Presentation on theme: "CHAPTER 30 CHEMICAL SIGNALING WITHIN THE ANIMAL BODY."— Presentation transcript:
CHAPTER 30 CHEMICAL SIGNALING WITHIN THE ANIMAL BODY
HORMONES A hormone is a chemical signal produced in the body. It typically acts at a site distant from where it was produced. Most hormones are produced in glands that are completely enclosed in tissue. These glands are called endocrine glands. Hypothalamus Pineal gland Pituitary gland Thyroid gland Pancreas Testes (in males) Ovaries (in females) Adrenal glands Thymus Parathyroid glands (attached to the thyroid)
HORMONES There are three big advantages to using chemical hormones as messengers rather than speedy electrical signals (like nerve signals). Chemical molecules can spread to all tissues via the blood. Chemical signals can persist much longer than electrical ones. Many different kinds of chemicals can act as hormones.
HORMONES The glands that produce hormones are generally controlled by the nervous system. The endocrine system and the motor nervous system are the two main routes the CNS uses to issue commands to the organs of the body. The two are so closely linked that they are often considered a single system— neuroendocrine system. The hypothalamus is the main switchboard of the neuroendocrine system.
HORMONES The CNS regulates the body’s hormones through a chain of command. For example, the hypothalamus controls the pituitary gland with thyrotropic-releasing hormone (TRH). This causes the pituitary to release or thyroid- stimulating hormone (TSH). TSH then causes the thyroid gland to release thyroid hormones. The hypothalamus also secretes inhibiting hormones that keep the pituitary from secreting specific hormones.
HORMONES Hormones are effective messengers within the body because a particular hormone can influence a specific target cell. Cells that the body has targeted to respond to a particular hormone have receptor proteins shaped to fit that hormone and no other.
HORMONES Hormones secreted by endocrine glands belong to four different chemical categories: polypeptides glycoproteins amines steroids
HORMONES The path of communication taken by a hormonal signal is a series of simple steps: 1.Issuing the command - the hypothalamus controls the release of many hormones. 2.Transporting the signal - most are transported throughout the body by the bloodstream. 3.Hitting the target - the hormone binds to a receptor on the target cell. 4.Having an effect - when the hormone binds to the receptor protein, the protein changes shape and triggers a change in cell activity.
KEY BIOLOGICAL PROCESS: HORMONAL COMMUNICATION Dehydration Reduced urine volume causes increased water retention. Blood volume and pressure drops. Osmotic concentration in the blood increases. Osmoreceptors Hypothalamus Generally, a part of the neuroendocrine system receives sensory information and issues a command in the form of a chemical messenger (hormone). Posterior pituitary Antidiuretic hormone (ADH) The hormone is transported to target cells via the bloodstream. The hormone reaches the target cells and binds to the cell receptors. The hormone- recept or complex triggers changes in the target cells. Increased vasoconstriction leads to higher blood pressure. Bloodstream ADH
HOW HORMONES TARGET CELLS The steroid hormones are recognized by protein receptors located in the cytoplasm or nucleus of the target cell. Steroids are manufactured from cholesterol. Steroid hormones can pass across the lipid bilayer of the cell plasma membrane.
HOW HORMONES TARGET CELLS The complex of a steroid hormone and its receptor inside the target cell bind to DNA in the nucleus. This activates the transcription of a specific gene and a protein is subsequently synthesized.
HOW STEROID HORMONES WORK E E E Transport protein Cytoplasm Target cell Receptor protein Steroid hormone- receptor complex 2 Nucleus DNA mRNA Progesterone receptor Protein synthesis Tissue fluidBlood plasma Steroid hormone Plasma membrane Estrogen (E) is a lipid soluble steroid hormone and thus readily passes through the plasma membrane of cells lining the uterus. Inside the cell, estrogen binds to a specific receptor protein associated with the DNA in the nucleus. The estrogen-receptor complex activates the transcription of genes. Later, when progesterone enters the cell, it binds to the receptor and stimulates the cell to produce enzymes that help prepare the uterus to nourish an embryo in the event of a pregnancy. 5 4 Protein synthesis is induced. In this case, the protein produced is a receptor for another steroid protein, progesterone.
HOW HORMONES TARGET CELLS The receptors for peptide hormones are embedded in the plasma membrane. The binding of the hormone to the receptor triggers changes in the cytoplasmic end of the receptor protein. Using second messengers, this change is amplified and causes changes in the cell Second messengers activate enzymes. one of the most common is cyclic AMP (cAMP).
HOW PEPTIDE HORMONES WORK P P The peptide hormone binds with its membrane receptor. The hormone-receptor combination triggers a series of biochemical reactions that produces the second messenger. The second messenger triggers a series of reactions that leads to altered cell functions. Receptor Production of second messenger Alteration of cell activity Peptide hormone
HOW HORMONES TARGET CELLS A single hormone binding to a receptor in the plasma membrane can result in the formation of many second messengers in the cytoplasm. Cyclic AMP is made from ATP by an enzyme that removes two phosphate units. Each second messenger can activate many molecules of a certain enzyme.
KEY BIOLOGICAL PROCESS: SECOND MESSENGERS Adenylyl cyclase converts ATP into cyclic AMP (cAMP), and cAMP acts as a second messenger that activates enzymes called protein kinases. After a peptide hormone binds to its receptor, the hormone-receptor complex activates adenylyl cyclase. Protein kinases catalyze a wide variety of actions, depending on the nature of the first messenger. Because of the presence of a second messenger, the effect on the cell is greatly amplified. Altered cell function(regulates enzymes, synthesizes proteins, secretes molecules) Protein kinase (inactive) ATP Protein kinase (active) (Second messenger) cAMP Adenylyl cyclase 2 3 Hormone (first messenger) Receptor
THE HYPOTHALAMUS AND THE PITUITARY The pituitary gland is located beneath the hypothalamus and is the location where nine hormones are produced. These hormones act principally to influence other endocrine glands. The pituitary consists of two lobes: Posterior pituitary regulates water conservation and, in women, milk letdown and uterine contraction. Anterior pituitary regulates other endocrine glands.
THE HYPOTHALAMUS AND THE PITUITARY The hypothalamus and the posterior pituitary are connected by a tract of neurons. Hormones are produced by cell bodies in the hypothalamus and transported to the posterior pituitary. Antidiuretic hormone (ADH) regulates the kidney’s retention of water. Oxytocin initiates uterine contractions during childbirth and milk release in mothers.
THE HYPOTHALAMUS AND THE PITUITARY The anterior pituitary is a complete gland that produces the hormones that it secretes. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to produce thyroxine, which in turn stimulates oxidative respiration. Adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to produce hormones. Growth hormone (GH) simulates the growth of muscle and bone throughout the body.
THE HYPOTHALAMUS AND THE PITUITARY Follicle-stimulating hormone (FSH) In females, it triggers the maturation of egg cells and stimulates the release of estrogen. In males, it regulates sperm development. Luteinizing hormone (LH) In females, it triggers ovulation of a mature egg. In males, it stimulates the gonads to produce testosterone.
THE HYPOTHALAMUS AND THE PITUITARY Prolactin (PRL) stimulates the breasts to produce milk. Melanocyte-stimulating hormone (MSH) stimulates, in reptiles and amphibians, color changes in the epidermis. Its function in humans is poorly understood.
THE HYPOTHALAMUS AND THE PITUITARY The hypothalamus controls production and secretion of the anterior pituitary hormones by means of a family of special hormones. Neurons in the hypothalamus secrete both releasing and inhibiting hormones. Cell body Axons to primary capillaries Hormones Portal venules Hypophyseal portal system Anterior pituitary Posterior pituitary Pituitary stalk Primary capillaries
THE HYPOTHALAMUS AND THE PITUITARY Negative feedback (feedback inhibition ) often controls the release of hormones from the hypothalamus and anterior pituitary. When enough of the target hormone has been produced, the hormone then feeds back to the hypothalamus and anterior pituitary and inhibits the release of stimulating hormones.
THE PANCREAS The pancreas has both exocrine and endocrine functions. It secretes digestive enzymes and hormones. The hormones, produced in the islets of Langerhans, are insulin and glucagon. Insulin promotes the uptake of glucose and the accumulation of glycogen in the liver and triglycerides in fat cells. Glucagon causes liver cells to release stored glucose and to break down triglycerides. Between meals Blood glucose Pancreas Blood glucose After a meal Pancreatic islets Insulin secretion Glucagon secretion Insulin secretion Glucagon secretion Cellular uptake of glucose Release of stored glucose, break down of fat
THE PANCREAS Diabetes mellitus is a serious disorder in which affected individuals are unable to take up glucose from the blood. There are two kind of diabetes mellitus: Type I is a hereditary autoimmune disease in which the islets of Langerhans are attacked, resulting in abnormally low insulin secretion. Type II is when cells don’t respond to insulin, sometimes due to a reduction in the number of insulin receptors in the target tissue.
THE THYROID, PARATHYROID, AND ADRENAL GLANDS The thyroid gland makes several hormones. Thyroxine increases metabolic rate and promotes growth. Calcitonin inhibits the release of calcium from bones and promotes the uptake of calcium by bones.
THE THYROID, PARATHYROID, AND ADRENAL GLANDS The parathyroid glands are four small glands attached to the thyroid. These glands produce parathyroid hormone (PTH), a hormone that is absolutely essential for survival because it regulates calcium levels in the blood. Calcium ions are necessary for muscle contractions, such as those of the heart. PTH stimulates the release of calcium from bone. Calcitonin (released from the thyroid gland) has the opposite effect.
MAINTENANCE OF PROPER CALCIUM LEVELS IN THE BLOOD Ca ++ LOW CALCIUM LEVEL STIMULATES PTH SECRETION Inactive osteoblast Bone matrix (a)(b) Bone matrix HIGH CALCIUM LEVEL STIMULATES CALCITONIN SECRETION PTH stimulates osteoclast (breaking down bone matrix) Osteocyte (in lacuna) Calcitonin stimulates active osteoblast (increasing bone matrix)
THE THYROID, PARATHYROID, AND ADRENAL GLANDS The adrenal glands are located just above the kidney and each is comprised of two parts. The medulla is the inner core and produces epinephrine and norepinephrine. The cortex is the outer region and produces the steroid hormones cortisol and aldosterone.
THE THYROID, PARATHYROID, AND ADRENAL GLANDS The adrenal medulla releases epinephrine (adrenaline) and norepinephrine in times of stress. These hormones act as emergency signals that stimulate rapid deployment of body fuel. The adrenal cortex produces Cortisol, which acts to maintain nutritional well- being. It is also released in times of stress but can become a chronic problem if stress continues. Aldosterone, which affects water reabsorption in the kidney and affects both blood volume and blood pressure.