-Humoral pathway

This pathway called humoral because it Include hormones and neurotransmitters. GIT hormones are secreted from certain area of GIT and released into portal circulation to influence the function of other parts in GIT to regulate movement and secretion of the digestive enzyme ,this can be classified into 3 groups :
1-Gastrin family: function mainly on stomach to increase gastric secretion .
2-secretin family: secretin influence the secretion and movement of the small intestine ,and cholecystokinin -pancreozyme (CCK-PZ) ,which act mainly on the secretion of gall bladder and pancreas .
3-small poly peptides: are really neurotransmitters which may have local function on certain area of GIT example vasoactive intestinal poly peptide (VIP),substance P (neurotensin) common pathway to regulate vomiting, villikinin which regulate movement of the intestinal villi.
Ingestion of food
The amount of food that a person ingests is determined by intrinsic desire for food called hunger .
The type of food that a person preferentially seeks is determined by appetite.
Chewing and swallowing are the first steps in processing of ingested food.
1- Chewing (Mastication):
Chewing has three functions:
A- It mixes food with saliva, lubricating it to facilitate swallowing
B - it reduce the size of food which facilitates swallowing.
C- It mixes carbohydrates with salivary amylase to begin carbohydrate digestion.
It include as both voluntary and involuntary components, involuntary component involves reflexes initiated by the presence of a bolus food in the mouth. Sensory information is relayed from mechanoreceptors in the mouth to the brain stem. While voluntary chewing occur at any time.
The teeth is designed for chewing. The incisor providing a strong cutting action, and the molars for grinding action.
Chewing process is caused by chewing reflex. The presence of a bolus of food in the mouth causes reflex inhibition of muscles or mastication which allows the lower jaw to drop. The drop in turn initiates a stretch reflex of the jaw muscles ( the masseter, medial pterygoid, and temporalis muscles) that lead to rebound contraction,
This automatically raises the jaw to cause closure of the Teeth but it also compresses the bolus against the lining of the mouth and push the food to come in contact with buccal receptors, which inhibit the jaw muscles again allowing the jaw to drop and rebond another time; this is repeated again and again.
2- Swallowing: (deglutition ):
Swallowing is initiated voluntarily In the mouth but thereafter it is under involuntary
or reflex control. Swallowing center is located in the medulla. Sensory information ( food in the mouth detected by somatosensory receptors located near pharynx), this afferent information is carried to medullary swallowing center via vagus and gloss pharyngeal nerves. The information is coordinated in medulla, motor (efferent) to striated muscle of the pharynx and upper esophagus.
There are 3 phases involved in the swallowing:
A- Oral phase: it is initiated when the tongue forces a bolus of food back toward the pharynx, which contains high density of receptors, which initiate the involuntary swallowing reflex in medulla
B- Pharyngeal phase: The purpose of this phase to propel the food bolus from the mouth through the pharynx to esophagus in the following step:
1- The soft palate is pulled upward, creating a narrow passage for food to move into the pharynx, so food cannot reflux into nasopharynx.
2- Epiglottis move to cover opening of larynx to prevent food from entering the trachea.
3- Upper esophageal sphincter relaxes allowing food to pass from pharynx to esophagus.
4-Aperistaltic wave of contraction is initiated in pharynx and propel food through the open sphincter. The breathing is inhibited during the pharyngeal phase of swallowing:
C- Esophageal phase: it is controlled by swallowing reflex. in this phase, food propelled through the esophagus to the stomach the esophageal secretions are entirely mucous provide lubrication for swallowing. Once the bolus has passed through the upper esophagus sphincter in pharyngeal phase. The reflex closes the sphincter. so food cannot reflux into pharynx. Primary peristaltic wave coordinated by swallowing reflex, travels down the esophagus propelling the food along the secondary wave which is mediated by the enteric nervous system, begins at site of distension and travels down ward.


structure of structure of upper GIT
Disorders of Swallowing

Damage to the 5th, 9th, or 10th cerebral nerve , swallowing center and brain stem can cause paralysis swallowing mechanism .
As well as deep anesthesia ,cause blocked the reflex mechanism of swallowing, in this case large quantities of vomiting materials come from the stomach into the pharynx; then, instead of swallowing the materials again, they suck them into the trachea. As a result, such patients choke to death on their own vomitus.

Disorders of esophagus
Achalasia or Megaesophagus is a condition in which the lower esophageal sphincter fails to relax during swallowing. As a result of damaging in the neural network of the myenteric plexus,lead to lost its ability to transmit a signal to cause “receptive relaxation” of the gastroe sophageal sphincter the food fails to pass from the esophagus into the stomach Antispasmotic drugs (drugs that relax smooth muscle) can be helpful.
Secretion of saliva:
Secretory cells are found in acinus. Each acinus is connected to the ductal system,acinus consists of a single layer of cuboidal epithelial cells surrounding a lumen, a central opening where the saliva is deposited after being produced by the secretory cells.
The three forms of produced: serous, mucoserous and mucous.

The daily normal secretion of saliva is between 500-1500 ml, it is hypotonic and contains high concentration of K+ ions and bicarbonate ions and lower concentration of Na +and CL- ions. Saliva has PH 6.0-7.4 6.0-7.0 this range is important for digestive action of ptyalin
Saliva consists of two types of protein secretion:-
1- Serous secretion: (watery saliva) containing ptyalin (?-amylase) which is an enzyme for digesting starches. Very small amount of lingual lipase which begins the process of fat digestion.
2- Mucous secretion: containing mucin (glycoprotein) for lubricating purposes. The parotid glands secrete serous type, submandibular and sublingual glands secrete both. The buccal glands secrete only mucous.
Salivary glands are controlled by parasympathetic nervous signals from the salivary nuclei which are located at junction of medulla and Pons.

The appetite area of the brain too, regulates these effects, is located in anterior hypothalamus, and it functions to a great extent in response to signals from the taste and smell areas of the cerebral cortex or amygdala.
Factors that induce salivation
A- Taste and tactile stimuli from the tongue and other area of mouth and pharynx. Sour and smooth objects increase salivation more time.
B- impulse arriving in the salivary nuclei from higher centers of CNS. When a person smell or eats favorite foods, salivation is greater than when disliked food is smelled or eaten.
C- response to reflex originating in the stomach and upper intestine when very irritating foods are swallowed or when a person is nauseated.
The swallowed saliva may help to remove the irritating factor in the GIT by diluting or neutralizing the irritant substances.
Parasympathetic nerve stimulation causes the salivary cells to secrete a large volume of watery fluid that is high in electrolytes but low in proteins.
While Sympathetic nerve stimulation causes the salivary gland to secrete a small volume of fluid containing a high concentration of mucous.(in excitation)
Under basal conditions, saliva is secreted all time except during sleep when the secretion become very little.

Important role of saliva in protection of the mouth:
1-cooling hot food to maintain healthy oral tissues.
2-The saliva oral hygiene, it helps to prevent the harmful effect of bacteria by continuous washing away the pathogenic bacteria.
3- Saliva contains many factors that can kill bacteria by ions, proteolytic enzymes and antibodies.
4-Saliva digests starch by ?-amylase and fat by lingual lipase.
5- Saliva Lubricates the food to make swallow easy and moisten the mouth
6-Saliva content also fluoride which is important for preventing dental caries.
7-Na+ and CL- which is present in concentration less than that of plasma (hypotonic)this is important for taste sensation if it was isotonic taste buds will not be stimulated by salt this decrease in concentration occur because of the active reabsorption of Na+ which is followed by CL- reabsorption .