Physical Aspects of the Human Body
Description
The updated edition of the first of three volumes on Medical Physics focuses even more on body systems related to physical principles such as body mechanics, energy balance, and action potentials. Thanks to numerous newly incorporated didactic features, the introductory text into the broad fi eld of medical physics is easy to understand and supports self-study. New: highlighted boxes emphasize special topics; math boxes explain more advanced mathematical issues; each chapter concludes with a summary of the key concepts, questions, a self-assessment of the acquired competence, and exercises. The appendix contains answers to questions and solutions to exercises.
Reviews / Votes
Review of the 1rst edition:
"I used both volumes for my Medical Physics class and what I can say is that the students and myself loved it! The first volume discusses very well the physics of the human body while the second one discusses more the instrumentation. Overall, a very complete set of books for either a one-semester or a two-semester class."
Dr. Gregory Guisbiers, University of Arkansas at Little Rock
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Hartmut Zabel received his doctorate in 1978 from the LM University of Munich in the field of physics on a topic in condensed matter physics. He then spent a year as a postdoctoral fellow at the University of Houston, Texas, and joined the faculty of the University of Illinois at Urbana-Champaign in 1979 as Assistant Professor, where he was promoted to Associate Professor in 1983 and Full Professor of Physics in 1986. In 1989 he received a call to the Ruhr University Bochum and held the chair for experimental physics/condensed matter physics from 1989 to 2012. He maintained his connection to the University of Illinois as Adjunct Professor of Physics. After his retirement in 2012, he was first a Senior Professor at the Ruhr University and from 2014 to 2018 Distinguished Guest Professor at the Johann Gutenberg University in Mainz.
In addition, he was a guest researcher at various universities and institutions, i.a. at Brookhaven National Laboratory (USA), Risø National Laboratory (Denmark), University of Kyoto, National Institute of Science and Technology, Gaithersburg-Washington, KTH Stockholm, and Uppsala University (Sweden). He was also member and chairperson of various scientific committees and advisory bodies, including those at the Paul Scherrer Institute in Switzerland, the Institut Laue-Langevin (Grenoble, France), Argonne National Laboratory, and the Helmholtz Center Berlin. In 1996 he was elected a Fellow of the American Physical Society, in 2001 he received an honorary doctorate from the KTH in Stockholm,
In addition to his scientific work at the University of Illinois and the Ruhr University Bochum with over 500 publications in peer-reviewed scientific journals on the structure, dynamics, magnetism and superconductivity of solids, he was supervisor and co-supervisor of more than 50 doctoral students in Urbana, Bochum and Mainz, organizer and co -organizer of numerous international workshops and conferences, editor and co-editor of five books, and guest lecturer at many summer schools in Europe. i.a. he was a guest lecturer in the European Graduate School "HERCULES" in Grenoble for the last 30 years, lecturing on the topic of scattering experiments with synchrotron radiation and neutrons.
At the beginning of 2000, the medical department at the Ruhr University Bochum developed a new study concept based on the model of the University Hospital Charité in Berlin: problem-oriented learning (POL). As a representative of the physics department, Hartmut Zabel was involved in the curriculum development. In addition to the standard physics course for medical students, he also supervised the physics-related seminars in the POL teaching format. Finally, he developed a new lecture series on "Medical Physics" for physics students and initiated a master course "Medical Physics" at the Ruhr University Bochum, which was later established and certified.
Content
1 Brief overview of body parts and functions
Table of important physical properties of the human body Distinctive systems in the body 11 Average cell size 20 µm Range of cell sizes 4 µm to 1 mm Total number of cells (rough estimate) 3?×1013 Number of genes (estimate) 25 000 Number of proteins (estimate) 2?×?104 Cell types 210 Outer skin area ~2 m2 Senses of the body More than 8
1.1 Introduction
It is well known that body parts and functions are controlled by chemical and biochemical processes. What is perhaps less obvious is that our bodies also follow strict physical principles. However, this becomes clear when we examine different parts of our body. Every movement requires forces, moments, and mechanical stability. The body's energy balance follows the principles of thermodynamics. The sensory system, including hearing and vision, is based on acoustic and optical principles. The respiratory system, circulatory system, and kidneys all obey the laws of diffusion, hydrostatics, and hydrodynamics. The propagation of signals along nerve fibers can be described by electrical circuits. Chapters 2-12 are devoted to the description of some organs, sensors, and systems and emphasize their connection to fundamental physical principles. Attempting such a description inevitably leads to simplification. However, the aim of this textbook is not to underpin the complexity of biological systems but rather to draw attention to the connections with physical principles. Therefore, the chapters in this volume are not a substitute for textbooks on physiology.
In this first chapter we give a very brief overview of the main organs and systems of the human body, which will be deepened in later chapters. Most of these organs are not specific to humans but can be found in all mammals and even in most vertebrates.
1.2 Overview
1.2.1 Cell
Cells with an average size of 20 µm are the fundamental building blocks of living matter [1, 2, 3]. The human body consists of about 3?×?1013 eukaryotic cells [2], i.e., cells that contain a nucleus. They are stacked together like bricks of a house. The cross section of a typical cell is schematically shown in Fig. 1.1. All cells have a wall to distinguish between inside and outside. The chemical and electrical gradients across the wall are essential for cell functioning and intercell communication. Inside the cells, there is another smaller nucleus that holds the genetic material in the form of a double-stranded helical chain, known as deoxyribonucleic acid (DNA). Each DNA molecule contains a sequence of paired nucleobases, which read like letters of a book that constitutes the genetic code. Genes are like chapters in this book. About 1000 pairs constitute one chapter. Estimates are that 80% of about 25 000 genes in the DNA encode about 2?×?104 different functional proteins in the human body that do their daily job [4]. Proteins are made up of 21 different amino acids arranged in chains and folded up to complex three-dimensional structures. They build ion channels and molecular motors; form receptors, enzymes, and hormones; take care of oxygen transport; strengthen tissues and bones in the body; regulate water and ion concentrations; and are responsible for many more tasks. Proteins vary greatly in size; some hold more than 100 000 atoms [5]. Only about 5000 proteins have been described at an atomic resolution so far [6]. Although almost all cells contain complete and identical genetic information, they specialize in different tasks. Muscle cells develop a surprising tensile force, liver cells specialize in performing important tasks for food metabolism, and nerve cells transmit electrical signals as fast as 100 m/s. We can distinguish between about 210 different cell types with specific tasks [7]. Only stem cells are not specialized. The specialization of all other cells for particular tasks is only possible through a high degree of self-organization and communication between the cells.
Fig. 1.1: Schematics of a human cell. The cell membrane separates the cytoplasm from the extracellular space. The cytoplasm contains, among many other parts, the genetic information inside the nucleus and the mitochondria with its genetic information, acting as a powerhouse for the cell functions. The cell membrane is a double lipid layer perforated by many ion channels to maintain an electrical potential across the cell membrane or change it by depolarization upon a stimulus (adapted from OpenStax Anatomy and Physiology, 2016, © creative commons).
Comparing cells with bricks is, after all, a gross oversimplification. When engineers build a complex system, they start with simple building blocks that fit together to form something more complex. In contrast, in organisms, the complexity does not begin at the cell level but already at the molecular level of DNA, ribosomes, lysosomes, and many more. This incredible complexity organizes life. First, cells organize to form tissues: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. In turn, tissues assemble to form organs with characteristic and distinct shapes and functions like the liver and the kidneys. Several organs work together in a system, such as the digestive system that involves 10 different organs. The body contains 11 distinct systems: 1. cardiovascular/circulatory system; 2. respiratory system; 3. digestive system/excretory system; 4. endocrine system; 5. lymphatic system/immune system; 6. sensory system; 7. locomotor system; 8. nervous system; 9. renal system/urinary system; 10. integumentary system; and 11. reproductive system. All 11 systems interact and are responsible for the human body's life. These interactions take place under the promise of constancy in a variable environment. For instance, core body temperature, arterial blood pressure, and partial oxygen/carbon dioxide pressures of blood are kept constant by an active negative feedback system, like a thermostat. This control mechanism is known as homeostasis, according to Bernard,1 who first stated this principle [8, 9]. Body temperature homeostasis is one example that is further discussed in Chapter 4, and further homeostatic systems are described in the following chapters.
Finally, cells do not live forever. Cells have a life cycle, comprising phases of growth, rest, cell division, and cell death. Understanding the cell cycle's controlling mechanisms is essential for coping with cancer and treating tumors through radiation therapy. These topics are considered in Chapters 8-10 of Vol. 2.
1.2.2 Circulation
For maintaining all body functions, blood circulation is essential. As the name implies, blood circulation is a closed circuit, where the flow is mechanically powered by the heart acting as a pump. A dense mesh of blood vessels penetrates any body part. Blood circulation is a transport system for oxygen, nutrients, and heat to their destinations, including muscles, bones, and all other organs. Oxygen is taken up from the surrounding air during inhalation and binds to hemoglobin by diffusing through membranes in the lung. In return, during expiration, carbon dioxide, as a residue of combustion, is exhaled. Figure 1.2 shows a simplified schematic of blood circulation. It has an oxygen-rich and an oxygen-poor part, along with a high-pressure part and a low-pressure part. The color coding (red: oxygen-rich, blue: oxygen-poor) originates from our visual perception. Oxygen-rich blood has a much brighter red color than oxygen-poor blood. Circulation is discussed in more depth in Chapter 8.
Fig. 1.2: Schematic of the human circulatory system. The right ventricle of the heart (1) takes in oxygen-poor blood from the extremities (9, 10) and pumps it into the lungs (2, 3) for oxygen enrichment. After returning from the lung into the left atrium and ventricle of the heart (4, 5), the blood is ejected into the periphery (6-8) to supply all body tissues with oxygen. Blood pressures in the left circulation (red) are higher than in the right circulation (blue) at similar locations. The left ventricle muscle is also stronger than the right ventricle muscle (reproduced from http://www.online-sciences.com/, © creative commons).
1.2.3 Heart
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