Digestive System Flashcards
Integrated processes of the digestive system:
ingestion
mechanical digestion and propulsion
chemical digestion
secretion
absorption
defecation
What does the lining of the digestive tract protect us from?
corrosive effects of digestive acids
mechanical stresses, such as abrasion
bacteria either ingested with food or that reside in digestive tract
What is lined on the digestive tract to protect us?
mucosa
What is the smooth muscle tissue controlled by?
rhythmic cycles of activity controlled by pacesetter cells that undergo spontaneous depolarization.
Stages of Peristalsis:
Initial state > contraction of muscles behind bolus > contraction of longitudinal muscles ahead of bolus > wave of contraction in circular muscle layer forces bolus forward.
Segmentation:
cycles of contraction that churn and fragment the bolus
mixes contents with intestinal secretions
does not push materials in any one direction
aims to mechanically break down food.
Local factors
primary stimulus for digestion
responds to changes in the pH, physical distortion of of the wall, or the presence of chemicals.
Neural control mechanisms
Short reflexes: chemoreceptors or stretch receptors
- controlled by myenteric reflexes: controlling neurons in the myenteric plexus
Long reflexes: interneurons + motor neurons in CNs- more control over digestive activities.
- may involve parasympathetic motor fibers in the glossopharyngeal, vagus, or pelvic nerves.
Hormonal control mechanisms
hormones that affect the digestive tract are produced by enteroendocrine cells, cells in the epithelium of the digestive tract.
Functions of the oral cavity:
sensory analysis
mechanical digestion
lubrication
- mucus and saliva
limited chemical digestion
- of carbohydrates and lipids
What are the four primary functions of the tongue
Mechanical digestion by compression, abrasion, and distortion
Assistance in chewing and preparing food for swallowing
Sensory analysis by touch, temperature, and taste receptors
secretion of mucins and lingual lipase
Enzyme - Substrate: Lipase
Lipids
Enzyme - Substrate: Amylase
Carbohydrates
Enzyme - Substrate: Proteases
Proteins
Enzyme - Substrate: Pepsin
Proteins
Parotid glands secrete
salivary amylase
Sublingual glands secrete
mucus (buffer and lubricant)
Submandibular glands secrete
salivary amylase, buffers, and mucins
The majority of saliva is
water, remaining parts are electrolytes, buffers, glycoproteins, antibodies, enzymes, and wastes.
Functions of saliva include
cleaning oral surfaces
moistening and lubricating food
maintaining pH of mouth near 7
Controlling populations of bacteria and limiting acids that they produce
Dissolving chemicals that stimulate taste buds
Initiating digestion of complex carbohydrates with salivary amylase
Food is forced from
oral cavity to vestibule and back across surfaces of teeth.
Steps of Swallowing (Deglutition)
Buccal phase > pharyngeal phase > esophageal phase > Bolus Phase
Buccal Phase
VOLUNTARY
compression of bolus, retraction of tongue forces bolus into the oropharynx (bolus pushes on the soft palate to close off nasopharynx), then oropharynx and moves bolus towards stomach.
Tongue also stops it from going anteriorly.
Pharyngeal Phase
INVOLUNTARY
Elevation of the larynx and folding of the epiglottis direct the bolus past the closed glottis.
Nothing goes through the airway, only the esophagus is opened.
Esophageal Phase
INVOLUNTARY
contraction of pharyngeal muscles forces the bolus through the entrance to the esophagus. Bolus is pushed toward the stomach by a peristaltic wave (by CN IX and X)
Stretch, caused by food, in the esophagus will cause it to relax.
Sphincters
Bolus enters the stomach
the approach of the bolus triggers the opening of the lower esophageal sphincter.
Stomach
temporary storage of ingested food
mechanical digestion w/ muscular contractions
chemical digestion of food with acid and enzymes
Chyme
partially digested food mixed with acidic secretions of stomach
Acid
helps break down plant cell walls/CT in meat
activates pepsinogen -> pepsin
kills microorganisms
denatures proteins
What is the tissue type of the stomach?
simple columnar epithelium w/ additional layers of smooth muscle
Pepsinogen + HCL >
pepsin
As the stomach contents become more fluid
pH approaches 2.0
Preliminary digestion of proteins by pepsin increases
T/F: Are nutrients absorbed by the stomach?
FALSE
Production of acid and enzymes by gastric mucosa is controlled by
CNS
Short reflexes of ENS
Hormones of digestive tract