Lecture 7 : Gastrointestinal System I : Overview, Ingestion, and Swallowing Flashcards
Organs of the digestive system include two groups :
the alimentary canal & accessory digestive organs
Digestive System =
Gastrointestinal System =“Gut”
Alimentary Canal =
Gastrointestinal tract = GI tract = Gut tube
Inside the tube (lumen) is outside the body – food passes through the _______ organs during digestive activity.
alimentary canal
________ provide chewing, enzymes and buffers that assist in mechanical and chemical breakdown of food.
Accessory organs
Six (6) essential digestive functions and processes :
Ingestion
Propulsion
Mechanical breakdown
Digestion
Absorption
Defecation
Ingestion
taking in food and water via the mouth
Propulsion
movement of food/water by swallowing (voluntary) or peristalsis (alternating waves of contraction of smooth muscle)
Mechanical breakdown
increases surface area of food, preparing for chemical digestion by enzymes:
In mouth: chewing, tongue mix food with saliva
Churning: pummeling of food in stomach
Segmentation: back and forth movement in SI
Digestion
enzymes secreted into lumen break food into chemical building blocks (catabolic process)
Absorption
movement of nutrients from lumen to blood or lymph
Defecation
elimination of solid waste (feces): indigestible substances and metabolic wastes
endocrine & exocrine ____ will aid in digestive processes
gland secretions
GI _____ moves food in an _____ direction and facilitates mixing
Motility
aboral
Aboral =
from mouth to anus
Motility (movement) due to smooth muscle layers of the muscularis externa
Two types of movement:
- Peristalsis:
mostly propulsive (forward movement) - Segmentation:
mostly for mixing and mechanical breakdown
The _____ is the Serous Membrane in the Abdominal Cavity
Peritoneum
Peritoneum:
slippery, continuous serous membrane sac
_______ – lines the inner surface of the body wall
Parietal peritoneum
_________ - lines the surface of digestive organs
Visceral peritoneum
___________– fluid filled potential space between the peritoneal layers (sterile space)
Peritoneal cavity
_____ organs are surrounded or suspended by peritoneum
Intraperitoneal
_______ lie posterior to peritoneum
Retroperitoneal organs
Most digestive organs are intraperitoneal and are suspended from the body wall by a _____
dorsal mesentery
some intraperitoneal digestive organs are also suspended from the wall by _____
ventral mesenteries
some digestive organs are _____ because they have lost their mesentery during development
retroperitoneal
______ are folds of peritoneum that suspend organs in abdomen
Mesenteries
Abdominal cavity is completely lined by _____
parietal peritoneum
______ is sterile space with slippery fluid
Peritoneal cavity
Functions of Mesenteries
Provide routes for blood vessels, lymphatics and nerves to reach the abdominal viscera
Hold the organs in place – highly organized
Store fat
Create channels and spaces in which infections can travel
>Endometriosis
> ovarian cancer
_______ attach to the stomach
Greater and Lesser Omentum
The Mesentery
Small intestine
Mesocolon for parts of large intestine (colon)
The alimentary canal (GI tract) wall has four (4) layers
(Innermost) : Mucosa
Submucosa
Muscularis Externa
Adventitia/Serosa
Mucosa
innermost layer of the alimentary canal
Mucosa (has 3 layers)
Epithelium – usually simple columnar; rich in mucous secreting cells
Lamina propria – loose areolar connective tissue with lymphoid follicles (MALT)
Muscularis mucosa – thin smooth muscle layer
Functions of Mucosa:
Secrete mucus, digestive enzymes and hormones
Absorb the end products of digestion into the blood
Protect against infectious disease this is the protective barrier of the alimentary canal
Submucosa :
Connective tissue between mucosa and muscularis externa
Areolar connective tissue with blood vessels, lymphatic vessels, lymphoid follicles, nerve fibers, glands; location of submucosal plexus
Muscularis Externa :
Major smooth muscle layer of the alimentary canal
Muscularis Externa (2 layers)
Inner circular smooth muscle
Outer longitudinal smooth muscle
stomach has 3 layers
Muscularis Externa
Function:
Segmentation & peristalsis
Churning actions of stomach
Muscularis Externa
Other facts:
myenteric nerve plexus between muscle layers
Inner circular smooth muscle can contribute to sphincters
Outermost layer :
Serosa or Adventitia
Serosa (visceral peritoneum)
Areolar connective tissue with mesothelium (simple epithelium
Adventitia (if no peritoneum)
Dense connective tissue
Digestive system activities are controlled by the __________
nervous and endocrine systems
Enteric nervous system (ENS)
consists of neurons wall of the gut which are involved in local reflexes
Nerves of the sympathetic and parasympathetic nervous systems innervate the _____
enteric neurons of the digestive tract (involved in long reflexes).
Autonomic nerves also carry sensory feedback from _____
GI organs to CNS.
The ANS, ENS and GI hormones control GI organs and _______ of the digestive system
coordinate motility and secretions
______ resides in wall of GI tract
Enteric Nervous System
Enteric Nervous System =
“Third Division” of ANS
consists of Intrinsic Nerve Plexuses (ganglia plus networks of nerves)
Myenteric Plexus :
Between layers in muscularis externa
Submucosal Plexus :
In submucosa layer
Enteric Nervous System Controls local _____ reflexes
gut
Enteric nervous system (ENS)
Neurons arranged in ____ within wall of GI tract
ganglia
Ganglia and axons form intrinsic nerve plexuses:
submucosal plexus and myenteric plexus
Respond to stimuli within GI tract – mediate _____ that regulate digestive system activity
short reflexes
Pacemaker cells:
Interstitial cells of Cajal
modified smooth muscle cells that act like pacemakers
Intermediary between intrinsic nerve plexus and smooth muscle
_______ control GI smooth muscle and glands
Short reflexes (ENS), Long reflexes (ANS) and hormones
_____ reflexes promote digestive system activity:
Long and short
Motility : muscle contraction
Secretion of digestive juices or hormones
Stimuli: Digestive activity is provoked by range of mechanical and chemical stimuli
stretch of wall by food in lumen
changes in osmolarity (solute concentration)
pH of contents and end products of digestion
CNS regulation of GI activity in response to sights, smells, thoughts, anxiety, fear
Effectors : digestive activity is affected by the action of smooth muscle and glands.
stimulate smooth muscle in walls of GI tract to increase motility (mixing and propulsion)
activate or inhibit glands that secrete digestive juices into lumen or hormones into blood
Digestive activity is controlled by:
intrinsic nervous controls (short reflexes within ENS)
extrinsic nervous controls (long reflexes via ANS)
Enteroendocrine cells :
hormone producing cells within the gut wall
release their hormones into interstitial fluid in extracellular space
enter the blood and are distributed to target cells in the same organ or different organs where they affect secretion or contraction
Autonomic Nerves travel to GI tract in ____
Mesenteries
Blood supply through 3 branches of :
abdominal aorta
Parasympathetic innervation through:
vagus nerve and sacral spinal levels
Sympathetic innervation from :
thoracic levels
The oral cavity performs :
ingestion, mechanical breakdown, digestion and propulsion
Epithelium of the Oral Cavity:
Stratified squamous epithelium (wear and tear)
Tonsils :
Palatine and lingual tonsils provide immune defense
____________ involved in mastication and manipulation of food.
Teeth, tongue and hard palate
___________ block nasopharynx during swallowing
Soft palate and uvula
_____ contain skeletal muscles to control muscles of palate and pharynx.
“Arches”
The tongue aids in:
chewing, initiates swallowing and aids in speech
Tongue:
Interlacing bundles of skeletal muscle
Mix food with saliva to produce a bolus
Articulation: form sounds during speech
Taste buds located on sides of papillae; contain taste cells
Salivary glands secrete saliva which is delivered to ____ through ducts
oral cavity
Why Saliva?
Cleanse the mouth (prevent tooth decay)
Dissolve food chemicals – taste
Moistens food to help compact the bolus
Begin digestion of starch by enzyme amylase
What is Saliva?
Mostly water – 97 to 99%
Electrolytes
Digestive enzymes (amylase & lipase)
Proteins mucin, lysozyme, and IgA
Metabolic wastes
____ input increases salivation (watery, enzyme rich)
Parasympathetic
_____ input decreases salivation: stimulate mucous secretion (dry mouth), constrict blood vessels
Sympathetic
Salivary output ______
1.5 Liters per day or more
The Pharynx provides a common pathway for :
food, fluids and air
Mucosa of the Oropharynx & Laryngopharynx contains ______ (continuous with the oral cavity)
stratified squamous epithelium
______ contains skeletal muscle
Longitudinal and circular layers
Muscularis externa
The pharynx is involved in propulsion of food:
swallowing – a voluntary activity that also has some involuntary aspects (coordination).
The Esophagus propels food from the laryngopharynx to the :
stomach
Mucosa of esophagus contains ____________ (continuous with the oral cavity)
non-keratinized stratified squamous epithelium
Transition to simple columnar near stomach
_____ contains esophageal glands (mucus-secreting for lubrication)
Submucosa
Muscularis externa contains _____ in the upper third, _____ in middle third,________ in inferior third – role in peristalsis – propel food to stomach
skeletal muscle
skeletal/smooth
smooth muscle
Adventitia –
dense CT, no serous layer
esophagus lies posterior to the ____
trachea
______ blocks the opening of the larynx to divert food into the esophagus
epiglottis
There is a ____ at each end of the esophagus
sphincter
Upper esophageal sphincter –
skeletal muscle
prevents passage of air into esophagus while breathing
Lower esophageal sphincter (LES)-
(also called gastroesophageal sphincter)
smooth muscle
prevents reflux of stomach contents into esophagus – thickening of smooth muscle that is reinforced by diaphragm
Issues of lower esophageal sphincter :
GERD
Achalasia
GERD =
Gastroesophageal reflux disease – acid reflux from stomach inflames epithelium and esophagus wall
Achalasia –
difficulty opening LES sphincter, or weakness of peristalsis – failure of myenteric plexus coordination?
_____ = Swallowing
Deglutition
We swallow 600 times per day!
Dysphagia
difficulty swallowing
Can be due to nervous system or muscular system issue
Oral phase: voluntary
Tongue pushes bolus back
Sensory receptors in pharynx initiate next phase
Swallowing : Pharyngeal-Esophageal phase
Nasopharynx blocked by soft palate
Larynx rises, epiglottis blocks airway
Coordinated by brainstem centers and cranial nerves
(Propulsion of food into Esophagus)
Continuation of pharyngeal-esophageal phase (involuntary):
Pharyngeal constrictor muscles push food into upper esophagus
Peristalsis will take over in esophagus
Propulsion through Esophagus: Peristalsis
Alternating waves of muscle push food through esophagus – peristalsis
Muscle transition : Upper 1/3 esophagus is skeletal muscle, Middle 1/3 is skeletal + smooth mixed, Lower 1/3 is smooth