Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Blood cells

Introduction The blood is a mixture of cellular elements, fluid, proteins and metabolites. Blood has four major elements: Red blood cells (erythrocytes) transport oxygen from the lungs to the peripheral tissues. White blood cells (leukocytes) have a defensive role, destroying infecting organisms, such as bacteria and viruses, and assisting in the removal of dead or damaged tissues. Platelets (thrombocytes) are the first line of defence against…

Nervous tissue

Introduction The nervous system allows rapid and specific communication between widely spaced areas of the body by the action of specialized nerve cells (neurons), which gather and process information and generate appropriate response signals. The nervous system is divided into two main parts: The central nervous system (CNS), comprising the brain and spinal cord. The peripheral nervous system (PNS), comprising the nerves which run between the…

Contractile cells

Introduction Several cell types are specialized to generate motile forces through contraction. This chapter presents an overview of the main types of contractile cells. The general structure of each type of cell is described, together with details of their fine structure and how this relates to the molecular basis of contraction. There are four main groups of contractile cells. Contractile cells are specially adapted to generate…

Support cells and the extracellular matrix

Introduction The cells that form tissues can be divided into two types: parenchymal cells , which provide the main function of a tissue, and support cells , which provide the structural scaffolding of a tissue. Support cells comprise a set of highly developed cell types with complex metabolic functions and produce an extracellular matrix, which largely defines the physical characteristics of a tissue. Support cells and…

Epithelial cells

Introduction Epithelial cells are sheets of specialized cells that cover and line the interior and exterior surfaces of the body, for example, the outer layers of the skin and the inner luminal surface of the gastrointestinal tract. They have diverse functions such as secretion, absorption and protection (as a barrier), made possible by many specialized surface and internal modifications, with cells attached to each other by…

The cell

Introduction Cells of all types have several common defining attributes and are composed of a fluid material ( cytosol ) that contains smaller elements, termed subcellular structures, which provide the framework for cellular activities. Each cell is contained within a cell wall composed of a specialized cell membrane. The fluid inside the cell, the cytosol, is a dense proteinaceous liquid that contains many of the essential…

Histology

Introduction Histology is the study of the microscopic structure of biological material and the ways in which individual components are structurally and functionally related. Histology is central to biological and medical sciences, standing at the crossroads between a range of disciplines. Anatomy: sometimes referred to as microscopic anatomy or microanatomy, histology places gross anatomy into context, enabling the understanding of cell and tissue microstructure and how…

Special Senses

20.1 Overview Sense organs include the ear, olfactory mucosa, taste buds, cutaneous receptors, interoceptors (monitor the internal environment), proprioceptors in muscles, tendons, and joints, and eye. Specialized receptor organs in ears sense hearing and balance. The ear has three parts: external, middle, and inner (labyrinth). The external ear, consisting of the auricle ( pinna ) and external acoustic meatus, conducts sound waves from the external environment…

Eye and Adnexa

19.1 Overview Eyes are complex, paired photoreceptor organs. Each is roughly spherical, about 2.5 cm in diameter. Eyes communicate with the brain via the optic (II) cranial nerve. They develop as an outgrowth of the brain, mostly from neuroectoderm, and from surface ectoderm and mesoderm, which give rise to adnexa. The wall has three concentric coats. The mainly protective outer fibrous layer consists of an opaque sclera…

Female Reproductive System

18.1 Overview The female reproductive system consists of paired ovaries and the genital tract, including fallopian tubes ( oviducts, or uterine tubes ), uterus, cervix, and vagina, located in the pelvis—the internal genitalia. External genitalia consist of labia majora, labia minora, and clitoris. Mammary glands (see Chapter 2 ) and placenta are not classified as genital organs but are functionally associated with them. Ovaries, the center…

Male Reproductive System

17.1 Overview The male reproductive system includes the paired primary sex organs, the testes , which have both exocrine and endocrine functions, and several secondary sex organs consisting of excretory ducts and accessory glands. The scrotum and penis , an erectile organ through which the distal urethra passes, are external genitalia. The testes reside outside the body cavity in the scrotum, where they are suspended and…

Urinary System

16.1 Overview The urinary system comprises two kidneys , two ureters , a urinary bladder , and a urethra . Kidneys filter blood and produce urine, by which waste products and foreign substances leave the body. Urine formation involves filtration, secretion, and reabsorption of fluid by renal corpuscles and tubules in kidneys. About 180 L of fluid is filtered daily, but only 1-2 L of urine is produced,…

Respiratory System

15.1 Overview The respiratory system is divided functionally into a conducting portion that conveys air from outside the body to the lungs and a respiratory portion where exchange of gases between the air and blood occurs. The conducting airways moisten, warm, and cleanse the air, whereas the respiratory portion provides O 2 obtained from the air and removes excess CO 2 from the bloodstream. The conducting…

Liver, Gallbladder, and Exocrine Pancreas

14.1 Overview of the Liver The wedge-shaped liver, the largest and heaviest internal organ (weighs about 1.5 kg in an adult), is essential to life and is the most versatile and vascular organ. It sits just below the diaphragm in the upper right quadrant of the abdominal cavity and is protected completely by the rib cage. It comprises two main lobes of almost equal size— right and…

Lower Digestive System

13.1 Development of the Foregut, Midgut, and Hindgut The early embryo starts as a flattened, trilaminar disc with three primary germ layers: ectoderm, mesoderm, and endoderm. Its ventral surface, covered by endoderm, communicates with the yolk sac. Later, lateral and cephalocaudal folding forms a long, cylindrical endodermal tube extending the length of the embryo; this becomes the primitive gut tube and then the digestive tract. Splanchnic…

Upper Digestive System

12.1 Overview The digestive system—a long, tortuous, hollow tube—comprises the mouth (or oral cavity ), pharynx, and digestive tube or tract (also called the alimentary canal ). Associated with this tract are accessory glands of digestion: salivary glands, liver, gallbladder, and pancreas, which lie outside the wall of the tube but are connected to it via ducts. The digestive system engages in many functions such as…

Integumentary System

11.1 Overview The integument, the largest organ of the body, is composed of skin and skin appendages — nails, hair, sweat glands, and sebaceous glands. The total weight and overall surface area of skin in the adult are 3-5 kg and 1.5-2 m 2 , respectively. Skin thickness, between 0.5 and 3 mm, varies regionally; skin is thickest on the back and thinnest on the eyelid. At mucocutaneous junctions,…

Endocrine System

10.1 Overview The endocrine system comprises glands and tissues composed of parenchymal cells, which synthesize and secrete products called hormones. The term hormone derives from a Greek word meaning to set in motion. Like the nervous system, the endocrine system has diverse regulatory functions that control and coordinate activities of many other organs and tissues. Because the two systems have integrally linked functions, they are often…

Lymphoid System

9.1 Overview The extensive lymphoid —or immune — system protects the body against potentially harmful effects of pathogens, foreign substances, infectious agents (bacteria and viruses), and abnormal cells. Its major functions are thus to serve as a source of immunocompetent cells that can react with and neutralize antigens and to distinguish self from nonself. The system comprises lymphoid tissues and organs whose main constituents are aggregates…