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Industrial chemical processes often involve resource intensive separation steps. While most biochemical synthetic methods themselves do not need separation steps, other physiological processes do. One example is the filtering of blood which removes potentially harmful organic and inorganic materials. Water, as well as useful minerals, glucose, and proteins are separated from the harmful materials and recycled back into the blood stream. If the water and useful compounds were excreted along with the harmful compounds, the organism would have to consume gallons of water and many grams of minerals on a constant, daily basis to recover the loss.
The filtration aspect of the kidney can be thought of as a collection of hundreds of thousands to over a million independent assembly lines carrying out the same intricate task. The assembly line here is the nephron, a tubular structure with specialized regions along its length. The great quantity of useful water that is excreted is reabsorbed back into the blood as the nephron first descends into the deeper tissues of the kidney. This part of the nephron is the descending limb of its “loop of Henle.” The cells lining the descending limb are permeable to water and impermeable to ions. As the limb descends through progressively saltier (hypertonic) regions of the kidney, water in the relatively un-salty (hypotonic) filtrate passively flows out of the nephron’s lumen (interior space) and into the surrounding salty tissues via osmosis. The concentrated filtrate then travels up the ascending limb of the loop of Henle, which ascends back towards the surface of the kidney through progressively less salty (increasingly hypotonic) interstitial regions. In contrast with the descending limb, the cells that line the lumen of the ascending limb are permeable to ions and impermeable to water. Useful ions in the filtrate are reabsorbed as they flow down their concentration gradient into the surrounding kidney tissues through protein channels, while water is excluded.
Further along the nephron, protein pumps actively transport useful ions and substances between the lumen and the kidney cells and vice versa. Active transport requires an energy input by depleting ATP molecules. More water is also absorbed, so that by the time the filtrate reaches the bladder as fully formed urine, it contains only one percent of the volume of the early filtrate.
Nephron showing movement of ions, water, glucose, and proteins
from the tubules to the bloodstream. Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.
“Tubular reabsorption is the movement of fluid and solutes from the tubular system into the peritubular capillaries. This process allows the body to retain fluid and desired solutes. At a glomerular filtration rate of 125 ml/min., the kidneys produce 180 liters of filtrate daily. Yet the average urine output is only 1,000 to 1,500 ml. Through reabsorption, 99% of the glomerular filtrate is returned to the bloodstream. The proximal tubule is the major site of reabsorption in the tubular system… it reabsorbs, and thus, returns to the plasma, up to 100% of the filtered solutes that the body does not routinely wish to discard, such as glucose, amino acids, and bicarbonate and reabsorbs a large percentage of solutes, such as sodium, potassium, chloride, calcium, and magnesium, and water…reabsorption involves both passive and active transport mechanisms. Passive transport includes osmosis and diffusion while active transport mechanisms, such as primary and secondary transport and endocytosis, require the use of energy to move substances against an electrochemical gradient. Reabsorption of fluid and solutes is regulated to meet the body’s physiological needs.” (Chmielewski 2003:187-188)
Renal anatomy and overview of nephron function
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this is very nice information about human kidney, it really fruitful in future, i found another article about human kidney and its fitness here http://healthcarencare.com/human-kidney-and-its-function/ , this article should also increase my knowledge
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- Your Kidneys & How They Work
Your Kidneys & How They Work
On this page:
- Why are the kidneys important?
- How do my kidneys work?
- How does blood flow through my kidneys?
- Clinical Trials
The kidneys are two bean-shaped organs, each about the size of a fist. They are located just below the rib cage, one on each side of your spine.
Healthy kidneys filter about a half cup of blood every minute, removing wastes and extra water to make urine . The urine flows from the kidneys to the bladder through two thin tubes of muscle called ureters, one on each side of your bladder. Your bladder stores urine. Your kidneys, ureters, and bladder are part of your urinary tract .
Why are the kidneys important?
Your kidneys remove wastes and extra fluid from your body. Your kidneys also remove acid that is produced by the cells of your body and maintain a healthy balance of water, salts, and minerals—such as sodium , calcium , phosphorus , and potassium —in your blood.
Without this balance, nerves, muscles, and other tissues in your body may not work normally.
Your kidneys also make hormones that help
- control your blood pressure
- make red blood cells
- keep your bones strong and healthy
Watch a video about what the kidneys do .
How do my kidneys work?
Each of your kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus , and a tubule . The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.
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.
The tubule returns needed substances to your blood and removes wastes
A blood vessel runs alongside the tubule. As the filtered fluid moves along the tubule, the blood vessel reabsorbs almost all of the water, along with minerals and nutrients your body needs. The tubule helps remove excess acid from the blood. The remaining fluid and wastes in the tubule become urine.
How does blood flow through my kidneys?
Blood flows into your kidney through the renal artery . This large blood vessel branches into smaller and smaller blood vessels until the blood reaches the nephrons. In the nephron, your blood is filtered by the tiny blood vessels of the glomeruli and then flows out of your kidney through the renal vein.
Your blood circulates through your kidneys many times a day. In a single day, your kidneys filter about 150 quarts of blood. Most of the water and other substances that filter through your glomeruli are returned to your blood by the tubules. Only 1 to 2 quarts become urine.
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions.
What are clinical trials, and are they right for you?
Clinical trials are part of clinical research and at the heart of all medical advances. Clinical trials look at new ways to prevent, detect, or treat disease. Researchers also use clinical trials to look at other aspects of care, such as improving the quality of life for people with chronic illnesses. Find out if clinical trials are right for you .
What clinical trials are open?
Clinical trials that are currently open and are recruiting can be viewed at www.ClinicalTrials.gov .
This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases
(NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings
through its clearinghouses and education programs to increase knowledge and understanding about health and
disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully
reviewed by NIDDK scientists and other experts.
A nephron is the basic unit of structure in the kidney. A nephron is used separate to water, ions and small molecules from the blood, filter out wastes and toxins, and return needed molecules to the blood. The nephron functions through ultrafiltration. Ultrafiltration occurs when blood pressure forces water and other small molecules through tiny gaps in capillary walls. This substance, lacking the blood cells and large molecules in the bloodstream, is known as an ultrafiltrate. The ultrafiltrate travels through the various loops of the nephron, where water and important molecules are removed, and into a collecting duct which drains into the bladder.
The glomerulus is the specialized configuration of capillaries within the nephron that make kidneys possible. Vertebrates are the only group to have developed kidneys, which is mostly used to conserve water in terrestrial environments. Fish and other primitive vertebrates excrete ammonia as a byproduct of protein reactions. Ammonia is toxic in the bloodstream, and must be removed. Reptiles and birds excrete uric acid, which is a more concentrated form of ammonia. Mammals have even more derived nephrons, which contain an extended loop, called the loop of Henle. Mammals produce urea from ammonia, and concentrate the urea in the urine to a high extent. This promotes the extraction of water from the ultrafiltrate, and allows mammals to live in some of the driest environments on Earth. A camel, for instance, will continually filter most of the water from its blood, recollect a large majority of that water, and reuse it continually.
Function of a Nephron
A nephron is responsible for removing waste products, stray ions, and excess water from the blood. The blood travels through the glomerulus, which is surrounded by the glomerular capsule. As the heart pumps the blood, the pressure created pushes small molecules through the capillaries and into the glomerular capsule. This is the, more physical function of the nephron. Next, the ultrafiltrate must travel through a winding series of tubules. The cells in each part of the tube have different molecules that they like to absorb. Molecules to be excreted remain in the tubule, while water, glucose and other beneficial molecules work their way back into the bloodstream. As the ultrafiltrate travels down the tubules, the cells become more and more hypertonic compared to the ultrafiltrate. This causes a maximum amount of water to be extracted from the ultrafiltrate before it exits the nephron. The blood surrounding the nephron returns to the body via the interlobular vein, free of toxins and excess substances. The ultrafiltrate is now urine, and moves via the collecting duct to the bladder, where it will be stored.
Structure of Nephron
The picture below is of a general nephron. This nephron contains a loop of Henle, so it is a mammalian nephron. While the loop of the nephron is special to mammals, the rest of the structure is seen in all vertebrate animals. The glomerulus is the net of capillaries inside of the glomerular capsule (aka Bowman’s capsule). While the picture shows the glomerular capsule and the rest of the renal tubule look to be the same in the graphic below, they are in fact composed of a wide variety of cell types, intended to extract and retain certain chemicals within the tubules.
Each nephron consists of one main interlobular artery feeding a single renal tubule. Each kidney in a vertebrate has hundreds to millions of nephrons, each of which produces urine and sends it to the bladder. The cells in each nephron are arranged so that the most concentrated cells are at the bottom of the nephron, while the cells at the top are less concentrated. The cells near the exit of the nephron are the most concentrated, and therefore extract as much water as possible from the ultrafiltrate before it is sent to the bladder.
Related Biology Terms
- Kidney – An organ containing hundreds, or millions of individual nephrons, used to concentrate urine from the blood.
- Liver – An organ in the body which metabolizes certain molecules in the blood, and controls the levels of a variety of important blood components.
- Renal – Relating to the kidneys.
1. Imagine this scenario in a nephron. The cells at the start of the loop of Henle are more concentrated than the cells at the end. Which of the following would be true, if this were the case?
A. The organism would retain more water
B. The organism would retain less water
C. This would not affect the amount of water retained
2. Why do mammals require a loop of Henle in each nephron, while fish do not?
A. Mammals create more waste
B. The urine mammals create is more concentrated
C. Fish have access to as much water as they need to process waste
3. Why can you survive with only 1 kidney?
A. Each nephron is extremely efficient
B. Your other organs will pick up the task of filtration
C. Two kidneys actually over filter the blood
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