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The pH control by Acids and Bases in our body
Table of Contents
Introduction…………………………………………………………………………2
Acids and bases in the digestion…………………………………………………….3-4
In the vaccul cavity………………………………………………………………….3
In the stomach……………………………………………………………………….3-4
In the intestine……………………………………………………………………....4
Acids and bases in constructing macromolecules…………………………………..4-6
Proteins……………………………………………………………………………..4
Lipids……………………………………………………………………………....5-6
Nucleic Acids………………………………………………………………………6
pH maintaineance…………………………………………………………………...6-10
Conclusion………………………………………………………………………….11
References…………………………………………………………………………..12
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The pH control by Acids and Bases in our body
Introduction
Acids and bases are important participants in the biochemistry of every living thing. We are
alkaline by design, but acid by function- breathing, digesting, thinking, circulation, hormonal
production and so on. Every thing we see around us including the food we take to maintain our
health is all either acidic or basic in nature. Therefore it is very mandatory to maintain the proper
pH in our body.
The pH of the body refers to the pH of the fluids that is present inside and outside the cells;
hence pH level has profound effects on all body chemistry, health and disease. Our body pH is
very important because pH controls the speed of our body's biochemical reactions. It does this by
controlling the speed of enzyme activity as well as the speed that electrical impulse moves
through our body.
In this booklet/ assignment, we will be mainly focusing on how are acids and bases are being
used in our body to control the pH of the blood; the homeostatic function of the buffer system in
the blood, digestion that is how antacids which are all basic compounds are neutralizing
hydrogen ions from hydrochloric acid secrete by the stomach and also how acids are helpful
when it exist in the aggregated form (macromolecules construction), for examples amino-acid
aggregated to form protein.
We will be also focusing on abnormal functioning of body like metabolic acidosis due to failure
of kidney, ulcer in the stomach (eroding of stomach lining due to the over production of
hydrochloric acid) and respiratory acidosis dysfunctional of lungs; excess of carbon dioxide
accumulation in lung as a result of imbalance in the pH in our body.
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The pH control by Acids and Bases in our body
Acid and bases in the digestion food
Most diets cause an unhealthy acid pH. Diets appear to be the major influence in maintaining
appropriate pH levels throughout the body. When food is metabolized and broken down, it leaves
certain chemical and metallic residues. When the residues combines with our body fluids, it
yields either acid or alkali potentials of pH. The diets are either ‘acid-forming’ or ‘alkalineforming’ in nature.
In the buccal cavity
Salivary amylase does not function in the acidic medium. Its actions stopped when bolus are
mixed with highly acidic secretion of gastric juice. Normally saliva is alkaline in nature with a
pH of 7.2 or above. It helps strengthening and repair of the teeth. The alkaline saliva in one's
mouth may change and become acidic in a stressful situation, or even with a simple health
change such as a sinus infection. Almost everyone develops a more acidic mouth as they age, or
take medications.
In the stomach
Hydrochloric acid is produce by the parietal cells, facilitated by hormone gastrin. The
hydrochloric acid is strong acid and helps to break down the food. Hydrochloric acids have
strong concentration and it will pierce through if we keep piece of wood. Hydrochloric acid is
produced at pH 1 and when it is mixed with other gastric juice, hydrochloric acid’s pH change to
2 to 3. The hydrochloric acid produced has following function:
 It denature the proteins and break some chemical bond
 Activate pepsinogen
 Neutralize the salivary amylase
 It is an effective disinfectant, sine many types of bacteria cannot tolerate high acidity.
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The pH control by Acids and Bases in our body
But this acidity is neutralized by the epithelial cell which produces and secretes bicarbonate
solution that coats the inner lining of stomach. Bicarbonate is alkaline and it neutralizes the acid
produced by parietal cell. The bicarbonates are produced to protect the stomach from digesting
itself and acidic environment. In come cases, impairment of blood supply to the stomach or over
production of acid, the neutralization fails. Hence they get gastric ulcers. Sometime
abnormalities are brought by specific bacteria such as helicobacter pylori responsible for
stomach ulcer.
In the intestine
The pH of the pancreatic secretion is on the alkaline side ranging from 7 to 8.2. Pancreatic juice
is alkaline in nature due to the high concentration of bicarbonate ions. This is useful in
neutralizing the acidic gastric acid, allowing for effective enzyme action. This helps to neutralize
the acidic chime coming from the stomach. Pancreatic secretion consists of an aqueous
bicarbonate component from the duct cells and enzymatic component. And along with the bile, is
enough to make the intestinal contents nearly neutral. This stop the actions of pepsin, it provides
suitable environment for the pancreatic and intestinal enzymes.
Acids and bases in constructing Macromolecules
Proteins
Proteins are polymers of amino acids that are responsible for most of the cellular activity in
living organism. Some examples are hemoglobin, enzymes, antibodies which are involved in
metabolic reactions and also structural proteins such as collagen and keratin. Proteins are long
chain of amino acids held together by peptide bonds. Amino acids are composed of an amino
group, a carboxyl group and the particular side-chain that defines their chemical nature.
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Individual proteins are constructed from twenty amino acids, which may be sub grouped
according to the acidic, basic, uncharged polar character of their side chains.
All amino acids have an amino groups, -NH2 and a carboxyl group, -COOH. Polypeptide is just a
single chain of amino acids whereas protein is made up of several polypeptide molecules.
Peptide bond is formed by the union of two amino acids by condensation reaction. The carboxyl
group of one amino acid reacts with the amino group of second amino acids. Thus losing a
molecule of water from the –COOH and - NH2 group.
The covalent bond is formed between the remaining C of the carboxyl group and N of the amino
group. And this C-N bond is known as peptide bond. The new molecule which is formed by the
union of two amino acids is a dipeptide. The condensation of other amino acids produces a
tripeptide. Likewise, condensation of more amino acids forms a poly peptide molecule.
Lipids
The most important groups of lipids in living organism are triglycerides, phospholipids and
steroids. Lipids are a class of hydrophobic covalent compounds that perform multiple functions
within cells. Triglyceride which is commonly known as fats provides an excellent means of
energy storage molecules. The structural units of lipids are fatty acids, containing long chains of
4-24 carbon atoms joined to a carboxylic acid group. The structures of triglycerides consist of
three fatty acid chains attached to a glycerol molecule as a backbone. The –COOH group has
tendency to ionize to produce hydrogen ions:
COOH ↔ COO- + H+
Due to production of hydrogen ions fatty acids are acids. When fatty acids react with glycerol a
condensation reaction occurs and ester linkages are formed between them losing a molecule of
water from the –OH of the fatty acids carboxyl group and the –OH of glycerol. The process is
repeated for each of the hydroxyls which involve the –COOH groups of the fatty acids, so they
have no longer acidic properties.
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Phospholipids are made up of two hydrophobic fatty acid chains attached to a hydrophilic
phosphate group.
Nucleic Acids
Genetic information is stored and transferred in the form of nucleic acids deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA). Like many other molecules, nucleic acids are polymers of
smaller units which are known as nucleotides.
Both DNA and RNA are nucleic acids or polynucleotide. Polynucleotides are polymers made up
of many smaller units called nucleotides linked together. A nucleotide is made up of three
smaller molecules like a phosphate group, a pentose (5-carbon) sugar and a nitrogenous base.
Nucleotides are linked together by condensation reactions to form polynucleotide. If nucleotide
contains ribose, then the resulting polynucleotide is ribonucleic acid (RNA). In same manner, if
the If nucleotide contains deoxyribose, then the resulting polynucleotide is deoxyribonucleic acid
(DNA).
Maintaining of blood pH
The normal body pH is in the range of 7.35-7.45 or about 7.4 on the average. And the normal
body pH is not neutral, but is slightly alkaline. Consequently, a pH of 7.2 is alkaline chemically
speaking since it is above 7.0.
Normally pH remains relatively constant both outside and inside the cells. Alterations in the
acid-base balance are resisted by extracellular and intracellular chemical buffers and by
respiratory and renal regulation. In the first place, kidneys and blood buffers attempt to correct
metabolic disorders and lungs attempt to correct respiratory disorders. It is done in following
ways:
Blood has essentially two components: blood plasma and red blood cell (RBC) or erythrocytes.
Blood plasma contain many compounds, including proteins, metal ions, and inorganic
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The pH control by Acids and Bases in our body
phosphates. The erythrocytes contain hemoglobin molecules, as well as the enzyme carbonic
anhydrase, which act as the catalyst for the formation of carbonic acid (H2CO3) as well as its
decomposition.
CO2 (aq) + H2O (l) ↔
H2CO3 (aq)
The substances inside the erythrocytes are protected from extracellular fluid (blood plasma) by a
cell membrane that allows only certain molecules to diffuse through it.
The pH of blood plasma is maintained at about 7.40 by several buffer systems, the most
important of which is the HCO3 - /H 2CO3 system. In the erythrocytes, where the pH is 7.25, the
principle buffer systems are HCO3-/ H2CO3 and heamoglobin. We can safely treat hemoglobin
molecule as a monoprotic acid of the form HHb.
HHb (aq) ↔ H+ (aq) + Hb-(aq)
Where HHb represents the hemoglobin and Hb- the conjugate base of HHb.
Oxyheamoglobin(HHbO2), formed by the combination of oxygen with hemoglobin, is a stronger
acid than HHb.
HHbO2 (aq) ↔ H+ (aq) + HbO2- (aq)
Carbon dioxide produced by metabolic processes diffuses into erythrocytes, where it is rapidly
converted to H2CO3 by carbonic anhydrase:
CO2 (aq) + H2O (aq) ↔ H2CO3 (aq)
The ionization of the carbonic acid:
H2CO3 (aq) ↔ H+ (aq) + HCO3 – (aq)
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The pH control by Acids and Bases in our body
Consuquences
Have two important consequences. First, the bicarbonate ion diffuses out of the erythrocytes and
is carried by the blood plasma to the lungs. This is the major mechanism for removing of carbon
dioxide. Second, the H+ ions shift the equilibrium in favour of the nonionized oxyhemoglobin
molecule:
H+ (aq) + HbO2- (aq) ↔ HHbO2 (aq)
Because HHbO2 releases oxygen more readily than does its conjugate base HbO2- , the formation
of acid promotes the following reaction from left to right:
HHbO2 (aq) ↔ HHb (aq) + O2 (aq)
The O2 molecules diffuse out of the erythrocytes and are taken up by other cells to carry out
metabolism. When venous blood returns to the lungs, the above processes are reversed. The
bicarbonate ions now diffuse into the erythrocytes, where they react with hemoglobin to form
carbonic acid:
HbO2- (aq) + HCO3 – ↔ Hb-(aq) + H2CO3 (aq)
Most of the acid is then converted to CO2 by carbonic anhydrase:
H2CO3 (aq) ↔ H2O (l) + CO2 (aq)
The carbon dioxide diffuses to lungs and is eventually exhaled. The formation of Hb- ions (due
to the reaction between HHb and HCO3 shown in the left column) also favours the uptake of
oxygen at the lungs.
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The pH control by Acids and Bases in our body
Hb-(aq) + O2 (aq) ↔ HbO2- (aq)
Because Hb- has a greater affinity for oxygen than does HHb. When the arterial blood flows back
to the body tissues, the entire cycle is repeated.
A normal adult produces huge quantities of CO2 daily from the metabolism of. In the blood,
CO2 reacts with water to form carbonic acid, which dissociates to H+ and HCO3-. In the lung
capillaries they are converted back to CO2 and water and the CO2 is expired.
As a secondary respiratory compensation, the lungs react to metabolic acidosis and alkalosis.
Metabolic acidosis stimulates breathing causing hyperventilation while metabolic alkalosis
suppresses it. These are attempts to correct pH by changing the concentration of carbon dioxide
and carbonic acid in the blood.
Maintaining of blood pH by Kidney
The kidneys play two important roles in the maintaining of the acid-base balance: to reabsorb
bicarbonate from and to excrete excess hydrogen ions into urine. About 4500 ml of bicarbonate
are filtered into the primary filtrate of urine daily, but only 2 ml of it are finally excreted. 70-80%
of bicarbonate is reabsorbed in the first part of proximal tubule, 10-20% in the loop of Henle and
5-10% in the distal tubule and collecting ducts.
Renal tubules actively secrete hydrogen ions. Most of this takes place in the distal part of the
nephron, but active transport of hydrogen ions occurs in the proximal tubule, too. The H-ATPase
of the apical cell membrane secretes hydrogen ions into urine. For each hydrogen ion secreted,
one bicarbonate molecule is transported to the interstitial fluid; from there it diffuses into the
bloodstream.
The maximal hydrogen ion gradient, against which the transport mechanism can secrete H+ ions,
corresponds to a urine pH of 4.5 in humans. However, three important molecules remove free
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hydrogen ions from the tubular fluid permitting more acid to be secreted: H+ is bound to
ammonia, phosphate and bicarbonate to form NH4+, H2PO4-, CO2 and H2O.
The source of the hydrogen ions secreted by the tubular cells is not completely certain. It is
probably produced by dissociation of H2CO3. The acid-secreting cells contain carbonic
anhydrase, which facilitates the rapid formation of H2CO3 from CO2 and water. The renal acid
secretion is mainly regulated by the changes in the intracellular pCO2, potassium concentration,
carbonic anhydrase activity and adrenocortical hormone concentration.
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The pH control by Acids and Bases in our body
Conclusion
What we eat and drink will impact where our body's pH level falls as our body's pH will control
the activity of every metabolic function happening in our body. If we left unchecked, an
imbalanced pH in body will interrupt all cellular activities and functions, from the beating of the
heart to the neural firing of brain. A delicate balance must be maintained between acids and
bases in the blood, body fluids and cells.
If the pH deviates too far to the acid side or too far to the alkaline side, cells become poisoned by
their own toxic waste and die. Just as acid rain can destroy a forest and alkaline wastes can
pollute a lake, an imbalanced pH continuously corrodes all body tissue, slowly eating into the
our veins and arteries like corrosives eating into marble
We had seen the both pros-helps in digestion and so on and cons-cause serious burns, ulcer,
dysfunctioning of vital organs, denature the proteins molecules in living cells and etc.. of acids
and bases either in excess or less amount. So it is advisable not to misuse acid and base since it
can cause damage to human health and sometime it a lethat too. Fortunately, the body has the
complex but efficient fail-safe mechanism for maintaining the proper acid-base balance and to
keep it suitable for life primarily through buffer system as we discussed earlier.
In nutshell, we hereby conclude that everything that we eat and drink contains either acids or
bases. For, it has been found too crucial to not to eat what not things in which it may be lethal to
one’s life. As we usually say our mouth is our health, it necessary to eat suitable and healthy
food. Eating a very highly acidic or basic food stuffs could be deadful as our body cannot
maintain their pH.
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References
Acid/Base Balance (n.d). Retrieved from 12th September 2011 from
http://tuberose.com/Acid_Base_Balance.html
Acids-bases/ how does your stomach keep from digesting itself? (n.d.) Retrieved 12th September
2011 from http://health.howstuffworks.com/human-body/systems/digestive/question464.htm
Chang, R. (2008). Chemistry. New Delhi: Tata McGraw Hill Education Private Limited.
http://herkules.oulu.fi/isbn9514253620/html/x274.html
Jones, M. & Jones,G. (2007).Advanced biology. Cambridge University Press: New York.
Phillips, E, (Monday, November 27, 2006) Mouth acidity and testing pH. Retrieved from
6thSeptember 2011 from http://askdrellie.blogspot.com/2006/12/mouth-acidity-and-testingph.html
Retrieved from 12th September 2011 from http://science.kennesaw.edu/~bodavis/LECT04.PDF
Retrieved from 12th September 2011 from http://en.wikipedia.org/wiki/Acid-base_homeostasis
Retrieved from 12th September 2011 from http://www.livestrong.com/article/43925-importance-
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