In the collecting duct, secretion will occur before the fluid leaves the ureter in the form of urine. The end product of all these processes is urine, which is essentially a collection of substances that has not been reabsorbed during glomerular filtration or tubular reabsorbtion.
Urine is mainly composed of water that has not been reabsorbed, which is the way in which the body lowers blood volume, by increasing the amount of water that becomes urine instead of becoming reabsorbed.
The other main component of urine is urea, a highly soluble molecule composed of ammonia and carbon dioxide, and provides a way for nitrogen found in ammonia to be removed from the body. Urine also contains many salts and other waste components. Red blood cells and sugar are not normally found in urine but may indicate glomerulus injury and diabetes mellitus respectively. Normal kidney physiology : This illustration demonstrates the normal kidney physiology, showing where some types of diuretics act, and what they do.
Glomerular filtration is the renal process whereby fluid in the blood is filtered across the capillaries of the glomerulus. Glomerular filtration is the first step in urine formation and constitutes the basic physiologic function of the kidneys. It describes the process of blood filtration in the kidney, in which fluid, ions, glucose, and waste products are removed from the glomerular capillaries. Many of these materials are reabsorbed by the body as the fluid travels through the various parts of the nephron, but those that are not reabsorbed leave the body in the form of urine.
Blood plasma enters the afferent arteriole and flows into the glomerulus, a cluster of intertwined capillaries. The visceral layer lies just beneath the thickened glomerular basement membrane and is made of podocytes that form small slits in which the fluid passes through into the nephron. The size of the filtration slits restricts the passage of large molecules such as albumin and cells such as red blood cells and platelets that are the non-filterable components of blood.
These then leave the glomerulus through the efferent arteriole, which becomes capillaries meant for kidney—oxygen exchange and reabsorption before becoming venous circulation. The positively charged podocytes will impede the filtration of negatively charged particles as well such as albumins. The process by which glomerular filtration occurs is called renal ultrafiltration. The force of hydrostatic pressure in the glomerulus the force of pressure exerted from the pressure of the blood vessel itself is the driving force that pushes filtrate out of the capillaries and into the slits in the nephron.
Osmotic pressure the pulling force exerted by the albumins works against the greater force of hydrostatic pressure, and the difference between the two determines the effective pressure of the glomerulus that determines the force by which molecules are filtered. These factors will influence the glomeruluar filtration rate, along with a few other factors.
Regulation of GFR requires both a mechanism of detecting an inappropriate GFR as well as an effector mechanism that corrects it. List the conditions that can affect the glomerular filtration rate GFR in kidneys and the manner of its regulation. Glomerular filtration rate GFR is the measure that describes the total amount of filtrate formed by all the renal corpuscles in both kidneys per minute.
The glomerular filtration rate is directly proportional to the pressure gradient in the glomerulus, so changes in pressure will change GFR. GFR is also an indicator of urine production, increased GFR will increase urine production, and vice versa.
The filtration constant is based on the surface area of the glomerular capillaries, and the hydrostatic pressure is a pushing force exerted from the flow of a fluid itself; osmotic pressure is the pulling force exerted by proteins. Many factors can change GFR through changes in hydrostatic pressure, in terms of the flow of blood to the glomerulus.
GFR is most sensitive to hydrostatic pressure changes within the glomerulus. A notable body-wide example is blood volume. Glomerular filtration rate GFR is the measure that describes the total amount of filtrate formed by all the renal corpuscles in both kidneys per minute. The glomerular filtration rate is directly proportional to the pressure gradient in the glomerulus, so changes in pressure will change GFR.
GFR is also an indicator of urine production, increased GFR will increase urine production, and vice versa. The filtration constant is based on the surface area of the glomerular capillaries, and the hydrostatic pressure is a pushing force exerted from the flow of a fluid itself; osmotic pressure is the pulling force exerted by proteins.
Many factors can change GFR through changes in hydrostatic pressure, in terms of the flow of blood to the glomerulus. GFR is most sensitive to hydrostatic pressure changes within the glomerulus.
A notable body-wide example is blood volume. Klabunde Blood volume is determined by the amount of water and sodium ingested, excreted by the kidneys into the urine, and lost through the gastrointestinal tract, lungs and skin.
The amounts of water and sodium ingested and lost are highly variable. To maintain blood volume within a normal range, the kidneys regulate the amount of water and sodium lost into the urine. For example, if excessive water and sodium are ingested, the kidneys normally respond by excreting more water and sodium into the urine.
The details of how the kidneys handle water and sodium are beyond the scope of this cardiovascular web site; therefore, the reader is encouraged to consult general medical physiology textbooks to learn more about this topic. The following paragraphs briefly describe how renal excretion of water and sodium are regulated and how blood volume affects cardiovascular function. Blood is filtered at the glomerulus.
This filtrate contains sodium, water and other substances. The kidneys are innervated by sympathetic nerves of the autonomic nervous system. Sympathetic nervous activity decreases blood flow to the kidney, making more blood available to other areas of the body during times of stress.
The arteriolar myogenic mechanism maintains a steady blood flow by causing arteriolar smooth muscle to contract when blood pressure increases and causing it to relax when blood pressure decreases. Tubuloglomerular feedback involves paracrine signaling at the JGA to cause vasoconstriction or vasodilation to maintain a steady rate of blood flow. Answer the question s below to see how well you understand the topics covered in the previous section. Skip to main content. Module 9: The Urinary System.
Search for:. Regulation of Renal Blood Flow Learning Objectives By the end of this section, you will be able to: Describe the myogenic and tubuloglomerular feedback mechanisms and explain how they affect urine volume and composition Describe the function of the juxtaglomerular apparatus.
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