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π Practice 1 - Alimentary (Digestive) System: Exam Summary
1. SPLANCHNOLOGY - OVERVIEW
Internal organs = organs located in cavities of the head, neck, chest, abdomen, and pelvis.
Types of internal organs:
| Type | Structure | Examples |
|---|---|---|
| Tubular (hollow) | Mucosa β Submucosa β Muscular layer β Serosa/Adventitia | Esophagus, stomach, intestines |
| Parenchymal | Stroma (framework) + Parenchyma (functional part) | Liver, pancreas |
Layers of a tubular organ wall:
- Mucosa - epithelial layer + lamina propria + muscularis mucosae
- Submucosa - submucosal lymphatic layer, Meissner's plexus (inner + outer)
- Muscular layer - smooth muscle + Auerbach's (myenteric) plexus
- Serosa/Adventitia - blood & lymphatic vessels
Glands:
- By origin: Ectodermal, Mesodermal, Endodermal
- By ducts: Exocrine (have ducts - secrete enzymes) vs. Endocrine (no ducts - secrete into blood)
- By structure: Alveolar, Tubular, Compound (tubular, alveolar, tubuloalveolar)
2. ORAL CAVITY
Divisions:
- Oral vestibule (vestibulum oris): Between lips/cheeks and teeth/gingiva
- Oral cavity proper (cavitas oris propria):
- Roof: hard + soft palate
- Floor: tongue + mucosa
- Sides: dental arches + gums
- Opens posteriorly via fauces into oropharynx
Hard palate:
- Bone: Palatine process of maxilla + horizontal plate of palatine bone
- Covered by mucous membrane
Soft palate (velum palatinum):
- Contains palatine aponeurosis
- 5 muscles: tensor veli palatini, levator veli palatini, palatopharyngeus, palatoglossus, m. uvulae
Floor of oral cavity (diaphragma oris):
- Mylohyoid muscle (paired) forms the diaphragm
- Above it: geniohyoid, genioglossus, hyoglossus
- Below it: anterior belly of digastric
3. TEETH
Key facts:
- Deciduous (primary): 20 teeth; formula = 2.1.0.2; eruption begins ~6 months; complete by age 2
- Permanent (secondary): 32 teeth; formula = 2.1.2.3; complete ~18-21 years (3rd molars by 17-25 years)
Parts of a tooth:
| Part | Description |
|---|---|
| Crown (corona dentis) | Portion above the alveolus |
| Neck/Cervix (cervix dentis) | Between crown & root; surrounded by gingiva |
| Root (radix dentis) | Within the dental alveolus |
Tooth composition:
- Dentine (70% hydroxyapatite) - main body
- Enamel - covers crown (hardest, up to 2 mm)
- Cementum - covers root (bone-like, thinner)
- Pulp - loose connective tissue with vessels & sensory nerves; divided into crown pulp and root pulp
- Periodontal ligament (periodontium) - dense fibrous tissue 0.2 mm wide connecting tooth to alveolar bone
Tooth types & root numbers:
| Tooth | Shape | Roots |
|---|---|---|
| Incisors | Blade-like (cutting) | 1 |
| Canines | Cone-shaped (tearing) | 1 |
| Premolars | Cusped (grinding) | 1-2 |
| Molars | Multicusped (grinding) | 2-3 (upper molars: 3) |
Dental formulas (WHO numbering):
- Permanent: quadrant 1 (upper right), 2 (upper left), 3 (lower left), 4 (lower right); teeth 1-8
- e.g., left maxillary canine = 23, right mandibular last molar = 48
- Deciduous: quadrants 5-8; teeth I-V
- e.g., lateral incisor upper right = 52
4. TONGUE
Functions: deglutition, taste, speech, mastication, salivation, suckling
Parts:
- Apex (tip), Body (corpus), Root (radix), Dorsum
- Sulcus terminalis separates anterior 2/3 from posterior 1/3
- Foramen caecum - remnant of thyroglossal duct (at apex of sulcus terminalis)
Papillae (4 types):
| Type | Location | Taste buds? | Function |
|---|---|---|---|
| Filiform | Entire dorsum | No | Friction for food bolus |
| Fungiform | Entire dorsum (scattered) | Yes (few) | Sweet perception |
| Foliate | Posterolateral margin | Yes (many) | Sour & salty |
| Vallate | Row anterior to sulcus terminalis | Yes | Bitter |
Taste buds also found on: epiglottis, pharyngeal arches, pharynx epithelium, soft palate
Muscles:
| Intrinsic (change shape) | Extrinsic (move tongue) |
|---|---|
| Superior longitudinal | Genioglossus |
| Inferior longitudinal | Hyoglossus |
| Transverse | Styloglossus |
| Vertical | Palatoglossus |
Innervation:
| Region | General sensation | Taste |
|---|---|---|
| Anterior 2/3 | Lingual n. (CN V3) | Chorda tympani (CN VII) |
| Posterior 1/3 | Glossopharyngeal n. (CN IX) | Glossopharyngeal n. (CN IX) |
| Epiglottis | Internal laryngeal n. (CN X) | Internal laryngeal n. (CN X) |
5. FAUCES
- Opening connecting oral cavity to oropharynx
- Boundaries: soft palate/uvula (above), palatoglossal arch (anterior pillar), palatopharyngeal arch (posterior pillar), tongue (below)
- Between the arches: tonsillar fossa containing the palatine tonsil
6. PHARYNX
- 12-14 cm musculomembranous tube from cranial base to Cβ (lower border cricoid), then continues as esophagus
- Digestive and respiratory tracts cross here
3 Parts:
| Part | Key features |
|---|---|
| Nasopharynx | Behind posterior nares; pharyngeal tonsil + tubal tonsils; auditory tube openings |
| Oropharynx | Communicates via fauces; palatine tonsils |
| Laryngopharynx | Level Cβ; piriform fossae; anterior wall = posterior larynx |
Waldeyer's Ring (lymphoid ring):
- Lingual tonsil (anteroinferior)
- Palatine tonsils (lateral)
- Tubal tonsils (lateral)
- Pharyngeal/adenoid tonsil (posterosuperior)
Pharyngeal wall layers:
Mucosa β Submucosa β Pharyngobasilar fascia β Pharyngeal muscles β Buccopharyngeal fascia
Pharyngeal muscles:
| Constrictors | Elevator muscles |
|---|---|
| Superior constrictor (4 parts: pterygopharyngeal, buccopharyngeal, mylopharyngeal, glossopharyngeal) | Stylopharyngeus |
| Middle constrictor (chondropharyngeal, ceratopharyngeal) | Salpingopharyngeus |
| Inferior constrictor (thyropharyngeal, cricopharyngeal) | Palatopharyngeus |
7. ESOPHAGUS
- Muscular tube, 25-30 cm long; Cβ to Thβββββ
- Newborn: begins at Cβββ, ends at Thβββ
- 3 Parts: cervical, thoracic, abdominal
- 9 endoscopic segments: tracheal, aortic, aorto-bronchial, bronchial, subbronchial, retropericardial, supradiaphragmatic, intradiaphragmatic, subdiaphragmatic
5 Constrictions (narrowings):
- Pharyngo-esophageal junction (beginning)
- Aortic arch crossing
- Left main bronchus crossing
- Esophageal hiatus of diaphragm
- Gastric cardiac orifice (cardia)
Wall structure:
- Mucosa: 7-10 longitudinal folds
- Submucosa
- Muscular layer: inner circular + outer longitudinal
- Upper 1/3: striated muscle
- Middle 1/3: mixed (smooth + striated)
- Lower 1/3: smooth muscle
- Adventitia/Serosa
8. STOMACH
Parts:
- Cardia (pars cardiaca) - cardiac orifice at Thβββββ
- Fundus (fundus gastricus) - dome-shaped upper part
- Body (corpus gastricum) - main portion
- Pyloric part (pars pylorica) - antrum + pyloric canal; ends at pyloric orifice at Thββ-Lβ
Curvatures:
- Lesser curvature - upper right; has incisura angularis (angular notch)
- Greater curvature - lower left
Wall layers:
- Mucosa - gastric folds (rugae); gastric pits (foveolae); gastric areas (areae gastricae)
- Glands: Chief cells (pepsin, lipase), Parietal/oxyntic cells (HCl + intrinsic factor for Bββ), Mucous neck cells, Neuroendocrine cells
- Submucosa
- Muscular layer: longitudinal + circular + oblique fibers
- Serosa (visceral peritoneum extension)
Ligaments of the stomach:
| Ligament | Notes |
|---|---|
| Hepatogastric + hepatoduodenal | = omentum minus |
| Gastrocolicum | Upper part of omentum majus |
| Gastrosplenicum | |
| Gastrophrenicum | |
| Gastropancreaticum |
Position (Syntopy):
- Anterior: diaphragm, anterior abdominal wall, liver
- Posterior: aorta, IVC, pancreas, spleen, left kidney, left adrenal gland
Blood supply:
Right & left gastric aa., right & left gastro-omental aa., short gastric aa., posterior gastric aa.
9. CLINICAL CASES - KEY ANSWERS
| # | Scenario | Answer | Key nerve/muscle |
|---|---|---|---|
| 1 | Superior laryngeal nerve lesion β voice change | A - Inferior pharyngeal constrictor | External laryngeal branch of SLN |
| 2 | Swallowing difficulty, food enters airway | B - Oblique arytenoid + ary-epiglottic mm. | Close larynx during swallowing |
| 3 | Parotid surgery β facial nerve cut | D - Buccinator | CN VII (facial nerve) |
| 4 | Adenoids, nasal obstruction | B - Pharyngeal tonsil | Enlarged = adenoid |
| 5 | Midfacial/mandibular hypoplasia, cleft palate | A - 1st pharyngeal arch | Mandible, maxilla, mastication mm. |
| 6 | No general sensation, anterior 2/3 tongue | A - Trigeminal nerve (lingual n.) | CN V3 |
| 7 | No taste, posterior 1/3 tongue after tonsillectomy | C - Glossopharyngeal nerve | CN IX |
| 8 | Posterior belly digastric paralysis | D - Facial nerve | CN VII |
| 9 | Gag reflex afferent limb | C - Glossopharyngeal nerve | CN IX (afferent); CN X (efferent) |
| 10 | Styloid process muscles paralyzed | A - Facial + glossopharyngeal + hypoglossal | Stylohyoid (VII), styloglossus (XII), stylopharyngeus (IX) |
| 11 | Unable to swallow; which nerve unaffected? | B - Spinal accessory nerve | SCM + trapezius - NOT involved in swallowing |
10. TEST ANSWERS (Quick Reference)
| Q | Answer | Q | Answer | Q | Answer |
|---|---|---|---|---|---|
| 001 | C | 007 | A,B,D | 013 | C |
| 002 | D | 008 | A,B,C,D | 014 | C |
| 003 | A,B | 009 | A,B | 015 | C |
| 004 | A,B,C,D,E | 010 | A,B | 016 | A,B |
| 005 | A,D | 011 | A,C | 017 | A,B,C |
| 006 | A,B,C,D,E | 012 | A,B,C,D | 018 | B,C,D |
| 019 | A,B,D |
High-yield mnemonics:
- Esophageal muscle layers: "USS" = Upper = Striated, Middle = miXed, Lower = Smooth
- Waldeyer's Ring: "Lingual + Palatine + Tubal + Pharyngeal" tonsils (ring around pharyngeal openings)
- Tongue sensation: Anterior 2/3 = CN V3 (general) + CN VII (taste); Posterior 1/3 = CN IX (both)
- Styloid process muscles: Stylohyoid (VII), Styloglossus (XII), Stylopharyngeus (IX)
- Palate muscles: "TL-PPU" = Tensor, Levator, Palatopharyngeus, Palatoglossus, Uvulae
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