what is a gland
a specialized cell, group of cells, or organ that secretes substances to be used by or eliminated from the body
explain the endocrine system (general)
a major regulatory system of the body which uses hormones to produce homeostatic adjustments as well as other functions
what are the 6 main functions of the endocrine system
- maintain constant internal environment via regulation of metabolism and H2O/electrolyte balance
- adaptive stress response
- growth and development
- reproduction
- red blood cell production
- integrating with the autonomic nervous system in regulating both the circulation and digestive functions
explain hormones within the endocrine system
- all endocrine tissues secrete hormones
- they are chemical substances that are secreted directly into the blood at low quantities, and exert a physiological effect at a distant target tissue
what are the 2 major categories of hormones in the endocrine system
- hydrophilic (water loving)
- lipophilic (lipid loving)
explain hydrophilic hormones
- highly water soluble and how low lipid solubility
- can be found unbound to carrier molecules within the plasma
what are the two main types of hydrophilic hormones
- peptide hormones
- peptides: short chains of aa
- proteins: long chain of aa
- amine hormones (catecholamines)
- norepinephrine
- epinephrine
- thyroid hormones
explain what makes amine hormones unique
- thyroid hormones are unique because they are not hydrophilic
- catecholamines are unique because they are found both free and bound to carrier molecules
explain hormone synthesis of peptide hormones
they are synthesizes and secreted by the same cellular machinery that makes proteins within cells
1. synthesis
2. packaging
3. storage
4. secretion
explain the first step of the synthesis of peptide hormones - synthesis
large precursor proteins called preprohormones are synthesized by endoplasmic reticulum (ER) ribosomes
explain the second step of the synthesis of peptide hormones - packaging
as they travel through the ER and Golgi complex, these preprohormones are processed into active hormones and package into secretory vesicles
explain the third step of the synthesis of peptide hormones - storage
these hormone-containing secretory vesicles can be stored until the cell receives the appropriate signal
explain the fourth step of the synthesis of peptide hormones - secretion
the appropriate signal initiates exocytosis of the vesicles and the hormones are released into the blood
explain lipophilic hormones
- highly soluble in lipids and are poorly soluble in water
- generally require carrier molecules for transport throughout the body
what are the types of lipophilic hormones
- amine thyroid hormones
- steroid hormones
explain the steroid produced in the adrenal cortex
the key enzyme that leads to cortisol synthesis is found only in the adrenal cortex, so only this organ can make cortisol
explain the hormone synthesis of lipophilic hormones - steroid hormones
- all are synthesized from a single molecule cholesterol
- which steroid is produced by a particular tissue depends on the specific enzymes within the cells of that tissue
explain the storage and release of steroid hormones
- since they are so lipophilic, they are not stored
- they are released as they are synthesized
- to regulate the amount of steroid hormones released, you need to regulate synthesis
explain hormones interacting with their target cells
- in order for hormones to achieve their desired effect, only free, unbound hormones can interact with a receptor at its target cell
- this isnt an issue for hydrophilic hormones and catecholamines since they are mainly found in unbound state
- more to consider for lipophilic hormones who are bound to carrier molecules
explain the importance of the dynamic equilibrium of hormones
- at any given time, not 100% of a steroid hormone in the blood is bound to its carrier molecules
- the hormones are dynamically unbinding an rebinding, resulting in a small fraction of hormone that is unbound at any given time
- it is the unbound hormone that is active and able to act on target cells
where are the receptors of hydrophilic hormones located
peptide hormones and catecholamines bind to specific receptors on the outer surface of the plasma membrane of their target cells and they are hydrophilic, thus unable to freely cross the lipid bilayer of the plasma membrane
where are the receptors of lipophilic hormones located
steroid hormones and thyroid hormones are lipophilic and can easily slip through the plasma membrane and bind to specific receptors inside their target cells
what happens after a hydrophilic hormone binds its receptor (peptide & catecholamines)
- binding of these hormones to their surface receptors produces effects within cells by activating second messenger systems
- these pathways are able to amplify the initial signal, as low concentrations of hormones trigger pronounced cellular responses
what are the 2 major second messenger systems that lead to downstream cellular effects
- cyclic AMP (cAMP)
- Calcium (CA2+)
-
Module 1 Section 135
-
Module 1 Section 241
-
Module 1 Section 342
-
Module 1 Section 446
-
Module 1 Section 542
-
Module 1 Section 641
-
Module 2 Section 122
-
Module 2 Section 226
-
Module 2 Section 328
-
Module 2 Section 413
-
Module 2 Section 534
-
Module 3 Section 117
-
Module 3 Section 226
-
Module 3 Section 313
-
Module 3 Section 419
-
Module 3 Section 523
-
Module 3 Section 631
-
Module 3 Section 725
-
Module 4 Section 132
-
Module 4 Section 215
-
Module 4 Section 322
-
Module 4 Section 440
-
Module 4 Section 59
-
Module 4 Section 640
-
Module 5 Section 120
-
Module 5 Section 217
-
Module 5 Section 323
-
Module 5 Section 426
-
Module 6 Section 128
-
Module 6 Section 220
-
Module 6 Section 339
-
Module 6 Section 427
-
Module 6 Section 535
-
Module 6 Section 614
