GI: pharynx, esophagus, stomach

basic sciences exam 4

pharynx

shared pathway for respiratory/digestive; connects nasal/oral cavities to larynx, esophagus

12-14 cm long

divisions of the pharynx

nasopharynx, oropharynx, laryngopharynx

nasopharynx

functions primarily in respiration

contains pharyngeal tonsils (adenoids)

openings of eustachian (auditory) tubes

above soft palate

oropharynx

extends from soft palate to epiglottis

contains palatine tonsils (lymphatic/immune)

lingual tonsils (lymphatic/immune)

valleculae (spaces b/w base of tongue, epiglottis)

laryngopharynx (hypopharynx)

extends from epiglottis to esophagus

posterior to larynx

directs food into esophagus

contains epiglottis

epiglottis

top of larynx, behind tongue

made of elastic cartilage covered by mucous membrane

functions in swallowing

when swallowing, the epiglottis functions to

fold down and cover the glottis, the opening to the larynx; prevents food and liquid from entering trachea (windpipe)

pharynx composed of ___ muscle arranged in what two layers?

skeletal

outer circular layer: superior, middle, inferior pharyngeal constrictors

inner longitudinal layer: stylopharyngeus, salpingopharyngeus, palatopharyngeus

pharynx innervation

motor: cranial nerves IX and X

sensory: oropharynx: CN IX, laryngopharynx: CN X (vagus)

pharynx blood supply comes from

branches of external carotid artery

ascending phayrngeal, facial, maxillary arteries

pharynx functions

swallowing, airway protection, resp coordination, sensory/motor control

swallowing- oral phase

voluntary; food mixed w saliva to form bolus, pushed into oropharynx by tongue

swallowing- pharyngeal phase

involuntary; soft palate elevates, epiglottis folds to cover laryngeal inlet, constrictor muscles push bolus towards esophagus

swallowing- esophageal phase

bolus enters esophagus via upper esophageal sphincter

airway protection during swallowing

epiglottis

vocal cords close to seal airway

breathing temporarily inhibited

air passage through pharynx

passes from nasal cavity through oropharynx then laryngopharynx into larynx and trachea

swallowing sensory and motor control

oropharynx sensory: glossopharyngeal nerve (CN IX)

pharyngeal muscles, sensory to laryngopharynx: vagus nerve (CN X)

pharyngeal plexus

coordinates muscle activity

gag reflex

protects against aspiration, triggered by stimulation of oropharynx

swallowing reflex

initiated by sensory input from oropharynx

dysphagia (swallowing disorders)

difficulty swallowing, coughing during meals, aspiration

what causes dysphagia

neuromuscular dysfunction, stroke, head/neck cancer, structural abnormalities

nuclear medicine role: dysphagia

radionuclide swallow study (scintigraphic evaluation)/ esophageal transit studies

uses Tc99m labeled food bolus to assess oropharyngeal/laryngopharyngeal transit, aspiration, residue.

provides quantitative data on swallowing efficiency

head and neck cancers (squamous cell carcinoma)

most common malignancy in oropharynx/laryngopharynx

often linked to HPV, smoking, alcohol use

symptoms include sore throat, dysphagia, hoarseness, weight loss

nuclear medicine role in head and neck cancers

F18 FDG PET/CT

used for staging, planning, monitoring recurrence

helps detect primary tumors, nodal involvement, distant mets

laryngopharyngeal reflux (LPR)

reflux of gastric contents into laryngopharynx; causes inflammation, mucosal damage

chronic cough, hoarseness, throat clearing, globus sensation

nuclear medicine role in LPR

scintigraphy w 99mTc labeled liquid, detects retrograde flow into pharynx

useful in functional assessment when endoscopy is inconclusive

aspiration pneumonitis

inhalation of food/liquid into lungs due to impaired swallowing or airway protection

coughing, recurrent pneumonia, breathlessness

nuclear medicine role in aspiration pneumonitis

radionuclide aspiration studies (salivagram)

detect aspirated material in trachea/lungs

helps assess risk of aspiration during swallowing

esophagus

serves as conduit for food/liquids from pharynx to stomach

25 cm in adults

esophagus extends from…

lower border of pharynx (C6) to cardiac orifice of stomach (T11)

regions of esophagus

cervical, thoracic, abdominal

cervical esophagus

begins at cricopharyngeus muscle (upper esophageal sphincter) in neck

thoracic esophagus

passes through superior and posterior mediastinum

adjacent to aorta, LA, bronchi

abdominal esophagus

short segment that enters abdominal cavity through esophageal hiatus of diaphragm

upper esophageal sphincter (UES)

formed by cricopharyngeus muscle

prevents air from entering esophagus while breathing

lower esophageal sphincter (LES)

functional sphincter at gastroesophageal junction

prevents gastric contents reflux into esophagus

layers of esophageal wall

mucosa, submucosa, muscularis externa, adventitia

esophagus: mucosa

lined w non keratinized stratified squamous epithelium

esophagus: submucosa

contains mucous glands, blood vessels

esophagus: muscularis externa

skeletal muscle (upper)

skeletal/smooth (middle)

smooth muscle (lower)

esophagus: adventitia

outermost connective tissue layer (no serosa except in abdominal portion)

esophagus: arterial blood supply

cervical: inferior thyroid artery

thoracic: bronchial/esophageal branches of aorta

abd: left gastric, inferior phrenic arteries

esophagus: venous blood supply

drains into azygos system, left gastric, portal vein

esophagus: innervation

vagus (CN X): parasympathetic

sympathetic trunk: sympathetic fibers

enteric nervous system: coordinates peristalsis

esophagus functions

swallowing, peristalsis, sphincter function, neural control

primary peristalsis

initiated by swallowing

secondary peristalsis

triggered by esophageal distension (e.g. residual food)

UES opens during

swallowing

LES prevents

gastroesophageal reflux

maintains tonic contraction, relaxes during swallowing

esophagus: neural control

enteric nervous system: coordinates local reflexes

CN X: provides parasymp. motor innervation

symp. fibers: modulate tone and blood flow

esophageal motility disorders

achalasia, diffuse esophageal spasm, scleroderma-related dysmotility

symptoms include dysphagia, regurgitation, chest pain

nuc med role: esophageal motility disorders

tc99m labeled liquid or solid bolus to assess transit, motility, residue

quantitative data on esophageal function, useful for diagnosis/therapy monitoring

gastroesophageal reflux disease (GERD)

incompetence of LES, allows gastric contents to reflux into esophagus

heartburn, regurgitation, chronic cough, hoarseness

nm role: reflux scintigraphy

detects retrograde flow of gastric contents into esophagus

can quantify frequency and severity of reflux episodes

esophageal cancer (squamous cell and adenocarcinoma)

malignant tumors from esophageal epithelium

progressive dysphagia, weight loss, hoarseness, chest pain

nm role in esophageal cancer (squamous cell and adenocarcinoma)

F18 FDG PET/CT

staging, planning, monitoring

primary tumor nodal involvement, distant mets

89 Zr trastuzumab PET

for HER2 positive esophageal cancers

post treatment eval (residual disease, recurrence, treatment related inflammation)

FDG PET/CT

response to chemo

differentiates bw residual tumor and post treatment changes

stomach

j shaped organ in upper left quadrant of abdomen bw esophagus and SI

3 major roles of the stomach

reservoir for food

breaks solid food down into small particles and combines w secretion of gastric juice, making chyme

controls rate of emptying of gastric content into duodenum

fundus

dome shaped upper portion of stomach, often filled w gas on imaging

body (corpus)

central region, largest part of stomach; major site for gastric secretions and mechanical digestion

antrum

lower portion of stomach leading into pylorus. grinds food and regulates emptying into duodenum

cardia

esophagus connects to stomach

pylorus

connects duodenum to stomach via pyloric sphincter

layers of the stomach wall

gastric mucosa

submucosa

muscularis externa

serosa

stomach: gastric mucosa

simple columnar epithelium

gastric pits/glands that secrete acid and enzymes

stomach: submucosa

connective tissue w blood vessels, lymphatics, nerves

stomach: muscularis externa

three layers of smooth muscle (longitudinal, circular, oblique). unique to stomach

aids in churning/mixing of food

stomach: serosa

outermost layer, part of visceral peritoneum

cardiac glands

secrete mucus

fundic/body glands

rich in parietal cells, secrete HCl and intrinsic factor; chief cells secrete pepsinogen, gastric lipase

pyloric glands

secrete mucus and gastrin via enteroendocrine cells

gastric mucosa of stomach contains

cardiac, fundic, pyloric glands

tight junctions bw epithelial cells

has rapid cell turnover

three layers of muscularis mucosae in stomach

circular, longitudinal, oblique

stomach arterial blood supply

branches from celiac trunk (L gastric, R gastric, R/L gastroepiploic arteries)

stomach venous blood supply

drains into portal vein system

stomach innervation

parasym: vagus nerve (secretion and motility)

symp: celiac plexus (inhibits activity)

stomach physiology

mechanical/chemical digestion, storage, controlled emptying, hormonal reg., absorption, defense mechanisms

stomach: mechanical digestion

churns and mixes food w gastric secretions through peristaltic contractions

three layers of muscularis are powerful for mixing/grinding

chyme

ingested food turned to semi liquid mixture through gastric digestion and mixing w secretions

parietal cells prod hydrochloric acid (HCl), which does what

denatures proteins

activates pepsinogen into pepsin

provides acidic environment to kill pathogens

chief cells secrete pepsinogen, which…

are precursors to pepsin (for protein digestion)

mucous cells secrete alkaline mucus to…

protect epithelium of stomach from acid

enteroendocrine cells release what hormones

gastrin, to stimulate acid secretion and motility

what regulates stomach emptying into duodenum

pyloric sphincter, based on duodenal feedback (pH, nutrient content, stretch)

gastrin

stimulates acid secretion, gastric motility

g-cells

somatostatin

inhibits gastric sec.

delta cells, also neuroendocrine cells

ghrelin

stim hunger

g cells, when stomach is empty

stomach absorbs few nutrients but will absorb…

water

alcohol

certain meds (e.g. aspirin)

defense mechanisms of stomach

mucosal barrier- prevents autodigestion by acid, enzymes

rapid epithelial turnover- dmged cells quickly replaced

tight juntions- no acid leakage into tissues

gastric cancer

adenocarcinoma most commonly

from gastric mucosa

risk factors are H pylori infection, smoking, diet, genetic predisposition

nm relevance gastric cancer

F18 FDG PET/CT

for staging, response to treatment, recurrence, mets

68 Ga FAPI PET/CT

emerging modality, higher sensitivity to subtypes like signet ring cell carcinoma

Radioimmunotherapy

investigational agents like 211 At Trastuzumad for HER2 positive gastric cancer

fibroblast activation protein inhibitory (FAPI)

ref to class of radiotracers used to image and detect tumors, other fibrotic disease

FDG PET (gastric cancer) may show uptake in…

active gastritis, intestinal metaplasia, dysplasia, but specifically is limited

68 Ga FAPI has higher sensitivity in detecting

gastric tumors, esp signet ring cell carcinoma and diffuse type gastric cancers

gastroparesis

delayed emptying w/o obstruction

diabetes, post surgery, meds, idiopathic origins

dumping syndrome

rapid gastric emptying, often post surgery

nm relevance in gastric emptying disorders

GE scintigraphy: gold standard

tc 99 meals to measure over 2-4 hrs

GE scintigraphy helps diagnose

gastroparesis, functional dyspepsia, post surgical gastric dysfunction; helps guide dietary and pharmacologic mgt