Endocrine System

• Exocrine glands secrete into ducts (canal or passages)
• endocrine glands produce hormones and secrete them directly into the tissue (intercellular/extracellular fluid)
• for endocrine glands, hormones pass into the capillaries and are carried around in the blood, no ducts- ductless glands
• Endocrine glands work more slowly than the nervous system in coordinating homeostasis.
• the pancreas has both an endocrine and exocrine part
• The islets of Langerhans are clusters of cells within the pancreas that make up the endocrine portion of the pancreas
• islets of langerhans also have beta cells which release insulin when there's high levels of glucose in the bloodstream
• Islets of langerhans contain alpha cells which release glucagon when there's low levels of glucose in the bloodstream
• the exocrine part of the pancreas secretes digestive enzymes into the small intestine via pancreatic ducts
• insulin helps to lower blood sugar by stimulating liver, muscle and fat cells to take up glucose from the bloodstream
• the endocrine part of the pancreas is islets of Langerhans (pancreatic islets) which secrete insulin (beta cells) and glucagon (alpha cells)
• glucagon raises blood sugar by causing glycogenolysis (breakdown of stored carbohydrate called glycogen) in the liver and releasing it as glucose into the bloodstream
• after eating, blood glucose concentration increases rapidly
• when we eat food containing carbohydrates, they are broken down into simple sugars like glucose during digestion
• hypothalamus and pituitary gland are located in the brain
• the thyroid and parathyroids are located in the neck
• the adrenal glands and pancreas are located in the pelvic cavity
• The gonads include the ovaries in females, located in the pelvic cavity, and the testes in males, located outside this cavity in the scrotum.
• the pineal gland is located in the brain
• the thymus lies ventral to the thorax
• hormones influence target cells or target organs - those with receptor sites (proteins) specific to particular hormones.
• hormones are chemical messengers
• Hormones change the functioning of cells by changing the type, activities or quantities of proteins produced.
• Hormones include steriods and protein or amine
• steroid hormones are soluble in lipids
• steroid hormones can pass through cell membrane by diffusion, then combining with receptor protein in the cell.
• the receptor that receives steroid hormones is a receptor in the cytosol on mitochondria or in nucleus. Receptor is specific. Hormone – Receptor complex passes into nucleus and activates genes which control production of particular proteins.
• Steroid hormones are slower acting (effects take place in hours/days)
• examples of steroid hormones are : testosterone, cortisol
• After passing through the plasma membrane and nuclear envelope, a steroid hormone binds to a receptor protein (cytosol, on mitochondria in nucleus) and enters the nucleus.

  The hormone-receptor complex then binds to DNA, and this leads to activation of certain genes and protein synthesis.
• •Amine, Peptides and Protein hormones are insoluble in lipids.
• Amines, Peptides and Protein hormones attach to receptor (specific) molecule on cell membrane of target cell.
• When amines, peptides and protein hormones bind with their receptors they cause changes inside the cell by opening ion channels or stimulating enzyme activity.
• The receptor-Hormone complex produced by amine, protein, and peptide hormones causes secondary messenger to diffuse through cell membrane and activate enzymes.
• amine, peptide, and protein hormones are faster acting (take seconds or minutes to come into effect).
• examples of amine are noradrenaline & adrenaline, thyroxine, melatonin (which is created by the pineal gland)
• examples of peptide hormones are ADH, oxytocin
• examples of protein hormones are FSH, LH, insulin, growth hormone
• Peptide hormones, called first messengers, bind to a specific receptor protein in the plasma membrane. A protein relay in the membrane ends when an enzyme converts ATP to cAMP, the second messenger, which activates an enzyme cascade.
• Cyclic adenosine monophosphate (cAMP, cyclic AMP or 3'-5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is derived from adenosine triphosphate (ATP) and used for intracellular signal transduction in many different organisms, conveying the cAMP-dependent pathway.