from the venules that come from the interlobular capillaries and connects them to the inferior vena cava (Watson, 2018).
Within the kidneys, the nephron is a functional component that helps regulate soluble and water substances in the blood through filtering, reabsorbing what it needs and excreting the rest as urine. The nephron is essential for maintaining homeostasis of blood volume, blood pressure and plasma osmolarity (Muthayya, 2010).
The glomerulus is a network of capillaries that receives its blood supply from a particular arteriole within the renal circulation system (Muthayya, 2010). It is here that solutes and fluids are filtered out of the blood and transferred into the interstitial space between the glomerulus and the surrounding membrane of the Bowman’s capsule (Muthayya, 2010).
The glomerulus is surrounded by the Bowman’s capsule. It is made up of visceral and parietal layers. Below the thickened glomerular basement membrane, the visceral layer lies (Jones, 2015). It only allows small molecules and fluid, like glucose and ions, to pass through to get into the nephron. Under normal circumstances, red blood cells and large proteins would not be able to pass through the glomerulus. However, in particular conditions, they may be able to pass through and cause blood and proteins to enter into the urine (Jones, 2015).
The renal corpuscle is made up of two parts, the glomerulus and the Bowman’s capsule. It’s from here where glomerular filtrate leaves the renal corpuscle and enter the renal tubule to undergo filtration, reabsorption and secretion. The renal tubule is made up of three parts, The Proximal Convoluted Tubule (PCT), the Loop of Henle and the Distal Convoluted Tubule and Collecting Duct.
Firstly, the proximal tubule is the first location of reabsorption, it is here where water reabsorbs back into the bloodstream and where a large amount of salt and water reabsorption takes place too. The water reabsorption takes place due to passive diffusion and active transport along the basolateral membrane (Grey, 2012). Water and glucose also follow sodium through the basolateral membrane by an osmotic gradient, which is a process called co-transport. Within the proximal convoluted tubule around 2/3rds of water and 100% of the glucose in the nephron is reabsorbed by co-transport (Grey, 2012).
Secondly, the loop of Henle is a U-shaped tube that consists of an ascending limb and a descending limb. (Grey, 2012) It allows fluid to transfer from the proximal to the distal tubule. The ascending limb of Henle’s loop is impermeable to water, but it can be highly permeable to ions, this causes a large drop in the osmolarity of fluid passing through the loop, going from 1200 mOSm/L to 100 mOSm/L. On the other hand, the descending limb is highly permeable to water and completely impermeable to ions, which causes a large amount of water to be reabsorbed, increasing the osmolarity to around 1200 mOSm/L (Grey, 2012).
Finally, the distal convoluted tubule and collecting duct is the final location of reabsorption within the nephron. Dissimilar to the other components of the nephron, the distal tubule is permeable to water and can vary depending on the hormone stimulus that enables the complex regulation of blood osmolarity, pressure, volume and pH (Grey, 2012). Usually, the distal convoluted tubule is permeable to ions and impermeable to water, which the osmolarity of fluid even lower. However, the anti-diuretic hormone, which is produced and released from the pituitary gland as a part of homeostasis, will work on the distal convoluted tubule to help increase its permeability of the tubule to increase its reabsorption of water (Mitchell and Stephenson, 2019). This reabsorption will result in an increase in blood pressure and volume. Other hormones will also be introduced to help stimulate other important changes within the distal convoluted tubule that work with other homeostatic functions of the kidney (Mitchell and Stephenson, 2019).
The collecting duct is quite similar to the function of the distal convoluted tubule and usually responds in the same way to hormones (William et al, 2014). On the other hand, however, it is different in terms of its histology. As the osmolarity of fluid through the distal convoluted tubule and collecting duct is highly changeable depending on the hormone stimulus (William et al, 2014). After passing through the collecting duct, the fluid is transferred into the ureter, where it leaves the kidney as urine. The urinary system works in sync with a number of different systems within the body to help maintain homeostasis. The kidneys are one of the main organs in the urinary system and the body that helps maintain the water/salt balance of the blood and acid-base balance (William et al, 2014).
Water makes up the greater part of all bodily cells and bodily fluids, with around 60% of humans body weight consisting of water (Louden, 2015). This is advised to be maintained, in order to keep a homeostatic environment within the body. Within the makeup of this water, 70% of it is intracellular, meaning it is inside the body cells and the other 30% is extracellular, located in the body fluids; 10-15% forms the in the blood and the remaining 15-20% is in the interstitial spaces within the tissues (Louden, 2015), which bathes all the bodily cells. Each of these three forms of fluid is each separated by the cell walls, a thin semipermeable membrane and the capillary walls, which allows water to constantly pass through from one of these areas to another (Louden, 2015).
Water within our bodies is not static. Freshwater will be taken in by the body every day and passed out by a number of different ways. The total water taken in and passed out must balance one another in order to maintain equilibrium within the body (Louden, 2015). On average a healthy person will intake around 1.5 L water and other fluids every day, as well as over 1 L of food. This is balanced by the body passing out around 400-500 mL of water vapour through the lungs, 500-600 mL by the skin through sweat, 1000-1500 mL as urine and a small amount of 100-150 mL passed out by faeces (Louden, 2015).
When fluid volume decreases within our body, the concentration of sodium in the blood will increase, due to increased osmolarity, which will eventually stimulate the hypothalamus (Tortora and Grabowski, 2002). The hypothalamus is an osmoreceptor, which is a sensory end organ that reacts to the changes in osmotic pressure, which in turn has an effect of the pituitary gland (Mitchell and Stephenson, 2019). The pituitary gland reacts by producing an antidiuretic hormone called ‘Vasopressin’ also known as ADH, into the bloodstream, causing the kidneys to start retaining water. This will result in the urine becoming more concentrated and an increase in water being returned to the extracellular fluid (ECF), therefore correcting the volume depletion (Tortora and Grabowski, 2002)
Electrolyte balance is also essential in maintaining fluid balance. It is the correct concentration of different ions within the body, usually magnesium, sodium and potassium (Butterworth et al, 2013). If there is too little or too much of these electrolytes this can cause a number of different problems, such as cardiac arrhythmias. The normal magnesium level should be around 0.6-1.0mg/dl; the normal serum sodium level should be around 135-145mg/dl and the normal potassium level should be around 3.5-4.5mg/dl within a patient (Butterworth et al, 2013).
In our case the patient will need either oral rehydration or electrolyte and fluid replacement therapy, which will involve adult nurses being responsible for delivering and monitoring certain Intravenous (IV) fluids such as saline 0.9% solution or Hartmann’s solution. These would be the main recommended fluids as they remain in the ECF for longer and they match blood tonicity, which is the measurement of effective osmotic pressure gradient (Docherty and McIntyre, 2012). Issues like pulmonary oedema and hypotension can be created when using other colloid solutions as they move more easily into the intracellular fluid, making them less effective.
Other issues that nurses should consider while they look after patient with fluid balance problems would include: the accurate monitoring and measurement of IV fluids over a 24-hour period, which also requires them to include correct documentation and prescription of fluids and what type of fluids they are being given (Mitchell and Stephenson, 2019). They have to look after the correct measurement of oral input and urine output; also, being aware of the patient’s electrolyte levels and the correct administration of elements that they are prescribed with (Mitchell and Stephenson, 2019).
To conclude, this essay has demonstrated knowledge and understanding of the specific chosen scenario of the renal system, in specific relation to ‘fluid balance’. It has started off by describing how the chosen system functions and what issues and concepts that can come from it. The relevant homeostatic mechanism has been outlined, linking in with what relevant observations and treatment that can be done to aid in keeping the body in equilibrium.
I feel that homeostasis is of the utmost importance when it comes to the human body. Without it the body would simply not be able to function and would become more vulnerable to certain conditions and diseases.
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