endocrine

• Hormones


  Chemical substances, secreted by endocrine cells into the extracellular fluids, & affect the behaviour of other glands or tissues
• Hormones


  Your body's chemical messengers. They travel in your bloodstream to tissues or organs. They work slowly, over time, and affect many different processes.
• Classification of hormones


  • Peptides (proteins, glycoproteins & modified amino acids)
  • Steroids (Hormones from lipids/cholesterol, adrenal cortex & sex hormones)
• Hormone affects


  • Only certain tissue cells or organs, referred as target cells / target organs
  • Target cells must have specific protein receptors (so that hormone can attach)
  • Hormone binding influences the working of the cells
• Effects caused by hormones


  1. Changes in plasma membrane permeability or electrical state

  2. Synthesis of proteins/enzymes in the cell

  3. Activation/inactivation of enzymes

  4. Stimulation of mitosis
• Steroid hormone mode of action

  1. Diffuse through the plasma membrane of target cells

  2. Enter the nucleus

  3. Bind to a specific protein within the nucleus

  4. Bind to specific sites on the cell's DNA

  5. Activate genes that result in synthesis of new proteins
• Nonsteroid hormone mode of action

  1. Hormone binds to a membrane receptor (Hormone does not enter the cell)

  2. The activated receptor sets off a series of reactions that activates an enzyme

  3. The enzymes catalyzes a reaction that produces a second-messenger molecule (cAMP)

  4. Oversees additional intracellular changes to promote a specific response
• Endocrine gland stimuli


  • Hormonal stimuli
  • Neural stimuli
  • Humoral stimuli
• Endocrine glands are activated by other hormones
• Changing blood levels of certain ions stimulate hormone release
• Nerve impulses stimulate hormone release, most are under control of the sympathetic nervous system (e.g. under stress)
• Pituitary Gland


  Size of a pea, hangs by a stalk from the hypothalamus, protected by the sphenoid bone, has two functional lobes (Anterior pituitary and Posterior pituitary)
• Hormones of the Posterior Pituitary

  • Oxytocin (Stimulates contractions of the uterus during labor, causes milk ejection in nursing women)
  • Antidiuretic hormone (ADH) (Can inhibit urine production by reabsorbing more water from the forming urine - urine volume decrease & blood volume increase)
• Hormones of the Anterior Pituitary

  • Growth hormone (GH) (Stimulates protein synthesis in cartilage, bone & muscle, promotes fat metabolism)
  • Prolactin (PRL) (Stimulates and maintains milk production following childbirth, plays a role in carbohydrate & fat metabolism)
  • Adrenocorticotropic hormone (ACTH) (Regulates endocrine activity of the adrenal cortex, to produce its hormones)
  • Thyroid-stimulating hormone (TSH) (Influences growth and activity of the thyroid, to produce thyroid hormones)
  • Follicle-stimulating hormone (FSH) (Stimulates follicle development in ovaries, stimulates sperm development in testes)
  • Luteinizing hormone (LH) (Triggers ovulation, stimulates testosterone production in males)
• Thyroid Gland

  Found at the base of the throat, consists of two lobes and a connecting isthmus, produces Thyroid hormone and Calcitonin
• Thyroid Hormone


  Increases metabolic rate (stimulate all cells to metabolize at a faster rate), composed of Thyroxine (T4) and Triiodothyronine (T3)
• Iodine deficiency leads to goiters (enlargement of the thyroid gland due to constant stimulation from anterior pituitary)
• 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 (PTH) which 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) and medulla (inner neural tissue region), sit on top of the kidneys
• Hormones of the Adrenal Cortex


  • Mineralocorticoids (mainly aldosterone - regulate water & mineral content in blood)
  • Glucocorticoids (including cortisone and cortisol - promote normal cell metabolism, control inflammation)
  • Sex hormones (mostly androgens, some estrogens)
• Hormones of the Adrenal Medulla


  Epinephrine (adrenaline) and Norepinephrine (noradrenaline) - prepare the body to deal with short-term stress ("fight or flight")
• Pancreatic Islets (islets of Langerhans)


  The pancreas has both endocrine and exocrine functions, the pancreatic islets produce Insulin (allows glucose to cross plasma membranes into cells) and Glucagon (allows glucose to enter the blood), these hormones maintain blood sugar homeostasis
• Pineal Gland / Pineal Body


  Found on the third ventricle of the brain, secretes melatonin which helps establish the body's wake and sleep cycles
• Thymus Gland


  Located in the upper thorax, posterior to the sternum, largest in infants and children, produces thymosin which matures some types of white blood cells and is important in developing the immune system
• Hormones of the Ovaries


  • Estrogens (stimulate development of secondary female characteristics, mature female reproductive organs, promote breast development, regulate menstrual cycle)
  • Progesterone (acts with estrogen to bring about the menstrual cycle, helps in the implantation of an embryo in the uterus, helps prepare breasts for lactation)
• Hormones of the Testes

  Produce several androgens, Testosterone is the most important (responsible for adult male secondary sex characteristics, promotes growth and maturation of male reproductive system, required for sperm cell production)
• Endocrine Function of the Placenta


  Produces hormones that maintain the pregnancy and play a part in the delivery of the baby, including Human chorionic gonadotropin (hCG), Human placental lactogen (hPL), and Relaxin