the human biology

Endocrine System&nsbp;&nsbp;&nsbp;&nsbp;&nsbp;Unit 2 Human Biology


The endocrine system is a group of specialized organs and body tissues that produce, store, and secrete chemical substances known as hormones. These hormones regulate the body growth, metabolism, and sexual development and function. The hormones are released into the bloodstream and affect one or several organs throughout the body. The endocrine system works alongside the Nervous System to co-ordinate functions of all the body systems. (Internet source 1).

The endocrine system made up of major glands that include:

  • Hypothalamus
  • Pituitary
  • Thyroid
  • Parathyroids
  • Adrenals
  • Pineal body
  • Reproductive organs (Ovaries and Testes)
  • Pancreas


It is also known as' master gland' because it controls the activity of most of the other endocrine glands. The hypothalamus is the link between the nervous system and the endocrine system and it is connected to several areas of the brain by nerve fibres, and receives information from the brain about the emotions and about conditions in other parts of the body. The hypothalamus responds to the information it receives from the brain and the blood by producing hormones known as releasing hormones, the releasing hormones travel to the pituitary gland where they regulate the anterior pituitary hormones. (Minett P., et al., 1999, p148).

Pituitary Gland

The pituitary gland located in a bony cavity just below the base of the brain beneath the hypothalamus and it is not larger than a pea. It is considered the most important part of the endocrine system because it secretes several hormones that regulate the function of other endocrine glands. The pituitary gland divided into two parts: The interior lobe and the posterior lobe. (Internet source 1). Each one of those lobes has separate functions. The anterior lobe regulates the activity of thyroid and adrenal gland as well as reproductive glands and it produces several hormones that include:

  • Growth hormones, which stimulates growth of bone and tissue.
  • Thyroid stimulating hormones (TSH) - stimulates the thyroid gland to produce thyroid hormones.
  • Adrenocorticotrophic hormone (ACTH), which stimulate and controls the growth and hormonal output of the adrenal cortex.
  • Luteinizing hormone (LH) and folic stimulating hormone (FSH), which in woman stimulates the development of the graafian folic in the ovary which secretes hormone oestrogen. In men it stimulates testes to produce
  • Prolactin stimulates the secretion of milk from the breasts following birth.

The posterior lobe of the pituitary secretes two hormones which are manufactured in the hypothalamus, and stored in the posterior lobe:

  • The anti-diuretic hormone (ADH), which controls water loss by the kidneys
  • Oxytocin stimulates the uterus during child birth and stimulates milk production. (Helen Mc Guinness, 2002, pp254-255).

Thyroid Gland

The thyroid gland located in the neck and it's controlled by the anterior lobe of the pituitary. The main secretions of the thyroid gland are Triodothyronine (T3) and Thyroxine (T4) which both regulate the body metabolism. It also plays an important role in bone growth and development of the brain in children. Thyroid hormones help maintain normal blood pressure, heart rate, digestion, muscle tone, and reproductive function. (Helen Mc Guinness, 2002, p257).

Parathyroid Glands

The parathyroid glands are four small glands located at the back of the thyroid glands. They release a hormone known as parathyroid hormone, which plays a role in regulating the calcium level in the blood. (Minett P., et al., 1999, p147).

Adrenal Glands

Adrenal glands also known as suprarenal glands, they are small and triangular shaped situated on top of both kidneys. The adrenal glands are made up of two parts: the outer part which is called adrenal cortex, and the inner part which is called the adrenal medulla. The outer part or adrenal cortex secretes hormones known as corticosteroids which regulate the body metabolism, the balance of salt and water in the body, the immune system, and sexual function. (Internet Source 2).

The inner part of the adrenal gland produces hormones called catecholamines such as adrenaline. These hormones controlled by the sympathetic nervous system and are released to help the body cope with physical and emotional stress by increasing the heart rate and the blood pressure. (Internet Source 1).

Pineal Gland

The pineal gland is located in the middle of the brain. It secrets hormone called melatonin, which may help regulate the circadian rhythms, patterns of repeated activity that associated with the environment cycle of day and night such as wake-sleep rhythms. (Helen Mc Guinness, 2002, pp256-257).

Reproductive Glands

The reproductive glands are the main source of sex hormones. In the males, the testes which they are situated in the groin, in a sac called the scrotum. They have two functions: secretion of the hormone testosterone, which affect many male characteristics e.g. sexual development, growth of facial hair and pubic hair as well as sperm production. In females the ovaries and they are located on both sides of the uterus; they produce two hormones called estrogen and progesterone as well as eggs. These hormones control the development of female characteristics e.g. breast growth and they are involved in reproductive functions such as menstruation and pregnancy. (Internet Source 1).


The pancreas is an elongate organ, located toward the back of the abdomen behind the stomach. The pancreas involved in a wide variety of functions in the endocrine and exocrine system. An endocrine secretion is the hormone insulin which is secreted directly into the blood stream. Insulin lowers the level of sugar in the blood and helps the body cells to take up and use or store it as glycogen. The exocrine or external secretion is the secretion of pancreatic juice to aid with digestion. (Helen Mc Guinness, 2002, p260).

The Nervous System

The nervous system is a major system which controls and regulates communication system in the body. The nervous system composed of organs such as brain, spinal cord, nerves and ganglia. Also these consist of various tissues including nerve, blood, and connective tissue. Together all carry out the complex activities of the nervous system. The nervous system has two main parts which both have a unique structure and functional characteristics:

a) Central nervous system: it consists of the brain and spinal cord and all their nerves and organs which control the voluntary and involuntary acts e.g. breathing and moving the joints.

i. The brain: is a large mass of soft tissue contained inside cranium. The brain consists of over 10 billion nerve cells and coordinates most of the voluntary movement.

ii. The spinal cord: is an ovoid column of tissues. The spinal cord extends from the medulla oblongata in the brain stem to the second lumber vertebra in the spinal cord, and is the centre of reflective action.

b) Peripheral nervous system: consists of a series of nerves which resides or extends outside the central nervous system. The main function is connecting the central nervous system to the limbs and organs. It is divided into two parts :

i. Somatic nervous system: is part of the peripheral nervous system which is associated with the voluntary control of the body's activities (movement) through action of skeletal muscles and the reception of external stimuli which helps to keep the body in touch with its surroundings.

ii. Automatic nervous system: is part of the peripheral nervous system that acts as control below the consciousness and controls visceral functions.

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