30-Second Philosophies

The 50 most important structures and systems in the human body, each explained in half a minute

All rights reserved. No part of this publication may be reproduced or transmitted in any form by any means, electronic or mechanical, including photocopying, recording, or by any information storage-and-retrieval system, without written permission from the copyright holder.

Distributed worldwide (except North America) by Thames & Hudson Ltd., 181A High Holborn, London WC1V 7QX, United Kingdom

INTRODUCTION

Gabrielle M. Finn

Anatomy is both within and all around us. By learning a little anatomy, we come to understand how our bodies are built: An anatomical drawing that depicts the bones, muscles, ligaments, tendons and organs of the body is a map of the inner landscape we all share. Yet at the same time, our experience of the body, our knowledge of its skeleton and organs, informs the way we see the world. For this reason, human anatomy has a widespread symbolism in popular culture, from the hearts printed on Valentine’s Day cards to the skull as a symbol of danger.

Gruesome history

Traditionally, many people may have seen anatomy as an academic discipline, of interest to only medical students, but in recent years the subject has had a boom in popularity. This is due largely to its entry into the public arena through touring exhibitions of cadaveric specimens and televised human dissections by anatomists, such as Gunther von Hagens and Alice Roberts. Behind this new interest lies a long and gruesome history.

The origins of anatomical study were in animal vivisection and the dissection of human corpses. The ancient Greek physician Galen based his ideas of human anatomy on knowledge gained from dissections and vivisections of pigs and primates. The Renaissance artist Leonardo da Vinci, creator of The Last Supper and the Mona Lisa, was famed for his anatomical drawings and derived his knowledge of the inside of the human body from working with corpses supplied by doctors in hospitals in Milan and Florence. Anatomy has also been associated with crime, as in the case of the nineteenth-century murders perpetrated in Scotland by William Burke and William Hare. A pair of Irish immigrants, they robbed graves and embarked on a serial-killing spree in 1827–28 in order to sell corpses to Dr Robert Knox, an anatomy lecturer with students from Edinburgh University medical school. The pair were caught: Hare was granted immunity for testifying, and Burke was hanged on 28 January 1829; ironically, his remains ended up in the medical school’s anatomy museum.

Despite the fact that anatomy describes the blueprint for the living body, one of the subject’s most common associations is death – the bones that structure our living bodies are our final physical remains.

Evolution and variation

Anatomy is an ancient discipline, and you might think that there is nothing new to know in the field. Yet, remarkably, human anatomy continues to evolve. This evolution is very slow, but it exists and persists. Take, for example, the coccygeal bones at the base of the spine: These used to be the point at which the human tail started. Another example of continual evolution is the palmaris longus muscle in the forearm; due to its limited function, this muscle has become redundant, and evolution in some individuals has resulted in its absence in around 15 per cent of people.

One of the biggest challenges facing anyone who wants to study anatomy is anatomical variation. As we have seen, anatomy provides a blueprint for how all bodies are structured; however, in a world with a population heading for an estimated 7 billion people, variation will and does exist. A primary example is found in the arteries within the pelvis; there are fifty-four known variations of how these vessels distribute themselves. Moreover, variation exists not only from person to person, but also from side to side within an individual body. Some people have a larger ear on the right than on the left; or a person may have a single horseshoe-shaped kidney instead of the normal two kidneys; or the pathways followed by nerves may vary from the accepted convention. This book presents the most commonly encountered anatomy.

Anatomy – systems and functions

Anatomy has its own technical language, in which muscles and bones have lengthy Latin or Greek names. Simple physical actions, such as the movement of the lower limb (leg), have multiple anatomical descriptions depending on the direction of the movement. There are in excess of 200 bones, 600 muscles and numerous veins, arteries and nerves. Don’t let that put you off. This book does not attempt to explain the location and function of each individual structure; instead, it breaks the body down into functional systems and describes the fifty most relevant components, using illustrations and avoiding complex terminology.

Another consideration is that anatomical structures – whether a single muscle in the thigh or a digestive organ, such as the stomach – do not work alone. Although the text maps out individualized functions for each structure, the reality is that everything works together. The function of one organ might rely on a hormone produced by another, or the movement at a joint may result from the actions of three or four muscles working together. Think about the bigger picture.

Medical pioneers

Great breakthroughs in anatomy have often taken the form of correcting earlier errors. The Englishman William Harvey (1578–1625) – featured on here – was the first to establish the true role in the body of the heart (top) and lungs (below).

How this book works

Traditionally, anatomy is regarded as the study of the body’s form or structure, whereas physiology describes its functioning. However, form and function cannot be mutually exclusive. This book does not divorce the two; it describes both how the body is built and how it works.

The construction of the human body can be described in one of two ways: regionally or systematically. A regional approach to writing about anatomy would be to describe the individual areas of the body, such as the leg, the arm or the head; a systematic approach would describe the body systems – digestive, musculoskeletal, reproductive and so on. The approach in 30-Second Anatomy is based on these systems. The book is organized into seven chapters, each addressing a system of the body. By the end, it is hoped that you’ll have dissected your way through the body, learning the bare bones of its anatomy, in a simple, easy-to-follow manner.

Each anatomical component is presented as a 30-second anatomy. Accompanying this is the 3-second incision for those who simply want a quick slice. The 3-minute dissection that follows serves to illustrate the claim of Sigmund Freud, the Austrian neurologist and founder of psychoanalysis, that ‘Anatomy is destiny’. It provides examples of weird and wonderful aspects of human anatomy and describes what happens when bodily structures go wrong.

The first chapter deals with the skeletal system. The human body is constructed around the skeleton; the bones are a scaffolding onto which everything else is built. The second chapter looks at the muscular system and how humans move. The next two chapters are oriented around the main organs of the cardiovascular and digestive systems, addressing key functions, such as breathing and eating, and how the blood is pumped around the body. Next comes a tour of the special senses – skin, sight and hearing, to name but a few. The sixth chapter considers overall control of bodily function – the brain and the nervous system. Finally, we end with a nod to the circle of life by examining the reproductive system. Within each chapter you will also find a profile of a key anatomist.

The structure of this book is such that you can dip in and out, reading the odd entry here and there, or you can go through it system by system, or read it cover to cover. So why not lift the hood on your anatomy – and read on to enjoy finding out the mechanics of how you work!

Mapping the body

The brain and nervous system interact with all the other body systems to control the functions of the body. Anatomists have mapped how sensory fibres issuing from nerves in the spinal cord supply and receive input from specific areas of skin up and down the human frame.

THE SKELETAL SYSTEM

GLOSSARY

cartilage Type of connective tissue consisting largely of water, minerals and the proteins collagen and elastin. There are three types: hyaline cartilage covers the surface of joints and allows bones to move easily against one another; elastic cartilage provides structure for body parts that need to be pliable, such as the ears or nose; and fibrocartilage provides solidity in the spine’s intervertebral discs or the knee’s menisci.

cartilaginous joint One of three types of joints in the body (with fibrous and synovial joints); cartilaginous joints, held together by flexible cartilage that allows for limited movement, are found in between the vertebrae in the spine.

cortical bone Dense, strong outer layer surrounding a bone’s relatively light honeycomb-like inner structure. Also known as compact bone, it is called cortical because it forms the cortex (outer coating) of the bone. Cortical bone makes up 80 per cent of the weight of the human skeleton.

femur Also known as the thighbone, bone that reaches from the hip joint to the knee joint; typically 48 centimetres (19 inches) in length and capable of supporting up to thirty times a person’s weight, the femur is the longest and strongest in the body.

fibrous joint Found only in the skull, a type of joint that connects bones with fibrous tissue and allows for no movement.

flat bone Bone that takes the form of a wide plate to provide protection for a body organ or a surface for the attachment of muscles; examples include the sternum (breastbone) and scapula (shoulder blade). Flat bone is one of five bone types: long, short, flat, irregular and sesamoid.

humerus Long bone that connects the scapula (shoulder blade) to the radius and ulna of the forearm.

irregular bone Bone with unusual form that cannot be classified within the categories of long, short, flat and sesamoid bones. Examples include the vertebrae, which protect the spinal cord.

ligament Type of connective tissue that connects bones to one another and limits movement between them.

limb Appendage on the side of the body. Humans have four limbs – two upper (arms) and two lower (legs). Each has four sections: shoulder, arm, forearm and hand in the upper limb; buttock, thigh, leg and foot in the lower limb.

long bone Elongated bone, one longer than it is wide. Examples include the humerus and radius in the arm, and the femur and tibia in the leg. Small bones, such as the phalanges (in the fingers and toes), are classified as long bones because of their elongated shape.

sesamoid bone Rounded piece of bone, usually set within tendon, often less than 5 millimetres (¼ inch) in length. A larger example of a sesamoid bone is the kneecap (patella), which is embedded in the tendon of the thigh’s extensor muscle and serves to protect the knee joint.

short bone Bone as wide as it is long; examples include the carpals and tarsals in the wrist and foot.

synovial joint Type of joint which is designed to facilitate movement; it is filled with a lubricating fluid. There are six types of synovial joint: pivot joints allow rotation, as, for example, in the neck; hinge joints allow for a body part to be straightened or retracted, as in the elbow; ball-and-socket joints, for example, in the hip, allow for radial movement; saddle joints, found in the thumb, permit up-and-down and forward-and-backward movement, but not rotation; plane joints, such as those between the intertarsal bones of the feet, allow for gliding of bones; and ellipsoid joints, for instance, in the wrist, allow for the same movement as ball-and-socket joints, but to a lesser extent.

tendon Band of connective tissue that attaches a muscle to a bone.

trabecular bone Lighter inner part of bone, also called cancellous bone, which is protected by a stronger outer layer (cortical bone); trabecular bone often contains red bone marrow, in which red blood cells are produced.

vertebra One of the interconnecting bones that form the spinal column. Children have thirty-three vertebrae, but in adults five unite to make the sacrum and four combine to form the coccyx, reducing the number of bones to twenty-six.

TYPES OF BONE TISSUE

the 30-second anatomy

Bones combine to form the skeleton, the supporting framework on which everything in the body rests – without their bones, humans would have difficulty standing upright. Bone is a hard material made by specialized bone cells called osteoclasts, which combine minerals, such as calcium, with phosphate and a protein called collagen. The osteoclasts can form two types of bone: trabecular bone, which looks spongy, is relatively light and makes up the inside of most bones; while cortical bone forms a very dense and strong coat around the trabecular bone. The combination of trabecular and cortical bone makes the skeleton strong and keeps it light. If this were not the case, humans would need much bigger muscles to move the skeleton around, as well as a good deal more food to provide the necessary extra energy. Trabecular bone has another important function: It acts as a reservoir for calcium, which can be extracted from the bone and used elsewhere when other body systems are running low. The bones are constantly changing and renewing themselves – adult humans completely replace their skeleton every ten years or so.

3-SECOND INCISION

Bone is the scaffolding for the human body, and there are two types: hard cortical bone and light trabecular bone.

3-MINUTE DISSECTION

The skeleton consists of 206 bones and makes up around 40 per cent of body weight. Bones come in all shapes and sizes, from the long bones in the limbs, to the flat and sesamoid bones in the spine, skull, hands and feet. The femur in the lower limb is the largest at around 48 centimetres (19 inches) long. The smallest is the stapes, around 2.5 millimetres ( images inch) long and weighing around 4 milligrams.

RELATED TOPICS

THE SKULL

THE SPINE & RIBCAGE

THE PELVIS

THE LOWER LIMBS

THE UPPER LIMBS

3-SECOND BIOGRAPHY

HEROPHILOS

c. 335–280 BC

A Greek physician, the first to systematically perform scientific dissections of human corpses, who is deemed to be the first anatomist

30-SECOND TEXT

Judith Barbaro-Brown

A ‘broken leg’ – for a skier or anyone else – may range from a crack in the outer cortical layer to a complete fracture of the bone into two pieces.

THE BONE JOINTS

the 30-second anatomy

Classified according to how the

30-SECOND

ANATOMY

CONTENTS

INTRODUCTION

Gabrielle M. Finn

Gruesome history

Evolution and variation

Anatomy – systems and functions

How this book works

THE SKELETAL SYSTEM

THE SKELETAL SYSTEM

GLOSSARY

TYPES OF BONE TISSUE

the 30-second anatomy

THE BONE JOINTS

the 30-second anatomy