1.0 Overview of urine formation
The kidney is the chief regulator of all body fluids primarily responsible for maintaining homeostasis (equilibrium) of fluids and electrolytes (salts) in the body[ CITATION LAK03 \l 2057 ]. The kidney has five main functions namely: regulation of fluid and electrolyte, regulation of acid-base balance, excretion of the waste products of protein metabolism, hormonal function and protein conservation. All kidney functions except the hormonal function are carried out through urine formation which involves three processes: filtration, re-absorption and secretion. These processes occur at different parts of the nephron, the basic functional unit of the kidney[ CITATION MUR97 \l 2057 ].
Blood enters the glomerulus (through the afferent arteriole) which has a semi permeable membrane to allow free passage of water and electrolytes but is relatively impermeable to large molecules such as proteins. The electrolytes and water filter into the Bowman’s capsule, which surrounds the glomerulus, and then into the tubules at a constant rate called the glomerula filtration rate. As the filtrate moves through the tubules all the glucose, about 99% of water, 80% of the electrolytes (chlorides, sodium, bicarbonates, calcium, magnesium, phosphates, potassium etc.), various organic acids and bases and hydrogen ions are reabsorbed. These substances are either actively (against a concentration gradient thus requiring energy) or passively reabsorbed into the network of capillaries surrounding the nephrone tubule. Reabsorption occurs at the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and the collecting duct. While reabsorption moves substances (to be conserved) from the nephron tubules to blood, secretion moves substances (to be excreted) from the blood capillaries into the tubular lumen. Substances that are secreted include potassium, hydrogen ions, ammonia, uric acid and some drugs like penicillin. Like reabsorption secretion occurs both actively and passively but unlike reabsorption which occurs in almost all segments of the nephron secretion only occurs at the proximal tubule. The final filtrate and the secreted substances form urine which trickles into a series of progressively larger collecting duct[ CITATION MUR97 \l 2057 ].
2.0 Mechanisms involved when alcohol is consumed
Most of the effects of alcohol are a result of alteration of the brain functions. Alcohol is water and lipid soluble thus is readily absorbed through the GIT and crosses the blood brain barrier. In the brain alcohol decreases the activity of the network of nerves thus acts as a depressant. Albeit being a depressant alcohol can increase someone’s activity by inhibiting circuits and cells resulting in disinhibition. Alcohol also exerts its effects on the brain indirectly through alcohol-induced nutrient deficiencies (which can result in brain damages) or alcohol metabolic substances such as acetaldehyde which get to the brain through the circulatory system. The effect of alcohol in the brain manifests in form of impaired judgement, reduced visual acuity, reduced motor neural control, drowsiness, gross intoxication, loss of inhibition, reduced alertness, euphoria, sensory impairment, confusion, tremors, hallucinations and many other behavioural effects associated with alcohol consumption[ CITATION Bil03 \l 2057 ].
It is worth noting that the body responds to alcohol differently depending on the amount of alcohol consumed, the period of time over which alcohol is consumed, whether it is taken alongside other drugs, the individual’s history of previous consumption, genetics (ethnicity and gender of the person), the physical and psychological state of the person and the environment when it is consumed[ CITATION Bil03 \l 2057 ]. It is suffice to say that alcohol affects multiple organs including the liver, the pancreas and the kidney. The multiple organ effects of alcohol are as a result of the toxic effects of alcohol on these organs which depend on the dose and the duration of exposure. Alcohol basically causes injury to all tissues but the degree of injury varies with the liver and the kidney developing the highest incidences and severity[ CITATION LAK03 \l 2057 ].
3.0 The effects of alcohol on the kidney functions
Acute and chronic consumption of alcohol, especially in concert with liver disease, can affect the structure and the functions of the kidney leading to severe physiological consequences. One of the major functions of the kidney is the regulation of blood volume through the formation of urine that is either more concentrated or diluted than the plasma from which it is formed. During dehydrated state the kidney reabsorbs more water so that the urine is more concentrated; this increased reabsorption of water is mediated by the Antiduretic hormone (ADH). Conversely when there is excess water in the body the kidney increases urine flow and reabsorbs solute without water thus the urine is dilute. Through these actions of the kidney the volume and the concentration of the blood is maintained within a fairly constant range. Alcohol has the potential of producing urine flow within 20 minutes of consumption which is marked in chronic alcoholics leading to classical symptoms of dehydration. It is generally accepted among scholars that the increased urine flow is as a result of alcohol’s acute inhibition of ADH secretion. The increased water loss and other mechanisms associated with alcohol consumption results in electrolyte disturbances as shown in table 1 below. Alcohol also impairs the acid-base balance that is regulated by the kidney[ CITATION Bil03 \l 2057 ]. Functions of the kidney can also be affected indirectly due to alcohol induced liver disease.
References
Boggan, B. (2003, January 23). Alcohol, Chemistry and You Effects of Ethyl Alcohol on Organ Function . Retrieved May 14, 2011, from chemcases.com: http://chemcases.com/alcohol/alc-07.htm
Epstein, M. (1997). Alcohol’s Impact on Kidney Function. Alcohol Health and Research World , 84-96.
Kaplan, L., Oesce, A., & Kazmierczak, S. (2003). Clinical Chemistry: Theory, Analysis and Correlation. New York: Mosby Inc.
