The balance of the Starling forces (the hydrostatic pressure and the oncotic pressure within the glomerular capillaries and Bowman's capsule) determines the net filtration pressure. > span class="crosslink">Cross-linked collagen fibers in the basement membrane act as a sieve that prevents large proteins from passing through it into the urine. These proteins include albumin and immunoglobulins. The kidney removes these molecules through excretion because it cannot remove them through filtration alone.
The filtration barrier consists of three layers: the glomerulus, the tubules, and the interstitium. The glomerulus is a spongy network of blood vessels and fibrous tissue that filters out small particles from the bloodstream. It does this by creating a high negative charge on its surface so that any positive ions or protein fragments that pass through its walls will be attracted to it by electrostatic force. Next, the tubules carry the filtered materials into the urinary system where they can be expelled from the body. Last, the interstitium contains fluid that drains away from the glomeruli to maintain proper blood pressure. This liquid includes plasma water as well as sodium chloride and other electrolytes.
GFR increases as renal artery pressure (or renal blood flow) rises. As renal artery pressure (or renal blood flow) decreases, so will the GFR.
Net filtration pressure is the driving force behind the filtration of plasma into the Bowman's space and subsequently into the urinary space. The higher the net filtration pressure, the more plasma will be filtered. Lower net filtration pressures will result in less plasma being filtered.
The net filtration pressure is determined by the balance between the hydrostatic pressure and the oncotic pressure. As the oncotic pressure increases, so will the net filtration pressure. A high oncotic pressure can be achieved by increasing serum albumin levels or decreasing osmolarity through the addition of free water. A low oncotic pressure can be achieved by decreasing serum albumin levels or adding anticoagulants to the system (such as heparin).
Hydrostatic pressure is determined by the amount of fluid surrounding the kidney cells. High fluid volumes lead to high hydrostatic pressures. Oncotic pressure is determined by the concentration of serum proteins. High protein concentrations lead to high oncotic pressures.
Glomerular filtration occurs when glomerular hydrostatic pressure surpasses Bowman's capsule luminal hydrostatic pressure. The osmotic pressure, which is normally higher in the glomerular capillary, acts as an opposing force. 1st Figure: The glomerulus is a spongy structure within the kidney that filters blood cells and proteins from the fluid that flows into it from the urinary tract. 2nd Figure: The glomerulus is made up of tufts of fibers called podocytes that surround and cover an extensive network of tiny capillaries. These capillaries are so small that they can't be seen with the naked eye. They can be viewed under the microscope. There are several types of filtering units within the glomerulus. The main one is the glomerulus itself. It consists of a spongy mass of tissue covered by a layer of epithelial cells. This mass is called the glomerulus because it looks like a miniature sea sponge. The outer covering of the glomerulus is called the glomerular membrane. It contains many channels called slit diapers through which water and small molecules pass from the bloodstream into the urine but not large molecules such as proteins.
The forces that drive filtration at the glomerulus are hydraulic. That is, the force acting on particles in the filtrate is due to the pressure difference between inside and outside the glomerular capsule.
The hydrostatic pressure of the glomerular capillary is the primary factor promoting filtration (Pgc). The hydrostatic pressure of Bowman's space (Pt) and the oncotic pressure of the blood are the factors opposing filtration (pb). The surface area of the glomerulus available for filtration (SA) determines how much plasma water will be filtered.
In health, the balance between these forces is such that sufficient plasma water is removed from the blood to maintain osmolarity within normal limits. However, if Pgc becomes greater than Pt or if SA is increased without an increase in Pgc, then filtration will occur. For example, if Pgc increases due to a rise in blood pressure then more plasma water will be filtered into the urine; if it decreases due to low blood pressure then less plasma water will be filtered into the urine.
Filtration occurs in patients with nephrotic syndrome because the oncotic pressure of the blood is reduced so that it can pass through the leaky basement membrane into the urinary space where it can be re-absorbed by adjacent proximal tubule cells.
Nephron size varies among individuals but on average there are about 600,000 nephrons in a human kidney.
What is the underlying cause of glomerular filtration? Blood pressure in the glomerular capillaries causes the filtration process to begin. As more blood flows through the capillaries, more particles are filtered out. The rate at which this process occurs is called the filtration rate. A healthy kidney has a high filtration rate.
The nephron is the functional unit of the kidney that performs filtration. It is made up of an endothelial cell layer, an epithelial cell layer, and portions of the surrounding tissue such as blood vessels, lymphatic vessels, and nerves. The nephron filters plasma water and small molecules from the blood that cannot pass through the membrane of the red blood cell. This filter is known as the glomerulus. The remaining components of the nephron include tubules that reabsorb most of the fluid that enters them from the glomerulus and produce urine that is released into the bladder.
Nephrons are the fundamental functional unit of the kidney. One nephron can filter about 500 ml of blood per day. The total number of nephrons in a human being is approximately 2 million. The filtering ability of the kidney is highly dependent on the number of functioning nephrons.
Hydraulic pressure (blood pressure) in the capillaries of the glomerulus drives filtration. It is worth noting that the kidneys filter far more fluid than the amount of urine excreted (about 1.5 liters per day). This means that there must be a mechanism for removing excess water from the body while maintaining normal blood pressure. This mechanism is pressure filtration through the kidney's filtration system. Pressure filtration allows the glomeruli to remove large particles from the blood stream by mechanical sieving, while small molecules pass through into the urinary tract where they are reabsorbed by active transport processes into the bloodstream via the renal tubules.
Pressure-driven filtration requires high hydraulic pressure in order to overcome the forces that resist passage of fluid across a membrane. The filtration process can only occur at certain points along the nephron (the functional unit of the kidney), and these points are called the glomerulus and the renal tubule. In the glomerulus, the walls between the capillaries and the bladder contain fenestrations that allow protein in the blood plasma to pass through into the urinary space behind the glomerular basement membrane.
What role does its high-pressure condition play in its filtrate creation function? It is fed and drained by arterioles (high-pressure arteries that are bigger in diameter than venules), and the afferent arteriole is greater in diameter than the efferent arteriole. The more filtrate generated, the higher the capillary pressure. This high pressure helps push fluid out into the surrounding tissue. This allows for better distribution of water and nutrients around the body while reducing the risk of injury from blood leaking into the tissue.
The kidney filters the blood to remove toxic substances and waste products. Healthy kidneys maintain a constant concentration of sodium and potassium in the blood. Potassium is vital for many body functions including keeping muscles contractions strong, nerve impulses transmitted correctly, and other important things. Sodium is needed for normal cell function and control of body temperature. Too much sodium in the blood can lead to dehydration because more water is required to balance out the salt levels in the blood. Also, excessive sodium consumption can cause high blood pressure which may lead to heart disease.
The nephron is the basic functional unit of the kidney. It is composed of a glomerulus, which is a part of the renal cortex, and the renal tubule, which is a long tube that extends deep into the medulla. The glomerulus is like a miniature filter: blood flows in one end and urine comes out the other.