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9.10: Calcium Homeostasis- Interactions of the Skeletal System and Other Organ Systems - Biology

9.10: Calcium Homeostasis- Interactions of the Skeletal System and Other Organ Systems - Biology


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Learning Objectives

  • Describe the effect of too much or too little calcium on the body
  • Explain the process of calcium homeostasis

Calcium is not only the most abundant mineral in bone, it is also the most abundant mineral in the human body. Calcium ions are needed not only for bone mineralization but for tooth health, regulation of the heart rate and strength of contraction, blood coagulation, contraction of smooth and skeletal muscle cells, and regulation of nerve impulse conduction. The normal level of calcium in the blood is about 10 mg/dL. When the body cannot maintain this level, a person will experience hypo- or hypercalcemia.

Hypocalcemia, a condition characterized by abnormally low levels of calcium, can have an adverse effect on a number of different body systems including circulation, muscles, nerves, and bone. Without adequate calcium, blood has difficulty coagulating, the heart may skip beats or stop beating altogether, muscles may have difficulty contracting, nerves may have difficulty functioning, and bones may become brittle. The causes of hypocalcemia can range from hormonal imbalances to an improper diet. Treatments vary according to the cause, but prognoses are generally good.

Conversely, in hypercalcemia, a condition characterized by abnormally high levels of calcium, the nervous system is underactive, which results in lethargy, sluggish reflexes, constipation and loss of appetite, confusion, and in severe cases, coma.

Obviously, calcium homeostasis is critical. The skeletal, endocrine, and digestive systems play a role in this, but the kidneys do, too. These body systems work together to maintain a normal calcium level in the blood (Figure 1).

Calcium is a chemical element that cannot be produced by any biological processes. The only way it can enter the body is through the diet. The bones act as a storage site for calcium: The body deposits calcium in the bones when blood levels get too high, and it releases calcium when blood levels drop too low. This process is regulated by PTH, vitamin D, and calcitonin.

Cells of the parathyroid gland have plasma membrane receptors for calcium. When calcium is not binding to these receptors, the cells release PTH, which stimulates osteoclast proliferation and resorption of bone by osteoclasts. This demineralization process releases calcium into the blood. PTH promotes reabsorption of calcium from the urine by the kidneys, so that the calcium returns to the blood. Finally, PTH stimulates the synthesis of vitamin D, which in turn, stimulates calcium absorption from any digested food in the small intestine.

When all these processes return blood calcium levels to normal, there is enough calcium to bind with the receptors on the surface of the cells of the parathyroid glands, and this cycle of events is turned off (Figure 1).

When blood levels of calcium get too high, the thyroid gland is stimulated to release calcitonin (Figure 1), which inhibits osteoclast activity and stimulates calcium uptake by the bones, but also decreases reabsorption of calcium by the kidneys. All of these actions lower blood levels of calcium. When blood calcium levels return to normal, the thyroid gland stops secreting calcitonin.


Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems

Calcium is not only the most abundant mineral in bone, it is also the most abundant mineral in the human body. Calcium ions are needed not only for bone mineralization but for tooth health, regulation of the heart rate and strength of contraction, blood coagulation, contraction of smooth and skeletal muscle cells, and regulation of nerve impulse conduction. The normal level of calcium in the blood is about 10 mg/dL. When the body cannot maintain this level, a person will experience hypo or hypercalcemia.

Hypocalcemia, a condition characterized by abnormally low levels of calcium, can have an adverse effect on a number of different body systems including circulation, muscles, nerves, and bone. Without adequate calcium, blood has difficulty coagulating, the heart may skip beats or stop beating altogether, muscles may have difficulty contracting, nerves may have difficulty functioning, and bones may become brittle. The causes of hypocalcemia can range from hormonal imbalances to an improper diet. Treatments vary according to the cause, but prognoses are generally good.

Conversely, in hypercalcemia, a condition characterized by abnormally high levels of calcium, the nervous system is underactive, which results in lethargy, sluggish reflexes, constipation and loss of appetite, confusion, and in severe cases, coma.

Obviously, calcium homeostasis is critical. The skeletal, endocrine, and digestive systems play a role in this, but the kidneys do, too. These body systems work together to maintain a normal calcium level in the blood.

Calcium is a chemical element that cannot be produced by any biological processes. The only way it can enter the body is through the diet. The bones act as a storage site for calcium: The body deposits calcium in the bones when blood levels get too high, and it releases calcium when blood levels drop too low. This process is regulated by PTH, vitamin D, and calcitonin.

Cells of the parathyroid gland have plasma membrane receptors for calcium. When calcium is not binding to these receptors, the cells release PTH, which stimulates osteoclast proliferation and resorption of bone by osteoclasts. This demineralization process releases calcium into the blood. PTH promotes reabsorption of calcium from the urine by the kidneys, so that the calcium returns to the blood. Finally, PTH stimulates the synthesis of vitamin D, which in turn, stimulates calcium absorption from any digested food in the small intestine.

When all these processes return blood calcium levels to normal, there is enough calcium to bind with the receptors on the surface of the cells of the parathyroid glands, and this cycle of events is turned off.

When blood levels of calcium get too high, the thyroid gland is stimulated to release calcitonin, which inhibits osteoclast activity and stimulates calcium uptake by the bones, but also decreases reabsorption of calcium by the kidneys. All of these actions lower blood levels of calcium. When blood calcium levels return to normal, the thyroid gland stops secreting calcitonin.


HOMEOSTASIS AND THE HUMAN ORGAN SYSTEMS

The Human Body is very complex. It involves numerous organs working closely together to carry out a specific task. This functional association of organs are called organ systems or, in some references, body systems or biological systems. The main function of the organ systems is to maintain the homeostatic environment or internal condition of the human body. Thus, making humans work with great efficiency and flexibility. Disruption of this internal balance may lead to certain diseases, complications, and worst, even death.


  • Skeletal Muscles are generally responsible in sustaining body movements and posture. This type of muscle is usually attached to a bone.
  • Smooth Muscles are generally responsible in providing contractile movements to the hollow or void organs of the body such as blood vessels, alimentary canal, urinary bladder and the uterus. Without the smooth muscles, it would be impossible to swallow foods, excrete waste products such as feces and urine, etc.
  • Cardiac Muscles, from the name itself, can only be found in the heart. It is responsible for the rhythmic contraction of the heart. Without it, it would be impossible for the heart to pump.







In other words, the lymphatic system generally acts as the “Armed Forces” of the human body, because it fights off foreign intruders that are harmful to the body’s normal physiological processes.


In males, the reproductive system consists of the Penis, Testicles, Prostate Gland, Seminal Vesicle, Vas Deferens, Epididymis and the Urethra.



  1. How many organ systems are there in the Human Body? Identify each of them.
  2. Which, do you think, is the most important among the organ systems? Why?

Please provide your answers in the comment section below.

Randolf Flores, the contributor, is a graduate of Bachelor of Science Major in Biology at the Far Eastern University, Manila. He is currently taking up Master of Arts in Science Education at the Rizal Technological University, Mandaluyong City.

Please spare some time in answering this e-learning short quiz that I prepared below, so you can assess for yourself how much you've learn about the human organ systems.

Dugdale, D. (2012, November 02). Lymph system. Retrieved February 08, 2014, from the US National Library of Medicine Website: http://www.nlm.nih.gov/medlineplus/ency/article/002247.htm

Guyton, A. & Hall, J. (2006). Textbook of Medical Physiology 11th Edition. Philadelphia:Elsevier Inc.

Norman Parathyroid Center. (2013, December 2013). Introduction to Parathyroid Glands. Retrieved February 08, 2014, from http://www.parathyroid.com/parathyroid.htm

Sekar T., et al. (2006). Biology (Zoology). Chennai:Tamil Nadu Textbook Corporation.


Blood Glucose Levels

The endocrine functions of the pancreas and liver coordinate efforts to maintain normal blood glucose levels. When pancreatic cells detect low blood glucose levels, the pancreas synthesizes and secretes the hormone glucagon. Glucagon causes the liver to convert the polymerized sugar glycogen into glucose through a process known as glycogenolysis. Glucose then travels through the blood to allow all cells of the body to use it.

If pancreatic cells detect high blood glucose levels, the pancreas synthesizes and releases the hormone insulin. Insulin causes polymerization of glucose into glycogen, which is then stored in the liver through a process known as glycogenesis.

The nervous and digestive systems also play a role in maintaining blood glucose levels. When the stomach is empty and blood glucose levels are low, the digestive system and the brain respond by making you feel hungry—your stomach may “growl,” and you may feel pain or discomfort in your midsection. These sensations prompt you to eat, which raises blood glucose levels.


Critical Thinking Questions

The skeletal system is composed of bone and cartilage and has many functions. Choose three of these functions and discuss what features of the skeletal system allow it to accomplish these functions.

It supports the body. The rigid, yet flexible skeleton acts as a framework to support the other organs of the body.

It facilitates movement. The movable joints allow the skeleton to change shape and positions that is, move.

It protects internal organs. Parts of the skeleton enclose or partly enclose various organs of the body including our brain, ears, heart, and lungs. Any trauma to these organs has to be mediated through the skeletal system.

It produces blood cells. The central cavity of long bones is filled with marrow. The red marrow is responsible for forming red and white blood cells.

It stores and releases minerals and fat. The mineral component of bone, in addition to providing hardness to bone, provides a mineral reservoir that can be tapped as needed. Additionally, the yellow marrow, which is found in the central cavity of long bones along with red marrow, serves as a storage site for fat.


Watch the video: Ξέρουμε να τρώμε; Οστεοπόρωση (January 2023).