Other Endocrine Glands

• Production of melatonin by the pineal gland

  Stimulated by darkness and inhibited by light
• Thyroid hormones

  • Thyroxine (T4) and Triiodothyronine (T3) are secreted by follicular cells in response to thyroid stimulating hormone
• Structure of T3 and T4

  Based on two molecules of the amino acid tyrosine, T3 has three iodine atoms attached while T4 has four iodine atoms attached
• Thyroxine is much less active than triiodothyronine but lasts longer
• Approximately 80% of thyroid hormones produced are thyroxine and only 20% are triiodothyronine. Enzymes convert T4 into T3
• Thyroxine's role in body metabolism

  Regulates reactions breaking down complex molecules to release energy and synthesising complex molecules from simple ones
• Thyroxine's effect on body temperature

  Brings about the release of energy and helps maintain body temperature
• Calcitonin


  • Released by the thyroid gland to regulate levels of calcium and phosphate in the blood
• Increased blood calcium concentration

  Thyroid gland releases calcitonin, reducing calcium reabsorption by kidneys and bone breakdown
• High blood phosphate concentration

  Calcitonin moves phosphate into bone and reduces its reabsorption by kidneys
• Parathyroid glands


  Secrete parathyroid hormone (PTH, or parathormone), which increases calcium levels in the blood and phosphate excretion in the urine
• Thymus


  Located in the chest just above the heart and just behind the sternum
• Thymus

  Largest in infants and children, begins to shrink after puberty
• Thymus

  Secretes a group of hormones called thymosins
• Thymosins


  Influence the maturation of disease-fighting cells called T-lymphocytes
• Adrenal Glands

  Two adrenal glands, one above each kidney, each with an inner adrenal medulla and an outer adrenal cortex
• Adrenal Medulla

  Produces adrenaline and noradrenaline
• Adrenal Medulla - Adrenaline


  Similar effect to the sympathetic division of the autonomic nervous system, prepares the body for fight-or-flight responses
• Adrenal Medulla - Noradrenaline


  Increases the rate and force of the heartbeat
• Adrenal Cortex

  Produces more than 20 different hormones known as corticosteroids
• Adrenal Cortex - Aldosterone


  Acts on the kidney to reduce sodium and increase potassium in the urine
• Adrenal Cortex - Cortisol


  Promotes normal metabolism, helps the body withstand stress and repair damaged tissues
• Pancreas


  Soft organ approximately 15cm long, lies just below the stomach and alongside the duodenum
• Pancreas - Exocrine part


  Secretes digestive enzymes into the small intestine through the pancreatic duct
• Pancreas - Endocrine part


  Comprised of clusters of special cells called islets of Langerhans (pancreatic islets)
• Islets of Langerhans

  Secrete two important hormones: Insulin and Glucagon
• Insulin

  Secreted by beta cells of the islets of Langerhans, reduces the amount of glucose in the blood, promotes glucose uptake by body cells, converts glucose to glycogen and fat in the liver, forms glycogen from glucose in skeletal muscles, and stores glucose as fat in fat storage tissue
• Insulin

  1. Reduces the amount of glucose in the blood by promoting the uptake of glucose from the blood by the cells of the body

  2. In the liver, causes the conversion of glucose to glycogen and fat; in skeletal muscles, causes formation of glycogen from glucose; in fat storage tissue, causes glucose to be converted into fat

  3. The level of secretion is determined by the amount of glucose in the blood and is controlled through a negative feedback system
• Glucagon


  1. Acts in the opposite way to insulin by increasing the blood glucose level, mainly by promoting the breakdown of glycogen to glucose in the liver

  2. Stimulates the breakdown of fat in the liver and in fat storage tissues
• Gonads


  • Testes
  • Ovaries
• Androgens


  • Male sex hormones responsible for the development and maintenance of male sex characteristics
• Oestrogens and Progesterone

  • Female sex hormones produced by the ovaries, stimulating the development and maintenance of female characteristics
  • Regulate the menstrual cycle and are involved in changes during pregnancy
• Other Endocrine Tissues

  • Stomach and small intestine secrete hormones that coordinate the exocrine glands of the digestive system
  • Kidneys secrete hormones, including erythropoietin (EPO) which stimulates production of red blood cells
  • Heart secretes a hormone that helps reduce blood pressure
  • Placenta secretes hormones during pregnancy to maintain the pregnancy, stimulate development of the foetus, and stimulate the mother’s mammary glands
• The thyroid causes an increase in metabolic rate, oxygen consumption, and heat production leading to faster weight loss
• Beta cells release insulin


  To increase blood glucose levels
• Alpha cells release Glucagon


  To decrease blood glucose levels
• Thyroid Gland

  1. Controls body metabolism à regulates reactions where complex molecules are broken down to release energy (CATABOLIC) or synthesised (produced) from simple molecules (ANABOLIC)

  2. Overall release of energy is main effect à heat à increases body temperature

  3. Decreases Calcium and phosphate levels in blood
• The thyroid causes an increase in metabolic rate and therefore oxygen consumption and heat production causing faster weight loss
• Pineal Gland


  1. Secretes the hormone melatonin which regulates sleep patterns

  2. Production of melatonin by pineal gland is stimulated by darkness and inhibited by light
• Beta cells release insulin to increase blood glucose levels. Alpha cells release Glucagon to decrease blood glucose levels