How Does Tetany Affect the Human Body?
Tetany refers to a condition during which the nerves innervating a specific muscle becomes overstimulated and causes involuntary contractions of muscles called Spasms.Tetany is also referred to as Tetanic Seizures.
Symptoms of Tetany
Includes spasms of the carpal(wrist) muscles, an extension in interphalangeal joints(joint present between bones of fingers of hands and toes of feet)
Spasms in the larynx(laryngospasm)
Convulsion episodes
Tingling sensation in distal extremities called paresthesias.
Heart dysfunction, vomiting.
Causes of Tetany
Hypocalcemia-This conditions define a below-normal level of calcium in plasma. Note, the basic concentration of calcium ions in a healthy adult is about 8-10.5 mg/dl in serum. Low level of free calcium levels in the plasma increases the depolarization of the neurons thereby increasing neuronal excitability.
What are the Possible ways by which Hypocalcemia can Occur?
(a) Decreased levels of parathormone- Parathormone(PTH) is a hormone released by the parathyroid gland(Glands present behind thyroid gland).PTH functions as maintaining serum calcium levels by exercising its effect on bone, kidneys and intestine. Basically, its main function is to maximize the calcium levels within the plasma. Now, this can be achieved by various methods.
Firstly, calcium is oozed out from bone to plasma.
Secondly, it can increase absorption of calcium present within the food through the intestine to maximize calcium within the plasma.
Lastly, it maximizes the plasma calcium levels through increased resorption of calcium from renal tubules thereby increasing calcium levels in plasma and reducing it within the urine.
Accidental damage to the parathyroid gland, autoimmune disorders, congenital defects can also lead to decreased PTH secretion.
(b) Low vitamin D levels can also cause hypocalcemia as vitamin D helps in absorbing calcium. Low Vitamin D levels can be caused by lack of exposure to sunlight, malnutrition etc.
(c) Other factors include loss of calcium because of the kidney and gastrointestinal diseases.
Low levels of Magnesium- As magnesium is very vital to PTH synthesis.
Alkalosis- An increase in blood pH causes albumin, a blood protein, to bind with free calcium in the plasma. This causes decreased availability of free calcium ions. Severe alkalosis may lead to tetany. Alkalosis may be caused by continuous vomiting(loss of gastric acids), increased intake of alkaline foods etc.
Clostridium Tetany Toxin- A neurotoxin is released by the infection of clostridium Tetany which inhibits the release of neurotransmitters. This can lead to increased muscle tone and muscle spasm. The disease caused so is called tetanus(lockjaw disease)
Hypokalemia-This refers to decreased potassium(K+) concentration in the blood. As we know, potassium is essential for repolarization of nerve cells, a decrease in potassium levels can lead to the various manifestations of tetany.
Treatment of Tetany
Intravenous or oral calcium supplemented with vitamin D
Magnesium administration to maintain optimum Mg2+ levels.
Administration of isotonic fluids, ammonium chloride in case of emergency(in case of alkalosis).
Antibiotics and antitoxin just in case of C.infection. For the prevention of tetanus, DPT(Diphtheria, Pertussis, Tetanus) vaccination in childhood is suggested.
Difference Between Tetany and Tetanus
Role of Calcium Ion in Tetany
Calcium ion concentration plays a vital role in the muscle contraction in the following way :
As an action potential reaches the muscle cells, the sarcoplasmic reticulum releases calcium in the sarcoplasm.
The calcium that is released goes and binds to the TpC subunit of troponin protein.
The active site on actin is exposed as Ca2+ binds with troponin
The myosin head forms a cross-bridge with action and contraction takes place.
If the levels of calcium decrease below normal, it increases the permeability of Na+ ions causing recurring depolarization and contractions. This condition is called tetany. Low calcium levels may be caused due to low parathormone levels.
FAQs on Tetany: Meaning, Causes, Symptoms, and Treatment
1. What is tetany as explained in the CBSE Biology syllabus?
Tetany is a medical condition characterised by involuntary and sustained muscle contractions, or spasms. It is not a disease itself but a symptom resulting from the increased excitability of peripheral nerves. This hyper-excitability causes the nerves to overstimulate the muscles, leading to rapid, spontaneous spasms. The underlying cause is typically a metabolic imbalance, most commonly hypocalcemia (low calcium levels in the blood).
2. What are the primary causes of tetany?
The main cause of tetany is a significantly low level of calcium in the blood (hypocalcemia). As per the 2025-26 NCERT syllabus, key factors leading to this condition include:
- Hypoparathyroidism: A deficiency in parathyroid hormone (PTH), which is essential for regulating blood calcium levels.
- Vitamin D Deficiency: Insufficient Vitamin D impairs the body's ability to absorb calcium from the diet.
- Alkalosis: A condition where body fluids have excess base (alkali), which reduces the amount of active (ionized) calcium available to cells.
- Kidney Failure: Impaired kidney function can disrupt the body's balance of calcium and phosphate.
3. What are the common symptoms that indicate tetany?
The symptoms of tetany arise from heightened neuromuscular excitability. Common signs a student should know are:
- Paresthesias: A tingling or numbness, often described as a 'pins and needles' sensation, typically felt in the fingertips, toes, and around the mouth.
- Carpopedal Spasm: Involuntary and painful spasms of the muscles in the hands and feet. This can cause the classic sign of the wrist and knuckle joints flexing while fingers extend.
- Laryngospasm: Spasms of the larynx (voice box), which can obstruct the airway, causing difficulty breathing and a high-pitched sound.
- Muscle Cramps: Generalised and often painful muscle cramps and twitching.
4. How does a low calcium level in the body fluid lead to tetany?
Calcium ions (Ca²⁺) play a crucial role in stabilising the membranes of nerve cells. Specifically, they regulate the voltage-gated sodium channels. When the concentration of extracellular calcium is low (hypocalcemia), these sodium channels become more permeable to sodium ions (Na⁺). This lowers the threshold required to trigger an action potential. As a result, nerves become hyper-excitable and can fire signals with minimal stimulation, or even spontaneously. This continuous firing of nerve impulses to the muscles causes the involuntary, sustained contractions and spasms characteristic of tetany.
5. What is the key difference between tetany and tetanus?
While both conditions involve severe muscle spasms, their causes are completely different. The primary distinction is:
- Tetany: This is a physiological condition caused by a metabolic issue, most notably low blood calcium (hypocalcemia). It is non-infectious and relates to hormonal or nutritional imbalances.
- Tetanus: This is an infectious disease caused by a potent neurotoxin produced by the bacterium Clostridium tetani. The toxin interferes with neurotransmitter release in the central nervous system, leading to rigid, spastic paralysis.
6. Which hormone deficiency is primarily responsible for causing tetany, and why?
The deficiency of parathyroid hormone (PTH) is the primary hormonal cause of tetany. PTH, secreted by the parathyroid glands, acts as a hypercalcemic hormone, meaning its main job is to increase blood calcium levels. When PTH is deficient (a condition called hypoparathyroidism), the body cannot effectively:
- Stimulate the release of calcium from bones.
- Increase calcium reabsorption in the kidneys.
- Promote the activation of Vitamin D to absorb calcium from the gut.
7. Can you explain the difference between a simple muscle spasm and the condition of tetany?
A muscle spasm is a broad term for any single, involuntary contraction of a muscle, which can be caused by various factors like fatigue, dehydration, or injury. Tetany, however, is a more specific and systemic clinical syndrome. It refers to a state of neuromuscular hyper-excitability that causes a series of involuntary spasms. While tetany's main symptom is muscle spasms, the term itself describes the entire condition resulting from a specific metabolic cause, almost always hypocalcemia, rather than just an isolated muscle cramp.
