Leaving Certificate Agricultural Science

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Leaving Certificate Agricultural Science
The Endocrine System
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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.

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Main Hormones and Their Functions
Hormone Gland Function
ADH / Growth Hormone Pituitary Increases water re-absorption by the kidney / bone elongation
Thyroxine Thyroid Regulates Metabolism, growth and development
Adrenalin Adrenals Raises heart rate, breathing rate, blood pressure and blood glucose levels
Insulin Pancreas Uptake of glucose from blood.
Oestrogen Ovaries Endometrium Formation, female secondary sexual characteristics
Testosterone Testes Sperm Production, male secondary sexual characteristics
Melatonin Pineal Sleep Pattern, Ovulation, Sexual Maturity
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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.

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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.

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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.

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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.

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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.

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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.

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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.