Lecture 17 - Digestive 1 Flashcards
Classification of organs within the digestive system
- Digestive organs
- > collectively make up the GI (gastrointestinal) tract, also called digestive tract or alimentary canal, food goes through lumen of organ - Accessory digestive organs
- > food does not pass through these organs, they only assist digestion
List all GI tract organs
- > oral cavity
- > pharynx
- > esophagus
- > stomach
- > small intestine
- > large intestine
List all accessory digestive organs
- > teeth
- > tongue
- > salivary glands
- > liver
- > gall bladder
- > pancreas
Digestive system functions
- > ingestion
- > digestion
- > propulsion (move things along)
- > secretion (subsances are release from digestive organs to help with digestion)
- > Absorption
- > elimination of wastes
Peristalsis vs Segmentation
*both are involved with food propulsion along GI tract*
Peristalsis
- > the ripple-like movement of musclular contractions that forces material to move further along GI tract
Segmentation
- > the churning/mixing of materials, helping mix the materials with digestive organ secretions
Structures of the oral cavity
- > cheecks, lips and palate
- > tongue
- > salivary glands
- > teeth
Characteristics of the cheeks and lips
- > cheeks form lateral walls of OC and are comprised mostly of the buccinator muscles
- > the gingivae (gums) cover the alveolar processes of the teeth
- > superior/inferior labial frenulum connect lips to gingivus
characteristics of the palate
- > the anterior 2/3 is called the hard palate and is comprised of bone (maxilla and palatine)
- > posterior 1/3 is the soft, muscular palate containing the uvula which posteriorly extends from the soft palate
role of the uvula during swallowing
during swallowing, the soft palate elevate the uvula and closes off the posterior entrance to the nasopharynx
characteristics of the tongue
- > manipulates and mixes ingested materials during chewing
- > helps compress the partially digested material into a bulus
- > the inferior surface of the tongue attaches to the floor of the oral cavity by a thin midline mucus membrane called the lingual frenulum
functions of salivary glands
- > moisten ingested materials to become a slick bolus
- > moisten, cleanes and lubricates the structures of the oral cavity
- > chemical digestion of ingested materials
- > antibacterial action
- > dissolves material so taste receptors on the tongue can be stimulated
name all salivary glands and where they are
Parotid glands - > largest SG in size, near ear, produces more serous cells
Submandibular glands - > under mandible, produces 70% of total saliva, more serous cells
Sublingual glands - > under tongue, produces 3-5%of saliva, more mucous cells
Mucous cells vs serous cells
Mucous cells
- > secrete mucin, a stringy viscous solution
Serous cells
- > secrete saliva that is 97-99% water,
Dentition
the colective term for teeth
Anatomy of teeth
- > exposed area is called crown (made of enamel) which leads into the neck
- > root of the tooth fits in the dental alveoli
- > dentin forms the primary mass of the tooth, harder than bone
- > each root is covered with cementum
Explain the deep internals of the tooth
- > the center of the tooth is a pulp cavity that contains connective tissue called pulp
- > the root canal opens into the connective tissue through an opening called the apical foramen
- > blood vessels and nerves pass through the apical foramen and are housed in the pulp
What are the major types of teeth
Deciduous teeth (baby/milk teeth) - > erupt between 6-30 months, 20 in total
Permanant teeth - > replace the deciduous teeth and are around 32 in number
what are the different types of permanant teeth
incisors - > most anteriorly placed, shaped like chisels, have single root
canines - > posterolateral to insisors, pointed tip for puncturing and tearing
premolars - > posterolateral to canines, have flat crowns with prominant ridges called cusps for crushing and grinding
Molars - > thickest, most posterior teeth, also used for crushing adn grinding
characteristics of the pharynx; what controls and supplies it?
- > shared by the respiratory and digestive systems
- > three skeletal muscle pairs of pharyngeal constrictors form wall of pharynx and participate in swallowing
- > CN X (vegas) innervates most pharyngeal muscles
- > branches of external carotid arteries supply and internal jugular veins drain the pharynx
Pharyngeal constrictors
Superior constrictor - > skeletal muscle = voluntary control
Middle constrictor - > mixed (skel+smoo) = partial voluntary control
Inferior constrictor - > smooth muscle = involuntary
steps of Deglutition
***SWALLOWING***
- Oral/buccal stage
- Pharyngeal stage
- Esophageal stage
Stage 1 of deglutition
Oral/Buccal stage
- > upper esophageal sphincter is closed
- > food is chewed and mixed with saliva in preperation for swallowing
- > tongue presses against hard palate, forcing the bolus into the oropharynx
stage 2 of deglutition
Pharyngeal stage
- > tongue blocks the mouth
- > soft palate and uvula rise, blocking the nasopharynx
- > larynx and epiglottis cover trachea
- > upper esophageal sphincter relaxes, and bolus travels down into esophagus
stage 3 of deglutition
- > pharyngeal constrictor muscles contract and move the bolus inferiorly down the esophagus
- > the upper esophageal sphincter closes behind the bolus
Tunics of the wall of the abdominal GI tract
from deep (lumen) to superficial
- > mucosa
- > submucosa
- > muscularis
- > adventitia or serosa
Componants of mucosa
- > superficial epithelium
- > an underlying areolar connective tissue, called the lamina propria
- > a thin layer of smooth muscle called the musculairs mucosae
componants of the submucosa
- > lymphatic ducts
- > mucin-secreting glands
- > blood vessels
- > nerves
the nerves and their associated ganglia are called the submucosal nerve plexus (meissner plexus)
what are the layers of smooth muscle in the muscularis
*responsible for peristalsis/segmentation*
- inner circular layer
- > constricts the lumen and forms sphincter - outer longitudinal layer
- > shortens the tube
Exceptions
- > esophagus has a mix of both smooth and skeletal muscle
- > stomach contains three layers of smooth muscle
Myenteric nerve plexus
*auerbach plexus*
- > located in between inner circular and outter longitudinal layers of muscularis
- > nerve fibres and associated ganglia in between the two layers of muscle of the muscularis
Adventitia or serosa
- > outermost layer of the wall of the abdominal GI tract
- > loose areolar connective tissue with collagen and elastic fibres
Esophagus
- > tubular passageway that conducts ingested material from pharynx to stomach
- > passes through an opening in the diaphragm as it connects to the stomach called the esophageal hiatus
why is the esophagus collapsed in on itself
- > as substances pass through it, the lumen expands and extends into the C-shaped space of trachea
- > it would push against spinal cord
stomach
- > eventually processes the bolus into a paste-like soup called chyme
- > possesses three layers of muscle (logitudinal, circular, oblique layer)
regions of the stomach
- > cardia
- > fundus
- > body
- > pyloris
• inferior border is called the greater curvature; superior is called the lesser curvature
Rugae
- > the internal surface of the stomach is thrown into folds called gastric folds (rugae) which increases surface area to help with absorption and allows for stomach to stretch
Wall of the stomach
- > lined by simple columnar epithelium althoght little absorption occurs in the stomach
- > stomach lining is indented by numerous depressions called gastric pits (house gastric glands)
What are the types of secretory cells that form the gastric epithelium
- Surface mucous cells - > secretes mucin
- mucous neck cells - > secretes acidic mucin
- Parietal cells - > secretes HCL and intrinsic factors
- Chief cells - > secretes pepsinogen (digestive enzyme, unactive form of pepsin)
- Enteroendocrine cell - > secretes gastrin (stimulates the release of gastric acid which is a digestive fluid)
Stomach Sphincters
The stomach has two important smooth muscle sphincters
- cardiac sphincter (lower esophageal sphincter) regulates the entrance of a bolus from the esophagus into the stomach
- pyloric sphincter regulates the release of chyme from the stomach into the small intestine
Does the esophagus absorb any nutrients
no it only transports
