Experiment 10 –Enzymes Enzymes are proteins that act as catalysts for biological reactions. Enzymes, like all catalysts, speed up reactions without being used up themselves. They do this by lowering the activation energy of a reaction. All biochemical reactions are catalyzed by enzymes. Since enzymes are proteins, they can be denatured in a variety of ways, so they are most active under mild conditions. Most enzymes have optimum activity at a neutral pH and at body temperature. Enzymes are also very specific –they only act on one substrate or one class of related substrate molecules. The reason for this is that the active site of the enzyme is complementary to the shape and polarity of the substrate. Typically, only one kind of substrate will “fit” into the active site. In this experiment, we will work with the enzyme amylase. This enzyme is responsible for hydrolyzing starch. In the presence of amylase, a sample of starch will be hydrolyzed to shorter polysaccharides, dextrins, maltose, and glucose. The extent of the hydrolysis depends on how long it is allowed to react –if the starch is hydrolyzed completely, the resulting product is glucose. You will test for the presence or absence of starch in the solutions using iodine (I2). Iodine forms a blue to black complex with starch, but does not react with glucose. If iodine is added to a glucose solution, the only color seen is the red or yellow color of the iodine. Therefore, the faster the blue color of starch is lost, the faster the enzyme amylase is working. If the amylase is inactivated, it can no longer hydrolyze starch, so the blue color of the starch-iodine complex will persist. You will also test for the presence of glucose in the samples using Benedict’s reagent. When a blue solution of Benedict’s reagent is added to a glucose solution, the color will change to green (at low glucose concentrations) or reddish-orange (at higher glucose concentrations). Starch will not react with Benedict’s reagent, so the solution will remain blue.

1. Objective
 To describe the movement of food and
motility along the GIT.
Brief introduction
 The GIT stretches from the mouth-
esophagus- stomach- intestines- anus.
 The motor activity of the GI helps to perform
its 3 main primary function : churning,
propulsive and reservoirs

2.  Involves contraction and relaxation of GI muscles and
sphincters.
 Tonic, and rhythmic contraction of the smooth muscle are
responsible for the churning ( grinding fragment and
mixing) propulsive or peristalsis( propel food chyme.) and
reservoir action (store) for holding luminal content
 The GIT is lined by smooth muscles except pharynx,
upper third of esophagus and external anal sphincter.
 The smooth muscles act as a unit communicating through
low resistance gap junctions.

3.  all this results in elimination of nondigested
and nonabsorbed food or material and its
digestive products in a caudal direction.
 The contractions needed for theses are either:
◦ Phasic: periodic contractions followed by relaxation.
◦ Tonic: sustained contractions/tone without regular
periods of relaxation (oral stomach, sphincters)
 Muscles involved are:
◦ Circular in the inner layer: contract to decrease GIT
diameter.
◦ Longitudinal in the outer layer: contract to shorten
the GIT segment

4.  the segments of the GIT which food pass are
hollow , low pressure organs separated by
circular muscles or sphincters.
 Sphincters function as barriers to flow by
maintaining a positive resting pressure that
serves to separate two adjacent organs and
regulate both antegrade (forward) and
retrograde(reverse) movement.
 Stimuli proximal to sphincter cause relaxation
whereas that to distal induces sphincteric
contraction.

5.  Are unique oscillatory depolarizations and
repolarizations of membrane potential of
smooth muscles.
 They cause continuous basal contractions (
several per minute) albeit weak in the GIT
muscles even without action potential.
 Action potential strengthens and brings
about stronger phasic contractions

6. The frequency ranges from 3-12 per minute (3 in
stomach, 12 in duodenum & 9 in ileum)
These waves originate from the pacemakers called
interstitial cells of Cajal which creates the bioelectrical
slow wave potential that leads to contraction of the
smooth muscle.
Mechanism: Opening voltage – gated Ca2+ channels
depolirize the cell and followed by opening of ca2+
activated K+ channels which repolirize the cell.

7.  these activities are regulated by both
neuronal and hormonal stimuli
 Modulation of the smooth muscle contraction
is largely a function of the ca2+ which is
regulated by several agonist
 i.e activation of G protein –linked receptors
which results in formation of inostol 1,4,5-
triphosphate (IP3) and release of ca2+ from
intracellular stores, or both opening and
closing of plasma membrane ca2+ channels.

8.  Luminal food and digestive products activate
mucosal chemical and mechanical receptors
to regulate the GI motility.ie the high lipid
and elevated osmolarity food in Gastric slow
its emptying to duodenum by activating the
chemoreceptors and osmoreceptors that
increas the release of cholecystokinin.

9.  We chew to:
◦ Mix food with saliva to lubricate it for swallowing
◦ Mix CHO’s with salivary amylase
◦ Reduce food particles to small pieces to facilitate
swallowing.
 Chewing can be voluntary or involuntary
(brainstem)
◦ Voluntary chewing overrides involuntary chewing

10.  Initiated voluntarily in the mouth.
 Has 3 phases:
 Oral phase: the tongue pushes food bolus towards
pharynx ( somatosensory receptors located in the
pharynx activate the swallowing centre in the
medulla thereby initiating the involuntary phase

11. 16-

12. b) Swallowing:
Def.
•Swallowing is the
transport of food from
mouth to stomach
Steps:
• It consists of 3 phases or
steps;
1) Buccal Phase: food is
pushed back into pharynx
from mouth

13.  Pharyngeal phase
1. Soft palate is pulled up narrowing and
preventing reflux into the nasopharynx.
2. Epiglottis covers larynx and the larynx moves up
to block airway and prevent reflux.
3. UES relaxes and food passes into esophagus
4. Initiates a peristaltic wave that propels food
down the open UES.
 Breathing is inhibited during this phase.

14. b) Swallowing:
3) Oesophageal Phase:
food pass through
esophagus to stomach by
peristaltic movements

15.  Esophageal phase
 Controlled by swallowing reflex and the ENS.
 UES closes to prevent reflux into pharynx
 Primary peristaltic wave from the swallowing
reflex propels food downward.
 Secondary peristaltic wave from ENS propels
remaining food down to the stomach

17.  UES closes to prevent air entry by diverting it
to the glottis and away from the eosophagus
during inspiration but during swallowing the
closure the glottis and inhibition of
respiration but with relaxation of UES
 Primary and secondary peristaltic waves.
 LES opened by vagus nerve Vaso active
intestino peptide (VIP) in receptive relaxation.
 LES prevents gastroesophageal reflux (GER).

18.  The esophagus is 25 cm
ms tube
 It is guarded by 2
sphincters;
1. Upper esophageal
sphincter prevents air from
entering the GIT
2. Lower esophageal
sphincter prevents gastric
contents from re-entering
the esophagus from the
stomach
 Esophageal peristalsis
sweeps down the
esophagus
Motility of GIT

20.  Receptive relaxation mediated by vagovagal
reflex (VIP) to receive food.
 Mixing and digestion by the contractions
from the midbody caudally with retropulsion.
◦ Baseline contractions at 3-5 waves per minute.
◦ Strength of contractions increased by PNS and
Gastrin.
◦ Decreased by SNS and GIP.

21.  The stomach consists of
fundus, body and pylorus
 Proximal area (fundus and
body) has a thin wall and
contracts weakly and
infrequently → holds large
volumes of food (to store food)
because of receptive
relaxation
 Distal area (pylorus) has thick
wall with strong and frequent
peristaltic contractions that
mix and propel food into the
duodenum.
 Also, distal area is responsible
for gastric emptying into
duodenum
Motility of GIT

22. 16-9a

23. 16-9b

24.  Gastric emptying:
◦ Every 3 hours
◦ Stomach contains about 1.5 L after a meal
◦ Liquids empty faster than solids (< 1mm3)
◦ Isotonic foods empty faster than hyper/potonic
◦ Regulated based on the H+(receptors in duodenum
communicating with ENS) and
◦ Fats through the action of Cholecystokinin (CCK)

25. 1. To enhance digestion: by mixing chyme with
pancreatic secretions and digestive enzymes
2. To enhance absorption by exposing chyme to the
intestinal mucosa
3. To propel unabsorbable chyme in to the Large
intestine.
 Basal contractions are 12 in duodenum and 9 in
ileum
 Innervated by SNS from celiac and sup. mesenteric
ganglia and PNS from vagus.

26. Two contraction
patterns:
Segmentation
contraction &
peristaltic
contractions

27. 1 ~ 5 cm
and cutting
Segmentation movements

28. Orad cauda
d
Motility of GIT

29.  A wave of contraction sweeping from the
stomach through the small intestine to clear
residual chyme.
 Mediated by motilin
 The first wave occurs 90min after the last
meal, the 2nd 75min later then they become
more frequent.
 They are perceived as hunger pains.

30.  Controlled by the vomiting centre receiving
stimuli from Chemoreceptor Trigger Zones
(ctz), vestibular system, Back of throat and
GIT.
 Involves reverse peristalsis
 May be accompanied by nausea.

31.  Ileocecal sphincter tonically contracted to
prevent reflux of Large Intestines bacteria
into ileum.
 Segmental contractions to mix contents in
the cecum and proximal colon.
 Mass movements occurring 1-3 X a day to
push feces further distally.
 Water absorption in the distal colon.

32.  Gastro colic reflex (long arc reflex):
◦ Mediated by PNS (afferent) and Cholecytokinin
(CCK) & gastrin (eff).
 Defecation:
◦ Urge comes when rectum is 25% full.
◦ Rectosphincteric reflex: Stretching of the rectum
leads to contraction which opens up the internal
anal sphincter
◦ Voluntary opening of the external anal sphincter
◦ Passive but intraabdominal pressure may be
increased via valsava maneuver.

33. End
Thank you