Download The Digestive System

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The Digestive System
Digestive System Components
A. Alimentary canal (also called the Gastrointestinal “GI” Tract)– continuous, muscular digestive
tube that winds through the body (30 ft. long when dead & relaxed, shorter when alive due to
muscular tone.) The GI tract is considered outside the body.
http://ww
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1.
2.
3.
4.
5.
6.
oral cavity
pharynx
esophagus
stomach
small intestine
large intestine
B. Accessory Digestive Organs
1. salivary glands
2. tongue
3. teeth
4. pancreas
5. liver
6. gallbladder
Digestive Processes
http://trc.ucdavis.edu/biosci10v/bis10v/week10/digestive.gif
A. Ingestion: taking food into digestive tract (through mouth)
http://www.youtube.com/watch?v=Ri8bBhw9ms
B. Propulsion: moving food through alimentary canal
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a. swallowing: voluntarily initiated
b. peristalsis: involuntary - alternate waves of contraction & relaxation of muscles in the
organ walls (squeeze food one direction along tract)
C. Mechanical digestion: (physical) chewing, tongue mixing food w/ saliva, churning food in
stomach, and segmentation (rhythmic local constrictions that can move the food back & forth)
within the small intestine → mixes food w/ digestive juices
D. Chemical digestion: catabolic steps by enzymes secreted into lumen (hollow open tube of
intestine); begins in mouth and is complete in the small intestine
E. Absorption (small intestine) – digested product (food that has been broken down into molecules)
from lumen passes through mucosal cells into blood or lymph
F. Defecation – elimination of indigestible substances (fecal matter: fiber, bacteria, mites,
protozoans, viruses)
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Supporting Structures
A. Peritoneum – serous membrane that lines the organs
and the abdominal cavity. This membrane secretes serous
fluid for protection.
1. Visceral peritoneum – covers external surface
of organs & is continuous w/ the parietal
peritoneum
2. Parietal peritoneum – lines the wall of the
abdominal cavity
http://www.finejewelrydesigns.com/images/peritoneum-chart.jpg
B. Mesentery/Mesocolon – a double layer of the
peritoneum that extends to the digestive organs,
anchoring every organ to the wall of the abdominal
cavity.
A. Hold organs in place and stores fat
(curtain over intestines for protection)
B. Contains blood vessels, lymph vessels,
and nerves. Provides a place for these
vessels and nerves, yet prevents
entanglement and allows them to pass
through to other areas.
C. Greater Omentum a double layer of the peritoneum that extends over the organs in the
digestive system. Functions in fighting disease by holding a great number of lymph nodes.
D. Histology:
1. Mucosa (inner-most layer, moist
epithelial membrane)
 secretes mucus, digestive
enzymes, and hormones
 absorbs products of digestion into
blood
 protects against infectious disease
2. Submucosa - connective tissue w/
blood vessels, lymph vessels, nerves, &
elastic fibers that allow the organ to
return to normal shape
3. Muscularis – muscle layer, has an
inner-circular (runs around the lumen)
and an outer-longitudinal (runs
lengthwise w/ lumen) layer of smooth
muscle; inner circular layer also thickens
to form sphincters
4. Serosa – the visceral peritoneum in GI
tract; layer that wraps the organs
http://www.lib.mcg.edu/edu/eshuphysio/program/section6/6ch1/6ch1img/page4.jpg
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E. Innervation:
1. Enteric plexi – a “network” of branched nerves attached to the submucosa within the
walls of the GI tract. Includes the Submucosal plexus and the Myenteric plexus
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/ginerves.gif
2. The Enteric Nervous System is linked to the Central Nervous System
 the parasympathetic nervous system stimulates digestion “rest and digest”
 the sympathetic nervous system inhibits digestion “fight or flight”
Oral Cavity & Associated Organs
A. Mouth – mucosal lined cavity continuous w/ oropharynx (throat)
1. Hard and Soft Palate (roof of mouth)
1. hard – anterior
2. soft – posterior; rises to close off nasopharynx when swallowing
3. uvula – flap attached to soft palate - involved in sleep apnea
2. Tongue – mixes food w/ saliva = bolus
a. intrinsic muscles – change shape of tongue
(rolls tongue in)
b. extrinsic muscles – alters position of tongue
(stick tongue out, touch roof of mouth)
c. lingual frenulum – holds tongue to floor of
mouth, limits movement (function: prevents us
swallowing tongue)
d. filiform papillae = roughness – specks on
tongue NOT tastebuds (cats have pronounced
filiform papillae needed to lap &
“grab” food)
http://kbb.uludag.edu.tr/image/oralkaviteders/Resim-6.jpg
from
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3. Salivary glands
a. Parotid – anterior
to ear, between
masseter muscle and
skin (large muscle in
jaw)
b. Submandibular –
medial aspect of
mandible body;
opens at lingual
frenulum
c. Sublingual – under
tongue laterally –
lies on both sides of
tongue, underneath
http://health.yahoo.com/media/mayoclinic/images/image_popup/ah6a192.jpg
d. Saliva
characteristics:
 1000-1500 ml produced on average per day
 pH of 6.75 – 7 (slightly acidic)
 Cleans mouth, dissolves food so you can taste, moistens food
 Contains salivary amylase (from parotid gland) that starts the breakdown of
starch only
 Contains mucin (mixes w/ water → mucus), lysozyme (also in tears & cells,
it’s a chemical that breaks down cells, attacks & kills bacteria), and IgA
(antibody→fights infection)
 Sympathetic effect = decrease in production → dry mouth
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4. Teeth
a. deciduous teeth – 20 “baby teeth”
b. permanent teeth – 32 including
wisdom
c. anatomy:
 crown – exposed part;
covered by enamel
 root – part embedded in jaw
bone
 neck – connect crown &
root (just below gumline)
 gingival – gum
 enamel – hardest substance
in body, mineralized Ca+
salts – covers outer crown;
cells that make enamel
degenerate after tooth
erupts through gums;
 dentin – bone like
http://www.mydr.com.au/content/images/categories/dental/tooth_
material under enamel =
anatomy_vs2.gif
bulk of tooth (gets
damaged when bacteria gets through enamel)
 pulp/cavity – supplies nutrients & tooth sensation; connective tissue, blood
vessels, nerves
 periodontal ligament (membrane) – anchors tooth in jaw
Pharynx –passageway for food, fluid, and air (air only →unique to
nasopharynx)



nasopharynx – air only
oropharynx – behind oral cavity, food/fluids/air
laryngopharynx – near larynx (larynx connected to esophagus or trachea) , food/fluids/air
http://www.youtube.com/watch?v=DB_E2BygPJk&feature=related glottis & epiglottis
Esophagus – food enters when epiglottis (at top of larynx) closes off trachea to food
1. Esophagus- pierces diaphragm to enter abdomen
2. Joins stomach at gastroesophageal or cardiac sphincter (at top of stomach; improper
function → acid reflux)
3. Uses peristalsis to move food to stomach
http://www.youtube.com/watch?v=hm1nEPHxJ0E&feature=related
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Stomach – mainly a storage area where chemical breakdown of protein
begins & food is converted to chyme
Functions:
1. Holding place for food so that it can
enter the duodenum gradually
2. Churns and mixes food – becomes
“chyme”
3. Begins digesting proteins
4. Absorbs water, aspirin, alcohol, and
electrolytes
Borborygmi
Main structures: “J-shaped”
= “stomach
1. Cardiac Sphincter growling”
2. Cardia
3. Fundus
4. Body
5. Pylorus
6. Pyloric Sphincter
7. Rugae: folds in mucosa that allow
for stretching when stomach is full
http://www.rivm.nl/interspeciesinfo/Images/stomach_tcm75-26442.gif
3 layers of smooth muscle in muscularis instead of 2:
1. **Inner oblique smooth muscle layer (diagonal)
found only in the stomach that allows the stomach to
churn food
2. Middle circular smooth muscle layer (around
stomach)
3. Outer longitudinal smooth muscle layer (lengthwise)
Gastric glands: made of cells found in deep pits in the mucosa
of the stomach
1. mucus made by mucous cells
2. HCL made by parietal cells
 needed to activate pepsinogen into
pepsin (digests proteins) and kill
Collectively
bacteria
these
3. Intrinsic factor made by parietal cells
substances,
not including
 required for vitamin B12 absorption in
the gastrin,
small intestine
are called
4. pepsinogen made by chief cells
gastric juice
 breaks down proteins into smaller
component
 must be activated by HCL first – called pepsin once activated
5. enteroendocrine cells or G-cells – releases gastrin into the blood which stimulates the
stomach