Question

Where are the following glands located in the human body ?

(i) Pituitary (ii) Thyroid (iii) Pancreas (iv) Adrenals

Answer 1

Pituitary gland The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea. It weighs less than an ounce and is one of the most important organs in the body. It is located at the base of the brain and is closely connected to the hypothalamus. The pituitary gland secretes nine hormones that regulate homeostasis by stimulating other endocrine glands to produce and secrete their own hormones. The pituitary gland has two components: the anterior (front) pituitary (or adenohypophysis) and the posterior (back) pituitary (neurohypophysis). The anterior lobe makes up most of the gland and releases the majority of the hormones. The smaller posterior lobe stores hormones but does not make them. It links the endocrine system with the nervous system by way of the hypothalamus.The pituitary gland is known as the ‘master’ endocrine gland. The hypothalamus controls the production of hormones in both lobes. The pituitary gland produces many important hormones, some of which act on other glands to make them produce hormones. The pituitary gland releases at least 9 hormones that have important effects on the body—these include the thyroid stimulating hormone (TSH), adrenocorticotrophic hormone stimulates the adrenal glands. Thyroid The butter-fly shaped thyroid gland is one of the largest endocrine glands. The thyroid gland is in the front of the neck, just below the thyroid cartilage or “Adam’s apple”. The isthmus bridges the two lobes of the thyroid and is located below the cricoid cartilage.

The thyroid gland controls how quickly the body uses energy (metabolism), calcium levels in the blood, how the body makes proteins, and how sensitive the body is to other hormones. It produces thyroid hormones, the principal ones being triiodothyronine (T3), thyroxine which can sometimes be called tetraiodothyronine (T4) and calcitonin. These hormones regulate the heart rate, the rate of metabolism and affect the growth and rate of function of many other systems in the body. T3 and T4 are made from iodine and tyrosine. Calcitonin slows down the rate at which bone is broken down decreasing the amount of calcium dissolved in the blood.

Parathyroid Gland The parathyroid gland controls calcium levels in the blood. The parathyroid is a small of glands around by the thyroid gland. They produce the parathyroid hormone or PTH, which increases the rate at which broke bone is broken down. As a result, more calcium is released into the blood. Parathyroid hormone works in partnership with calcitonin from the thyroid gland. The 2 hormones have the opposite effect. Through negative feedback they keep the calcium level in the blood stable. Hormonal output from the thyroid is regulated by the thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which itself is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus. The thyroid gets its name from the Greek word for “shield” because of its shape. The most common problems of the thyroid gland are overactive thyroid gland, called hyperthyroidism, and an underactive thyroid gland, called hypothyroidism. Thymus The thymus is a specialized organ of the immune system. The thymus “educates” T-lymphocytes (T cells), which are critical cells of the adaptive immune system.

Adrenal Glands The small, triangular adrenal glands (also known as suprarenal glands) sit atop the kidneys. Each is divided into two distinct anatomic and functional organs. The adrenal cortex (the outer region which secretes corticosteroid hormones that affect metabolism (that is how food is stored and used), chemicals in the blood, and characteristics such as body shape and hairiness. The smaller, inner region—the adrenal medulla (which is part of the sympathetic nervous system)—is the body’s first line of defense against physical and emotional stress. They are mainly responsible for releasing hormones in response to stress through the synthesis of corticosteroids such as cortisol and catecholamines such as epinephrine (adrenaline) and norepinephrine. They also produce androgens. The adrenal glands affect kidney function through the secretion of aldosterone, a hormone that helps regulate the osmolarity of blood plasma. The adrenal glands help us deal with dress and as well as maintain homeostasis. Disorders of the adrenal glands include congenital defects such as adrenal hyperplasia, tumors, autoimmune disorders, infection, and impaired blood supply.