The digestive system- 2 Flashcards
What are the accessory digestive organs?
-Salivary glands
-Exocrine pancreas
-Biliary system
>liver
>Gall bladder
How many layers does the digestive tract have?
4
What are the 4 major layers of the digestive tract?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa (outer layer)
Innermost layer
Mucosa
2 functions/ characteristics of mucosa
Highly folded- greatly increases the absorptive area
Lines luminal surface of the digestive tract
what lines the luminal surface?
Mucosa
3 layers of the mucosa
- Mucous membrane
- Lamina propria
- Muscularis mucosa
Serves as protective surface
Modified for secretion and absorption
Mucous membrane
What 3 cells does the mucous membrane contain?
- Exocrine gland cells
- Endocrine gland cells
- Epithelial cells
secrete digestive juices
Exocrine gland cells
secrete blood-borne gastrointestinal hormones
Endocrine gland cells
specialised for absorbing digestive nutrients
epithelial cells
- Houses gut-associated lymphoid tissue (GALT)
- Important in defense against disease-causing intestinal bacteria
Lamina propria
Sparse layer of smooth muscle
Muscularis mucosa
what is under the mucosa?
Submucosa
Nerve network found in the submucosa
submucosal plexus
Functions and characteristics of the submucosa
- Thick layer of connective tissue
- Provides digestive tract with distensibility and elasticity
- Contains larger blood and lymph vessels
- Contains a nerve network known as the submucosal plexus
Provides digestive tract with distensibility and elasticity
Submucosa
Major smooth muscle coat of digestive tube
Muscularis Externa
The two layers of the muscularis externa
- Circular layer (inner layer)
- Longitudinal layer (outer layer)
Contraction decreases diameter of lumen
Circular layer (inner layer) of the muscularis externa
Contraction decreases diameter of lumen
Circular layer (inner layer) of the muscularis externa
Contraction shortens the tube
Longitudinal layer (outer layer) of the muscularis externa
Contractile activity of what produces propulsive and mixing movements
Muscularis Externa
Myenteric plexus
Nerve network of the muscularis externa
-Lies between the two muscle layers
help regulate gut activity
Submucosal plexus + Myenteric plexus + hormones
outer connective tissue layer
Serosa
Function and characteristics of serous fluid (secreted from serosa)
- Fluid is watery and slippery
- Lubricates and prevents friction between digestive organs and surrounding viscera
Continuous with mesentery throughout much of the tract
-What is the function of this?
- ->Serosa
- Attachment provides relative fixation
- Supports digestive organs in proper place while allowing them freedom for mixing and propulsive movements
Regulation of digestive function is complex and synergistic; why is digestive motility and secretion regulated?
to maximise digestion and absorption
4 factors involved in regulation of digestive system function:
- Autonomous smooth muscle function
- Intrinsic nerve plexuses
- Extrinsic nerves
- GI hormones
3 sensory receptors
Chemoreceptors Mechanoreceptors (pressure receptors) Osmoreceptors
sensitive to osmolarity
Osmoreceptors
sensitive to stretch or tension
Mechanoreceptors (pressure receptors)
sensitive to chemical components within GIT
Chemoreceptors
endocrine system
Hormonal regulation
nervous system
neural regulation
Mechanoreceptors and chemoreceptors
Mechanical and chemical regulation
activate and inhibit accessory glands
Mechanoreceptors and chemoreceptors
Neural regulation
Short (intinsic) controls
-Mediated by enteric nervous system
>entire reflex arc is located within GI tract wall
Long (extrinsic) control
-involves CNS and autonomic nervous system
Hormonal regulation
Hormones produced by enteroendocrine cells
Name the:
4 layers of the GI tract
4 factors of the GI tract
3 sensory receptors of the GI tract and what they stimulate
4 layers
- Mucosa (innermost layer)
- Submucosa
- Muscularis externa
- Serosa (outer layer)
4 factors
- Autonomous smooth muscle function
- Intrinsic nerve plexuses
- Extrinsic nerves
- GI hormones
3 sensory receptors
-Chemoreceptors-sensitive to chemical components within GIT
-Mechanoreceptors (pressure receptorssensitive to stretch or tension
-Osmoreceptors-sensitive to osmolarity
STIMULATE: Effector cells
-Smooth muscle
> contraction for motility
-Exocrine gland cells
>Secretion of digestive juices
-Endocrine gland cells
>Secretion of gastrointestinal and
pancreatic hormones (GI hormones)
Receptor activation results in…
two neural reflexes (short and long)
Short neural reflexes
intrinsic nerve reflexes influence motility or secretion in response to local stimulation (within GIT)
Long neural reflexes
extrinsic autonomic nerve activity to modify smooth muscle or glandular responses
> Correlate activity between different regions of digestive system
Modify digestive system activity in response to external stimuli
Components of the oral cavity (mouth)
- Lips
- Palate
- Tongue
- Teeth
- Saliva (salivary proteins)
- Taste buds
Lips
- Forms opening
- Help procure, guide and contain food in mouth
- Important in speech
- Well-developed tactile sensation
Palate
- Forms roof of oral cavity (separates mouth from nasal passages)
- Uvula (seals off nasal passages during swallowing)
Tongue
- Forms floor of oral cavity
- Composed of skeletal muscle
- Movements aid in chewing and swallowing
- Play NB role in speech
- Taste buds
Mechanically breakdown food
Teeth
What happens in the mouth?
- Teeth mechanically breakdown food
>Grind and breakdown food into smaller pieces to make
swallowing easier and increase food surface area on which
salivary enzymes can act.
2.Food mixes with saliva - Taste buds are stimulated
What happens when taste buds are stimulated?
- Increases salivary, gastric, pancreatic and bile secretions.
- Although chewing can be voluntary, it’s a rhythmic reflex controlled by skeletal muscles of the jaw, lips, cheeks, and tongue
Saliva
- secretion associated with the mouth
- Produced by 3 major pairs of salivary glands
Name the 3 major pairs of salivary glands
Parotid
Submandibular
Sublingual
Describe saliva’s negative feedback mechanism:
Receptors:
- Pressure receptors and chemoreceptors in the mouth
- Cerebral cortex ( Thinking, seeing, and smelling food)
Describe saliva’s negative feedback mechanism:
Receptors:
-Pressure receptors and chemoreceptors in the mouth
[Simple reflex]
-Cerebral cortex ( Thinking, seeing, and smelling food)
[Conditioned reflex]
They stimulate the salivary center in the medulla which sends nerve impulses to the salivary glands via the autonomic nerves.
Saliva is secreted
Saliva composition
- 99.5% H2O
- 0.5% electrolytes
- Proteins
What is responsible for the perception of salty tastes?
Saliva is salty-contains NaCl
Perception of sweet tastes
Absence of glucose
Salivary proteins
- Amylase
- Mucus
- Lysozyme
Begins the digestion of carbohydrates
Amylase
Facilitates swallowing by moistening food
Mucus-provides lubrication
Antibacterial action
Lysozyme destroys bacteria
-Saliva rinses away material that could serve as food source for bacteria
4 other functions of salivary proteins:
-Solvent for molecules that stimulate taste buds
-Aids speech by facilitating movements of lips and tongue
-Helps keep mouth and teeth clean
-Rich in bicarbonate buffers
>Neutralises acid in food or acid produced by bacteria in
mouth
Chamber at the back of the throat
The pharynx
Function of pharynx
Serves as a passageway for digestive system:
-Links mouth and oesophagus for food (oropharynx)
Serves as a passageway for respiratory system:
-Provides access between nasal cavity and trachea for air
(nasopharynx)
Motility associated with pharynx and oesophagus
swallowing
Explain the initiation of swallowing:
- Initiated when a bolus is formed
> voluntarily forced by tongue to back of throat
into pharynx - Bolus in pharynx stimulates pressure receptors (pharyngeal pressure receptors)
- Most complex reflex in body involving multiple coordinated responses
- Although initiated voluntarily, cannot be stopped once started - ALL-or-NONE response
pharynx’s pressure receptors
pharyngeal pressure receptors
2 stages of swallowing
- Oropharyngeal
2. Oesophageal
Peristalsis in the Esophagus
Ringlike peristaltic contraction sweeping down oesophagus
Peristalsis in the Esophagus
Ringlike peristaltic contraction sweeping down oesophagus
