saliva (function and composition) +deglutation + mastication

Composition of Saliva

Saliva is made up of:

• Water → ~99.5%

• Solids → ~0.5% (organic + inorganic)

1. Organic Solids

Mainly enzymes and proteins:

• Enzymes:

  • Ptyalin (salivary amylase)

  • Lysozyme

  • Lactoperoxidase

  • Carbonic anhydrase

  • Lingual lipase

  • RNase, DNase

• Other components:

  • Kallikrein

  • Blood group substances

  • Secretory IgA (immunity)

  • Nerve growth factor

👉 Mnemonic: “PLLC LRD + KING”

• P → Ptyalin (amylase)

• L → Lysozyme

• L → Lactoperoxidase

• C → Carbonic anhydrase

• L → Lingual lipase

• R → RNase

• ‘ D → DNase

+ KING

• K → Kallikrein

• I → IgA

• N → Nerve growth factor

• G → Group substances (blood group

Inorganic Solids

• Cations:

  • Sodium (Na⁺)

  • Potassium (K⁺)

  • Calcium (Ca²⁺)

  • Magnesium (Mg²⁺)

• Anions:

  • Chloride (Cl⁻)

  • Bicarbonate (HCO₃⁻)

  • Phosphate

  • Sulfate

  • Bromide

Tonicity of Saliva

• Always hypotonic compared to plasma

• Contains lower Na⁺ and Cl⁻ than plasma

• Depends on flow rate:

  • ↑ Flow rate → ↑ tonicity (but still hypotonic)

• Overall tonicity ≈ 70% of plasma

Tonicity

Mnemonic: “Saliva = Slim (Hypotonic)”

• Always hypotonic

• ↓ Na⁺, Cl⁻ than plasma

• ↑ Flow → ↑ tonicity (still hypotonic)

• ≈ 70% of plasma

pH and Potassium (K⁺) Conte.nt

pH

• Final saliva is alkaline (~pH 8)

• Initially slightly acidic in glands → becomes alkaline in ducts due to bicarbonate secretion

Factors affecting pH:

• ↓ Flow → ↑ bicarbonate addition → ↑ pH

• ↑ Flow (especially parasympathetic) → ↑ bicarbonate → ↑ pH

..Potassium (K⁺)

• Always higher than plasma

• ↑ Flow rate → ↓ K⁺ concentration

👉 Mnemonic: “K stays King but falls with flow”

• Always higher than plasma

• ↑ Flow → ↓ K⁺

Functions of Saliva

👉 Mnemonic: “DIGEST PLATE + PROTECT”

1. Digestive Function

• Contains ptyalin (salivary amylase)

• Breaks starch → oligosaccharides

• Works best at pH ~6.8

• Continues briefly in stomach (inside food bolus)

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2. Protective Functions

• Cleans oral cavity

• Prevents infection

• Contains:

  • Lysozyme (antibacterial)

  • IgA (immunity)

  • Lactoferrin (bacteriostatic)

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3. Lubrication & Speech

• Keeps mouth moist

• Helps in speech

• Dry mouth → difficulty speaking

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4. Taste

• Dissolves food → helps taste perception

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5. Mastication & Swallowing

• Mucin lubricates food

• Essential for swallowing (deglutition)

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6. Buffering Action

• Bicarbonate neutralizes gastric acid → reduces heartburn

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7. Dental Protection

• Proline-rich proteins:

  • Strengthen enamel

  • Bind tannins → reduce toxicity

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8. Protection of Oral Mucosa

• Dilutes hot/irritant foods → prevents injury

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9. Thermoregulation (in animals)

• Panting helps in heat loss

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10. Excretory Function

• Eliminates:

  • Heavy metals

  • Thiocyanate

  • Morphine

Functions of saliva

👉 Mnemonic: “DIGEST PLATE + PROTECT”

D – Digestion

• Ptyalin → starch → oligosaccharides

• Works at pH 6.8

I – Immunity

• IgA, lysozyme, lactoferrin

G – Gustation (Taste)

• Dissolves food

E – Enamel protection

• Proline-rich proteins

S – Speech

• Lubrication

T – Swallowing

• Mucin helps deglutition

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PLATE (Extra roles)

• P → Protective (oral hygiene)

• L → Lubrication

• A → Acid buffering (HCO₃⁻)

• T → Temperature regulation (animals)

• E → Excretion (metals, drugs)

Why is saliva hypotonic?

Ducts reabsorb Na⁺ & Cl⁻ → less than plasma

Why is saliva alkaline?

Bicarbonate secretion in ducts

Effect of ↑ flow rate?

↑ HCO₃⁻, ↓ K⁺, ↑ tonicity

Main enzyme of saliva?

Ptyalin (salivary amylase)

Role in immunity?

IgA, lysozyme, lactoferrin

Q: Why saliva needed for swallowing?

Mucin lubrication

Dental protection factor?

: Proline-rich proteins

Saliva is hypotonic because:

A. High K⁺ secretion
B. Water secretion in ducts
C. Reabsorption of Na⁺ and Cl⁻
D. Protein secretion

C

pH of saliva becomes alkaline due to:

A. H⁺ secretion
B. Bicarbonate secretion
C. Sodium reabsorption
D. Enzyme activity

B

With increased salivary flow rate:

A. K⁺ increases
B. HCO₃⁻ decreases
C. Saliva becomes more hypotonic
D. HCO₃⁻ increases

D

‘4. Enzyme responsible for starch digestion in saliva:

A. Pepsin
B. Trypsin
C. Ptyalin
D. Lipase

C

5. Which provides immunity in saliva?

A. Albumin
B. IgA
C. Hemoglobin
D. Fibrinogen

B

6. Salivary K⁺ compared to plasma:

A. Lower
B. Equal
C. Higher
D. Absent

C

7. Function NOT of saliva:

A. Lubrication
B. Protein digestion
C. Taste facilitation
D. Antibacterial action

B

8. Optimal pH of salivary amylase:

A. 2
B. 4
C. 6.8
D. 9

C

Dry Mouth (Xerostomia)

A patient complains of difficulty speaking and swallowing dry food.

Q: What is the cause?Q: Symptoms explained?

👉 ↓ Salivary secretion

Q: Symptoms explained?

Difficulty swallowing → no lubrication

Speech issues → dry oral cavity

Sjögren’s Syndrome

Autoimmune destruction of salivary glands.

Findings:

• Dry mouth

• Dental caries

• Oral infections

Why?
👉 Loss of:

• Lubrication

• Antibacterial action

• Buffering

High Flow Salivation (e.g., chewing)

Q: What changes occur?

👉 ↑ HCO₃⁻, ↓ K⁺, ↑ pH

CHEWING (MASTICATION) — Quick Sheet

• Mastication = Chewing

• Mostly voluntary, but initiated reflexly when food enters the mouth

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⚙Functions of Mastication

👉 Mnemonic: “CG-SLIT D”

• C → Cuts food

• G → Grinds food

• S → Stimulates salivation

• L → Lubricates food

• I → Improves taste

• T → Turns food into swallowable bolus

• D → Dental health

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✅ Explained Simply:

1. Breaks large food → smaller particles

2. Increases saliva secretion

3. Mixes food with saliva

4. Lubricates → helps swallowing

5. Helps starch digestion + taste

6. Maintains dental hygiene & strength

💪 Muscles of Mastication

👉 Mnemonic: “MaTeP + B”

Main Muscles (Jaw movement)

1. Masseter

Elevates mandible

Closes mouth (clenching teeth)

2. Temporalis '‘

Retracts mandible

3. Pterygoids (Medial & Lateral)

Protrude mandible

Help in opening mouth

Alternate contraction → grinding movement

Accessory Muscle

4. Buccinator

Prevents food from collecting in cheeks

Keeps food between teeth

🧠 Ultra-Short Revision (20 sec)

• Mastication = voluntary + reflex start

• Functions:
  👉 Cut + Grind + Saliva + Lubrication + Taste + Teeth health

• Muscles:
  👉 Masseter, Temporalis, Pterygoids, Buccinator

Most powerful chewing muscle?

Masseter

Which muscle retracts mandible?

👉 Temporalis

Q: Which muscle prevents food from collecting in cheeks?

👉 Buccinator

Grinding movement is due to?

👉 Alternate pterygoids

🧠 DEGLUTITION (SWALLOWING)

• Movement of food from mouth → esophagus

• Voluntary start + involuntary completion (reflex)

👉 Also called deglutition reflex

• Respiration stops during swallowing → deglutition apnea

• Reflex center → medulla + pons

• Receptors → pharynx (near opening)

• Reflex Pathway

  👉 Mnemonic: “RACECeE” (Race-C)

  • R → Receptors (pharynx)

  • A → Afferent nerves

  • C → Centers (medulla & pons)

  • E → Efferent nerves

  • E → Effectors (muscles)

Nerves involved

👉 Mnemonic: “5, 9, 10, 12 = Swallowing crew”

• CN V → Trigeminal

• CN IX → Glossopharyngeal

• CN X → Vagus

• CN XII → Hypoglossal

Stages of Deglutition

🔄 stages of Deglutition

👉 Mnemonic: “OPE”

Stage	Type	Key Feature
Oral	Voluntary	Tongue pushes food
Pharyngeal	Involuntary	Airway protection
Esophageal	Involuntary	Peristalsis

stages of Deglutition

🥄 1. Oral Phase (Voluntary)

👉 Mnemonic: “Tongue Push”

• Tongue presses against hard palate

• Pushes bolus → pharynx

• Triggers reflex

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🚫 2. Pharyngeal Phase (MOST IMPORTANT)

👉 Goal:
✔ Move food to esophagus
❌ Prevent entry into nose & trachea

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🔐 Protective Mechanisms

👉 Mnemonic: “NELR” (No Entry Lungs & Nose Rule)

• N → Nose closed (soft palate up)

• E → Epiglottis closes airway

• L → Larynx moves up

• R → Respiration stops

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🔽 Sequence of Events

1. Soft palate ↑ → closes nasopharynx

2. Vocal cords close + larynx moves up

3. Epiglottis covers airway

4. Pharyngeal muscles contract

5. UES relaxes → food enters esophagus

6. Breathing stops (deglutition apnea)

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🌀 3. Esophageal Phase

👉 Mnemonic: “PER”

• P → Peristalsis (primary)

• E → Entry into stomach

• R → Reflex UES contraction

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🔁 Key Points:

• Peristalsis speed → 3–5 cm/sec

• Time → ~10 sec

• Secondary peristalsis if needed

• UES closes → prevents backflow

Q: Which phase is voluntary?

Oral phase

“Q: Where is swallowing center?

👉 Medulla & pons

Q: Why doesn’t food enter trachea?

👉 Epiglottis + vocal cord closure + larynx elevation

.What is deglutition apnea?

.👉 Temporary stoppage of breathing

What triggers swallowing reflex?

👉 Food touching pharyngeal receptors

❗ Dysphagia (difficulty swallowing)

-Cause → nerve/muscle problem

Aspiration

• Failure of airway protection → food enters lungs

Achalasia

LES fails to relax → food stuck

🧠 DISORDERS OF DEGLUTITION — Quick Sheet

1. ↓ / Absence of Deglutition Reflex

👉 Definition:
Failure or loss of swallowing reflex

⚠ Effects:

• Food enters nose → regurgitation

• Food enters airway → aspiration (dangerous)

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📌 Causes

👉 Mnemonic: “NAC”

• N → Nerve damage (CN IX, X – medullary lesions)

• A → Anesthesia of pharynx (e.g., cocaine)

• C → CNS lesions (medulla)

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🎯 Key Concept:

👉 Reflex failure = airway not protected

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2. Aerophagia

👉 Definition:
Swallowing of air along with food/liquids

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📌 Causes

👉 Mnemonic: “NUT”

• N → Nervous individuals

• U → Upper esophageal sphincter tone ↓

• T → Tension / anxiety

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⚙ Fate of Swallowed Air

👉 Mnemonic: “BBF”

• B → Belching (comes up)

• B → Bowel (travels down)

• F → Flatus (expelled)

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3. Dysphagia

👉 Definition:
Difficulty in swallowing

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📌 Causes

👉 Mnemonic: “PMOF”

• P → Pharyngitis (common cause)

• M → Motor dysfunction (pharynx/esophagus)

• O → Obstruction (foreign body)

• F → Inflammation (oral cavity)

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⚠ Clinical Importance

• Can indicate:

  • Neurological disorder

  • Structural obstruction

  • Infection

What happens if swallowing reflex is absent?

👉 Aspiration + nasal regurgitation

Which nerves are involved in deglutition reflex?

👉 CN IX & X

What is aerophagia?

Swallowing air

Common cause of dysphagia?

👉 Pharyngitis

What causes aerophagia in nervous people?

👉 ↓ UES tone

FLOWCHART — Disorders of Deglutition

Deglutition Disorders

│

┌───────────────┼────────────────┐

│ │

Reflex ↓ / Absent Dysphagia

│ │

┌────┼─────┐ Causes:

│ │ - Pharyngitis

CN IX/X Anesthesia - Motor issues

Lesions (cocaine) - Obstruction

│ │ - Oral inflammation

Aspiration Nasal regurgitation

A 55-year-old man presents with frequent nasal regurgitation of liquids and occasional choking on food. On examination, he has a history of medullary stroke.

Q: What is the most likely cause of his symptoms?
A. Upper esophageal sphincter hypertonia
B. Absence of deglutition reflex due to CN IX/X lesion
C. Aerophagia
D. Pharyngitis

B

Case:
A 22-year-old anxious student reports excessive belching and passing large amounts of flatus. There is no dysphagia.

Q: The most likely mechanism is:
A. Decreased UES tone with involuntary air swallowing
B. CN IX/X paralysis
C. Pharyngeal obstruction
D. Acute pharyngitis

Answer: A

Explanation:

Aerophagia occurs in nervous individuals due to ↓ UES tone.

No dysphagia → reflex and motor pathways intact.

:Case:
A 35-year-old man complains of difficulty swallowing both solids and liquids. Examination shows pharyngeal muscle weakness.

Q: The most likely type of dysphagia is:
A. Oropharyngeal (motor)
B. Esophageal (mechanical)
C. Aerophagia
D. Absent deglutition reflex

.Answer: A

Explanation:

• Difficulty with both solids and liquids from the start → motor/oropharyngeal dysphagia.

• Esophageal dysphagia usually starts with solids first.

A 60-year-old patient has trouble swallowing solids for 2 months but liquids are fine. He reports occasional chest discomfort.

Q: The most likely cause is:
A. Absent deglutition reflex
B. Esophageal obstruction (mechanical)
C. Aerophagia
D. CNS lesion

Explanation:

Solids affected first → mechanical obstruction.

Reflex and liquids intact → CNS/reflex likely normal.

During a clinical exam, a patient is unable to swallow water properly. He coughs, chokes, and fluids come out of his nose. The examiner suspects a cranial nerve lesion.

Q: Which nerve lesion is most likely?
A. CN V
B. CN IX/X
C. CN XII
D. CN VII

Answer: B

Explanation:

• CN IX (Glossopharyngeal) & X (Vagus) → afferent + efferent swallowing reflex.

• CN XII → tongue movement, but not primary reflex.