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First discount alendronate 35 mg mastercard, the type of muscle contraction (isometric order alendronate 70mg without a prescription, rhythmic) all influ- centrality of oxygen usage to work output gave rise to the ence the body’s responses and adaptations. Second, the apparent These many aspects of exercise imply that its interaction excess in oxygen consumption during the first minutes of with disease is multifaceted. There is no simple answer as to recovery has been termed the oxygen debt (Fig. In fact, physical activity “excess” oxygen consumption of recovery results from a can be healthful, harmful, or irrelevant, depending on the multitude of physiological processes and little usable infor- patient, the disease, and the specific exercise in question. Third, and more 551 552 PART VIII TEMPERATURE REGULATION AND EXERCISE PHYSIOLOGY O2 deficit Steady state chondrion reaches its capacity at about the same time. Iso- Resting level metric work intensity is usually described as a percentage of 0. Analogous to work levels relative to maximal oxy- Time (min) gen uptake, the ability to endure isometric effort, and many Oxygen uptake before, during, and after physiological responses to that effort, are predictable when FIGURE 30. For prolonged work, this energy is sup- although it can be increased by appropriate training. This maximal oxygen uptake is a useful but imperfect predictor plied by the oxidation of foodstuff, with the oxygen carried of the ability to perform prolonged dynamic external work to working muscles by the cardiovascular system. Maximal oxygen uptake is decreased, all else being equal, Blood Flow Is Preferentially Directed to by age, bed rest, or increased body fat. Working Skeletal Muscle During Exercise Maximal oxygen uptake is also used to express relative work capacity. A world champion cross-country skier obvi- Local control of blood flow ensures that only working mus- ously has a greater capacity to consume oxygen than a cles with increased metabolic demands receive increased novice. However, when both are exercising at intensities blood and oxygen delivery. If the legs alone are active, leg requiring two thirds of their respective maximal oxygen up- muscle blood flow should increase while arm muscle blood takes (the world champion is moving much faster in doing flow remains unchanged or is reduced. At rest, skeletal mus- this, as a result of higher capacity), both become exhausted cle receives only a small fraction of the cardiac output. In at roughly the same time and for the same physiological dynamic exercise, both total cardiac output and relative reasons (Fig. In the discussion that follows, relative as and absolute output directed to working skeletal muscle in- well as absolute (expressed as L/min of oxygen uptake) crease dramatically (Table 30. Cardiovascular control during exercise involves sys- The energy costs and relative demands of some familiar ac- temic regulation (cardiovascular centers in the brain, with tivities are listed in Table 30. For millen- cally, many arguments claim primacy for either cardiac out- nia our ancestors successfully used exercise both to escape put (oxygen delivery) or muscle metabolic capacity (oxy- being eaten and to catch food; therefore, it is no surprise gen use) limitations. However, it may be that every link in that cardiovascular control in exercise is complex and the chain taking oxygen from the atmosphere to the mito- unique. During strenuous exercise, sympathetic drive can begin to limit vasodilation in active muscle. When exer- Area mL/min % mL/min % cise is prolonged in the heat, increased skin blood flow and Splanchnic 1,400 24 300 1 sweating-induced reduction in plasma volume both con- Renal 1,100 19 900 4 tribute to the risk of hyperthermia and hypotension (heat ex- Brain 750 13 750 3 haustion). Although chronic exercise provides some heat ac- Coronary 250 4 1,000 4 climatization, even highly trained people are at risk for Skeletal muscle 1,200 21 22,000 86 hyperthermia and hypotension if work is prolonged and wa- Skin 500 9 600 2 ter is withheld in demanding environmental conditions. Muscle blood flow increases relative to the resting condition, as does cardiac output, but the higher mean intramuscular pressure limits these flow increases much more than when exercise is rhythmic. Initially, the blood flow increase is blunted inside a statically contract- motor cortex is activated: The total neural activity is ing muscle, the fruits of hard work with too little oxygen roughly proportional to the muscle mass and its work in- appear quickly: a shift to anaerobic metabolism, the pro- tensity. This neural activity communicates with the cardio- duction of lactic acid, a rise in the ADP/ATP ratio, and fa- vascular control centers, reducing vagal tone on the heart tigue. Maintaining just 50% of the MVC is agonizing after (which raises heart rate) and resetting the arterial barore- about 1 minute and usually cannot be continued after 2 ceptors to a higher level. A long-term sustainable level is only about 20% of lactic acid is formed in actively contracting muscles, which maximum.

Motor neurons possess a large peri- and one main process discount alendronate 35mg line, the axon or neurite karyon with coarse Nissl bodies buy 70 mg alendronate otc, while (A–D3). The perikaryon is the trophic center of the cell, and processes that become separated Impregnation with silver (Golgi’s from it degenerate. It contains the cell nu- method) stains the entire cell including all cleus (A4) with a large, chromatin-rich neuronal processes; the cell appears as a nucleolus (A5) to which the Barr body (sex brown-black silhouette (B–D). The processes of other neurons often end at small dendritic appendices, spines (thorns), which give the dendrites a rough appearance (D). The axon conducts the nerve impulse and begins with the axon hillock (AD7), the site wherenerveimpulsesaregenerated. Atacer- tain distance from the perikaryon (initial segment) it becomes covered by the myelin sheath (A8), which consists of a lipid-con- taining substance (myelin). The axon gives off branches (axon collaterals) (A9) and fi- nally ramifies in the terminal area (A10) to end with small end-feet (axon terminals, or boutons) on nerve cells or muscle cells. The bouton forms a synapse with the surface membrane of the next cell in line; it is here that impulse transmission to the other cell takes place. Depending on the number of processes, we distinguish between unipolar, bipolar, or multipolar neurons. The Nerve Cell: Structure and Staining Patterns 19 2 6 1 5 4 E Impregnation of F Impregnation of 2 boutons (synapses) neurofibrils 7 3 3 8 B Nerve cell in the 3 brain stem 9 3 3 C Nerve cell in the anterior horn of the spinal cord 9 A Neuron, diagram D Pyramidal cell in the cerebral cortex 11 7 3 10 B–D Equivalent images of nerve cells: cellular stain (Nissl) and silver impregnation (Golgi) Kahle, Color Atlas of Human Anatomy, Vol. The availability of methods for studying the structure and function of cells, tissues, and The longest processes of nerve cells, the organs is often the limiting factor in ex- axons (which can be up to 1m long in panding our knowledge. Certain terms and humans), cannot be traced to their target interpretations can only be understood if area in histological sections. In order to the background of the method used is demonstrate the axonal projections of neu- known. Therefore, the methods commonly rons to different brain regions, axonal trans- used in neuroanatomy are presented here port (p. The Nissl Very long fiber connections can be visual- method has proven helpful because of excel- ized (C–E) by means of tracers (e. However, the different types of taining the cell bodies of the corresponding nerve cells are essentially characterized by population of neurons; the tracers are then their long processes, the dendrites and the taken up by the axon terminals or by the cell axon, which are not stained by the Nissl bodies of the projection neurons, respec- method. When using retrograde transport (C), these processes as possible, thick sections the tracer is injected into the assumed tar- (200µm) are required. By means of retrograde transport can be demonstrated in such thick sections. When it is now possible to stain individual nerve using anterograde transport (E), the tracer is cells by filling them with a dye using rec- injected into the region of the cell bodies of ordingelectrodes(A). Labeled axon terminals technique is that electrical signals can be will be visible in the assumed target zone if recorded from the neuron in question at the the labeled neurons indeed project to this same time. An important characteristic of nerve cells is their specific neurotransmitter or messenger substance by which communication with other nerve cells is achieved. By means of immunocytochemistry and the use of anti- bodies against the messenger substances themselves, or against neurotransmitter- synthesizing enzymes, it is possible to visual- ize nerve cells that produce a specific trans- mitter (B). Again, these immunocytochemi- cally stained nerve cells and their processes Kahle, Color Atlas of Human Anatomy, Vol. Methods in Neuroanatomy 21 C–E Visualization of projections by means of retrograde and an- terograde axonal transport of tracers C Retrograde transport A Visualization of a neuron by means of an intracellularly in- jected marker D Retrograde transport from differ- ent projection zones of a neuron E Anterograde transport to different projection zones of a neuron B Immunocytochemical visualization of a cholinergic neuron using an antibody against choline acetyltransferase Kahle, Color Atlas of Human Anatomy, Vol. The mitochondria are the site (A–C) of cellular respiration and, hence, of energy generation. Numerous enzymes are local- Electron micrographs show the cell nucleus ized in the inner membrane and in the (A–C1) to be enclosed by a double-layered matrix, among others the enzymes of the membrane(A2). Itcontainsthenuclearpores citric acid cycle and respiratory-chain (oxida- (BC3) that probably open only temporarily. The karyoplasm of the nucleus contains finely dispersed chromatin granules, which The Golgi complex consists of a number of consist of DNA and proteins.

A number of anatomical structures throughout the body are named in honor of the early anatomists order alendronate 35 mg online. Thus we have graafian follicles buy alendronate 70 mg with amex, Stensen’s and Wharton’s ducts, fallopian tubes, Bartholin’s glands, the circle of Willis, and many others. Because these terms have no descriptive basis, they are not particularly useful to a student of anatomy. Nineteenth Century The major scientific contribution of the nineteenth century was the formulation of the cell theory. It could be argued that this theory was the most important breakthrough in the history of bi- ology and medicine because all of the body’s functions were eventually interpreted as the effects of cellular function. The term cell was coined in 1665 by an English physician, Robert Hooke, as he examined the structure of cork under his mi- croscope in an attempt to explain its buoyancy. What Hooke actu- ally observed were the rigid walls that surrounded the empty cavities of the dead cells. The significance of cellular structure did not be- come apparent until approximately 150 years after Hooke’s work. Rather, he thought that a spermatozoan contained a teen years later, René H. Dutrochet described the differences be- miniature human being called a homunculus. The development of the microscope added an entirely new Two German scientists, Matthias Schleiden and Theodor dimension to anatomy and eventually led to explanations of Schwann, are credited with the biological principle referred to as basic body functions. Schleiden, a botanist, suggested in 1838 that each invaluable for understanding the etiologies of many diseases, and plant cell leads a double life—that is, in some respects it behaves thus for discovering cures for many of them. Although Leeuwen- as an independent organism, but at the same time it cooperates hoek improved the microscope, credit for its invention is usually with the other cells that form the whole plant. The first Schwann, a zoologist, concluded that all organisms are composed scientific investigation using a microscope was performed by of cells that are essentially alike. Nineteen years later, the addi- Francisco Stelluti in 1625 on the structure of a bee. In 1858, the German pathologist Rudolf Malpighi and Others Virchow wrote a book entitled Cell Pathology in which he pro- Marcello Malpighi (mal-pe′ge) (1628–94), an Italian anatomist, posed that cells can arise only from preexisting cells. He discovered nism of cellular replication, however, was not understood for the capillary blood vessels that Harvey had postulated and de- several more decades. In 1672, the Dutch teaching career, science was sufficiently undeveloped to allow anatomist Regnier de Graaf described the ovaries of the female him to handle numerous disciplines at once. By the time of his reproductive system, and in 1775 Lazzaro Spallanzani showed death, however, knowledge had grown so dramatically that sev- that both ovum and sperm cell were necessary for conception. Francis Glisson (1597–1677) described the liver, stomach, and intestines, and suggested that nerve impulses cause the emptying of the gallbladder. Thomas Wharton (1614–73) and Niels Twentieth Century Stensen (1638–86) separately contributed to knowledge of the Contributions to the science of anatomy during the twentieth century have not been as astounding as they were when little was homunculus: L. History of Anatomy © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 1 History of Anatomy 17 (a) (b) (c) FIGURE 1. Because of the proliferation of scientific literature niques of such cognate disciplines as chemistry, physics, electron- toward the end of the nineteenth century, over 30,000 terms for ics, mathematics, and computer science have been incorporated structures in the human body were on record, many of which into research efforts. In 1895, in an attempt to reduce the confusion, There are several well-established divisions of human the German Anatomical Society compiled a list of approxi- anatomy. The oldest, of course, is gross anatomy, which is the mately 500 terms called the Basle Nomina Anatomica (BNA). Stringent courses in gross anatomy in professional classroom and in publications. Gross anatomy also forms the basis throughout the century, under the banner of the International for the other specialties within anatomy. At the Seventh International Congress (see chapter 10) deals with surface features of the body that held in New YorkCity in 1960, a resolution was passed to elimi- can be observed beneath the skin or palpated (examined by nate all eponyms (“tombstone names”) from anatomical terminol- touch). Structures like Stensen’s duct and Wharton’s duct, for example, are now properly referred to as the parotid duct and submandibular duct, respectively. Be- Microscopic Anatomy cause eponyms are so entrenched, however, it will be extremely Structures smaller than 0.