Describe the PHYSIOLOGICAL STRUCTURE OF MOUTH

1. Gastro intestinal tract –part I
Dr. Radhakrishna G Pillai
Department of Life Sciences
University of Calicut

2. Introduction
• The gastrointestinal (GI) tract,
also called the gut
• Muscular tube approximately
9m (30 feet) in length
• Running from the mouth to
the anus
• Mechanically and chemically
break down foods
• Into simple components that
can be absorbed by the body

3. GI Tract
• It produces various enzymes that help in the
chemical digestion of food
• It produces various hormones that play a role in
regulating digestion, appetite and satiety
• Different parts with different functions
• Home to myriad micro-organisms (mostly
bacteria): many are essential to health
• These form a large part of the human
microbiome

4. Mouth
• Opening of the GI tract : receives food, tastes it and prepares it for swallowing
• The average volume of the adult mouth is 72 ml in men and …. ml in women
• 55
• The mouth is lined by mucous membranes and consists of two major regions:
– Vestibule – the space between the inner surface of the cheeks/lips and the teeth
– Oral cavity proper – the space inside the teeth, where food is chewed and mixed
with saliva before being swallowed.

5. Tongue and sense of taste
• The tongue is a muscular structure
• Approx 10cm long and weighs 60-70g
• It is anchored posteriorly
to the hyoid bone via small
muscles and
• Attached to the floor of
the mouth by a thin flap of
tissue, the lingual frenulum

6. Tongue and sense of taste
• Tiny extensions called papillae make its surface
rough textured
• Papillae help to grip food as it is moved
around the mouth and mixed with saliva
• The papillae contain taste buds
Taste buds contain
gustatory cells that act as
taste receptors

7. Taste buds
• Food molecules dissolve in saliva and enter
taste buds
• Taste receptors are activated
Nerve impulses are relayed
to the gustatory cortex of
the brain, where they are
perceived as distinct tastes

8. Sensing tastes
• In humans, there are five primary tastes
• Each taste has only one corresponding
type of receptor
• Each receptor is specific to its stimulus
• The five tastes are sensed through different
mechanisms based on the molecular composition
of the tastant
• A salty substance (containing NaCl) provides the
sodium ions (Na+) that enter the taste neurons and
excite them directly

9. Sensing tastes
• Map of the tongue showing the distribution of
different taste receptor types are misleading –
distributed across
• Sour molecules are acids
• Binding of an acid or other sour-tasting molecule
triggers a change in the ion channel and these
increase hydrogen ion (H+) concentrations in the
taste neurons, thus depolarizing them
• Sweet, bitter, and umami tastants require a G-
protein coupled receptor

10. • These molecules bind to their respective
receptors, thereby exciting the specialized
neurons associated with them

11. Taste and age
• Tasting abilities change with age
• In humans, the senses decline dramatically by age 50
and continue to decline
• A child may find a food to be too spicy, whereas an
elderly person may find the same food to be bland
and unappetizing

12. Olfaction and taste
• The sense of taste is intimately linked to
olfaction (sense of smell)
• Food cannot be tasted properly if the nose is
blocked
• As soon as the olfactory apparatus detects the
smell of food, the parasympathetic nervous
system is activated
• Salivary glands stimulated - release extra saliva,
preparing the mouth to receive the food

13. Retronasal and ortho nasal olfaction
• Retronasal olfaction -perception of odours
emanating from the oral cavity during eating and
drinking
• The retronasal olfactory pathway, which
contributes to the flavor of foods or drinks, is
commonly associated with the sense of taste
• Also named as “gustatory olfaction”
• Orthonasal olfaction- during sniffing- through
olfactory epithelium of nose

14. Retronasal and ortho nasal olfaction

15. Gustatory pathway
• Taste neurons project from taste cells in the
tongue, esophagus, and palate to the medulla
in the brainstem
• From the medulla, taste signals travel to the
thalamus
• Then to the primary gustatory cortex
• Information from different regions of the
tongue is segregated in the medulla, thalamus,
and cortex

17. Dentition
• Adults normally have 32 teeth, which are evenly
distributed between the upper and lower jaws
• The teeth comprise:
• Eight incisors – flat, chisel-like teeth that bite into food
and break it into small manageable pieces
• Four canines – sharp, fang-like teeth just outside the
incisors that grip and tear food
• Eight premolars – small teeth between the canines and
molars that grind up and cut into food
• Eight molars – square teeth in the rear of the mouth
that grind food to increase its surface area

18. Dentition

19. General structure of teeth
• Their central portion, the
pulp cavity, is composed of
living tissue – mostly blood
vessels and sensory nerve
endings
• Teeth are susceptible to
erosion as a result of wear
and tear as well as
exposure to acidic foods
Teeth are mainly composed of a bony material
(dentine) covered by a layer of white enamel

20. Mastication
• Carried out by the teeth
• The tongue moves food towards the premolars
and molars
• If teeth are missing, the gums can also chew
food- requires much more effort
• Chewing makes food easier to swallow
• Increases the surface area that is available to
the digestive enzymes-enhance chemical
digestion

21. Salivary glands
• The mouth has three pairs of salivary glands
• Sublingual glands – located below the tongue
• Submandibular glands – located below the
mandible
• Parotid glands –
located to the side of
the earlobes
• SGs innervated by the
parasympathetic branch
of the autonomic NS

22. Saliva
• The salivary glands continuously produce small amounts of
saliva to keep the mouth moist (basal secretion)
• In a typical 24-hour period 0.5-1.5L of saliva is secreted
• Eating induces a significant increase in saliva production
(induced secretion)
• The submandibular glands do most of the basal secretion
• The parotid glands are the major contributors to secretion
induced by the presence of food
• The sublingual glands only produce around 5% of both
basal and induced saliva secretion
• The volume of saliva that is produced can be increased or
decreased according to the nature of the food

23. Swallowing
• Towards the end of mastication
• The tongue and roof of the mouth gather and
shape the chewed food into a pellet called bolus
• Moisture and mucus bind and coat the bolus
• Pushed towards the back of the mouth and into
the oropharynx
• Bolus in the posterior pharyngeal wall trigger the
swallowing reflex (deglutition)

24. Muscular contractions in swallowing
• Involves precisely coordinated muscular
contractions
• The pharynx walls contract around the bolus
• The epiglottis closes over the airway, preventing
food from entering the trachea and bronchial
tree
• The bolus is then funnelled, through the upper
oesophageal sphincter, into the oesophagus

25. Movement of food through oesophagus

26. • Voluntary nervous system help to swallow
• Involuntary nervous system takes over
swallowing once the liquid or food enters the top
of your esophagus
• Stretching from food stimulates the smooth
muscles on the walls of esophagus
• This stimulates network of nerves inside muscles
known as intrinsic nerves, start a coordinated
muscle action called peristalsis
Peristalsis

27. Peristalsis
• Peristalsis squeezes esophageal
muscles from top to bottom
• This pushes food and liquid along
• Sphincters act like one-way valves
• They relax to let food and liquid
pass into the stomach and then
tightens to prevent backflow,
called reflux
• Food enters stomach