Digestive System Flashcards
Activities of digestion
Motility Secretion Digestion Absorption Circulation Excretion
Types of digestive systems
Monogastric
Modified monigastric
Ruminants/cranial fermenters
Hindgut/caudal fermentors
Layers of GI tissues
Serosa Longitudinal muscle Circular muscle Submucosa Mucosa
How does GI function as a syncythium?
Visceral single unit smooth muscle
Autoexcitable
Gap junctions
Slow, very energy efficient
Electrical activity
Continous
Slow intrinsic electrical activity
No stable RMP
Types of waves
Slow waves- determined by rhythmicity of GI contraction, no real AP, produced by interstitial cells of Cajal (“pacemakers”), no contractions
Spike potential/waves- true AP, occurs when RMP higher than 40mV, higher slow wave potential=increased frequency of spike potential, opening of Ca++ and Na+ channels
Spike potentials stimulated by
Stretch
Ach
Parasympathetic
Hyper repolarization of spike waves caused by
Norepinephrine
Sympathetic
Peristalsis
Moves food forward towards anus
Contractile ring
Stimulated by gut distention
Mixing movements
Local intermittent constrictive contractions
Every few cm, duration 5-30s
Enteric nervous system
Internal control
Begins at esophagus to anus
Very abundant in neurons
Controls secretion and movement
Autonomic nervous system
External control
Sympathetic or pa sympathetic stimulation
Myenteric plexus
ENS
Most external plexus btw longitudinal and circular muscle layers
Controls mainly movements
Excitatory
Submucosal plexus
ENS
Most internal plexus, in submucosa
Controls secretion and local blood flow
Parasympathetic innervation
Stimulates GI activity
Vagal Nerve
Ach+VIP+GRP
Sympathetic innervation
Inhibits GI activity
Noradrenaline (alpha receptors)
Somatostatine
Neuropeptide Y
Gastric
Produced by G-cells in stomach, duodenum, pancreas
When there is distention or stimulation of Vagal N
Stimulates contraction of stomach
Stimulates release of acid
Motility
Produced in stomach, jejunum, duodenum
In presence of alkaline products
Strengthens stomach contractions
Stimulates pepsin production
Cholecystokinin
CCK
Produced in duodenum by preconceived of proteins/lipids in duodenum
Stimulates emptying of gallbladder
Stimulates secretion of pancreatic enzymes
Inhibits gastric emptying
Secretin
Produced in duodenum as response to gastric juice
Mild inhibition of motility
Stimulates pancreatic juice secretion
Food ingestion mechanisms
Prehension
Mastication
Salivation
Swallowing
Salivary glands
Parotid-serous
Mandibular-mixed
Sublingual-mucus
Zygomatic-mixed
Saliva contains
Serous= alpha-amylase (starch) Mucus= mucin-lubrication and surface protection
First secretory step of salivation
Acini secretes amylase, mucin and electrolytes
Second secretory step of salivation
Modification by duct cells
Active Na+resorption
Saliva becomes alkaline
Saliva contains
97-99,5% water Organic ions Mucin Bicarbonate Organic products=antibacterial IgA, Lactoferrin, Lisosyme Enzymes= alpha-amylas Lingual lipase= hydrolyzes triglycerides
Functions of saliva
Lubrication, solubilization, allowing flavor, grass floating, deglutition into food bonus, oral flora control, enzymatic activity, thermoregulation, wound healing, maintenance of skin/hair
Three steps of swallowing
Voluntary- initiating process
Pharyngeal stage- involuntary, food from pharynx to esophagus
Esophageal stage- involuntary, food into stomach
Deglutition reflex
Swallowing center in medulla oblongada
Sensitive/afferent info from glossopharyngeal N (9)+trigeminal N (5)
Automatic when stimulated
Efferent info to motorimpukses via vagus N (10), trigeminal
N (5) and glossopharyngeal N (9)
Primary peristalsis of esophagus
Continuation f movement starting in pharynx to stomach every 8-10s
Controlled by ENS+extrinsic
Secondary peristalsis of esophagus
Results from distention of esophagus
Continued until food reaches stomach
ENS
Functions of stomach
Storage-accommodation
Mixing into chyme by mixing+propulsion
Slow emptying
Functional areas of stomach
Fundus, body, Antrum
Proximal region- food from esophagus, storage
Distal region- grinding+screening, into small particles
Receptive relaxation
Fundus relaxes to make room for bolts
Vagus N (10) stimulated by vagovagal reflex due to stretching of stomach
Releases NO+VIP
Mixing/propulsion
In distal region
Mixing waves towards Antrum
Interstitial cells of Cajal generates slow waves in basic rhythm
Peristaltic AP induces muscle contraction
Food pushed in both directions=propulsion
Stomach emptying
Intense anthrax peristaltic contractions=20% of mixing
Contractions become intense
Pylorus sphincter contraction allowing only water+fluids to pass
Depends on chemical and physical properties
Regulation of stomach emptying
Signals=increased gastric volume speeds up emptying by ENS/intrinsic and extrinsic/vagal control
Stretching of walls= increases gastric stimulating Antrum contractions and pyloric relaxation
Intestinal signals= chyme into duodenum starts enterogastric reflex
Inhibitory feedback if too much chyme-intrinsic/extrinsic/hormonal
Cholecystokinin
CCK
Senses high lipids= decrease motility and emptying
Gastric inhibitor peptide
GIP
Senses lipids and proteins= decreases motility and emptying
Secretion
Senses acidic substances
Inhibits anthral contractions
Surface mucus cells
Secretes mucus
Mucus neck cells
Secretes mucus
Parietal cells
Produces HCl and IF (intrinsic factor)
Chief cells
Produced pepsinogen and gastric lipase
G-cells
Produces hormone gastric
HCl
Produced by parietal cells in fundus+body
CO2+Cl- from blood- CO2+H2O=HCO3-+H+=H+ +Cl=HCl
What increases HCl secretion?
Vagus N (10)+ENS increases Ach Gastrin+Histamine
Histamine
Produced in stomach my ECL-cells
Stimulated by Ach and Gastrin
Intrinsic factor
Produced by parietal cells
A glycoprotein essential for absorbation of B12 in ilium
Regulated by Vagus N (10)+ENS, Gastrin+Histamine
Pepsinogen
Produced by chief cells in fundus+body
Zymogen, activated by HCl
Pepsin
Active form of pepsinogen
Proteolytic enzyme
Needs pH 1,8-3,5
Regulated by Ach (vagus+ENS)
Mucus
Produced by mucus neck cells+surface mucus cells in Antrum
Glycoproteins (viscid mucus) coats stomach mucosa=protection from HCl+pepsin
Alkaline due to bicarbonate
Increases by food intake and mucosa irritation
Lubrication
Gastrin
Endocrine
Produced by G-cells in Antrum and duodenum
In response to peptides, amino acids, stretching
Stimulates ECL-cells to produce Histamine=increase HCl
Histamine
Endocrine
Produce by ECL-cells in fundus+body
Induces HCl secretion
Stimulated by Ach+Gastrin
Somatostatine
Produced in Antrum
Blocks gastrin secretion
Cephalic phase
30%
CNS stimulated by taste/sight/smell/thought of food
Increase ps HCl and pepsin production
Parasympathetic by vagal N (10)= Ach and ENS
Gastric phase
50-60% Stimulated by stretching+ chemoreceptors Parasympathetic by vasovagal reflex and ENS Stimulates Gastrin+Histamine secretion Inhibited by high acidity=stops Gastrin
Intestinal phase
5-10%
Stimulated by low pH and partially digested food in duodenum
Increases Gastrin
Inhibited by distention of duodenum, presence of fatty acids and hypertonic chyme
Enterogastrix reflex (short+long, ENS+CNS)
Hormones secretion- CCK, secretin, GIP
Small intestines
Duodenum, jejunum, ilium
Digestion, absorption, endocrine organ, immune barrier
Three functions of motility in small intestines
Mixing chyme with enzymes mm= help digestion
Maximizing chyme contact with mucosa= help absorption
Propulsion of chyme into large intestines
Digestive period
Food intake Mixing contractions (segmentation contractions) Propulsive contractions
Interdigestive period
Fasting
MMC
Segmentation/mixing contractions
Presence of chyme, stretching
Causes segmentation
Determined by electrical slow waves
Propulsive contractions/peristalsis
Slow migration of content to large intestines
MMC
Migrating myoelectric complex
Waves cleaning intestines every 45-180 min during fasting
Stimulated by motilin (ENS+CNS)
Three phases of MMC
Prolonged period of resting, no contractions
Increased frequency of AP/contractility, irregular and mixing
Few minutes of peak electrical and mechanical activity, Regular contraction/propulsion
Motility regulation
Stretching of duodenum wall+gastroenteritis reflex
ENS+ANS (parasympathetic=increase, sympathetic=decrease)
Hormonal control
-increased by Gastrin, CCK, insulin, motilin, serotonin
-decreased by secretin, glucagon
Chyme arriving to duodenum leads to
Neutralization of acidity
Chemical digestion of macromolecules
Pancreatic+bile secretion
Exocrine
Acini secretes pancreatic juice into duodenum
Endocrine
Pancreatic islets produce insulin, glucose, somatostatin into bloodstream
Acinar cells
Produce pancreatic enzymes (zymogen) and water
Centriacinar/duct cells
Secretes bicarbonate, water, ions Na+ and K+
Pancreatic juice
Water and ions
Bicarbonate-increases pH, naturalized HCl, inhibits pepsin
Pancreatic enzymes as zymogen to be activated in duodenum
Protein digestion
Trysinogen, chymotrypsinogen, procarboxy peptidase
Carbohydrates digestion
Pancreatic amylase
Fats digestion
Pancreatic lipase, cholesterol esterase, phospholipase
Nuclease
Deoxyribonucleases, ribonucleases
Mucus
Produced by mucus neck cells+surface mucus cells in Antrum
Glycoproteins (viscid mucus) coats stomach mucosa=protection from HCl+pepsin
Alkaline due to bicarbonate
Increases by food intake and mucosa irritation
Lubrication
Gastrin
Endocrine
Produced by G-cells in Antrum and duodenum
In response to peptides, amino acids, stretching
Stimulates ECL-cells to produce Histamine=increase HCl
Histamine
Endocrine
Produce by ECL-cells in fundus+body
Induces HCl secretion
Stimulated by Ach+Gastrin
Somatostatine
Produced in Antrum
Blocks gastrin secretion
Cephalic phase
30%
CNS stimulated by taste/sight/smell/thought of food
Increase ps HCl and pepsin production
Parasympathetic by vagal N (10)= Ach and ENS
Gastric phase
50-60% Stimulated by stretching+ chemoreceptors Parasympathetic by vasovagal reflex and ENS Stimulates Gastrin+Histamine secretion Inhibited by high acidity=stops Gastrin
Intestinal phase
5-10%
Stimulated by low pH and partially digested food in duodenum
Increases Gastrin
Inhibited by distention of duodenum, presence of fatty acids and hypertonic chyme
Enterogastrix reflex (short+long, ENS+CNS)
Hormones secretion- CCK, secretin, GIP
Small intestines
Duodenum, jejunum, ilium
Digestion, absorption, endocrine organ, immune barrier
Three functions of motility in small intestines
Mixing chyme with enzymes mm= help digestion
Maximizing chyme contact with mucosa= help absorption
Propulsion of chyme into large intestines
Digestive period
Food intake Mixing contractions (segmentation contractions) Propulsive contractions
Interdigestive period
Fasting
MMC
Segmentation/mixing contractions
Presence of chyme, stretching
Causes segmentation
Determined by electrical slow waves
Propulsive contractions/peristalsis
Slow migration of content to large intestines
MMC
Migrating myoelectric complex
Waves cleaning intestines every 45-180 min during fasting
Stimulated by motilin (ENS+CNS)
Three phases of MMC
Prolonged period of resting, no contractions
Increased frequency of AP/contractility, irregular and mixing
Few minutes of peak electrical and mechanical activity, Regular contraction/propulsion
Motility regulation
Stretching of duodenum wall+gastroenteritis reflex
ENS+ANS (parasympathetic=increase, sympathetic=decrease)
Hormonal control
-increased by Gastrin, CCK, insulin, motilin, serotonin
-decreased by secretin, glucagon
Chyme arriving to duodenum leads to
Neutralization of acidity
Chemical digestion of macromolecules
Pancreatic+bile secretion
Exocrine
Acini secretes pancreatic juice into duodenum
Endocrine
Pancreatic islets produce insulin, glucose, somatostatin into bloodstream
Acinar cells
Produce pancreatic enzymes (zymogen) and water
Centriacinar/duct cells
Secretes bicarbonate, water, ions Na+ and K+
Pancreatic juice
Water and ions
Bicarbonate-increases pH, naturalized HCl, inhibits pepsin
Pancreatic enzymes as zymogen to be activated in duodenum
Protein digestion
Trysinogen, chymotrypsinogen, procarboxy peptidase
Carbohydrates digestion
Pancreatic amylase
Fats digestion
Pancreatic lipase, cholesterol esterase, phospholipase
Nuclease
Deoxyribonucleases, ribonucleases
