Control center~ area where information is received
After comparing information to a set point, control center sends out signal that directs an effector to respond
In endocrine and neuroendocrine pathways this signal, efferent signal, is a hormone (or neurohormone), which acts on particular effector tissues and elicits specific physiological or developmental changes
A common feature of control pathways is feedback loop.
Negative feedback: effector response reduces in initial stimulus, and eventually response ceases
Positive feedback: reinforces the stimulus and leads to an even greater response
G-protein activation (leads to binding of GTP molecule in the place of GDP—allows interaction of protein with target cell)
Gated Ion-channel receptors—channels that open and close in response to signals and specific molecules (ligands)
Neurotransmitters and muscle cells, action potentials
Catalyze transfer of phosphate groups from ATP to the amino acid tyrosine activation, responses, multiple new proteins & pathways
Cell-surface Receptors for Water-soluble Molecules
Receptors are bound in plasma membrane, projecting outwards
When the signal molecule binds to a receptor, a signal transduction pathway is produced
This causes changes in cellular proteins converting chemicals into specific responses, activation of enzymes, secretion of molecules, rearrangement of the cytoskeleton, and regulation of transcription of genes in the nucleus of the target cell.
Hormones can produce different responses in contact with various cell-surface receptors.
Example: Multiple effects of epinephrine including decreased blood flow to digestive tract and increased glucose to skeletal muscles
When oxygen levels in blood fall, blood vessels release NO
NO dilates the blood vessels, increasing blood flow
Oxygen levels increase again
Have a wide variety of functions in the body, including
contraction of the reproductive tract, inducing labor,
intensifying pain, and the accumulation of platelets
Relationship Between Hypothalamus and Pituitary Gland
The hypothalamus receives information from nerves throughout the body and from other parts of the brain, initiating endocrine signals appropriate to environmental conditions.
It contains different sets of neurosecretory cells, some producing direct-action hormones that are stored in and released from the posterior pituitary. Other hypothalamic cells produce tropic hormones that are transported by portal blood vessels to the anterior pituitary, an endocrine gland. These tropic hormones control release of hormones from the anterior pituitary.
Both tropic and nontropic hormones are produced by the anterior pituitary. The four strictly tropic hormones are thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and adrenocorticotropic hormone (ACTH). Each acts on its target endocrine tissue to stimulate release of hormone(s) with direct metabolic or developmental effects.
Prolactin, melanocyte-stimulating hormone (MSH), and β -endorphin are nontropic anterior pituitary hormones. Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates. MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals. Endorphins inhibit the perception of pain. Growth hormone (GH) promotes growth directly and has diverse metabolic effects; it also stimulates the production of growth factors by other tissues (a tropic effect).
Thyroid Hormones -The thyroid gland consists of 2 lobes located on the ventral surface of the trachea. -This gland produces two similar hormones synthesized from the amino acid tyrosine: triiodothyronine (T 3 ) and tetraiodothyronine (T 4 ). -These hormones are responsible for vertebrate development and maturation such as skeletal growth, mental development, and the metamorphosis of a tadpole into a frog. -Goiter occurs when there is an iodine deficiency.
Parathyroid Hormone and Calcitonin: Control of blood calcium levels -The amount of calcium ions in the blood is essential in regulating skeletal muscles. The usual calcium level is maintained at 10mg/100mL. -When blood calcium level falls, the parathyroid glands, embedded in the surface of the thyroid, secrete parathyroid hormone (PTH) to increase release and absorption of calcium ions. -A rise in blood calcium level promotes the thyroid gland to release calcitonin, which reduces the release and uptake of calcium ions. -PTH stimulates osteoclasts in the bone to release calcium into blood. -PTH also directly stimulates uptake of calcium in kidneys. -PTH indirectly allows kidneys to convert vitamin D into its active hormonal form, which stimulate uptake of calcium in the intestines.
Insulin and Glucagon: Control of Blood Glucose Levels -The pancreas is considered both an endocrine and exocrine gland with important functions in endocrine and digestive systems. -Endocrine cells called islets of Langerhans are scattered throughout the tissues of the pancreas. -Each islet contains populations of either alpha or beta cells. -When blood glucose level rises, beta cells release the hormone insulin, which stimulates all body cells to take up glucose from blood and slows glycogen breakdown in the liver. -As blood glucose level drops, alpha cells release the hormone glucagon signaling liver cells to increase glycogen hydrolysis, convert amino acids and glycerol into glucose, and release glucose into the blood. -Glucose is a major fuel for cellular respiration and a source of carbon skeletons for the synthesis of organic compounds. The recommended blood glucose level is set at about 90mg/100mL.
Adrenal Hormones: Response to Stress -The adrenal glands are adjacent to the kidneys and each adrenal gland are made of the adrenal cortex, or outer portion, and adrenal medulla, or the central portion. -The adrenal medulla releases hormones called catecholamines synthesized from tyrosine. Among the catecholamines are epinephrine and nonepinephrine, which are secreted due to short-term stress response. -The adrenal cortex synthesizes and releases a family of steroids called corticosteroids. Glucocorticoids and mineralocorticoids are released as a result of long-term stress response. -The adrenal medulla is stimulated by nerve signals while the adrenal cortex is stimulated by ACTH from the blood vessels.
Gonadal Sex Hormones -The gonads produce and secrete three major categories of steroid hormones: androgens, estrogens, and progestins. -Estrogens, such as estradiol, are responsible for the development and maintenance of the female reproductive system. -Androgens, especially testosterone, are synthesized by the testes and they stimulate the development and maintenance of the male reproductive system. -Progestins are involved in preparing and maintaining the uterus, which supports growth and development of an embryo. -Both of the gonadotropic hormones (FSH and LH) in males and females stimulate activities of the gonads and control the synthesis of steroid hormones.
Melatonin and Biorhythms -The pineal gland is a small mass of tissue near the center of the brain. -This gland makes and secretes melatonin, a modified amino acid. -Melatonin’s primary functions are related to the biological rhythms associated with reproduction. Thymus Gland -The thymus gland is an organ that lies underneath the top of the breast bone. -The thymus gland is an organ that lies underneath the top of the breast bone.