it includes physiology of deluttition , digestion and assimilation

1. MASTICATION,
DEGLUTITION,
DIGESTION &
ASSIMILATION
Dr. Neelam Bhandari
P.G STUDENT 1st year
Dept. of prosthodontics

2. Mastication & Deglutition
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

3. CHEWING CYCLE
 Duration: 0.6 to 1sec depending on
food type
 Murphy summarised 6 phases in
chewing cycle:

4. Centric
Occlusion
Preparatory
Phase
Food
Contact
Phase
Crushing
Phase
Grinding movement
at occlusal tables
Grinding
Phase
Tooth
contact
Phase
Tongue positions food in
oral cavity. Mandible deviates
towards chewing side
Sensory receptors triggered
due to food contact
Starts with high velocity, slows as food gets crushed
All reflex muscular
adjustments for
tooth contact made
Mandible return to single terminal point

5.  The coordination of occlusal contacts,
jaw motion and tongue movement
during mastication require a very
intricate control system.
 Involves guiding influences from:
◦ Teeth and supporting structures
◦ TMJ
◦ Masticatory muscles
◦ Higher centres in brain

6. MASTICATORY
APPARATUS
 Teeth
 Specialized occlusal form
 Opposing contacts
 Contours
 Sluiceways
 Tongue
 Level w.r.t occlusal plane
 Muscles of mastication
◦ Temporalis, Masseter, Lat. Pterygoid
◦ Medial Pterygoid,

7. DEGLUTITION
 Swallowing is a reflex response.
 It involves coordination of nearly 20
different muscles with motor neurons
distributed from mesencephalic to
posterior medullary levels.
 Neurons responsible for coordination
form the swallowing center – neuronal
groups fire automatically in a particular
sequence to achieve a necessary pattern
of muscle activity to produce swallowing.

8.  Swallowing is initiated by the voluntary
action of collecting the oral contents
on the tongue and propelling them
backwards into the pharynx.
 This starts a wave of involuntary
contraction in pharyngeal muscles that
pushes the material into oesophagus.
 Inhibition of respiration and glottic
closure are part of reflex response.

9. PERISTALSIS
 Reflex response that is initiated when
the gut wall is stretched by the
contents of the lumen – from
oesophagus to rectum.
 Stretch initiates circular contraction
behind the stimulus and area of
relaxation in front of it.
 Rate: 2-25 cm/sec

11. Stages of Duglutition

12. Lower Esophageal Sphincter

13. DIGESTION
 Digestion is the breakdown of food into
smaller components that can be more
easily absorbed and assimilated by the
body.
 These smaller substances are absorbed
through the small intestine into the blood
stream.

14.  Digestion is a form of catabolism that is often
divided into two processes based on how food
is broken down: mechanical and chemical
digestion.
 The term mechanical digestion refers to the
physical breakdown of large pieces of food into
smaller pieces which can subsequently be
accessed by digestive enzymes. In chemical
digestion, enzymes break down food into the
small molecules the body can use.

15.  In the human digestive system, food enters the
mouth and mechanical digestion of the food
starts by the action of mastication and the
wetting contact of saliva.
 Saliva, a liquid secreted by the salivary glands,
contains salivary amylase, an enzyme which
starts the digestion of starch in the food.
 After undergoing mastication and starch
digestion, the food will be in the form of a
small, round slurry mass called a bolus. It will
then travel down the esophagus and into
the stomach by the action of peristalsis.

16.  Gastric juice in the stomach starts protein
digestion. Gastric juice mainly
contains hydrochloric acid and pepsin.
 At the same time protein digestion is occurring,
mechanical mixing occurs by peristalsis. This
allows the mass of food to further mix with the
digestive enzymes.

17.  After some time (typically 1–2 hours in
humans, 4–6 hours in dogs, 3–4 hours in
house cats), the resulting thick liquid is called
chyme.
 When the pyloric sphincter valve opens, chyme
enters the duodenum where it mixes with
digestive enzymes from the pancreas, and
then passes through the small intestine, in
which digestion continues.
 When the chyme is fully digested, it is
absorbed into the blood. 95% of absorption of
nutrients occurs in the small intestine.

18.  Water and minerals are reabsorbed back into
the blood in the colon (large intestine) where
the pH is slightly acidic about 5.6 - 6.9.
 Some vitamins, such as biotin and vitamin
K produced by bacteria in the colon are also
absorbed into the blood in the colon.
 Waste material is eliminated from
the rectum during defecation.

19. Phases of gastric secretion
 Cephalic phase - This phase occurs before
food enters the stomach and involves
preparation of the body for eating and
digestion.
Sight and thought stimulate the cerebral
cortex. Taste and smell stimulus is sent to
the hypothalamus and medulla oblongata.
After this it is routed through the vagus
nerve and release of acetylcholine occurs.
Gastric secretion at this phase rises to 40% of
maximum rate.

20.  Gastric phase - This phase takes 3 to 4 hours.
It is stimulated by distension of the stomach,
presence of food in stomach and decrease
in pH.
 As protein enters the stomach, it binds
to hydrogen ions, which raises the pH of the
stomach.
 This triggers G cells to release gastrin, which
in turn stimulates parietal cells to secrete hcl,
which lowers the pH to the desired pH of 1-3.
 Acid release is also triggered
by acetylcholine and histamine.

21.  Intestinal phase - This phase has 2 parts, the
excitatory and the inhibitory.
Partially digested food fills the duodenum.
This triggers intestinal gastrin to be released.
Enterogastric reflex inhibits vagal nuclei,
activating sympathetic fibers causing the
pyloric sphincter to tighten to prevent more
food from entering, and inhibits local reflexes.

22.  PARTS OF GIT
 Oral cavity
 In humans, digestion begins in the Mouth, where
food is chewed. Saliva is secreted in large amounts
in the oral cavity, and is mixed with the chewed food
by the tongue. Saliva cleans the oral cavity, moistens
the food, and contains digestive enzymes such as
salivary amylase.
 An additional enzyme, lingual lipase, hydrolyzes long-chain
triglycerides into partial glycerides and free fatty
acids.
 Swallowing transports the chewed food into
the esophagus. The mechanism for swallowing is
coordinated by the swallowing center.

23.  Pharynx
 The pharynx is the part of the neck and throat
situated behind the mouth and nasal cavity,
and cranial, or superior, to the esophagus.
 It is part of the digestive
system and respiratory system.
 A flap of connective tissue,
the epiglottis closes over the trachea when
food is swallowed to prevent choking or
asphyxiation.

24.  Esophagus
 The esophagus is a narrow muscular tube
about 20-30 centimeters long, which starts
at the pharynx , passes through
the thoracic diaphragm, and ends at
the cardiac orifice of the stomach. The wall
of the esophagus is made up of two layers
of smooth muscles.
 The chewed food is pushed down the
esophagus to the stomach
through peristaltic contraction of these
muscles.

25. Stomach
 The stomach is a small, 'J'-shaped pouch with
walls made of thick, distensible muscles,
which stores and helps break down food.
 Food enters the stomach through the cardiac
orifice where it is further broken apart and
thoroughly mixed with gastric acid, pepsin and
other digestive enzymes to break down
proteins.
 Food in the stomach is in semi-liquid form,
which upon completion is known as chyme.

26.  When the chyme reaches the opening to
the duodenum known as the pylorus,
contractions "squirt" the food back into the
stomach through a process called retropulsion,
which exerts additional force and further grinds
down food into smaller particles.
 Gastric emptying is the release of food from
the stomach into the duodenum; the process is
tightly controlled with liquids being emptied
much more quickly than solids.

27.  Small intestine
 It has three parts: the Duodenum, Jejunum and Ileum.
After being processed in the stomach, food is passed
to the small intestine via the pyloric sphincter. Here it
is further mixed with three different liquids:
 Bile, which emulsifies fats to allow
absorption, neutralizes the chyme and is used to
excrete waste products such as bilin and bile acids.
 Pancreatic juice made by the pancreas, which
secretes enzymes such as pancreatic
amylase, pancreatic lipase, and trypsinogen .
 Intestinal juice contains enzymes such
as enteropeptidase, erepsin, trypsin, chymotrypsin, m
altase, lactase and sucrase .

28.  The pH level increases in the small intestine
as all three fluids are alkaline.
 A more basic environment causes more
helpful enzymes to activate and begin to help
in the breakdown of molecules such as fat
globules.
 The small intestine and remainder of the
digestive tract undergoes peristalsis to
transport food from the stomach to
the rectum and allow food to be mixed with
the digestive juices.

29.  Large intestine
 After the food has been passed through the
small intestine, the food enters the large
intestine.
 Within it, digestion is retained long enough to
allow fermentation due to the action of gut
bacteria, which breaks down some of the
substances that remain after processing in the
small intestine.
 some of the breakdown products are
absorbed.

30.  In general, the large intestine is less vigorous
in absorptive activity.
 In humans, the large intestine is roughly 1.5
meters long, with three parts: the cecum ,
the colon and the rectum.
 The large intestine absorbs water from
the chyme and stores feces until it can
be egested.

31. Protein digestion
 Protein digestion occurs in the stomach
and duodenum in which 3 main
enzymes, pepsin secreted by the stomach
and trypsin and chymotrypsin secreted by the
pancreas, break down food proteins
into polypeptides that are then broken down by
various exopeptidases
and dipeptidases into amino acids.

32. Fat digestion
 Digestion of some fats can begin in the
mouth where lingual lipase breaks down
some short chain lipids into diglycerides.
 However fats are mainly digested in the
small intestine.
 Pancreatic lipase from the pancreas
and bile from the liver which helps in the
emulsification of fats for absorption fatty
acids.
 Complete digestion of one molecule of fat
(a triglyceride) results in 3 fatty acid
molecules and one glycerol molecule.

33. Carbohydrate digestion
 In humans, dietary starches are composed
of glucose units arranged in long chains called
amylose, a polysaccharide. During digestion, bonds
between glucose molecules are broken by salivary
and pancreatic amylase. This results in simple
sugars glucose and maltose that can be absorbed
by the small intestine.
 Lactase is an enzyme that breaks down
the disaccharide lactose to its component parts,
glucose and galactose. Glucose and galactose can
be absorbed by the small intestine.
 Sucrase is an enzyme that breaks down the
disaccharide sucrose. Sucrose digestion yields the
sugars fructose and glucose which are readily
absorbed by the small intestine.

34.  Digestive hormones
 There are at least five hormones that aid and
regulate the digestive system in mammals.
 Gastrin
 Secretin
 Cholecystokinin (CCK)
 Gastric inhibitory peptide (GIP)
 Motilin

35. ASSIMILATION
Carbohydrate Absorption:
 Hexoses are rapidly absorbed by the
wall of small intestine (before the meal
reaches terminal ileum).
 Its transport is dependent on Na+ in
intestinal lumen
 This is because Na+ and Glucose share
same cotransporter, or symport:
Sodium Dependent Glucose
Transporter (SGLT)

36.  SGLT1 uptake of dietary glucose from gut
SGLT2 transport glucose out of the renal
tubules
 Glucose is transported by Glucose
Transporter (GLUT 2) into interstitium and
to capillaries.
 Transport via GLUT is secendory active
transport as the energy for this is provided
indirectly by active transport of Na+ out of
the cell.

37. Protein Absorption
 At least 7 transport systems transport
amino acids into enterocytes:
◦ 5 require Na+ and transport AA with Na+
◦ 2 of these 5 also require Chloride ion.
◦ 2 systems transport independent of Na+
 Di- and Tripeptides are transported
into enterocytes by a system called
PepT1
◦ Peptide Transporter 1
◦ This requires H+ instead of Na+

38.  AA released from peptides plus AA
absorbed from brush border are
transported out of enterocytes.
 They enter hepatic portal blood from
there.
 Absorption is rapid in duodenum and
jejunum but slow in ileum
 Only 2-5% protein in small intestine
escape digestion and absorption.
 This too is digested by bacteria in
colon.

39. Fat Absorption
 Traditionally fats were thought to enter
enterocytes by passive diffusion but
now role of carriers is known.
 There are also carriers that export lipids
back into lumen.
 Fate of Fatty Acids depend on their size:
Less than 10-12 carbon atoms Pass through enterocyte unmodified
Actively transported to portal Blood

40. More than 10-12 Carbon atoms Re esterified to triglycerides
in enterocytes
Cholesterol Esters
Coated with a layer of protein
Cholesterol and phospholipid
CHYLOMICRONS