Expert: John Locke - 12/3/2009

Question
QUESTION: Describe the circulatory route taken by a red blood cell from its site of production, in some part of the body inferior to the diaphragm, to the point where it picks up oxygen. Then describe the route the oxygen molecule would take to get to the biceps muscle and where it would end up in the cell. Explain the role of oxygen in the muscle cell and name the substance produced that is important for muscle contraction. Explain in detail the role that this substance plays in the process of muscle contraction and relaxation.

(Can you please state specifically where the blood cell is produced and the major vessels and structures through which it passes. Also how oxygen moves through membranes and how it is carried in the blood. please? thank you.)

ANSWER: Thanks for using AllExperts. Red blood cells (RBCs) begin life in the bone marrow--mostly in the ribs, vertebrae, and pelvis in adults--where they grow from erythrocyte precursor cells in a well-determined sequence. You can read more about it here:

http://www.som.tulane.edu/classware/pathology/Krause/Blood/EP.html
http://www.nsbri.org/HumanPhysSpace/focus3/erythropoiesis.html

Immature red blood cells released into the circulation are known as reticulocytes. They are released into capillary beds, which then drain into the venous side of the blood circulation. These RBCs then drain into the right atrium of the heart through the superior/inferior vena cava; blood then flows through the right ventricle and into the lungs via the pulmonary artery, where it is oxygenated within the pulmonary capillaries. A small amount of oxygen dissolves directly in the bloodstream, but most of it is bound to hemoglobin molecules located within RBCs. Oxygen binds directly to iron molecules located within the hemoglobin molecule; four O2 molecules can bind to a single molecule of hemoglobin.

Blood then flows into the left atrium from the pulmonary vein, into the left ventricle, and from there into the aorta and the arterial side of the blood circulation. The arteries subdivide into smaller arterioles and from there into capillaries, where oxygen molecules are released from the RBC. These O2 molecules diffuse across the capillary walls into the tissue, where they diffuse across the cell membrane and enter the cytoplasm. Oxygen molecules function in the production of ATP via the electron transport chain; this process occurs in the mitochondria. See here:

http://biology.suite101.com/article.cfm/electron_transport_chain_etc

ATP is the major energy source for all cellular processes, including muscle contraction; you may read about the process of muscle contraction here:

http://meat.tamu.edu/muscontract.html

This is the pathway that blood would take from below the diaphragm to the biceps muscle:
Inferior vena cava-->R atrium-->R ventricle-->Pulmonary artery-->Lungs-->Pulmonary vein-->L atrium-->L ventricle-->Aorta-->Subclavian artery-->Axial artery-->Brachial artery-->Biceps muscle.

---------- FOLLOW-UP ----------

QUESTION: Dr Locke, I have a completely different question but it still has something do with circulation. I've already come up with an answer, but if you could clear up some things.. please.. thanks you. :)

An Olympic sprinter has prepared for his event at 2000 meters above sea level by training for 2 weeks at this altitude. Describe the ways the body will adjust its oxygen carrying capacity and efficiency in this athlete during this training period.

MY ASNWER: The key to training 2000 meters above sea level are the density of air and differences in atmospheric pressure. At sea level, air is extremely dense due to higher atmospheric pressure, which results in more molecules of gas per liter of volume air. At levels of high altitude, the atmospheric pressure is less dense, resulting in less molecules of gas per liter of volume air. This leads to a decrease in partial pressures of gases in the body. This decrease in partial pressures causes a variety of physiological changes in the body that occur at 2000 meters above sea level. At a high altitude there is less oxygen, and the longer it takes for the body to adapt.
1.   There will be decrease in maximum cardiac output and a decreased maximum heart rate.
2.   An increased number of red blood cells.
3.   A high excretion of base via the kidneys to restore acid-base balance.
4.   A chemical change that will cause the RBC more efficient in unloading oxygen to the tissues.
5.   An increase in the number of mitochondria and oxidative enzymes.

Describe in detail the route by which atmospheric oxygen will be carried to his quadriceps muscle, and a description of how oxygen is transported in the blood.

MY ANSWER: The mechanism by which oxygen in the atmosphere is inhaled is called inspiration. Inspiration is a type of pulmonary ventilation that begins with the onset of the contraction of the diaphragm. The rib cage (external intercostals) increases in volume. As the pressure on a gas inside the respiratory tract decreases; its volume expands. Air enters, inflating the lungs, either through the nose or the mouth. Passing through the nasal cavity, air becomes warmer, and the amount of water vapor increases. Humidification and filtration continue as the air passes through the nasopharynx and trachea and bronchial passageways before entering the alveoli of the lungs. Once the oxygen is in the alveoli it diffuses into the surrounding capillaries. 98.5% of the oxygen is carried on the haeme portion of the haemoglobin of the RBC. 1.5% of it is physically dissolved in the water of the plasma and RBC. From the lungs, the now oxygenated RBC drains back into the left atria of the heart via four pulmonary veins. With the aid of the bicuspid valve, the RBC is pumped into the left ventricle. It passes through the semi lunar aortic valve and ascends the aortic arch. The descending aorta continues with the aortic arch. It’s followed by the thoracic aorta and then the abdominal aorta. The oxygenated RBC travels down the abdominal aorta, which subdivides into the right and left common iliac. The common iliacs subdivide into external and internal iliac arteries. However, for the RBC to reach the quadriceps muscles, they have to take the external iliac artery route. From the external iliac artery, the RBC moves further into the femoral artery, then into the deep fermoral artery, and finally arriving in the lateral femoral circumflex artery. At that point the oxygen molecules will diffuse into the surrounding capillaries into the tissue of the muscle, where they diffuse into the cell membrane and enter the cytoplasm.

Upon completion of a 200 meter race (at sea level) his blood pressure is monitored over a 30 minute period, during which time it returns to normal resting levels. Describe in detail the process by which this althele’s blood pressure returns to normal.

I DON'T HAVE AN ANSWER ..


Answer
Thanks for using AllExperts. Your first two answers are extremely thorough and complete, so far as I can tell. The third question depends upon on a reversal of the factors that lead to elevation of blood pressure during exercise initially. There are a variety of such factors; let me try to elucidate them here:

1. CNS receptors for oxygen and carbon dioxide detect changes consistent with lessening of physical metabolic demand. This does not directly affect BP, but it will drive some of the changes described below.

2. Catecholamine levels decrease as the athlete rests. Decreasing amounts of these chemicals reduce cardiac stimulation, allow for peripheral blood vessels to dilate, and decrease ventilatory activity.

3. Heart rate, stroke volume, and cardiac output decrease as the athlete rests after the race. These contribute to lower blood pressure by a simple volume effect: less blood is ejected from the left ventricle with each stroke, which produces less stretch in the ascending aorta, which corresponds to lower pressure in both the central and peripheral arteries. HR, SV, and CO decrease by a combination of decreased catecholamine stimulation, decreased stimulation of the arotic/carotid baroreceptors, and decreased oxygen demand.

4. Peripheral arteries supplying the skin are already dilated, so they don't change significantly at first (peripheral arteries initially constrict during exercise, but dilate as exercise progresses to improve heat loss via convection). They will eventually constrict to decrease heat loss, representing an increase in peripheral resistance. Vessels supplying the visceral organs dilate following exercise as sympathetic stimulation decreases.

The major determinants of arterial blood pressure are stroke volume and peripheral resistance. The changes above after exercise have the effect of decreasing stroke volume significantly, with a smaller increase in peripheral resistance as the arteries of the skin constrict.

A fairly good overview can be found here (free registration may be required):
http://emedicine.medscape.com/article/88484-overview

Let me know if you have other questions.