AP-BIOLOGY -Lesson 1- Endocrine system

Endocrine System

Apart from the nervous system there is another system that plays a major role in regulation called the endocrine system. The endocrine system is made up of a group of glands which are found at various parts of the body and release chemicals called hormones. Below is Diagram showing the location of these glands. Each gland is responsible for releasing its own chemical (hormone) and hence various jobs from regulating metabolism , growth and reproduction just to name a few..

  
                     

CELL SIGNALLING (cell communication)

The effect that chemicals have on certain cells to respond is called cell signaling. These chemicals or hormones are released into the blood stream and affect specific cells called target cells. These glands have secreting cells which squirts out the chemicals. How does the body know which cell should be affected? The target cells have receptors to receive the hormone. Let’s review the analogy we used in class …

 I (secreting cell) throw a ball (hormone) which Eni (target cell) catches because she have gloves on (receptor). I mean anyone of you can get hit by the ball but guess what you don’t have gloves (no receptors) to catch …so you Eni is our best bet to respond…look at the image below it may help you to understand.

This mode of cell signaling (you might see this term in exam questions) is not only found in the endocrine system but other cells use it also. For example the nervous system use secreting cells at the end of terminal bodies and secrete chemicals which affect target cells with receptors. This is an example of signaling ( communication)  over a short distance hence it is referred to as LOCAL REGULATORS.  Here is a few examples of local regulators.

 ( a) Gap junction- cell communicate with other cells that have direct contact.

(b)    Autocrine - where the secreting cell affects if self hence it is also the target cell.

(c)     Paracrine - secreting cells affect cells that  are close by.

(d)    Neurohormone- secreting cells found on the terminal bodies of the neuron secrete chemicals which travels through the blood and affect target cells close by.

(e)     Neurocrine- secreting cells found on the terminal bodies of the neuron secrete chemicals which affect target cells at the synapse.

Endocrine- this is a type of cell signaling however because the signals travels through long distances it is not classified as a Local regulator. In endocrine signaling secreting cells release chemicals which travel through the blood that affect target cells.

The diagram below shows the diffrent types of cell signalling.

CHEMICAL CLASSES OF HORMONES

Steroids- ( lipid soluble) are lipids and include all sex hormones ( testosterone, estrogen and progesterone) and substances from the adrenal cortex, such as cortisone. Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells.

  Peptides and Amines- (water soluble) Peptides are short chains of amino acids; most hormones are peptides. They are secreted by the pituitary, parathyroid, heart, stomach, liver, and kidneys. Examples include insulin. Amines are derived from the amino acid tyrosine and are secreted from the thyroid (thyroxine) and the adrenal medulla. Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors.

 

Table showing the main differences of water soluble and fat soluble hormones

Water soluble Hormone	Fat soluble hormone
Polypeptide and amines	Steroid hormones
Do not pass easily through the cell membrane ( because the lipid bi-layer of the cell membrane)	Pass easily through the cell membrane
Receptors are found on the outside of the target cell	Receptors are found on the inside of the target cell
Diffuses through the blood no transport protein	Travels into the cell by a transport protein

Look at the diagram below: (a) peptides and Amines hormones - just bind to surface receptors on the outside of target cells (b) Steroid hormones - need a transport protein to carry it into the target cell were the receptor is located.