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What Does The Kidney Secrete

Hormonecontrol Of Water And Salt


Water reabsorption is controlled by the in . ADH is released from the in the brain. Dropping levels offluid in the blood signal the hypothalamusto cause the pituitary to release ADH into the blood. ADH acts toincrease water absorption in the kidneys. This puts more water backin the blood, increasing the concentration of the urine. When toomuch fluid is present in the blood, sensors in the heart signal thehypothalamus to cause a reduction of the amounts of ADH in the blood.This increases the amount of water absorbed by the kidneys, producinglarge quantities of a more dilute urine.

Aldosterone,a hormone secreted by the kidneys, regulates the transfer of sodiumfrom the nephron to the blood. When sodium levels in the blood fall,aldosterone is released into the blood, causing more sodium to passfrom the nephron to the blood. This causes water to flow into theblood by osmosis. Reninis released into the blood to control aldosterone.

What Substance Do The Kidneys Secrete

The kidneys filter urea, excess water and some mineral salts from the blood. This solution of unwanted products is referred to as urine.

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General Function Of The Kidney

The kidney has evolved so as to enable humans to exist on land where water and salts must be conserved, wastes excreted in concentrated form, and the blood and the tissue fluids strictly regulated as to volume, chemical composition, and osmotic pressure. Under the drive of arterial pressure, water and salts are filtered from the blood through the capillaries of the glomerulus into the lumen, or passageway, of the nephron, and then most of the water and the substances that are essential to the body are reabsorbed into the blood. The remaining filtrate is drained off as urine. The kidneys, thus, help maintain a constant internal environment despite a wide range of changes in the external environment.

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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 Urinary System Is One Of The Bodys Systems Which Helps Us To Dispose Of The Waste Products Naturally Produced Within The Body The Main Structures In This System Are:

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  • Two kidneys which lie behind the other major organs in the lower back area. They are bean-shaped organs and measure about 11cm long, 6cm wide and 3cm deep. They have 5 main functions, which will be discussed at a later stage.
  • Two ureters which run from the kidneys to the bladder carrying urine.
  • One bladder which collects urine from the kidneys, via the ureters, and stores it temporarily.
  • One urethra through which the urine is excreted out of the body, allowing the bladder to empty and dispose of the waste.

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The Role Of Hormones In Renal Function

Certain hormones and hormonelike substances are intimately related to renal function. Some of these, such as ADH , are produced outside the kidney and travel to the kidney via the blood as chemical messengers. Others are produced within the kidney and appear to exert only a local effect. The role of ADH in controlling diuresis has already been discussed. ADH regulates water excretion by increasing the permeability of the collecting ducts to water and salt and by accelerating water and ion transfer in a direction determined by the osmotic gradient. The receptors at the base of the brain form part of the feedback mechanism that stimulates ADH output if the osmotic concentration of extracellular fluid is high, so as to concentrate the urine, and reduces ADH output and so dilutes the urine if osmotic concentration of ECF and of plasma falls.

The most recently identified hormone that influences renal function is secreted by special stretch receptor cells in the atria of the heart in response to a rise in atrial pressure, as during heart failure. This hormone, called atrial natriuretic peptide , exerts a vasodilator effect on the kidney and also reduces tubular reabsorption of sodium. Both actions result in increased urinary elimination of salt and water and tend to restore atrial pressure toward the normal. It is probably an important hormone controlling the volume of the extracellular fluid.

Can A Person Without A Medical Disease Or Condition Have A High Erythropoietin Level

Yes. For example, erythropoietin has been misused as a performance-enhancing drug in athletes such as cyclists , long-distance runners, speed skaters, and Nordic skiers. When misused in such situations, erythropoietin is thought to be especially dangerous of the blood, raising the risk for blood clots, heart attacks, and strokes. Erythropoietin has been banned by the Tour de France, the Olympics, and other sports organizations.

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Regulation Of Kidney Function

  • Diabetes Insipidus: Deficiency of ADH causes Diabetes insipidus. This hormone is synthesized by the hypothalamus but is secreted from the posterior pituitary. Due to the under secretion of ADH, a large amount of water is excreted out of the body, and the urine formed is highly dilute. This may occur due to hypothalamic destruction or neurohypophyseal destruction.Symptoms include intense thirst, dilute urine and excessive urination .
  • Hypertension due to oversecretion of renin: If renin is secreted from juxtaglomerular cells in large amounts, then there will be more activation of angiotensinogen to angiotensin, which in turn leads to more constriction of blood vessels resulting in hypertension.
  • Role Of The Kidneys In The Regulation Of Intra

    What is the adrenal gland, and what does it do?

    Seriki A Samue1*, Adebayo O Francis1 and Odetola O Anthony2

    1Department of Human Physiology, College of Medicine, Bingham University, Karu, Nigeria2Department of Human Physiology, Faculty of Medicine, Nnamdi Azikiwe University, Awka, Nigeria

    *Address for Correspondence: Seriki A. Samuel, Department of Human Physiology, College of Medicine, Bingham University, Karu, Nigeria, Tel: +2348036041121; Email: [email protected]

    Dates:Submitted: 05 July 2018; Approved: 16 July 2018; 17 July 2018

    How to cite this article: Samuel SA, Francis AO, Anthony OO. Role of the Kidneys in the Regulation of Intra- and Extra-Renal Blood Pressure. Ann Clin Hypertens. 2018; 2: 048-058. DOI: 10.29328/journal.ach.1001011

    Copyright:© 2018 Samuel SA, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

    Keywords: Hypertension; Renin Angiotensin System; Natriuresis; Sodium balance homeostasis

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    Is There Anything Else I Should Know

    If anemia is due to a vitamin B12, folate, or iron deficiency, then the anemia may persist even when enough erythropoietin is produced. The red blood cells produced in these deficiencies may not be normal in size, shape, and/or hemoglobin content.

    Pregnant women, chronic smokers, and people with lung disease, or who live at high altitudes may have increased levels of erythropoietin.

    Anephron Structure And Function

    The basic unit of the kidney is the nephron, which functions to eliminate metabolic waste products and regulate water, electrolyte and acidbase balance. The human kidney contains approximately one million nephrons. Most of the nephrons are located toward the outer surface of the cortex, but about 15% are located deep in the cortex. Each nephron consists of a renal corpuscle attached to a renal tubule . The renal tubule is differentiated into a proximal convoluted tubule, closest to the renal corpuscle, an intermediate looped segment, the loop of Henle, and a distal convoluted tubule that flows into a collecting duct. The different parts of the renal tubule have specialized roles in water absorption and ion pumping. The loops of Henle and the collecting ducts extend into the medulla of the kidney. The collecting ducts flow into larger ducts called calyces, which eventually merge to flow into the ureters. Urine is collected in the bladder and excreted through the ureters and urethra.

    Figure 5.20. Diagram of nephron with all its parts laid out in linear order, along with the functions of each part.

    D.H. Sweet, in, 2014

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    How Do Kidneys Work:

    As blood flows through the body it picks up waste and carries this to the kidneys using the kidney arteries. The waste in your blood comes from the normal breakdown of active tissues and from the food you eat. Your body uses food for energy and selfrepair. After the body has taken what it needs, from the food, the waste is sent to the blood. The kidneys filter out the waste products and excess fluids from the body and dispose of them in the form of urine, via the bladder. The clean blood flows back to the other parts of the body. If your kidneys did not remove this waste, it would build up in the blood and cause damage to your body.

    The actual filtering occurs in tiny units inside your kidneys called nephrons. Each kidney contains about a million nephrons. In the nephron, a glomerulus intertwines with a urine collecting tube called tubules. A complicated chemical exchange takes place, as waste materials and water in your blood enter your urinary system.

    In addition to removing waste, the kidneys have other important functions. These are carried outwith the help of three hormones, which are released in the kidneys.

    Difference Between Renin And Rennin

    Urinary System CH17
    It is secreted from the juxtaglomerular cells of the kidneys. It is secreted by the gastric glands present in the stomach.
    It is secreted in active form. It is secreted in inactive form as prorennin.
    It is an enzyme that converts the inactive angiotensinogen to active angiotensin I. It is a proteolytic enzyme that digests milk protein Casein.
    Its secretion is stimulated when there is low GFR or decreased sodium load in tubular fluids. Its secretion is stimulated by the presence of food in the stomach.

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    Waste Ions And Hydrogen Ions Secreted From The Blood Complete The Formation Of Urine

    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. This process is called secretion. 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.

    Frequently Asked Questions On Regulation Of Kidney Function

    Q.1. What is the role of ANF in the regulation of kidney function?Ans:1. ANF carries out vasodilation, i.e., dilating the blood vessels and thereby decreasing the blood pressure.2. It also provides negative feedback inhibition to the hormone renin, angiotensin and ADH, which results in decreasing the GFR.3. ANF also enhances the excretion of sodium and water by the kidneys.

    Q.2. How is kidney function regulated?Ans:The regulation of kidneys functioning is under the control of a complex hormonal mechanism regulated by the Antidiuretic hormone , Renin-Angiotensin-Aldosterone System and Atrial Natriuretic Factor . Kidney functions are also auto regulated as well as regulated by the neural system.

    Q.3. What is a Juxtaglomerular apparatus?Ans:It consists of three types of cells:-a. Juxtaglomerular cells

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    How Does The Urinary System Work

    The body takes nutrients from food and changes them to energy. After the body has taken the food components that it needs, waste products are left behind in the bowel and in the blood.

    The kidney and urinary systems help the body to get rid of liquid waste called urea. They also help to;keep chemicals and water in balance. Urea is produced when foods containing protein are broken down in the body. Urea is carried in the blood to the kidneys. This is where it is removed, along with water and other wastes in the form of urine.

    The kidneys have other important functions. They control blood pressure and produce the hormone erythropoietin. This hormone controls red blood cell production in the bone marrow. The kidneys also control the acid-base balance and conserve fluids.

    What Is Being Tested

    Kidneys and how they function with the renin-angiotensin system, EPO, ADH, and Aldosterone

    Erythropoietin is a hormone produced primarily by the kidneys, with small amounts made by the liver. EPO plays a key role in the production of red blood cells , which carry oxygen from the lungs to the rest of the body. This test measures the amount of erythropoietin in the blood.

    The body uses a dynamic feedback system to help maintain sufficient oxygen levels and a relatively stable number of RBCs in the blood.

    • Erythropoietin is produced and released into the blood by the kidneys in response to low blood oxygen levels . The amount of erythropoietin released depends on how low the oxygen level is and the ability of the kidneys to produce erythropoietin.
    • EPO is carried to the bone marrow, where it stimulates production of red blood cells. The hormone is active for a short period of time and then eliminated from the body in the urine.
    • As oxygen levels in the blood rise to normal or near normal levels, the kidneys slow production of EPO.

    However, if your kidneys are damaged and do not produce enough erythropoietin, then too few RBCs are produced and you can becomes anemic. Similarly, if your bone marrow is unable to respond to the stimulation from EPO, then you may become anemic. This can occur with some bone marrow disorders or with chronic diseases, such as rheumatoid arthritis.

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    Is Erythropoietin Available As A Prescribed Medication

    Yes. Using recombinant DNA technology, erythropoietin has been synthetically produced for use as a treatment for persons with certain types of anemia. Erythropoietin can be used to correct anemia by stimulating red blood cell production in the bone marrow in these conditions. The medication is known as epoetin alfa or as darbepoietin alfa . It can be given as an injection intravenously or subcutaneously .

    Secretion Of Active Compounds

    The kidneys release a number of important compounds, including:

    • Erythropoietin: This controls erythropoiesis, or the production of red blood cells. The liver also produces erythropoietin, but the kidneys are its main producers in adults.
    • Renin: This helps manage the expansion of arteries and the volume of blood plasma, lymph, and interstitial fluid. Lymph is a fluid that contains white blood cells, which support immune activity, and interstitial fluid is the main component of extracellular fluid.
    • Calcitriol: This is the hormonally active metabolite of vitamin D. It increases both the amount of calcium that the intestines can absorb and the reabsorption of phosphate in the kidney.

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    How Does Blood Flow Through My Kidneys

    Blood flows into your kidney through the renalartery. 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.

    Red Blood Cell Production

    Kidney Disease: Know The Signs

    Erythropoietin is an essential hormone for red blood cell production. Without it, definitive erythropoiesis does not take place. Under hypoxic conditions, the kidney will produce and secrete erythropoietin to increase the production of red blood cells by targeting CFU-E, proerythroblast and basophilic erythroblast subsets in the differentiation. Erythropoietin has its primary effect on red blood cell progenitors and precursors by promoting their survival through protecting these cells from apoptosis, or cell death.

    Erythropoietin is the primary erythropoietic factor that cooperates with various other growth factors involved in the development of erythroid lineage from multipotent progenitors. The burst-forming unit-erythroid cells start erythropoietin receptor expression and are sensitive to erythropoietin. Subsequent stage, the colony-forming unit-erythroid , expresses maximal erythropoietin receptor density and is completely dependent on erythropoietin for further differentiation. Precursors of red cells, the proerythroblasts and basophilic erythroblasts also express erythropoietin receptor and are therefore affected by it.

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    Kidneys And Acidbase Balance

    The kidneys have two very important roles in maintaining the acidbase balance:

  • They reabsorb bicarbonate from urine.
  • They excrete hydrogen ions into urine.
  • The kidneys are slower to compensate than the lungs, but renal physiology has several powerful mechanisms to control pH by the excretion of excess acid or base. The major, homeostatic control point for maintaining a stable pH balance is renal excretion.

    Bicarbonate does not have a transporter, so its reabsorption involves a series of reactions in the tubule lumen and tubular epithelium. In response to acidosis, the tubular cells reabsorb more bicarbonate from the tubular fluid, and the collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to an increase in the formation of the NH3 buffer.

    In response to alkalosis, the kidneys may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering the rates of glutamine metabolism and ammonium excretion.



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