Digestive system
Lecture 44
● Autonomic nervous system
○ Responsible for involuntary control
○ sympathetic
■ Heightened mental alertness
■ Increased metabolic rate
■ Decreased digestive and urinary functions
■ Increased respiratory rate and dilation of respiratory pathways
■ Increased heart rate and blood pressure
■ Activation of sweat glands
○ Parasympathetic
■ Decreased metabolic rate
■ Decreased heart rate and blood pressure
■ Increased secretion by salivary and digestive glands
■ Increased motility in digestive tract
■ Increased blood flow in digestive tract
○ Autonomic tone
■ Maintaining heart rate: acetylcholine and norepinephrine released
continuously maintaining autonomic tone
● Gi tract
○ Long twisting tube that ends at the anus
○ Accessory glands: salivary glands, liver, pancreas, gallbladder – accessory bc
food is not moved into but they secrete substances into GI tract
● 3 phases of digestion
○Cephalic phase – starts w/ anticipation of ingestion and ends when last mouthful
swallowed
■ Response to food base stimuli
■ Secretory responses – salivary, gastric, duodenal, pancreatic
■ Non-secretory responses – mixing, motinity, etc
○Gastric phase – timing when food is present in stomach
○Intestinal phase – begins when chyme enters duodenum
● Saliva
○ Water and glycoprotein
○ Digestive enzymes
■ Amylase: starches → simple sugars
■ Lipase: triglycerides → fatty acids and glycerol
○ Lysozyme → kills bacteria
○ Dental plaque – when bacteria mixes with sugar or starch
● Mastication – chewing
○ Bolus – chewed food mixed with saliva
○ Brain controls this
● Swallowing
○ Retraction of tongue forces bolus into oropharynx
, ○Peristalsis – involuntary constriction and relaxation of muscles of digestive tract
creating wave like movements that push contents of canal forward
● Achalasia
○ Dysfunction of lower esophageal sphincter
○ LES fails to open when swallowing
○ Related to damaged nerves in esophagus or due to damage of LES
● Gastroesophageal reflux disease (GERD)
○ Acid reflux
○ Occurs when LES doesn’t close properly allowing digestives juices to rise into
esophagus
○ Treatment: antacids, H2 receptor blockers, proton pump inhibitors
Lecture 45
● Stomach – cephalic responses
○ Sight, smell, taste, thoughts of food cause parasympathetic stimulation
■ In response stomach releases
● Mucus – coat walls of stomach
● HCl – help w chemical digestion and also killing bacteria
○ Denatures proteins
○ Helps break down plant cell walls & connective tissue
in meat
○ Necessary for function of cells that secrete
pepsinogen
● Pepsinogen – breaks down proteins
● Gherlin – hunger hormone – when stomach is empty these
levels are high
● Gastrin – enhancing gastric mucosal growth, gastric motility,
and secretion of hydrochloric acid (HCl) into the stomach
● Gastric phase
○ Begins when food arrives to stomach
○ Stretch receptors activated to release hormones and enzymes
○ Gastrin released into bloodstream leading to
■ Protein digestion
■ Powerful contractions called mixing waves
■ Stimulates gastric motility
○ Gastric lipase – digests fat
○ Intrinsic factor – B12 absorption
● Determinants of gastric emptying
○ Volume
■ Greater volume, greater rate of gastric emptying
○ Osmotic pressure
■ Greater osmolality, decreased rate of gastric emptying
○ Nutrient density
■ Greater nutrient density, decreased rate of gastric emptying
Lecture 44
● Autonomic nervous system
○ Responsible for involuntary control
○ sympathetic
■ Heightened mental alertness
■ Increased metabolic rate
■ Decreased digestive and urinary functions
■ Increased respiratory rate and dilation of respiratory pathways
■ Increased heart rate and blood pressure
■ Activation of sweat glands
○ Parasympathetic
■ Decreased metabolic rate
■ Decreased heart rate and blood pressure
■ Increased secretion by salivary and digestive glands
■ Increased motility in digestive tract
■ Increased blood flow in digestive tract
○ Autonomic tone
■ Maintaining heart rate: acetylcholine and norepinephrine released
continuously maintaining autonomic tone
● Gi tract
○ Long twisting tube that ends at the anus
○ Accessory glands: salivary glands, liver, pancreas, gallbladder – accessory bc
food is not moved into but they secrete substances into GI tract
● 3 phases of digestion
○Cephalic phase – starts w/ anticipation of ingestion and ends when last mouthful
swallowed
■ Response to food base stimuli
■ Secretory responses – salivary, gastric, duodenal, pancreatic
■ Non-secretory responses – mixing, motinity, etc
○Gastric phase – timing when food is present in stomach
○Intestinal phase – begins when chyme enters duodenum
● Saliva
○ Water and glycoprotein
○ Digestive enzymes
■ Amylase: starches → simple sugars
■ Lipase: triglycerides → fatty acids and glycerol
○ Lysozyme → kills bacteria
○ Dental plaque – when bacteria mixes with sugar or starch
● Mastication – chewing
○ Bolus – chewed food mixed with saliva
○ Brain controls this
● Swallowing
○ Retraction of tongue forces bolus into oropharynx
, ○Peristalsis – involuntary constriction and relaxation of muscles of digestive tract
creating wave like movements that push contents of canal forward
● Achalasia
○ Dysfunction of lower esophageal sphincter
○ LES fails to open when swallowing
○ Related to damaged nerves in esophagus or due to damage of LES
● Gastroesophageal reflux disease (GERD)
○ Acid reflux
○ Occurs when LES doesn’t close properly allowing digestives juices to rise into
esophagus
○ Treatment: antacids, H2 receptor blockers, proton pump inhibitors
Lecture 45
● Stomach – cephalic responses
○ Sight, smell, taste, thoughts of food cause parasympathetic stimulation
■ In response stomach releases
● Mucus – coat walls of stomach
● HCl – help w chemical digestion and also killing bacteria
○ Denatures proteins
○ Helps break down plant cell walls & connective tissue
in meat
○ Necessary for function of cells that secrete
pepsinogen
● Pepsinogen – breaks down proteins
● Gherlin – hunger hormone – when stomach is empty these
levels are high
● Gastrin – enhancing gastric mucosal growth, gastric motility,
and secretion of hydrochloric acid (HCl) into the stomach
● Gastric phase
○ Begins when food arrives to stomach
○ Stretch receptors activated to release hormones and enzymes
○ Gastrin released into bloodstream leading to
■ Protein digestion
■ Powerful contractions called mixing waves
■ Stimulates gastric motility
○ Gastric lipase – digests fat
○ Intrinsic factor – B12 absorption
● Determinants of gastric emptying
○ Volume
■ Greater volume, greater rate of gastric emptying
○ Osmotic pressure
■ Greater osmolality, decreased rate of gastric emptying
○ Nutrient density
■ Greater nutrient density, decreased rate of gastric emptying
