kuliah 1. fungsi mekanik sistem pencernaan
TRANSCRIPT
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
1/29
FUNGSI MEKANIK
SISTEM PENCERNAAN
Rahmatina B. HermanBagian Fisiologi
Fakultas Kedokteran Universitas Andalas
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
2/29
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
3/29
Introduction
The primary function of the digestive system is totransfer nutrients, water and electrolytesfrom the
ingested food into the bodys internal environment
The ingested food is essential as:
- an energy source from which the cells can
generate ATP to carry out their particular
energy-dependent activities
- a source of building supplies for the renewal
and addition of body tissues
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
4/29
The digestive system performs:
Introduction..
1. Motility along gastrointestinal tract
2. Secretionof digestive juices3. Digestion of food
4. Absorption the small absorbable units
Excretionof the waste materials
Regulationof digestive function through neuralreflexes and hormonal pathways
Protectionagainst any damages
Four basic digestive processes:
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
5/29
General Principle of Gastrointestinal Motility
Characteristics of gastrointestinal wall:Layers of the wall (inward):
- Serosa: continues onto mesentery
- Muscularis: smooth muscles> longitudinal layer: outer
> circular layer: inner
- Submucous: smooth muscles
> muscularis mucosae, usually longitudinal- Mucosa
Each layer functions as syncytium
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
6/29
General Principle of Gastrointestinal Motility..
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
7/29Organization of the intestine wall into functional layers
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
8/29
Basic Electrical Activity
Slow Waves:- undulating changes in the resting membrane
potential (-50 - 60 mVolts)
- intensity: 515 mVolts
- frequency: 3-12/min (3 in the body of the stomach,
12 in the duodenum, 8-9 in the terminal ileum)
- might be caused by a slow undulation of the
sodium-potassium pumping activities- rarely cause muscle contraction
- Basic Electrical Rhythm (BER) control the
appearance of intermittent peristaltic
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
9/29
Basic Electrical Activity..
Spike Potential:- is true action potential
- generated at the peaks of the slow waves, when
the peaks rise above - 40 mVolts
- the depolarizing portion of each spike potential is
due to Ca++influx through Ca-Na channel and
repolarizing portion is due to K+ efflux
- stimulation by stretch, acetylcholine,parasympathetics, and specific GI hormones
- rate: 1-10/minute
- duration: 10-20 msecond
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
10/29
Basic Electrical Activity..
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
11/29
Contraction of GI Smooth Muscles
Rhythmic:- during the spike potentials generated at the
peaks of the slow waves, the large quantities of
Ca++
enter the fibers through Ca-Na channel- Ca++acting through a calmodulin control
mechanism, activate the myosin filaments
attractive forces between the myosin and theactin filaments muscle contraction
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
12/29
Contraction of GI Smooth Muscles..
Tonic:- is continuous contraction, often lasting several
minutes or even several hours
- not associated with the BER
- often decreases or increases in intensity, but continues
- might be caused by:
> repetitive spike potential
> hormones or other factors that bring about
continuous depolarization of the smooth muscle
membrane, without causing action potentials
> continuous Ca++influx, bought about in ways not
associated with changes in the membrane potential
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
13/29
Basic electrical rhythm (BER) relation to muscle contraction
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
14/29
Gastrointestinal Motility
Propulsivemovement- The basic propulsive movement is peristalsis
- Reflex response through myenteric plexus that isinitiated by distention peristaltic reflexor
myenteric reflex- Constriction at the upper of the stretch and
relaxation (receptive relaxation) at the lower of thestretch
- The wave contraction moves in an oral-to-analdirection
- The peristaltic reflex plus the anal-ward direction ofthe peristalsis movement is called the law of gut
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
15/29
Peristalsis
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
16/29
Gastrointestinal Motility..
Mixing:- The reflex initiated by stretching of the gut wall
- Quite different in in different parts of the gut
- Segmentation contraction and relaxation in arhythmic pattern
- Local constriction occurs in every few centimeters
- The next constriction occurs at the next site, so that
the chyme is divided and push back and forth whichmixes the luminal content
- Mixing process is also performed by peristalsis and
sphincter activities
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
17/29
Migrating Motor Complex
Modification of the pattern of electrical and motoractivity in GI smooth muscle during fasting orbetween periods of digestion
The cycles of motor activity migrate from corpus of
stomach to the distal ileumThey migrate slowly at a rate of 6-12 cm/ minute andoccur at intervals 1.5-2 hours
Each wave end within 6-10 minutes
Function: to clear the stomach and small intestines ofluminal contents in preparation for the next meal
Immediately stopped by ingestion of food and returnto peristalsis
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
18/29
Mastication (Chewing)
ReflexRhythmic: by motor branch of the 5thcranial nerve
Important for digestion of all foods, especially:
- cellulose membrane of fruits and vegetables
- grinding the food to a very fine particulate consistency- increases the total surface area of food exposed to the
intestinal secretion
- increases the ease of enzymatic activities- prevent excoriation of the GIT
- increases the ease with which food is emptied from the
stomach into the small intestine and succeeding
segments
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
19/29
Swallowing (Deglutition)
A. Voluntary stage:squeezed into pharynx by pressure of tongue
B. Pharyngeal stage (involuntary): reflex- soft palate is pulled upward to close posterior nares- form a palatopharyngeal slit by palatopharyngeal folds- prevent passage of food into trachea by epiglottis and
vocal cords- pharyngoesophageal sphincter relaxes- the food is propelled into esophagus
C. Esophageal stage (involuntary)peristaltic:
primary peristalsis: continuation from pharynx secondary peristalsis: due to distention of esophagus
The swallowing center inhibits the respiratory center
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
20/29
Swallowing (Deglutition)..
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
21/29
Gastroesophageal Sphincter
2-5 cm above the junction of esophagus-stomach
Normally remains tonically constricted
Prevention of stomach content reflux into esophagus
Additional prevention of reflux by valve-like closure of
the distal end of the esophagus- valve-like mechanism of the short portion of esophagus
that lies immediately beneath diaphragm beforereaching stomach
- increased intra-abdominal pressure caves the esophagusinward at this point at the same time that this pressureincrease the intra-gastric pressure
- the valve-like closure of the lower esophagus preventsfrom forcing stomach contents into esophagus (during
walking, coughing, or breathing hard)
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
22/29
Motor Functions of The Stomach
A.Storage of large quantities of food- As food enters the stomach, it forms concentric circles- Vagovagal reflex: reduces the tone in the muscular wall of
the body of the stomach
B. Mixing the food with the gastric secretions until it forms
a semifluid mixture- peristaltic constrictor rings- propulsive movement toward pylorus- retropulsion
C. Emptying of the stomach- role of antrum: constriction movement- role of pylorus (pyloric sphincter): pyloric pump
Hunger contractions: hunger pang- usually do not begin until 12-24 hours after the last ingestion
- reach greatest intensity in 3-4 days and the gradually weaken
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
23/29
Motor Functions of The Stomach..
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
24/29
Regulation of Stomach Emptying
The weak gastric factors that promote emptying:- Effect of gastric food volume on rate of emptying
> vagovagal and myenteric reflexes
- Effect of hormone gastrin
The powerful duodenal factors that inhibit emptying:
- Enterogastric nervous reflexes from duodenum> degree of distention of duodenum
> especially sensitive to the presence of irritant and acids
> also breakdown products of protein digestion
> degree of osmolality
- Hormonal feedback from duodenumcholecystokinin, secretin, gastric inhibitory peptide
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
25/29
Motor Function of The Small Intestine
A.Mixing contractions (segmentation contractions)- BER with background excitation by the ENS
B. Propulsive movements (peristalsis)- increased due to:
distention gastroenteric reflexes through the ENS hormone gastrin, cholecystokinin, insulin, serotonin irritation peristaltic rush diarrhea
- decreased due to: hormone secretin and glucagon peristalsis in the fasting: migrating motor complex
C. Movements caused by the muscularis mucosa and
muscle fibers of the villi
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
26/29
Motor Function of The Small Intestine..
Segmentation movement of the small intestine
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
27/29
Motor Function of The Colon
A. Mixing movements - haustrationsB. Propulsive movementsmass movements
- slow analward movement of haustral contractions- mass movement : modification of peristalsis initiated
by: gastrocolic and duodenocolic reflexes
irritation and distention
parasympathetic stimulation
C. Defecation :- intrinsic defecation reflex- parasympathetic defecation reflex- internal anal sphincter
- external anal sphincter (voluntary)
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
28/29
Motor Function of The Colon..
Defecation reflex
-
7/25/2019 Kuliah 1. Fungsi Mekanik Sistem Pencernaan
29/29