notes about our GIT system

1. GIT System
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2. NA 5/12

3. Surface representation of the
abdominal regions
Gray Anatomy
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4. • Two horizontal lines; one at the lower rib
margins and the other passing through the
iliac tubercles. The other two are vertical,
passing through the middle of each clavicle.
• The result is nine regions: the right
hypochondriac region, epigastric region, left
hypochondriac region,
• right lumbar region, umbilical region, left
lumbar region,
• right inguinal region, hypogastric
region, and the left inguinal region.
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5. • The digestive system is responsible for
breaking down of food and supplying the
body with water, nutrients, and electrolytes
needed to sustain life. The functioning of
digestive system starts from the mouth and
ends at the anus
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6. * Saliva is secreted by 3 pairs of salivary glands: PAROTID,
SUBMANDIBULAR (SUBMAXILLARY) AND SUBLINGUAL in adddition
to numerous small glands.
* Each gland is formed of groups of acini, the secretion of which is carried by a
duct which opens into the buccal cavity.
* The acini concists of 2 types of cell:
1) serous cells (secrete thin/watery saliva rich in enzyme ptyalin : digesting
starch)
2) mucous cells (secrete thick / viscid saliva rich in mucin : lubricating and for
surface protective purpose
/submandibular
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The beginning…………

7. * Parotid: watery saliva. Submandibular and sublingual: mixed
secretion,
* Combined parotid and submandibular glands constitues 90%
of the saliva volume
/submandibular
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8. Composition of saliva
• Daily secretion of saliva ranges between 800 – 1500 mm,
pH : 6-7
• Water – 99.5%, solids – 0.5%
• Organic substances:
Digestive enzymes: ptyalin and lingual lipase.
IgA, lysozyme,
Free amino acids, antibodies, uric acid, creatinine, etc
• Inorganic substances:
Ions in saliva ; Na+, K+, Cl-, HCO3 and other ions
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9. Funtions of Saliva
* Oral hygiene: flow: wash away pathogenic bacteria. Lysozyme: attack
bacteria, Thiocyanate ions: bactericidal. Protein antibodies: destroy
oral bacteria. Avoid dental caries
* Articulation, moist
* Mucin : lubrication, facilitate deglutition
* Facilitating taste sensation, solvent for molecules that stimulates taste
bud.
* Salivary buffer : HCO3 and mucin keep the oral pH at 7: enhance
enamel protection (acidity increase calcium solubility) and neutralize
gastric acidity, relieve heartburn.
* Dilution medium for irritating substances
* Digestive function : ptyalin : CHO, lingual lipase : start lipid digestionNA 5/12

10. Control of Salivary Secretion:
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Salivary secretion is entirely under nervous control. No
chemical or hormonal control. Unlike other GIT glands.
Salivary secretion production is unique in that it is
increased by both parasympathetic and sympathetic
activity, however the activity of former is more important
Stimulation of paraysmpathetic nerves causes secretion
of watery profuse saliva. It dilates the blood vessels of
salivary glands.
Sympathetic stimulation causes moderate increase of
secretion of thick saliva rich in mucus, enzyme along
with vasoconstriction.

11. • Parasympathetic : dilates the blood vessels of gland
Secretion of watery saliva
Increased stimulation in response to
– conditioned reflexes (taste, smell)
Decreased stimulation due to
– sleep, fear, dehydration
• Sympathetic : vascoconstriction of the blood vessels of gland
Stimulates
- secretion (mostly enzymes)
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12. Reflex regulation of salivary
secretion
*Conditioned (psychic) reflexes: Acquired reflexes, develop by learning
& training. Occurs before food enters the buccal cavity. Seeing,
smelling, hearing abt food or even thinking of food stimulates
salivation
Eg : sight of food excites visual receptor, impulses arise and
transported by afferent nerve fibres to the visual centre which in turn
stimulates the salivary nuclei in the brain stem. Then impulses are
transported by efferent parasympathetic (predominantly)
and symp. Nerve fibres to the salivary glands.
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13. Reflex regulation of salivary
secretion
*Unconditioned reflexes: presence of food in buccal cavity.
Inborn reflexes (inherent). The introduction of food in the
buccal cavity / mech stimulation lead to reflex salivary
secretion. Stimulation of the taste buds from which
impulses arise and transported via afferent nerve fibres in
the 7th and 9th cranial nerves to the brain stem, stimulate
salivary nuclei resulting in salivary secretion.
* Salivary glands are supplied by both parasympathetic
(most prominent role) and sympathetic nerves.
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14. Control of Salivary Secretion
My name
is
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Thick
secretion

15. • Mastication is the process of breakdown
of large food particles into small pieces.
• Involves teeth: chewing tool, as well as
the movements of lips, cheeks, tongue
and mandible.
• Functions of mastication: helps
swallowing and digestion (↑ total surface
area of food to the action of
dig.enzyme, reduces the mech. damage
to the GIT mucosa and stimulation of
the taste and smell receptors. NA 5/12

16. Deglutition (swallowing)
• Deglutition is the act of
transferring food from the
buccal cavity/ mouth to the
stomach.
• 3 stages:
• (1) Voluntary (buccal) stage which initiates
the swallowing process;
• (2) pharyngeal stage which is involuntary ,
passage of food through the pharynx into
the esophagus; and
• (3) esophageal stage: involuntary, transports
food from the esophagus to the stomach NA 5/12

17. Deglutition (swallowing)
* Voluntary stage: after mastication and formation of a
suitable bolus: tongue is voluntarily elevated against the
hard palate so the bolus is propelled backwards into the
pharynx.
The mouth must must be closed (swallowing becomes
difficult if the mouth is open e.g in dental check up
Voluntary (buccal stage)
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18. Deglutition (swallowing)
Voluntary (buccal stage)
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19. Deglutition (swallowing)
Pharyngeal stage: Look at Figure B, C and D
(less than 6 seconds) NA 5/12

20. Deglutition (swallowing)
* Pharyngeal stage : swallowing reflex.
* As the bolus is pushed backwards, it stimulates certain receptors
located at the pharyngeal opening specially in the tonsillar pillars
(swallowing receptor areas) and the resulting signals are transported
via afferent fibres in the 5th and 9th cranial nerves to a swallowing
centre in the medulla oblongata. From this centre, motor impulses to
the pharynx and upper esophagus that cause swallowing are
transmitted via efferent fibres in the 5th, 9th, 10th and 12th cranial
nerves
* The swallowing centre inhibits the respiratory centre during the
pharyngeal stage : temporary apnea, which also prevents food
entrance into the trachea
Pharyngeal stage
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21. Deglutition (swallowing)
* Esophageal stage: involuntary stage in which peristaltic
movement occurs in the esophageal wall propelling the bolus
from its upper end to the stomach.
* 2 types of peristaltic movements: primary and secondary
peristalsis
PERISTALSIS:
series of involuntary
wave-like muscle
contractions which
move food along the
digestive tract
Esophageal stage NA 5/12

22. * Primary peristalsis: simply continuation of peristaltic
wave that begins in the pharynx. 8-10 seconds. Additional
effect of gravity pulling the food downward faster.
* Secondary peristalsis: if the primary peristalsis fails to
propel all food that has entered the esophagus. It originates
in the esophagus itself as a result of distension of its wall by
food and continues until all esophageal contents are
emptied into the stomach.
* Secondary peristalsis : iniated partly by intrinsic neural
circuits in the myenteric nervous system, another part
iniated from the reflexes begin in the pharynx.
Deglutition (swallowing)
Esophageal stage NA 5/12

23. * impulses generated are transported via afferent vagal nerve
fibres to the vagus nucleus in the medulla oblongata leading to
its stimulation, and impulses then return back again to the
esophagus via glossopharyngeal and vagal efferent nerve fibres.
* Musculature of upper third of esophagus : striated ms and
controlled by glossopharyngeal and vagal efferent nerve fibres.
* Musculature of lower two third of esophagus : smooth ms,
indirectly controlled by vagi through the connections with the
meyenteric nervous system.
* Effects of bilateral vagotomy.
Deglutition (swallowing)
Esophageal stage NA 5/12

24. Stomach
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25. Surface projection of stomach
• Stomach: Its position also varies
with that of the body so that it
is impossible to indicate it on the
surface with any degree of accuracy.
The measurements given refer to a moderately
filled stomach with the body in the supine
position.
With the patient in the erect posture
With the patient lying down.
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26. • Functions of stomach
• Gastric juice,
• Cells of gastric mucosa
• Phases of gastric secretion
• Peptic ulcer
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27. Oesophagus
Lower Oesophageal
Sphincter
Fundus
Body
Antrum
Duodenum
Pylorus
Functional Anatomy of Stomach
Fundus
Body
Antrum
• Storage
• Storage
• Mucus
• HCl
• Pepsinogen
• Intrinsic factor
• Mixing/Grinding
• Gastrin
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28. Functions of stomach
• 1 : Mechanical functions:
Storage of food. Serves as reservoir. Food
remains in stomach for several hours.
Mixing of food with gastric juice is performed by
gastric motility until it forms a semisolid food
paste known as chyme
Slow emptying of food into duodenum, proper
time for digestion and absorption by small
intestine
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29. Functions of stomach
2 : Digestive functions:
Carbohydrate, lipid, protein
3: Absorptive function: little in absorptive function,
nutrients, ethanol, water,
4: Reflex function: presence of food stimulates
secretion of pancreatic juice and expulsion of bile
5: Gastric juice and its function
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30. DIGESTIVE & ABSORPTIVE FUNCTION
• Carbohydrate digestion and lipid digestion
continues in stomach by salivary amylase and
lingual lipase in the unmixed interior of the food
mass.
• Digestion by Pepsin – optimum pH 2 – 3. Ability of
digests proteins particularly collagen. Digests to
proteoses, peptones and large polypeptides.
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31. DIGESTIVE & ABSORPTIVE
FUNCTION
• Ethyl alcohol absorption: alcohol is lipid soluble
and therefore can diffuse across the gastric
epithelium. But it can be absorbed more rapidly
by small intestine because of greater surface
area. Delay in gastric emptying decreases the
rate of alcohol absorption.
• Aspirin absorption: can absorb weak acids like
acetylsalicyclic acid (aspirin). In highly acidic
environment the weak acids remain in un-ionized
form which is lipid soluble.
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32. • Gastric juice composition and function:
- Water, electrolytes,
- hydrochloric acid
- conversion of pepsinogen to pepsine
- bacteriostatic effect / antiseptic : kills bacteria
- pepsin
- protein digestion
- mucus
protective coating, lubricant. Protects from HCL and pepsin
part of gastric mucosa
Imbalance between hydrochloric and mucus: hyperacidity,
gastric
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33. NA 5/12

34. Three phases of gastric secretion:
1) Cephalic phase –before food reach the stomach30%
of acid response to meal
2) Gastric phase (predominant) – arrival of food : 60% of
acid response to meal
3) Intestinal phase : when food reach duodenum : 10% of
acid response to meal (insignificant). inhibition of gastric
activity when chyme enters the duodenum.
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35. Small intestine
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36. Small intestine : functions
• Mechanical function: The mixing and propulsive
movements of small intestine help in thorough
mixing of chyme with the digestive juices:
pancreatic juice, bile juice) and propel it towards
large intestine
• Digestive function: pancreatic enzymes and bile
• Absorption: end products of digestion of fat,
carbohydrate and fats are absorbed thorough
circulation
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37. • The three major classes of nutrients that undergo digestion are proteins, lipids
(fats) and carbohydrate
• Proteins are degraded into small peptides and amino acids before absorption.
Chemical breakdown begins in the stomach by pepsin and continues in the small
intestine. Proteolytic enzymes, including trypsin and chymotrypsin, are secreted
by the pancreas and cleave proteins into smaller peptides. Carboxypeptidase,
which is a pancreatic brush border enzyme, splits one amino acid at a time.
• Lipids (fats) are degraded into fatty acids and glycerol. Pancreatic lipase breaks
down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase
works with the help of the salts from the bile secreted by the liver and the gall
bladder. The bile salts emulsify the triglycerides in the watery surroundings until
the lipase can break them into the smaller components that are able to enter the
intestinal villi for absorption.
• Some carbohydrates are degraded into simple sugars e.g glucose. Pancreatic
amylase breaks down some carbohydrates . Other carbohydrates pass undigested
into the large intestine and further handling by intestinal bacteria.
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38. Large intestine
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39. Large intestine
• Absorptive function: absorption of water and electrolytes is
the chief function of colon.
• Secretory function: mucin, lubricate fecal matter
• Synthesis function: bacterial flora synthesize folic acid, vit
B12, and vit K
• Storage function: after the absorption of nutrients, water
and other substances, the unwanted substances form
faeces. The faeces are stored in sigmoid colon (pelvic colon)
until they can be expelled by the process of defecation.
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40. SGS Questions
1- Describe the functions of saliva.
2- Discuss the control of salivary secretion. Explain about conditioned
and unconditioned reflex of salivary secretion
3- Explain the stages and events of deglutition (swallowing).
4- Discuss the composition and functions of gastric juice.
5- Discuss 3 phases of gastric secretion
6- What are the functions of small intestine