introduction to biomechanics for engineering students -...

Introduction to Biomechanics for engineering students

by

Ingrid Svensson

2016

Biomechanics, LTH, 2016

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Hello and welcome to the course in Biomechanics! During the next eight weeks you are going to increase your knowledge in the function of the human body and get an understanding and training in how this can be expressed in mechanical terms. You might have come in touch with anatomy and physiology earlier in your studies at the university but, for some of you, it might be quite new. To handle this difference in pre-knowledge, I have put together some pages with “An Intense Course in Anatomy and Physiology” to get you faster into the medical sphere of concepts if you consider your self as new in this area. You can also read the text as a fresh-up of earlier knowledge. These pages will also be used as a frame for the course in terms of anatomy and physiology. The text is aimed to suit students with different native languages so some key expressions are given both in English, Latin and Swedish. I hope that you will find the pages interesting and that you will enjoy the course! Sources: Människans anatomi och fysiologi, Bertil Sonesson och Gun Sonesson, Liber 1993. Människans fysiologi, Olav Sand, Øystein V. Sjaastad, Egil Haug, 2002. MEDICINE Engelsk-Svensk-Engelsk Fackordbok, P. H. Collin,Norstedts, 2002. Human Anatomy & Physiology, Elaine N. Marieb, Katja Hoehn, Pearson, 2010. Lund in July 2016 Ingrid


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An Intense Course in Anatomy and Physiology

Physiology is in general the science of the normal function of living creatures. In this course we will limit our self’s and concentrate on the human body. In order to try to get an overview of how all the complicated processes interact in the human body it is very useful to divide the processes into some main groups. The groups often used are the digestion, the respiration, the circulation, the locomotion, the neural system, the endocrine system, the lymphatic system, the excretion system and the sexual organs. A principal engineering sketch of how all these groups work together is presented in figure 1.

Fig. 1. Principal sketch of the functional structure of the human body The cell is the smallest functional unit in living structures. A human being starts his life as a unicellular organism in the moment of fertilization when the egg and the sperm melt together. The fertilized egg carries predisposition to all organ systems that are going to be developed in the becoming individual in the embryonic stem cells. In the small scale, the life functions of the cell go on in the cell organs and, in a bigger perspective the different organ systems take care of this. So, both the single cell as well as the multi-cellular organism, the human being, represents life on earth. The benefit in nature in creating multi-cellular organisms of high complexity is the possibility to get stable environments for individual cells, homeostasis. A human being is more capable of adaptation to changes in the environment than the individual cells are.

matspjälkningsapparaten – apparatus of digestive

andningsapparaten – apparatus of respiration

kroppscell – body cell

urinvägar – paths for urine

intercellulärt vätskerum – intercellular room for fluid blod plasma – blood plasma intracellulärt vätskerum – intracellular room for fluid

cirkulationsapparaten – apparatus of circulation

air

food


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As 65% of the human body consist of water a lot of the cells in the body is surrounded by water. But, the water appears both within the cells, intracellular, and outside the cells, extracellular, see figure 1. The extracellular fluid is found in the intercellular room and in the blood. The composition of this fluid (e.g. its salt content, pH-factor, etc.) and its temperature constitute the inner environment of the body and has a great importance for the possibilities of surviving for the cell. Some of the main organ groups will briefly be described here and the intention is to give an overview of the subject in order to make the mechanical modelling of the biological tissues easier further on.

The circulatory system

Fig. 2. The circulatory system

The circulatory system is built up by the heart (cor) and a system of arteries and veins and makes the blood circulate in the body, see figure 2. The blood vessels that carry blood from the heart are called arteries and the ones carry blood back to the heart are called veins. The heart works as the pump in the system and makes the blood flow through contractions that give pressure differences. The primary issue of the circulatory system is to distribute oxygen,

vener – veins artärer – arteries kapillärer – capillaries hjärta - heart


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nutritive substances and construction elements to the cells in the body and to carry away carbon dioxide and waste products. But the circulatory system is also responsible for heat control, it transfers pressure changes and it distributes different signal substances that control and coordinates the function of the different organ systems in the body. The blood flow transports oxygen from the lungs and nutrients from the liver through the elastic parallel-connected arteries and capillaries to the tissues. The exchange between oxygen and waste products, such as carbon dioxide, takes place in the capillaries. The waste is taken back to the lungs to be expelled (the big circulation). At the same time the blood obtains more oxygen in the lungs to be taken out to the tissues (the small circulation, pulmonary circulation). So, actually, the heart can be considered as working as two separate pumps and the circulation pattern is as follows: blood returns through the veins to the right atrium of the heart; from there it is pumped by one of the pumping functions trough the right ventricle into the pulmonary artery, and then into the lungs. From the lungs it returns through the pulmonary veins to the left atrium of the heart and it is pumped, by the other pump mechanism, from here through the left ventricle into the aorta and from the aorta further out into the smaller arteries. In rest, each half of the heart pumps about 5 litres of blood per minute. This corresponds approximately to the total blood volume in the system. The importance of the circulatory system as a transport system can be illustrated by the fact that unconsciousness will set in already 30-40 seconds after the heart stops to beat and there is a risk of permanent damage in the brain tissues if the heart beat is stopped for more than about 3-4 minutes. But, the circulation of blood to the brain has the highest priority and in a crisis, the blood flow is redirected through changed flow resistance in other organs. In the blood there are white corpuscles (leucocytes, leuko-white) that take part in the immunodeficiency. Leucocytes are also present in the bone marrow, i.e. the marrow acts as a storage space for them. The leucocytes defend the body against microorganisms through antibodies. When the body is threatened by serious infections, a big number of leucocytes are released from the bone marrow and they invade the infected area. The red corpuscles (erythrocytes) contain haemoglobin that carries oxygen to the tissues in one way and carbon dioxide on the return. The transport capacity will of course decrease if the number of red corpuscles is reduced from the normal value but if there are too many of them, the viscosity of the blood increase and the heart has to work harder. Another type of blood cell is the platelet (thrombocyte). The thrombocytes are involved in the haemostasis, i.e. the mechanisms stopping the bleeding when blood vessels are ruptured. The thrombocytes form plugs that mechanically stop the bleeding. But this process can also be destructive. A heart attack or a stroke might occur if a vein or an artery is blocked by a blood clot (thrombosis). Fibrinogen is a substance in blood plasma that produces fibrin, a protein, which helps the blood coagulate.


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The respiratory system

Fig. 3. The respiratory system There has to be a constant flow of oxygen into the body to supply the process of oxidation of nutrition so energy could be released. In humans, the exchange between oxygen and carbon dioxide takes place in thin tissues in the lungs. The total area of these tissues is very big, about 75-80 m2 for a grown up. The tissues are well protected in the moist environment. It has to be moist because the gases must be resolved in liquid if they should be able to diffuse from blood to air in the lungs. The respiration process takes place in the organs of respiration: the nasal cavity, the throat (pharynx), the voice box (larynx - struphuvud), the wind pipe (trachea – luftstrupe), the bronchi (luftrör) and the lungs (pulmo - lunga). The two lungs are situated in the chest cavity, protected by the rib cage and supported by the diaphragm. The heart is situated between the lungs. The right lung has three lobes, the left only two. Air goes down into the lungs through the trachea and bronchi. The cilia (flimmerhår), situated at the inner surfaces of the trachea, filtrate and moisture the air in order to protect the easily damaged mucous membranes (slemhinnor) of the alveoli. The air passes to the alveolar sacs. The alveolar sacs are made up of clusters of alveoli like grapes in a bunch. The gas exchange, oxygen-carbon dioxide, occurs

näshålan - the nasal cavity struphuvudet - the voice box (larynx) luftstrupe - the wind pipe (trachea) lungorna - the lungs (pulmo)


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in the blood vessels that are wrapped around each individual alveolus. The oxygen is needed for the metabolism of the cells and through the respiration carbon dioxide is ventilated and balance of the pH factor is obtained in the blood and other body fluids. The respiratory system is also the foundation of the speech. Air is pressed from below through the narrow slit (rima glottides) between the cords (plica vocalis - stämband) in the voice box. The rima glottides together with the plica vocalis is often called glottis. A pulsating air stream builds up in the glottis and propagates through longitudinal oscillations into the resonance areas, i.e. the throat, the oral cavity, the nasal cavity, the sinus and the chest, where the oscillations are filtered and amplified and the result is speech or song. The difference in the voice of different people is controlled by the activity of several muscle groups while speaking. Varying the activity in the respiratory muscles will influence the volume of the sound. The frequency of the longitudinal oscillations is given by the stresses in the cords that come from contractions of the muscles in the voice box. The airflow through glottis makes the cords vibrate almost perpendicular to the airflow and thus the cords open and close the slit. The slit is closed for a longer period than it is open when sound of low frequency is created and the opposite goes for high frequencies. On top of that, the cords become thinner for high frequencies than for low. The spectrum for the human voice goes from about 40 to 2000 Hz.

The digestive system

The food is processed mechanically and chemically in digestive system in order to split the food so the nutrients, salts and water can be assimilated. The process starts with chewing in the oral cavity where the food is divided into smaller pieces and mixed with saliva. The salvia consists of more than 99% water but also mucin, a compound of sugars and protein facilitating the chewing. Enzymes, like amylase that converts starch into maltose and lysozyme that in combination with antibodies reduces the amount of bacteria in the oral cavity.

The process continues in the throat, in the gullet (oesophagus-matstrupe), in the stomach and in the guts (intestine – tarmar). The partly digested food comes first to the small intestine


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where nutrients are absorbed and continues then to the large intestine where most of the water is absorbed, (9.9 litres of 10). The digestive tube (from mouth to anus) is about 7 m long. In addition there are glands (körtlar) as the liver and the pancreas (bukspottskörtel) involved in the chemical part of the digestion. Secretion containing different types of enzymes necessary for the process is produced in the glands. The gall, secreted by the liver, is used to digest fatty substances and to naturalize acids. The pancreas produces enzymes that convert fat, carbohydrate and proteins into components that can be absorbed in the guts. The result is energy released to the body and also distribution of components for heating, growing and reconstruction. Leftover leaves the body as excrement and urine.

The locomotion system The organ system in focus in this course is the locomotion system and we will go into detail with the different parts further on in the course. However, in order to give a short overview, some facts in general of the locomotion system are given here. The organs for motions, i.e. the skeleton, joints and muscles, are responsible for more than half of the body mass, i.e. the skeleton makes about 15 % and the muscles 45 % of the body mass of an adult human. The skeleton gives stability for the construction of an upright position and it also provides anchorages for soft tissues. The skeleton bones function as shelter for inner organs, e.g. the brain and the heart, as well as a prerequisite of locomotion, speech and the performance of outer work. More than 200 individual bones interconnected by joints build up the skeleton. The bones also serve as depots of minerals (e.g. calcium and phosphor) and further, the red blood cells are produced and stored in the red bone marrow within the long skeletal bones. To provide locomotion the skeletal bones are joined together through the joints that have a very low friction due to the lubricated contact layer covered with cartilage. The joints are stabilized through systems of supporting ligaments and tendons and different joints have different amount of freedom for motion. In mechanical terms we can consider them as friction free joints with a different number of degrees of freedom (i.e. axis of rotation). The muscles are responsible for posture, balance and the motion of the body. They also contribute to keeping the body warm through generating heat when contracting. The skeletal system and the muscle system are strongly coupled both structurally and functionally. The muscle tissue continues through the tendons into the bone tissue and ensures secure fixations. Physiologically, the muscles and the bones are also coupled through the content of calcium. The contractions in a muscle can only take place if the concentration of calcium is within quite narrow limitations. Since the most of the calcium depot is in the skeleton, diseases in the skeleton may also influence the muscle function. On the other hand, the muscles also influence the skeleton. During hard muscle work, like intensive sport practicing, the muscles are growing and the skeleton becomes denser, it gets stronger. On the contrary, if you stay in bed, you will soon notice both smaller muscles and a weaker skeleton. Some skeletal bones and muscles that we are going to mention often during the course are given in the next pictures and the related table.


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Fig. 4 Skeletal bones in Swedish, English and “Latin”

1. kranium, skalle skull cranium 2. ansiktsskelett face skeleton viscerocranium 3. nyckelben collarbone Clavicula 4. skulderblad shoulder blade Scapula 5. överarmsben Humerus 6. bröstkorg chest Thorax 7. kotpelare column columna vertebralis 8. strålben Radius 9. armbågsben Ulna 10. bäcken Pelvis 11. handrotsben carpal bones Carpus 12. mellanhandsben Metacarpus 13. fingerben finger bones phalanges 14. lårben femur 15. knäskål kneecap Patella 16. vadben Fibula 17. skenben Tibia 18. fotrotsben Tarsal 19. tåben toe bones phalanges 20. manubrium (sterni) 21. bröstben breastbone Sternum

1. 2.

3. 4. 5. 6. 7. 8. 9.

10. 11.

12. 13.

14. 15.

16. 17.

18. 19.

20. 21.


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Anterior view Posterior view


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Useful expressions in Latin Bumps in the skeleton: Capitulum, litet huvud, small round end of a bone Caput, huvud, the head (in plural: capita) Facies, yta, surface Condylus, ledhuvud, rounded end of a bone that articulates with another Spina, bentagg, bone prickle (spine) Trochanter, benknöl, bony lumps (e.g. the two lumps on either side of the top end of the femur where muscles are attached) “Inverted bumps” in the skeleton: Alveol, urholkning, hålighet, hollow Cavum, håla, cavity Fossa, grop, pit Sinus, hålighet, hollow Openings in the skeleton Apertura, öppning, opening Fissura, springa, spricka, crack Porus, öppning, opening In vivo, levande, alive, an experiment that takes place in the living body In vitro, död, dead, an experiment that takes place in the lab on isolated tissue


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Planes of reference, motions, and directions

Sagittal plane – Divides body into right and left parts Frontal plane – Divides body into front and back parts Transverse plane – Divides body into upper and lower parts Terms Posterior (Dorsal) – in frontal plane, towards the backside Anterior (Ventral) – in frontal plane, towards the front Superior (Cranial) – in transverse plane, above Inferior (Caudal) – in transverse plane, below Medial – in sagittal plane, towards the midline Lateral – in sagittal plane, away from the midline Superficial – towards the surface Deep – away from the surface Proximal – towards the trunk Distal – away from the trunk Palmar – palm of hand Plantar – bottom of foot **Supine (Anatomical) Position – standing erect, facing for-

forward, hands by side, palms facing forward


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Directions

• If a motion takes place in the transversal plane along the transversal axis and in directed inwards the centre of the body it is called medial. If it has the opposite direction, it is called lateral.

• A motion in the frontal plane, along the vertical axis, directed upwards is called

superiort and if it is directed downwards inferiort

• It is possible to move in the sagittal plane, along the sagittal axis, forwards is the motion called anteriort and backwards it is called posteriort.

• The part of a skeletal bone that is closest to the heart is called the proximal part while

the part that is most far from the hart is called the distal part.


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Test your skills Fill in the blank or provide a short answer

1. Groups of cells that have a common function are termed ______________.

2. The larynx is an organ of the _________________ system.

3. The system that has the ability to store minerals, such as calcium, is called the ________________ system.

4. The breakdown of ingested foods into simple molecules that can then be absorbed into the bloodstream is called _______________.

5. The ____________________ refers to all the chemical reactions in the body.

6. The body’s ability to maintain stable internal conditions is referred to as ____________.

7. The navel is ____________ to the spine.

8. A cut that is made along the midline is called a ______________ section.

9. The function of the ____________system is to control the body functions via hormones.

Answers: 1. Tissues 2. Respiratory 3. Skeletal 4.Digestion 5. Metabolism 6. Homeostasis 7. Ventral or anterior 8. Mid sagittal or median 9. Endocrine

introduction to biomechanics for engineering students -...

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