Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2002-11-05
2004-03-02
Lo, Weilun (Department: 3761)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S523000, C604S544000, C604S319000
Reexamination Certificate
active
06699216
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of improving kidney function. More specifically, this invention relates to a method of improving the hydrostatic forces and hemodynamics of the kidney through the manipulation of pressures within the urinary collecting system.
BACKGROUND OF THE INVENTION
A fundamental understanding of renal physiology can be readily found in the available medical literature, such as “Section 6: Alterations in Urinary Function and Electrolytes”,
Harrison's Principle of Internal Medicine
, McGraw-Hill, 1994, 13th ed., p. 235-262. The main function of the kidneys is to maintain the constancy of the body's internal environment by regulating the volume and composition of the extracellular fluids. To accomplish this, the kidneys balance precisely the intake, production, excretion, and consumption of many organic and inorganic compounds. This balancing requires that the kidneys perform several more specific functions.
One of the specific functions of the kidneys is the excretion of inorganic compounds. The renal excretion of sodium ion (Na
+
), potassium ion (K
+
), calcium ion (Ca
++
), magnesium ion (Mg
++
), hydrogen ion (H
+
), and bicarbonate ion (HCO3
−
) exactly balances the intake and excretion of these substances through other routes, for example, the gastrointestinal tract and the skin.
Another specific function of the kidneys is the excretion of organic waste products. Normally the kidneys excrete such waste products as urea and creatinine in amounts that equal their rate of production.
A third specific function of the kidneys is the regulation of blood pressure through the formation and release of renin. Renin is a major component of the renin-angiotensinaldosterone mechanism which directly affects the tension in the walls of arteries. In addition, the renin-angiotensinaldosterone mechanism also controls blood pressure by controlling body fluid volume.
A fourth function of the kidneys is the regulation of the production of erythrocytes through the formation and release of renal erythropoietic factor.
Finally, the last specific kidney function is the activation of Vitamin D. Vitamin D which is ingested must undergo two activation steps in the body before it can regulate calcium metabolism. The first activation step occurs in the liver, and the second occurs in the kidney.
An understanding of renal physiology requires familiarity with the anatomy of the kidney. The kidneys are located retroperitoneally in the upper dorsal region of the abdominal cavity and have bean-like shapes, as shown in FIG.
2
. The concave curve or innermost part is called the renal pelvis, while the convex curve or outermost part is called the renal cortex. Between the cortex and the pelvis lies the renal medulla. The artery supplying the kidney is the renal artery, and the vein draining the kidney is the renal vein. The ureter, which drains the kidney of water, mineral and wastes, empties into the bladder, which in turn empties through the urethra. The renal artery, renal vein and ureter attach to the kidney at the renal pelvis.
On a microscopic level, each kidney is made up of approximately one million smaller units called nephrons. This basic functional unit of the kidney, as shown in
FIG. 1
, is composed of a glomerulus
10
with its associated afferent
12
(i.e., entering) and efferent
14
(i.e., exiting) arterioles and a renal tubule
16
. The glomerulus
10
consists of a tuft of 20-40 capillary loops protruding into Bowman's capsule
18
, a cup-like shaped extension of the renal tubule which is the beginning of the renal tubule. The epithelial layer of Bowman's capsule
18
is only about 400 Å thick, which facilitates passage of water and inorganic and organic compounds. In addition, the capillary endothelium is fenestrated (i.e., porous) with an incomplete basement membrane which further facilitates passage of water and inorganic and organic compounds. The renal tubule has several distinct regions which have different functions: the proximal convoluted tubule
20
, the loop of Henle
22
, the distal convoluted tubule
24
, and the collecting duct
26
that carries the final urine to the renal pelvis and the ureter.
There are two basic types of nephrons, cortical nephrons and juxtamedullary nephrons. The cortical nephrons comprise about 85% of all nephrons in the kidney and have glomeruli located in the renal cortex. In addition, cortical nephrons have short loops of Henle which descend only as far as the outer layer of the renal medulla. The juxtamedullary nephrons are located at the junction of the cortex and the medulla of the kidney. Juxtamedullary nephrons have long loops of Henle, which penetrate deep into the medulla and sometimes reach the tip of the renal papillae. These nephrons are important in the counter-current system, by which the kidneys concentrate urine.
The constancy of the body's internal environment is maintained, in large part, by the continuous functioning of its roughly two million nephrons. As blood passes through the kidneys, the nephrons clear the plasma of unwanted substances (e.g., urea) while simultaneously retaining other, essential substances (e.g., water). Unwanted substances are removed by glomerular filtration and renal tubular secretion and are passed into the urine. Substances that the body needs are retained by renal tubular secretion and are returned to the bloody by reabsorptive processes.
Glomerular filtration, i.e., the amount of fluid movement from the capillaries into Bowman's capsule, is the initial step in urine formation. The plasma that traverses the glomerular capillaries is filtered by the highly permeable glomerular membrane, and the resultant fluid, the glomerular filtrate, is passed into Bowman's capsule. Glomerular filtration rate (GFR) refers to the volume of glomerular filtrate formed each minute by all of the nephrons in both kidneys. The glomerular filtrate then passes along the renal tubule and is subject to the forces in the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and finally the collecting duct. The renal tubule functions either to secrete or reabsorb organic or inorganic compounds into or from the glomerular filtrate. Both of these renal tubular functions involve active transport mechanisms as opposed to passive transport mechanisms.
Glomerular filtration is proportional to the membrane permeability and to the balance between hydrostatic and oncotic forces. The hydrostatic pressure driving glomerular filtration is the gradient between intrarenal blood pressure and the pressure within the Bowman's capsule (presumed to be approximately atmospheric). The intrarenal pressure is for all intents and purposes equivalent to the systolic and diastolic blood pressures measured peripherally. Since the intrarenal blood pressure in all living beings is greater than atmospheric pressure, the hydrostatic pressure can be conceptualized as the pressure driving fluid out of the glomerular capillary and into Bowman's capsule. The colloid oncotic pressure gradient is the difference between the concentrations of particles on either side of a water permeable membrane through which the particles cannot pass. Since there are many particles within the capillaries that cannot pass through the capillary endothelium including cells, platelet, and macromolecules, the colloid oncotic pressure gradient can be conceptualized as the pressure driving fluid into the glomerular capillary. When the hydrostatic pressure exceeds the oncotic pressure, filtration occurs. Conversely, when the oncotic pressure exceeds the hydrostatic pressure, reabsorption occurs.
In the body, the major determinant of GFR is the hydrostatic pressure within the glomerulus. In addition, the renal blood flow (RBF) through the glomeruli has a great effect on GFR; when the rate of RBF increases, so does GFR. There are several factors which control the RBF: (1) an intrinsic phenomenon observed in the renal capillaries called
Bogart Michael G.
Dippert William H.
Lo Weilun
Reed Smith LLP
The Trustees of Columbia University in the City of New York
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