Histo: Hormone structure, synthesis, storage, and secretion (lecture) Flashcards
(32 cards)
What are the functions of the endocrine system?
To coordinate and integrate cellular activity within the whole body; maintain homeostasis (constant internal environment); regulate energy balance and fuel mobilization, utilization and storage
What are glands?
Discrete organ systems that produce a chemical messenger that exerts a biological effect
What are hormones?
Chemical messengers that exert biological effects on distant target cells
What are the different structural types of hormones?
Proteins and peptides ranging in size from small peptides to large glycoproteins; steroids; small amino acid derivatives (amines)
What are the different classes of hormone signaling?
Endocrine, exocrine, paracrine, and autocrine
What is endocrine signaling?
Product released into circulation (ductless); affects distant cells
What is exocrine signaling?
Product released into a duct for delivery to a surface (sweat/skin) or organ lumen (digestive enzymes/gut)
What is paracrine signaling?
Product released into interstitial space, affecting neighboring cells (localized)
What is autocrine signaling?
Produce released and affects releasing cell
What type of hormone is insulin?
Peptide, endocrine
Where is insulin produced?
Beta-cells of islets of Langerhans in pancreas; stored in storage granules
Where is insulin released to?
Circulation
What causes insulin to be released?
Elevated glucose levels in blood
What is the function of insulin?
Stimulate glucose uptake in target cells – fuel (glucose) utilization and energy homeostasis
The pancreas is located near the….
Duodenum (small intestine)
The exocrine tissue of the pancreas contains what kind of cells?
Acinar cells (appears darker in staining) - digestive enzymes
The islets of Langerhans of the pancreas contain what kind of cells?
Alpha, Beta, Delta, PP (appears lighter in staining)
What is the structure of insulin?
2 peptide chains (A has 21 a.a.s, B has 30 a.a.s) held together by disulfide bonds.
Monomer, dimer, or hexamer
What are the steps in insulin synthesis?
- Transcription of gene into mRNA
- Initial translation of signal sequence on ribosome and binding to rough ER
- Synthesis of preproinsulin in lumen of ER
- Processing (folding, cleavage of signal sequence off, formation of disulfide bonds) to proinsulin in lumen of ER
- Processing (cleavage of C chain off) to mature insulin in the Golgi
- Package and storage in secretory vesicle/granule
Can take a few hours - days
What is the structure of an insulin hexamer?
Quaternary; 2 central Zn2+ ions in center important for holding the structure together, coordinated by B10 histidine
What is the importance of Zn in insulin hexamer structure?
Holds cell together for proper storage of insulin in secretory vesicles in the Beta cells
What is the importance of the monomer form of insulin?
Insulin signaling and interacting with receptors
What is the function of the hexamer form of insulin?
It is the fully mature storage form
What are the steps of insulin secretion?
- Glucose uptake by Beta cell and conversion to G-6-P
- Glycolysis, Krebs cycle, electron transport, and ATP generation
- Elevated ATP - ATP inhibits K+ channels, K+ accumulates in cytoplasm
- Resulting in membrane depolarization (-70 mV to -50 mV)
- This opens voltage sensitive Ca2+ ion channels
- Resulting Ca2+ influx triggers exocytosis of insulin storage vesicles/granules
