Introduction
Inorganic ions are atoms with unshared electrons in their outer shell and are thus charges species. They carry either a positive or a negative charge. They are almost always paired with another ion of opposite charge.
Inorganic ions are present in living bodies either in free form dissolves in the cytoplasm or grouped with some complex organic compounds. They are involved in various vital processes in living bodies. Although they are present in trace amounts in our body, their importance cannot be denied. Any changes in their concentrations within the human body can result in some serious consequences.
Inorganic ions are often termed as minerals when mentioned in context with the human body. In this article, we will discuss some important inorganic ions in the human body concerning their occurrence, sources. and role in maintaining homeostasis. We will also study the clinical conditions resulting from changes in their normal concentrations.
Classification
Based on their requirement in the daily diet of a normal individual, inorganic ions or minerals in the human body are divided into two categories:
Macro-minerals
They are also called principal elements. These inorganic ions are required in the daily diet in an amount greater than 100 mg/day. These include;
- Sodium
- Phosphorus
- Magnesium
- Sodium
- Potassium
- Sulfur
- Chloride
Micro-nutrients
These are also called trace elements. These inorganic ions are required in amounts less than 100 mg/day. Some important trace elements include iron, copper, iodine, magnesium, etc.
A very important inorganic ion not included in this classification is hydrogen. Hydrogen ions are not required to be taken in the form of diet as they are produced from water in the body. However, they are the most important inorganic ions in the human body. Let us start our discussion by studying hydrogen ions.
Hydrogen Ions
These are the most important ions to maintain balance and equilibrium in living systems. They are released in the cells during various metabolic processes. They are found in the cytoplasm of cells as well as in the intercellular fluid, blood, CSF and other body fluids.
Importance
The concentration of hydrogen ions is measured in terms of pH which is a negative log of its concentration. pH is measured on a scale from 1 to 14. The value of pH is inverse relation with the hydrogen ions concentration i.e. the higher is the pH, the lower is the concentration of hydrogen ions.
Enzyme action
The fluids in the human body has a normal pH of around 7.4. The maintenance of normal pH is essential for all the metabolic processes taking place in a cell. Any changes in the normal pH affects the enzyme structure and renders them ineffective. The abnormal amount of hydrogen ions interact with the side chains of amino acids and change their secondary and tertiary structures, causing denaturation of enzymes.
ATP synthesis
Hydrogen ions are also used for ATP synthesis within the cells. They are moved against the concentration gradient, from the mitochondrial matrix to the intermembranous space, using the energy of electrons. As they return to the mitochondrial matrix, they release energy that is used to phosphorylate ADP to ATP by ATP synthase.
Oxygen delivery
Hydrogen ions present in the blood play a role in oxygen delivery to the cells by the hemoglobin. When blood passes through tissues, the carbon dioxide produced by cells during metabolism enters the blood. It reacts with water to generate hydrogen ions. As the concentration of hydrogen ions increases, they bind to amino acid side chains, decreasing the oxygen affinity of hemoglobin. This causes hemoglobin to release oxygen in tissues. The reverse of this happens in the lungs. This specific effect of hydrogen on hemoglobin’s oxygen-carrying capacity is called Bohr’s effect.
Any changes in the normal pH of blood will affect the delivery of oxygen to the cells.
Clinical conditions
Any alteration in the normal pH of the body can result in one of the following two conditions;
Acidosis
It is a condition in which the pH of the blood falls below the normal i.e. hydrogen ions concentration becomes greater than normal. It may be metabolic or respiratory. The signs and symptoms depend on the underlying reason. Death may ensue in a short time if pH falls way below the normal level as all the enzymes top working and proteins of the body are denatured.
Alkalosis
It is a condition in which the pH of blood becomes greater than the normal pH i.e. the concentration of hydrogen ions decreases below the normal value. It may also be due to metabolic or respiratory causes. Severe alkalosis is always fatal due to the denaturation of enzymes and proteins.
Sodium ions
It the second most important positively charged ion present in our body. The concentration of sodium ions is higher in extracellular fluids as compared to the cytoplasm of the cells. It is a principal element that must be taken in diet for the normal functioning of the human body.
Body Requirements and sources
Sodium requirement for an average human being is around 5 to 10 grams per day. It is usually taken in the form of common-salt present in our foods. The usual daily intake of sodium is greater than its requirements. Extra sodium is excreted by the body urines. In patients of hypertension, less intake of slats is required to maintain a normal blood pressure.
Importance
The normal concentration of sodium ions in our blood is around 135 to 145 mEq/l. It is an extracellular cation present abundantly in body fluids but being in less concentration within the cells. The following are some of the important functions performed by sodium in the human body.
Fluid Balance
Being an abundant extracellular cation., sodium plays an essential role in maintaining the fluid balance in our body. The volume of extracellular fluids like blood is determined by the concentration of sodium in these fluids. As sodium ions are pumped out of the cell, water follows, and the fluid volume increases. If the concentration of sodium decreases, water moves into the cells and the fluid volume decreases.
Conduction of Nerve impulses
Sodium ions along with the potassium ions are involved in the conduction of nerve impulses in our body. Nerve impulses are conducted in the form of a wave of depolarization that travels along the nerves. During this process, sodium ions move into the nerve and depolarize the cells. If the concentration of sodium on either side of the nerve cell membrane is disturbed, nerve impulses cannot be conducted appropriately.
Absorption of Nutrients in Intestine
Sodium ions are required for the absorption of glucose and amino acids in the small intestine. These molecules are absorbed into the intestinal cells via co-transport channels that are driven by sodium ions. For this purpose, sodium ions are first actively transported out of the intestinal cells into the lumen. The energy stored in the concentration gradient is then used to drive the sodium-glucose or sodium-amino acid cotransporters.
Heart Contraction
Sodium ions are involved in initiating and controlling the rhythmic contractions of the heart. The rhythmic nerve impulses are continuously generated in the SA node without any stimulus due to the slow influx of sodium ions. The SA node is the pacemaker of the heart controlling the heart rate. Any alterations in the normal concentration of sodium ions will result in abnormal heart rate.
Clinical conditions
The two clinical conditions resulting from any increase or decrease in normal concentration of sodium ions are Hypernatremia and Hyponatremia, respectively.
Hyponatremia
It is a condition in which the concentration of sodium ions falls below the normal levels in blood. It may be due to loss of electrolytes from the body as happens in diarrhea or vomiting or may be due to hormonal insufficiency as in Addison’s disease. It is characterized by decreased blood pressure leading to circulatory failure.
Hypernatremia
In this condition, sodium ions are present in blood in excess concentrations. It may be due to hormonal diseases like Cushing’s syndrome, dehydration caused by loss of water as in diabetes insipidus, or rapid IV administration of sodium salts. Hypernatremia is characterized by an increase in blood volume and blood pressure.
Potassium Ions
These are also positively charged ions abundantly present in our body. contrary to the sodium ions, potassium ions are the major intracellular ca6tions, being in higher concentration within the cytoplasm of the cells.
Body requirements and Sources
Potassium ions also fall in the category of principal elements and must be taken in daily diet. An average human being must intake 3 to 4 grams of potassium daily. It is abundantly present in fruits like bananas, oranges, vegetables like potatoes, and in meat like that of chicken and liver.
Importance
The intracellular concentration of sodium is around 136 mEq/l. However, its concentration in extracellular fluid is very low, the plasma concentration being as low as 3.5 to 5 mEq/l. Its concentration in plasma is much raised during hemolysis of RBCs. The following are some of the key functions performed by potassium ions in our body.
Osmotic Pressure Maintenance
Potassium ions serve the same function in maintaining intracellular fluid volume and osmotic pressure, as performed by sodium ions in the case of extracellular fluid. When the sodium ions enter the cells, water also moves in. Thus, water and fluid balance is maintained within the cells.
Electrolytes and Acid-Base Balance
Potassium ions are involved in maintaining the electrolyte and acid-base balance within the cells. As they are the major cations present within the cells, their positive charge neutralizes the negative charges of organic ions and proteins and thus, cell remains neutral as a whole. If the concentration of potassium ions falls within the cells, hydrogen ions will rush into the cells to maintain electrical neutrality. This will decrease the pH of the cell, disrupting the acid-base balance.
Nerve impulse Transmission
Potassium ions are also required for the proper conduction of nerve impulses. The outflux of potassium ions in the 4th phase of nerve impulse repolarizes the cell, restoring the negative charge inside the membrane. It is essential for preparing the cell to conduct additional impulses once the first impulse is over.
Cardiac contractions
Potassium ions are also involved in repolarizing cardiac muscles after they have undergone contraction. Any changes in extracellular potassium ions concentration severely affects the cardiac contractions and can result in cardiac arrest.
Clinical conditions
Any increase or decrease in the concentration of potassium ions can result in hyperkalemia or hypokalemia.
Hypokalemia
It is characterized by less than normal concentration of potassium ions in the blood. It may be due to hormonal imbalance or administration of potassium fluids in blood. It can result in irritability and tachycardia leading to cardiomegaly and cardiac arrest.
Hyperkalemia
It is the increased concentration of potassium ions in blood. It mostly occurs due to renal failure or hormonal imbalance. Hyperkalemia can cause mental confusion, depression of the CAN and bradycardia ultimately leading to cardiac arrest.
Calcium
Calcium is the most abundant inorganic ion present in our body having great importance. It is a positively charged ion majorly present in the cytoplasm of cells. Bones and teeth are the major organs having a lot of calcium.
Body requirements and Sources
Calcium requirements of a healthy human are around 800 mg/day. Milk and milk products are the ideal sources of calcium in our diet. Besides, leafy vegetables, egg yolk, fish, and beans, etc. also contain a lot of calcium in them.
Importance
Calcium makes around 1 to 1.5 kg of our body weight. Although 99% of calcium is present in bones and teeth, around 1% calcium in the cytoplasm of other cells and extracellular fluid performs several important functions in our body. calcium concentration in plasma is around 9-11 mg/dl. Here are some of the major functions of calcium in the human body.
Development
Calcium is needed along with phosphate ions for the formation, growth, and development of bones and teeth. It provides strength to the skeletal tissues when stored in the form of hydroxyapatite matrix.
Muscle contraction
Calcium ions are neede3d for normal muscle contraction. When the nerve impulse reaches a muscle fiber, calcium ions are released from its sarcoplasmic reticulum. These calcium ions bind to troponin C, removing the tropomyosin from myosin-binding sites on actin. As a result, actin-myosin cross-bridges are formed and contraction of muscle fiber takes place.
Blood coagulation
Calcium is an important clotting factor that is needed to form blood clots so that blood loss can be prevented from a site of injury in a blood vessel.
Enzyme activation
Calcium is involved in direct activation of some enzymes like ATPase, pancreatic lipase, and succinate dehydrogenase. It also0 interacts with calmodulin to activates some enzymes like adenylate cyclase, Ca+ dependent protein kinase, etc.
Second messenger
Calcium acts as a second messenger for some hormones like epinephrine in regulating glycogenolysis in the liver.
Cardiac Impulse and Contraction
The influx of calcium ions is responsible for the depolarization of cardiac conduction fibers as well as cardiac muscles. The contraction of cardiac muscles is also made possible after calcium interacts with troponin C.
Clinical conditions
Hypercalcemia and Hypocalcemia are the two clinical conditions caused by disturbance in plasma concentration of calcium ions.
Hypercalcemia
It is an increase in calcium ion concentration and is usually associated with hyperparathyroidism. It is characterized by lethargy, muscle weakness, loss of appetite, tachycardia and increased risk of fractures.
Hypocalcemia
It is a decrease in calcium ions within the body and is usually associated with hypoparathyroidism. It can cause tetany, muscle irritability, and convulsions.
Phosphate ions
These are the negatively charged inorganic ions abundantly present in our body. The body of an average man contains around 1 Kg of phosphate ions. Most of the phosphate ions present combined with calcium in bones and teeth.
Body requirements and Sources
Its requirements are equivalent to calcium. An adult male needs to take 800 mg of phosphate ions daily in his diet. Milk, cereals, meat, and eggs are the rich sources of phosphate ions.
Importance
The plasma concentration of phosphate ions is around 3-4 mg/dl. It is more abundantly present in the cells. Here are some of its important functions in the human body.
Development
Along with the calcium ions, phosphate ions are involved in forming the matrix of bones and teeth, providing them strength. Phosphate ions are essential for the development of teeth and bones.
ATP synthesis
Phosphate ions are required for the synthesis of high energy compounds like ATP, GTP, etc. The bonds between the phosphate ions in ATP release a high amount of energy when they are broken.
Nucleic acid synthesis
Phosphate ions are one of the three components of nucleotides. Thus, they are involved in the synthesis of nucleic acids like DNA and RNA.
Protein and Enzyme activation
Phosphate ions are needed for the activation of various enzymes and proteins. They become activated upon phosphorylation by kinases.
Acid-Base balance
Phosphate ions are the most important intracellular buffers that regulate the pH within the cytoplasm of cells.
Chloride ions
These are the negatively charged inorganic ions present in extracellular fluids. Its concentration in the body is almost similar to that of sodium ions, the major extracellular cations.
Body requirements and Sources
Its average daily requirement is 5 to 10 grams. It is usually taken along with sodium in the form of NaCl present in cooked food.
Importance
Chloride ions perform their role in synergy with the sodium ions. they are involved in maintaining the osmotic pressure, fluid balance and acid-base balance 9in our body just like sodium.
They are required to make HCl present in gastric juice, necessary to digest proteins in the stomach. HCl also kills bacteria and other pathogens in food when it enters the stomach.
Salivary amylase is an enzyme to digest starch that is activated by chloride ions.
Iron ions
These are the positively charged ions present in or body. Around 70% of irons ions in our body are present n hemoglobin within the red blood cells. the rest of iron is present in myoglobin and other proteins like transferrin, ferritin, etc.
Importance
As a component of hemoglobin and myoglobin, iron is needed for the transport of oxygen and carbon dioxide in our bodies.
It is an essential component of cytochromes that are a component of the electron transport chain.
Iron is a component of peroxidase enzyme, a lysosomal enzyme necessary for bacteria and other phagocytosed particles in the white blood cells.
Clinical conditions
Three clinical conditions associated with the abnormal iron metabolism in our body are as follows;
- Iron-deficiency Anemia, is a pretty common condition in individuals with an iron-deficient diet
- Hemosiderosis, characterized by excess iron in the body
- Hemochromatosis, in which abnormal iron deposits are formed in liver, spleen, skin and pancreas
Copper Ions
These are the positively charged inorganic ions present in our body.
Importance
Copper is an essential component of several important proteins and enzymes like cytochrome, oxidase, catalase, superoxide dismutase, ALA synthase, etc.
Copper ions are needed for the synthesis of hemoglobin, collagen, and elastin.
It is required for the normal development of the nervous system.
Clinical conditions
Wilson disease is a rare clinical condition caused by abnormal copper metabolism in our body. it is characterized by abnormal copper deposition in the liver and brain causing hepatic cirrhosis and brain damage. The copper deposition in kidneys can cause renal failure.
Summary
Inorganic ions are the charged elements present in our body performing vital functions.
They are classified into principal elements and trace elements based on their dietary requirements.
Hydrogen is the most important inorganic ion that maintains the acid-base balance in our body.
Sodium ions are needed for the maintenance of osmotic pressure and fluid balance, nerve impulse conduction, and automatic rhythmicity of the heart.
Chloride ions maintain osmotic pressure and acid-base balance in synergy with sodium ions.
Potassium ions are needed for nerve impulse conduction.
Calcium ions play a major role in the development of bones and teeth along with phosphate ions.
Iron ions are a component of hemoglobin and myoglobin.
Copper ions are a component of several important enzymes.
Frequently Asked Questions
What are macro-minerals?
The minerals having a dietary requirement of more than 100mg/day are called macro-minerals. These include sodium, phosphorus, magnesium, potassium, sulphur and chloride.
What are trace elements?
The minerals having dietary requirements less than 100mg/day are called trace elements or micronutrients. Essential trace elements are copper, iodine, magnesium and iron, etc.
What is the role of sodium in our body?
Sodium is the most important mineral involved in maintaining fluid balance in the body, conducting nerve impulses, glucose absorption from the intestine and heart contraction. Any abnormality in sodium levels leads to cardiovascular abnormalities.
What is the role of potassium in our body?
Potassium maintains fluid balance, nerve impulse conduction, and acid-base balance in the body. Both hypokalemia (decrease in potassium levels) and hyperkalemia (increase in potassium levels) can lead to cardiac arrest.
References
- “Inorganic Ions”. RSC.
- Harper’s Illustrated Biochemistry, 31st Edition
- https://commons.wikimedia.org/wiki/File:Ions.svg
- https://commons.wikimedia.org/wiki/File:Chlormequat_chloride_ions_ball.png