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
Gastrin is produced by
Stomach and duodenum
Cholecystokinin (CCK) and secretin are produced by
duodenum
Function of Gastrin:
Stimulate parietal and chief cells
increase contraction of gastric wall
Function of Cholecystokinin
Production of pancreatic enzymes
Contracts gall bladder
Relaxes hepatopancreatic sphincter
Mechanical chewing makes a bolus that increases surface area for
chemical breakdown
Esophagus hiatus
pierces the diaphragm that transports food from the oral cavity down to the stomach
peristalsis
will move food down even if we’re upside down
Collagen fibers in the adventitia help
keep the esophagus in place.
What takes place in the esophagus? Segmentation or peristalsis?
Peristalsis
How does food enter and go through the stomach?
CARDIA > FUNDUS > BODY (enzymes and acids) > PYLORIC PART (sphincter guards the exit).
Mucosa- directly touches the food.
Stomach collapses when there’s no food.
In this state the mucosa makes folds
Rugae
Gastric pits
mucus cells- alkaline (high pH) mucus will line the whole stomach wall and neutralize acids if they try to get out of the stomach.
Parietal
makes HCL (lowers pH) and intrinsic factor (helps make RBCs)
G cells
enteroendocrine cells- makes a hormone called gastrin- it will stimulate all digestive processes- stimulate muscular layer to contract and digest food.
Chief cells
makes pepsinogen (inactive form of pepsin) interacts with HCL and activates it to become pepsin. Helps to start digesting proteins.
What is the main way to differentiate between accessory organs and primary organs of the digestive system?
Accessory Organs: help with breaking down food.
Primary Organs: involved with the digestive tract.
Cephalic Phase
Thoughts or smells of food, but food has not entered the digestive tract. Stimulated by the vagus nerve. Preparation phase.
Gastric Phase
Food is in the stomach. Both submucosal and myenteric plexuses are stimulated and now start the contraction of muscle layers and increase all other activities,
Intestinal phase
if food is leaving there is no need of pepsinogen- need o deal with chyme as it enters the intestine.
Gastroenteric reflex
stomach is stimulated and starts intestinal motility.
Gastroileal reflex
food in stomach and will open the illiosecal, small intestine, and have food come from small to large intestine.
Pancreatic islet
(endocrine) hormone secretions
pancreatic acini
(exocrine) secretes stuff to the surface
exocrine pancreas
secretes alkaline, enzyme rich fluid to help neutralize acid going out of the stomach and damaging the small intestine.
Secretin
detects a decrease in the pH and promotes alkaline secretion
Why does CCK need to be inactivated beforehand?
To ensure that we don’t release enzymes that can damage our own tissues.
Alpha cells
produce glucagon
Beta cells
produce insulin
An increase of blood glucose leads to
beta cells secreting insulin
A decrease of blood glucose leads to
alpha cells secreting glucagon
increased breakdown of fat and synthesis and release of glucose
Hepatocytes make
bile
Where is bile collected?
interlobular bile duct
T/F: Blood and Bile are moving in the same direction
F
What will stimulate CCK?
Food at the duodenum.
Function of bile:
to break up lipids and make more surface area to have lipid enzymes work on it.
Bile salts help emulsify
lipids
Where is backup of bile stored?
Gallbladder
Enterohepatic Circulation:
At the end of the small intestine, we reclaim the bile salts and put them back in the liver.
Gallbladder
holds bile
reabsorbs water from bile and leaves salts.
What increases the surface area of the small intestine?
circular folds and intestinal villi
Lacteals
where lipids that are absorbed go into circulation.
Duodenal submucosal glands
produce lots of mucus for when chyme arrives from the stomach in order to not injure cells.
During absorption, we must breakdown macromolecules to
monomers
Physiology of the small intestine:
Lipids > Micelles > epithelial cells > chylomicrons > interstitial fluid > lacteals
happens mostly in the jejunum
What is the issue if food gets stuck at the cecum?
if food gets trapped here, it will block the appendix and cause inflammation. This area has a lot of bacterial so if it bursts then it will become a major issue.
Rectum:
haustras: promotes absorption and churning
no villi
makes a lot of mucus to dehydrate and compact all of these materials.
segmentation occurs here
Short Reflex of Defecation
Short reflex: intrinsic myenteric defecation reflex- triggers peristalsis in the sigmoid colon and rectum
Two sphincters here
External sphincter is under
voluntary control
Internal sphincter is under
involuntary control
Long Reflex of Defecation
parasympathetic defecation reflex
coordinated by sacral parasympathetic neurons
stimulates mass movements.
What is needed to open the external sphincter
somatic nervous system
Absorption
period following a meal
Postabsorption
normal blood glucose levels are maintained
body relies on internal energy reserves
most cells break down lipids or amino acids
