Digestive Physiology Flashcards
What are the digestive activities in the GI tract?
- Ingestion
- Secretion
- Digestion
- Motility
- Absorption
- Defecation
What happens during ingestion?
• Mechanical breakdown (from large to smaller particles) o Chewing (mouth) o Churning (stomach) o Segmentation (small intestine)
What happens during secretion?
- Gastric mucosa and accessory organs will secrete
* Aids in the digestion and absorption
What happens during digestion?
• Chemical breakdown
o From polymer to monomer for absorption
What happens during motility?
• Propulsion (swallowing, peristalsis, mix and propel)
o Swallowing (oropharynx)
o Peristalsis (esophagus, stomach, small intestine, large intestine)
- Starts with voluntary to involuntary actions of peristalsis
- Wave of contractions and relaxation
o For better mixing and propel
What happens during absorption?
- Absorption by mucosa lining, aided by microvilli
* Once absorbed -> transported to the lymph vessels and blood vessels
What happen during defecation?
• Elimination for undigested food via anus
Describe the events in the site of ingestion of oral cavity
• Mastication (mechanical breakdown of food, chewing)
o Teeth
o Muscles of mastication (masseter, tempolaris etc)
• Taste
o On tongue and sends signals to gastro centre in the brain
• Salivary glands
o Forms bolus by mixing food and saliva
o Enters esophagus and initiates swallowing
What are the properties and functions of saliva?
• Protection
o By producing lysozyme -> contains IgA -> prevents decay of tooth by killing bacteria
• Lubrication
o By mucoid secretion of saliva
• Formation of bolus
• Digestion of carbohydrates
o By salivary amylase
What are the regulation of saliva?
• ~1l of saliva produced a day
o aids in swallowing process by voluntary/reflexes
• controlled by Autonomic Nervous System (ANS)
o Sympathetic
- From T1-T3 help produce viscous saliva
o Parasympathetic
- From cranial nerve (7&9) help initiate watery salivary secretion
• Cerebral cortex and brain do take part in controlling
o Salivation decreases when person is asleep, rest, fatigue, scared
What is the regulation of the GIT?
- Receptors
- Emotional (cephalic reflexes)
- Enteric Nervous System (ENS)
- GI peptides
- Hormone producing cells of stomach and small intestine
- ANS Sympathetic
- ANS Parasympathetic
Where are receptors for the regulation of the GIT?
GI tract wall
Where the role of cephalic reflexes for the regulation of the GIT?
Smell of food
Where the role of Enteric Nervous System (ENS) for the regulation of the GIT?
o Self-contained (intrinsic)
o Stimulates the inside/outside of tract
o Involves CNS/ANS centres
- Centres: responds to different stimuli
- Stimulis: stretching of organ for food in lumen, osmolarity, pH of content
- Stimulated by chemical and mechanical receptors -> activates/inactivates -> gland that secrete digestive juice/hormones, or stimulate muscles to mix the content along the tract
Where the role of GI peptides for the regulation of the GIT?
o Regulatory role as hormones or paracrines
o Eg: gastrin, CCK, secretin
Where the role of hormone producing cells for the regulation of the GIT?
• Stomach and small intestine have hormone producing cells -> stimulated -> release product into interstitial fluid in extracellular space
o Blood and interstitial fluid -> distribute hormones -> to target cells in the same digestive organs -> induce for secretion or contraction
Where the role of ANS of parasympathetic for the regulation of the GIT?
enhance secretion of GI juices & digestion
Where the role of ANS of sympathetic for the regulation of the GIT?
decreases/inhibits hormones
What are the motility patterns in GI tract?
- Peristalsis
* Segmentation
What happens during peristalsis?
- Food comes from mouth
- Adjacent segments of alimentary tract organs -> alternately contract and relax -> moves the food along the tract distally
- One directional movements allows movement of food from one end to another
- Takes place in esophagus and large intestine
- Reverse peristalsis: vomiting
What happens during segmentation?
• Nonadjacent segments of alimentary tract organs -> alternately contract and relax -> moving food forward then backward -> for food mixing and slow food propulsion will occur
• Not in one direction movement, but zigzag movement
o For proper mixing and max absorption of chyme
• Takes place in small intestine
What are the phases of swallowing?
• Involves 22 muscles
• 3 phases
o Buccal phase
o Pharyngeal phase
o Esophageal phase
Describe the phases of swallowing
• Buccal phase
o Upper esophageal sphincter contract
o Food in the mouth -> mechanically broken down -> mix with saliva to form bolus
• Pharyngeal phase
o Tongue presses against hard palate -> forcing bolus into the oropharynx to laryngopharynx
o Voluntary control (eg. poisoned food can be spat out)
o Do not talk and eat (confuses the epiglottis to open or close)
• Pharyngeal-esophageal phase
o Begins as uvula and larynx rise to prevent food (or regurgitation) from entering the respiratory passageways
o Tongue blocks off the mouth, epiglottis close the larynx
o UES relaxes food enter the esophagus
• Esophageal phase
o Constrictor muscles of pharynx contract -> forcing food into esophagus inferiorly (peristaltic activity begins) -> contract and relax -> propel food
o UES contracts (closes) after food enters
o Peristalsis moves food from esophagus to stomach in 8 seconds
• Gastroesophageal sphincter surrounding the cardiac orifice opens -> food enters the stomach
What are the features of the oesophagus?
- Muscular tube that brings down food from pharynx to stomach
- Has no digestive/absorptive functions
- A conduit
• Motility by peristalsis
o Progressive wave of muscles contraction and relaxation alternation of inner circular and outer longitudinal muscles -> propel bolus of food to the stomach
What is the gastric motility?
• Stomach stores food mix with gastric juice for digestion -> forms chyme -> empties it as chyme
• Peristaltic contraction (3-5/min)
o Mix the content and empties part of chyme into duodenum (each contraction)
- Propulsion
a. Peristaltic waves moves from fundus to pylorus
b. Allows mixing of the bolus with gastric content -> forms chyme
c. Pyloric valve and LES closed - Grinding
a. Mixing action occur close to the pylorus - Retropulsion
a. Pyloric end of stomach acts as pump -> delivers small amounts of chyme into duodenum, simultaneously forcing most of its contained material backward into the stomach
b. Small amount of chyme will enter
c. Most amount propelled in main stomach area & mixed again with stomach content
What is vomiting?
• Protective reflex
• Complex reflex coordinated in the brain stem
o Toxic gas of stomach/noxious -> stimulate excessive salivation -> deep breaths -> vomit occur when:
- Intra-abdominal pressure or intragastric pressure overcomes LES pressure -> content of stomach thrown out via esophagus to mouth and out
What are the stimulis that contributes to vomiting?
o Stomach distension o Seas sickness/dizziness o Pain o Increased intracranial pressure o Others: noxious chemicals, toxins, drugs