ABSTRACT (Blood Urine Barrier -glomerular filtration barrier)
Blood Urine Barrier also known as the glomerular filtration barrier is a highly specialized blood filtration interface that displays a highly conductance to small and midsized solutes in plasma but remain relative impermeability to macromolecules. Its integrity is maintained by physiochemical and signaling interplay among its three core constituents. Thus; the glomerular endothelial cell; the basement membrane and the visceral epithelial cells otherwise known as the podocytes. Interferances with the integrity of the blood urine Barrier is the appearance of significant diseases mostly associated with the urinary system.
Keyword: Podocytes, Epithelial cells, protenuria, macromolecule.
Blood Urine Barrier also known as glomerular filtration Barrier takes part in the first step of urine formation. It is surrounded by a cup-like sac known as Bowman capsule. It is permeable to micro molecule an impermeable to macro molecules. Absence of the barrier would allow recirculation of renal waste on one hand and loss of water and oxygen on the other hand which will therefore counter-balance renal function leading to several pathological conditions. Blood entering the glomerular capillaries is filtered into the Bowman capsule from where it enters the remainder of the nephron. The glomerular barrier is highly permeable and nearly 20% of the plasma volume entering the glomerular capillaries is filtered into the nephron. However, filtration is also highly selected and only allows water and small molecules pass through the glomerular barrier.
The glomerular barrier is composed of three basic layers which separates blood from Bowman space.
Thus; the glomerular capillary endothelial cells, which allows for high fluid permeability. The glomerular basement membrane, which is the extracellular matrix component of the glomerular filtration barrier that separates the vasculature from the urinary space.
The podocytes, a specialized type of epithelial cells with foot-like processes that support the glomerular basement membrane. The anatomy, physiology and pathology of these three will be looked at in these work.
Main Component of Blood Urine Barrier
Endothelial Cells: There are three main component of blood urine barrier which are the glomerular endothelial cells; which account for about I kilogram of adult human body which line the blood vessels and lymphatic vessels forming an interphere between circulating blood and the rest of the vessel walls.
The endothelial cells is a thin layer of squamous cells, when in direct contact with blood, they are called vascular endothelial cells, when indirect contact with lymph, they are called lymphatic endothelial cells when found in the interior surface of the heart chamber is called endomidium.
Physiology: The main job of the endothelial cell is to provide a barrier between the blood and the rest of the body tissues. The endothelial cells provide the selective permeable layer across the blood transporting vessel in a controlled manner were chemicals and white blood cells moves according to where they are needed.
Endothelial cells play a major role in blood vessel formation by deciding into more endothelial cells and differentiating into other cells that make up blood vessel walls.
Inflammation: The body responds to pathogens or terms, by causing the site of infection to become swollen, red, and hot. The epithelium helps this along by increasing blood flow and allowing white blood cells to move through the infected tissue.
Blood Pressure: It produces substances that makes blood vessels dilute and contract thus played an important role in controlling blood flow.
Water Regulator: Endothelial cells in the glomeruli (bundles of blood capillaries in the kidney) control the concentration of urine by regulation how much water is reabsorbed into the blood and which substances are in excess in the blood and mist be excreted in the urine.
Hypertension: A condition present when blood flows through the blood vessels with a force greater than normal. It is also known as high blood pressure.
Atherosclerosis: Harding of the artery resulting from bud up of plaque: which is made up of cholesterol, fat, clothing agents, cell debris and other substances.
Hypercholesterolemia also called dysilipidmia is the presence of high levels of cholesterol in the blood. It is a form of high blood lipid and educated level of lipoproteins in the blood.
Coronary Artery Disease (CAD): happens when the arteries that supplies blood to the heart muscles becomes hardened or narrowed over time, weakens heart muscle and contributes to heart failure disease.
Podocytes are cells in the Bowman capsule in the kidney (visceral epithelial cells), that wrap around the outside of blood vessel and controls the rate of filtration.
The Bowman capsule filters the blood, retain large molecules such as protein but filters smaller molecules like water, salt and sugar forming urine. The podocytes has long processes, foot process, foot projections or pedicels for which they are named. Foot process wrap around the capillaries and leave slit between them through which blood is filtered. It helps in urine production in glomerular filtration rate.
The four processes also known as pedicels that extends from the podocytes wrap themselves around the capillaries of the glomerulus to form the filtration slits.
The pedicles increases the surface area of the cells enabling efficient filtration. It also poses a well developed endoplamsic reticulum and a large glogi apparatus, indicative of a high capacity for protein synthesis and post translational modifications. There is also growing evidence of a large number of multivesilcular bodies and other lysosomal components seen in these cells, indicating a high endocytic activity.
Adjacent podocytes interdigitate to cover the basal lamina which is intimately associated with the glomerular capillaries. The pedicles of the podocytes interdigitate and leave the gaps or thin fellers slits between them.
The slits are covered by slit diagrams which are composed of a number of cell surface protein including nephrin, podocalyxin and p-cadherin, which restrict the passage of large macromolecules such as albumin and gamma globulin and ensure that they remain in the blood stream.
Protein required a proper functioning of slit diaphragm include Nephrin, NEPH1, NEPH2, podocin and CO2AP. Small molecules such as H20, glucose and ionic salts are able to pass through the filtration slits and form an ultrafiltrate in the tubular fluid, which is further processed by the nephron to produce urine.
- A loss of the foot processes of the podocytes is a hallmark of minimal change disease, which has sometimes been called foot process diseases.
- Description of the filtration slits or destruction of the podocytes can lead to massive proteinuriars where large amount of protein are lost from the blood.
Glomerular Basement Membrane
Is a layer of extracellular matrix that separate the blood from the filtrate that will become urine. The GBM of the kidney is the base lamina layer of the glomerulus. The glomerular capillary endothelial cells, the glomerular basement membrane and the filtration slits between the podocytes perform filtration function of the glomerulus, separating the blood in the capillaries from the filtrates that forms the Bowman capsule. The GBM is a fusion of the endotheliar cell podocyte basal laminas. It consists of mesangial cells.