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Home , Ascending colon, Large intestine, Sigmoid colon, Transverse colon

COLON MOTILITY

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• Important

• Further explanation 1 Contents

. Mind map...... 3 . Colon Function…………………………………4 . Physiology of Colon Regions……...…………6 . Absorption and Secretion…………………….8 . Types of motility………………………………..9 . Innervation and motility…………………….....11 . Reflex……………………………..13 . ……………………………15

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Mind map 3 COLON FUNCTIONS: Secretions of the Large Intestine:  Secretion. • The mucosa of the large intestine has many crypts of 3 Colon consist of : Lieberkühn. • Absence of villi. • Ascending • Transverse • The epithelial cells contain almost no . • Descending • Presence of goblet cells that secrete mucus (provides an • Sigmoid adherent medium for holding fecal matter together). • • • Stimulation of the pelvic nerves1 from the can cause: Functions of the Large Intestine: o marked increase in mucus secretion. o This occurs along with increase in peristaltic motility 1. Reabsorb and compact material of the colon. into . 2. Absorb produced by . • During extreme parasympathetic stimulation, so much 3. Store fecal matter prior to defecation. mucus can be secreted into the large intestine that the person has a bowel movement of ropy2 mucus as often as every 30 minutes; this mucus often contains little or no 1: considered a part of parasympathetic in large intestine . fecal material. 2: resembling a rope in being long, strong, and fibrous 3: anatomical division. 4

It prevents backflow of contents from colon into . It remains closed and open only when an intestinal peristaltic wave reaches it.

Relaxed By: Contracted By: Gastrin, CCK, B Distension of the adrenergic , Secretin, Ach, alpha

adrenergic 5 PHYSIOLOGY OF COLON REGIONS:

The physiology of different colon regions: Bacterial Action in the Colon: (1st part)

• Colon bacilli bacteria are capable of digesting small amounts of cellulose.

• The ascending colon is specialized for processing • K, , , and delivered from the terminal various gases can be formed by bacteria. • When rediolabeled chyme is instilled (put gradually) into cecum, half of the instilled volume empties from ascending colon in 87 min.

• The bacteria-formed is • This period is short in comparison with the especially important because the • The ascending colon is not the primary site of storage, mixing and amount of this vitamin in the daily removal of water. * ingested foods is normally insufficient to maintain adequate blood

. 6 The physiology of different colon regions: CONT. (2st parts) transverse colon

• The transverse colon is specialized for the storage • The descending colon is a conduit between the and dehydration of feces. transverse and .”transportation” • The labeled material is retained for about 24 hrs. • Labeled feces begin to accumulate in the sigmoid colon about 24 hours after the label is instilled in the cecum • The transverse colon is the primary site for the removal of water and and the storage of • This region has the neural program for power propulsion feces. that is involved in defecation reflex.

rectosigmoid region, anal canal, and pelvic floor musculature

• The physiology of the rectosigmoid region, anal canal, and pelvic floor musculature maintains fecal continence (the ability to voluntarily control urinary and fecal discharge). • The sigmoid and rectum are reservoirs with a capacity of up to 500mL1. • The puborectalis muscle and external anal comprise a functional unit that maintain continence . • Fibers of puborectalis join behind the anorectum and pass around it to form a U-

shaped sling (physiological valve)* 7 1: 25% of 500ml in sigmoid can trigger defecation. ABSORPTION AND SECRETION:

Chyme absorption and Absorption and Secretion of Electrolytes and Formation of Feces: Water: (physiological division) • The large intestine can absorb a maximum of 5 to 8 absorbing colon storage colon liters of fluid and electrolytes each day. Most of the the distal colon • The mucosa, like that of the small intestine, has a absorption in the functions principally high capability for active absorption of , Cl large intestine for feces storage and water. occurs in the until a propitious • It secretes bicarbonate ions and Potassium. proximal one half of time for feces the colon giving this excretion and is Reabsorption in the large intestine includes: portion the name therefore called the absorbing colon storage colon • Water, Sodium and Chlor. • Vitamins – K, , and B5 • Organic wastes – Urobilinogens and Sterobilinogens • Bile • Toxins

• Ammonia (By Catalyzing Urea by Urease). 8 INNERVATIONS & MOTILITY: Motility in the Large Intestine: Sensory innervation and continence: . The proximal half of the colon is concerned Mechanoreceptors in the rectum detect distention and with absorption and the distal half with MR+ENS supply the ENS. storage. . The transit of small labeled markers through The anal canal in the region of the skin is innervated the large intestine occurs in 36-48 hrs. SS+CNS by somatosensory that transmit signals to CNS.

This region has sensory receptors of pain, temperature SS+CNS and touch . Movements of the colon

Contraction of them with small 1-Mixing 2-Propulsive 3-Antiperistalsis blocks the passage of movements movements (Mass volumes in the Movement feces and maintains (Haustrations) Movements) puborectalis continence rectum

muscle 9 2. 1. sequential At: At: an followingin a order logical or sequence. . . . the the circular muscle divide the colon into In In Ring The The contracting segment and receiving segment segment on either side TYPES OF MOVEMENTS: . Net Net increase in motility of the respective state longerfor addition, addition, there is uniform repetition of along the length of the of the length along Ascending 1 + - the the like forward forward propulsion pockets 1 - 1 haustra contractions Mixing (Haustrations) migration of 3 called called movements movements along along the st part of transverse part of (about (about 2.5 cm) of haustra remain remain in their haustra occurs occurs when colon colon. bowel periods . in response to stretch in the occurs occurs . . 3 : : pocket haustra means two fingers contraction in between them space calledwhichpocket. and byproducts of inthe . agents agents such as parasites and enterotoxins . May be be May . At: At: Start The The motor events in disappearance of following a meal ( . circular muscle and and is preceded by of of Irritants,e.g., castor oil, threatening Descending can can ileal at the middle of transverse of the middle at colon triggered by increased the delivery 2 - initiate mass mass initiate Propulsive chyme ( descending descending Mass Mass Movements small intestine + into ascending ascending into colon and and the downstream haustral gastrocolic rest part part rest the transverse the movements relaxation relaxation the of colon movement contractions. contractions. of transverse of . . ) reflex . and 2 ). 10 CONT.

3-Antiperistalsis

It starts at the junction of ascending and transverse colon and traveling towards the cecum. It mixes contents and help water absorption.

**(Gastrocolic & dudenocolic reflexes): increase the colon movement by filling the Stomach or . 11 CONTROL OF COLONIC MOTILITY

The intramural plexuses directly control the contractile behavior of the colon.

Stimulatory Inhibitory acetylcholine & substance P VIP & NO onto colonic as neurotransmitter smooth muscle cells

The extrinsic autonomic nerves to the colon modulate the control of the colonic motility by the enteric . Parasympathetic nervous system increase the motility of colon: (Vagus supplies ascending colon and proximal 2/3 of transverse colon) and (Pelvic splanchnic

nerves supply distal 1/3 part of transverse colon and the remainder of large intestine) 12 RECTUM & DEF. REFLEX:

The Rectum Defecation Reflex:

1 Distension of the rectum. Internal and Last portion external1 Stimulation of the stretch receptors in the of the anal 2 rectum. digestive tract A. Short reflex: Stimulation of myenteric plexus in sigmoid colon and rectum. Terminates at B. Long reflex: stimulation of parasympathetic2 motor the anal canal 3 neurons in sacral spinal cord. C. stimulation of somatic motor neurons.

A. Increased local . B. Relaxation of internal anal sphincter and contraction of 4 .

2: for increasing peristaltic movement.

1: external sphincter is important in voluntary continence specially at high volume in sigmoid. 13

ADDITIONAL SLIDE DEFECATION REFELX : 14 ال إراديا FECAL INCONTINENCE The spinal reflex of defecation operates without interference from higher centers.

Spinal cord lesion

In infants Weakness of (physiological) IAS and EAS

Causes Diarrheal conditions and Weakness of Diminished pulborectalis rectal capacity Altered rectal or anal

sensation 15 Summary

16 • • • • • • • • • • • • secretin. secretin. Gastrin colon. The of Vit K Na About The Most secretion Pelvic The Tenia transverse ,descending The colon is divided into + and + and HCO . K, biotin, biotin, K, . B + and + and Cl ileoceacal distal colon function is the of colon lacks of of absorption occur in proximal half of the coli and 0.5 0.5 nerves ( and and CCK relaxes the L of water is absorbed daily from the - are are 3 + are haustra parasympathic 5 valve prevents backflow contents of from CHO are CHOare absorbed. absorbed and and folic resulting from bacterial secreted are are characteristic to the , sigmoid sigmoid rectum , and , finally ,cecum storage ileoceacal ) increase the mucus valve unlike the , ascending ascending , , villi. colon. colon. colon . • • injury have fetal incontinence higher center that Defecation and Mass duodenocolic movement is mainly initiated by is is a spinal reflex which is influenced by ’ s s whya reflex. person person with . Summary Gastrocolic spinal spinal cord

17 Summary

18 Answerkey: C. NO. GIP. B. VIP. A. 2 D. Chlor. C. Bicarbonate. Water.B. Sodium. A. 1 D. Powerful D. Powerful of EAS. C. Genetic. Obesity. B. Diarrheal A. Condition. 4 D. B C. Secretin. Gastrin. B. CCK. A. 3 D. Substance P. - - - - what is can cause fecal incontinence: Iliocecal valve can contracted by: Neurotransmitter stimulate that the motility colon: of which one of the following is secreted in colon: - Adrenergic. 1 :C, 2 :D, 3 :C, 4 :A , 5 :A, 6 :C, 7 D. Rush D. Rush Movement. C. Antiperistalsis Movement. Mixing B. contraction (Haustration). Propulsive A. Movement. muscle divide the colon into 8 D. Psoas Major. C. Puborectalis. IAS. B. A .EAS. 7 D. Between Descending and sigmoid Colons. C. Between Ascending and transverse colons. Between B. Caecum and ascending colons. BetweenA. Transverse and descending colons. 6 D. Pelvic Plexus. C. Vagus. Submucosal B. Plexus. MyentericA. Plexus. 5 - - - - :C, the the muscle is U that Antiperistalsis Movement at: start Ring In Defecation Reflex, The Short Reflex Stimulate: 8 - like contractions (about of the circular2.5 cm) :B - Shaped: pockets: MCQs

19 Ans: VitaminAns: K and Thiamine (B1). Q4:Twoof the Vitamins thatcan formed ByBacteriain Colon: 3 2 1 Ans Q3:What aremuscles that involvedin Defecation? Ans Q2:Twoof substancesthatcan reabsorbedbycolon: 3 2 1 Ans: Q1:whatare typesof motilityof colon: ------External Sphincter Anal Internal Anal Sphincter Puborectalis Antiperistalsis. movement. Propulsive (Haustration). Mixing : : Water, Bile andsalt. Chlor Sodium, SAQs

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