Leaving Certificate Agricultural Science The Endocrine System
Introduction • The Endocrine System is the set of hormone secreting glands within the body. • An Endocrine gland is a ductless organ and makes and secretes specific chemical messengers into the blood. • An Exocrine gland secretes directly or by a duct to the outside of the body e.g. sweat gland, salivary gland • The pancreas is both an endocrine and exocrine gland (Islets of Langerhans secrete insulin) • A Hormone is a chemical messenger, secreted by a endocrine gland into the blood which alters the effect of a specific tissue.
Endocrine VS. Nervous System • NS is fast acting, ES is slower (growth) • NS is electrical, ES is chemical. • NS has fast transmission, ES is slow (blood) • NS is short lived response, ES is long lasting. • NS affects local, ES has widespread affect.
The Pituitary Gland • The Pituitary gland is located in the hypothalamus (front of the brain) and is the most important part of the endocrine system. • The Pituitary gland has two parts, the anterior and posterior. • The Anterior part produces two hormones, ADH and Oxytocin. • ADH is involved in water level control in the blood. • Oxytocin controls lactation (milk let down) and is released from the pituitary when an animal is suckled. • The Posterior part of the Pituitary produces a number of important hormones. • These include FSH (Follicle Stimulating Hormone), LH (Luteinizing Hormone), Prolactin and Growth Hormones. • The Pituitary also releases hormones which control the Adrenal and Thyroid glands.
The Thyroid Gland • The thyroid glands are found on the trachea. • The main hormone produced is called thyroxine. • This hormone controls the growth and development of animals. • Iodine is required for its production. • Lack of thyroxine causes deformation and retardation. • The glands swell if not enough hormone is produced – this is called goitre in humans.
Parathyroid & Thymus • These are located on either side of the thyroid. • They produce two hormones: Parathormone and Calcitonin. • These hormones control the level of calcium, magnesium and phosphate in the body. • The Thymus A very small gland located on the neck. • Has some involvement in the production of lymphocytes (white blood cells), which are involved in immune response.
The Pancreas • The Pancreas produces insulin. • It is produced in the pancreas in the Islets of Langerhans. • Insulin is required for the intake of glucose in cells and prevents the excess breakdown of glycogen. • If insulin is lacking, one outcome is the passing of glucose in the urine. • This is called diabetes mellitus. • This can cause coma because the brain needs glucose. • Synthetic Insulin is now available for diabetics. • It must be injected because if it was eaten it would be digested.
The Adrenal Glands • The adrenal glands are found near the kidney. • They produce over fifty different hormones which are vital for life. • Hydrocortisone is produced in the adrenal glands and is required to control blood pressure and controls the loss of blood. • Adrenalin is secreted from the adrenal glands during stress. • It redirects blood to the head and increases the heartbeat. • It makes the individual more acute to their surroundings. • It is usually secreted when frightened. • Another hormone called non-adrenalin, turns off the effects of adrenalin.
The Gonads • The gonads are the sex glands - the testes and ovaries. • The hormones produced are involved in the reproductive systems of the animal. • These include testosterone, oestrogen and progesterone. • These hormones will be looked at in more detail in Animal Reproduction.