Download Lecture 4: Digestive System

Lecture 4: Digestive System
M/O Chapter 26
24. Follow a food substance through the digestive tract, naming all required structures the food passes
through/beside, and describing generally what happens at each location.
25. Differentiate between intraperitoneal and retroperitoneal location of digestive organs.
The digestive system is a single muscular tube that runs from the mouth to the anus. Each different region of the tube has a distinct
structure, enabling that area’s unique function. Also associated with the long tube are accessory glands that secrete various cocktails
into the tube. The entire tube is known as the alimentary canal (mouth to anus)...the GI (gastrointestinal) tract is stomach to anus.
Digestive System Functions
1. Digests (or breaks down) food into smaller particles
A. Chemical digestion
B. Mechanical digestion
2. Absorbs nutrients found within the tube, moving them from
the outside world (inside the tube) into the body (via the
bloodstream).
3. Eliminates solid waste that cannot be digested or absorbed
Digestive System Structures
1. Oral cavity
A. Teeth (mechanical digestion)
B. Salivary glands (chemical digestion)
2. Pharynx
A. Deglutition (swallowing)
B. 17 different muscles are involved in this REFLEX. Which
nerves control these muscles?
3. Esophagus
A. Transports BOLUS of food to the stomach
B. Lined with mucus glands
C. Can stretch to accommodate size of bolus
4. Stomach
A. Begins protein digestion by secreting pepsin (a proteindigesting enzyme)
B. Kills pathogens that made it through the mouth...
C. Stores food and releases it slowly into the SI
D. Mechanical digestion via churning of the extremely
muscular walls
5. Small intestine (SI)
A. Chemical digestion aided by accessory organs (mostly in
duodenum):
i. Liver and pancreas (accessory organs) secrete
substances into the SI that help with digestion
a. Liver produces bile (stored in gall bladder), which
helps emulsify fats
b. Pancreas produces digestive enzymes and
bicarbonate solution (to neutralize acid and digest
other nutrients)
B. Absorption of nutrients (mostly in jejunum and ileum)...
surface area is increased in 4 ways
i. Length, Plicae circularis, Villi, Microvilli
C. Immune system line of defense
6. Large intestine (LI)
A. Absorbs water
B. Eliminates waste
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Accessory glands
1. Liver
A. The liver has 8 million functions, including
blood de-tox.
B. Liver cells are organized into hepatic lobules
with a central vein in the middle.
C. The central vein will ultimately flow into the
hepatic vein, which as you know, flows into the
inferior vena cava.
D. At the corners of each hepatic lobule are
“hepatic triads”
i. Hepatic portal vein (from GI tract!)
ii. Hepatic artery (from celiac trunk)
iii. Bile duct
E. Between the hepatic triad and the central vein
run sinusoids. This is how blood gets to the
central vein from the triad vessels.
i. Kupffer cells are macrophages that patrol
the sinusoids and gobble up debris,
including old RBC.
2. Pancreas
A. The pancreas has endocrine and exocrine
functions.
B. Endocrine cells secrete substances (hormones)
INTO the body...
i. Endocrine cells are found in the pancreatic
islets (aka islets of Langerhans)
ii. These cells produce insulin (beta cells) and
glucagon (alpha cells)
iii. Insulin and glucagon are hormones that are
secreted into the blood to manage blood
glucose concentrations.
C. Exocrine cells secrete substances OUTSIDE
the body! (Secreting goop into the GI lumen is
considered “outside” the body.)
i. These cells secrete digestive juices into the
GI tract.
ii. Bicarbonate ions raise the pH of the slush
as it exits the stomach
iii. Digestive enzymes help break slush into
absorbable chunks.
Mesentery and the Peritoneal Cavity
The abdominopelvic cavity contains several serous membranes.
1. Parietal peritoneum: The serous membrane that lines the entire abdominopelvic cavity
2. Visceral peritoneum: The part of the serous membrane that covers the surface of the gut organs
A. Organs that are completely covered by visceral peritoneum are “intraperitoneal”.
B. Organs that touch the posterior surface of the body wall are not completely covered by visceral peritoneum are
“retroperitoneal”.
3. Mesenteries are layers of peritoneum that contain blood vessels and nerves passing from the outer body wall, into the abdominal
cavity to support the organs found within this cavity.
A. Greater omentum: It is like an apron on the anterior portion of the gut, covering the abdominal cavity. Hangs off the greater
curvature of the stomach.
B. Lesser omentum: Connects the lesser curvature of the stomach with the liver.
C. Mesentery proper: A fan-shaped mesentery that attaches to most of the small intestine.
D. Mesocolon: The mesentery that attaches to the large intestine.
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Lab 4: Gross Anatomy of the Digestive System
Reading: M&O Ch. 26
Part 1: Teeth
1. On the isolated skulls, identify the following tooth types:
A. incisors
B. canines
C. premolars
D. molars
Part 2: Regions
On the cadavers (and the bisected head, where possible) identify the following
structures.
1. Cranial region
A. labia (lips)
B. oral cavity
C. vestibule
D. gingivae (gums)
E. tongue
F. lingual frenulum
G. hard palate
H. soft palate
I. parotid gland
J. parotid duct
K. submandibular (submaxillary) gland
L. sublingual gland
2. Abdominal (peritoneal) cavity
A. parietal peritoneum
B. visceral peritoneum
Part 3: Alimentary Canal
On the cadavers, identify the following structures.
1. Esophagus
2. Stomach (intraperitoneal)
A. cardiac region
B. fundus
C. body
D. pylorus
E. pyloric sphincter
F. rugae
G. greater curvature
H. lesser curvature
I. greater omentum
J. lesser omentum
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3. Small intestine
A. duodenum (partly intraperitoneal, mostly retroperitoneal)
i. duodenal papilla
B. jejunum (intraperitoneal)
C. ileum (intraperitoneal)
D. mesentery proper
4. Large intestine
A. cecum (intraperitoneal)
i. ileocecal valve
B. appendix (intraperitoneal)
C. ascending colon (retroperitoneal)
D. transverse colon (intraperitoneal)
E. mesocolon
F. descending colon (retroperitoneal)
G. sigmoid colon (intraperitoneal)
H. rectum (retroperitoneal)
5. Anus
Part 4: Accessory structures
1. Liver
A. left lobe
B. right lobe
C. quadrate lobe
D. caudate lobe
E. gallbladder
F. falciform ligament
i. round ligament (in falciform ligament)
G. coronary ligament
H. common bile duct
I. cystic duct
J. common hepatic duct
2. Pancreas (retroperitoneal)
A. head
B. body
C. tail
D. pancreatic duct
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External Brain 4: Digestive System
24. Follow a food substance through the digestive tract, naming all required structures the food passes
through/beside, and describing generally what happens at each location.
25. Differentiate between intraperitoneal and retroperitoneal location of digestive organs.
Your Task
1. Write a story that outlines the path of a single piece of food you eat. Start at the beginning, end at the end, and include ALL
required structures during the trip.
2. Distinguish between the different types of teeth. Answer the following questions:
A. How many roots does each tooth type have?
B. What is the other major difference between premolars and molars? (Hint: it’s not something visible in the adult)
3. Briefly describe tooth development, starting at birth and finishing in adulthood.
4. Why do you think deciduous teeth are necessary, considering they are eventually replaced with permanent teeth?
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