1
Q
Main functions of the digestive system
A
- Take in food
- Break it down into nutrient molecules
- Absorb molecules into the bloodstream
- Rid body of any indigestible remains
2
Q
Alimentary canal (gastrointestinal or GI tract or gut) what does it do? what does it consist of?
A
- Continuous muscular tube that opens to the outside at both ends
- Digests food
- Absorbs nutrients
- mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
3
Q
Accessory digestive organs
A
- Assist in digestion; secrete chemicals or mechanically breakdown particles
- -Teeth, Tongue, Gallbladder
- -Digestive glands
- —produce secretions that help break down foodstuffs
- —Salivary glands, Liver, Pancreas
4
Q
Six “steps” to breaking down food
- Ingestion:
- Propulsion:
- Mechanical breakdown:
- Digestion:
- Absorption:
- Defecation:
A
- Ingestion: eating
- Propulsion: movement of food through the alimentary canal, which includes:
- -Swallowing
- -Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation
- Mechanical breakdown: includes chewing, mixing food with saliva, churning food in stomach, and segmentation
- —Segmentation: local constriction of intestine that mixes food with digestive juices
- Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks
- Absorption: passage of digested fragments from lumen of GI tract into blood or lymph
- Defecation: elimination of indigestible substances via anus in form of feces
5
Q
Peritoneum surrounds most of
A
Peritoneum surronds most of GI tract
-serous membranes of abdominal cavity that consists of:
- Visceral peritoneum
- –membrane on external surface of most digestive organs
- Parietal peritoneum
- –membrane that lines body wall
- Peritoneal cavity
- -Fluid-filled space between two peritoneums
- -Fluid lubricates mobile organs
6
Q
Mesentery
- Layers are
- Extends from
- Provides routes for
- Holds
- Stores
A
- Double layer of peritoneum
- Layers are fused
- Extends from body wall to digestive organs
- Provides routes for blood vessels, lymphatics, and nerves
- Holds organs in place
- Stores fat
7
Q
Intraperitoneal VS Retroperitoneal
A
- Intraperitoneal (peritoneal) organs
- -located within the peritoneum
- Retroperitoneal organs
- –located outside, or posterior to the peritoneum
- –most of the pancreas, duodenum, and parts of large intestine
8
Q
Peritonitis
- Can be caused by
- Peritoneal coverings
- Dangerous and lethal if it becomes
- Treatment
A
Peritonitis
- Inflammation of peritoneum
- Can be caused by piercing abdominal wound, perforating ulcer, or ruptured appendix
- Peritoneal coverings stick together
- –helps localize infection
- Dangerous and lethal if it becomes widespread (sepsis)
- Treatment
- –debris removal and megadoses of antibiotics
9
Q
Histology of the Alimentary Canal (Introduction)
-All digestive organs have the same
A
- All digestive organs have the same four basic layers, or tunics
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
10
Q
Mucosa
A
Mucosa
- Lines lumen
- Functions
- -different layers perform one or all three
- -Secretion
- — mucus, digestive enzymes, and hormones
- -Absorbtion
- —end products of digestion
- -Protection
- — against infectious disease
- Made up of three sublayers
- -Epithelium, Lamina propria, Muscularis mucosae
11
Q
Epithelium
- -Mouth, esophagus, and anus are made up of
- Secretes
- -Protects digestive organs from
- -Eases
- May secrete
A
Epithelium
- Simple columnar epithelium and mucus-secreting cells in most of tract
- -Mouth, esophagus, and anus are made up of stratified squamous epithelium
- Secretes mucus
- -Protects digestive organs from enzymes
- -Eases food passage
- May secrete enzymes and hormones
- -i.e. in stomach and small intestine
12
Q
Lamina propria -Made up of -Rich supply of --Needed for -Also contains --Follicles are part of Muscularis mucosae
A
Lamina propria
- Made up of loose areolar connective tissue
- Rich supply of capillaries located here
- -Needed for nourishment and absorption
- Also contains lymphoid follicles that help defend against microorganisms
- -Follicles are part of MALT (mucosa-associated lymphoid tissue)
- Muscularis mucosae
- -Smooth muscle that produces local movements of mucosa
13
Q
Submucosa made up of -surrounded by -lots of -helps organs to
A
Submucosa
- areolar connective tissue
- blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus that supply surrounding GI tract tissues
- lots of elastic tissues
- -help organs to regain shape after storing large meal
14
Q
Muscularis externa
-responsible for
inner and outer layer
A
- Muscle layer
- responsible for segmentation and peristalsis
- inner circular muscle layer
- -Circular layer thickens in some areas to form sphincters
-outer longitudinal layer
15
Q
Serosa
- what kind of tissue that is covered with____
- Replaced by ____ in esophagus
- Retroperitoneal organs have both a
A
- Outermost layer
- Is the visceral peritoneum
- -areolar connective tissue covered with mesothelium (single layer of squamous epithelium) in most organs
- Replaced by fibrous adventitia in esophagus
- -Dense connective tissue that holds esophagus to surrounding structures
- Retroperitoneal organs have both an adventitia and a serosa
16
Q
Splanchnic circulation
Hepatic portal circulation-recieves blood from
blood goes directly to
A
Splanchnic circulation
- arteries branch off aorta
- serves digestive organs
- -Hepatic, splenic, and left gastric arteries
- -Inferior and superior mesenteric arteries
Hepatic portal circulation
- -recieves blood from digestive organs (nutrient rich!)
- -blood goes directly to the liver for processing
17
Q
Enteric Nervous System -Also called the -The nervous system of the -Major nerve supply to Enteric neurons
A
Enteric nervous system
- Also called the gut brain
- The nervous system of the GI tract
- Major nerve supply to GI tract wall that controls motility
Enteric neurons
- more neurons than spinal cord
- communicate extensively with each other
18
Q
Intrinsic Nerve Plexuses
A
-Two main interconnecting intrinsic nerve plexuses:
- Submucosal nerve plexus
- -Regulates glands and smooth muscle in mucosa
- Myenteric nerve plexus
- -Controls GI tract motility
19
Q
(Short and Long Reflexes)
short reflexes
controlled by
respond
long reflexes
respond to
parasympathetic system
sympathetic system
A
Short reflexes
- -controlled by enteric nerve plexuses (gut brain)
- -respond to stimuli in GI tract
- -Long reflexes
- —respond to stimuli inside or outside of gut,
- —i.e. from the autonomic nervous system
- –Parasympathetic system-enhances digestive process
- –Sympathetic system-inhibits digestion
20
Q
Regulation of Digestive Activity (Stimuli)
Mechanical and chemical stimuli
A
Mechanical and chemical stimuli
- Receptors located in walls of GI tract organs
- stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion
21
Q
Basic Concepts of Regulating Digestive Activity (Effectors)
A
- Effectors of digestive activity are smooth muscle and glands
- Remember reflexes?
- -receptors initiate
- -Stimulation of smooth muscle
- –mix and move contents
- -Activation or inhibition digestive glands
- –secrete digestive juices or hormones
22
Q
Basic Concepts of Regulating Digestive Activity (Nervous and Hormonal)
-Nervous system control
Intrinsic controls:
Extrinstic control
- Hormonal controls
- -hormones from the
- -stimulate target cells to
- —Target cells can be in the
A
-Neurons (intrinsic and extrinsic) and hormones control digestive activity
- Nervous system control
- -Intrinsic controls:
- –involve short reflexes (enteric nervous system)
- -Extrinsic controls
- –involve long reflexes (autonomic nervous system)
- Hormonal controls
- -hormones from the stomach and small intestine
- -stimulate target cells to secrete or contract
- —Target cells can be in the same or in different organs
A+P 2
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