The human digestive system

The system used in the human body for the process of digestion. The human digestive system consists primarily of the digestive tract, or the series of structures and organs through whichfood and liquids pass during their processing into forms absorbable into the bloodstream. The system also consists of the structures through which wastes pass in the process of elimination and other organs that contribute juices necessary for the digestive process.

The digestive tract begins at the lips and ends at the anus. It consists of the mouth, or oral cavity, with its teeth, for grinding the food, and its tongue, which serves to knead food and mix it withsaliva; the throat, or pharynx; the esophagus; the stomach; the small intestine, consisting of theduodenum, the jejunum, and

the ileum; and the large intestine, consisting of the cecum, a closed-end sac connecting with the ileum, the ascending colon, the transverse colon, the descending colon, and the sigmoid colon, which terminates in the rectum. Glands contributing digestive juices include the salivary glands, the gastric glands in the stomach lining, the pancreas, and the liver and its adjuncts—the gallbladder and bile ducts. All of these organs and glands contribute to the physical and chemical

breaking down of ingested food and to the eventual elimination of nondigestible wastes. Their structures and functions are described step by step in this section.

The tissues

A tissue are a group of cells with a similar structure that do the same type of activity. Tissues are present in complex animal and plants. Sponges, jellyfish, algae, fungi do not have tissues.

ANIMAL TISSUES.
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covering>>Epithelial >>Protection>> Skin, blood vessels,interior of organs.

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Glandular>> Secretion>> Glands, glandular epithelium of theintestine.
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Adipose>>Reserve/insulation>> All the body
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Cartilaginous>> Skeleton >>ears, inter-vertebrate disc, tracheal rings...

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Bone Skeleton Skeleton
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Blood>> Transport>> All the body
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Muscular >>Smooth>>Movement>>Internal organs
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Striated>> Movement>> Skeletal Muscles
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Cardiac>> Movement>> Heart
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Nerve>> Information/responses>> Nervous system
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Respiratory system

A respiratory system's function is to allow gas exchange. The space between the alveoli and the capillaries, the anatomy or structure of the exchange system, and the precise physiological uses of the exchanged gases vary depending on the organism. Inhumans and other mammals, for example, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.

Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skinplays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leavesknown as stomata.

The nervous system

The nervous system is a network of specialized cells that communicate information about an organism's surroundings and itself. It processes this information and causes reactions in other parts of the body. It is composed of neurons and other specialized cells called glial cells,(plural form glia), that aid in the function of the neurons. The nervous system is divided broadly into two categories: the peripheral nervous system and the central nervous system. Neurons generate and conduct impulses between and within the two systems. The peripheral nervous system is composed of sensory neurons and the neurons that connect them to the nerve cord, spinal cord and brain, which make up the central nervous system. In response to stimuli, sensory neurons generate and propagate signals to the central nervous system which then processes and conducts signals back to the muscles and glands. The neurons of the nervous systems of animals are interconnected in complex arrangements and use electrochemical signals andneurotransmitters to transmit impulses from one neuron to the next. The interaction of the different neurons form neural circuits regulate an organism's perception of the world and what is going on with its body, thus regulating its behavior. Nervous systems are found in many multicellular animals but differ greatly in complexity between species.

The human senses

The human body is a beautifully engineered structure. The body has a general plan. We all have arms, legs, a head, ears, and eyes on the outside of our bodies. We also have similar parts on the inside of our bodies. We all have one heart, two lungs, one brain, two kidneys, and one stomach.

Understanding and learning about the human body is a complicated subject. If you just take an organ or system and emphasize its function, you must tell students how the system fits into the rest of the body's functions.

You can introduce the parts of the body, both internal and external, by using the organs that allow humans to operate their senses. Thenervous system controls the actions and sensations of all the parts of your body by using a complex network of nerves, which carry electrical signals to and from the brain. The brain and spinal cord compose the central nervous system, acting as the central clearing house. One part of your nervous system controls your body's relationship to the external environment (somatic) and another part controls your body's internal organs (autonomic). The human body has five major senses which operate to gather information from the world around us, sight, hearing, smell, taste, and touch. Any stimulus to one of the sense areas is detected by sensory nerves and is sent to the brain for interpretation.