DIGESTIVE SYSTEM:
The digestive system is the digestive tract: this is a series of hollow organs joined together like a twisting tube, it starts at the mouth and goes to the anus. Other organs in the body help break down and absorb food. The organs that make up the digestive tract are the mouth, esophagus, stomach, small and large intestines which is also called the colon, the rectum and anus. These organs have a lining inside of the called the mucosa. The mucosa produces juices to help break down food. The digestive tract also has a layer of muscle that helps move the food through the tract and break it down


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RESPIRATORY SYSTEM:
The respiratory system contains a group of tissue and organs that help the human body breathe. the airways is the main parts of this system: the lungs, blood vessels and muscles that enable breathing, the airway pipes carry oxygen-rich air to your lungs and carbon dioxide. The airway includes the nose and air passage or (nasal cavities), the mouth, the lurynx (voice box), the tracher(windpipe) and bronchial tubes and there branches. when the air enters the body through the nose or mouth, the air then travle through the your voice box and down the windpipe. The windpipe then splits into two bronchial tubes that enters your lungs. A thin flap of tissue or the epiglottis covers your windpipe when you swallow. This stops the food or drink from entering the air passage that leads to your lungs. besides the mouth and parts of the nose, all of airways have hairs that are coated with sticky mucus, called the cilia. this trapes germs and other foreign particles that enter your airways when you breathe in air.lung_anatomy.jpg
CIRCULATORY SYSTEM:
The circulatory system brings the body's cells what they need for survival: oxygen and nutrients. At the center of this system is the heart. The heart cciculates blood throughout the veins and arteries. Arteries carry oxygen-rich blood away from the heart, giving the oxygen-rich blood to tissues. returning the used up red blood cells back to the heart through the veins for reoxygenation.

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NERVOUS SYSTEM:

The nervous system is a network that controls and coordinates all the activities by transmitting messages or signals from the brain to the different regions of the body and vice versa. The nervous system works with the help of nerves or neurons, which conduct the signals or impulses between the two components of the nervous system, i.e. central and peripheral nervous system. The neurons can be of different types, such as sensory and motor neurons. In addition to neurons, glial cells, which surround and support the neurons, also participate in the transmission of signals. The sensory neurons generate and transmit the stimuli received from the sensory organs like the eye, nose or skin, to the central nervous system, i.e. to the brain and the spinal cord. The brain in turn processes these stimuli and sends them back to the other parts of the body telling them to react to a particular type of stimulus. The motor neurons are responsible for receiving signals from the brain and spinal cord and transmitting them to the other organs of the body. The neurons use electrochemical signals or neurotransmitters in the transmission of signals or impulses from one neuron to another.
The human brain can be divided into three parts, forebrain, midbrain and hindbrain, that regulate some specific functions of the body. The forebrain consists of the cerebrum, which is the largest part of the brain and is the center of intelligence, memory, emotion, personality, speech and the ability to feel. The outer layer of cerebrum is cortex, which receives the information collected by the sensory nerves and sends them to other regions of the brain for further processing. The inner part consists of the thalamus, hypothalamus and pituitary gland. The thalamus transmits the messages from the sensory organ to the cortex, while the hypothalamus is responsible for regulating pulse, appetite and automatic processes. Pituitary glands secrete hormones that regulate growth, metabolism, sexual maturity and response to stress.

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MUSCULAR SYSTEM:
Muscles are one of the most important parts of the human body. Without muscles, the body will not be able to move. They’re incredibly complex things that turn energy into motion.The muscular system works because it can move – it can bend and straighten. Muscles work in opposing teams in order to create a full range of movement. One set of muscles on one side moves, and the other side then pulls the muscles back into the original position, which creates a movement.Your muscular system works the way it does simply because it has to – if your muscles don’t flex and bend, you will not be able to move around easily. Turning a doorknob would be impossible. Even walking would be hard. If your knees cannot bend, you will not be able to walk comfortablyThe muscular system also interacts with other parts of the body. During inhalation, the muscles between the ribs relax, allowing the lungs to draw in air. When you digest food, muscles in your esophagus interact with the digestive system. Your nervous system tells your muscles when to move. Even your skeletal system needs your muscular system because your muscles keep your bone structure intact.
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THE SKELETAL SYSTEM:

  • The skeletal system works to support your body. Without your skeletal frame, you would be unable to move. Humans are vertebrates, meaning we have bony, articulated (jointed) endoskeletons. An endoskeleton is a frame within the body that offers support as it grows and develops. The skeletal system offers protection, support, blood cell formation, stores minerals and energy and aids movement.Bones are made of connective tissue. Connective tissue is found all over your body and comes in different forms. Bones are mostly made up of collagen fibrils. Their surfaces are covered with special cells made of calcium compounds. This is what gives the bones their structure and strength.A human adult has a total of two hundred and six bones. Bones are considered to be living organs because they are made up of nerve, muscle and epithelial tissue, as well the connective tissue that binds everything together. If you were to look at the cross section of a long bone, such as your femur, you would see a shaft in the middle that is hollow. This central cavity contains either red or yellow marrow. Red is newly produced marrow. As bones age, the red marrow converts into yellow. This special, yellow marrow is an energy source.Within the bones, red and white blood cells are produced, along with platelets. There is a fibrous sheath called a periosteum that contains blood vessels which supply oxygen and nutrients to the bone tissues. Blood vessels get in and out of the bones by little openings called nutrient canals.

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