Biomedical Sciences

Essential Laboratory Medicine

Raymond Iles, Suzanne Docherty, Raymond Iles, Suzanne Docherty

• Publisher: Wiley
• Year: 2011
• Print ISBN: 9780470997741, 9780470997758
• eBook ISBN: 9781119962410
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Human Anatomy & Physiology
• Index: Biological Sciences

Biomedical Sciences is an indispensable, all encompassing core textbook for first/ second year biomedical science students that will support them throughout their undergraduate career. The bookincludes the key components of the IBMS accredited degree programmes, plus sections on actual practice in UK hospital laboratories (including the compilation of a reflective portfolio).

The bookis visually exciting, and written in an interesting and accessible manner while maintaining scientific rigour. Highlighted boxes within the textlink the theory to actual clinical laboratory practice for example, the histopathology chapter includes a photographically illustrated flow chart of the progress of a specimen through the histopathology lab, so that students can actually see how the specimen reception/inking/cut-up/cassette/block/section/stain system works, with an emphasis on the safety procedures that ensure specimens are not confused).

Chapter 1

Anatomy and Physiology of Major Organ Systems

Professor Ray K. Iles, B.Sc., M.Sc., Ph.D., CBiol, FSB, FRSC, Dr Iona Collins, BMedSci, MBBS, FRCS and Dr Suzanne M. Docherty, BmedSci, MBBS, Ph.D.

No area of medical science is truly self-contained; all systems interact, so as we study our chosen speciality we have to put this in a holistic context of human biology. This is as true for the clinical laboratory specialist as for any other medical professional. This introductory chapter is not aimed to be a comprehensive text on anatomy and physiology as there are numerous extremely good volumes published on this subject. However, the reader may wish to dip into these explanatory notes as a refresher or source of direction for further study. After all, students of clinical biomedical science will find they have to read around our specific substantive chapters on haematology, clinical chemistry, microbiology and especially histopathology if they do not have a grasp of anatomical systems.

1.1 The Skeletal System

The obvious functions of the skeleton are to provide support, leverage and movement and protection of organs, for example the skull protects the brain, the rib cage the lungs, heart, liver and kidneys, and the pelvis the bladder. In addition, the skeletal system is a storage site for calcium and phosphate minerals and lipids (yellow marrow) and critically a site for the production of blood cells (red bone marrow).

The characteristics of bone are that they are very lightweight yet very strong – resistant to tensile and compressive forces. Interestingly, healthiness (bone density) depends on continuous stressing or loading (i.e. activity). Bones are characterized by their shape (Figure 1.1) into long bones, short bones, flat bones and irregular bones.

Figure 1.1 The human skeleton and the four bone categories which are shape descriptors. Essentials of Human Anatomy & Physiology, 9th Edition, Marieb, 2008 © Pearson Education Inc.

1.1.1 The Anatomical Structure of a Bone

Best exemplified by long bones, the bone itself is subdivided by internal and external structures. The bone is covered by a layer of cartilage called the periosteum underneath which is a layer of dense compacted calcified compact bone: however, beneath this layer can either be a hollow chamber (medullary cavity) filled with the specialist tissue of the bone marrow or a spongy bone of small cavities. The spongy bone is always found at the end structures of articulating long bones and is a region of continued bone turnover lying above a line of active bone cells called the epiphyseal line. This spongy bone region is called the epiphysis, whilst the bone marrow dominant region between the two epiphyseal lines is termed the diaphysis where highly active bone turnover (remodelling) does not continuously occur (Figure 1.2).

Figure 1.2 Structural components of the long bone. Essentials of Human Anatomy & Physiology, 9th Edition, Marieb, 2008 © Pearson Education Inc.

Bone is derived from connective tissue and there are two types of connective tissue in the skeletal system – calcified bone and cartilage. Cartilage tissue forms a covering of articular surfaces, ligaments and tendons, as well as sheaths around bone (periosteum).

Bone tissue is calcium phosphate (Ca₃(PO₄)) crystals embedded in a collagen matrix peppered with bone cells. Thus bone is 60% minerals and collagen and 40% water where the collagen enables bones to resist tensile forces (i.e. are elastic) and minerals which enable bones to resist compressive forces, but this does makes them brittle.

Bone (osseous tissue) is, however, living tissue and therefore has an abundant blood and nerve supply: periosteal arteries supply the periosteum (see Figure 1.3(a)); nutrient arteries enter through nutrient foramen supplies compact bone of the diaphysis and red marrow (see Figure 1.3(b)) and metaphyseal and epiphyseal arteries supply the red marrow and bone tissue of epiphyses (see Figure 1.3(a)).

Figure 1.3 Detail of the blood supply of a long bone (a) and example of entry position, the nutrient foramina, is indicated in (b). Essentials of Human Anatomy & Physiology, 9th Edition, Marieb, 2008 © Pearson Education Inc.

1.1.2 Spongy Bone and Compact Bone

Bone tissue is of two types – spongy and compact. Spongy bone forms ‘struts’ and ‘braces’ with spaces in between. Spaces contain bone marrow allowing production and storage of blood cells (red marrow) and the looser structure allows the bone to withstand compressive forces. Compact bone makes up the outer walls of bones, it appears smooth and homogenous and always covers spongy bone. Denser and stronger than spongy bone, compact bone gives bones their rigidity. Spongy and compact bone are biochemically similar, but are arranged differently. In compact bone the structural unit is the osteon (see Figure 1.4).

Figure 1.4 Microanatomy of the bone. Essentials of Human Anatomy & Physiology, 9th Edition, Marieb, 2008 © Pearson Education Inc.

1.1.3 Osteocytes – Mature Bone Cells

There are two types of bone cell:

• Osteoblasts – bone forming cells.
• Osteoclasts – bone destroying cells.

In the formation of new bone osteoblasts cover hyaline cartilage with bone matrix. Enclosed cartilage is digested away leaving the medullary cavity. Growth in width and length continues by the laying down of new bone matrix by osteoblasts. Remodelling to ensure the correct shape is effected by osteoclasts (bone-destroying cells). In mature bones osteoblast activity decreases whilst oesteoclast remodeling activity is maintained. However, bone remodelling requires both oesteocytes. Triggered in response to multiple signals stress on bones means that there is considerable normal ‘turnover’ – bone is a dynamic and active tissue; for example, the distal femur is fully remodelled every 4 months.

Osteoclasts carve out small tunnels and osteoblasts rebuild osteons: osteoclasts form a leak-proof seal around cell edges and then secrete enzymes and acids beneath themselves. The resultant digestion of the bone matrix releases calcium and phosphorus into interstitial fluid. Osteoblasts take over bone rebuilding, continually redistributing bone matrix along lines of mechanical stress.

1.1.4 How Bones Grow

Bone growth only occurs in those young enough to still have an active, unfused epiphyseal plate (roughly < aged 16–19). The epiphyseal plates fuse earlier in females than in males – generally, females have stopped growing by around the age of 16, while for males this is around 18 to 19 (see Figure 1.5).

Figure 1.5 Histological appearance of epiphyseal plate. Essentials of Human Anatomy & Physiology, 9th Edition, Marieb, 2008 © Pearson Education Inc.

Cartilage cells are produced by mitosis on the epiphyseal side of plates (ends of bones) – this is continuous with articular cartilage at the end of the bone. Cartilage cells are destroyed and replaced by bone on the diaphyseal side of plates (middle of long bone) and a zone of resting cartilage anchors the growth plate to the bone. The epiphyseal plate is at the top of Figure 1.5, and this is where new cartilage cells are being created by mitosis. As they are ‘pushed away’ from the epiphyseal plate by new cartilage cells being created ‘behind’ them, osteoblasts lay down a calcium phosphate matrix in and around the cartilage cells, ossifying the area. This gradually takes on the structure of bone. The epiphyseal plate cartilage is continuous with the articular cartilage at the end of the bone, and new cartilage (and bone formation) is occurring in both areas rather than strictly just at the epiphyseal plate. Furthermore, the bone has to be remodelled as it increases in length, or the whole bone would be as wide as the epiphysis – but what you actually need is a narrower diaphysis (shaft) in the middle of the bone. The thick articular cartilage, at either end of the bone, is continuous with the thin (but tough) periosteum around the outside of the rest of the bone. Periosteum has a rich blood supply which is important when you consider bones grow not only in length but in width.

Periosteal cells (from membrane around the bone) differentiate into osteoblasts and form bony ridges and then a tunnel around a periosteal blood vessel. Concentric lamellae fill in the tunnel to form an osteon (s...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• List of Contributors
• Preface
• Chapter 1: Anatomy and physiology of major organ systems
• Chapter 2: Pathophysiology
• Chapter 3: Clinical cell biology and genetics
• Chapter 4: Cellular pathology
• Chapter 5: Clinical chemistry
• Chapter 6: Medical microbiology
• Chapter 7: Clinical immunology
• Chapter 8: Haematology and transfusion science
• Chapter 9: Professional practice and biomedical science
• Appendix
• Index