May 28, 2022
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Renal System Diseases Overview

The Renal System is also known as the urinary system. Its function is to filter blood and create urine as a waste by-product. The organs that make up the Renal System include;

  • The kidneys.
  • Renal Pelvis.
  • Two Ureters.
  • Bladder.
  • Urethra.
    Renal system - A nephron 2021
    The Nephron

Functions of the Renal System.

The renal system helps the body to eliminate liquid waste called urea and to keep sodium, potassium, and water in balance.

Urea, which is produced when protein-rich foods are broken down in the body, is carried in the bloodstream to the kidneys, where it is removed along with water and other wastes in form of urine.

Other important kidney functions include;

  • blood pressure regulation.
  • The production of erythropoietin. Erythropoietin is important in controls the red blood cells production in the bone marrow.
  • They also regulate acid-base balance and conserve fluids.

Brief Anatomy and Physiology of Renal System

The kidneys remove urea from the blood through tiny filtering units called Nephrons. Each nephron consists of a ball formed of small blood capillaries called a glomerulus and a small tube called the Renal tubule. Urea together with water and other waste products from the urine and pass through the nephrons down to the renal tubules of the kidneys.

Muscles in the ureter walls are continually relaxing and tightening forcing urine into the bladder. The bladder, which is held in place by ligaments that are attached to other organs and the pelvic bones, has its walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. Normal healthy urine is transparent yellow in color.

Renal Diseases.

Traditionally, diseases of the kidneys re divided into 4 major groups according to the predominant involvement of corresponding morphological components:

  • Glomerular diseases – most often immunologically-mediated and may be acute or chronic.
  • Tubular diseases – more likely to be caused by toxic or infectious agents and are often acute.
  • Interstitial diseases – likewise commonly due to infectious agents and quite often involve the interstitium as well as tubules.
  • Vascular diseases – these include changes in the nephron as a consequence of increased intra-glomerular pressure such as hypertension or impaired blood flow.

Other Renal system diseases include congenital anomalies, obstructive uropathy, and tumors of the kidneys.

Congenital Anomalies

Congenital anomalies range in severity from minor anomalies that may not produce clinical manifestations to major anomalies that are incompatible with extrauterine life. These malformations are grouped into three namely;

  • Abnormalities in the number of renal tissues – these include anomalies with deficient renal parenchyma (e.g. unilateral or bilateral renal hypoplasia) or with excess renal tissues (e.g. renomegaly or supernumerary kidneys).
  • Anomalies of position, form, and orientation – these are renal ectopia (pelvic kidney), renal fusion (horseshoe kidney), and persistent fetal lobation.
  • Anomalies of differentiation – this group consists of morphological forms such as renal cystic dysplasia

The nephrotic syndrome

The Nephrotic Syndrome also being a kidney disease, is characterized by finding massive proteinuria (protein loss of more than 3gms per 24 hrs), hypoalbuminemia (urinary loss of albumin due to the inadequate hepatic synthesis of albumin, leading to low levels of Albumin in the blood.), edema (appears due to falling in colloid osmotic pressure consequent upon hypoalbuminemia)and hyperlipidemia (increased blood level of lipids, cholesterol, triglycerides) (harsh Mohan, p. 660 )

IgA, which is characterized by aggregates of IgA deposited principally in the mesangium, is emerging as the most common form of glomerulopathy. The disease is common in children and young adults and is characterized by recurrent bouts of hematuria that are often precipitated by mucosal infections. Mild proteinuria is usually present and occasionally nephrotic syndrome may develop.

Acute tubular necrosis (ATN)

Are also known as acute renal failure results (ARF) from the destruction of tubular epithelial cells and is characterized by sudden cessation of renal function. It is mainly caused by general poisons, shock, drugs, heavy metals, mismatched blood transfusions, radiographic constant medium, and crush injuries. Grossly the kidneys are enlarged and swollen and on the cut section, the cortex is widened and pale while the medulla is dark.

Obstructive uropathy

Is caused by an obstruction in the urinary tract increasing the susceptibility to infections and stone formation. Can occur at any age and in either sex. The obstruction may be unilateral or bilateral, complete, sudden, or insidious. Complete bilateral obstruction may result in irreversible renal failure, whereas long-standing chronic partial obstruction may cause various functional abnormalities and anatomic changes. The important cause of obstructive uropathy is nephrolithiasis which is the formation of urinary calculi at any level of the urinary tract.

Cortical tubular adenomas

Are a type of kidney tumor which are more common than benign renal neoplasms. They are frequently multiple and associated with chronic pyelonephritis or benign nephrosclerosis. Grossly the tumors may form tiny nodules of up to 3 cm in diameter, which are encapsulated and white or yellow. They are composed of tubular cords or papillary structures projecting into cystic space. The cells of the adenoma are usually uniform, cuboidal with no atypicality or mitosis.

Renal blood vessels that enormously profuse the kidney are affected secondarily in a majority of renal diseases. These diseases disturb the renal blood flow controlling mechanisms (systemic and local hemodynamics, hormonal, and intrinsic intrarenal mechanisms) giving rise to primary renal vascular lesions. These diseases are as under hypertensive vascular diseases, thrombotic microangiopathy, renal cortical necrosis, and renal infarcts.

Elevated arterial blood pressure is a major health problem and when it becomes persistent and sustained has damaging effects on the specific organs. It is divided into 2 groups which are; primary (where the cause of the increase in blood pressure is unknown) and secondary (increase in blood pressure is caused by diseases of the kidney, endocrine, or other organs). According to the clinical course both the primary and secondary hypertension can be benign (which is the moderate elevation of blood pressure over the years) or malignant (which is marked and sudden increase of blood pressure to 200/140mmhg or more in a known case of hypertension or in a previously normotensive individual; the patients may develop papilledema, retina hemorrhages and hypertensive encephalopathy.

Renal hypertension

Renal Hypertension is produced by renal diseases and is subdivided into 2 groups namely; renovascular hypertension (e.g. in occlusion of a major renal artery, pre-eclampsia, polyarthritis nodosa, and fibromuscular dysplasia of renal artery) and renal parenchymal hypertension (e.g. in various types of glomerulonephritis, pyelonephritis, interstitial nephritis, diabetic nephropathy, amyloidosis, polycystic kidney disease and renin producing tumors)

Both benign and malignant tumors also occur in the kidney and may arise from renal tubules (adenoma, adenocarcinoma), embryonic tissue (mesoblastic nephroma, Wilms’ tumor), mesenchymal tissues (angiomyolipoma, medullary interstitial tumor), and from the epithelium of the renal pelvis.

Benign tumors

are usually small and are often an incidental finding at autopsy or nephrectomy. Cortical tubule adenomas are more common than other benign tumors and are frequently multiple and are associated with chronic pyelonephritis or benign nephrosclerosis. They form nodules of up to 3 cm in diameter and are encapsulated whitish or yellowish in color. They are composed of tubular cords or papillary structures projecting into the cystic space the cells of the adenoma are usually uniform, cuboidal with no atypicality or mitosis. However, the size of the tumor, rather than histologic criteria is considered a more significant parameter to predict the behavior of the tumor (those larger than 3 cm re potentially malignant and metastasizing).

Oncocytoma

is also a benign epithelial tumor arising from collecting ducts. The tumor is encapsulated and has a variable size and has a characteristic mahogany brown or tan color. The tumor cells are plump with abundant, finely granular, acidophilic cytoplasm and round nuclei with numerous mitochondria. Other benign tumors include angiomyolipoma, mesoblastic nephroma, and juxtaglomerular tumor.

Malignant Tumors

The two most common primary malignant tumors of the kidney are adenocarcinoma and Wilms’ tumor.

Adenocarcinoma

also known as Renal Cell Carcinoma or Hypernephroma or Grawitz tumor, arises from the tubular epithelium and occurs most commonly in 50 to70 years of age with male preponderance. Various etiological factors implicated in the etiology of RCC are as follows:

  • Tobacco – this is a major risk factor for Renal Cell Carcinoma and accounts for 20-30% of the cases. Cigarette smokers have a two-fold higher risk of developing RCC.
  • Cystic diseases of the kidney – both hereditary and acquired cystic diseases of the kidney have an increased risk of development of RCC. Patients on long-term dialysis develop acquired cystic disease which may evolve into RCC and adenomas.
  • Other risk factors are exposure to asbestos, heavy metals, and petrochemical products, obesity, and estrogen therapy (in women), analgesic nephropathy, and tuberous sclerosis.

Based on cytogenetics of sporadic and familial tumor, RCC has been reclassified into the clear cell (most common pattern, have a variety of patterns, separated by delicate vasculature and are well-differentiated), papillary (tumor cells re cuboidal with small round nuclei and arranged in a papillary pattern over the fibrovascular stalks), granular cell (tumor cells have abundant acidophilic cytoplasm and have more marked nuclear pleomorphism, hyperchromatism, and cellular atypia), chromophobe (this type shows a mixture of pale clear cells with perinuclear halo and acidophilic granular cells), sarcomatoid (this is the most anaplastic and poorly differentiated form and the tumor is characterized by whorls of a typical spindle tumor cells) and collecting duct type (the rare type that occurs in the medulla, composed of a single layer of cuboidal tumor cells arranged in the tubular and papillary pattern).

Grossly, RCC commonly arises from the poles of the kidney as a solitary and unilateral tumor, more often in the upper pole. The tumor is generally large, golden yellow, and circumscribed. Papillary tumors have grossly visible papillae and may be multifocal.

There is also the frequent presence of tumor thrombus in the renal vein which may extend into the vena cava. RCC is generally a slow-growing tumor and may have been present for years before it is detected. The classical clinical evidence for the diagnosis of renal cell carcinoma is the triad of gross hematuria, flank pain, and palpable abdominal mass.

Systemic symptoms of fatigability, weight loss, cachexia, and intermittent fever that unassociated with evidence of infection are found in many cases at presentation. Also, a number of Paraneoplastic syndromes such as; polycythemia (by erythropoietin), hypercalcemia (by parathyroid hormone and prostaglandins), hypertension (by renin), effects of feminization or masculinization (by gonadotrophins), and crushing’s syndrome (by glucocorticoids).

Wilms’ tumor

You can also call it nephroblastoma. It is an embryonic tumor that derives itself from primitive renal epithelial and mesenchymal components. It is the most common abdominal malignant tumor of young children, and we see it mostly between 1 to 6 years of age with equal sex incidences. It hs the following etiologic associations:

  • A defect in chromosome 11p13 which result in abnormal growth of metanephric blastema without differentiation into normal tubules and glomeruli.
  • We can also see a higher incidence of monozygotic twins and cases with family history.
  • Association of Wilm’s tumor with some other congenital anomalies has been observed, especially of the genitourinary tract.
  • A few other malignancies we know to have higher incidences of Wilm’s tumor. These include osteosarcoma, botryoid sarcoma, retinoblastoma, neuroblastoma, etc.

The tumor is usually quite large, spheroidal, replacing most of the kidney. It is generally solitary and unilateral but a few cases may have a bilateral tumor. On the cut section, the tumor shows characteristic variegated appearance – soft, fish flesh-like, grey-white to the cream-yellow tumor with foci of necrosis, hemorrhages, and grossly identifiable myxomatous or cartilaginous elements.

Invasion into a renal vein is grossly evident in half the cases. Microscopically, nephroblastoma shows a mixture of primitive epithelial-mesenchymal elements. Most of the tumor consists of small, round to spindled, anaplastic, sarcomatoid tumor cells. In these areas are present abortive tubules and poorly formed glomerular structures.

Mesenchymal elements such as smooth and skeletal muscles, cartilage and bone, fat cells, and fibrous tissues may be seen. The most common feature is a palpable abdominal mass in a child. Other common abnormalities are hematuria, pain, fever, and hypertension. The tumor rapidly spreads via blood to the lungs.

Leukemic infiltration of the kidneys is a common finding, particularly in chronic myeloid leukemia. The kidney is a common site for blood-borne metastases from different primary sites, chiefly from cancer of the lungs, breast, and stomach.

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