M4 GIT Flashcards
What are the 6 major organs of the GIT?
- Oral cavity (mouth)
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine (including rectum and anus)
What are the 6 accessory organs of the GIT?
- Teeth
- Tongue
- Salivary Glands
- Liver
- Gall Bladder
- Pancreas
What are the 6 key steps (or processes) of the GIT?
- Ingestion
- Motility (movement of contents ingested)
- Digestion (Mechanical and chemical)
- Secretion
- Absorption
- Defecation
What are the layers of the GI?
(Inner to Outer)
Lumen (inner cavity)
Mucosa
Submucosa
Muscularis Externa
Serosa
Body wall
What are the 2 layers of the Muscularis Externa and their functions?
- Inner circular smooth muscle - contracts inwards
- Outer longitudinal smooth muscle - contracts along GIT
+ Myenteric plexus (intrinsic nerve plexus)
Responsible for peristalsis and segmentation.
What are the 3 layers of the Mucosa and their functions?
- Epithelium
- Lamina propria - connective tissue
- Muscularis mucosa
Responsible for Protection, absorption and secretion
What does the Submucosa contain?
Submucosal plexuses
Capillaries and lymph
Responsible for transport and regulation
Which areas of the GI feature Stratified squamous epithelium for protective purposes?
Oral cavity, pharynx, esophagus and anal canal.
Which area of the GI features columnar epithelium upon villi to increase surface area for absorption?
Small Intestine.
Which area of the GI features both Columnar epithelium and tubular glands for further absorption and protection?
Large Intestine
Which area of the GI features gastric glands mainly focusing on secretion?
Stomach
What is bolus?
Small rounded mass of chewed food substance.
What are the 3 steps in peristalsis?
- Contraction of circular muscles behind food mass.
- Contraction of longitudinal muscles ahead of food mass.
- Contraction of circular muscles propels food forward.
Where does peristalsis occur?
Esophagus, stomach, small/large intestines.
What is peristalsis?
contraction and relaxation of adjacent sections to propel food forward.
What is segmentation?
Contraction and relaxation of non-adjacent sections to move food forward and backward as a form of mechanical digestion (food is churned and mixed)
What is the purpose of segmentation?
Mixes chyme with digestive secretion and increases exposure to epithelium for absorption.
Where does segmentation occur?
Small and large intestines
Where can the submucosal plexus be found and what is its purpose?
Submucosal layer.
Control local blood flow, gastrointestinal secretion and absorption from GIT into blood/lymph vessels.
Where can the Myenteric plexus be found and what is its purpose?
Between the circular and longitudinal muscles.
Regulates gastric motility and contractility.
What is enteric plexus?
Nerve plexuses relating to the intestines.
Myenteric and submucosal plexuses.
What nervous system controls the GIT?
Autonomic
- Parasympathetic nervous system via the vagus nerve. (CN X)
- Sympathetic nervous system via splanchic nerves.
What happens to the GIT when PNS activates?
Acetylcholine released
Promoting vasodilation to GIT, increasing secretion, motility and relaxation of sphincters.
What happens to the GIT when SNS activates?
Norepinephrine is released
Ceases digestive activities.
How do internal and external stimuli affect digestive activities?
Stimuli is received by the CNS or first detected by chemo/osmo/mechanoreceptors (internal stimuli).
Signaled to intrinsic (local) nerve plexuses, effects smooth muscles/glands, causing a change in digestive or secretory activities.
What are short reflexes?
Occur entirely within the gastrointestinal wall.
What are long reflexes?
Involves the CNS.
- External stimuli
What are the 4 functions of the oral cavity?
Ingestion - sensory analysis before swallowing
Mastication - teeth, tongue, palatal surfaces (chewing)
Lubrication - mixing with mucus and salivary secretions.
Partial digestion - break down of carbs (salivary amylase) and lipids (lingual lipase)
What are the 4 functions of the tongue?
- Mechanical digestion
- Chemical digestion (lingual lipase) - carbs and lipids
- Lubrication
- Sensory analysis (taste, temp and texture)
What are the 3 glands of the oral cavity?
- Parotid (Cheek)
- Submandibular (Jaw)
- Lingual (Below tongue)
What does the Parotid gland produce?
Salivary amylase (Carb/starch)
What does the Submandibular gland produce?
Buffers (pH 7)
Glycoprotein - Mucin
Salivary amylase
What does the Lingual gland produce?
Lingual lipids - fats/lipids
Mucus
What control is the salivary reflex?
Autonomic (Parasympathetic)
Which 3 sensory nerves in the mouth signal to the medulla to drive salivary secretion?
- Trigeminal (CN V)
- Facial (CN VII)
- Glossopharyngeal (CN IX)
Which 3 receptors receive information to drive salivary secretion?
Mechanoreceptor in tongue +palate
Chemoreceptor in taste buds.
What sensory inputs can drive salivary secretion?
Smell
Sight
thought of food
Unpleasant stimuli
What is deglutition
Swallowing
What is Uvula
Gateway to nose
Is Swallowing voluntary?
Yes
What is the first phase of deglutition?
Buccal phase
Uvula open, esophageal sphincter shut.
Bolus pushed to the pharynx, activating mechanoreceptors.
Afferent nerves (trigeminal + glossopharyngeal) 5+9 stimulate the swallow centre in the medulla.
What is the second phase of deglutition?
Pharyngeal phase
Uvula and glottis close, epiglottis folds down, seals trachea.
Sensory receptor in oropharynx stimulated. afferent signals via trigeminal, Glossopharyns and Vagus nerves. (V, IX, X)
What is the third phase of deglutition?
Esophageal phase
Motor impulse from swallowing centre (medulla) carried to pharynx + esophagus via glossopharyngeal and vagus nerve (IX, X)
Peristaltic contraction propel bolus toward stomach.
Gastroesophageal sphincter opens allowing bolus to enter. (normally closed to prevent stomach acid rising)
Which hormone stimulates the secretion of digestive enzymes from the pancreas and bile from the gallbladder?
Cholecystokinin (CCK)
The stomach secretes hydrochloric acid (HCl) primarily to:
Activate pepsinogen into pepsin.
The proteolytic enzyme breaks down proteins into peptides, kills bacteria, and denatures proteins.
What is the primary role of bile in digestion?
Emulsifies fats for easier digestion
Which part of the small intestine is primarily responsible for most nutrient absorption?
Jejunum
Highly folded and lots of microvilli
Which enzyme is responsible for breaking down fats in the small intestine?
Lipase.
Primarily secreted by pancreas.
What is the main function of the large intestine?
Absorption of water and electrolyte.
Form and solidify stool.
Which hormone is released by G cells in the stomach to stimulate gastric acid secretion?
Gastrin
What is the primary purpose of the mucous layer in the stomach?
Protects the stomach lining from acid and enzymes
Which structure prevents food from entering the trachea during swallowing?
Epiglottis
