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As it happens the renal glomerular filtration? How can it be changed?

Updated on May 30, 2013

The renal system has various functions in the human body. These are: the excretion of degradation products of metabolism, such as urea, creatinine, bilirubin, excretion of exogenous chemical substances such as drugs, food additives and pesticides; regulation of fluid and electrolyte balance, blood pressure regulation, the regulation of acid-basic along with the lungs and body fluids tampons; regulation of red blood cell production and the production of the active form of vitamin D.

Microscopically renal system presents its basic unit the nephron. This has the function of glomerular filtration, tubular reabsorption and tubular secretion.

The glomerular filtrate appears very similar to plasma (however, for example, it is known that the filtrate should not be present proteins). In it contains mainly ions and organic solutes of low molecular weight. Among the most common substances are freely filtered ions Na, K, Cl-and HCO3-. Organic substances such as urea and glucose, amino acids and peptides also have free filtration.

It is estimated that the total glomerular filtration rate in an adult male is equivalent to 180 liters per day. If we imagine that the plasma volume is 3 liters, we can say that the kidneys filter plasma 60 times a day.

The filter fact that huge volume of plasma, enables the kidneys excrete large quantities of residual constituents and regulate the internal environment with great accuracy.

The filtration to occur it is necessary that a barrier is exceeded. This barrier is composed of the glomerular capillary endothelium, a basement membrane, and a single layer of epithelial cells.

The capillary endothelium is perforated by many fenestrae. It is freely permeable to all blood except red blood cells and platelets.

The basement membrane is a mesh acellular gel-like glycoproteins and proteoglycans.

The epithelial cells are called podocytes in the region. This anatomical arrangement allows a large fluid filtration but restricts the passage of large molecular weight proteins.

The filterability of solutes is inversely related to its size. Moreover molecules with negative charges are filtered less easily when compared to the positively charged molecules of the same molecular size. This is because the negative charge of the basement membrane is an important barrier to negatively charged molecules, including plasma proteins. This explains why the non-occurrence of filtration of albumin that although its diameter is enough to pass through the pores of the glomerular membrane, it is not filtered because of its negative charge.

Some renal diseases resulting in the loss of negative charges exist in the basal membrane. Consequently, we have a clinical condition characterized by albuminuria or proteinuria.

Glomerular filtration rate is determined by the sum of the colloid osmotic and hydrostatic forces acting through the glomerular membrane (resulting in effective pressure filtration) and the glomerular capillary filtration coefficient (resulting from the local capillary permeability surface area and filtration thereof).

Modification of Intensity of Glomerular Filtration

Some factors make the glomerular filtration rate (GFR) is amended:

GFR increases with increasing coefficient of the glomerular capillary filtration: This coefficient is typically about 400 times greater than other capillaries in the body. Some diseases can lower the coefficient reducing the number of functional glomerular capillaries (thereby decreasing the surface area renal) or increase the thickness of the capillary membrane. Chronic hypertension uncontrolled and interstitial nephritis are examples of these two mechanisms, respectively.

GFR is changed by increasing or decreasing the hydrostatic pressure in the glomerular capillaries. The hydrostatic pressure is determined by three variables: the pressure (increased blood pressure tends to elevate the hydrostatic pressure and thereby increase glomerular filtration. However, this effect is damped by mechanisms of self-regulation), the resistance of afferent arterioles (with increasing resistance, decreases the hydrostatic pressure and glomerular filtration rate) and the resistance of efferent arterioles (increased resistance with increased glomerular filtration. However if the constriction is severe, there will be an increase colloid osmotic pressure and consequently a reduction in filtration glomerular).

GFR decreases by increasing the hydrostatic pressure in Bowman's capsule: in some disease states associated with urinary tract obstruction, the hydrostatic pressure in Bowman's capsule can increase dramatically causing the reduction in glomerular filtration.

GFR decreases by increasing the colloid osmotic pressure of glomerular capillaries. The increased concentration of plasma proteins produces an increase colloid osmotic pressure which in turn decreases the effective pressure filtration and thereby the intensity of glomerular filtration.


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