Endocrine I January 7th
The human contains roughly 30 chemical messengers known as hormones, which regulate activities such
as sleep, body, temperature, hunger, and stress management. These hormones are products of the
endocrine system, which along with the nervous system controls and coordinates our body processes.
The endocrine system uses chemical messengers to relay information and instructions between cells.
How do cells communicate?
Transmission – Through gap junctions; must be between two cells of the same type
Mediators – Ions, small solutes, lipid soluble materials
Distribution – usually limited to adjacent cells of the same type that are interconnected by connexons
Paracrine communication – use of chemical messengers to transfer information from cell to cell within a
Transmission – Through extracellular fluid
Mediators – Paracrine Factors
Distribution – Primarily limited to a local area where paracrine factor concentrations are relatively high;
target cells must have appropriate receptors
Transmission – Through the blood stream
Mediators – hormones
Distribution – Target Cells are primarily in other tissues and organs must have appropriate receptors
Transmission – Across synaptic clefts
Mediators – Neurotransmitters Distribution – Limited to very specific area; target cells must have appropriate receptors
What are hormones?
Travel through bloodstream
From one tissue to specific cells in another type of tissue
What are three main groups of hormones?
Amino Acid Derivatives – small molecules that are structurally related to amino acids, the building blocks
Derivatives of Tyrosine: Thyroid Hormones (T4) / Catecholamines (Epinephrine)
Peptide Hormones – chain of amino acids. Most peptide hormones are synthesized as prohormones –
inactive molecules that are converted to active hormones before or after they are secreted.
Glycoproteins – These proteins are more than 200 amino acids long and have carbohydrate side chains.
The glycoproteins include thyroid-stimulating hormone (TSH), Luteinizing Hormone (LH), and follicle
stimulating hormone (FSH) from the anterior lobe of the pituitary gland as well as several hormones
produced in other organs.
Short Polypeptides/Small Proteins - This group of peptide hormones is large and diverse. It includes
hormones that range from short chain polypeptides such as antidiuretic hormone (ADH) and oxytocin
(OXT) (each 9 amino acids long), to small proteins such as growth hormone (GH; 191 amino acids) and
prolactin (PRL; 198 amino acids). This group includes all the hormones secreted by the hypothalamus,
heart, thymus, digestive tract, pancreas, and posterior lobe of the pituitary gland, as well as several
hormones produced in other organs.
Lipid Derivatives – There are two classes of lipid derivatives: elcosanoids, derived from arachidonic acid,
a 20 carbon fatty acid; and steroid horm