Know Thyself - Anatomy and Physiology of the Circulatory System (in brief):
The circulatory system, consisting of the heart and blood vessels, is responsible for the distribution of blood and its necessary components to bodily tissues. Blood consists of water (83%), red blood cells, immune cells (also known as white blood cells), nutrients, dissolved gases, hormones, and waste products. The most important nutrient, being oxygen, is transported by the red blood cells. The body's waste gas, carbon dioxide, is scavenged by these cells and taken back to the oxygen rich environment in the vessels of the lungs. It is here that gas exchange occurs: carbon dioxide is exchanged for oxygen. The heart is the "middle man" in this process as it acts as a pump from the body's vessels to the lungs while simultaneously pumping blood received from the lungs back to the body.
From the heart the blood flows through the aorta (the largest artery in the body) through smaller branching arteries, then into smaller vessels known as arterioles, and then into the vast network of microscopic blood vessels known as capillaries (60,000 miles to be exact). It is in these tiny vessels that the blood actually delivers its gas/nutrient payload to the cells. Interestingly, the entire network of capillaries are capable of holding 4-5L of blood if all were opened at the same time. but because an average individuals total blood volume is only approximately 5L, only about 5% of the blood is actually found in capillaries at any given time. Therefore, to ensure adequate pressure in the high pressure arteries and adequate blood return to the heart in the low pressure veins, capillary beds or networks are systematically opened and closed, depending on need.
The amazing task of pressure regulation is accomplished by a complex interaction of nerves in the heart and blood vessels (baroreceptors), the kidneys, and the brain as well as hormonal influences by organs such as the adrenal glands, lungs, liver, and pituitary gland. Numerous stimuli can act as vasodilators, which cause the smooth muscle in the blood vessel lining to relax. This relaxation effect decreases blood pressure due to the vessels expansion. In turn, the constriction of blood vessels can be accomplished by the actions of vasoconstrictors. See the list below for more information:
Common Vasodilators - heat, high levels of carbon dioxide, Nitric Oxide (NO), Adenosine, bradykinin (associated with trauma), potassium ions, etc.
Common Vasoconstrictors - cold, high levels of oxygen, adrenaline, insulin, antidiuretic hormone (a hormone produced by the kidneys), angiotension II (resulting from renin secretion by the kidneys), calcium ions, etc.
Symptoms of Hypertension: High Blood Pressure is known as the "silent killer" due to it's oft lack of distinguishing symptoms. However, some individuals notice headaches, dizziness, bounding heartbeat (can be felt as pulsations in chest, neck or ears), and vision changes due to increased blood pressure.
Common Causes of Hypertension: Stress, lack of rest, diet, and dehydration are all common causes of high blood pressure.
STRESS: Continual exposure to stressors with corresponding mental anxiety leads to stress-induced hypertension. This is why: the autonomic nervous system's sympathetic nervous response, which is activated during periods of stress, restricts blood flow to digestive organs, and prepares the body for intense physical exercise ("flight or fight"). Unless you do plan to exercise, this physiologic response does not contribute to good blood pressure regulation.
LACK OF REST: Poor sleep has a number of detrimental effects on blood pressure. Some people with hypertension have reduced their systolic blood pressure by as much as 40mmHg just by going to sleep!
DIET: One of the most powerful antihypertensive agents are plant-based foods. Fresh fruits and vegetables are rich in phytonutrients (especially antioxidants) which help to limit the damage done to the Nitric Oxide (NO) compounds in the blood vessels responsible for vasodilation. Diets low in antioxidants have the reverse effect, causing a condition clinically known as post-prandial hypertension (after-meal high blood pressure).
DEHYDRATION: Our bodies are 70% water by volume. When the kidneys sense a drop in blood volume due to dehydration they secrete anti-diuretic hormone (decreases urine production) and initiate a hormonal process known as the renin-angiotension-aldosterone response. This response constricts the blood vessels in the extremities (arms and legs) and limits the further loss of water through the urine. The result is that blood pressure is elevated but the purifying work of the kidneys is limited. A high salt diet compounds this problem by bringing more of the body's water into the bloodstream via osmosis and, thus, further elevating the blood pressure.
It has been said that "the cure is in the cause." Thus, eliminating the causative agency will often, in time, normalize the blood pressure.
(1) CDC. Vital signs: awareness and treatment of uncontrolled hypertension among adults—United States, 2003–2010. MMWR. 2012;61(35):703–9.