UNIT 6 - The endocrine systeam Flashcards
(43 cards)
what is the endocrine system
Group of hormone-secreting organs or tissues distributed throughout the body that help regulate body metabolism.
Endorcine glands
- No ducts
- Secrete their products (hormones) into the blood
Hormone
●Chemical molecule secreted into blood by an endocrine gland that causes a regulatory effect in a specific target tissue.
Target tissue
●Tissue whose cells have specific receptor molecules (proteins) on their surface (in the plasma membrane) or within the cell that will interact with a specific hormone.
Characteristics of the endocrine systeam
●Helps regulate body functions (along with nervous system).
●Effects are slower than the nervous system, but are longer lasting.
●Hormones are transported from the endocrine gland to the target tissue by the blood.
●Regulates metabolic activities.
Classes of hormones - two types
1 Amino- acid based hormones
2 steroid hormones
1.- Amino- Acid Based Hormones
▪ Modified amino acids, short chains of amino
acids, or entire proteins.
▪ Water soluble.
▪ Most hormones are of this type.
2.- Steroid Hormones
▪ Derived from cholesterol; include:
◦ sex hormones (estrogen, progesterone, testosterone).
◦ hormones from the adrenal cortex (corticosteroids).
▪ Lipid soluble.
General effects of a hormone
Hormones alter cellular activity.
Some examples of general hormone effects include:
●Opening or closing of ion channels to change the membrane permeability and/or membrane potential
●Synthesis of proteins
●Activation or inactivation of enzymes
●Secretion of another hormone or substance
●Initiation of mitosis
Mechanism of hormone Action - two mechanisms
Transcriptional regulation (Direct Gene Activation) & Second Messenger System
Transcriptional Regulation (Direct Gene Activation) - Mechanism
- This method is used by hormones that can enter the cell such as steroid hormones and the thyroid hormones (T3 and T4)
Second Messenger systeam - Mechanism
- This method is used by hormones that do not enter the cell, for example the amino-acid based hormones (except T3 and T4)
Transcriptional regulation - steps 4
First step:
Hormone diffuses across the plasma membrane of target cell.
The hormone binds to a specific receptor that is located either in the cytoplasm or in the nucleus.
The hormone-receptor complex binds to a specific region of DNA near the initiation site of certain genes.
This stimulates production of mRNA from these genes and synthesis of the corresponding proteins.
Second messenger systems- Steps 3
- Hormone binds to a receptor protein on the surface (in the plasma membrane) of the target tissue.
- Binding of the hormone triggers formation of a “second messenger” inside the cell.
- Second messenger initiates a cascade of reactions that activates metabolic enzymes, so the cell begins to perform new activities.
Example of a second messenger system
Cyclic AMP second messenger system
(cyclic AMP= cAMP )
cAMP Second Messenger System - steps 4
Binding of the hormone to its receptor on the surface of a cell causes activation of the enzyme adenylate cyclase through the activity of a G protein.
Adenylate cyclase catalyzes the conversion of ATP to cAMP, the second messenger.
cAMP, the 2nd messenger, attaches to and activates specific enzymes called protein kinases.
Protein kinases phosphorylate enzymes (add phosphates). This alters the enzymes’ activity – either activating it or inhibiting it.
cAMP Second Messenger System
▪ Each hormone molecule that binds causes hundreds of cAMP molecules to be made.
▪ Each cAMP activates many protein kinases.
▪ Each protein kinase then catalyzes hundreds of reactions.
→ This results in large amplification of the initial signal.
Onset of Hormonal Effects
▪ Notice that with transcriptional regulation, new enzymes must be made.
▪ In the second messenger system, enzymes are already present, and their activity is just altered via phosphorylation.
Variations in receptor Numbers
●The amount of receptor made by a target cell can change.
●Often changes occur in response to hormone levels in the blood.
Variations in receptor number -
DOWN-REGULATION:
Target cell decreases its number of receptors for a particular hormone.
→ This makes target cell less negative to hormone.
Variations in receptor numbers -
UP-REGULATION:
Target cell increases its number of receptors for a particular hormone.
→ This makes target cell more sensitive to hormone.
Control of hormone release - Humoral
- Some endocrine glands are sensitive to the concentration of a specific substance in the blood (like an ion or nutrient), which controls release of a related hormone.
- Regulates levels by negative feedback.
Examples of humural regulation
◦ Calcium & parathyroid hormone (PTH)
↓ in blood calcium triggers parathyroid gland to release PTH, which brings calcium levels back up to normal.
◦ Blood glucose & insulin
↑ in blood glucose triggers pancreas to release insulin, which then decreases blood glucose levels.
Neural
●Some glands release their hormones in response to direct nervous stimulation.
