Endocrine system Flashcards
Hormone
A hormone (hormon to excite or get moving) is a mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body
Exocrine glands
secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ,
Endocrine glands
secrete their products (hormones) into the in- terstitial fluid surrounding the secretory cells rather than into ducts. From the interstitial fluid, hormones diffuse into blood capillaries and blood carries them to target cells throughout the body.
Endocrine glands
The endocrine glands include the pituitary, thyroid, parathy- roid, adrenal, and pineal glands
Upregulation
If the quantity of a hormone is deficient the number of receptors may increase
Downregulation
Too much of an hormone causes the number of target cell receptors to decrease
Paracrine
These are a type of local hormones that act on neighbouring cells
Autocrine
These hormones act on the same cell that secreted them
These inactivate quickly
Two types of hormones
- Lipid soluble
* Water soluble
Lipid soluble hormones
- Steroid hormone - derived from cholesterol
- Thyroid hormone
- Nitric oxide gas
Water soluble hormones
- Catecholamines (amine hormones)
* Peptide hormones
Lipid soluble hormones in blood
lipid-soluble hormone molecules are bound to trans- port proteins. The transport proteins, which are synthesized by cells in the liver, have three functions:
- They make lipid-soluble hormones temporarily water-soluble, thus increasing their solubility in blood.
- They retard passage of small hormone molecules through the filtering mechanism in the kidneys, thus slowing the rate of hormone loss in the urine.
- They provide a ready reserve of hormone, already present in the bloodstream.
The function of the human endocrine system
Maintain homeostasis e.g. insulin and glucagon maintain the blood glucose level within tight limits - irrespective of food intake.
Respond to a wide variety of external stimuli - such as the use of adrenaline and noradrenaline in the preparation for ‘fight or flight’.
Follow various cyclic and developmental programs – sex hormones regulate sexual differentiation, maturation, the menstrual cycle and pregnancy
Types of hormones
- Catecholamines - produced by the adrenal glands such as adrenaline and noradrenaline
- Peptide - insulin & parathyroid hormone
- Steroid - cortisol / sex steroid and vitamin D
Classes of steroids
- Corticosteroids - released by the adrenal cortex
* Sex steroids - made by the gonads
Coticosteroid classes
- Glucocorticoids - a class of corticosteroids involved in regulation of glucose metabolism
- Mineralcorticoids - a class of corticosteroids which influence the salt and water balance
Hormones with extracellur receptors
Hormones which are not lipid soluble therefore cannot diffuse into the plasma membrane.
Only for water soluble hormones
Function of water soluble hormone
- The hormone binds to receptor on the surface of the plasma membrane and acts as the first messenger
- The hormone receptor complex activates a membrane protein called a G protein
- The activated G protein in turn activates adenylate cyclase
- Adenylate cyclase converts ATP into cyclic AMP because the enzyme’s active site is on the inner surface of the plasma membrane.
- This reaction occurs in the inner cytosol of the cell
- Cyclic AMP (the second messenger) activates one or more protein kinases.
- The donor of the phosphate group is ATP which is converted into ADP
- Activated protein kinases phosphorylate one or more cellular proteins.
- Phosphorylation activates some of these proteins and inactivates others.
- Phosphorylated proteins in turn cause reactions which produce different physiological responses
- Different protein kinases exist within different target cells and within different organelle.
- Phosphorylisation of protein kinase may also inhibit certain proteins.
Function of lipid soluble hormone
A lipid soluble hormone diffuses from the blood and through the lipid bilayer of the plasma membrane into a cell
• The hormone binds to and activates the receptors located within the cytossol or nucleus.
• The activated receptor - hormone complex then alters gene expression : it turns specific genes of the nuclear DNA on or off
• As the DNA is transcribed , new mRNA forms and leaves the nucleus and enters the cytosol
• There it directly synthesising a new protein, often an enzyme on the ribosome
• The new proteins alter the cell’s activity and cause responses typical of that hormone.
Circadian / Diurnal rhythm
This is the daily cycle of biological activity based on a 24-hour period.
Melatonin
- Secreted by the pineal gland
- Helps regulate biological rhythm
- Melatonin does not induce sleep / it promotes sleep and good nights rest
