HUMAN BODY ANATOMY

Embryogenesis, the first eight weeks of development after fertilization, is an incredibly complicated process. It’s amazing that in eight weeks we’re transforming from a single cell to an organism with a multi-level body plan. The circulatory, excretory, and neurologic systems all begin to develop during this stage. Luckily, like with many complex biological concepts, fertilization can be broken down into smaller, simpler ideas. The big idea of embryogenesis is going from a single cell to a ball of cells to a set of tubes.  Starting from the very beginning Step 1 : a  zygote  is the single cell formed when an egg and a sperm cell fuse; the fusion is known as fertilization Step 2 : the first 12-to 24-hours after a zygote is formed are spent in  cleavage  – very rapid cell division The zygote’s first priority is dividing to make lots of new cells, so it’s first few days are spent in rapid mitotic division. With each round of division, it doubles in cell number. This divisio

Making Tubes Step 5 : During  gastrulation  the three germ layers form; the cell mass is now known as a gastrula Step 5a : The  primitive streak  forms Step 6 : The  notochord   is formed Week 3 of development is the week of  gastrulation . A germ layer is a layer of cells that will go on to form one of our organizational tubes. Our anatomy can really be boiled down to an inner tube (our digestive tract), and a series of tubes that wrap around it. The three germ layers that will translate into these tubes are the  ectoderm , the  mesoderm , and the  endoderm . Germ Layer What does the prefix mean? Goes on to form: Ectoderm Outer, external Epidermis (outer layer of skin), hair, nails, brain, spinal cord, peripheral nervous system Mesoderm Middle Muscle, bone, connective tissue, notochord, kidney, gonads, circulatory system Endoderm Within Epithelial lining of the digestive tract; Stomach, colon, liver, pancreas, bladder, lung The first step of gastrulation is t

EMBRYOGENESIS DIVIDED IN PARTS

WHAT IS A TISSUE? The term  tissue  is used to describe a group of cells found together in the body. The cells within a tissue share a common embryonic origin. Microscopic observation reveals that the cells in a tissue share morphological features and are arranged in an orderly pattern that achieves the tissue’s functions. From the evolutionary perspective, tissues appear in more complex organisms. For example, multicellular protists, ancient eukaryotes, do not have cells organized into tissues. Although there are many types of cells in the human body, they are organized into four broad categories of tissues: epithelial, connective, muscle, and nervous. Each of these categories is characterized by specific functions that contribute to the overall health and maintenance of the body. A disruption of the structure is a sign of injury or disease. Such changes can be detected through  histology , the microscopic study of tissue appearance, organization, and function. The next four po

EPITHELIAL TISSUE KEY FACTS Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another. Epithelial layers are avascular, but innervated. Epithelial cells have two surfaces that differ in both structure and function. Glands, such as exocrine and endocrine, are composed of epithelial tissue and classified based on how their secretions are released. Functions of the Epithelium Epithelia tissue forms boundaries between different environments, and nearly all substances must pass through the epithelium. In its role as an interface tissue, epithelium accomplishes many functions, including: Protection for the underlying tissues from radiation, desiccation, toxins, and physical trauma. Absorption of substances in the digestive tract lining with distinct modifications. Regulation and excretion of chemicals between the underlying tissues and the body cavity. The secretion of hormones into the blood vascular system. The secretion

CONNECTIVE TISSUE DEFINITION Connective tissue , group of tissues in the body that maintain the form of the body and its organs and provide cohesion and internal support. The connective tissues include several types of fibrous tissue that vary only in their density and cellularity, as well as the more specialized and recognizable variants—bone, ligaments, tendons, cartilage, and adipose(fat) tissue. COMPONENTS OF CONNECTIVE TISSUE All forms of connective tissue are composed of (1) extracellular  fibres, an amorphous matrix called ground substance, and  stationary and migrating cells. The proportions of these components vary from one part of the body to another depending on the local structural requirements. In some areas, the connective tissue is loosely organized and highly cellular; in others, its fibrous components predominate; and in still others, the ground substance may be its most  conspicuous  feature. The anatomical classification of the various types

Muscle Tissue Definition Muscle tissue is a specialized tissue found in animals which functions by contracting, thereby applying forces to different parts of the body. Muscle tissue consists of fibers of muscle cells connected together in sheets and fibers. Together these sheets and fibers and known as muscles, and control the movements of an organisms as well as many other contractile functions. There are three different types of muscle found in animals, depending on their use. While these muscles differ slightly, they function in a similar way. Function of Muscle Tissue Muscle tissue functions as a single unit, and is often connected to the same nerve bundles. A nerve impulse traveling from the brain or another outside signal tells the muscle to contract. The nerve impulse is transferred almost instantaneously to all the nerve cells in the muscle tissue, and the entire muscle contracts. At the cellular level, each muscle cell has a complex of proteins containing actin an