Movements in the GIT( the guyton and hall physiology)

movements in GIT
1. Propulsive Movements -------- Peristalsis

2. Mixing Movements
Moves food forward along GIT at an appropriate rate for digestion and absorption
A contractile ring appears around the gut and then moves forward
Stimulation at any point in the gut can cause a contractile ring to appear in the circular muscle, and this ring then spreads along the gut tube
Directional movement toward Anus
Can occur in either direction but normally occurs towards anus

Requires active myenteric plexus

Stimulus for intestinal peristalsis
Distention of the gut
Irritation
Parasympathetic nervous signals
Peristalsis is absent:
Congenital absence of myenteric plexus
Atropine (paralyzes cholinergic nerve endings)

Peristalsis also occurs in
Bile ducts
Glandular ducts
Ureters
Many other smooth muscle tubes of the body
Law of the Gut or Peristaltic Reflex or Myenteric reflex:
Peristaltic reflex plus anal direction of movement of peristalsis is called "law of the gut”

Contractile ring normally begins on orad side of distended segment

The gut sometimes relaxes several centimeters downstream toward the anus, called "receptive relaxation," thus allowing food to be propelled easily anally

1. Movements in the GIT source: The  Guyton  and Hall Physiology Maryam Fida (o-1827)

2. Movements in the GIT 1 . Propulsive Movements -------- Peristalsis 2. Mixing Movements

3. Propulsive movements or Peristalsis Moves food forward along GIT at an appropriate rate for digestion and absorption A contractile ring appears around the gut and then moves forward Stimulation at any point in the gut can cause a contractile ring to appear in the circular muscle, and this ring then spreads along the gut tube Directional movement toward Anus Can occur in either direction but normally occurs towards anus Requires active myenteric plexus Stimulus for intestinal peristalsis Distention of the gut Irritation Parasympathetic nervous signals Peristalsis is absent : Congenital absence of myenteric plexus Atropine (paralyzes cholinergic nerve endings) Peristalsis also occurs in Bile ducts Glandular ducts Ureters Many other smooth muscle tubes of the body Law of the Gut or Peristaltic Reflex or Myenteric reflex: Peristaltic reflex plus anal direction of movement of peristalsis is called "law of the gut” Contractile ring normally begins on orad side of distended segment The gut sometimes relaxes several centimeters downstream toward the anus, called "receptive relaxation," thus allowing food to be propelled easily anally

4. Mixing movements Keeps intestinal contents thoroughly mixed at all times . TYPES: 1. Peristaltic contractions causing mixing Occurs when forward progression is blocked by sphincter. Peristaltic wave can then only churn the contents, rather than propelling them 2. Local intermittent constrictive contractions Occurs every few centimeters in gut wall. These constrictions usually last only 5-30 seconds; then new constrictions occur at other points, "chopping" & "shearing" the contents first here and then there

5. What is Hunger and Appetite Hunger: “ The amount of food that a person ingests is determined by intrinsic desire for food is called HUNGER. Appetite: “ The type of food that a person preferentially seeks is determined by Appetite”

6. It is the mechanical processing of food and made it ready to swallow Mastication (chewing) Breaking Mixing é saliva Grinding Softening

7. Mastication ( chewing ) Incisors (front teeth): cutting action with a force of 55 pounds Molars ( post teeth ): grinding action with force 200 pounds Muscles of chewing are innervated by motor branch of trigeminal( 5 th cranial nerve ) Controlled by nuclei in the brain stem & reticular area, areas of hypothalamus, amygdala Chewing reflex Presence of food bolus in mouth  initiates reflex inhibition of muscles of mastication  drooping lower jaw  stretch of jaw muscle  rebound contraction  jaw raised up  closure of teeth  compression of bolus again…………. FUNCTIONS: Chewing is important for digestion of fruits and raw vegetables – Breakage of indigestible cellulose surrounding fruits & vegetables Increase Surface Area of chewed food  digestible particles Digestive enzymes act only on the surfaces of food particles Rate of digestion increased Prevents excoriation of the gastrointestinal tract

8. Deglutition (Swallowing) Phases 1. Preparatory phase 2. Oral phase (buccal or voluntary ) bolus is forced into the oropharynx 3. Pharyngeal phase ( involuntary ) controlled by the medulla and lower pons 4. Oesophageal phase ( involuntary ) controlled by the medulla and lower pons

9. 1. Preparatory phase starts as soon as liquids are taken into the oral cavity or after the bolus has been masticated. The liquid or bolus is position on the dorsum of the tongue , with the oral cavity sealed by the lip and the tongue. The positioning of a liquid on the dorsum of the tongue before transporting it to the final swallow-preparatory position may be facilitated through suction created by moving the tongue posteriorly

10. Oral phase These combined movements make a smooth path for the bolus as it is pushed from the oral cavity by the peristaltic- Iike action of the tongue . Solid food is actually pushed by the tongue, whereas fluids flow ahead of the lingual contractions. During this phase, the oral cavity maintains an anterior and lateral seal , and is stabilized by the muscles of mastication. introduced by the withdrawal of the soft palate from its rest position against the root of the tongue, where it is held by the tensor palati muscles . In this phase the soft palate moves upward and the tongue drops downward and backward. At the same time, the larynx and hyoid move upward . The elevation of the hyoid may actually be initiated as the bolus is positioned in the swallow-preparatory phase. When a large bolus is to be swallowed, most or all of it is moved into the preparatory position and is then neatly sectioned by the tongue in consecutive swallows until the oral cavity is empty.

11. The pharyngeal phase: contraction of the constrictor muscles of the pharynx occurs accompanied by receptive relaxation of the upper esophageal sphincter. This phase begins as the bolus passes from the tongue through the fauces . The pharyngeal tube is raised and the nasopharynx sealed by closure of the soft palate against the posterior pharyngeal wall. Entire pharyngeal stage < 6 sec Initiated as a reflex

12. 3. Pharyngeal phase Palatopharygeal folds approximate  forming sagital slit  food pass to post pharynx Vocal cords of larynx approximate  The hyoid and the base of the tongue move forward These movements + prevention of the ligament pulling epiglottis upwards  epiglotis swing backwards  cover opening of larynx Sealing passage of food into nose & trachea Most essential is tight approximation of vocal cords Finally, there is an abrupt elevation of the larynx as the bolus reaches the laryngo -pharynx and, this is then followed by opening of the oesophageal sphincter. Food moves from post pharynx upper oesophagus b/w swallow pharyngeoesophageal sphincter remains closed  no air into oesophagus during respiration Whole pharygeal ms contraction  propulsion of food

13. The oesophageal phase: It is involuntary, passage of food to the stomach is rapid in the upper part & slow in the lower end Two types of peristalsis: Primary peristalsis : continuation of pharyngeal peristalsis Sec peristalsis : develops if primary peristalsis fail to propel food completely into the stomach due to local myenteric reflex or stimulation of vagal afferents medulla( deglutition center) glossopharyngeal ,& vagal efferents Peristalsis: Produced by a series of localized reflexes in response to distention of wall by bolus. Wave-like muscular contractions: Circular smooth muscle contract behind, relaxes in front of the bolus. Followed by longitudinal contraction (shortening) of smooth muscle. Rate of 2-4 cm/sec. After food passes into stomach, LES constricts.

14. Motility of Esophagus The esophagus prevents air from entering the GI tract through the function of the upper esophageal sphincter. The esophagus prevents GI contents from re-entering the esophagus from the stomach through the function of the lower esophageal sphincter. The contraction that sweeps down the esophagus is the result of intrinsic and extrinsic stimuli. Achalasia is a condition in which the lower esophageal sphincter does not open, causing food to accumulate in the esophagus. Lower Esophageal Sphincter (Gastroesophageal Sphincter): NARROW LOWER END OF ESOPHAGUS Normally tonically constricted “Receptive relaxation “ appears ahead of peristalsis Protects lower end of esophagus by preventing reflux of acidic stomach contents Valve like closure of distal end of esophagus is protective

15. Receptor Afferent Center Efferents Nervous pathways Phases of deglutition around the pharyngeal opening V, IX, X deglutition center V, IX, X , XI, XII