What are hormones?
Hormones are specific molecules produced by the endocrine system, that act as messengers to perform important and critical functions of the body. They are directly released by the endocrine glands (without ducts) within the body into the circulatory system and reach the organs or areas of the body that require attention. The word hormones is derived from the greek word ‘to set in motion’.
They regulate specific biological activities including growth, development of the body skeleton, muscles, metabolism, movements, water usage and storage, electrolyte balance, and sexual development including physical appearance.
Both plants and animals have hormones to carry out important functions. In plants the hormones are called phytohormones and endogenous growth inhibitors. A combination of these determine normal growth process in plants.
3 Types of hormones in animals
Animals have three types of hormones based on their chemical composition and origin. They are :
- Steroid Hormones
- Peptide Hormones
- Amine Hormones
What is an endocrine system?
An endocrine system maybe defined as a set of glands that secrete hormones directly into the blood. As the body’s chemical messengers, hormones transfer information and instructions from one set of cells to another.
Do hormones act only on the part of the body they are meant for?
Yes, although the organism’s body has several hormones in the blood at any given time, the designated hormones affect the cells that are genetically programmed to receive and respond to its message because hormones are target specific.
Hormone levels in the body are affected by factors such as stress, infections and changes in the balance of fluids and minerals in blood.
What are the different endocrine glands in animals?
1. Pineal Gland :
The pineal gland is located near the centre of the brain, dorsal to the diencephalon and produces the hormone Melatonin, which affects reproductive development, sleeping patterns and seasonal functions.
2. The Pituitary Gland :
It is a pea shaped gland located at the base of the brain and is considered to be the master gland and secretes several hormones like Growth Hormone, TSH, LSH, ACTH, MSH, Vasopressin and Oxytocin.
3. Hypothalamus :
It is a neuro – endocrine part of the brain and links the nervous system and the endocrine system through the pituitary gland. It secretes hormones like TRH, GnRH, GHRH, CRH, Somatostatin and Dopamine.
4. The Thyroid Gland :
It is located in the neck, ventral to the larynx and is one of the largest glands. It produces three very important hormones, Triiodothyronine, Thyroxine and Calcitonin. The hormones released are important for metabolism and a healthy skeletal structure.
5. The Parathyroid Glands :
These are two pairs of small, oval shaped glands embedded on the dorsal surface of the thyroid gland present in the neck. They secrete Parathormone, which helps in regulation of Calcium and Phosphate ions in the bones and blood.
6. The Thymus Gland :
It is located in front of the heart, in the upper part of the sternum. It produces the hormone Thymosine which helps in the maturation of T – lymphocytes.
7. The Adrenal Gland :
The adrenal glands are located above the kidneys and hence are called as suprarenal glands.
There are two regions in the adrenal glands :
- Adrenal Cortex – it secretes hormones like Cortisol, Aldosterone and Androgens.
- Adrenal Medulla – it secretes hormones like Adrenaline and Noradrenaline. Adrenaline is also called the fight or flight hormone and is released when the body faces stressful situations involving danger, anger and excitement.
8 The Pancreas :
It is located just below the stomach within the curve of the intial part of the small intestine, the duodenum. It is both exocrine (with ducts) and endocrine in function. It secretes Insulin, Glucagon, Somatostatin and Pancreatic polypeptide. They are important for maintaining metabolism. Insulin controls blood sugar levels.
9 The Gonads :
There are two types of gonads. One for the female species and one for the male species.
A. The Ovaries : They are the female sex organs and lie on either side of the female abdominal cavity. Ovaries produce the female hormones Oestrogen/Estrogen and Progesterone.
- Oestrogen/Estrogen – It controls changes at female puberty, like the feminine voice, soft skin, and development in mammary glands.
- Progesterone – It controls uterine changes in the menstrual cycle and helps maintain pregnancy.
B. The Testes : A pair of testes make the male sex organs and are located in the scrotum, outside the male body. Testes produce the male hormone, Testosterone. Testosterone controls changes in the male body at puberty, like a deeper voice, development of penis, facial and body hair.