The cardiovascular system carries blood from the heart to all parts of the body through a series of tubes, all but the smallest of which are muscular. The muscle in these tubes is of two types: smooth muscle is characteristic…
The musculoskeletal system comprises the specialized connective tissues of the articulated bony skeleton (including bone, cartilage and tendon) and the skeletal muscles that act across the articulations. Connective tissues are characterized by a sparse population of cells within an abundant…
Blood is an opaque fluid with a viscosity greater than that of water (mean relative viscosity 4.75 at 18 °C), and a specific gravity of 1.06 at 15 °C. It is bright red when oxygenated, as in the systemic arteries,…
The nervous system has two major divisions, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain, spinal cord, optic nerve and retina, and contains the majority of neuronal cell bodies. The PNS…
Cells evolved as single, free-living organisms, but natural selection favoured more complex communities of cells, multicellular organisms, where groups of cells specialize during development to carry out specific functions for the body as a whole. This allowed the emergence of…
Cell Structure General characteristics of cells The shapes of mammalian cells vary widely depending on their interactions with each other, their extracellular environment and internal structures. Their surfaces are often highly folded when absorptive or transport functions take place across…