Question

Peristalsis: Have you ever laughed so hard that you had your drink come out of your nose? Have you ever swallowed something so quickly and then had to cough it up because it went down the wrong pipe? This usually doesn’t happen because under normal circumstances after you swallow your food, your epiglottis closes up over your wind pipe/traches that leads down to your lungs and your soft palate lifts up to block the way to your nose. Your tongue pushes back to your pharynx and then down your esophagus. How does food travel down through your esophagus? It’s not gravity. Q: Take a small drink of water. Bend down and touch your toes and swallow the water. Why were you still able to swallow the water when you were upside down?

Answer 1

The process in which food or water moves from mouth into stomach is called swallowing or deglutition.It occours in 3 phases_A.oral stage-when food moves from mouth to pharynx.B.pharyngeal stage_food moves from pharynx to esophagus.C_esophageal stage_when food moves from esophagus to stomach.

Food moves via GIT_mouth-pharynx-esophagus-stomach-small intestine-large intestine-defecation.

Pharynx is a common path for both food and wind.

All the stages of deglutition are detailed below.

A.oral stage-voluntary stage-food moves from mouth i?to pharynx via series of actions.sequence of events are_1.bolus formed (food mixed with saliva and masticated)placed over tongue.

2.anterior part of tongue is retracted and depressed.

3.posterior part of tongue is elevated and retracted against hard palate.This pushes bolus towards pharynx.The postive pressure created due to forceful contraction of tongue muscles pushes food into pharynx.

B.Pharyngeal stage__ it is an involuntary stage(pharynx to esophagus).pharynx is a common path for food and air.Itd ivides into larynx and esophagus.larynx lies anteriorly and continues as respiratory tract and esophagus lies behiend and continues as GITract.Since pharynx communicates with mouth,nose,larynx,and esophagus foof/water can enter into four paths_back into mouth,upward into nasopharynx,forward into larynx,downward into esophagus.

However due to various movements it is made to enter only into the esophagus.Entrance into other paths is prevented as follows_

1.back into mouth-position of tongue against soft palate,high intraoral pressure developed due to movement of the tongue.

2.upward into nasopharynx_due to elevation of soft palate elong with its expension called uvula_so water or food is prevented form coming out via nose.

3.forward into larnx_approximation of the vocal cords,forward and upward movement of larynx,backward movement of epiglottis to seal the opening of larynx_all these movements arrest respiration for few seconds called deglutition apnea.

4.As the other 3 paths are closed,bolus/water has to passonly via esophagus. This occours due to_a-upward movement of larynx stretches the opening of esophagus._b-simultaneously upper3-4cm of esophagus relaxes._c-at the same time peristtaltic contractions start in pharynx due to contraction of pharyngeal muscles_puses food into esophagus.

C_Next is ESOPGAGEAL stage_involuntary stage_(esophagus to stomach).The movements of esophagus are specifically organized for this function and called peristaltic waves.Peristalsis means a wave of contraction,followed by a wave of relaxation of muscles of GIT,which travel away from GIT.(propelled down along GIT_abnormal peristalsis can cause_diarrhoea,constipation,vomiting).

When foodxwater reaches esophagus,the peristaltic waves are initiated.usually 2 types_1.primary peristaltic contractions_ in upper part of esophagus_pass down propelling food towards stomach

2.secondary peristaltic conteactions_ produed in distal esophagus as primary waves are not sufficient and works like primary wave(propel food by producing positive pressure).

Distal 2-5 cm of esophagus act like a sphoncter and called lower esophageal sphincter_It is constricted always_when bolus/water enters this part of esophagus_it relaxes so that contents enter the stomach.After food moves into stomach_it relaxed again blocks the back flow of food into esophagus.The relaxation and constriction of sphincter occour in sequence with arrival of peristaltic contractions of esophagus.

All these action are called deglutition reflex_stimulus is when food/water enter oropharyngeal region,receptors present here are stimulated.

Afferent_glossopharyngeal nerve to the deglution center in medulla oblongata of brain.

Efferent fibres _impulses from deglutition cdntre travel through glossopharyngeal and vagus and reach softpalate and pharynx causing pharyngeal and esophageal stages of deglution respectively.

Thus from this discussion we can deduct that even if gravity has a little role,deglution is a reflex action and mediated by peristalsis which is unidirectional so food/water moves down the GIT even if you are upside down.