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34. chemical coordination

  1. Hormone and chemical coordination Learning outcomes Structure and function of endocrine system. Water and lipid soluble molecules. Relationship of hypothalamus and pituitary glands.
  2. Hormones A hormone is a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the body. Hormones may reach all parts of the body, but only certain types of cells, target cells, are equipped to respond.
  3. Systems of Internal Communication Animals have two systems of internal communication and regulation: The nervous system The endocrine system
  4. Systems of Internal Communication The nervous system conveys high- speed electrical signals along specialized cells called neurons. The endocrine system, made up of endocrine glands, secretes hormones that coordinate slower but longer-acting responses to stimuli.
  5. Hormones Advantages of using chemical messengers: Chemical molecules can spread to all tissues through the blood. Chemical signals can persist longer than electrical ones. Many different kinds of chemicals can act as hormones; different hormones can target different tissues.
  6. Glands Many hormones are secreted by ductless endocrine glands. Obtain raw materials from and secrete hormones directly into the bloodstream. Exocrine glands have ducts for discharging secretions onto a free surface. Sweat glands, salivary glands, enzyme- secreting glands in the digestive tract.
  7. Hormones Hormones convey information via the bloodstream to target cells throughout the body. Pheromones carry messages outside the body – to other individuals.
  8. Hormones Three major classes of molecules function as hormones in vertebrates: Proteins and peptides Amines derived from amino acids Steroids
  9. Hormones Signaling by any of these molecules involves three key events: Reception Signal transduction Response
  10. Hormones The hypothalamus regulates the neuroendocrine system, maintaining homeostasis in the body. The hypothalamus can use motor nerves to send short-lived electrical messages or hormones to send chemical messages with a longer duration.
  11. The Chain of Command  The hypothalamus produces seven different “releasing” hormones that travel to the pituitary gland.  Each releasing hormone stimulates the pituitary to release a corresponding hormone which travels to an endocrine gland and causes it to start producing a particular endocrine hormone.
  12. Membrane-Bound Receptors  Many hormones are too large, or too polar, to pass through plasma membranes.  Bind to transmembrane proteins that act as receptor sites on target cell membranes.  Hormone is first messenger.  Causes activation of a second messenger in the cytoplasm.  cAMP
  13. Nuclear Receptors  Steroid hormones are lipid soluble molecules that bind to hormone receptors in the cytoplasm of the target cell.  Site of activity is the nucleus.  Steroids are manufactured from cholesterol.  Estrogen, progesterone, testosterone, cortisol.
  14. Nuclear Receptors  Thyroid hormones and insect-molting hormone (ecdysone) also act through nuclear receptors.  Binds to transmembrane protein that uses ATP to move it into the cell.
  15. Control Pathways and Feedback Loops  A common feature of control pathways is a feedback loop connecting the response to the initial stimulus.  Negative feedback regulates many hormonal pathways involved in homeostasis.
  16. The Pituitary  The pituitary gland is located below the hypothalamus.  Nine major hormones are produced here.  These hormones act primarily to influence other endocrine glands.
  17. The Pituitary The posterior lobe of the pituitary regulates water conservation, milk letdown, and uterine contraction in women. The anterior lobe regulates the other endocrine glands.
  18. The Anterior Pituitary  Thyroid stimulating hormone (TSH) – stimulates the thyroid gland to produce thyroxine which stimulates oxidative respiration.  Luteinizing hormone (LH) plays an important role in the menstrual cycle. It also stimulates the production of testosterone in males.
  19. The Anterior Pituitary  Follicle-stimulating hormone (FSH) – plays an important role in the menstrual cycle. In males, it causes the testes to produce a hormone that regulates sperm production.  Adrenocorticotropic hormone (ACTH) – stimulates the adrenal gland to produce steroid hormones. Some regulate glucose production, others balance sodium & potassium in the blood.
  20. The Anterior Pituitary Growth hormone (GH) – stimulates the growth of muscle and bone. Prolactin – stimulates milk production. Melanocyte-stimulating hormone (MSH) – in reptiles & amphibians, this hormone stimulates color change.
  21. The Posterior Pituitary  Antidiuretic hormone (ADH) regulates the kidney’s retention of water.  Oxytocin initiates uterine contraction during childbirth and milk release in mothers.  These hormones are actually synthesized in the hypothalamus and stored in the posterior pituitary.
  22. Biological Clocks  The pineal gland is located in the brain of most vertebrates.  Evolved from a light sensitive “third eye”.  Primitive fish & some reptiles still have a third eye.
  23. Biological Clocks  In other vertebrates it functions as an endocrine gland secreting melatonin.  Melatonin controls color change in amphibians & reptiles.  Release of melatonin is controlled by light/dark cycles.  The primary functions of melatonin appear to be related to biological rhythms associated with reproduction.  Circadian rhythms – 24 hours long.
  24. The Thyroid  The thyroid gland, located in the neck, produces:  Thyroxine – increases metabolic rate and promotes growth.  Two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4).  Calcitonin – stimulates calcium uptake by bones.
  25. The Thyroid  The hypothalamus and anterior pituitary control the secretion of thyroid hormones through two negative feedback loops.
  26. The Thyroid  The thyroid hormones play crucial roles in stimulating metabolism and influencing development and maturation.
  27. The Parathyroids  The parathyroid glands are four small glands attached to the thyroid.  The hormone they produce is parathyroid hormone (PTH) which regulates the level of calcium in the blood.  Essential that calcium is kept within narrow limits for muscle contraction, including the heart.
  28. Calcium Homeostasis  Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin, play the major role in calcium (Ca2+ ) homeostasis in mammals.
  29. Calcium Homeostasis  Calcitonin, secreted by the thyroid gland, stimulates Ca2+ deposition in the bones and secretion by the kidneys, thus lowering blood Ca2+ levels.  PTH, secreted by the parathyroid glands, has the opposite effects on the bones and kidneys, and raises Ca2+ levels.  Also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food.
  30. The Adrenals  Mammals have an adrenal gland above each kidney.  Adrenal medulla is the inner core which produces adrenaline (epinephrine) and norepinephrine.  Adrenal cortex is the outer shell that produces the steroid hormones cortisol and aldosterone.
  31. Adrenal Medulla The adrenal medulla releases adrenalin (epinephrine) and norepinephrine in times of stress. Identical to the effects of the sympathetic nervous system, but longer lasting.  Accelerated heartbeat, increased blood pressure, higher levels of blood sugar and increased blood flow to heart and lungs.
  32. Adrenal Cortex The adrenal cortex produces the steroid hormone cortisol (hydrocortisone). Reduces inflammation.  Synthetic derivatives such as prednisone are used as anti-inflammatory agents. Stimulates carbohydrate metabolism.
  33. Adrenal Cortex The adrenal cortex also produces aldosterone. Aldosterone acts in the kidney to promote the uptake of sodium & other salts from the urine. These salts are important in nerve conduction. Aldosterone and PTH are the only two hormones essential for survival.
  34. The Pancreas  The pancreas is located behind the stomach and is connected to the small intestine by a small tube.  It secretes digestive enzymes into the digestive tract (exocrine function).  Endocrine function – production of insulin and glucagon.
  35. Glucose Homeostasis  The islets of Langerhans in the pancreas secrete insulin and glucagon.  Insulin removes glucose from the blood.  Glucagon returns glucose to the blood.