Download Title: The Endocrine System

Title: The Endocrine System
Introduction – The endocrine system is involved in the many non-dramatic ways that our
bodies maintain homeostasis on a daily basis. It establishes our circadian rhythm,
regulates smooth and cardiac muscle and promotes growth. The truly dramatic effects of
the endocrine system can be seen during the “tween” and early teen years, when
hormones released by this system bring about the physical differences and behaviors that
we associate with puberty.
Hormones interact with the nervous system (though more slowly) to control and integrate
organ systems
1- The nervous system and the endocrine system act together to coordinate all the
functions of the body
a- The nervous system acts through the stimulation of nerve impulses
conducted along the axon eventually releasing mediator molecules called
neurotransmitters
b- The endocrine system controls the body through the release of mediator
molecules called hormones
c- The means of control are very different
2- Hormone –
3- Responses by the body produced by the endocrine system are slower than that of
the nervous system. The response often takes minutes (blood glucoses) to years
(secondary sex characteristics) to be achieved.
4- The nervous and endocrine systems often work together as a “super system”
II- Endocrine Glands
1- Endocrine glands – secrete their products (hormones) into the interstitial fluid
surrounding the secretory cells, rather than into ducts from the interstitial fluid the
hormones diffuse into blood vessels that carry them to target cells throughout the
body. When they reach the target area the hormones diffuse out of the blood
vessels into the interstitial fluid and contact the target cells.
a- Most hormones require very small amounts to be functional, therefore
circulating levels are often very low
b- The endocrine glands include:
2- Exocrine glands – Secrete their products into ducts that carry into body cavities,
into the lumen of an organ or onto the skin surface (sweat glands, oil glands,
mucus glands)
3- Hormone Receptors – As a rule the 50 (or so) hormones in the body only affect a
few types of cells. These are called the target cells. Hormones influence the
target cells by binding to specific receptor sites composed of proteins or
gylcoproteins.
a- Glycoprotein
b-Only target cells have receptor sites (i.e., TSH only effects the thyroid gland
because only the thyroid gland has receptor sites)
c- Most target cells have between 200 -100,000 receptors for a particular
hormone. When a hormone is present in excess, the target cell becomes less
receptive to the hormone. However, if a hormone is deficient the number of
receptor site will grow in order to make the cells more sensitive.
4- Chemical Classes of Hormones
a- Hormones can be broadly classified into hormones that are water soluble
and those that are fat soluble
1- Fat-soluble hormones include the steroid hormones, the thyroid
hormones and nitric oxide. Steroid hormones are derived from
cholesterol. The two thyroid hormones (T3,T4) are derived from
adding iodine to the amino acid tyrosine. The gas nitric oxide acts as
both a hormone and as a neurotransmitter.
2- The water-soluble hormones are derived from amine, peptide and
protein groups. Amine hormones are made by modifying specific
amino acids, they all contain a –NH3+ group. Histamine (Histadine),
Serotonin (tryptophan). Peptide hormones are small chain (<50 AA’s)
amino acids (oxytocin) Protein hormones (50+ AA’s) include growth
hormone and insulin
3- Shapes by Class
a- Steroid hormones (lipid Soluble)
b- Thyroid hormones (Lipid Soluble)
c- Gas Hormones
d- Amines (Water Soluble)
e- Peptides and Proteins