The lymphoid system is responsible for the immunological defense of the body. Some of its component organs— bone marrow , lymph nodes , thymus , and spleen —are surrounded by connective tissue capsules, whereas its other components, members of the…
The circulatory system is composed of two separate but related components: the cardiovascular system and the lymphatic vascular system. The function of the cardiovascular system is to carry blood in both directions between the heart and the tissues. The function…
Blood, a specialized connective tissue, is a bright- to dark-red, viscous, slightly alkaline fluid (pH 7.4) that accounts for approximately 7% of the total body weight with a total volume of approximately 5 L in an average adult. It is…
The human nervous system is composed of perhaps a trillion neurons, each with a large number of interconnections. Some of these neurons possess receptors that are specialized for receiving different types of stimuli (e.g., mechanical, chemical, thermal), which are transduced…
Muscle cells are specialized for contraction that permits movement. Organisms harness the contraction of muscle cells and the arrangement of the extracellular components of muscle to permit locomotion, constriction, pumping, and other propulsive movements. Muscle cells are called striated or…
Cartilage and bone are both specialized connective tissues that function in supporting parts of the body. The former has a firm pliable matrix that resists mechanical stresses; the latter is one of the hardest tissues of the body, and protects…
Connective tissue is derived from mesoderm , the middle germ layer of the embryonic tissue, except in certain areas of the head and neck, where mesenchyme develops from neural crest cells of the developing embryo and is known as ectomesenchyme…
Epithelium Epithelial tissue forms two distinct structural and functional forms: sheets of contiguous cells ( epithelia ), which cover the external and internal surfaces of the body, and clusters of cells ( glands ), which originate from invaginated epithelial cells.…
Cells of similar structure and function assemble to form structural and functional associations, known as tissues , in all multicellular organisms. Groups of these tissues are assembled in various organizational and functional arrangements into organs , which carry out functions…
Summary The nucleus , the largest organelle of the cell, houses the nucleoplasm , nucleolus, and the chromatin . The nucleus is separated from the cytoplasm by a double membrane, known as the nuclear envelope , which is perforated by…