Anatomy

Anatomy is the branch of morphology focused on the internal and external structures of organisms. It investigates the structural organization of living things, including their systems, organs, and tissues. This science examines the appearance, position, and materials of various body parts. It also explores how these parts relate to one another. Anatomy is distinct from physiology, which studies how parts function. While a physiologist studies how a liver regulates bodily functions, an anatomist examines the liver's shape, size, and blood supply.

Scientists divide the discipline into macroscopic and microscopic branches. Macroscopic anatomy, or gross anatomy, involves examining body parts with the naked eye. This includes superficial anatomy, which studies external features by sight. Microscopic anatomy requires optical instruments to study tiny structures. One specific area is histology, the study of tissues. Another is embryology, which examines organisms in their immature stages.

Anatomy can be organized by location or by system. Regional anatomy studies the relationships between all structures in a specific area, like the abdomen. In contrast, systemic anatomy focuses on a discrete body system. A system is a group of structures working together for a unique function, such as the digestive system. Researchers use both invasive and non-invasive methods to study these organizations. Dissection involves opening a body to study organs directly. Endoscopy uses a video camera through a small incision to explore internal structures.

Modern technology has revolutionized how we see inside the body. Historically, anatomy relied on the dissection of carcasses and cadavers. In the 20th century, medical imaging provided new ways to visualize structures. Techniques include X-rays, ultrasound, and magnetic resonance imaging (MRI). Angiography uses X-rays or magnetic resonance to visualize blood vessels. These advanced tools allow for highly detailed and accurate visualizations without invasive surgery.

Animal bodies are composed of four basic tissue types. Connective tissue, often called fascia, provides shape and holds organs in place. It contains an extracellular matrix made of proteins like collagen. This tissue includes bone, cartilage, and adipose tissue.

Epithelial tissue consists of closely packed cells that form layers. These cells can be squamous, cuboidal, or columnar. In the skin, keratinocytes make up about 95% of the cells.

Muscle tissue contains myocytes that contract to produce force and motion. It is divided into smooth, skeletal, and cardiac muscle.

Finally, nervous tissue uses neurons to transmit information throughout the body.

Most complex animals are triploblastic, meaning they develop from three germ layers. These layers are the ectoderm, mesoderm, and endoderm. All tissues and organs in these animals derive from these three layers. For example, nervous tissue comes from the ectoderm, while connective tissues come from the mesoderm. The gut develops from the endoderm. Even simple invertebrates may only have two layers, called diploblastic.

Vertebrates share a fundamental body plan during their embryonic stages. They all possess a notochord, which is a stiffening rod. They also have a dorsal hollow neural tube and pharyngeal arches. A tail is typically located posterior to the anus. In these animals, the spinal cord is protected by the vertebral column. This structural similarity shows how anatomy connects different species through shared evolutionary history.