Lessons In How Your Body Works
Beginning Anatomy and Physiology-Written for Smart Kids and Patients Who Want To Understand the Basics
DO NOT MAKE ANY MEDICAL DECISION FOR YOURSELF WITHOUT ADVICE FROM YOUR DOCTOR. THIS IS NOT COMPREHENSIVE ENOUGH TO TRUST FOR MEDICAL DECISIONS.
- Introduction
- The Heart, the Vessels and the Blood Your Pump, your Pipes and your Juice
Introduction
Anatomy (how it is put together) and physiology (how it functions) isn't simple, but any journey of understanding begins with the first steps. Be grateful that doctors are far ahead in the study of anatomy and physiology. But too often physicians do not take the time to explain the simplest concepts to patients. Basic knowledge can help patients understand how different therapies will affect them. Patients can make better decisions with this information.
H. L. Mencken said that the best teaching reduces knowledge to a simple combination of the obvious and the wonderful that we can actually comprehend. Sure anatomy and physiology is much more complex than presented here. In preparing this for you I want you to know that I don't understand everything about this myself. I am always learning and refining what I know. Nonetheless, doctors don't give patients enough time to combine the obvious and the wonderful. That's what I've tried to do here.
This writing is reduced to the basic obvious knowledge that I want my patients to have. And it is full of wonder. Studying we are put together and how we work always amazes me.
Of course these subjects are more complex than will be fully explored here. Nonetheless, at the Natural Medicine Clinic we want to teach patients basic understandings of normal human functioning. When it is possible, the goal of therapy is the restoration of normal function, normal physiology. Our philosophy is that simple and basic understanding will give patients more authority in making their own medical decisions.
Enjoy. Ask your doctor questions. We'll learn more here together.
DO NOT MAKE ANY MEDICAL DECISION FOR YOURSELF WITHOUT ADVICE FROM YOUR DOCTOR. THIS IS NOT COMPREHENSIVE ENOUGH TO TRUST FOR MEDICAL DECISIONS.
The Heart, the Vessels and the Blood Your Pump, your Pipes and your Juice
The Heart-Your Pump
Your heart is about the size of your fist. It weighs about one pound. It pumps blood through about 50,000 miles of vessels. We function normally on about 30% of the capacity of our hearts. We reserve about 70% of capacity from our resting heart rate to our possible maximum heart rate.
The heart's function is circulation of blood, carrying oxygen and nutrients to the tissues, removing waste and used up air (carbon dioxide, a gas). Arteries carry oxygenated blood away from the heart. Veins return used blood to the heart.
First exception: The exception is pulmonary (lung) circulation where used blood is sent through pulmonary arteries to the lungs. In the lungs it gathers new oxygen and the pulmonary veins bring that freshened blood back to the heart for pumping to the body.
Second exception: To modify some substances and to detoxify the blood, to aid in absorption, all the blood from the digestive system is filtered from vein to vein through the liver. This is called portal circulation.
The heart is in the front of the body below the sternum (the big hard bone between the breasts). Rapid compression and release of the sternum to manually pump the heart is what we call CPR-cardio pulmonary resuscitation.
The pericardium (peri means around; cardium means heart) is a tough fibrous sack that holds the heart loosely enough to allow it to expand and contract. Pericarditis is an infection of that sack typically causing symptoms of chest pain and fever. It can compromise the pumping function of the heart.
Constrictive pericarditis is compression of the sack. Landing the chest against the steering wheel in a car accident is an example of a cause of constrictive pericarditis.
The heart muscle has three layers. The thin outside layer (epicardium) is tightly bound to the heart. The very thin inside layer (endocardium) is also only a few cells thick. It is exquisitely smooth to facilitate easy blood flow. The myocardium is the main big thick middle muscle layer of the heart. Its fibers can pump on their own without signal from the nervous system. Taken out of the body and put on a table, for a while these fibers will pump on their own.
Myocardial (middle layer of the heart muscle) infarction (serious disruption of blood flow) is what we call a heart attack .
The muscles are like one house divided into four rooms (chambers). Two rooms receive blood (the atria) and two rooms pump blood out (the ventricles). The doors between the rooms we call heart valves.
The right heart accepts used blood and moves it to the lungs for new oxygen. The left heart accepts blood from the right heart and moves it to the body. The right and left heart function separately and can fail separately. The left ventricle is the main pump to the body and the largest strongest part of the heart muscle.
Heart valves are like silky little parachutes that open and close to keep blood from flowing into the wrong room. The silky part is attached to a hard ring and to muscles, which open and close the valves, the doors.
Rheumatic Fever damages the valves. Stenosis occurs when a valve cannot open properly because it is too tight . Insufficiency occurs when they cannot close properly.
The heart runs on electricity from chemically charged atoms called ions.
Blood pressure measures how hard the blood is pushing against the pipes (vessels). Blood pushes hardest when the muscle is contracting and weakest in the fraction of a second when the pump is resting. The hardest pushing is the top number called systole. The resting pressure is the lowest number called diastole. Systole is high pressure squeezing. Diastole is relaxation.
When our heart rate increases for any reason, it is at the expense of resting. The diastole is shortened. The heart feeds its own muscles during rest. Thus, in exercise for example, when the heart rate increases, the heart itself gets less blood. It important in to see how it works when the heart is stressed with exercise, a stress test. A thallium stress test puts dye into the heart to see which pipes are not working.
If the vessels of the heart have serious blockages in their flow chest pain can occur. Angina is the cramping choking feeling that can occur when the heart is not getting enough blood to supply its own need. Chest pain is not always related to the heart-it can come from the lungs or from the digestive system.
Atrial fibrillation means the movement of oxygenated blood to the big left ventricular pump is occurring by simple gravity. The atrium chamber has lost its ability coordinate a pumping action that fully empties itself. The heart is not operating at maximum efficiency but it can still work okay because of our big reserve capacity.
Ventricular fibrillation means the big pump isn't working and this is life threatening.
There are two nodes in the heart that and fibers from them that establish a coordinated heart rate. When that is not occurring normally, pace makers are used to restore normal electrical impulse to the coordinated beat of the heart.
A normal resting heart rate (pulse) is more than 60 and less than 100 beats a minute. Tachycardia means the heart is beating too fast. Bradycardia means the heart is beating too slowly. Arrhythmia is a change in the normal pattern of the heart beat itself.
A target maximum heart rate for healthy young adults is in the range of 200. Athletes will have lower resting heart rates, hearts that increase the rate more slowly with exercise, and higher safe maximum heart rates. If the heart rate exceeds 300 it is very dangerous. For calculating maximum safe heart rate we use this formula:
220 minus your age = an acceptable maximum heart
Example: 220 - 55 years old = 165
Exercising to 80% of that maximum rate is good enough for conditioning our skeletal muscles and it represents low risk.
Example: 80% of 165 = 132
Twenty percent of all circulation goes to the brain. The brain is greedy for blood and protects its own blood supply before it will protect any other organ. However, the blood supply to the heart itself is given before the brain can decide where blood should go.
The Vessels-Your Pipes
The aorta is the first artery from the heart. It comes off the heart in big looping arch and moves into channels of vessels supplying the entire body. Arteries decrease in size as they move from the aorta. The smallest are called capillaries. They are microscopic and are so small that only one red blood cell at a time can pass throughthem. The trade of oxygen for carbon dioxide happens in the capillary. Every cell in the body lies close to a capillary-a grocery store and garbage dump.
The big vessels that we can see with our eyes account for only about one mile of the 50,000 miles of arteries and veins. These vessels are elastic so they can expand and contract to maintain the blood pressure and move the blood. The vast volume of circulation occurs in the tiny capillaries. The capillaries are where the arteries meet the veins, so a capillary both vein and artery.
Arterioles are the faucets on the pipes that part stop or slow blood flow (vasoconstriction) or open the pipe to increased flow (vasodilatation). We don't have enough blood to fill the whole system at the same time. Arterioles get signals from the nervous system to regulate where blood is flowing.
The veins do not have as much muscle inside of them as do arteries. Veins pump blood back to the heart by the pressure created by the same muscles that move our bones (skeletal muscles). That's why a long airplane flight or a long bed rest can cause circulatory problems. Arteries can shut themselves down and slow or stop bleeding. Veins cannot constrict as well and major bleeding is most difficult to control in the veins.
Veins do have back flow valves. When the muscles are relaxed these valves prevent blood from flowing by gravity back down and hold its progressive movement to the heart.
When blood is not moving it has a tendency to clot. A thrombus is a blood clot that is not moving. An embolus occurs when the clot is floating the vessels. The area where an embolus lands can die because the plug will block its blood supply. Example: A clot in the leg could break loose and float through the veins through the right heart into the lung-a pulmonary embolus. Symptoms might be chest pain, shortness of breath and coughing up blood.
An embolus moving out of the heart in the arteries could go to the brain and cause a stroke. A stroke is called a cerebrovascular accident-a blood vessel problem that interrupts the blood supply to the hungry brain tissue.
The Blood-Your Life's Juice
An adult has about 1½ gallons of blood. About 45% of that is red blood cells. About 55% is clear yellow liquid called plasma. About 1%, a very important 1%, is white blood cells.
Blood has three jobs. One is to transport gasses (oxygen and carbon dioxide), nutrients, waste, hormones and chemicals. The second is to protect us by being able to clot and to perform immune functions. The third is to keep constant the internal environment of our bodies.
Alcohol dilates (opens up) the vessels on the surface of the body. When blood comes to the surface the temperature of the air cools it. A beer on a hot day might be cooling. A shot on a ski slope could increase the possibility of hypothermia.
New red blood cells are made in the bone marrow. A red blood cell has life of about 120 days, so our blood is completely new about every four months. Red blood cells are young or old, but they are all the same, performing the same function-feeding the tissues with oxygen and getting rid of carbon dioxide.
Hemoglobin refers to the amount of the red blood cell that can carry oxygen to the cells and carry carbon dioxide back to the lungs. We have about 4 to 5 million red blood cells and every one has about 300 molecules of hemoglobin.
Hematocrit refers to the % of the blood that is red blood cells.
Carbon monoxide is produced when gas is not completely burned. It will attach in our red blood cells to the places oxygen should be and it won't let go. Breathing carbon monoxide causes a suffocation of the tissues and eventually death. Treatment for carbon monoxide poisoning is breathing oxygen.
The white blood cells start out the same but then are directed to change to perform different jobs. Eosinophils are the WBCs that respond to allergies. Neutrophils are the main bacteria fighters. Monocytes are wandering through our systems cleaning up debris and garbage. Lymphyocytes are varied and have many immune functions.
Human blood is sterile in normal circumstances. Bacteremia is a bacteria being carried in the blood. Viremia is a virus being carried in the blood. Septicemia is an organism actually multiplying and growing in the blood. Septicemia is very dangerous.
Platelets are little pieces of fiber that collect on signal to create plugs that stop bleeding until clotting can occur. They are the first defense in repair of the vessels. Clotting is a complex process involving several different factors. Clotting is complicated because it must be so well controlled. We want to clot when we need to. But inappropriate clotting creates big problems-stroke for example.
DO NOT MAKE ANY MEDICAL DECISION WITHOUT ADVICE FROM YOUR HEALTH CARE PROVIDER. THIS IS NOT COMPREHENSIVE ENOUGH TO TRUST FOR MEDICAL DECISIONS. |
