Thursday, February 18, 2021
SIMPLE AND RADICAL NEPHRECTOMY
Simple nephrectomy refers to the surgical removal of the kidney without the renal fascia or ipsilateral adrenal gland. This technique may be employed to treat non-neoplastic, irreversible kidney disease that poses an ongoing threat to the patient’s health. Possible indications include chronic pyelonephritis, chronic renal obstruction, extensive untreated nephrolithiasis, trauma, and ischemic nephropathy secondary to renal artery stenosis.
Renal artery stenosis (RAS) is deﬁned as an anatomic narrowing of the main renal artery or its segmental branches, which can lead to secondary renovascular hypertension (RVH) and renal failure if sufﬁciently advanced. The pathophysiology and diagnosis of this lesion are demonstrated in Plates 4-36 and 4-37. Brieﬂy, the major causes are atherosclerosis, which accounts for about 90% of cases, and ﬁbromuscular dysplasia (FMD), which accounts for most of the remainder. Atherosclerosis, which tends to occur in older individuals with classic risk factors, involves the intimal layer of the artery and develops circumferentially to occlude a progressive fraction of the vessel lumen. FMD, in contrast, causes collagenous dysplasia of either the intimal or medial arterial layers.
Percutaneous nephrolithotomy (PCNL) is a minimally invasive procedure for the treatment of kidney stones. In this procedure, a surgical access tract is established between the skin and the renal collecting system. The tract is typically created under ﬂuoroscopic guidance, with needle puncture followed by tract dilation.
EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY
Extracorporeal shock wave lithotripsy (ESWL) is a noninvasive procedure for the treatment of nephrolithiasis. In this procedure, acoustic shock waves are generated external to the patient and focused on the renal stones, which are fragmented into small pieces that can be spontaneously passed in the urine. The skin and surrounding renal parenchyma receive a much smaller dose of energy and therefore remain largely unharmed.
Saturday, February 6, 2021
HEMODIALYSIS, PERITONEAL DIALYSIS, AND CONTINUOUS THERAPIES
When kidney dysfunction is severe enough to cause homeostatic abnormalities that cannot be corrected with diet or medications, dialysis is performed to artiﬁcially replace the kidney’s major functions. The major goals of dialysis are to support the elimination of nitrogenous waste products, restore ﬂuid and electrolyte homeostasis, and restore normal plasma pH. The major indications are listed in the plate.
A renal biopsy yields a small piece of renal parenchyma for histopathologic examination. Because many renal diseases have essentially indistinguishable clinical ﬁndings, renal biopsy is often crucial for establishing the correct diagnosis and devising an effective treatment plan. The procedure is generally uncomplicated and, in most cases, can safely be performed by a nephrologist at the bedside.
INHIBITORS OF THE RENIN-ANGIOTENSIN SYSTEM
As shown on Plate 3-19, the renin-angiotensin system plays an essential role in the regulation of systemic blood pressure. In brief, renin is released from juxta-glomerular cells in response to decreased renal tubular ﬂow, sympathetic input, or decreased stretch of afferent arterioles. Renin catalyzes the conversion of angiotensinogen to angiotensin I, which is rapidly converted by angiotensin-converting enzyme (ACE) into angiotensin II (AII). AII increases blood pressure through direct vasoconstrictor effects on systemic vessels and through various other mechanisms, including increased sodium reabsorption from the renal tubules, potentiation of sympathetic tone, and stimulation of aldosterone and antidiuretic hormone release.
ACTIONS AND MECHANISM
In the connecting tubule and cortical collecting duct, principal cells are responsible for K+ secretion through two major mechanisms. First, the reabsorption of Na+ through apical ENaC channels leaves a negative charge in the tubular lumen, which promotes the secretion of potassium through apical ROM-K channels. Second, increased ﬂow rates through the distal nephron stimulate K+ secretion through apical maxi-K channels.
ACTIONS AND MECHANISM
In the distal convoluted tubule, Na+ and Cl− are reabsorbed across the apical surface of the tubular epithelium on NCC symporters. The thiazide diuretics enter the nephron through the organic anion pathway in the proximal tubule, then they bind to the apical surface of NCC symporters and inhibit them.
In the thick ascending limb (TAL), Na+, K+, and Cl- are reabsorbed across the apical surface of the tubular epithelium on NKCC2 transporters. Such reabsorption is essential for the maintenance of a high medullary interstitial solute gradient, which permits urine concentration in the collecting duct (see Plate 3-15). In addition, recycling of the reabsorbed potassium back into the lumen through apical ROMK channels establishes the positive intraluminal charge required for reabsorption of Ca2+ and Mg2+ (see Plate 3-11).
Monday, December 21, 2020
Monday, November 9, 2020
CARBONIC ANHYDRASE INHIBITORS
Carbonic anhydrase (CA) catalyzes the interconversion of carbon dioxide and water to bicarbonate (HCO ) ions and protons. There are multiple CA isoforms, which serve different functions in cells throughout the body. In the renal tubules, the epithelial cells involved in acid-base handling such as those in the proximal tubule, thick ascending limb, and the cortical collecting duct possess cytoplasmic CA-II and luminal membrane- bound CA-IV. Several other CA isoforms also appear to be present throughout the nephron, with their locations and functions still under active investigation.
In the nephron, water reabsorption is a passive phenomenon that relies on the transcellular osmotic gradients established during the reabsorption of solutes, especially sodium. Osmotic diuretics alter these gradients to produce diuresis. After intravenous administration, such agents undergo ﬁltration at the glomerulus but then cannot be reabsorbed. As sodium and water are reabsorbed, osmotic diuretics become more concentrated in the tubular lumen, eventually generating an osmotic gradient that interferes with further ﬂuid reabsorption. In the proximal tubule, the decreased ﬂuid reabsorption also establishes a transepithelial sodium concentration gradient, normally prevented by the iso-osmotic reabsorption of water, that limits further sodium reabsorption.
TUMORS OF THE BLADDER
More than 90% of bladder cancers arise from the mucosa and are known as urothelial (transitional cell) carcinomas. These tumors are the main focus of this section. Less common tumors include squamous cell carcinomas (5% in the United States, but most common worldwide), adenocarcinomas (2%), small cell carcinomas, and nonepithelial tumors. Metastatic tumors from other primary sites including the prostate, ovary, uterus, colon, rectum, and lung have also been described.