How does the nervous system interact with the digestive system

The human body contains trillions of cells, 78 different organs and more than 60,000 miles of blood vessels if you stretched them end-to-end. Incredibly, all of these cells, vessels and organs work together to keep you alive.

Each organ belongs to one of ten human body systems. These body systems are interconnected and dependent upon one another to function. Your heart does not beat unless your brain and nervous system tell it to do so. Your skeletal system relies on the nutrients it gains from your digestive system to build strong, healthy bones.

There are 10 body systems:

1. Circulatory
2. Respiratory
3. Nervous
4. Muscular
5. Skeletal
6. Digestive
7. Endocrine (hormones)
8. Lymphatic, or immune system
9. Reproductive
10. Integumentary (skin, hair)

A body system is a group of parts that work together to serve a common purpose. Your cardiovascular system works to circulate your blood while your respiratory system introduces oxygen into your body.

Each Body System Works with the Others

Each individual body system works in conjunction with other body systems. The circulatory system is a good example of how body systems interact with each other. Your heart pumps blood through a complex network of blood vessels. When your blood circulates through your digestive system, for example, it picks up nutrients your body absorbed from your last meal. Your blood also carries oxygen inhaled by the lungs. Your circulatory system delivers oxygen and nutrients to the other cells of your body then picks up any waste products created by these cells, including carbon dioxide, and delivers these waste products to the kidneys and lungs for disposal. Meanwhile, the circulatory system carries hormones from the endocrine system, and the immune system’s white blood cells that fight off infection.

Each of your body systems relies on the others to work well. Your respiratory system relies on your circulatory system to deliver the oxygen it gathers, while the muscles of your heart cannot function without the oxygen they receive from your lungs. The bones of your skull and spine protect your brain and spinal cord, but your brain regulates the position of your bones by controlling your muscles. The circulatory system provides your brain with a constant supply of oxygen-rich blood while your brain regulates your heart rate and blood pressure.

Even seemingly unrelated body systems are connected. Your skeletal system relies on your urinary system to remove waste produced by bone cells; in return, the bones of your skeleton create structure that protects your bladder and other urinary system organs. Your circulatory system delivers oxygen-rich blood to your bones. Meanwhile, your bones are busy making new blood cells.

Working together, these systems maintain internal stability and balance, otherwise known as homeostasis. Disease in one body system can disrupt homeostasis and cause trouble in other body systems. If you become ill with the AIDS virus that affects your immune system, for example, you may develop pneumonia in your respiratory system, a yeast infection in your reproductive system, Candida that affects your esophagus in your digestive system or the skin cancer known as Kaposi’s sarcoma.

For more information on the connection between body systems, talk to your health professional at Revere Health. We offer family practice and 39 medical specialties to help all ten of your body systems work together. 

Sources:
Organs of the Body
Cleveland Clinic
AIDS.org

VIVO Pathophysiology

The nervous system exerts a profound influence on all digestive processes, namely motility, ion transport associated with secretion and absorption, and gastrointestinal blood flow. Some of this control emanates from connections between the digestive system and central nervous system, but just as importantly, the digestive system is endowed with its own, local nervous system referred to as the enteric or intrinsic nervous system. The magnitude and complexity of the enteric nervous system is immense - it contains as many neurons as the spinal cord.

The enteric nervous system, along with the sympathetic and parasympathetic nervous systems, constitute the autonomic nervous system.

The principal components of the enteric nervous system are two networks or plexuses of neurons, both of which are embedded in the wall of the digestive tract and extend from esophagus to anus:

• The myenteric plexus is located between the longitudinal and circular layers of muscle in the tunica muscularis and, appropriately, exerts control primarily over digestive tract motility.
• The submucous plexus, as its name implies, is buried in the submucosa. Its principal role is in sensing the environment within the lumen, regulating gastrointestinal blood flow and controlling epithelial cell function. In regions where these functions are minimal, such as the esophagus, the submucous plexus is sparse and may actually be missing in sections.

The image below shows part of the myenteric plexus in a section of cat duodenum. Pass your mouse cursor over the image to outline several enteric neurons.

In addition to the two major enteric nerve plexuses, there are minor plexuses beneath the serosa, within the circular smooth muscle and in the mucosa.

Within enteric plexuses are three types of neurons, most of which are multipolar:

• Sensory neurons receive information from sensory receptors in the mucosa and muscle. At least five different sensory receptors have been identified in the mucosa, which respond to mechanical, thermal, osmotic and chemical stimuli. Chemoreceptors sensitive to acid, glucose and amino acids have been demonstrated which, in essence, allows "tasting" of lumenal contents. Sensory receptors in muscle respond to stretch and tension. Collectively, enteric sensory neurons compile a comprehensive battery of information on gut contents and the state of the gastrointestinal wall.
• Motor neurons within the enteric plexuses control gastrointestinal motility and secretion, and possibly absorption. In performing these functions, motor neurons act directly on a large number of effector cells, including smooth muscle, secretory cells (chief, parietal, mucous, enterocytes, pancreatic exocrine cells) and gastrointestinal endocrine cells.
• Interneurons are largely responsible for integrating information from sensory neurons and providing it to ("programming") enteric motor neurons.

Enteric neurons secrete an intimidating array of neurotransmitters. One major neurotransmitter produced by enteric neurons is acetylcholine. In general, neurons that secrete acetylcholine are excitatory, stimulating smooth muscle contraction, increases in intestinal secretions, release of enteric hormones and dilation of blood vessels. Norepinephrine is also used extensively for neurotransmission in the gastrointestinal tract, but it derives from extrinsic sympathetic neurons; the effect of norepinephrine is almost always inhibitory and opposite that of acetylcholine.

The enteric nervous system can and does function autonomously, but normal digestive function requires communication links between this intrinsic system and the central nervous system. These links take the form of parasympathetic and sympathetic fibers that connect either the central and enteric nervous systems or connect the central nervous system directly with the digestive tract. Through these cross connections, the gut can provide sensory information to the CNS, and the CNS can affect gastrointestinal function. Connection to the central nervous system also means that signals from outside of the digestive system can be relayed to the digestive system: for instance, the sight of appealing food stimulates secretion in the stomach.

In general, sympathetic stimulation causes inhibition of gastrointestinal secretion and motor activity, and contraction of gastrointestinal sphincters and blood vessels. Conversely, parasympathetic stimuli typically stimulate these digestive activities. Some of the prominent communiques enabled by nervous interconnections within the digestive tract have been named as reflexes and serve to illustrate a robust system of control. Examples include the gastrocolic reflex, where distention of the stomach stimulates evacuation of the colon, and the enterogastric reflex, in which distention and irritation of the small intestine results in suppression of secretion and motor activity in the stomach.

Congenital and acquired derangements in the structure or function of the enteric nervous system are well recognized as causes of digestive tract disease. Examples include small intestinal motility disorders, gastric outlet obstructions and megacolon.

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