Download Digestive System

The Digestive System
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Subdivisions of the Abdomen
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Commonly used abdominal incisions:
Any incisions or scars present? Presence of an incision may
speculate what the surgeon might have done.
A.Subcostal incision on the right---------------------open bladder
surgery (cholecystectomy).
B.Barely visible round scars around the umbilicus may suggest
closed or laparoscopic cholecystectomy
C.Left subcostal incision----------------to approach the spleen
D.Suprapubic incisions is used to access pelvic organs---------------(C-section,hysterectomy)
E.An oblique incision approximately at the meeting point of
umbilical region and ® inguinal region is frequently used for
appendeceptomy.
F.A scar in one or both inguinal region may be indicative of
previous hernia surgery.
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Digestive sytem:
-The organs that are involved in breaking down of food into
molecules that can pass through the walls of the digestive tract
and can be taken up by the cells.
Digestion process are in two stages:
- mechanical digestion
-Chemical digestion
-G I tract or Alimentary canal:
-A continuous tube the begins at the mouth and ends at the anus.
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Digestion
• Processing of food
• -2 Types of processing:
– Mechanical (physical)
•
•
•
•
•
Chew
Tear
Grind
Mash
Mix
– Chemical
• Catabolic reactions
• Enzymatic hydrolysis
– Carbohydrate
– Protein
– Lipid
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Digestion
• Phases
– Ingestion
– Movement
– Digestion
– Absorption
– Further digestion
**chyme partially digested food(a thick,
heavy,creamlike liquid).***
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Digestive System Organization
• Gastrointestinal (Gl) tract (Alimentary canal)
– Tube within a tube
– Direct link/path between organs
– Structures
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Mouth
Oral Cavity
Pharynx
Esophagus
Stomach
Duodenum
Jejenum
Ileum
Cecum
Ascending colon
Transverse colon
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Digestive System Organization
•
•
•
•
Descending colon
Sigmoid colon
Rectum
Anus
• Accessory structures
– Not in tube path
– Organs
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Teeth
Tongue
Salivary glands
Liver
Gall bladder
Pancreas
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Anatomy of the Mouth and
Throat
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Human Deciduous and
Permanent Teeth
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Dorsal Surface of the Tongue
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Tongue…
Figure 15—2. Surface of the tongue on the region close to
its V-shaped boundary, between the anterior and posterior
portions. Note the lymphoid nodules (lingual tonsil), glands,
and papillae.
The Major Salivary Glands
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Deglutition (swallowing)
• Sequence:
– Voluntary stage
• Push food to back of
mouth
– Pharyngeal stage
• Raise
– Soft palate
– Larynx + hyoid
– Tongue to soft palate
– Esophageal stage
• Contract pharyngeal
muscles
• Open esophagus
• Start peristalsis
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Deglutition (swallowing)
• Control
– Nerves
• Glossopharyngeal
• Vagus
• Accessory
– Brain stem
• Deglutition center
– Medulla oblongata
– Pons
– Disorders
• Dysphagia
• Aphagia
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Esophagus
• Surrounded by
– SNS plexus
– Blood vessels
• Functions
– Secrete mucous
– Transport food
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Peristalsis and Segmentation
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2 types of muscular action occur in the small intestines:
**Segmentation and peristalsis.**
Segmentation is the muscle action that mixes chyme and
digestive juices, like a cement mixer.
The second action is peristalsis, moving undigested food
remains toward the large intestine
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Esophagus
• Sphincters:
– Upper (pharyngoesophageal sphincter)
– Lower (LES)
• Abnormalities ??
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Stomach
• Usually “J” shaped
• Left side, anterior to the spleen
• Mucous membrane
– G cells – make gastrin
– Goblet cells – make mucous
– Gastric pit – Oxyntic gland – Parietal cells – Make
HCl
– Chief cells – Zymogenic cells
• Pepsin
• Gastric lipase
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Anatomy of the Stomach
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Stomach
• 3 muscle layers
– Oblique
– Circular
– Longitudinal
• Regions
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–
–
–
Cardiac sphincter
Fundus
Antrum (pylorus)
Pyloric sphincter
• Vascular
• Inner surface thrown into
folds – Rugae
• Contains enzymes that work
best at pH 1-2
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Stomach
• Functions
– Mix food
– Reservoir
– Start digestion of
– Absorbs
• Alcohol
• Water
• Protein
• Nucleic acids
– Activates some enzymes
– Destroy some bacteria
– Makes intrinsic factor – B
12 absorption.
• The stomach’s activity is
controlled by the PNS***
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1.The deep folds of the stomach wall that allow for size
changes of the stomach are called?
a.Rugby
b.Sphincter
c.Rugae
d.Glottal folds
2- the stomach’s activity is controlled by the _______ nervous
system.
3- the final “door” of the stomach that needs to open for chyme
to travel to the small intestine is located at the end of the ?
a. Fundus
f. ????
b. Epiglottis
c. Adventitia
d. Serosa
e. Cardiac region
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Small Intestine
• Extends from pyloric
sphincter  ileocecal
valve
• Regions
– Duodenum
– Jejunum
– Ileum
• Movements
– Segmentation
– Peristalsis
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The small intestines is small in diametre,not in length.
Beginning from the pyloric sphincter,the small intestines is
also the longest section of the alimentary canal ,with length of
up to 20 feet(up to 6 metres).
In small intestine, almost 80% of the absorption of usable
nutrients takes place when chyme comes in contact with the
mucosal walls.
Simple sugars, Aa, fatty acids, vitamins and water are all
absorbed here.*****
Some of the remaining 20% was already absorbed in the
stomach, with the rest being absorbed in the large intestines.
Any residue that cannot be utilised is sent on to the large
intestine for removal from the body as fecal matter(feces).
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Small Intestine
• Histology features
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–
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–
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Intestinal glands – Intestinal enzymes
Duodenal glands – Alkaline mucous
Paneth cells – Lysozyme
Microvilli
Lacteals
Plica circularis
Smooth muscle
Lymphatic tissue – GALT
Vascular
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Small Intestine
• Absorbs
–
–
–
–
–
80% ingested water
Electrolytes
Vitamins
Minerals
Carbonates
– Lipids
•
•
•
•
Monoglycerides
Fatty acids
Micelles
Chylomicrons
• Active/facilitated
transport
• Monosaccharides
– Proteins
• Di-/tripeptides
• Amino acids
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Structure of the Villi in the
Small Intestine
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The structure of the wall of the small intestine possesses
circular folds called plicae circulares and finger-like
protrusions into the lumen called villi.
The villi which posses microscopic extensions known as
microvilli. These villi are tightly packed, giving the mucosa
velvety texture and appearance.
The purpose of the microvilli ,villi and circular folds is to
provide an incredible increase in the surface area of the small
intestine.
Each villus contains a network of capillaries and a lymphatic
capillary called LACTEAL.
Intestinal glands are located between villi.
The capillaries absorb and transport sugars the result of
carbohydrate digestion) and amino acids (the result of protein
digestion) to the liver for further processing before they are
sent throughout the body.
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Glycerol and fatty acids(obtained from the digestion of fat),
are absorbed by the villi and converted into a lipoprotein
that travels on to the lacteal, where it is now a white, milky
substance called chyle.
Chyle goes directly into the blood stream via the left
subclavian vein for distribution throughout the body.
The walls of the small intestine secrete several enzymes
important for the final stages of chemical digestion and two
hormones that control the activity of the pancreas,
gallbladder and stomach.
The pancreas is stimulated to secrete as a result of the
hormone secretin that is produced by the small intestines.
gall bladder activity is stimulated by the hormone
cholecystokinin,which is produced by the small intestines.
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At the duodenum, additional secretions are added from the
pancreas and gall bladder.
The pancreas provides pancreatic juices, and the gall bladder
produces bile. Bile emulsifies fat, (that is it makes fat able to
disperse in water making the fat easier to breakdown.)
Pancreatic juice contains enzymes and sodium bicarbonate,
which neutralises the acidic chyme.
The small intestine also produces digestive enzymes that are
needed to complete chemical digestion.
These enzymes and (mucus) are produced by exocrine cells.
lactase, maltase,and sucrase are needed for the digestion of
double sugars such as disaccharides that are contained in
starches.
Peptidases--- needed to digest portions of the protein
structure called peptides.
Intestinal lipase—for digestion of certain fats.
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Hormone
secreting organ
action
Gastrin
stomach
stimulates release
gj.
Secretin
duodenum
stimulates release of bicarbonate and water from pancreas
and bile from liver.
Cck
duodenum
stimulates digestive enzyme release from the pancreas and
bile release from the gall bladder.
*** it is important to note that the secretion of these
substances is mainly due to the presence of chyme in the
small intestines.****
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Small Intestine
• Secretes digestive
enzymes
– Peptidases
• Amino• Di• Tri-
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–
–
–
Sucrases
Maltase
Lactase
Saccharidases
• Di• Tri-
– Lipase
– Nucleases
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Small Intestine
• Control
• Requires pancreatic
enzymes & bile to
complete digestion
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Large Intestine
• Extends from ileocecal valve to anus
• Regions
– Cecum – Appendix
– Colon
• Ascending
• Transverse
• Descending
– Rectum
– Anal canal
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The large intestines is responsible for :
-water reabsorption
-absorption of vitamins produced by normal bacteria in the large
intestines
-Packaging and compacting waste products for elimination
from the body.
-** because there are no villi in the large intestines, little nutient
absorption occurs here.***
-Approximately 1.5metres long 7.5 cm in diametre, large
intestine is divided into 3 main regions; the cecum, colon, and
rectum.
-A pouch-shaped structure, the cecum recieves any undigested
food ,such as cellulose and water from the ileum of the S.I.
-The infamous appendix is attached to the cecum, about 9cm
long, the appendix is a slender, hollow dead-end tube lined with
lymphatic tissue.
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Because it possesses lymphatic tissue it helps to fight
infection ,and also discovered to replenish the beneficial
bacteria in our digestive tract.
Appendicitis??
Peristalsis continues in the large intestine but at a slower
rate. As these slower, intermittent waves move fecal matter
toward the rectum, water is removed, turning the feces from
a watery soup to a semisolid mass.
Some of the water (used in digestion) and electrolytes are
reabsorbed by the cecum and asc. Colon. Although this is a
relatively small amount of water reabsorbed, it is crucial in
maintaining the proper fluid balance in the body.
As the rectum fills up with feces,a defecation reflex occurs,
which causes rectal muscles to contract and anal muscles to
relax.
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Defecation is controlled by a combination of voluntary and
Involuntary reflexes.
2 sphincters sorround the anal opening, IAS AND EAS. When
feces enters the rectum the wall stretches, triggering the
defecation reflex.
Diarrhea ----- if fecal matter moves through the large
intestines too rapidly, not enough water is adequately
reabsorbed.
Constipation----- if the fecal matter remains too long in the
large intestines, too much water is removed. Feces hardens.
Functions of the large intestines:
I bacteria aids further break down of indigestible material.
II produce B- complex vitamins
III produces most of the vitamin k
****bacteria outside the intestinal wall in the blood stream,
could be fatal***
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Anatomy of the Large Intestine
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Large Intestine
• Histology
– No villi
– No permanent circular folds
– Smooth muscle
• Taeniae coli
• Haustra
– Epiploic appendages
– Otherwise like rest of Gl tract
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Large Intestine
• Functions
– Mechanical digestion
• Haustral churning
• Peristalsis
– Chemical digestion –
Bacterial digestion
• Ferment carbohydrates
• Protein/amino acid
breakdown
– Absorbs
•More water
•Vitamins
–B
–K
– Concentrate/eliminate
wastes
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Feces Formation and Defecation
• Chyme dehydrated to
form feces
• Feces composition
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–
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Water
Inorganic salts
Epithelial cells
Bacteria
Byproducts of digestion
• Control
– Parasympathetic
– Voluntary
• Defecation
– Peristalsis pushes feces
into rectum
– Rectal walls stretch
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Liver
• Location
– R. Hypochondrium
– Epigastric region
• 4 Lobes
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–
–
–
Left
Quadrate
Caudate
Right
• Each lobe has lobules – Contains hepatocytes –
Surround sinusoids – Feed into central vein
• Weighing approx.1.5kg(3.3 pounds).
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Liver
• Functions
– Makes bile
• Detergent – emulsifies
fats
• Release promoted by:
– Vagus n.
– CCK
– Secretin
• Contains
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–
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Water
Bile salts
Bile pigments
Electrolytes
Cholesterol
Lecithin
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Liver
– Detoxifies/removes
• Drugs
• Alcohol
– Stores
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•
•
•
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–
–
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Glycogen
Vitamins (A, D, E, K)
Fe and other minerals
Cholesterol
Activates vitamin D
Fetal RBC production
Phagocytosis
Metabolizes absorbed food
molecules
• Carbohydrates
• Proteins
• Lipids
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Liver
• Dual blood supply
– Hepatic portal vein
• Direct input from small
intestine
– Hepatic artery/vein
• Direct links to heart
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The liver is the largest glandular organ in the body and the
largest organ in the abdomino -pelvic cavity.
This organ performs many functions that are vital for
survival.
The hepatic portal vein (carrying blood full of the end
products of digestion ) and the hepatic artery (providing
oxygen rich blood).
This blood flows past the hepatocytes(liver cells),which
process the substances in that blood. Blood then leaves each
lobule via a central vein ,which drains into the hepatic vein.
The hepatic vein then drains into the IVC, returning the
processed blood back to circulation.
The liver plays a central role in regulating the metabolism of
the body.
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Functions of the liver:
-Detoxifies(removes poisons) the body of harmful substances
such as certain drugs and alcohol
-Creates body heat
-- destroys old blood cells and recycles their usable parts
while eliminating unneeded parts such as the pigment
bilirubin.
--forms plasma proteins,such as albumin and globulins
--produces clottin factors fibrinogen and prothrombin
-- creates the anticoagulant heparin
--manufactures bile which is needed in the digestion of fats
---stores and modifies fat for more efficient usage by the
body cells.
--synthesis of urea,a byproduct of protein metabolism,so it
can be eliminated from the body.
--stores simple sugar glucose as glycogen
--stores iron and vitamins A,B12,D,E,and K
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The gall bladder is a sac shaped organ approx. 7.5 to 10cm
long.
While it is storing the bile,it concentrates the bile,this makes
it 6 to 10 times more concentrated than it was in the liver.
Pancreas:
the exocrine portion of this gland secretes buffers and
digestive enzymes through the pancreatic duct to the
duodenum. These buffers are needed to neutralise the
acidity of chyme in the S.I, with the buffer pH ranging from
7.5-8.8
The digestive enzymes excreted by the pancreas are:
-Carbohydrases
-Lipases
-Proteinases and nucleases
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The Duodenum and Related
Organs
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The Organs and Positions in the
Abdominal Cavity
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Structures of the Alimentary
Canal
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The walls of the alimentary canal:
The entire alimentary canal from the esophagus to the anal
canal.
Innermost layer that lines the lumen of the canal is the
mucosa (mucous membrane).
The mucosa layer is composed mainly of: (i) surface
epithelium (ii) connective tissue and(iii) thin smooth layer
sorrounding it.
The mucosa posses cells that secrete digestive enzymes to
break down food and goblet that secrete mucus for
lubrication.
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(2) submucosa:
composed of soft connective tissue,which contains blood
vessels,lymphatic tissue, similar to tonsils, called peyer’s
patches and nerve endings.
(3) Muscularis externa: composed of 2 layers of smooth
muscle.
Innermost circular layer and outer longitudinal layer.
The third additional layer is the oblique smooth, but it only
found in the stomach.
The outer most layer is serosa, composed of a single layer of
thin flat serous fluid ,producing cells supported by
connective tissue.
Like other serous membranes it has two layers :
(1) Parietal layer and (2) visceral layer.
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The visceral peritoneum covers the abdominal organs, and the
parietal peritoneum lines the wall of the abdominal cavity.
allows the friction –free movement of the digestive organs
against the abdominopelvic cavity.
The esophagus differs from the rest of the alimentary canal that
it possesses only a loose layer of connective tissue called the
adventitia peritoneum.
The stomach can hold up to 4 litres.
It takes about four hours for the stomach to empty after a meal.
Liquids and carbohydrates pass through fairly quickly.
Proteins takes a little more time, and fats takes even longer,
usually between 4 to 6 hours.
Secretes gastric acid and enzymes, which mixes with food,
chemical digestion.
Absorb small amounts of water and substances on a limited
bases,although alcohol is absorbed.
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Basic overview:
The funnel-shaped,terminal end of the stomach is called
pylorus.
Most of the digestive work of the stomach is performed by
the pyloric region.
The orientation of the muscle in the stomach and muscular
arrangement enables the stomach to churn food as it mixes
it with gastric juice excreted by gastric glands from gastric
pits .
With the combined efforts of muscle action and gastric
juices ,both physical and chemical digestion occur in the
stomach.
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Gastric juice is a general term for a combination of HCL,
Pepsinogen and mucus,(1.5ml) is produced per day by the
gastric glands.
Gastric glands and their functions.
Digestive cells
Chief cells
Parietal cells
Mucous cells
secretion type
pepsinogen
HCL
intrinsic factor
alkaline mucus
function
begins pro.dige
activates pepsino
aids in B12 abs
protect stom lin.
Endocrine cells
hormone gastrin
stim.gastric gland
**the stomach’s activity is controlled by the
parasympathetic nervous system ,i.e the vagus nerve .once
stimulated ,the stomach ‘motility is increased and does the
secretory rates of the glands.
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Three distinct phases of gastric juice production:
(1) Cephalic phase:
-Occurs as a result of site or smell of food.
Sensory impulses stimulates the parasympathetic nervous
system through the medulla oblongata, and the release
of gastrin is increased.
Gastrin reaches the stomach ,gastric activity is increased.
(2) Gastric phase;
Two-thirds of the gastric juices are secreted as the food
moves to the stomach. as food gets into the stomach,
the stomach distends, it sends signals back to the brain
,which fires a reply to the gastric glands to step up
their work.
As chyme passes into the pyloric sphincter to the first part
of the small intestine, this begins the intestinal phase of
gastric juice regulation.
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As the duodenum distends and senses the activity of the chyme,
intestinal hormones are released that cause the gastric glands in
the stomach to decrease gastric juice secretion because it is no
longer needed now that the food bolus (now called chyme) has
left the stomach.
Once the chyme begins its movement through the duodenum
and on to the rest of the small intestines,those inhibitory
responses are halted so gastric juice production can continue
once again when a new bolus of food enters the stomach.
***The rate of movement of chyme is very important.***
If chyme passes too quickly through the stomach, the food
particles may not be sufficiently mixed with gastric juices,
leading to____________???
Chyme that is not given time to be neutralised may lead to
acidic erosion of the intestinal lining
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(1) The finger-like projections of the wall of the small
intestines is called:
(a)Microvilli
(b)Villi
(c)Lacteals
(d)Rugae
(2) The duodenum releases this hormone to decrease gastric
activity:
(a) Cck
(b) Gastrin
(c) Secretin
(d) Both a and c
(3) This organ does most of the digestion and absorption in
your digestive tract:
(a) s.i
(b) L.i
(c) Liver
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