Overview of the Male Reproductive System
Human Endocrine System
Glands produce and release secretions. Endocrine glands (ductless) produce chemical substances called hormones and release them into the bloodstream. These glands include the hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, ovary and testes. Exocrine glands deliver secretions through a duct or tube to specific locations (salivary glands, sweat glands, mucous glands).
Hormones are chemical messengers that bind to target cells and affect cell activities. In general, the response of the body to hormones is slower and more long lasting than the response to nerve impulses. The release of hormones is controlled through a negative feedback system. Negative feedback systems are control mechanisms that operate by inhibiting a process or activity that originally led to starting the process or activity. For example, as glucose levels in the body increase, sensors in the pancreas signal the release of the hormone insulin. Insulin promotes the entry of glucose into cells, lowering glucose levels. As the glucose levels in the blood decrease, the pancreas stops secreting insulin.
Steroid hormones are produced from the lipid, cholesterol and are able to pass through cell membranes and bind to receptor proteins. Nonsteroid hormones are made from amino acids and generally cannot pass through the cell membrane. These hormones bind to a receptor site on the outside of a cell in order to initiate chemical reactions inside the cell.
Keywords: adrenal gland | hormones | human systems | ovary | pancreas | pituitary gland | testis | thyroid gland | human anatomy | human endocrine system
- Raven, P. H., & Johnson, G. B. (2002). Biology (6th ed.). McGraw-Hill.
- Campbell, N. E., & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.
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