Pencernaan Faal

The Digestive System
Hardian
Department of Medical Physiology Diponegoro
Topik perkuliahan
 Alokasi waktu: 3 jam tatap muka

 Topik perkuliahan
1. Mastikasi dan menelan.
2. Peristaltik
3. Getah lambung
Hardian - Department of Medical Physiology Diponegoro

Digestive System: Overview
 The alimentary canal or gastrointestinal (GI) tract

digests and absorbs food
 Alimentary canal – mouth, pharynx, esophagus,
stomach, small intestine, and large intestine
 Accessory digestive organs – teeth, tongue,
gallbladder, salivary glands, liver, and pancreas

Digestive System: Overview

Figure 23.1
Digestive Process
 The GI tract is a “disassembly” line

 Nutrients become more available to the body in
each step
 There are six essential activities:

 Ingestion, propulsion, and mechanical digestion
 Chemical digestion, absorption, and defecation

Digestive Process
Figure 23.2
Gastrointestinal Tract Activities
 Ingestion – taking food into the digestive tract

 Mastication – Processes involved in food
preparation, including moving unchewed food onto
the grinding surface of the teeth, chewing, it, and
mixing it with saliva in preparation for swallowing

 Deglutition – swallowing
 Propulsion – swallowing and peristalsis
 Peristalsis – waves of contraction and relaxation of
muscles in the organ walls
 Digestion:
 Mechanical digestion – chewing, mixing, and
churning food
 Chemical digestion – catabolic breakdown of
food

 Absorption – movement of nutrients from the GI

tract to the blood or lymph
 Defecation – elimination of indigestible solid wastes

Mastication
 Process of preparing food for swallowing, moving

food onto the grinding surfaces of the teeth, chewing
and mixing it with saliva in preparation for
swallowing
 Saliva acts as a lubricating agent.
 Saliva contains amylase for digestion of
carbohydrates, and may contain lingual lipase for
digestion of fats.

Salivary Glands
 Produce and secrete saliva that:

 Cleanses the mouth
 Moistens and dissolves food chemicals
 Aids in bolus formation
 Contains amylase – enzymes that break down
starch
 Three pairs of extrinsic glands – parotid,
submandibular, and sublingual
 Intrinsic salivary glands (buccal glands) – scattered
throughout the oral mucosa

Salivary Glands
Figure 23.9a
Saliva: Source and Composition
 Secreted from serous and mucous cells of salivary

glands
 A 97-99.5% water, hypo-osmotic, slightly acidic
solution containing
 Electrolytes – Na+, K+, Cl–, PO42–, HCO3–
 Digestive enzyme – salivary amylase
 Proteins – mucin, lysozyme, defensins, and IgA
 Metabolic wastes – urea and uric acid
Control of Salivation
 Intrinsic glands keep the mouth moist

 Extrinsic salivary glands secrete serous, enzyme-
rich saliva in response to:
 Ingested food which stimulates chemoreceptors and
pressoreceptors
 The thought of food
 Strong sympathetic stimulation inhibits salivation

and results in dry mouth
Neural Control of Salivation

Digestive Processes in the Mouth
 Food is ingested
 Mechanical digestion begins (chewing)
 Propulsion is initiated by swallowing
 Salivary amylase begins chemical breakdown of
starch
 The pharynx and esophagus serve as conduits to
pass food from the mouth to the stomach

Deglutition (Swallowing)
 Involves the coordinated activity of the tongue, soft

palate, pharynx, esophagus and 22 separate muscle
groups
 Buccal phase – bolus is forced into the oropharynx
 Pharyngeal-esophageal phase – controlled by the
medulla and lower pons
 All routes except into the digestive tract are sealed
off
 Peristalsis moves food through the pharynx to the
esophagus
The swallowing reflex is coordinated by the medulla oblongata,
which stimulates the appropriate sequence of contraction and
relaxation in the participating skeletal muscle, sphincters, and
smooth muscle groups.
Deglutition (Swallowing)
Bolus of
food
Tongue
Uvula
Pharynx Bolus
Epiglottis
Epiglottis
Glottis
Trachea Esophagus Bolus
(a) Upper esophageal (b) Upper esophageal (c) Upper esophageal

sphincter contracted sphincter relaxed sphincter contracted
Relaxed Relaxed muscles

muscles Circular muscles
contract, constricting
passageway and pushing Gastroesophageal
Bolus of food bolus down sphincter open
Longitudinal muscles
contract, shortening
passageway ahead of bolus
Gastroesophageal
sphincter closed Stomach
(d) (e)
Stomach
 Chemical
breakdown
of proteins
begins and
food is
converted to
chyme

Glands of the Stomach Fundus and Body
 Gastric glands of the fundus and body have a variety

of secretory cells
 Mucous neck cells – secrete acid mucus
 Parietal cells – secrete HCl and intrinsic factor

Glands of the Stomach Fundus and Body
 Chief cells – produce pepsinogen

 Pepsinogen is activated to pepsin by:
 HCl in the stomach
 Pepsin itself via a positive feedback
mechanism
 Enteroendocrine cells – secrete gastrin, histamine,
endorphins, serotonin, cholecystokinin (CCK), and
somatostatin into the lamina propria
Stomach Lining
 The stomach is exposed to the harshest conditions in

the digestive tract
 To keep from digesting itself, the stomach has a
mucosal barrier with:
 A thick coat of bicarbonate-rich mucus on the
stomach wall
 Epithelial cells that are joined by tight junctions
 Gastric glands that have cells impermeable to HCl
 Damaged epithelial cells are quickly replaced

Regulation of Gastric Secretion
 Neural and hormonal mechanisms regulate the

release of gastric juice
 Stimulatory and inhibitory events occur in three
phases
 Cephalic (reflex) phase: prior to food entry
 Gastric phase: once food enters the stomach
 Intestinal phase: as partially digested food enters
the duodenum
Cephalic Phase
 Excitatory events include:

 Sight or thought of food
 Stimulation of taste or smell receptors
 Inhibitory events include:

 Loss of appetite or depression
 Decrease in stimulation of the parasympathetic
division

The Phases of Gastric Secretion

Gastric Phase
 Excitatory events include:

 Stomach distension
 Activation of stretch receptors (neural activation)
 Activation of chemoreceptors by peptides, caffeine,
and rising pH
 Release of gastrin to the blood
 Inhibitory events include:
 A pH lower than 2
 Emotional upset that overrides the parasympathetic
division

Intestinal Phase
 Excitatory phase – low pH; partially digested food

enters the duodenum and encourages gastric gland
activity
 Inhibitory phase – distension of duodenum, presence
of fatty, acidic, or hypertonic chyme, and/or irritants
in the duodenum
 Initiates inhibition of local reflexes and vagal nuclei
 Closes the pyloric sphincter
 Releases enterogastrones that inhibit gastric
secretion

Release of Gastric Juice

Regulation and Mechanism of HCl Secretion
 HCl secretion is stimulated by ACh, histamine, and

gastrin through second-messenger systems
 Release of hydrochloric acid:
 Is low if only one ligand binds to parietal cells
 Is high if all three ligands bind to parietal cells
 Antihistamines block H2 receptors and decrease HCl

release

Regulation and Mechanism of HCl Secretion

Response of the Stomach to Filling
 Stomach pressure remains constant until about 1L of
food is ingested
 Relative unchanging pressure results from reflex-
mediated relaxation and plasticity
 Reflex-mediated events include:
 Receptive relaxation – as food travels in the
esophagus, stomach muscles relax
 Adaptive relaxation – the stomach dilates in
response to gastric filling
 Plasticity – intrinsic ability of smooth muscle to
exhibit the stress-relaxation response
Gastric Contractile Activity
 Peristaltic waves move toward the pylorus at the rate

of 3 per minute
 This basic electrical rhythm (BER) is initiated by
pacemaker cells (cells of Cajal)
 Most vigorous peristalsis and mixing occurs near the
pylorus
 Chyme is either:
 Delivered in small amounts to the duodenum or
 Forced backward into the stomach for further
mixing
Gastric Contractile Activity

Regulation of Gastric Emptying
 Gastric emptying is regulated by:

 The neural enterogastric reflex
 Hormonal (enterogastrone) mechanisms
 These mechanisms inhibit gastric secretion and

duodenal filling
 Carbohydrate-rich chyme quickly moves through the
duodenum
 Fat-laden chyme is digested more slowly causing
food to remain in the stomach longer
Regulation of Gastric Emptying
Figure 23.19
Motion of Small Intestine
 The most common motion of the small intestine is

segmentation
 It is initiated by intrinsic pacemaker cells (Cajal
cells)
 Moves contents steadily toward the ileocecal valve
 After nutrients have been absorbed:
 Peristalsis begins with each wave starting distal to
the previous
 Meal remnants, bacteria, mucosal cells, and debris
are moved into the large intestine
Control of intestinal motion
 Local enteric neurons of the GI tract coordinate

intestinal motility
 Cholinergic neurons cause:
 Contraction and shortening of the circular muscle
layer
 Shortening of longitudinal muscle
 Distension of the intestine

Intestinal Movements
 Chyme arrives in duodenum
 Weak peristaltic contractions move it slowly

toward jejunum:
 Myenteric reflexes
 Not under CNS control
 Parasympathetic stimulation accelerates local

peristalsis and segmentation
Intestinal Movements
 The Gastroenteric Reflex

 Stimulates motility and secretion:
 Along entire small intestine
 The Gastroileal Reflex
 Triggers relaxation of ileocecal valve
 Allows materials to pass from small intestine into
large intestine

The Movement of Digestive Materials
 By muscular layers of digestive tract

 Consist of visceral smooth muscle tissue
 Along digestive tract:
 Has rhythmic cycles of activity
 Controlled by pacesetter cells
 Cells undergo spontaneous depolarization:
 Triggering wave of contraction through entire
muscular sheet

 Pacesetter Cells
 Located in muscularis mucosae and muscularis
externa:
 Surrounding lumen of digestive tract
 Peristalsis
 Consists of waves of muscular contractions
 Moves a bolus along the length of the digestive
tract

 Peristaltic Motion
1. Circular muscles contract behind bolus:
 While circular muscles ahead of bolus relax
2. Longitudinal muscles ahead of bolus contract:
 Shortening adjacent segments
3. Wave of contraction in circular muscles:
 Forces bolus forward

 Segmentation
 Cycles of contraction:
 Churn and fragment the bolus
 Mix contents with intestinal secretions
 Does not follow a set pattern:
 Does not push materials in any one direction

Peristaltics

Peristaltics

Peristalsis and Segmentation
Figure 23.3
Peristaltic and segmentation Initial State
Longitudinal
muscle
Circular
muscle From To
mouth anus
Contraction of circular muscles behind

bolus
Contraction
Contraction of longitudinal muscles

ahead of bolus
Contraction
Contraction
Contraction in circular muscle layer

forces bolus forward
Figure 23.3
The Small Intestine
 Duodenal Glands
 Also called submucosal glands or Brunner glands
 Produce copious quantities of mucus:
 When chyme arrives from stomach

Intestinal Secretions
 Watery intestinal juice

 1.8 liters per day enter intestinal lumen
 Moisten chyme
 Assist in buffering acids
 Keep digestive enzymes and products of
digestion in solution

Activities of Major Digestive Tract Hormones

Small Intestine: Histology of the Wall
 The epithelium of the mucosa is made up of:

 Absorptive cells and goblet cells
 Enteroendocrine cells
 Interspersed T cells called intraepithelial
lymphocytes (IELs)
 IELs immediately release cytokines upon
encountering Ag

Intestinal Juice
 Secreted by intestinal glands in response to

distension or irritation of the mucosa
 Slightly alkaline and isotonic with blood plasma
 Largely water, enzyme-poor, but contains mucus

EKSOKRIN HEPAR DAN
PANKREAS

Liver
 The largest gland in the body

 Superficially has four lobes – right, left, caudate,
and quadrate
 The falciform ligament:
 Separates the right and left lobes anteriorly
 Suspends the liver from the diaphragm and anterior
abdominal wall

Liver
 Hepatocytes’ functions include:

 Production of bile
 Processing bloodborne nutrients
 Storage of fat-soluble vitamins
 Detoxification
 Secreted bile flows between hepatocytes toward the

bile ducts in the portal triads
Microscopic Anatomy of the Liver
Figure 23.24c, d
Composition of Bile
 A yellow-green, alkaline solution containing bile

salts, bile pigments, cholesterol, neutral fats,
phospholipids, and electrolytes
 Bile salts are cholesterol derivatives that:
 Emulsify fat
 Facilitate fat and cholesterol absorption
 Help solubilize cholesterol
 Enterohepatic circulation recycles bile salts
 The chief bile pigment is bilirubin, a waste product
of heme
Regulation of Bile Release
 Acidic, fatty chyme causes the duodenum to release:

 Cholecystokinin (CCK) and secretin into the
bloodstream
 Bile salts and secretin transported in blood stimulate

the liver to produce bile
 Vagal stimulation causes weak contractions of the
gallbladder

 Cholecystokinin causes:
 The gallbladder to contract
 The hepatopancreatic sphincter to relax
 As a result, bile enters the duodenum

Figure 23.25
Pancreas
 Location
 Lies deep to the greater curvature of the stomach
 The head is encircled by the duodenum and the tail
abuts the spleen

Pancreas
 Exocrine function
 Secretes pancreatic juice which breaks down all
categories of foodstuff
 Acini (clusters of secretory cells) contain zymogen
granules with digestive enzymes
 The pancreas also has an endocrine function –

release of insulin and glucagon

Acinus of the Pancreas
Figure 23.26a
Composition and Function of Pancreatic Juice
 Water solution of enzymes and electrolytes (primarily

HCO3–)
 Neutralizes acid chyme
 Provides optimal environment for pancreatic enzymes
 Enzymes are released in inactive form and activated in
the duodenum

Composition and Function of Pancreatic Juice
 Examples include
 Trypsinogen is activated to trypsin by
enteropeptidase (enterokinase)
 Procarboxypeptidase is activated to carboxypeptidase
 Active enzymes secreted
 Amylase, lipases, and nucleases
 These enzymes require ions or bile for optimal
activity

Regulation of Pancreatic Secretion
 Secretin and CCK are released when fatty or acidic

chyme enters the duodenum
 CCK and secretin enter the bloodstream
 Upon reaching the pancreas:
 CCK induces the secretion of enzyme-rich pancreatic
juice
 Secretin causes secretion of bicarbonate-rich
pancreatic juice
 Vagal stimulation also causes release of pancreatic juice

Regulation of Pancreatic Secretion
Figure 23.28
Digestion in the Stomach
 The stomach:
 Holds ingested food
 Degrades this food both physically and chemically
 Delivers chyme to the small intestine
 Enzymatically digests proteins with pepsin
 Secretes intrinsic factor required for absorption of
vitamin B12

Digestion in the Small Intestine
 As chyme enters the duodenum:

 Carbohydrates and proteins are only partially
digested
 No fat digestion has taken place

Digestion in the Small Intestine
 Digestion continues in the small intestine

 Chyme is released slowly into the duodenum
 Because it is hypertonic and has low pH, mixing is
required for proper digestion
 Required substances needed are supplied by the
liver
 Virtually all nutrient absorption takes place in the
small intestine
Control of Motility
 Other impulses relax the circular muscle

 The gastroileal reflex and gastrin:
 Relax the ileocecal sphincter
 Allow chyme to pass into the large intestine

Large Intestine
 Is subdivided into the cecum, appendix, colon,

rectum, and anal canal
 The saclike cecum:
 Lies below the ileocecal valve in the right iliac
fossa
 Contains a wormlike vermiform appendix

Large Intestine
Figure 23.29a
Large Intestine: Microscopic Anatomy
 Colon mucosa is simple columnar epithelium except

in the anal canal
 Has numerous deep crypts lined with goblet cells
 Anal canal mucosa is stratified squamous epithelium
 Anal sinuses exude mucus and compress feces
 Superficial venous plexuses are associated with the
anal canal
 Inflammation of these veins results in itchy
varicosities called hemorrhoids
Structure of the Anal Canal
Figure 23.29b
Bacterial Flora
 The bacterial flora of the large intestine consist of:

 Bacteria surviving the small intestine that enter the cecum
and
 Those entering via the anus
 These bacteria:
 Colonize the colon
 Ferment indigestible carbohydrates
 Release irritating acids and gases (flatus)
 Synthesize B complex vitamins and vitamin K
Functions of the Large Intestine
 Other than digestion of enteric bacteria, no further

digestion takes place
 Vitamins, water, and electrolytes are reclaimed
 Its major function is propulsion of fecal material
toward the anus
 Though essential for comfort, the colon is not
essential for life

Motility of the Large Intestine
 Haustral contractions
 Slow segmenting movements that move the
contents of the colon
 Haustra sequentially contract as they are stimulated
by distension
 Presence of food in the stomach:

 Activates the gastrocolic reflex
 Initiates peristalsis that forces contents toward the
rectum

Pencernaan Faal

Uploaded by

Copyright:

Available Formats

Pencernaan Faal

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Pencernaan Faal

Uploaded by

Copyright:

Available Formats

The Digestive System

 Alokasi waktu: 3 jam tatap muka

Hardian - Department of Medical Physiology Diponegoro

 The alimentary canal or gastrointestinal (GI) tract

Hardian - Department of Medical Physiology Diponegoro

Hardian - Department of Medical Physiology Diponegoro

 The GI tract is a “disassembly” line

 There are six essential activities:

Hardian - Department of Medical Physiology Diponegoro

 Ingestion – taking food into the digestive tract

Hardian - Department of Medical Physiology Diponegoro

Hardian - Department of Medical Physiology Diponegoro

 Absorption – movement of nutrients from the GI

Hardian - Department of Medical Physiology Diponegoro

 Process of preparing food for swallowing, moving

Hardian - Department of Medical Physiology Diponegoro

 Produce and secrete saliva that:

Hardian - Department of Medical Physiology Diponegoro

 Secreted from serous and mucous cells of salivary

 Intrinsic glands keep the mouth moist

 Strong sympathetic stimulation inhibits salivation

Hardian - Department of Medical Physiology Diponegoro

Hardian - Department of Medical Physiology Diponegoro

 Involves the coordinated activity of the tongue, soft

Trachea Esophagus Bolus

(a) Upper esophageal (b) Upper esophageal (c) Upper esophageal

Relaxed Relaxed muscles

Hardian - Department of Medical Physiology Diponegoro

 Gastric glands of the fundus and body have a variety

Hardian - Department of Medical Physiology Diponegoro

 Chief cells – produce pepsinogen

 The stomach is exposed to the harshest conditions in

 Damaged epithelial cells are quickly replaced

 Neural and hormonal mechanisms regulate the

 Excitatory events include:

 Inhibitory events include:

Hardian - Department of Medical Physiology Diponegoro

Hardian - Department of Medical Physiology Diponegoro

 Excitatory events include:

Hardian - Department of Medical Physiology Diponegoro

 Excitatory phase – low pH; partially digested food

Hardian - Department of Medical Physiology Diponegoro

Hardian - Department of Medical Physiology Diponegoro

 HCl secretion is stimulated by ACh, histamine, and

 Antihistamines block H2 receptors and decrease HCl

Hardian - Department of Medical Physiology Diponegoro

Hardian - Department of Medical Physiology Diponegoro

 Peristaltic waves move toward the pylorus at the rate

Hardian - Department of Medical Physiology Diponegoro

 Gastric emptying is regulated by:

 These mechanisms inhibit gastric secretion and

 The most common motion of the small intestine is

 Local enteric neurons of the GI tract coordinate

Hardian - Department of Medical Physiology Diponegoro

 Weak peristaltic contractions move it slowly

 Not under CNS control

 Parasympathetic stimulation accelerates local

 The Gastroenteric Reflex