Y khoa, y dược - Chapter 6: The renal system

Chapter 6 The Renal SystemThe Renal SystemThe Renal or urinary system is composed of two kidneys, two ureters, a bladder and the urethra. The kidneys are classically described as two bean shaped organs suspended at the rear or posteriorly within the abdomen (retroperitoneal). The structure of a kidney can be described in two distinct parts;The cortex on the outsideThe medulla on the inside   The Renal SystemEach kidney is connected to the bladder via a ureter. The urethra connects the bladder to the external environment and therefore provides the exit point for urine. Each kidney is composed of around one million excretory units called nephrons measuring around 3cm.Figure 6.1 An overview of the components of the renal systemThe Intricate Workings of a Nephron ·        The Bowman’s capsule and glomerulus       The Proximal convoluted tubule       The loop of Henle       The distal convoluted tubule       The collecting ductFigure 6.2 The Intricate Workings of a Nephron Overview of the Renal SystemThe kidney’s functions centre on excretion and secretion:ExcretoryWaste products of metabolism-urea and creatinineExcess fluid-concentration/dilation of urineAcid base balance regulationSecretaryBlood pressure regulationRed cell productionActivation of vitamin of D, and calcium uptakeThe UrineThe composition of urine constantly changes The colour of urine partially reflects its concentration i.e. the lighter the urine the less concentrated it is, it also reflects the amount of bilirubin and bile pigment present. Urine is composed of: 96% water 2% urea2% chemicals, including; sodium, potassium and ammonia It is necessary to generate and void around 30mls of urine per hour to eliminate the waste products of cellular metabolism (Clancy & McVicar 2002). Examining UrineExamination of a patient’s urine can consolidate many clinical findings, it is therefore essential for nurses to understand the basic components of urine and to comprehend the significance of increasing levels of certain waste or by-products and appreciate the importance of identifying substances that should not be found within the urine.Complete the following exercise before continuing:Construct a list of what you would expect to find within the urine The Process of Elimination Once the urine is formed and filtered within the kidneys, it is propelled down the ureters by peristaltic contraction of the smooth muscle of the ureteral walls. As the bladder fills and distends the individual is aware of the need to urinate.The elimination or passing of urine is initiated by a reflex action whereby the bladder wall begins to contract as a response to the increasing wall tension and the stimulation of stretch receptors. As the bladder continues to fill the contractions increase resulting in the internal urethral sphincter opening, the external sphincter relaxes and urine passes out.This appears a simple process but, due to the reliance on sphincters, and in the male, the prostate gland this can be a potentially problematic process. Renal DiseaseMany diseases and disorders can affect the kidneys:Renal failure can be acute or chronic, various areas of the kidney are prone to disease this includes the kidney’s tubular network which can become blocked due to stone (calculi) formationRenal StonesRenal colic is usually caused by calculi within the kidney, renal pelvis or ureter. Pain results from the associated local inflammation, dilatation, stretching and spasms. It is estimated that renal colic has an incidence of 12% for men and 4% for women (Leslie, 2006). Acute renal colic may be the most excruciatingly painful disease an individual can experience. The sudden onset of extreme and unbearable pain is often described as worse than childbirth. Renal colic affects approximately 1.2 million people each year and accounts for approximately 1% of all hospital admissions within the USA (Leslie, 2006). Exercise· What increases the likelihood of developing a renal or urinary calculus?· Do lifestyle choices affect an individual’s chance of developing a renal calculi?Add your answers to your portfolio.Urine Infection Patients experiencing urinary tract infections are a common presentation within all health settings. It is estimated that between 1-3% of all consultations relate to an infection of the urinary tract (UTI) and that in hospitalised patients UTIs account for 23% of all hospital acquired infections (Naish & Hallam 2007). Urine Infection 2The aetiology of infection can be different between men and women. Infection in males can be directly linked to prostate hypertrophy and subsequent urine stagnation within the bladder, leading initially to a localised urine infection and the potential for cystitis. Females are at particular risk of UTIs, this is possibly due to the close proximity between the anus and the urethra which in females can lead to the urethra becoming colonised by particular strains of bacteria.Bacteria can then ascend, or migrate, up the urinary tract infecting vital structures leading to the possibility of systemic illness (SIGN, 2006). Acute Renal Failure 1(ARF)ARF can be defined as an acute decline in renal function resulting in the internal environment being unable to excrete the waste products of cellular metabolism or maintain an optimum fluid balance.Raised urea and creatinine levels are the usual focal point of diagnosis in the asymptomatic patient.Acute Renal Failure 2ARF is a common medical emergency which affects around 5-7% of all hospitalised patients, furthermore on an average ward one in every 20 patients will be at an increased risk (Singri, 2003). The body’s internal compensatory mechanisms can directly cause ARF as can most treatment regimens.Healthcare staff play a vital role in the early recognition and prevention of ARF.The focal point being prevention. This involves requesting and accurately interpreting blood tests, and via the identification of patients at increased riskAcute Renal Failure 3Acute Renal failure can be divided into three categories:1. Pre-renal: a decreased effective renal perfusion 2. Renal: primary injury to the renal system I.e. acute tubular, glomerular, vascular or interstitial 3. Post renal: obstructive disorders Regardless of the cause (aetiology) physiological shock if left untreated will result in a temporary ‘pre-renal failure’ with anuriaOliguria is the cardinal signOliguria can be defined as <300/400 mls in 24hoursThe clinical features associated with even severe uraemia can be non-specific or asymptomaticAcute Renal Failure 4Investigations:Diagnosis is confirmed by a high blood urea and creatinine. Hyperkalaemia is common as the renal system fails to clear the waste products of cellular metabolism.Full blood count – Possible low platelets countArterial blood gas – acidosisChest X-ray – possible pulmonary oedemaECG – Large hyper inflated T wavesThe urinary sodium concentration is a useful investigation: if there is any doubt about whether the oliguria is pre-renal and amenable to fluid therapy or a result of tubular necrosis.Acute Renal Failure 5Prevention & Treatments:Measurement of fluid input & output (I.e fluid balance charts)These charts are notoriously inaccurate as they only reflect what is written in them; superfluous loss can only be estimated. Therefore patients at high risk should have a urinary catheter so that at least the output can be measured correctly.Aggressive fluid resuscitation is the foremost treatment in pre-renal failure.Nutritional needs are high and patients must be encouraged to maintain a calorie rich diet.Insulin and glucose are used to promote extracellular fluids/contents back into the cells.In extreme cases sodium bicarbonate is used to neutralise acidosis.Can you think of other treatments you have encountered?Chronic Renal Failure (CRF) Chronic renal failure is invariably a progressive process that results in end stage renal disease and the need for Dialysis or kidney transplantation (Parmar 2002).If left untreated progressive destruction of the nephrons will result in the kidneys maintaining the GFR by hyperfiltration resulting in hypertrophy of the functioning nephrons. Ultimately over time this innate compensatory mechanism will result in the nephrons becoming misshapen and ineffective.