Transcript Digestive System Notes

Transport Systems
Digestive
Function
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The nourishment of the body’s cells is
dependant on the relationship between
the digestive system and the
cardiovascular system.
The Digestive system is specialized to
ingest, propel, digest, and absorb food.
Oral Cavity
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Lips/Labia: muscular folds covered by mucosa
(internally) and stratified squamous (externally).
Cheeks: Internally-moist stratified squamous and
exteriorly – skin. (inside the cheek is the buccinator
muscle and the buccal fat pad.
Tongue: attached posteriorly in the oral cavity proper.
Anchored inferiorly by the frenulum. Intrinsic muscles
are within the tongue and extrinsic muscles are outside
the tongue but attached. There is a groove around the
center (terminal sulcus). Anterior to the terminal sulcus
covered by papillae some of which have taste buds.
Posterior no papillae but few taste buds – lots of
lymphoid tissue (lingual tonsils).
Oral Cavity Continued. . .
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Teeth – (32 in adult) 2 dental arches (maxillary and
mandibular) divided into 4 quadrants (LU, RU, LL, RL).
Each quadrant has 1 central and 1 lateral incisor, 1
canine, 1st and 2nd premolars or bicuspids, and 1st , 2nd,
and 3rd molars (wisdom teeth).
Permanent (2ndary teeth) –adult
Deciduous (Primary teeth)- children
They are set in alveoli along ridges of the mandible and
maxilla covered by dense connective tissue and stratified
squamous epithelia (gingiva).
Oral Cavity Continued...
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Muscles of Mastication: Temporalis,
masseter, medial pterygoid, lateral
pterygoid
Palate/Palatine Tonsils:
 Hard palate: bony part; anterior.
 Soft Palate: skeletal muscle and
connective tissue- uvula attached.
 Tonsils: Lateral wall of fauces
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Small Tubular Glands:
 lingual glands (within tongue)
 palatine glands (in palate)
 buccal glands (in cheeks)
 labial glands (in lips)
Salivary Glands: 3 pairs of large multi-cellular
glands:
 Parotid: Behind ear
 Submandibular: below mandible
 Sublingual: Below tongue
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All major salivary glands are compound
alveolar glands.
Alveolar glands secrete serous and
mucous secretions (saliva).
Upper Alimentary Canal
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Oropharynx follows the oral cavity and leads to
the laryngopharynx. This leads to the
esophagus which is accompanied by mucous
glands.
The esophagus extends between the pharynx
and the stomach. It lies in the mediastinum.
The esophagus passes through the esophageal
hiatus (diaphragm). It is lined with all four
tunics of tissue and is topped by the upper
esophageal sphincter and is terminated at the
lower esophageal sphincter.
Stomach
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All four tunics of tissue. 3 layers of smooth muscle for
mixing.
Regions: cardiac, fundus, body, greater and lesser
curvature, and the pyloric.
Opening to the duodenum of the small intestine is the
pyloric sphincter.
Rugae allow for change in stomach volume.
Gastric pits:
Parietal cells:
Chief cells:
Mucous neck cells:
Endocrine cells:
Small Intestine
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Duodenum: 180 degree turn. Short segment
that receives secretions from the gallbladder and
pancreas.
Jejunum: Gradual decrease in the diameter of
the small intestine due to and increase in villi
and microvilli.
Ileum: Lots of villi and microvilli. Terminates at
the Cecum with the ileocecal sphincter.
Large Intestine
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The cecum is the proximal end of the large
intestine that extends inferiorly to form the
appendix (lymphatic tissue).
Colons: Ascending, Transverse, Decending, and
Sigmoid.
Rectum is at the terminus of the Sigmoid colon.
It has a very thick muscular tunic and it
terminates at the superior end of the anal canal.
Anal Canal: Internal anal sphincter (smooth
muscle) and external anal sphincter (skeletal
muscle). End of anal canal turns from simple
columnar epithelium to stratified squamous.
Histology of the Alimentary Canal
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Mucosa: the inner most tunic composed of 3
layers.
1. Mucous epithelium – moist stratified
squamous epithelium (mouth, oropharynx,
esophagus, and anal canal) and simple
columnar in the remainder of the tract.
2. Lamina Propria – loose connective tissue
3. Muscluaris mucosae – thin smooth muscle
layer.
Histology of the Alimentary Canal
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Submucosa: thick connective tissue layer
containing nerves, blood vessels, and small
glands. Nerves form submucosal plexus
(parasympathetic).
Muscularis: the 3rd layer made of an inner layer
of circular smooth muscle and an outer layer of
longitudinal muscle. A nerve plexus – myenteric
lies between the 2 muscle layers with the
submucosal called the intramural.
Serosa – Outer most layer of connective tissue
which connects with visceral peritoneum.
General Physiology
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Ingestion: food into the oral cavity
Mastication: (chewing) performed by the teeth.
Increases surface area of the food bolus –
assists in the breakdown by enzymes.
Propulsion: movement of food through the
alimentary canal (24-36 hours to make it
through the length of the tract). Each part of
the digestive tract aids in moving the bolus (food
ball).
General Physiology
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Deglutition (swallowing): move food from
oral cavity into the esophagus.
Peristalsis: moves it the rest of the way
through wave-like contractions in the
smooth muscle tissue.
Mixing: occurs between the bolus and
secreted enzymes. Segmental
contractions are mixing contractions.