Endocrine system

• Endocrine system


  A messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs
• Hypothalamus


  The neural control center for all endocrine systems in vertebrates
• Endocrine system

  Second messenger system of the body, uses chemical messages (hormones) that are released into the blood to control several major processes
• Processes controlled by hormones

  • Reproduction
  • Growth and development
  • Mobilization of body defenses
  • Maintenance of homeostasis
  • Regulation of metabolism
• Hormones

  Produced by specialized cells, secreted into extracellular fluids, transferred by blood to target sites to regulate the activity of other cells
• Types of hormones

  • Amino acid-based (proteins, peptides, amines)
  • Steroids (made from cholesterol)
  • Prostaglandins (made from highly active lipids)
• Hormones affect only certain tissues or organs (target cells or organs)
• Target cells must have specific protein receptors
• Effects caused by hormones

  1. Changes in plasma membrane permeability or electrical state

  2. Synthesis of proteins, such as enzymes

  3. Activation or inactivation of enzymes

  4. Stimulation of mitosis
• Control of hormone release

  1. Hormone levels in the blood are maintained by negative feedback

  2. A stimulus or low hormone levels in the blood triggers the release of more hormone

  3. Hormone release stops once an appropriate level in the blood is reached
• Pituitary gland

  • Size of a grape
  • Hangs by a stalk from the hypothalamus
  • Has two functional lobes: Anterior pituitary and Posterior pituitary
• Hormones of the anterior pituitary

  • Two affect non-endocrine targets
  • Four stimulate other endocrine glands (tropic hormones)
• Characteristics of all anterior pituitary hormones

  • Proteins (or peptides)
  • Act through second-messenger systems
  • Regulated by hormonal stimuli, mostly negative feedback
• Growth hormone (GH)


  • General metabolic hormone
  • Major effects are directed to growth of skeletal muscles and long bones
  • Causes amino acids to be built into proteins
  • Causes fats to be broken down for a source of energy
• Functions of other anterior pituitary hormones

  • Prolactin (PRL)
  • Adrenocorticotropic hormone (ACTH)
  • Thyroid-stimulating hormone (TSH)
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
• Prolactin (PRL)


  • Stimulates and maintains milk production following childbirth
  • Function in males is unknown
• Adrenocorticotropic hormone (ACTH)


  Regulates endocrine activity of the adrenal cortex
• Thyroid-stimulating hormone (TSH)


  Influences growth and activity of the thyroid
• Follicle-stimulating hormone (FSH)


  • Stimulates follicle development in ovaries
  • Stimulates sperm development in testes
• Luteinizing hormone (LH)


  • Triggers ovulation
  • Causes ruptured follicle to become the corpus luteum
  • Stimulates testosterone production in males (referred to as interstitial cell-stimulating hormone (ICSH))
• Pituitary-hypothalamus relationship


  • Release of hormones is controlled by the hypothalamus
  • Hypothalamus produces two hormones that are transported to neurosecretory cells of the posterior pituitary
  • The posterior pituitary is not strictly an endocrine gland, but does release hormones
• Hormones of the posterior pituitary

  • Oxytocin: Stimulates contractions of the uterus during labor, Causes milk ejection
  • Antidiuretic hormone (ADH): Can inhibit urine production, In large amounts, causes vasoconstriction leading to increased blood pressure (vasopressin)
• Thyroid gland


  • Found at the base of the throat
  • Consists of two lobes and a connecting isthmus
  • Produces two hormones: Thyroid hormone and Calcitonin
• Thyroid hormone


  • Major metabolic hormone
  • Composed of two active iodine-containing hormones: Thyroxine (T4) - secreted by thyroid follicles, Triiodothyronine (T3) - conversion of T4 at target tissues
• Calcitonin


  • Decreases blood calcium levels by causing its deposition on bone
  • Antagonistic to parathyroid hormone
• Parathyroid glands


  • Tiny masses on the posterior of the thyroid
  • Secrete parathyroid hormone: Stimulate osteoclasts to remove calcium from bone, Stimulate the kidneys and intestine to absorb more calcium, Raise calcium levels in the blood
• Adrenal glands


  • Two glands: Cortex - outer glandular region in three layers, Medulla - inner neural tissue region
  • Sits on top of the kidneys
• Mineralocorticoids (mainly aldosterone)


  • Produced in outer adrenal cortex
  • Regulate mineral content in blood, water, and electrolyte balance
  • Target organ is the kidney
  • Production stimulated by renin and aldosterone
  • Production inhibited by atrial natriuretic peptide
• Glucocorticoids (including cortisone and cortisol)


  • Produced in the middle layer of the adrenal cortex
  • Promote normal cell metabolism
  • Help resist long-term stressors
  • Released in response to increased blood levels of ACTH
• Sex hormones


  • Produced in the inner layer of the adrenal cortex
  • Androgens (male) and some estrogen (female)
• Hormones of the adrenal medulla

  • Produces two similar hormones (catecholamines): Epinephrine and Norepinephrine
  • These hormones prepare the body to deal with short-term stress
• The pancreas is a mixed gland
• Pancreatic islets


  • The islets of the pancreas produce hormones: Insulin - allows glucose to cross plasma membranes into cells from beta cells, Glucagon - allows glucose to enter the blood from alpha cells
  • These hormones are antagonists that maintain blood sugar homeostasis
• Pineal gland


  • Found on the third ventricle of the brain
  • Secretes melatonin: Helps establish the body's wake and sleep cycles, May have other as-yet-unsubstantiated functions
• Thymus


  • Located posterior to the sternum
  • Largest in infants and children
  • Produces thymosin: Matures some types of white blood cells, Important in developing the immune system
• Hormones of the ovaries

  • Estrogens: Produced by Graafian follicles or the placenta, Stimulates the development of secondary female characteristics, Matures female reproductive organs, Helps prepare the uterus to receive a fertilized egg, Helps maintain pregnancy, Prepares the breasts to produce milk
  • Progesterone: Produced by the corpus luteum, Acts with estrogen to bring about the menstrual cycle, Helps in the implantation of an embryo in the uterus
• Hormones of the testes

  • Interstitial cells of testes are hormone-producing
  • Produce several androgens
  • Testosterone is the most important androgen: Responsible for adult male secondary sex characteristics, Promotes growth and maturation of male reproductive system, Required for sperm cell production
• Other hormone-producing tissues and organs

  • Parts of the small intestine
  • Parts of the stomach
  • Kidneys
  • Heart
  • Many other areas have scattered endocrine cells
• Endocrine function of the placenta

  • Produces hormones that maintain the pregnancy
  • Some hormones play a part in the delivery of the baby
  • Produces HCG in addition to estrogen, progesterone, and other hormones
• Most endocrine organs operate smoothly until old age