Endocrine system. Hormone. The term hormone is derived from a Greek verb meaning – to excite or arouse Hormone is a chemical messenger that is released in one tissue (endocrine tissue/gland) and transported in the bloodstream to reach specific cells in other tissues
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Derivatives of Tyrosine:
Derivatives of Tryptophan:
Dopamine, serotonin, melatonin
3 groups – glycoproteins, short peptides and small proteins
Proteins are more than 200 amino acids long and have carbohydrate side chains
Thyroid-stimulating hormone (TSH)
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
Short chain polypeptides
Antidiuretic hormone (ADH) and oxytocin (OXT) (each 9 amino acids long)
Growth hormone (GH; 191 amino acids) and prolactin (PRL; 198 aminoacids) from the pituitary gland
Includes all hormones secreted by:
Hypothalamus, heart, thymus, digestive tract, pancreas, and posterior lobe of the pituitary gland, as well as several hormones produced in other organs
Eicosanoids- derived from arachidonic acid, a 20-carbon fatty acid
prostaglandins - involved primarily in coordinating local cellular activities
Steroid hormones - derived from cholesterol
The reproductive organs (androgens by the testes in males, estrogens and progestins by the ovaries in females)
The cortex of the adrenal glands (corticosteroids)
The kidneys (calcitriol)
* bind to receptors on target cells
* being broken down by cells of the liver or kidneys
* being broken down by enzymes in the plasma or interstitial fluid
(hormone) and the
The actions of second messengers for hormones that bind to
receptors in the plasma membrane
Effects on Ca2+ Levels
Effects on cAMP Levels
Some G proteins use Ca2+ as a second
Many G proteins, once activated, exert their effects by changing the
concentration of cyclic-AMP, which acts as the second messenger within
Ca2+ acts as
If levels of cAMP increase,
enzymes may be activated
or ion channels may be
opened, accelerating the
metabolic activity of the
In some instances, G protein
activation results in decreased
levels of cAMP in the
cytoplasm. This decrease has
an inhibitory effect on the cell.
The calcium ions themselves serve as
messengers, generally in combination
with an intracellular protein called
Figure 16.2 1
Hormone (1st messenger)binds receptor.
G protein (GS)
cAMP acti-vates proteinkinases.
Receptoractivates Gprotein (GS).
Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).
Hormones thatact via cAMPmechanisms:
Triggers responses oftarget cell (activatesenzymes, stimulatescellular secretion,opens ion channel,etc.)
Figure 16.2, step 5
of target cell
Most hydrophobic steroids are bound to
plasma protein carriers. Only unbound
hormones can diffuse into the target cell.
Cell surface receptor
Steroid hormone receptors are in the
cytoplasm or nucleus.
Some steroid hormones also bind to
membrane receptors that use second
messenger systems to create rapid
The receptor-hormone complex binds to
DNA and activates or represses one or
Activated genes create new mRNA that
moves back to the cytoplasm.
Translation produces new proteins
for cell processes.
Figure 7-7, steps 1–5
Exocrine pancreas (99% of volume)
Cells (pancreatic acini) forming glands and ducts that secrete pancreatic fluid and enzymes with digestive function
Endocrine pancreas (1%)
Small groups of cells scattered in clusters (pancreatic islets) that secrete hormones
Hormones that are produced in the hypothalamus and stored in the neurohypophysis
MIT + DIT T3 / triiodothyronine
DIT + DIT T4 / thyroxin (tetraiodothyronine)
(contains T3 and T4)
Other amino acids
T4 & T3
The synthesis, storage, and secretion of thyroid hormones.
Thyroglobulin is synthesized anddischarged into the follicle lumen.
Tyrosines (part of thyroglobulinmolecule)
Iodine is attached to tyrosinein colloid, forming DIT and MIT.
Iodideis oxidizedto iodine.
Iodide (I–) is trapped(actively transported in).
Iodinated tyrosines arelinked together to form T3and T4.
Thyroglobulin colloid isendocytosed and combinedwith a lysosome.
Lysosomal enzymes cleaveT4 and T3 from thyroglobulincolloid and hormones diffuseinto bloodstream.
Colloid inlumen offollicle
To peripheral tissues
Figure 16.9, step 7
Elevates rates of oxygen consumption and energy consumption; in children, may cause a rise in body temperature
Increases heart rate and force of contraction; generally results in a rise in blood pressure
Increases sensitivity to sympathetic stimulation
Stimulates red blood cell formation and thus enhances oxygen delivery
Stimulates activity in other endocrine tissues (E, NE for example)
Accelerates turnover of minerals in bone
Activate genes that code for enzymes that are involved in glycolysis (Glucose oxidation)
In children, essential to normal development of Skeletal, muscular, and nervous systems
Figure 7-2 (1 of 2)
Figure 7-2 (2 of 2)