Class 11 Biology

Chemical Coordination

Endocrine Glands

Endocrine glands lack ducts and are hence, called ductless glands. Their secretions are called hormones.

Hormones: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

Human Endocrine System

The human endocrine system is composed of following glands.

  1. Hypothalamus
  2. Pituitary Gland
  3. Pineal Gland
  4. Thyroid Gland
  5. Pancreas
  6. Adrenal Gland
  7. Testis and Ovaries

The Hypothalamus

Hypothalamus is the basal part of diencephalon, forebrain and it regulates a wide spectrum of body functions. It contains several groups of neurosecretory cells called nuclei which produce hormones. These hormones regulate the synthesis and secretion of pituitary hormones. However, the hormones produced by hypothalamus are of two types, the releasing hormones (which stimulate secretion of pituitary hormones) and the inhibiting hormones (which inhibit secretions of pituitary hormones).

These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus.

endocrine system in human

The Pituitary Gland

The pituitary gland is located in a bony cavity called sella tursica and is attached to hypothalamus by a stalk. It is divided anatomically into an adenohypophysis and a neurohypophysis. Adenohypophysis consists of two portions, pars distalis and pars intermedia.

The pars distalis region of pituitary, commonly called anterior pituitary, produces following hormones:

Corpus luteum is a temporary endocrine structure in ovary, and is responsible for production of high level of progesterone.

The Pineal Gland

The pineal gland is located on the dorsal side of forebrain. Pineal secretes a hormone called melatonin. Melatonin plays a very important role in the regulation of a 24-hour (diurnal) rhythm of our body. For example, it helps in maintaining the normal rhythms of sleep-wake cycle, body temperature. In addition, melatonin also influences metabolism, pigmentation, the menstrual cycle as well as our defense capability.