The fascia, and is continued upward into the axillary vein. The cephalic runs along the outer side of the biceps, and between the pectoralis major and deltoid, piercing the costocoracoid membrane to join the axillary vein below the clavicle. The Deep Veins. — The axillary vein begins where the venae comites of the brachial artery and the basilic vein unite. It runs internal to the artery, and receives veins corresponding to its branches, as well as the cephalic. The subclavian vein is the continuation upward of the axillary, and runs at a lower level than its artery, from which it is separated by the phrenic nerve and scalenus anticus, to the inner border of that muscle, to join the internal jugular, forming the innominate. It receives the external jugular, and occasionally the anterior. The Inferior Vena Cava. — This large trunk arises at the fifth lumbar by the union of the two common iliacs. It ascends to the right of the aorta, grooves the posterior border of the liver, pierces the diaphragm, is enclosed by the serous layer of the pericardium, and empties into the right auricle. 214 THE CIRCULATORY APPARATUS Fig. 87 Fig. 88 Median cephalic. External cidaneuus nerve. The superficial veins of the flexor aspect of the upper extremity. The internal or long saphenous vein and its tributaries. (Gray ) DESCRIPTION OF THE VEINS 215 The Veins of the Lower Extremity. — The Superficial Veins. — They begin on the back of the foot in a plexus which receives the digital veins, and forms an arch from which -emerge the internal or long and the external or short saphenous veins. The long (internal) saphenous, from the inner part of the plexus, runs in front of the inner malleolus of the tibia, along with the long saphenous nerve, behind the inner border of the tibia and condyle of the femur; thence up along the antero-internal part of the thigh to join the femoral vein at the saphenous opening. The short (external) saphenous vein ascends behind the outer malleolus, and external to the tendo Achillis, with the external saphenous nerve, and pierces the deep fascia in the popliteal space to join the popliteal vein. The Deep Veins. — These are the venos comites of the arteries. The posterior tibial veins receive the peroneal, and join the anterior tibial to form the pop- liteal. This vessel then ascends, crossing superficial to the artery, from the inner to the outer side, and becomes the femoral at the opening in the lower border of the adductor magnus muscle. It receives the external saphenous and veins corresponding to the arterial branches. The femoral vein accompanies the artery, and becomes the external iliac at Poupart's ligament. It is at first outside, then behind, and at its termination internal to, the artery as it lies in Hunter's canal. It receives, in its lower part, veins corresponding to the branches of the superficial femoral artery; the long saphenous, and the inofunda vein. The external iliac joins the internal iliac near the lumbosacral articulation, being at first internal to, later behind, the artery, and they empty into the common iliac vein on either side, the latter tocming the inferior vena cava. The Portal System. — ^The portal vein, three inches long, arises from the union of the splenic and superior mesenteric veins behind the head of the pancreas, and ascends behind the duodenum and between the layers of the lesser omentum. Here it runs behind the hepatic artery and bile duct. Accompanied by the hepatic plexus of nerves and lymphatics, all enclosed in Glisson's capsule, it then enters the transverse fissure, forming near the right end the 'sinus,' and divides into: A right branch, to the right lobe, which distributes branches entering the hepatic substance with the hepatic arterial branches and ducts; and a left branch, distributed like the right. The portal vein also drains the pyloric, cystic, gastric, and par- umbilical veins. The portal vein and its tributaries convey blood to the liver from the following organs — spleen, pancreas, stomach, gall-bladder, umbilicus, duodenum, small and large intestines, appendix, and upper portion of the rectum. The vena portse receives the following tributaries: The superior mesenteric corresponding to the artery of the same name, receiving also the right gastro-epiploic vein, besides branches accompanying those of the artery. It joins the splenic vein. The splenic arises by five or six vessels uniting after leaving the hilum, and runs to the right below the artery, joining the above at a right angle to form the vena portee. It receives the vasa brevia, left gastro-epiploic, and pancreatic branches, and the inferior mesenteric vein. • The inferior mesenteric vein corresponds in branches and course to the artery, and empties into the angle of junction of the two preceding. The pyloric runs with the pyloric branch of the hepatic artery, and joins the vena portse; also the gastric vein which accompanies the gastric artery and receives the esophageal branches, joins the vena portse above the former.^ ^ See Chapter on Absorption, page 287, for description of the function of the portal system. BLOOD 217 BLOOD The blood is contained in the bloodvessels, which are practically a closed arrangement of tubes — the arteries, veins, and their connecting capillaries. Function. — The function of the blood is to transmit the various nutritive elements, absorbed from the organs of digestion to the tissues of the body, to carry to the tissues oxygen absorbed from the air in the lungs; to remove from the tissues the various waste products, such as urea, uric acid, water through the kidneys and skin, carbon dioxide (CO2) — the latter being carried to the lungs by the red cells which give it off with the expired air; to maintain the temperature of the body in warm-blooded animals. , Physical Characteristics. — Blood is alkaline in reac- tion, opaque in color, and appears as a homogeneous mass. Two kinds of blood are contained in the vascular system — in the arteries it is bright red in color, while in the veins it is dark bluish in color. The color of the blood is due to the coloring matter — hemoglobin — contained in the red cells. The bright red color of normal blood is due to the hemoglobin in combination with the oxygen, which it absorbs on coming in contact with the air in the lungs. The bluish color of venous blood is due to the hemoglobin absorbing the carbon dioxide from the tissues — a waste compound which is being carried to the lungs to be given off in the expired air. Constituents of Blood. — It consists of a liquid por- tion called the liquor sanguinis or plasma, red cells or erythrocytes, white cells or leukocytes, and blood plaques. (Of course the latter can only be seen with the microscope.) The Plasma. — This is a clear, slightly yellowish, transparent fluid, consisting mostly of the nutritive elements of the foods — proteins, carbohydrates, fats, inorganic salts — which have been rendered possible 218 THE CIRCULATORY APPARATUS of absorption by the process of digestion; and waste products (urea, cholesterin, etc., resulting from the breaking down of tissues following their functional activities), which are carried to the kidneys, lungs, and skin to be eliminated. Serum. — Serum is a clear, transparent, straw-colored fluid formed when blood coagulates or clots, due to the contraction of the fibrin which separates after several hours, following withdrawal or is found by whipping the blood with twigs, upon which the fibrin forms as whitish threads. The serum consists prac- tically of the same substances as the plasma, excepting the proteins which are found in the fibrin. Serum-albumin represents the protein constituents of the blood found in the plasma. It is absorbed from the digestive tract in the form of peptones which are formed from the proteins in a manner not definitely decided upon by physiologists. It replaces the proteins which have been used up in the disintegration of tissues (anabolism) . Paraglobulin is supposed to be similar to serum- albumin as regards its function, and can only be isolated from the blood serum by chemical methods. Fibrinogen is found in the blood, plasma, lymph, peri- cardial, and peritoneal fluids. It can only be studied by treating blood by chemical means before coagulation. Its importance in regard to its function and nutritive values is an undetermined quantity, aside from the fact that it contributes to the formation of fibrin. Fat is found in the serum as microscopic globules. The amount is very small (0.25 per cent.); however, after a hearty meal the quantity is increased. Sugar is present in the form of dextrose, which is a member of the carbohydrate group of body con- stituents derived from fruits, cereals, etc., taken as foods. Extractives include the nitrogenized bodies, urea, uric acid, creatin, xanthin, etc., various chemical com- binations and decompositions, which result from the breaking down of muscle and nerve tissues. They occur in very small amounts, being continually absorbed from the tissues by the blood, but seldom accumulate, as they are rapidly and continually passed off through the kidneys, bowels, skin, etc. Inorganic Salts. — Sodium and potassium chlorides, phosphates and sulphates, calcium and magnesium phosphates are found in the plasma. Sodium chloride is the most important. The alkalinity of the blood is due to the contained salts, some of which are alkaline in reaction. The Red Cells. — Red cells, corpuscles, or erythrocytes are seen after a drop of freshly drawn blood is examined under the microscope. They appear as disk-like cells, floating or swimming about in the blood plasma. After a few minutes they will be seen to group them- selves in a number of columns of varying lengths, resembling rolls of coins. Also a few white cells will be seen floating about in the plasma. A single cell is slightly yellow or greenish. Numbers when collected together appear red. The color is due to the presence within the cell of the coloring matter, hemoglobin. The diameter of a red cell is 1/2500 of an inch or 0.0075 mm.; 1/25000 or 0.0019 mm. in thickness. The average number of red cells in one cubic milli- meter of blood is 5,000,000 for the male; 4,500,000 for the female. Chemic Composition. — The corpuscle consists of hemoglobin, about 30 per cent, of total weight, the rest, 70 per cent., contains 68 per cent, water, 2 per cent, solid matter, e. g., cholestrin, lecithin, and inorganic salts. The function of the red cell is to carry oxygen to the tissues, where it enters into combination with them (oxidation). This phenomenon is made possible by the hemoglobin contained in the red corpuscle. When the red cells in the blood come in contact under the oxygen pressure, with the air we breathe into our lungs, the hemoglobin absorbs some of the oxygen, through a chemical union (oxyhemoglobin); immediately the blood becomes bright scarlet color on leaving the lungs; as the tissues are reached by this blood, when the oxygen pressure is low, the oxyhemoglobin gives up some of its oxygen to the tissues, and the blood becomes bluish in color (reduced blood); whereupon it returns through the veins to the lungs by way of the heart, to be oxidized again. The White Cells. — The white cells, corpuscles, or leukocytes are composed chemically of 90 per cent, water, the balance solid matter, mostly proteins, e. g., nuclein, nucleo-albumin, which contain phosphorus (as much as 10 per cent.), cell globulin, also lecithin, fat, glycogen, earthy and alkaline phosphates. The number of white corpuscles is much less than the red corpuscles, thus in 1 cubic millimeter the ratio is about 1 white to 700 red. The average number of white cells in a cubic millimeter of blood is between 7500 to 8000. The number may be increased or reduced by the following physiologic conditions: Taking of food rich in proteins raises the number 30 to 40 per cent.; in the newborn, 17,000 to 20,000 per cubic millimeter; latter days of pregnancy they are as high as 15,000 to 20,000; they are increased in various pathologic conditions, such as abscess, peritonitis, appendicitis, pneumonia. Starvation reduces the number. The white cells as seen under the microscope floating in the blood plasma, appear as grayish cells, about 2/5000 inch in diameter, adhering to the walls of the vessel. The cell structure appears as a homogeneous mass containing numerous granules consisting of fat, protein, and carbohydrate. A nuclei can be seen by the adding of a mild acid. They are ameboid, that is, they show movements similar to those seen in the amebae. As a result of this ameboid movement they assume a different shape from time to time. White cells have the properties of moving about and coming in contact with bacteria, and disintegrated tissues, then can be seen taking them into their substance and eliminating them from the cell or digesting the invader. They can by their movements slip through the wall of the capillary vessel and appear in the adjacent lymph spaces. This power of the white cell is best appreciated in the early stages of inflammation when the blood stream is always engorged with red and white corpuscles; the latter can be seen passing into, through, and outside the wall, and preparing to combat the invading germ causing the trouble. This action of the white corpuscles is called diapedesis. The large and small lymphocytes originate in the lymph glands, the solitary and combined glands of the intestines, etc. They are carried into the blood stream from these glands by means of the flowing lymph. The polymorphonuclear, eosinophiles, baso- philes, and leukocytes are derived from the bone- marrow only. They reach the circulation by entering the capillaries in the bone-marrow. Leukocytes disappear by a process of dissolution. The period of their life is unknown. Function of White Cells. — The polymorphonuclear, large and small, h mphocytes possess the properties of engaging and removing bacteria and broken-down tissue. They attack and destroy more or less effec- tively forms of intruding bacteria by surrounding, and incorporating the tissue or bacterium and elimi- nating them by a process of digestion. This swallowing action of these white cells caused Professor Metchni- koff to call them phagocytes, and the process as phago- cytosis. Thus these scavengers aid the human body in recovering from disease by combating and destroy- ing the invading bacterium. White cells are supposed, after breaking up, to contribute certain protein material to the blood plasma, which aids in the coagulation of blood. Blood Plaques. — ^These are colorless disks con- sisting of protoplasm. Their diameter is 1.5 to 3.5 micromillimeters. The number compared to the red cells is 1 to 18 or 20. They are concerned mostly with the coagulation of the blood, by their adhering and forming irregular masses (Schultze), acting as a nucleus for the fibrin filaments to spread from during coagulation of the blood. They can only be seen microscopically after subjecting the blood to treat- ment with osmic acid. Coagulation of Blood. — Blood when freshly drawn from a living body into a vessel is fluid. In a short time it becomes thickened or viscid, this increase in con- sistency becomes more marked until the vessel con- tains a dark reddish mass, resembling gelatin. Shortly a few drops of fluid appear on the surface of the mass, which gradually increases in amount, the vessel is seen to contain a deposit of a firm, organized mass — the clot — floating in a reddish-yellow fluid — the blood-serum. On examining a portion of the clot microscopically, it will show threads of fibrin with red and white corpuscles clinging to them. The Clotting of Blood. — This is supposed to be a chemic phenomenon due to the action of a ferment, derived from calcium chloride, and some authors suggest leukocytes acting on the fibrinogen of the blood plasma, and converting it into fibrin and thus forming the nucleus of the clot. If blood is freshly drawn into a vessel, then whipped with a bundle of fine twigs for a few moments, the fibrin will be deposited on these twigs as whitish threads. Blood treated in this manner will not clot when left in the vessel; the serum will be the only residue present. This blood, treated as above, is called defibrinated.
Key Takeaways
- The veins carry deoxygenated blood back to the heart and lungs for oxygenation.
- Understanding vein anatomy helps in assessing injuries and managing trauma.
- Blood consists of plasma, red cells (erythrocytes), white cells (leukocytes), and blood plaques.
Practical Tips
- Recognize that veins are crucial for fluid resuscitation during emergencies; knowing their locations can aid in administering IV fluids more effectively.
- Be aware of the differences between superficial and deep veins, as superficial veins are often used for medical procedures like IVs or blood draws.
- Understand that venous return is essential for maintaining cardiac output and overall circulation.
Warnings & Risks
- Improper handling of veins can lead to complications such as infection or thrombosis.
- Incorrect identification of veins during emergency procedures can result in serious medical errors.
- Overuse of peripheral IVs without proper care can cause phlebitis, a painful and potentially dangerous condition.
Modern Application
While the anatomical descriptions in this chapter are still relevant for understanding the circulatory system, modern techniques such as ultrasound have improved the accuracy of vein visualization. Additionally, advancements in IV therapy and blood transfusion protocols have made emergency care more effective. However, the foundational knowledge of veins remains crucial for any survival situation where basic medical procedures might be necessary.
Frequently Asked Questions
Q: What are the main functions of veins?
Veins primarily carry deoxygenated blood back to the heart and lungs for oxygenation. They also play a critical role in maintaining fluid balance and returning blood from various parts of the body.
Q: How can one identify superficial veins during an emergency?
Superficial veins are located closer to the skin's surface, making them easier to see and palpate. They often appear as blue or greenish-blue lines under the skin. Identifying these veins is crucial for administering IV fluids or drawing blood.
Q: What is the difference between superficial and deep veins?
Superficial veins are located near the surface of the skin, while deep veins are found deeper in the body, often alongside arteries. Superficial veins can be seen on the skin's surface, whereas deep veins cannot.
Q: How does blood clotting occur?
Blood clotting is a complex process involving various components such as fibrinogen and platelets. When an injury occurs, these components activate to form a clot that helps prevent excessive bleeding. Understanding this process can aid in managing injuries during emergencies.
Q: What are the key components of blood?
Blood consists of plasma (a liquid component), red cells (erythrocytes) which carry oxygen, white cells (leukocytes) that fight infections, and blood plaques. Each component plays a vital role in maintaining overall health and function.