Many hormones are peptides. The anterior and posterior pituitary glands produce many peptide hormones. The anterior pituitary gland secretes luteinizing hormone, follicle stimulating hormone, prolactin, adrenocorticotrophic hormone (ACTH), and growth hormone. The posterior pituitary gland secretes antidiuretic hormone and oxytocin. Additional peptide hormones include atrial-natriuretic peptide (ANP), produced by the heart; insulin and somatostatin, secreted by the pancrease; and cholecystokinin and gastrin secreted by the the gastrointestinal tract.

A crucial distinction exists between peptide hormones and steroid hormones. Peptide hormones, being polar, cannot cross the cell membrane, but steroid hormones can. This is a crucially important distinction to keep in mind for the MCAT. A peptide hormone must bind to receptors on the surface of the cell triggering a second messenger to be released in the cytoplasm.












The WikiPremed MCAT Course is a comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum. Please read our policies on Privacy and Shipping & Returns.  Contact Us. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course. WikiPremed offers the customers of our publications or our teaching services no guarantees regarding eventual performance on the MCAT.


Creative Commons License
WikiPremed is a trademark of Wisebridge Learning Systems LLC. The work of WikiPremed is published under a Creative Commons Attribution NonCommercial ShareAlike License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions.