Calcium found in the blood

Calcium is an essential mineral that mainly plays an important role in maintaining the integrity of bones and teeth. Calcium is also needed by the heart, nerves, and blood-clotting systems to effectively work (1). Different regulatory processes that occur in the bones, gut, and kidneys influence blood calcium levels; but the hormones, parathyroid hormones and calcitonin, are the two main agents responsible in calcium homeostasis. Blood calcium levels must be maintained within narrow limits for the normal processes of muscle contraction and membrane potentials to occur (2).

How is Calcium maintained in the blood?

Parathyroid hormone
       

As stated, the parathyroid hormone and calcitonin both help regulate blood calcium levels. The Parathyroid hormone (PTH) is produced by the parathyroid gland, which is located on the back of the thyroid gland in the throat. PTH is only released whenever blood calcium levels are low. 

• This hormone stimulates the osteoclasts, a type of bone cell, to break down bone that will then result to the release of  calcium into the bloodstream. 
• PTH also increases blood calcium levels by heightening the amount of calcium resorbed by the kidneys before excretion in to urine.
• PTH elevates calcium levels by triggering the formation of calcitriol, the biologically active form of Vitamin D, which increases absorption of dietary calcium through the intestines (3).

Calcitonin

On the other hand, calcitonin is a hormone released by the parafollicular cells of the thyroid gland that acts in opposition to PTH. 

• Calcitonin inhibits osteoclasts, slowing the breakdown of bone; and stimulates osteoblasts, a bone cell that is responsible in bone   formation. The process results in calcium being added to the bones to promote structural integrity. This in turn lowers calcium release that will in time, lowers blood calcium concentration. 
• The hormone also increases excretion of calcium in the urine that will further contribute to the decrease of blood calcium levels (3). 

In short, The Parathyroid Hormone (PTH) increases blood calcium levels 

while Calcitonin decreases blood calcium levels.

Iodine is needed by the thyroid gland. Why?

The thyroid gland is a butterfly-shaped organ located at the base of one’s neck, below the Adam’s apple. The purpose of this gland is to make, store, and release thyroid hormones into your blood. These hormones, which are also referred to as T3 (triiodothyronine) and T4 (thyroxine), affect almost every cell in your body, and help control the body’s metabolism.  With the release of thyroid stimulating hormone (TSH) by the pituitary gland, the thyroid gland is stimulated to release T3 and T4. Thyroid hormones are also crucial for brain development.

Iodine is a vital micronutrient required at all stages of life; fetal life and early childhood being the most critical phases of requirement. It can be acquired through diet (seafood, eggs and dairy) and can be metabolized in the human body by the hypothalamus and pituitary gland. It is the major mineral in the thyroid because it helps in the production and regulation of thyroid hormones. Lack of iodine can lead to several different problems, including poor thyroid function. When the thyroid gland lacks iodine it may increase the size of the goiter. This enlarged gland searches out any iodine in the body.

Thyroid Conditions

• Goiter: A general term for thyroid swelling. Goiters can be harmless, or can represent iodine deficiency or a condition associated with thyroid inflammation called Hashimoto’s thyroiditis.
• Thyroiditis: Inflammation of the thyroid, usually from a viral infection or autoimmune condition. Thyroiditis can be painful, or have no symptoms at all.
• Hyperthyroidism: Excessive thyroid hormone production. Hyperthyroidism is most often caused by Graves disease or an overactive thyroid nodule.
• Hypothyroidism: Low production of thyroid hormone. Thyroid damage caused by autoimmune disease is the most common cause of hypothyroidism .
• Graves disease: An autoimmune condition in which the thyroid is overstimulated, causing hyperthyroidism.
• Thyroid cancer: An uncommon form of cancer, thyroid cancer is usually curable. Surgery, radiation, and hormone treatments may be used to treat thyroid cancer.
• Thyroid nodule: A small abnormal mass or lump in the thyroid gland. Thyroid nodules are extremely common. Few are cancerous. They may secrete excess hormones, causing hyperthyroidism, or cause no problems. 
• Thyroid storm: A rare form of hyperthyroidism in which extremely high thyroid hormone levels cause severe illness.

Regulation of blood pressure by the two hormones

Anti-diuretic hormone (ADH) and Aldosterone work together to regulate water and electrolytes in the blood.

Anti-diuretic hormone (ADH) 

• a hormone that is produced by the hypothalamus and released by the posterior pituitary into the blood stream.
• It is also a hormone that helps to control blood pressure by acting on the kidneys and the blood vessels. 
• Its most important role is to conserve the fluid volume of your body by reducing the amount of water passed out in the urine. It does this by allowing water in the urine to be taken back into the body in a specific area of the kidney. Thus, more water returns to the bloodstream, urine concentration rises and water loss is reduced. Higher concentrations of anti-diuretic hormone cause blood vessels to constrict (become narrower) and this increases blood pressure. 
• Secretion of anti-diuretic hormone also occurs if the concentration of salts in the bloodstream increases. 

ADH plays a role in lowering osmolarity (reducing sodium concentration) by increasing water reabsorption in the kidneys, thus helping to dilute bodily fluids. To prevent osmolarity from decreasing below normal, the kidneys also have a regulated mechanism for reabsorbing sodium in the distal nephron. This mechanism is controlled by aldosterone, a steroid hormone produced by the adrenal cortex.

Aldosterone is released from the adrenal cortex in response to angiotensin I & II and targets the kidney tubules to conserve Na⁺ ions and H₂O while allowing excretion of K⁺ ions into the urine.  Water retention increases blood volume and therefore blood pressure.

Aldosterone also causes the kidneys to excrete potassium. The increased sodium causes water to be retained, thus increasing blood volume and blood pressure.

Maintaining our blood sugar level

To maintain this balance in our blood sugar the body works in a similar way to the thermostat on a central heating system. Our natural 'thermostat' clicks into action as glucose levels rise and fall.

In this homeostatic system, the following components are present:

• Pancreas: acts as the Monitor
• Islets of Langerhans : acts as the Control Center
• Liver, muscles & other body cells : act as Regulators

The body takes action in the following ways:

When the glucose levels fall too low

The hormone adrenaline is released from the adrenal glands and glucagon is produced from the pancreas. Glucagon works in the opposite way to insulin and increases blood glucose by encouraging the liver to turn some of its glycogen stores into glucose to give us quick energy. If the blood glucose level stays low for a period of time hypoglycaemia – low blood sugar level – can occur.

Symptoms include: irritability, aggressive outbursts, palpitations, forgetfulness, lack of sex drive, crying spells, dizziness, anxiety, confusion, forgetfulness, inability to concentrate, fatigue, insomnia, headaches, muscle cramps, excess sweating and excessive thirst.

Sounds familiar? Chances are that if you have a history of dieting then some or many of those symptoms are known to you. In themselves they can be burdensome, but more importantly they are the outward manifestations that your body is having trouble maintaining a good blood sugar level. They can certainly undermine the efforts of many dieters by triggering unhealthy eating which contributes to weight gain.

The pancreas detects an abnormally low blood glucose level and relays this information to the Islets of Langerhans. In response, the Islets of Langerhans increase their secretion of the hormone glucagon.

            

a). Glucagon promotes the conversion of glycogen to glucose in the liver, a process known as Glycogenolysis. In this process, the stored glycogen is converted to glucose phosphate, which then, through a series of reactions can be converted to free flowing glucose as needed.

            

b). Glucagon also promotes the conversion of fat stored in other (fat and muscle) cells of the body to glycerol and fatty acids, which can be further converted to glucose as needed.

            

Hence, blood glucose levels are restored.

When the glucose level rises too high

Insulin is produced by the pancreas to lower it. If the blood sugar level remains too high, this causes the symptoms of hyperglycaemia – high blood sugar level. The extreme form of this is diabetes which is a medical condition needing expert attention often entailing regular insulin injections. Weight cycling – weight gain, loss then gain – may make you more prone to diabetes. Obese people have a 77 times higher chance of developing diabetes than a person at their correct weight – the greater your weight the higher the risk of developing diabetes.

The pancreas, acting as the monitor, detects an abnormally high level of blood glucose and sends this information to the Islets of Langerhans in the pancreas (acting as the control center). The Islets of Langerhans in turn increase their secretion of the hormone Insulin.

            

a). Insulin increases the amount of glucose absorbed by muscles and other (fat) cells of the body, facilitating it's conversion and storage as glycogen, a process called glycogenesis.

           

b). Also, insulin aids the liver in the conversion of glucose to glycogen, which is then stored in the liver.

           

c). Now, if the blood glucose levels remain elevated, the Islets of Langerhans secrete a third hormone called Somatostatin. The function of this hormone is to inhibit the activity of glucagon (which promotes conversion of glycogen to glucose), thus preventing any unnecessary extra glucose being dumped into the blood stream.

           

 Hence, the elevated blood glucose levels are lowered to the normal levels.

Why does thymus gets smaller as we age?

The immune system undergoes dramatic changes with age - the thymus involutes, particularly from puberty, with the gradual loss of newly produced naive T cells resulting in a restricted T cell receptor repertoire, skewed towards memory cells. Coupled with a similar, though less dramatic age-linked decline in bone marrow function, this translates to a reduction in immune responsiveness. The thymic involution, the shrinking of the thymus with age, resulting in changes in the architecture of the thymus and a decrease in tissue mass.

Though the thymus is fully developed before birth newborns have an essentially empty peripheral immune compartment immediately after birth. Hence, T lymphocytes are not present in the peripheral lymphoid tissues, where naïve, mature lymphocytes are stimulated to respond to pathogens. In order to populate the peripheral system, the thymus increases in size and upregulates its function during the early neonatal period.

Moreover, most immunity is produced during infancy and childhood, where it is very much needed because the immune system is still weak. Thus, it gradually decreases in size as we age because it is no longer needed that much.