endocrine system

• the hypothalamus controls: 


  body temperature, water balance and your heart
• location of the hypothalamus

  at the base of the brain, joined to the pituitary gland via the infundibulum (stalk)
• role of the hypothalamus

  Produces hormones which are carried to the pituitary gland, certain hormones will enter the blood stream and either stimulate or inhibit hormone production in the anterior lobe. Other homones may pass through nerve fibres to the posterior lobe, where they are released. The pituitary gland will secrete hormones that control other endocrine glands.
• pituitary gland (hypophysis)

  It contains the anterior and posterior lobe. It is the size of a pea. The posterior is joined via nerves, it does not create hormones. The anterior is joined via blood vessels.
• anterior lobe releases: gonadotropins


  These hormones targets the ovaries and/or testes. Examples include follicle-stimulating hormone which stimulates follicular development and the production and maturation of sperm and luteinising hormone which triggers the release of an egg from the ovary in females and in males stimulates the testes
• anterior lobe releases: growth hormone (GH)


  Functions of GH include the stimulation of skeletal growth, the increase of amino acid uptake to build proteins. GH is secreted throughout life to maintain organ size
• anterior lobe releases: Thyroid stimulating hormone (TSH) 


  TSH stimulates the thyroid gland to produce hormones
• anterior lobe releases: Adrenocorticotropic hormone (ACTH) 


  ACTH controls the secretion of hormones from the adrenal gland's cortex
• anterior lobe releases: Prolactin (PRL)


  Prolactin works with other hormones to initiate and maintain milk production
• Posterior lobe releases: Oxytocin


  stimulates contraction of the uterus and cells in the mammary glands to release milk
• posterior lobe releases: Antidiuretic hormone (ADH)


  causes increased water retention (reabsorption of water) from the kidneys which results in a decreased amount of urine
• parathyroid gland releases: parathyroid hormone (PTH)


  controls calcium and phosphate levels in the blood
• pineal gland secretes: melatonin


  involved in sleep pattern regulation
• mechanics of PTH

  calcium is released from bones into the blood, increased absorption of calcium will occur in the intestine which leads to increased REabsorption in the kidneys
• thyroid glands


  effects nearly every tissue, regulates the base metabolic rate and is important in body changes to occur during seasonal changes
• thyroid glands secretes: triiodothyronine (T3)


  increases metabolic rate, it is converted from thyroxine by enzymes and is more active
• thyroid gland releases: calcitonin


  regulates calcium and phosphate levels in the blood. it is secreted by C-cells and reduces the reabsorption of calcium and moves phosphate into the bone and also reduces its reabsorption
• thymus secretes: thymosins


  infleunces the maturation of T-lymphocytes which are immunity cells
• the adrenal gland

  contains the adrenal medulla which secretes adrenaline and noradrenaline and the adrenal cortex which secretes more than 20 hormones known as corticosteroids
• the adrenal medulla secretes: adrenaline

  prepares the body for a fight-or-flight response in a threatening situation
• the adrenal medulla secretes: noradrenaline

  increases the rate and force of the heartbeat
• the adrenal cortex secretes: aldosterone

  reduces sodium amount and increases the potassium amount in urine
• the adrenal cortex secretes: cortisol


  promotes normal metabolism and helps the body withstand stress
• pancreas


  special cells called the islets of Langerhans release insulin and glucagon which regulates blood sugar level
• the beta cells secretes: insulin

  causes the conversion of glucose to glycogen to lower the blood sugar level
• the alpha cells secretes: glucagon


  promotes the breakdown of glycogen to glucose to increase blood sugar level
• the gonads: testes


  testes produces androgens which maintains male sexual characteristics
• the gonads: ovaries


  produces oestrogen and progesterone which stimulates and maintains female sexual characteristics. gonadotropins regulate the menstrual cycle
• other endocrine tissues: kidneys


  secretes erythropoietin (EPO) which stimulates erythrocyte production
• other endocrine tissues: the heart

  secretes a hormone to reduce blood pressure
• other endocrine tissues: the placenta

  secretes hormones to maintain pregnancy
• organisation and communication

  the nervous system coordinates the body via nerve impulses whereas the endocrine system coordinates the body via the release of chemical messengers (hormones)
• feedback system


  the body responds to a stimulus and the response alters the original stimulus. a negative feedback reduces stimulus while a positive feedback amplifies the stimulus
• stimulus

  change in the environment causing the system to operate
• receptor


  detects the change
• modulator (control centre)


  processes the information sent from the receptor and causes the effector to act
• effector


  carries out the response
• response

  the change implemented by the effector
• exocrine glands


  secretes into a duct exiting the body
• endocrine glands


  secretes into the extracellular fluid