NURS 1750 Lecture Notes - Lecture 10: Common Bile Duct, Bile Acid, Carboxypeptidase
28 Jun 2018
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Week Eleven (November 27 - December 1, 2017)
Anatomy and Physiology
Chapter Twenty-Four: The Digestive System
Overview of the Digestive Tract
The digestive system includes two groups of organs: the
gastrointestinal (GI) tract and the accessory digestive
organs.
- Organs of the gastrointestinal (GI) tract are:
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small and large intestines
- Accessory digestive organs include:
- Teeth
- Tongue
- Salivary glands
- Liver
- Gallbladder
- Pancreas
Functions of the Digestive System
1. Ingestion: taking food into mouth.
2. Secretion: release of water, acid, buffers, and enzymes into lumen of GI tract.
3. Mixing and Propulsion: churning and movement of food through GI tract.
4. Digestion: mechanical and chemical breakdown of food.
a. Mechanical digestion: the teeth cut and grind food before it is swallowed, and
then smooth muscles of the stomach and small intestine churn the food to further
assist the process. As a result, food molecules become dissolved and thoroughly
mixed with digestive enzymes.
b. Chemical digestion: the large carbohydrate, lipid, protein, and nucleic acid
molecules in food are split into smaller molecules by hydrolysis
5. Absorption: passage of digested products from GI tract into blood and lymph.
6. Defecation: elimination of feces from GI tract.
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Layers of the GI Tract
- The four layers of the GI tract, from deep to superficial, are the mucosa, submucosa,
muscularis, and serosa.
Mucosa
- Mucous membrane.
- Is the inner lining of the GI tract.
- Composed of three layers:
1. Epithelium
a. Nonkeratinized stratified squamous epithelium found in mouth,
pharynx, esophagus and anal canal serves a protective function
b. Simple columnar epithelium lines stomach and intestines and
functions in secretion and absorption.
c. Tight junctions firmly seal neighbouring simple columnar epithelial
cells to restrict leakage.
d. Epithelial cells in GI tract are replaced every 5-7 days
2. Lamina Propria
a. Areolar connective tissue containing blood and lymphatic vessels
b. Serves as routes by which nutrients absorbed into the GI tract
reach the other side of the body.
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Week Eleven (November 27 - December 1, 2017)
3. Muscularis Mucosae
a. Throws the mucous membrane of the stomach and small intestine
into many small folds, which increase the surface area for
digestion and absorption.
Submucosa
- Areolar connective tissue that binds the mucosa to the muscularis.
- Contains many blood and lymphatic vessels that receive absorbed food
molecules.
- Network of neurons called the submucosal plexus are located here.
Muscularis
- Muscularis of the mouth, pharynx, and superior and middle parts of the
esophagus contains skeletal muscle that produces voluntary swallowing. Permits
voluntary control of defecation.
- Muscularis of the rest of the tract consists of smooth muscle that is generally
found in two sheets: an inner sheet of circular fibers and an outer sheet of
longitudinal fibers.
- Involuntary contractions of the smooth muscle help break down food, mix it with
digestive secretions, and propel it along the tract.
Serosa
- Portions of GI tract that are suspended in abdominal cavity have a serosa.
- A serous membrane composed of areolar connective tissue and simple
squamous epithelium (mesothelium).
Neural Innervation of the GI Tract
- GI Tract is regulated by intrinsic set of nerves known as the enteric nervous system and
by an extrinsic set of nerves that are part of the autonomic nervous system.
Enteric Nervous System (ENS) “Brain of the Gut”
→ Neurons of the ENS are arranged into two plexuses: myenteric and
submucosal plexus.
- Myenteric Plexus
- Motor neurons supply the longitudinal and circular smooth muscle
layers of the muscularis.
- This plexus mostly controls GI tract motility (movement),
particularly the frequency and strength of contraction of the
muscularis.
- Submucosal Plexus
- Motor neurons of the submucosal plexus supply the secretory
cells of the mucosal epithelium, controlling the secretions of the
organs of the GI tract. (responsible for regulating digestive
secretions and reacting to the presence of food)
- Interneurons of ENS interconnect the neurons of the myenteric and submucosal
plexus.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The digestive system includes two groups of organs: the gastrointestinal (gi) tract and the accessory digestive organs. Organs of the gastrointestinal (gi) tract are: The four layers of the gi tract, from deep to superficial, are the mucosa, submucosa, muscularis, and serosa. Week eleven (november 27 - december 1, 2017: muscularis mucosae, throws the mucous membrane of the stomach and small intestine into many small folds, which increase the surface area for digestion and absorption. Areolar connective tissue that binds the mucosa to the muscularis. Contains many blood and lymphatic vessels that receive absorbed food molecules. Network of neurons called the submucosal plexus are located here. Muscularis of the mouth, pharynx, and superior and middle parts of the esophagus contains skeletal muscle that produces voluntary swallowing. Muscularis of the rest of the tract consists of smooth muscle that is generally found in two sheets: an inner sheet of circular fibers and an outer sheet of longitudinal fibers.
