Anatomy and Physiology

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Urine Formation

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Glomerular filtration

What is glomerular filtration? Glomerular filtration is the first step in making urine. It is the process that your kidneys use to filter excess fluid and waste products out of the blood into the urine collecting tubules of the kidney, so they may be eliminated from your body.

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What is urine formation all about ?

Firtly we need to know what is urine. Urine is tipically a a watery, typically yellowish fluid stored in the bladder and discharged through the urethra. Now what is urine formation about? Urine is formed in the kidneys. Urine has salts, toxins, and water that need to be filtered out of the blood. The kidneys filter unwanted substances from the blood and produce urine to excrete them. There are three main steps of urine formation: glomerular filtration, reabsorption, and secretion. These processes ensure that only waste and excess water are removed from the body.

How does glomerular filtration works

The glomerulus filters your blood As blood flows into each nephron, it enters a cluster of tiny blood vessels—the glomerulus. The thin walls of the glomerulus allow smaller molecules, wastes, and fluid—mostly water—to pass into the tubule. Larger molecules, such as proteins and blood cells, stay in the blood vessel.

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Here is a video to help further your understanding of glomerular filtration

Fun Fact Did you know an average adult produces 6.5 cups of urine a day

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Reabsorbtion

What is tubular Reabsorption? Tubulular reabsorption is the process that moves solutes and water out of the filtrate and back into you bloodstream. This process is known as reabsorption, because this is the second time they hve been absorbed; the first time being when they were absorbed into the bloodstream from the digestive tract after a meal.

How does reabsorption in the nephron work

The nephrons in your kidneys are specifically desinged to maintain body fluid homeostasis. this means keeping extracellular body fluid volumes stable as well as maintaining the right levles of the salts and material that are essential for the normal function of your tissues and organs.

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Reabsorption is a two process

The first step is the passive or active movement of water and dissolved substances from the fluid inside the tubule through the tubule wall into the space outside. The second step is for water and these substances to move through the capillary walls back into your bloodstream, again, either by passive or active transport.

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Reabsorption of sodium,nutrients,water and other ions

Sodium is the major positivelt charged electrolyte in extracellular body fluid. The amount of sodium in the fluid influeneces it's volume, which in turn determines blood volume and blood pressure. Most of the solute reabsorbed in the proximal tuule is in the form of sodium bicarbonate and sodium chloride, and about 70% of the sodium reabsorption occurs here.

Reabsorption in the late proximal convoluted tublule

The fluid entering the late promximal tubile has been dpleted of the essential substances. As bicarbonate was the negatively charged ion initially reabsorbed with sodium, chloride ions have been left behind in the tubule. Due to the extentsive reabsorption of water in the early section of the tubule, chloride ions are high concentrated, and it is now their turn reabsorption.

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Reabsorption in the early proximal convoluted tubule

The most essential in the filtrate are reabsorbed in the first half of the proximal convoluted tubule (early proximal tubule). The include glucose,aminoacids,phosphate,lactate and citrate, which "piggy-back" on sodium cotransporters (membrane proteins that link the movement of two or more specific solutes together) that move sodium down it's electrochemical gradient into tubule epithelial cells

Reabsorption in the loop of henle

The filtrate then enters the loop of loop henle (descending and ascending limbs), which is responsible for concentrating or diluting the tubular fluid using a process called countercurrent multiplication. The distal convoluted tubule and collecting ducts are then largely responsible for reabsorbing water as required to produce urine at a concentration that amintains body fluid homeostasis.

Reabsorption in the thick ascending limb

A further 25% of the sodium and potassium is reabsorbed through the walls of thick ascending limb of the loop of henle

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Reabsorption in the distal tubule and collecting duct

The tubular fluid now enters the distal tubule and collecting duct, or termianl nephron. The early distal tubule reabsorbs a further 5% of the sodium and the late distal tubule and collecting duct fine tune reabsorption of the last little bit (around 3%), determining exactly how much sodium will be excreted. These segments of the nephron have slightly different transporters, as well as the sodium/potassium ATPase that drives reabsorption of calcium and chloride. Sodium reabsorption in the late distal tubule and collecting duct is regulated by hormones, which stimulates or inhibit sodium reabsorbtion as necessary.

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Fun fact Pee can be a window to your overall health.

What is tubular secretion?

The filtrate absorbed in the glomerulus flows through the renal tubule, where nutrients and water are reabsorbed into capillaries. At the same time, waste ions and hydrogen ions pass from the capillaries into the renal tubule. The secreted ions combine with the remaining filtrate and become urine. The urine flows out of the nephron tubule into a collecting duct. It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder. Through this process, the ionic, acid-base and the balance of other body fluids are maintained.

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WHERE IN THE BODY DOES SECRETION OCCUR?

Secretion occurs in the proximal tubule section of the nephron, is responsible for the transport of certain molecules out of the blood and into the urine. Secreted substances include potassium ions, hydrogen ions, and some xenobiotics into filtrate.

Which harmone under secretion causes urine formation

Antidiuretic hormone (ADH) is a chemical produced in the brain that causes the kidneys to release less water, decreasing the amount of urine produced. A high ADH level causes the body to produce less urine. A low level results in greater urine production.

what is the difference between filtration and secretion?

Filtration permits solutes to pass through the membrane and is only limited by particle (molecule) size. Reabsorption is the movement of essential solutes and water from the filtrate back into the bloodstream, while secretion is the movement of solutes from the bloodstream into the filtrate.

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THAT'S ALL FOLKS

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