The digestive system• The digestive system is made up of the digestive tract, a series of holloworgans joined in a long, twisting tube from the mouth to the anus andother organs that help the body break down and absorb food .• Organs that make up the digestive tract are the mouth, esophagus,stomach, small intestine, large intestine also called the colon, rectum, andanus. Inside these hollow organs is a lining called the mucosa. In themouth, stomach, and small intestine, the mucosa contains tiny glands thatproduce juices to help digest food.• The digestive tract also contains a layer of smooth muscle that helpsbreak down food and move it along the tract. There are two solid digestiveorgans, the liver and the pancreas, produce digestive juices that reach theintestine through small tubes called ducts. The gallbladder stores thelivers digestive juices until they are needed in the intestine. Parts of thenervous and circulatory systems also play major roles in the digestivesystem.
The circulatory system• The circulatory system is an organ system that permits blood and lymph circulation totransport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide,hormones, blood cells, etc. to and from cells in the body to nourish it and help to fightdiseases, stabilize body temperature and pH, and to maintain homeostasis.• This system may be strictly seen as a blood distribution network, but some consider thecirculatory system as composed of the cardiovascular system, which distributes blood, andthe lymphati c system, which returns excess filtered blood plasma from the interstitial fluid(between cells) as lymph. While humans, as well as other vertebrates, have a closedcardiovascular system (meaning that the blood never leaves the network of arteries, veinsand capillaries), some invertebrate groups have an open cardiovascular system. The moreprimitive, diploblastic animal phyla lack circulatory systems. The lymphatic system, on theother hand, is an open system providing an accessory route for excess interstitial fluid to getreturned to the blood.• Two types of fluids move through the circulatory system: blood and lymph. Lymph isessentially recycled blood plasma after it has been filtered from the blood cells and returnedto the lymphatic system. The blood, heart, and blood vessels form the cardiovascular (fromLatin words meaning heart-vessel) system. The lymph, lymph nodes, and lymph vesselsform the lymphatic system. The cardiovascular system and the lymphatic system collectivelymake up the circulatory system.
The nervous system• The nervous system is the part of an animal’s body that coordinates the voluntary andinvoluntary actions of the animal and transmits signals between different parts of its body. Inmost types of animals it consists of two main parts, the central nervous system (CNS) and theperipheral nervous system(PNS). The CNS contains the brain and spinal cord. The PNSconsists mainly of nerves, which are long fibers that connect the CNS to every other part ofthe body. The PNS includes motor neurons, mediating voluntary movement, the autonomicnervous system, comprising the sympathetic nervous system and the parasympatheticnervous system and regulating involuntary functions, and the enteric nervous system, a semi-independent part of the nervous system whose function is to control the gastrointestinalsystem.• At the cellular level, the nervous system is defined by the presence of a special type of cell,called the neuron, also known as a "nerve cell". Neurons have special structures that allowthem to send signals rapidly and precisely to other cells. They send these signals in the formof electrochemical waves traveling along thin fibers called axons, which cause chemicalscalled neurotransmitters to be released at junctions called synapses. A cell that receives asynaptic signal from a neuron may be excited, inhibited, or otherwise modulated. Theconnections between neurons form neural circuits that generate an organisms perception ofthe world and determine its behavior. Along with neurons, the nervous system contains otherspecialized cells called glial cells (or simply glia), which provide structural and metabolicsupport.
Endocrine system• The endocrine system is the system of glands, each of which secretesdifferent types of hormones directly into the bloodstream (some of whichare transported along nerve tracts) to maintain homeostasis. Theendocrine system is in contrast to the exocrine system, which secretes itschemicals using ducts. The word endocrine derives from the Greek words"endo" meaning inside, within, and "crinis" for secrete. The endocrinesystem is an information signal system like the nervous system, yet itseffects and mechanism are classifiably different. The endocrine systemseffects are slow to initiate, and prolonged in their response, lasting from afew hours up to weeks. The nervous system sends information veryquickly, and responses are generally short lived. Hormones are substances(chemical mediators) released from endocrine tissue into the bloodstreamwhere they travel to target tissue and generate a response. Hormonesregulate various human functions, including metabolism, growth anddevelopment, tissue function, sleep, and mood. The field of study dealingwith the endocrine system and its disorders is endocrinology, a branch ofinternal medicine.
Reproductive system• The reproductive system or genital system is asystem of organs within an organism which worktogether for the purpose of reproduction. Manynon-living substances such as fluids, hormones,and pheromones are also important accessoriesto the reproductive system. Unlike most organsystems, the sexes of differentiated species oftenhave significant differences. These differencesallow for a combination of genetic materialbetween two individuals, which allows for thepossibility of greater genetic fitness of theoffspring.
Respiratory System• The respiratory system (or ventilatory system) is the biologicalsystem that introduces respiratory gases to the interior andperforms gas exchange. In humans and other mammals, theanatomical features of the respiratory system include airways,lungs, and the respiratory muscles. Molecules of oxygen and carbondioxide are passively exchanged, by diffusion, between the gaseousexternal environment and the blood. This exchange process occursin the alveolar region of the lungs. Other animals, such as insects,have respiratory systems with very simple anatomical features, andin amphibians even the skin plays a vital role in gas exchange. Plantsalso have respiratory systems but the directionality of gas exchangecan be opposite to that in animals. The respiratory system in plantsalso includes anatomical features such as holes on the undersidesof leaves known as stomata.
Alveolis• Alveolis are the basic structure of respiratorysystem