HomeostasisHomeostasisBlood Blood ppH RegulationH Regulation

Nabi B. Nabi B. Solangi, M.Phil. (PursuingSolangi, M.Phil. (Pursuing))Reg. No. 2K15Reg. No. 2K15--BPBP--7979

Supervised By.Supervised By.

Dr. Moolchand Malhi, Ph.D.Dr. Moolchand Malhi, Ph.D.Assistant ProfessorAssistant Professor

Department of Physiology and BiochemistryDepartment of Physiology and BiochemistryFaculty of A. H. and Vet. Sc. SAU Tando JamFaculty of A. H. and Vet. Sc. SAU Tando Jam

HOMEOSTASISHOMEOSTASISRegulation of Blood pH by renal system

HomeostasisHomeostasis Defined as maintenance of a relatively

stable internal environment◦ Does not mean that composition, temperature,

and other characteristics are absolutely unchanging

Homeostasis is essential for survival and function of all cells

Each cell contributes to maintenance of a relatively stable internal environment

Regulation of acid base balance by Kidneys

Activities of almost all enzyme systems within body are influenced by H+ concentration.

Substances that release H+ are referred as Acids and substance that tendency to receive H+ are referred to as Bases.

H+ is single free proton released by hydrogen atom.

HCl Ionization H+ +Cl-

H2CO3Ionize in water H++CO-

3Carbonic Acid Hydrogen ion+ Bicarbonate ions

Low pH corresponds to high H+ andHigh pH corresponds to low H+

Medium pH Impact

Arterial Blood 7.4 If decreases causes Acidosis*

Venous Blood 7.35 If increases causes Alkalosis**

Interstitial Fluid 7.35

Intra cellular 6-7.4

Urine 4.5-8

HCl 0.8

pH values*at the pH of 6.8 (acidosis), individual can live more than few hours.**at the pH of 8.0 (alkalosis), individual can live more than few hours.

Venous blood has high pH due to extra amount of CO2. While interstitial fluids have high pH as compare to the intracellular pH

Intracellular pH

Intra cellular pH is slightly lower than plasma pH.

During metabolism of cells they produce carbonic acid depending upon type of cells.

Carbonic acid ionizes to form hydrogen ion and bicarbonate ions ultimately give rise to H+ concentration which means lower pH as compare to plasma.

pH of urine

pH of urine ranges from 4.5 to 8.0 depending upon acid-base balance of extracellular fluid.

HCl is extreme acid body fluid having pH of 0.8. it is secreted by oxyntic (parietal) cells of stomach mucosa.

DEFENSE AGAINST DEFENSE AGAINST CHANGES OF HCHANGES OF H++ IN IN BODYBODY

There are three basic mechanisms to control hydrogen ion concentration (pH) within body.

Chemical acid base buffer system Respiratory System Renal System

React within fraction of seconds

Don’t add or eliminate H+

Only keep them tied until acid base balance is re-established

Acts within few minutes Eliminate CO2 and therefore

H2CO3 from body

Acts in hours to days Most powerful mechanism Secretes H+, reabsorbs and

produce HCO-3

First two mechanisms keep H+ concentration from changing too much until the third line of action gets in action.

Renal Control of acid base balance

Kidneys control acid-base balance by secreting acidic or basic urine. HCO-3 are filtered continuously in tubules, if excreted into urine it removes base from blood

RE ABSORPTION OF RE ABSORPTION OF CARBONATE AND CARBONATE AND EXCRETION OF HEXCRETION OF H+ + BY BY KIDNEYKIDNEY

Re absorption of carbonate and excretion of H+ is accomplished through the process of H+ secretion by the tubules

HCO-3 + H+ H2CO3

Here HCO-3 is filtered by the tubules at different stages and H+ is

secreted by the lumen of tubules.

This re absorption of HCO-3 and secretion of H+ occurs in almost all

parts of tubules except ascending and descending thin limbs of loop of Henle.

There are three basic mechanisms to regulate H+ concentration in extracellular fluid are as follows.

•Secretion of H+

•Re absorption of HCO-3

•Production of HCO-3

Secretion of H+

Cellular Mechanism for; (1) active secretion of hydrogen ions into the renal tubules, (2) tubular reabsorption of bicarbonate ions, (3) sodium ion reabsorption in exchange for hydrogen ion secreted. This pattern of hydrogen ion secretion occurs in proximal tubules, thick ascending segment of the loop of Henle and the early distal tubule

Active secretion of H+

Secretion of H+ takes place in distal, convoluted tubules and in collecting ducts.

The secretion is facilitated by hydrogen-transporting ATPase (a specific protein). About 5% of total H+ secretion takes place here which makes urine more acidic.

Bicarbonate ion is absorbed for each hydrogen ion secreted, and a chloride ion is passively secreted along with the hydrogen ion

Re absorption of HCO-3

H2CO3 ionize to form H+ and HCO-

3, in this way HCO-3

enters the interstitial fluid crossing basolateral membrane, taken into the peritubular capillary blood.

Thus at each H+ secretion an HCO-

3 enters to the blood

Production of new HCO-3

Buffering of secreted hydrogen ions by filtered phosphate;

New bicarbonate ion is returned to the blood for each NaHPO-

4 that reacts with the secreted hydrogen ion

When H+ transported to tubular lumen and binds with buffers other than HCO-

3, HCO-3 transported to interstitial

fluid through basal membrane which is said to produce by tubular cell

SummarySummaryLow pH corresponds to high H+ andHigh pH corresponds to low H+

There are three basic mechanisms to control hydrogen ion concentration (pH) within body.

•Chemical acid base buffer system•Respiratory System•Renal System

SummarySummary

There are three basic mechanisms to regulate H+ concentration in extracellular fluid are as follows.

•Secretion of H+

•Re absorption of HCO-3

•Production of HCO-3

THANKSTHANKS

ANY SUGGESTION……….!ANY SUGGESTION……….!

Nabi B. Solangi, M.Phil. (Pursuing)Reg. No. 2k15-BP-79

Department of Physiology and BiochemistrySindh Agriculture University, Tando Jam