Endocrine System Chemical Control

What are endocrine hormones? 1.Chemical signals from one cell to remote target cells. 2.Chemicals for direct cell-to-cell communication. 3.Chemicals that cross a gap between to adjacent cells.

Messenger Molecules Cells must communicate with one another to coordinate cell processes within tissues and to maintain homeostasis. Cell-to-cell communication is carried out via messenger molecules.

Three types of chemical signals are used for cell- to-cell communication.

Four methods of cell-to-cell communication are found in the human body, ranging from direct to remote communication.

A muscle cell needs to tell a neighboring muscle cell to contract. This will be accomplished by ___ communication: 1.Direct. 2.Synaptic. 3.Paracrine. 4.Endocrine.

When blood sugar is high, body cells must be stimulated to take up sugar. This is accomplished by ___ communication. 1.Direct. 2.Synaptic. 3.Paracrine. 4.Endocrine.

Aspirin helps relieve headaches because it: 1.Inhibits prostaglandin synthesis. 2.Stimulates prostaglandin synthesis.

Endocrine hormones Produced by endocrine (“ductless”) glands and secreted into the bloodstream. Endocrine hormones may affect a wide array of target cells to produce multiple effects. Two types: peptides (small proteins) and steroids (lipids).

Hormones and Receptors

Peptide Hormones Peptide hormones do not enter the cell directly. These hormones bind to receptor proteins in the cell membrane. When the hormone binds with the receptor protein, a secondary messenger molecule initiates the cell response. Because peptide hormones are water soluble, they often produce fast responses.

(cytoplasm) (nucleus) peptide or amino acid-derived hormone (first messenger) (extracellular fluid) cyclic AMP- synthesizing enzyme cyclic AMP ATP inactive enzyme (second messenger) active enzyme reactant product plasma membrane nuclear envelope receptor The hormone binds to a receptor on the plasma membrane of a target cell 1 The activated enzymes catalyze specific reactions 4 The second messenger activates other enzymes 3 Hormone–receptor binding activates an enzyme that catalyzes the synthesis of a second messenger, such as cyclic AMP 2

Steroid Hormones Steroid hormones enter through the cell membrane and bind to receptors inside of the target cell. These hormones may directly stimulate transcription of genes to make certain proteins. Because steroids work by triggering gene activity, the response is slower than peptide hormones.

gene plasma membrane ribosome hormone receptor steroid hormone mRNA (nucleus) RNA polymerase DNA (cytoplasm) new protein (extracellular fluid) A steroid hormone diffuses through the plasma membrane The hormone binds to a receptor in the nucleus or to a receptor in the cytoplasm that carries it into the nucleus The hormone–receptor complex binds to DNA and causes RNA polymerase to bind to a nearby promoter site for a specific gene RNA polymerase catalyzes the transcription of DNA into messenger RNA (mRNA) The mRNA leaves the nucleus, then attaches to a ribosome and directs the synthesis of a specific protein product nuclear envelope

If receptors for a hormone were blocked, the effect would be the same as if: 1.More hormone was added. 2.No hormone had been released. 3.More receptors had been added. 4.The receptors had not been blocked.

Your doctor injects a hormone as a treatment for a condition, and says it won’t take effect for at least 24 hours. What kind of hormone was used? 1.Peptide 2.Steroid 3.Amino acid derived

How do endocrine hormones “know” which cells are their target cells? WORKTOGETHERWORKTOGETHER

Role of the Hypothalamus The thalamus receives sensory information, relays some to the hypothalamus. Hypothalamus monitors the body for temperature, pH, other conditions. Hypothalamus signals pituitary gland if conditions need to be corrected.

Role of the Pituitary The pituitary is the “master gland” that signals other glands to produce their hormones when needed. The anterior lobe of the pituitary receives signals from the hypothalamus, and responds by sending out the appropriate hormone to other endocrine glands. The posterior pituitary receives oxytocin or antidiuretic hormone (ADH) from the hypothalamus, relays them to the body as necessary.

hypothalamus pituitary (anterior lobe) capillary bed endocrine cell blood flow blood flow capillary bed pituitary (posterior lobe) Oxytocin and ADH (blue triangles) are secreted into the blood via capillaries in the posterior pituitary Endocrine cells of the anterior pituitary secrete hormones (red squares) in response to releasing hormones; the pituitary hormones enter the bloodstream Neurosecretory cells of the hypothalamus produce oxytocin and ADH Releasing or inhibiting hormones (green circles) are secreted into capillaries feeding the anterior lobe of the pituitary Neurosecretory cells of the hypothalamus produce releasing and inhibiting hormones

Pituitary Hormones Pituitary HormoneFunctions Follicle-stimulating hormone Stimulates egg maturation in the ovary and release of sex hormones. Lutenizing hormone Stimulates maturation of egg and of the corpus luteum surrounding the egg, which affects female sex hormones and the menstrual cycle. Thyroid-stimulating hormone Stimulates the thyroid to release thyroxine. Adrenocorticotropic hormone Causes the adrenal gland to release cortisol. Melanocyte-stimulating hormone Stimulates synthesis of skin pigments. Growth hormoneStimulates growth during infancy and puberty. Antidiuretic hormoneSignals the kidney to conserve more water. OxytocinAffects childbirth, lactation, and some behaviors.

Endocrine Hormones GlandHormonesFunctions ThyroidThyroxineRegulates metabolism CalcitoninInhibits release of calcium from the bones ParathyroidsParathyroid hormoneStimulates the release of calcium from the bones. Islet cells (in the pancreas) InsulinDecreases blood sugar by promoting uptake of glucose by cells. GlucagonIncreases blood sugar by stimulating breakdown of glycogen in the liver. TestesTestosteroneRegulates sperm cell production and secondary sex characteristics. OvariesEstrogenStimulates egg maturation, controls secondary sex characteristics. ProgesteronePrepares the uterus to receive a fertilized egg. Adrenal cortexEpinephrineStimulates “fight or flight” response. Adrenal medulla Glucocorticoids Part of stress response, increase blood glucose levels and decrease immune response. AldosteroneRegulates sodium content in the blood. Testosterone (in both sexes) Adult body form (greater muscle mass), libido. Pineal glandMelatoninSleep cycles, reproductive cycles in many mammals.

Use the table on the last slide to diagnose the following endocrine issues: A patient who feels cold and listless all the time. A patient who is constantly keyed up and nervous. An elderly patient who is having chronic trouble falling asleep at night. WORKTOGETHERWORKTOGETHER

Homeostasis and Hormones Examples: Thyroid and temperature control Thyroid, Parathyroid, and calcium Pancreas and glucose control

Knowing the following: The thyroid produces thyroxine, which increases metabolism. Thyroid-stimulating hormone is released by the pituitary. Sketch a negative feedback loop that controls body temperature regulation. WORKTOGETHERWORKTOGETHER

Temperature Control

Knowing the following: Calcitonin from the thyroid inhibits calcium release from the bones. Parathyroid hormone stimulates release of calcium from the bones. Sketch a negative feedback loop that controls blood calcium level. WORKTOGETHERWORKTOGETHER

Blood Calcium

Knowing that: Insulin from the pancreas lowers blood glucose by stimulating body cells to take up glucose. Glucagon from the pancreas increases blood sugar by stimulating the liver to break down glycogen into glucose. Sketch a negative feedback loop that controls blood sugar. WORKTOGETHERWORKTOGETHER

Blood Sugar Control

Given this patient profile, can you make a diagnosis? Age – 14 Gender – Male Exam: Normal weight, low blood pressure Lab tests: High blood glucose, low levels of insulin. WORKTOGETHERWORKTOGETHER

Now how about this patient? Age – 40 Gender – Male Exam: Obese, high blood pressure Lab tests: High blood glucose, normal levels of insulin. WORKTOGETHERWORKTOGETHER

Other hormone roles Controlling sleep cycles (melatonin) Controlling reproductive cycles (melatonin, sex hormones) Growth (growth hormone) Responding to stress or emergencies (epinephrine and other hormones)

Hormones Everywhere! Many other organs besides the endocrine glands produce hormones. Kidneys produce several hormones that regulate blood pressure, which is essential for kidney function. The digestive system produces several hormones that regulate appetite.

Low body fat stimulates leptin production, which stimulates appetite. The mouse is obese because its low leptin levels give it an enormous appetite. Leptin injections return the mouse’s weight to normal. Humans sometimes have a leptin issue, too, but the problem is a bad leptin receptor on body cells. Alas, leptin injections won’t cure that. The obese mouse on the left does not produce enough leptin, a hormone produced by fat cells.

Finally… Summarize the roles of the pituitary and other endocrine glands in maintaining homeostasis in the human body.