Renal compensation

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Kidneys within the human body, where renal compensation takes place. Kidney (PSF).png
Kidneys within the human body, where renal compensation takes place.

Renal compensation is a mechanism by which the kidneys can regulate the plasma pH. It is slower than respiratory compensation, but has a greater ability to restore normal values. Kidneys maintain the acid-base balance through two mechanisms: (1) the secretion of H+ ions into the urine (from the blood) and (2) the reabsorption of bicarbonate HCO
3
(i.e., bicarbonate moves from urine back into the blood). [1] The regulation of H+ ions and bicarbonate HCO
3
is determined by the concentration of the two released within the urine. [1] These mechanisms of secretion and reabsorption balance the pH of the bloodstream. [1] A restored acid-base balanced bloodstream thus leads to a restored acid-base balance throughout the entire body.

Contents

Human pH

An ideal pH within the human body ranges from 7.35-7.45. [2] When the pH of the body falls below 7.35, an acidemia occurs. [2] Similarly, when the pH of the body rises above 7.45, an alkalemia occurs. [2] Renal compensation is one of the many compensatory mechanisms within the body which assist the pH level in ranging between 7.35 and 7.45 as the body cannot function properly when the pH falls out of this range. [2]

Respiratory and renal changes in acid-base elimination typically contrast each other, and respiratory pH disturbances often commence renal compensation. [3] The renal compensation process usually takes a few days to complete as it is dependent upon changes in the reabsorption of bicarbonate. [4] End-staged renal diseases as well as chronic kidney diseases increase the overall risk of individuals developing pneumonia due to the interactions between the kidneys and the lungs. [3] Both organs are targets of similar systematic diseases and loss of normal function of one organ can induce the disregulation of and abnormalities within the other.

Production in the Kidneys

In respiratory acidosis, the kidney produces and excretes ammonium (NH4+) and monophosphate, generating bicarbonate in the process while clearing acid. There is also an excretion of Cl- and a reabsorption of sodium, resulting in a negative urinary anion gap. [5]

In respiratory alkalosis, less bicarbonate (HCO3) is reabsorbed, thus lowering the pH.

Related Research Articles

In biology, homeostasis is the state of steady internal physical and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain pre-set limits. Other variables include the pH of extracellular fluid, the concentrations of sodium, potassium, and calcium ions, as well as the blood sugar level, and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.

<span class="mw-page-title-main">Kidney</span> Organ that filters blood and produces urine in humans

In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retroperitoneal space, and in adult humans are about 12 centimetres in length. They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder.

Azotemia is a medical condition characterized by abnormally high levels of nitrogen-containing compounds in the blood. It is largely related to insufficient or dysfunctional filtering of blood by the kidneys. It can lead to uremia and acute kidney injury if not controlled.

<span class="mw-page-title-main">Nephron</span> Microscopic structural and functional unit of the kidney

The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure called Bowman's capsule. The renal tubule extends from the capsule. The capsule and tubule are connected and are composed of epithelial cells with a lumen. A healthy adult has 1 to 1.5 million nephrons in each kidney. Blood is filtered as it passes through three layers: the endothelial cells of the capillary wall, its basement membrane, and between the foot processes of the podocytes of the lining of the capsule. The tubule has adjacent peritubular capillaries that run between the descending and ascending portions of the tubule. As the fluid from the capsule flows down into the tubule, it is processed by the epithelial cells lining the tubule: water is reabsorbed and substances are exchanged ; first with the interstitial fluid outside the tubules, and then into the plasma in the adjacent peritubular capillaries through the endothelial cells lining that capillary. This process regulates the volume of body fluid as well as levels of many body substances. At the end of the tubule, the remaining fluid—urine—exits: it is composed of water, metabolic waste, and toxins.

Diuresis is the excretion of urine, especially when excessive (polyuria). The term collectively denotes the physiologic processes underpinning increased urine production by the kidneys during maintenance of fluid balance.

<span class="mw-page-title-main">Acetazolamide</span> Chemical compound

Acetazolamide, sold under the trade name Diamox among others, is a medication used to treat glaucoma, epilepsy, acute mountain sickness, periodic paralysis, idiopathic intracranial hypertension, heart failure and to alkalinize urine. It may be used long term for the treatment of open angle glaucoma and short term for acute angle closure glaucoma until surgery can be carried out. It is taken by mouth or injection into a vein. Acetazolamide is a first generation carbonic anhydrase inhibitor and it decreases the ocular fluid and osmolality in the eye to decrease intraocular pressure.

<span class="mw-page-title-main">Collecting duct system</span> Kidney system

The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin.

<span class="mw-page-title-main">Renal physiology</span> Study of the physiology of the kidney

Renal physiology is the study of the physiology of the kidney. This encompasses all functions of the kidney, including maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.

<span class="mw-page-title-main">Metabolic acidosis</span> Imbalance in the bodys acid-base equilibrium

Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys to excrete excess acids. Metabolic acidosis can lead to acidemia, which is defined as arterial blood pH that is lower than 7.35. Acidemia and acidosis are not mutually exclusive – pH and hydrogen ion concentrations also depend on the coexistence of other acid-base disorders; therefore, pH levels in people with metabolic acidosis can range from low to high.

<span class="mw-page-title-main">Respiratory acidosis</span> Decrease in blood pH due to insufficient breathing

Respiratory acidosis is a state in which decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and decreases the blood's pH.

<span class="mw-page-title-main">Respiratory alkalosis</span> Increase in blood pH due to rapid breathing

Respiratory alkalosis is a medical condition in which increased respiration elevates the blood pH beyond the normal range (7.35–7.45) with a concurrent reduction in arterial levels of carbon dioxide. This condition is one of the four primary disturbance of acid–base homeostasis.

The anion gap is a value calculated from the results of multiple individual medical lab tests. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel.

<span class="mw-page-title-main">Metabolic alkalosis</span> Increase in blood pH due to imbalance in hydrogen ion and bicarbonate concentrations

Metabolic alkalosis is an acid-base disorder in which the pH of tissue is elevated beyond the normal range (7.35–7.45). This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations. The condition typically cannot last long if the kidneys are functioning properly.

In physiology, base excess and base deficit refer to an excess or deficit, respectively, in the amount of base present in the blood. The value is usually reported as a concentration in units of mEq/L (mmol/L), with positive numbers indicating an excess of base and negative a deficit. A typical reference range for base excess is −2 to +2 mEq/L.

Hyperchloremic acidosis is a form of metabolic acidosis associated with a normal anion gap, a decrease in plasma bicarbonate concentration, and an increase in plasma chloride concentration. Although plasma anion gap is normal, this condition is often associated with an increased urine anion gap, due to the kidney's inability to secrete ammonia.

<span class="mw-page-title-main">Renal tubular acidosis</span> Higher blood acidity due to failure of the kidneys to fully acidify urine

Renal tubular acidosis (RTA) is a medical condition that involves an accumulation of acid in the body due to a failure of the kidneys to appropriately acidify the urine. In renal physiology, when blood is filtered by the kidney, the filtrate passes through the tubules of the nephron, allowing for exchange of salts, acid equivalents, and other solutes before it drains into the bladder as urine. The metabolic acidosis that results from RTA may be caused either by insufficient secretion of hydrogen ions into the latter portions of the nephron or by failure to reabsorb sufficient bicarbonate ions from the filtrate in the early portion of the nephron. Although a metabolic acidosis also occurs in those with chronic kidney disease, the term RTA is reserved for individuals with poor urinary acidification in otherwise well-functioning kidneys. Several different types of RTA exist, which all have different syndromes and different causes. RTA is usually an incidental finding based on routine blood draws that show abnormal results. Clinically, patients may present with vague symptoms such as dehydration, mental status changes, or delayed growth in adolescents.

In renal physiology, net acid excretion (NAE) is the net amount of acid excreted in the urine per unit time. Its value depends on urine flow rate, urine acid concentration, and the concentration of bicarbonate in the urine. NAE is commonly expressed in units of milliliters per minute (ml/min) and is given by the following equation:

Acid–base homeostasis is the homeostatic regulation of the pH of the body's extracellular fluid (ECF). The proper balance between the acids and bases in the ECF is crucial for the normal physiology of the body—and for cellular metabolism. The pH of the intracellular fluid and the extracellular fluid need to be maintained at a constant level.

<span class="mw-page-title-main">Bicarbonate buffer system</span> Buffer system that maintains pH balance in humans

The bicarbonate buffer system is an acid-base homeostatic mechanism involving the balance of carbonic acid (H2CO3), bicarbonate ion (HCO
3
), and carbon dioxide (CO2) in order to maintain pH in the blood and duodenum, among other tissues, to support proper metabolic function. Catalyzed by carbonic anhydrase, carbon dioxide (CO2) reacts with water (H2O) to form carbonic acid (H2CO3), which in turn rapidly dissociates to form a bicarbonate ion (HCO
3
) and a hydrogen ion (H+) as shown in the following reaction:

<span class="mw-page-title-main">Acid–base disorder</span> Abnormality of the human bodys normal balance of acids and bases

Acid–base imbalance is an abnormality of the human body's normal balance of acids and bases that causes the plasma pH to deviate out of the normal range. In the fetus, the normal range differs based on which umbilical vessel is sampled. It can exist in varying levels of severity, some life-threatening.

References

  1. 1 2 3 "Video: Overview of the Role of the Kidneys in Acid-Base Balance". Merck Manuals Professional Edition. Retrieved 2023-04-03.
  2. 1 2 3 4 Hopkins, Erin; Sanvictores, Terrence; Sharma, Sandeep (2023), "Physiology, Acid Base Balance", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   29939584 , retrieved 2023-04-03
  3. 1 2 Carroll, Robert G. (2007). Elsevier's Integrated Physiology. ISBN   9780323043182 . Retrieved 2023-04-03.
  4. Sorino, Claudio; Scichilone, Nicola; Pedone, Claudio; Negri, Stefano; Visca, Dina; Spanevello, Antonio (October 2019). "When kidneys and lungs suffer together". Journal of Nephrology. 32 (5): 699–707. doi:10.1007/s40620-018-00563-1. hdl: 10447/375144 . ISSN   1724-6059. PMID   30523563. S2CID   202642130.
  5. Ha, Chung Eun; Bhagavan, N. V. (16 June 2015). Essentials of Medical Biochemistry. ISBN   9780124166875 . Retrieved 2023-04-03.