GI Physiology 4

vomiting

the expulsion of gastroduodenal content from GIT to the external environment via mouth.

vomiting

It is associated with retching that forces contents of the stomach into the esophagus.

activation of vomiting center or by an activation of the chemoreceptor-trigger zone (CTZ).

Vomiting may be initiated by either

reticular formation of medulla oblongata

Vomiting center is situated in the ________ near the vagal nucleus.

injury to the area or by raised intracranial pressure

Direct activation of the vomiting center occurs due to an

sympathetic and vagi

Visceral afferent pathway in the _______ relay impulses arising due to the irritation of mucosa of upper GIT.

vestibular nuclei

Afferent impulses from the ______ mediate nausea and vomiting of motion sickness.

Afferents from higher centers

mediate emetic response to stimuli, such as nauseating smell, sickening sights, emotion and memory

area postrema

Activation of Chemoreceptor Trigger Zone location

circulating emetic substances

The chemoreceptors present in CTZ are stimulated by

V, VII, IX, X, and XII

Efferent impulses from the vomiting center and CTZ, which give effect to act of vomiting, are transmitted via ____________ cranial nerves to upper GIT, and through spinal nerves to the muscles of respiration.

emetics

Drugs that induce vomiting are called

emetics

These chemicals stimulate the receptors that are present in the CTZ

antiemetics

prevent vomiting by inhibiting CTZ.

5-HT3 and D2

There are ________ receptors in area postrema

Serotonin

stimulates vomiting through 5-HT3 receptors

Ondensetron

a 5-HT3 receptor antagonist is an antiemetic.

Chlorpromazine; haloperidol

a D2 receptor antagonist and _______ are also effective antiemetics.

Corticosteroids, cannabinoids, and benzodiazepines

are useful antiemetics for chemotherapy-induced vomiting.

1. Distension of stomach

2. Tickling the back of throat

3. Painful injury of the genitourinary tract

4. Conditions associated with dizziness and nausea

5. Many chemicals or drugs can elicit vomiting

Important stimuli that activate these afferent fibers:

Pre-ejection phase

It is characterized by the feeling of nausea, excessive salivation and also deep, rapid and irregular breathing.

Jejunum

Genesis of reverse peristalsis that starts from the middle of the _____ sweeps the content of intestine and duodenum into the stomach.

pyloric sphincter

Relaxation of the _____ that allows the intestinal content to enter the stomach.

glottis

Forced inspiration occurs against the closed ______, lowering of the diaphragm increases intra-abdominal pressure.

abdominal muscles

Vigorous contraction of _________ forces the gastric contents to enter the esophagus.

lower esophageal sphincter

Relaxation of the _______ allows gastric content to enter the esophagus.

upper esophageal sphincter

With stronger retching and sharp rise in intraabdominal pressure, _________ relaxes, which allows vomitus to enter the pharynx and then from there into the mouth

Ejection phase

during which the GIT contents are actually expelled out.

central movement of vocal cords, closure of glottis and inhibition of respiration

Entry of vomitus into the trachea is prevented by

Dumping syndrome

This is a distressing syndrome consisting mainly of weakness, dizziness and sweating that develop in about two hours after meal in persons who have undergone gastrectomy or gastrojejunostomy (that bypasses stomach).

Hypoglycemia and Hypovolemia

Dumping syndrome occurs due to two causes:

Mucin secretion

The thin layer of surface mucus in the stomach and duodenum prevents the direct contact of acid and pepsin-containing fluid with surface epithelial cells.

Bicarbonate secretion

Surface epithelial cells in both the stomach and the duodenum secrete bicarbonate, which create an essentially pH-neutral microenvironment immediately adjacent to the cell surface.

Epithelial barrier

Intercellular tight junctions provide a barrier to the backdiffusion of H+

High mucosal blood flow

It rapidly carries away any acid that penetrates the cellular lining, and also provides oxygen, bicarbonate and nutrients to the epithelial cells.

Prostaglandins

Responsible for maintaining the gastric mucosal barrier

Peptic Ulcer

refers to an excavation of mucosa of duodenum or pyloric part of stomach.

Diminished ability of the gastroduodenal mucosal barrier and Excessive secretion of gastric Acid

Peptic ulcer can be caused by either of two ways.

Helicobacter Pylori

Factors that disturb mucosal barrier include bacterial Infection by

Zollinger- Ellison syndrome

Excess gastrin secretion , as seen in the ______________ in which patients are having gastrinomas (tumors that secrete gastrin)

motility of the small intestine

The main objective of the ________ is to thoroughly mix the chyme with the pancreatic, bile and intestinal juices.

Intestinal motility

propels chyme into the colon

285 cm

The length of small intestine is about three-fourths of the length of the whole of the GI tract.

2–4

It takes ____ hours for the chyme to traverse the small intestine.

muscularis externa

The ________ (outer longitudinal and inner circular muscles) is well developed in small intestine.

purely intrinsic

The basic electrical rhythm of intestinal smooth muscles is

small intestine

The frequency of slow wave (BER) is maximum in _________ that occurs regularly.

duodenum

The frequency is highest in _________ (about 15 per minute)

12

There are an average of __ BER cycles/min in the proximal jejunum

8

There are an average of __ BER cycles/min in the distal ileum.

BER

Peristaltic and other contractions are controlled by the

short segment of the intestine

A characteristic feature of slow waves of intestine is that they are localized to a

Migrating motor complexes (MMC)

Motility of the small intestine during interdigestive period, which includes:

mixing movements, propulsive movements, and movements of villi

Motility of the small intestine during digestive period (related to meals), which includes:

Peristaltic reflex, gastroileal reflex, and intestinointestinal reflex

Motility reflexes, which include the following:

MMC

sweep out the chyme remaining in the small intestine.

60- 90; 10

The MMCs occur every _____ minutes and last for about ____ minutes.

mixing movements

responsible for the proper mixing of chyme with digestive juices like pancreatic juice, bile juice and intestinal juice.

Segmentation contractions and pendular movements

The mixing movements of small intestine include the following:

Pendular movements

are small constrictive waves which sweep forward and backward or upward and downward in a pendular fashion, can be noticed only by close observation.

propulsive movements

involved in pushing the chyme from the small intestive towards the aboral end of intestine.

Peristaltic contractions and peristaltic rush

Propulsive movements includes

Law of intestine

The peristaltic waves always travel from the oral end towards the aboral end of the intestine.

Peristaltic rush

Refers to a very powerful peristaltic contraction, which occurs when intestinal mucosa is irritated intensely as in some infectious processes.

Peristaltic rush

This type of powerful contraction begins in duodenum, passes through entire length of small intestine and finally reaches the ileocecal valve within few minutes.

Peristaltic rush

they sweep the contents of intestine into the colon, thereby relieving the small intestine of irritant or excessive distension, as it occurs in cases of diarrhea.

alternate shortening and elongation

Movements of villi consist of _____________ of the villi is caused by contraction and relaxation of the muscle.

Villikinin

a hormone secreted from small intestinal mucosa is also believed to play an important role in increasing the movements of villi.

Gastroileal Reflex

Refers to a marked increase in the peristaltic contractions of ileum associated with relaxation of ileocecal sphincter, which occurs immediately after meals.

Gastroileal Reflex

This reflex is initiated by the distension of stomach by the food.

vagus

The peristaltic contractions are caused by reflex stimulation of

gastrin

the relaxation of ileocecal sphincter seems to be produced by the hormone

Intestinointestinal Reflex

Refers to the relaxation of smooth muscles of the rest of the small intestine in response to overdistension of one segment of the intestine

adynamic ileus or paralytic ileus

When the intestine is injured, excessively handled or mishandled, the smooth muscles of the intestine are inhibited This decreases the intestinal motility, sometimes even resulting in paralysis of the gut called

obstruction of small intestine

Severe abdominal cramps are experienced in localized _____

local ischemia

The intestinal wall produces severe cramping pain.

1-3

Large intestine contains mixture of chymes of many meals of _____ days

30-48

On average the total transit time of chyme of a meal through large intestine as recorded from passage of radiopaque markers is about _______ hours.

4 hours

The transit time of chyme In small intestine

6 hours

The transit time of chyme In ascending colon

8 hours

The transit time of chyme In transverse colon

12 hours

The transit time of chyme In descending and pelvic colons

2-3 days

The transit time of chyme From pelvic colon to rectum

fiber

Transit time depends on the _____ content of diet

storage of chyme

The major functions of colon are

2

Colon receives about __ liters of chyme per day from small intestine,

200 mL

Colon output

vagus nerve

Parasympathetic innervation to cecum, ascending, transverse and most part of descending colon comes via

pelvic nerves

innervation to the sigmoid colon, rectum, and anal canal comes via

intestinal cells near inner border of circular muscles and outer border of the circular muscle

There are two types of pace making (rhythm generating) cells in the colon.

intestinal cells near inner border of circular muscles

produce regular slow waves of high amplitude like that of gastric slow waves.

intestinal cells near outer border of the circular muscle

produces waves with low amplitude and high frequency oscillations

myenteric potential oscillations (MPO)

low amplitude and high frequency oscillations called

circular muscles

these muscles do not fire action potentials

longitudinal muscle

These muscles also exhibit myenteric potential oscillations MPO.

longitudinal muscle

sometimes fire action potentials at the peak of MPO that elicit contractions of the large intestine

haustral shuttling

similar to the segmentation contractions of small intestine

mixing and propulsion

The haustral contractions perform two main functions:

peristalsis

is a progressive contractile wave preceded by a wave of relaxation.

48

It can take up to ___ hours for the chyme to traverse the colon.