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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…
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…
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…
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…
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,…
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…
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…
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…
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…
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,…
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…
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…
8.1 Overview The cardiovascular system consists of the heart —a muscular pump—and closed vessels through which blood circulates in the body. Arteries leave the heart, branch repeatedly, and have smaller diameters as they course toward the periphery. They deliver blood to capillaries , which are the thinnest vessels and are closest to body cells. Blood in capillaries is returned to the heart via veins . The…
7.1 Overview Blood is a specialized type of connective tissue that consists of cells suspended in a circulating fluid known as plasma. The total amount of circulating blood in men is 5-6 L; that in women, 4-5 L. Fresh blood is a red, viscous fluid, whereas plasma is translucent and yellow. Cellular elements of blood constitute about 45% of blood volume in adults, with plasma making up the…
6.1 Overview Cartilage and bone are specialized forms of connective tissue that have critical roles in providing the skeletal framework of the body. Although they share similarities, many important differences set them apart. As with other connective tissues, they derive from embryonic mesenchyme; both consist of cells embedded in an extracellular matrix. Cartilage matrix is a firm yet resilient gel, with physical attributes of a plastic;…
5.1 Overview The nervous system is divided anatomically into the central (CNS) and peripheral (PNS) nervous systems. The CNS comprises the brain, brainstem , and spinal cord ; the PNS, all nerve fibers ( axons and dendrites ), nerve endings , and collections of their cell bodies that lie outside the CNS. The autonomic nervous system , a subdivision of the PNS, is connected to the…
4.1 Overview Muscle tissue in the body is classified into one of three major categories according to structure, function, and location. Skeletal muscle is the most common and characteristic type; the other two kinds are cardiac muscle and smooth muscle. Skeletal muscle produces purposeful movements of the skeleton. Cardiac muscle forms the myocardium and is responsible for beating of the heart to pump blood. Smooth muscle…
3.1 Overview Adult connective tissue comprises a diverse family of tissues whose major function is to provide form and support to the body and organs and to connect and anchor parts. It is also a medium for exchange of nutrients, oxygen, and waste products between other tissues; it aids in defense and protection; and in certain sites, as in adipose tissue, it stores fat for cushioning…
2.1 Overview Epithelium is one of the four basic tissues, with a wide distribution and many functions. It consists of continuous sheets of cells that cover exposed body surfaces. It also lines internal cavities, such as those of the digestive, respiratory, cardiovascular, and genitourinary systems. During embryonic development, epithelium invaginates into underlying tissues to proliferate and form secretory glands. Its two classes are thus covering and…