Endocrine System

This chapter shows you position of each of the endocrine (ductless) glands and describes the function of the hormones produced by each.

Objectives

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

Summary

• 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.

Learning Activities

Library of Resources

Presentations and Blackboard quizzes can be accessed by students of Otago Polytechnic.