This chapter shows you position of each of the endocrine (ductless) glands and describes the function of the hormones produced by each.
After completing this section, you should know:
- The characteristics of endocrine glands and hormones
- The position of the main endocrine glands in the body
- The relationship between the pituitary gland and the hypothalamus
- The main hormones produced by the two parts of the pituitary gland and their effects on the body
- The main hormones produced by the pineal, thyroid, parathyroid and adrenal glands, the pancreas, ovary and testis and their effects on the body
- What is meant by homeostasis and feedback control
- The homeostatic mechanisms that allow an animal to control its body temperature, water balance, blood volume and acid/base balance
- Hormones are chemicals that are released into the blood by endocrine glands i.e. Glands with no ducts. Hormones act on specific target organs that recognize them.
- The main endocrine glands in the body are the hypothalamus, pituitary, pineal, thyroid, parathyroid and adrenal glands, the pancreas, ovaries and testes.
- The hypothalamus is situated under the cerebrum of the brain. It produces or controls many of the hormones released by the pituitary gland lying adjacent to it.
- The pituitary gland is divided into two parts: the anterior pituitary and the posterior pituitary.
- The anterior pituitary produces:
- Growth hormone that stimulates body growth
- Prolactin that initiates milk production
- Follicle stimulating hormone (FSH) that stimulates the development of ova
- Luteinising hormone (LH) that stimulates the development of the corpus luteum
- Plus several other hormones
- The posterior pituitary releases:
- Antidiuretic hormone (ADH) that regulates water loss and raises blood pressure
- Oxytocin that stimulates milk “let down”.
- The pineal gland in the brain produces melatonin that influences sexual development and breeding cycles.
- The thyroid gland located in the neck, produces thyroxine, which influences the rate of growth and development of young animals. Thyroxine consists of 60% iodine. Lack of iodine leads to goitre.
- The parathyroid glands situated adjacent to the thyroid glands in the neck produce parathormone that regulates blood calcium levels and the excretion of phosphates.
- The adrenal gland located adjacent to the kidneys is divided into the outer cortex and the inner medulla.
- The adrenal cortex produces:
- Aldosterone that regulates the blood concentration of sodium and potassium
- Cortisone and hydrocortisone that affect glucose, protein and fat metabolism
- Male and female sex hormones
- The adrenal medulla produces adrenalin responsible for the flight, fright, fight response that prepares animals for emergencies.
- The pancreas that lies in the first bend of the small intestine produces insulin that regulates blood glucose levels.
- The ovaries are located in the lower abdomen produce 2 important sex hormones:
- The follicle cells of the developing ova produce oestrogen, which controls the development of the mammary glands and prepares the uterus for pregnancy.
- The corpus luteum that develops in the empty follicle after ovulation produces progesterone. This hormone further prepares the uterus for pregnancy and maintains the pregnancy.
- The testes produce testosterone that stimulates the development of the male reproductive system and sexual characteristics.