Stomach

In some animals, including vertebrates, echinoderms, insects (mid-gut) and molluscs, the stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract. It is involved in the second phase of digestion, following mastication (chewing). The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially-digested food (chyme) to the small intestines.
The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos, ultimately from stoma (στόμα), "mouth". The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster

Anatomy of the Stomach

The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. The greater omentum hangs down from the greater curvature.
Two sphincters, keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region, not an anatomical sphincter) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.
The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor (motion) activity of its muscles.
In humans, the stomach has a relaxed, near empty volume of about 45 ml. It is a distensible organ. It normally expands to hold about 1 litre of food,^[4] but will hold as much as 2-3 litres (whereas a newborn baby will only be able to retain 30ml).

Lungs

The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately 2400 km (1500 mi) of airways and 300 to 500 million alveoli, having a total surface area of about 70 m² (8,4 x 8,4 m) in adults — roughly the same area as one side of a tennis court.^[1] Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 km (620 mi)

• The conducting zone contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles
• The respiratory zone contains the respiratory bronchioles, the alveolar ducts, and the alveoli.

The conducting zone and the respiratory stuffers (but not the alveoli) are made up of airways.
The conducting zone has no gas exchange with the blood, and is reinforced with cartilage in order to hold open the airways. The conducting zone warms the air to 37 degrees Celsius and humidifies the air. It also cleanses the air by removing particles via cilia located on the walls of all the passageways. The lungs are surrounded by the rib cage.
The respiratory zone is the site of gas exchange with blood.

• The sympathetic nervous system via noradrenaline acting on the beta receptors and causes bronchodilation
• The parasympathetic nervous system via acetylcholine which acts on the M-1 muscarinic receptors and maintains the resting tone of the bronchiolar smooth muscle. This action is related, although considered distinct from bronchoconstriction
• many other non-autonomic nervous and biochemical stimuli including, for example, carbon dioxide.

The pleural cavity is the potential space between the parietal pleura lining the inner wall of the thoracic cage and the visceral pleura lining the lungs.

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals.Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates the brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing, balance, taste, and smell.
Brains can be extremely complex. The cerebral cortex of the human brain contains roughly 15–33 billion neurons, perhaps more, depending on gender and age, linked with up to 10,000 synaptic connections each. Each cubic millimeter of cerebral cortex contains roughly one billion synapses. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body and target them to specific recipient cells.

The brain controls the other organ systems of the body, either by activating muscles or by causing secretion of chemicals such as hormones and neurotransmitters. This centralized control allows rapid and coordinated responses to changes in the environment. Some basic types of responsiveness are possible without a brain: even single-celled organisms may be capable of extracting information from the environment and acting in response to it.Sponges, which lack a central nervous system, are capable of coordinated body contractions and even locomotion. In vertebrates, the spinal cord by itself contains neural circuitry capable of generating reflex responses as well as simple motor patterns such as swimming or walking.However, sophisticated control of behavior on the basis of complex sensory input requires the information-integrating capabilities of a centralized brain.
Despite rapid scientific progress, much about how brains work remains a mystery. The operations of individual neurons and synapses are now understood in considerable detail, but the way they cooperate in ensembles of thousands or millions has been very difficult to decipher. Methods of observation such as EEG recording and functional brain imaging tell us that brain operations are highly organized, while single unit recording can resolve the activity of single neurons, but how individual cells give rise to complex operations is unknown

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system (including all vertebrates), that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδιά, kardia, for "heart".
The vertebrate heart is composed of cardiac muscle, which is an involuntary striated muscle tissue found only in this organ, and connective tissue. The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average 66 year lifespan, and weighs approximately 250 to 300 grams (9 to 11 oz) in females and 300 to 350 grams (11 to 12 oz) in males.^[1]
In invertebrates that possess a circulatory system, the heart is typically a tube or small sac and pumps fluid that contains water and nutrients such as proteins, fats, and sugars. In insects, the "heart" is often called the dorsal tube and insect "blood" is almost always not oxygenated since they usually respirate (breathe) directly from their body surfaces (internal and external) to air. However, the hearts of some other arthropods (including spiders and crustaceans such as crabs and shrimp) and some other animals pump hemolymph, which contains the copper-based protein hemocyanin as an oxygen transporter similar to the iron-based hemoglobin in red blood cells found in vertebrates.