Role of Kidney in Osmoregulation

Role of Kidney in Osmoregulation Water is a vital molecule for the human body. Approximately 98% of the human body is made up of water. Human beings cannot survive if their water content decreases below 12%; hence the homeostasis of water is an important mechanism. Water has many important functions in our body. Water acts as a transport medium in blood and secretion e.g. in digestive juices, tears. Water is a good lubricant and acts to reduce friction when combined with particular proteins e.g. mucus to aid external movement. Many chemical reactions take place in an aqueous medium (Jones M.et al.2000) The kidneys are highly specialised organs of the body and play an important role in homeostasis. Fig 1a shows the location of the kidney in the human body.The kidney maintains homeostasis by regulating water balance, waste removal and blood composition and pressure. The kidneys dispose of waste by-products of metabolism and hence prevent the build up of toxic products in the body and to regulate the chemical components of the bodys fluids by responding to any imbalances of body fluids. These functions are fulfilled by a process of filtration of blood, which mainly includes the movement of solutes between the internal fluid and external environment. The movement of solutes is normally through a transport epithelium, in the case of the kidney it is in the form of a tubular channel; this tubular channel gives the kidney a large surface area. As Fig 1b shows blood enters each kidney via the renal artery and leaves via the renal vein. The kidneys weigh less than 1% of the human body, they receive approximately 2 % of blood pumped with each heartbeat. Urine exits the kidney through a duct called the ureter. The ureters of both kidneys drain into a common urinary bladder. Urine leaves the body from the urinary bladder to the urethra which empties near the vagina in females or through the penis in males. (Campbell N. A. et al. 1999, Michael F. et al. 2001) At one end the nephron forms a cup-shaped structure called glomerulus. From the glomerulus a tube runs towards the centre of the kidney first forming a twisted region called the proximal convoluted tubule and then a long hair-pin loop in the medulla, it runs back upwards into the cortex where it forms another twisted region called the distal convoluted tubule, this then joins a collecting duct which leads down the medulla and into the renal pelvis The functional unit of the kidney is a nephron. Microscopic sections of the kidney show that the kidney is made up of thousands of nephrons. Fig1b shows the location of a nephron and Fig2 shows the detailed structure of a nephron. Each renal capsule is supplied with blood by the afferent arteriole a branch of the renal artery this splits into many capillaries in the capsule which then rejoin to form the afferent arteriole. The nephrons structure is closely related to its function of regulating solutes Osmoregulation is maintaining constant levels of water in the body. Cells cannot survive a huge deviation from its osmolality. Hence, cells have a continuous movement of water across their plasma membranes. A net gain of water will cause the cell to swell up and burst, while a net loss of water will cause the cell to shrivel up and die. Water is transported by osmosis around the body. Osmoregulation is accomplished by creating an osmotic gradient; this requires lots of energy and is done by maintaining solute concentrations in the body fluids. The osmolality of the body is fixed at a mean of 290 ±5 mosmos/g. The kidney is able to maintain a constant osmolality as its able to adjust the rate of water excretion over a wide range. The volume of the extra-cellular fluid is mainly determined by the concentration of sodium ions, hence slight adjustments to the renal excretion rate have a major impact on the extracellular fluid volume. Changes in tubular sodium transport is accompanied by parallel movements of water, this results in no net change in body fluid osmolality  (Campbell N. A. et al. 1999, Frederic H.M. 2006, Michael F. et al. 2001) The loop of Henle creates a longitudinal osmotic gradient across the medulla; this aids the reabsorption of water and other important solutes. Ascending and descending limb are parallel and adjacent to each other with a layer of tissue fluid in between. Fluid enters from the proximal convoluted tubules flows down the descending limb and then up the ascending limb. This is known as a counter-current flow. Thewalls of the descending limb are permeable to water, while the walls of the ascending limb are impermeable to water. The ascending limb of the Loop of Henle is made up of a thick walled tubule which is impermeable to the outward movement of water but not salt. The red arrows on fig3 show the movement of water amd solutes along the loop of Henle and the collecting duct. Also, the walls of the ascending limb contain pumps to remove sodium chloride from the lumen and add it to the surrounding interstitial fluid. Hence sodium and chloride ions are actively transported out of the ascen ding limb. This is the site of reabsorption in the kidney, here fluid from theà ¢Ã¢â€š ¬Ã‚ ¦enters and the kidney reabsorbs all the useful solutes and water. The permeability of the loop and the collecting duct depends on the osmolality of the blood and is controlled by a negative feedback mechanism by osmoreceptors in the hypothalamus A high concentration of salt builds up in the medullary tissue, this together with urea retention by these tissues, helps build up a high osmotic pressure in the medullary tissue. This creates a gradient of 200 mosm/g across the tubular wall at any point and causes a loss of water from the descending limb. The loss of water concentrates sodium and chloride ions in the descending limb. Salt concentration in the medullary tissue is highest at the apex of the loop, the tissue in the deeper layers of the medulla contain a very concentrated solution of sodium ions, chloride ions and urea. The fluid leaving the ascending limb is hypo-osmolar as compared to the fluid that enters and has a osmolality of approximately 100 mosm/g .Sodium and chloride ions diffuse out in the lower part of the ascending limb. Fluid passes down the collecting duct through the medullary tissue of increasing salt concentration, water can pass out of it by osmosis. The reabsorbed water is carried away by blood capil laries  (Campbell N. A. et al. 1999, Frederic H.M. 2006, Michael F. et al. 2001) Control of water regulation Osmoregulation by the kidney involves a negative feedback mechanism. The osmoreceptors are in the hypothalamus and the effectors are the pituitary gland and the walls of the distal convoluted tubules. Osmoreceptors detect alterations of water levels and send impulses to the pituitary gland which then increase or decrease the production of antidiuretic hormone (ADH). In the case of a low osmolality,when the nerve cells are stimulated by osmoreceptors action potentials travel down them, this causes ADH to be released from their endings into the blood capillaries in the posterior pituitary gland from here it is distributed throughout the body. ADH acts on the plasma membranes of the cells of the collecting ducts. ADH is picked up by a receptor on the plasma membrane which then activates an enzyme. This causes vesicles with water permeable channels to fuse with the plasma membrane hence ADH makes the membrane more permeable to water than usual. Hence more water will be reabsorbed by the collecting duct and more concentrated urine will be produced. On the other hand, when the blood water content rises the osmoreceptors are no longer stimulated and hence do not lead to the secretion of ADH. Hence, ADH secretion slows down and the collecting duct cells become less permeable to water, so less water is reabsorbed and more diluted urine is produced  (Campbell N. A. et al. 1999, Frederic H.M. 2006, Michael F. et al. 2001) In conclusion, the regulation of water is essential for the survival of human beings and is carried out by the kidneys and monitored by osmoreceptors in the hypothalamus and controlled by the pituitary gland. Each of these plays an equally important role in the regulation of water and without any one of them the body will not be able to function in a normal manner. [Words: 1328]

Compare & Contrast: Homelessness is More Appealing

Many of us will never be homeless, and not everyone understands the benefit of having a wife, but after reading the essays’, Homeless (Quindlen, A. n. d. ) and I Want a Wife (Brady, J. 1971), one can gain a better understanding of both. I am a wife. Therefore, I can certainly connect with the narrator’s story of I Want a Wife. This is a narrative essay, in which the narrator reflects on why she too would like to have a wife after a visit with a recently divorced male friend, who is looking for a new wife.The narrator gives a list of duties and activities she will and will not do if she had a wife, and she can visualize the benefits a wife could afford her with less responsibilities and more time for school or friends. My other essay of choice is quite different in theme, but it is still relatable. Anne Quindlen’s essay, Homeless (n. d. ) is a short descriptive essay with the narrator retelling of an account when she met a woman, who she believes is homeless, at t he bus terminal. It is during the encounter that the narrator reflects on homeless people in general, the homeless individual and about herself.Both of these essays’ are well written, however, I feel that Homeless (Quindlen, A. n. d. ), is a more appealing essay than I Want a Wife (Brady, J. 1971), as it allows the reader to become more engaged in the descriptions and reflect on the details of the story. Whenever I first start reading any type of literature, the first thing I notice is the writing style of the author and the point of view (POV) of the narrator. Key elements of the writing style for me are POV, tone, pace, and conciseness when possible. The point of view is important to the reader as it may not be theirs.This should cause the reader to pay closer attention to details. How much credibility does the narrator offer. The tone of a story is set at the very beginning. The tone along with a good hook should grab the reader’s attention so they want to continue reading. For me, both essays Homeless and I Want a Wife captured my interest with the very first sentence. When the opening sentence of an essay starts with â€Å"I belong to that classification of people known as wives,† (I Want a Wife) that certainly can catch the attention of another wife. This opening drew me in because I wanted to know what she meant by this statement.The tone is set; wives are in a class of their own, and the narrator has my attention. Now, she will tell us from her point of view why she wants a wife, too. Homeless, is similar in that it also grabs the reader just by introducing a character, location, and time of year in its brief opening sentence. However, I do think that this opening is more appealing than I Want a Wife. The details the narrator gives the reader create a clear mental image of the scene. In addition, the second sentence reveals just enough to keep the reader interested in what the narrator has to say, â€Å"I was doing a story on home less people,† (Homeless, para 1).Again, the tone is set; it is January at the bus terminal where the narrator, who is doing research on homeless people, meets such a person, Ann. It is also in the first sentence we know it is the narrator’s story as she describes her experience and conversation with Ann. With the narrator sharing her experience and conversation with the reader, she has invited them into her story making it more personal. Another similarity between these two essays is the author’s use of appropriate language for the material, the audience, and the year of publication.I Want a Wife, written in 1971, was a period when the feminist movement was active. Women were looking for equality in the work place but also at home. The essay, published in the magazine Ms. , makes me believe the writer’s original target audience is that of other wives, future wives, and anyone else who reads Ms. Magazine. Her simple statements, or as I like to call it, her laundry list as to why it would be great if she had a wife, are easy to relate to as many of us perform these duties on a daily basis. In Homeless, the setting of the story, January at the bus terminal, leaves it to the reader’s imagination of the year.The topic of the essay, homeless people, is timeless as it is has been an ongoing problem for decades. The language the narrator uses is simplistic yet descriptively concise. It still gives enough detail to help you feel connected to what the narrator is saying. You can feel her emotions through her words. I believe her target audience is everyone. As the narrator states, â€Å"[We] walk around it when it is lying on the sidewalk or sitting in the bus terminal—the problem, that is. † She is playing upon the reader’s emotions by pointing out how many people ignore the problem even when we come face to face with it at times.I feel this essay can transcend time because of the specific descriptive words the aut hor uses to engage the reader. In addition, until homelessness becomes obsolete, this will be an issue society will continue to discuss. I do not believe the same can be said about I Want a Wife. Reading this essay now seems irrelevant in 2013, whereas in 1971, this was a reality for some wives. While I found both essays well written and share similar key elements in writing style and appropriate language, I found Homeless, to be a more appealing read.The topic of the essay, homeless people, is a current issue we continue to face in society today, which makes it more relatable to the reader. It causes the reader to use their imagination, critical thinking skills, and reflect on a somewhat sensitive topic. I think the topic of I want a Wife, is appropriate for the period it was written, but it does not really apply to today’s families. The structure of the family has changed dramatically in the last forty years. No longer is it the norm for the wife to be the one to shoulder a ll of the family responsibility.In more households than not, it is now a shared responsibility. Even though Judy Brady’s essay can cause the reader to reflect on how life was for wives during that era, it does not really fit our society today. Reading the essay now, it seems more of a farce than the feminist statement it was of 1971. Another appealing aspect of Homeless is the description and detail the narrator uses. She creates visual images with her words that capture and engage the reader. Some of the visual images that were memorable to me are the description of Ann, her photo, and the narrator’s own ferocity for the love of her own home.The narrator’s description of the grime that creases Ann’s bags and raincoat give you a clear picture of her appearance. The description of the yellow house in the photo, â€Å"with the aluminum siding and a chain-link fence, a narrow driveway running up to a one-car garage, and a patch of backyard,† (Homeless para 2) gives the reader a distinct image of the house. It is through these descriptions that I have a better understanding of both the characters and their perspective of homeless.I Want a Wife, while well written and entertaining, it did not appeal to my emotional side like Homeless. I felt as though the narrator was giving us her laundry list and doing so without any emotion. She does not invite the reader into the story, as the structure is very chaotic and unorganized. In addition, she often repeats herself throughout the essay, which makes it difficult to get a clear picture of any one thought as she moves quickly from one idea to the next. Each essay shares similar key elements of writing style and appropriate language.They both capture their targeted audience with creative introductions that pull the reader into the story. The authors’ use of simple statements and descriptions allow for easy reading and understanding of the topic, however I believe that Homeless was more successful in engaging the reader’s senses. Anna Quindlen used specific descriptions and details to bring the reader into her story. Her topic is one that everyone understands; as it is, still an issue society faces today. She appeals to our emotions and causes the reader to reflect on their own life and those affected by it.

The Merced River Is The Southernmost Watercourse Of The...

METHODS Study sites The Merced River is the southernmost watercourse of the California Central Valley presently inhabited by Chinook salmon whose abundance has decreased by 75% since 1950 (Yoshiyama et al., 2000). From its headwaters located in Yosemite National Park, Sierra Nevada, the Merced River flows west to join the San Joaquà ­n River (river km 190) and drains a watershed approximately 3,297 km2 in size. Meanwhile, the elevation declines from 3,048 m to about 18.3 m. Only the first 82 river km are reachable by anadromous fish with access terminating at Crocker-Huffman Dam. We estimated the percent contribution of terrestrial organic carbon sources for juvenile Chinook salmon across four longitudinally-positioned sites: Merced River†¦show more content†¦Restoration planning identified the rehabilitation of the floodplain functions that foster recruitment of riparian vegetation and the quality of riparian habitat. Fall-run Chinook salmon is an important management species in the Merced Ri ver, and numerous state and federal resource programs include increasing its abundance in their goals. The vision has been to enhance channel, floodplain and riparian ecosystem processes and critical habitats for juvenile and adult salmonids, in coordination with local communities and stakeholders, to promote the recovery of healthy and diverse Chinook salmon and steelhead (Oncorhynchus mykiss) populations in the Merced River, while helping to meet the abundance goals of the Anadromous Fish Restoration Program. Robinson’s restoration reach is approximately 2.4 km long and is located 16 km downstream of Crocker-Huffman Dam. The project included a very complex suite of actions to restore Robinson’s reach which was degraded as a result of mining activities and recent flood impacts. Channel reconfiguration and the creation of a large floodplain with native vegetation increased the river channel’s ability to transport and deposit sediments under the river’s current flow regime; hence improving channel dynamics and salmon passage concerns. These actions within the channel produced improvements for salmon spawning and rearing through the creation of

Insider Dealings in Nigeria - 2188 Words

â€Å"EXAMINE THE EFFECTIVENESS OF THE PROVISIONS OF THE INVESTMENT AND SECURITIES ACT (ISA 2007) ON INSIDER TRADING AGAINST THE BACK DROPS OF THE PROVISIONS OF THE CAMA 1990 AND THE COMMON LAW ON THE DUTIES OF DIRECTORS OF COMPANIES IN PREVENTING INSIDER RELATED OFFENCES AND PROTECTING THE INTEGRITY OF THE SECURITIES MARKET IN NIGERIA PRIOR TO AND IN THE MODERN ERA OF THE INTERNET.† SUBMITTED BY AYODELE DOYINSOLA .O LAW/2007/100 DEPARTMENT OF LAW OBAFEMI AWOLOWO UNIVERSITY ILE-IFE OSUN STATE TO PROFESSOR M.T. OKRORODUDU-FUBARA IN PARTIAL FULFILMENT OF THE COURSE â€Å"LAW OF BUSINESS ASSOCIATION† (BUL 502) Concept of Insider dealing One of the areas of company law in which the general equitable rules seem to be inadequate to protect the†¦show more content†¦The law fails to provide for express prohibitions of insider trading. The duties stated were left to the discretion of the directors to determine. 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