Help with Circulatory Proteins and Hormones

A lipid soluble hormone is likely to make its way to the nucleus because it can easily pass through the hydrophobic membranes of cells. A water soluble protein is likely to attach to the outside of a cell and activate a signaling pathway since it cannot readily pass through the phospholipid bilayer (cell membrane). Hydrophilic hormones are the same as water soluble hormones. Fat soluble hormones must be carried by proteins through the blood.

Hormones secreted into the blood stream have the ability to travel anywhere in the body. Such hormones are endocrine hormones and they can act on organs far from their source. Substances that are secreted outside the body (or within a body cavity) are not hormones, since all hormones are released by endocrine glands into the blood. Rather, these substances are released by exocrine glands (i.e. sweat, digestive enzymes).

Epinephrine is a hormone secreted in order to facilitate "fight or flight" reactions by the body. Secretion of epinephrine from the adrenal medulla is initiated by sympathetic stimulation. Epinephrine will increase heart rate, blood pressure, and contraction force; however, the skeletal muscle arterioles will be dilated so that more blood is able to reach the muscles. The sympathetic nervous system is designed to direct blood toward skeletal muscle and the heart, and away from the digestive tract and skin.

Norepinephrine and epinephrine (on about an equal basis) on beta-1 receptors in the heart increase heart rate and contractility (force of contraction). These hormones are released from the adrenals in response to sympathetic stimulation.

Moving the heart rate between 60 and 100 bpm involves only the addition and removal of parasympathetic tone. Remember, parasympathetic: rest and digest; so, to raise the heart rate, parasympathetic tone would have to be withdrawn. Sympathetic tone would not be added until the heart rate exceeds 100 bpm.