Good afternoon everyone! For those of you who are a little lost with the Genitourinary system, I am attaching a short pathophysiology review which might help you understand the system better. If you go to docushare under Nursing 101 you will also see Case studies for the Genitourinary system. If you have any questions, please call me at 954-5492 Locke 214 is my office.
Summary Review of Renal and Urologic Systems
Structures of the Renal System
1. The kidneys are paired structures lying bilaterally between the twelfth thoracic and third lumbar vertebrae.
2. The kidney is composed of an outer cortex and an inner medulla.
3. The calcyces join to form the renal pelvis, which is continuous with the upper end of the ureter.
4. The nephron is the urine-forming unit of the kidney and is composed of the glomerulus, proximal tubule, loops of Henle, distal tubule, and collecting duct.
5. The glomerulus contains loops of capillaries. The capillary walls serve as a filtration membrane for the formation of the primary urine.
6. The proximal tubule is lined with microvilli to increase surface area and enhance reabsorption.
7. The loops of Henle transport solutes and water, contributing to the hypertonic state of the medulla.
8. The distal tubule adjusts acid-base balance by excreting acid into the urine and forming new bicarbonate ions.
9. The ureters extend from the renal pelvis to the posterior wall of the bladder. Urine flows through the ureters by means of peristaltic contraction of the ureteral muscles.
10.The bladder is a bag composed of the detrusor and trigone muscles and innervated by parasympathetic fibers. When accumulation of urine reaches 250 to 300ml, mechanoreceptors, which respond to stretching of tissue, stimulate the micturition reflex.
Renal Blood Flow
1. Renal blood flows at about 1000to 1200 ml/min, or 20% to 25% of the cardiac output.
Blood flow through the glomerular capillaries is maintained at a constant rate in spite of a wide range of arterial pressures (autoregulation).
2. The glomerular filtration rate (GFR) is the filtration of plasma per unit of time and is directly related to the perfusion pressure of renal blood flow.
3. Autoregulation of renal blood flow and sympathetic neural regulation of vasoconstriction maintain a constant GFR.
4. Renin is an enzyme secreted from the juxtaglomerular apparatus; it causes the generation of angiotensin, a potent vasoconstrictor. The rennin-angiotensin system is thus a regulator of renal blood flow.
5. Natriuretic hormone from the right atrium of the heart promotes sodium and water loss by inhibiting aldosterone.
Kidney Function
1. The major function of the nephron is urine formation, which involves the processes of glomerular filtration, tubular reabsorption, and tubular secretion and excretion.
2. Glomerular filtration is favored by capillary hydrostatic pressure and opposed by oncotic pressure in the capillary and hydrostatic pressure in the Bowman capsule. The balance of favoring and opposing filtration forces is known as net filtration pressure (NFP).
3. The GFR is approximately 120 ml/min, and 99% of the filtrate is reabsorbed.
4. The proximal tubule reabsorbs about 60% to 70% of the filtered sodium and water and 90% of other electrolytes.
5. Because most molecules are reabsorbed by active transport, the carrier mechanism can become saturated at a point known as the transport maximum. Molecules not reabsorbed are excreted with the urine.
5. The distal tubules actively reabsorb sodium and secrete potassium and hydrogen for the regulation of electrolyte and acid-base balance.
6. The concentration of the final urine is a function of the level of antidiuretic hormone (ADH) that stimulates the distal tubules and collecting ducts to reabsorb water. The countercurrent exchange system of the long loops of Henle and their accompanying capillaries establishes a concentration gradient within the renal medulla that facilitates the reabsorption of water from the collecting duct.
7. The distal nephron regulates acid-base balance by excreting hydrogen ions and forming new bicarbonate.
8. The kidney secretes or activates a number of hormones that have systemic effects, including 1, 25-OH2D3 and erythropoietin.
Tests of Renal Function
1. Tests that measure renal clearance indicate how much of a substance can be cleared from the blood by the kidneys per given amount of time.
2. Creatinine, a substance produced by muscle, is measured in both plasma and urine to calculate a commonly used clinical measurement of GFR.
3. Both the plasma creatinine concentration and the blood urea nitrogen (BUN) levels indicate glomerular function. Plasma creatinine is measured to monitor progressive renal dysfunction; BUN is an indicator of hydration status.
4. Urinalysis involves evaluation of color, turbidity, protein, pH, specific gravity, sediment and supernatant.
5. Presence of bacteria, red blood cells, white blood cells, casts, or crystals in the urine sediment may indicate a renal disorder.
Aging and Renal Function
1. As a person grows older, a decrease occurs in the number of nephrons. Both renal blood flow and glomerular filtration rate decline.
2. Tubular transport and reabsorption decrease with age. Response to acid-base changes and reabsorption of glucose are delayed. Drugs eliminated by the kidney can accumulate in the plasma, causing toxic reactions.
Information retrieved from McCance, K., Huether, S. (2002). Pathophysiology: The Biologic Basis for Disease in Adults & Children. (4th ed.) St. Louise, Missouri: Mosby
Have a great day.
Fernisa Sison
posted by Fernisa @ 12:20 PM
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