Transcript Digestive System A

Chapter 23A
Digestive System
Slides by Barbara Heard and W. Rose.
figures from Marieb & Hoehn 9th ed.
Portions copyright Pearson Education
Ch. 23: Digestive System
Introduction/Overview
Functional Anatomy
Physiology of Digestion & Absorption
Digestive System
Introduction/Overview
Digestive System Organs
Digestive Processes
Basic Concepts
Relations & Common Features of Digestive
Organs
Functional Anatomy
Physiology of Digestion & Absorption
Digestive System Organs (Fig 23.1)
Alimentary Canal = path through
Mouth to anus
Digests food and absorbs fragments
Mouth, pharynx, esophagus, stomach, small intestine,
and large intestine
Accessory organs = "off-to-the-side" helpers
Teeth, tongue, gallbladder
Digestive glands
Salivary glands
Liver
Pancreas
Figure 23.1 Alimentary canal and related accessory digestive organs.
Mouth (oral cavity)
Tongue*
Parotid gland
Sublingual gland
Submandibular gland
Salivary
glands*
Pharynx
Esophagus
Stomach
Pancreas*
(Spleen)
Liver*
Gallbladder*
Transverse colon
Small
intestine
Anus
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Duodenum
Jejunum
Ileum
Descending colon
Ascending colon
Cecum
Sigmoid colon
Rectum
Appendix
Anal canal
Large
intestine
Digestive Processes
• Six essential activities
1.
2.
3.
4.
5.
6.
Ingestion
Propulsion
Mechanical breakdown
Digestion
Absorption
Defecation
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Figure 23.2 Gastrointestinal tract activities.
Ingestion
Mechanical
breakdown
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Digestion
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Blood
vessel
Mainly H2O
Feces
Defecation
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Anus
Figure 23.3 Peristalsis and segmentation.
From
mouth
Peristalsis: Adjacent segments of alimentary
tract organs alternately contract and relax,
moving food along the tract distally.
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Segmentation: Nonadjacent segments of
alimentary tract organs alternately contract and
relax, moving food forward then backward.
Food mixing and slow food propulsion occur.
Basic Concepts
• Gut lumen is "outside"
• Digestion control mechanisms try to control
chemical environment in lumen to optimize
absorption
• Digestion is provoked by mechanical &
chemical stimuli (sensors in walls): stretch, pH,
osmolarity, which can cause secretion and
propulsion via reflexes (Fig. 23.4)
• Control by local as well as remote reflexes (Fig
23.4)
• Short reflexes: via enteric nerve plexus
• Long: via CNS
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GI Tract Regulatory Mechanisms
1. Mechanoreceptors and chemoreceptors
– Respond to stretch, changes in osmolarity
and pH, and presence of substrate and end
products of digestion
– Initiate reflexes that
•
•
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Activate or inhibit digestive glands
Stimulate smooth muscle to mix and move lumen
contents
GI Tract Regulatory Mechanisms
2. Intrinsic and extrinsic controls
– Short reflexes - enteric nerve plexuses (gut
brain) respond to stimuli in GI tract
– Long reflexes respond to stimuli inside or
outside GI tract; involve CNS centers and
autonomic nerves
– Hormones from cells in stomach and small
intestine stimulate target cells in same or
different organs to secrete or contract
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Figure 23.4 Neural reflex pathways initiated by stimuli inside or outside the gastrointestinal tract.
External stimuli
(sight, smell, taste,
thought of food)
Central nervous system
Long reflexes
Visceral afferents
Internal
(GI tract)
stimuli
Extrinsic visceral (autonomic)
efferents
Chemoreceptors,
osmoreceptors, or
mechanoreceptors
Local (intrinsic)
nerve plexus
("gut brain")
Effectors:
Smooth muscle
or glands
Short reflexes
Gastrointestinal
wall (site of short
reflexes)
Lumen of the
alimentary canal
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Response:
Change in
contractile or
secretory activity
Peritoneum and Peritoneal Cavity
• Peritoneum - serous membrane of
abdominal cavity
– Visceral peritoneum on external surface of
most digestive organs
– Parietal peritoneum lines body wall
• Peritoneal cavity
– Between two peritoneums
– Fluid lubricates mobile organs
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Figure 23.5a The peritoneum and the peritoneal cavity.
Abdominopelvic
cavity
Vertebra
Dorsal
mesentery
Parietal
peritoneum
Ventral
mesentery
Visceral
peritoneum
Peritoneal
cavity
Alimentary Liver
canal organ
Two schematic cross sections of abdominal cavity illustrate
the peritoneums and mesenteries.
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Peritoneum and Peritoneal Cavity
• Mesentery - double layer of peritoneum
– Routes for blood vessels, lymphatics, and
nerves
– Holds organs in place; stores fat
• Retroperitoneal organs posterior to
peritoneum
• Intraperitoneal (peritoneal) organs
surrounded by peritoneum
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Figure 23.5b The peritoneum and the peritoneal cavity.
Mesentery
resorbed
and lost
Alimentary
canal organ
Alimentary canal organ in
a retroperitoneal position
Some organs lose their mesentery and move,
becoming retroperitoneal, during development.
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Homeostatic Imbalance
• Peritonitis
– Inflammation of peritoneum
– Causes by e.g., piercing abdominal wound,
perforating ulcer, ruptured appendix
– Peritoneal coverings stick together, localizing
infection
– Dangerous and lethal if widespread
– Treated with debris removal and antibiotics
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Blood Supply: Splanchnic Circulation
• Branches of aorta serving digestive organs
– Hepatic, splenic, and left gastric arteries
– Inferior and superior mesenteric arteries
• Hepatic portal circulation
– Drains nutrient-rich blood from digestive
organs
– Delivers it to the liver for processing
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Figure 23.6 Basic structure of the alimentary canal.
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in
submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis externa
• Longitudinal muscle
• Circular muscle
Mesentery
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Nerve
Artery
Gland in mucosa
Vein
Duct of gland outside
Lymphatic vessel
alimentary canal
Serosa
• Epithelium
(mesothelium)
• Connective tissue
Lumen
Mucosa-associated
lymphoid tissue
Histology: all alimentary canal organs have same basic 4 layers
From lumen out (Fig 23.6):
• Mucosa = mucous membrane = epithelial layer of cells
Secrete: mucus, digestive enz, hormones
Absorb broken down compounds into blood
Protect against infection
• Submucosa
Connective tissie with blood vessels & lymphatics for
absorption, lymph nodes, elastic fibers (shape retention)
• Muscularis externa
Inner circular muscles
Outer longitudinal muscles
• Serosa
The peritoneum already mentioned
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Figure 23.6 Basic structure of the alimentary canal.
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in
submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis externa
• Longitudinal muscle
• Circular muscle
Mesentery
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Nerve
Artery
Gland in mucosa
Vein
Duct of gland outside
Lymphatic vessel
alimentary canal
Serosa
• Epithelium
(mesothelium)
• Connective tissue
Lumen
Mucosa-associated
lymphoid tissue
Enteric nervous system
• Submucosal plexus
In submucosa
Controls glandular secretions & thin
submucosal muscular layer
• Myenteric nerve plexus
Between circular & longitudinal muscle layers
Controls GI tract motility
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Enteric Nervous System
• Linked to CNS via afferent visceral fibers
• Long ANS fibers synapse with enteric
plexuses
Sympathetic impulses inhibit digestive activities
Parasympathetic impulses stimulate digestive
activities
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