Digestive system Flashcards
Functions of digestive system
Ingestion
Motility
Secretion
Digestion
Absorption
Elimination
Ingestion
Introduction of solid and liquid nutrients into the oral cavity
Motility
Voluntary and involuntary muscular contractions
-Mixing and moving materials
Secretion
Producing and releasing fluid products facilitating digestion
Digestion
Breakdown of ingested food into smaller structures
- Mechanical digestion
˗Material physically broken down by chewing and mixing
-Chemical digestion
˗ Uses enzymes to break molecules from complex > small
Absorption
Transport of digested molecules, electrolytes, vitamins, water to blood or lymph
Elimination
expulsion of indigestible components that are not absorbed
Two categories of digestive system
Organs of the gastrointestinal tract
Accessory digestive organs
Organs of the gastrointestinal tract
◦ Form a continuous tube
◦ Includes
o Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus
◦ Food broken down into smaller components to be absorbed
Accessory digestive organs
-Assist in breakdown of food
-Some produce secretions that empty into the GI tract
o Glands: Salivary glands, liver, pancreas
o Structures: tongue, teeth, gallbladder
GI system has 4 tunics
Mucosa
Submucosa
Muscularis
Adventitia or serosa
Mucosa
-Epithelium
-Lamina propria
-Muscularis mucosae
Epithelium of mucosa
simple columnar epithelium with microvilli
direct contact with shit in the lumen.
Lamina propria of the mucosa
Connective tissue with small blood vessels and nerves
Muscularis mucosae
smooth muscle
Submucosa
-Connective tissue, blood vessels, lymph vessels, nerves
-Submucosal nerve plexus
Submucosal nerve plexus
Nerves and ganglia innervating smooth muscle and glands
layers of the Muscularis
◦ A. Inner circular layer
◦ B. Outer longitudinal layer
Inner circular layer
part of muscularis
Muscle cells oriented in a circle
Outer longitudinal layer
part of muscularis
Smooth muscle cells that run along the length of the digestive tract
It is controlled by the myenteric nerve plexus
Enteric nervous system
-Submucosal nerve plexus combined with the myenteric nerve plexus
-Sensory: Detects changes in tract wall and chemical makeup of lumen content
-Motor: pushes things forword by closing lumen
-Thickened at several points to form a sphincter
Peristalsis
Involuntary constriction and relaxation within the digestive tract. This contraction and relaxation creates wave-like motions that push ingested material forwards.
Mixing
mechanincally blends ingested materials with secretions in order to break down food and shit lol xD
Adventitia
o Connective tissue with collagen and elastic fibers
o Found outside the peritoneal cavity
Serosa
o Same composition as adventitia
o Found within peritoneal cavity
Serous membranes of digestive system
-Parietal peritoneum lines resides on the outside- lines the abdominal wall.
-Visceral peritoneum covers the organs directly.
-Potential for peritoneal cavity; space between visceral and parietal layers
Intraperitoneal organs
Organs completely surrounded by visceral peritoneum
-Stomach, most of small intestine, parts of large intestine
Retroperitoneal organs
o Lie directly against posterior abdominal wall, only anterolateral portions covered with peritoneum
o Most of duodenum, pancreas, ascending and descending colon, rectum
Mesentery
-Double layer of peritoneum
Blood and lymph vessels, nerves, are sandwiched between the folds
o Multiple regions associated with different organs
-Greater omentum
-Lesser omentum
-Falciform ligament
-Mesentary proper
-Mesocolon
Receptors
◦ Monitor changes associated with GI tract and contents
located In mucosa and submucosa of GI tract
Baroreceptor
Detect stretch and pressure
Chemoreceptors
Detect specific substances of passing contents within the lumen
Autonomic nervous system
parasympathetic system increases activity
sympathetic decreases
Nervous control
◦ Sensory input from receptors > CNS
Long and Short reflexes
Long reflexes
Autonomic motor output = coordinated secretion and muscle contractions (long reflexes)
Short reflexes
Digestive reflexes that do not involve the CNS
Local, occur in enteric nervous system
where is Gastrin from
stomach
where is Secretin secreted
small intestine
where is Cholecystokinin (CCK) secreted
small intestine
Oral cavity and salivary glands
o Mechanical digestion begins here
o Saliva secreted from salivary glands in response to food
Pharynx
o Food bolus moved here, where swallowing occurs
o Mucus secreted here to facilitate swallowing
Esophagus
o Bolus transported from pharynx into stomach
o Lubricated by mucus secretions
Stomach
o Bolus mixed with gastric secretions by smooth muscle contractions
upper GI tract organs
◦ Oral cavity and salivary glands
◦ Pharynx
◦ Esophagus
◦ Stomach
Duodenum
Oral cavity organs
Mouth
Vestibule
cheek
lip
palate
uvula
Mouth
entrance to GI tract
Vestibule
Space between gum, lips, cheeks
Cheeks
buccinator muscles
Compress cheeks to hold solid material while chewing
Lips
orbicularis oris muscle
Internal surfaces attached to the gingivae
Attached at mucosa fold in midline, labial frenulum
Palate
roof of the oral cavity
Soft palate, posterior 1/3 - Hard palate, anterior 2/3
Uvula
conical projection from posterior soft palate
Elevates with soft palate during swallowing
Closes off posterior entrance into nasopharynx
Fauces
o Opening between oral cavity and oropharynx
o Bounded by muscular folds
◦ Palatoglossal arch palatopharyngeal
o Palatine tonsils housed between arches
Tongue
on inferior surface of cavity
o Primarily from skeletal muscle, with extrinsic and intrinsic muscles
o Numerous projections, papillae, involved with taste
o Attaches to floor by membrane, lingual frenulum
o Manipulates and mixes materials during chewing
o Important functions in swallowing and speech
Salivary glands
Produce saliva: intrinsic and extrinsic
Intrinsic salivary glands
(within oral cavity)
o Unicellular glands
o Continuously release secretions independent of food
˗ Contains lingual lipase; enzyme that begins digestion of fats
Extrinsic salivary glands
(outside oral cavity)
o Produce most saliva
o Three types
Parotid salivary glands
Submandibular salivary glands
Sublingual salivary gland
Parotid salivary glands
o Structurally the largest
o Produces 25–30% of saliva
o Saliva moves from parotid duct > oral cavity
o Extends from gland across masseter, opening near second upper molar
Submandibular salivary glands
o Produces 60–70% of saliva
o Submandibular duct opens from each gland to floor of cavity
Sublingual salivary gland
o Extends tiny ducts opening into inferior surface of cavity
˗ Contribute only 3–5% of saliva
types of Salivary gland cells
◦ Two types of secretory cells within salivary glands
mucus and serous
Mucous cells
Secrete mucin, forming mucus upon hydration
Serous cells
Secrete watery fluid containing electrolytes and salivary amylase
Salivary amylase: enzyme initiating digestion of starch
Saliva
◦ 1.0–1.5 L secreted daily
◦ 99.5% water and a mixture of solutes
◦ Salivary amylase, mucin, lysozyme added
◦ Moistens ingested food to help become bolus
◦ Initiates chemical breakdown of starch and fat
◦ Antibacterial substances inhibit bacterial growth (lysozyme, antibodies)
◦ Slightly acidic
Regulation of salivary secretions
-Basal level of salivation / receptors detect stimuli in oral cavity and stomach
-Send signal to salivary nuclei in brainstem
-Nuclei also receive signals from higher brain centers in response to thought of food
-Increased parasympathetic stimulation = saliva
Mastication
chewing
o Mechanically reduces bulk to facilitate swallowing
o Increases surface area to facilitate exposure to digestive enzymes
o Promotes salivation
o Controlled by nuclei in medulla and pons: mastication center
Teeth
– Collectively known as the dentition
– Exposed crown and constricted neck
– One or more roots, anchoring it to jaw
o Fit tightly into dental alveoli, sockets within alveolar processes
– Bound to processes by periodontal ligament in gomphosis joint
Dentin
primary mass of tooth
o Comparable to bone but harder
Enamel
on surface of dentin
o Calcium phosphate crystals, hardest substance in the body
Pulp cavity
center of tooth
Root canal
continuous with pulp cavity
o Blood vessels and nerves passing through here
Cementum
Hardened material ensheathing root
Gingivae
Gums
dense irregular CT
How many teeth of each kind do you have?
◦ 20 Deciduous teeth (baby teeth)
◦ 32 Permanent teeth, replacing deciduous
teeth
Incisors
most anteriorly placed teeth
Shaped like chisel for slicing food
Canines
posterolateral to incisors
Pointed tip for puncturing and tearing food
Premolars
posterolateral to canines
o Flat crowns with prominent ridges (cusps)
that crush and grind
Molars
grinding and crushing materials
Each quadrant of the mouth has
◦ In each quadrant
o 2 incisors, 1 canine, 2 premolars, 3 molars
Pharynx
◦ Funnel-shaped muscular passageway
o Passageway for air and food
Esophagus
– Normally collapsed, tubular passageway
– Begins at level of cricoid cartilage
– Connects to stomach
Superior esophageal sphincter
o Contracted ring of circular skeletal muscle at superior end
o Closed during inhalation of air
Inferior esophageal sphincter
o Contracted ring of circular skeletal muscle at inferior end
o Not strong enough by itself to stop stomach contents from regurgitating
Swallowing
Moving ingested materials from oral
cavity to stomach
Voluntary phase
first phase,
occurring after ingestion,
concious
Pharyngeal phase
o Involuntary reflex - sensory input to medulla
the bolus is propelled through the pharynx and into the esophagus
Stomach
◦ Chemical and mechanical digestion continuing here
o Digestion of protein and fat here – absorption limited
◦ Ingested materials spending 2 to 6 hours here
Chyme
formed from mixing bolus and secretions
Stomach anatomy
muscular J-shaped organ
◦ Greater curvature
lesser curvature
greater curvature
Larger convex inferolateral surface
Lesser curvature
Smaller concave superomedial surface
Four regions of stomach
Cardia
Fundus
Body
Pylorus
Cardia
o Entryway into stomach from esophagus
o Cardiac orifice, where cardia meets esophagus
Fundus
Dome-shaped region superior and lateral side
Body
Largest region of stomach, medial
Pylorus
o Funnel-shaped pouch forming terminal region
o Opening into duodenum of - pyloric orifice
o Pyloric sphincter – regulates entry of material in to small intestine
Gastric folds
Also known as Rugae, they are found on internal stomach lining when stomach empty
o Allow stomach to expand greatly when it fills with food
Histology of the stomach
◦ Lined by simple columnar epithelium
◦ Lining indented by depressions, gastric pits
◦ Gastric glands
o Extend deep into mucosa from base of each gastric pit
o Partially surrounded by muscularis mucosae
˗ Helps expel gastric secretions
Stomach muscularis
o 3 smooth muscle layers (not two)
o Inner oblique, middle circular, outer longitudinal
o The third layer assists churning and blending
◦ Serosa
◦ Visceral peritoneum
Gastric secretions
Produced by 5 types of secretory cells - 4 produce gastric juice, 1 secretes hormone
Surface mucous cells
o Line stomach lumen and extend into gastric pits
o Continuously secrete alkaline (basic) product containing mucin which helps prevent ulcer formation
Mucous neck cells
In gastric pit - produce acidic mucin which helps maintain acidic conditions while also protecting lining
Parietal cells
Intrinsic factor
◦ Required for absorption of vitamin B12 in ileum
◦ Necessary for production of normal erythrocytes
Hydrocloric acid
◦ Forms from H+ and Cl– secreted across cells’ surface, maintains low pH
Chief cells
o Most numerous secretory cells within gastric
glands
o Produce and secrete packets of zymogen
granules that contain pepsinogen
o HCl activates pepsinogen > pepsin
◦ Chemically breaks down large molecules
o Produce gastric lipase
G-cells
o Enteroendocrine cells that are widely distributed in gastric glands
o Secrete gastrin hormone
◦ Stimulates stomach secretions and motility
2 main functions of Motility in the stomach
Two primary functions: mixing the bolus to form chyme and emptying chyme from stomach to small intestine
Regulation of the digestive processes in the stomach
-Stomach, holding bag for partially digested food
-Regulated by nervous reflexes and hormones
Organized in three phases:
1. Cephalic
2. Gastric
3. Intestinal
Lower GI tract organs
◦ Process of digestion and absorption continues
◦ Elimination of indigestible / unabsorbable material
◦ Small intestine
o 3 continuous regions: duodenum, jejunum, ileum
o Duodenum - upper GI tract
o Receives chyme
o Most chemical digestion and absorption happens here
Accessory organs
o Liver produces bile and pancreas produces pancreatic juice
o Bile stored, concentrated, released by gallbladder
Large intestine
o Continues absorption of water, electrolytes, vitamins
o Feces produced and eliminated through anus`
Small intestine
◦ Ingested nutrients reside here at least 12 hours
◦ Absorbs most nutrients, water, electrolytes, and vitamins
Duodenum
o First segment, originates at pyloric sphincter
o Receives accessory gland secretions from liver, gallbladder, pancreas; chyme from stomach
Jejunum
o Middle region, two-fifths of total length of small intestine
o Primary region for chemical digestion and nutrient absorption
Ileum
o Last region, three-fifths of small intestine
o Distal end terminates at ileocecal valve
◦ Sphincter controlling entry of materials into large intestine
o Continues absorption of digested material
Circular folds
o Internal folds to increase surface area to increase nutrient absorption
o “Speed bumps” to slow movement of chyme
o More numerous in duodenum and jejunum, less in ileum
Villi
o Fingerlike projections of mucosa
o Increases surface area for absorption and secretion
o Contains an arteriole, capillary network, venule
Microvilli
o Extension of the plasma membrane: brush border
o Various enzymes embedded here, brush border enzymes
◦ Complete chemical digestion of most nutrients
o Proteins for transport of digestion products also embedded here
Lacteal
o Lymphatic capillary within villus
o Responsible for absorbing lipids and lipid-
soluble vitamins
Simple columnar epithelium w/ microvilli
Absorption
Goblet cells
Produce mucin
Enteroendocrine cells
Release hormones such as CCK
and secretin
Paneth cells
◦ Aid innate immune system
◦ Secrete lysozyme and anti-microbial agents
Submucosal gland
◦ Produces alkaline mucus secretion protecting duodenum from chyme
Accessory organ ducts:
Biliary apparatus
o Network of ducts draining left and right lobes of liver
o Include left and right hepatic ducts
o Merge to form single common hepatic duct
o Merges with cystic duct from gallbladder to form common bile duct
o Extends inferiorly to the duodenum
Liver
◦ Accessory digestive organ
◦ Production of bile is main function
◦ Largest internal organ
◦ Rt lobe larger than left
◦ Quadrate and caudate lobes within right lobe
Porta hepatis
Where blood (hepatic artery and vein), lymph vessels, bile ducts, nerves, enter and leave liver
liver histology
◦ Connective tissue capsule branches throughout organ
◦ Forms septa partitioning liver into small hepatic lobules
hepatic lobules = Structural and functional units of liver
o Within lobules are liver cells, hepatocytes
Hepatic sinusoids
Thin-walled capillaries with large gaps between cells
Bile canaliculi
Conducts bile produced by hepatocytes to hepatic
duct
Bile
Contains: Water, bicarbonate ions, bile salts and pigments, cholesterol, lecithin, mucin
Alkaline and helps with the digestion of lipids
CCK controls the
sphincter
Hepatic Portal System
Blood from the spleen, small, and large intestine is carried to the liver
Gallbladder
◦ Saclike organ attached to inferior surface of liver
◦ Stores, concentrates, and releases bile produced in liver
◦ Connected to common bile duct by cystic duct
◦ Sphincter valve controls flow of bile out
Pancreas
◦ Endocrine function:
Produces and secretes insulin (beta cells) and glucagon (alpha cells)
◦ Exocrine function:
Produces pancreatic juice to assist with digestive activities
Pancreatic juice
o Formed from secretions of acinar ccells and pancreatic duct cells
o Alkaline fluid
o Mostly water, HCO3–, digestive enzymes
◦ Pancreatic amylase to digest starch
◦ Pancreatic lipase to digest triglycerides
◦ Nucleases for digestion of nucleic acids
Cholecystokinin (CCK)
Stimulates the release of bile (galbladder) and pancreatic juice
o Inhibits stomach motility and release of gastric secretions
Secretin
o Causes release of a solution containing HCO3–
◦ Helps neutralize acidic chyme
o Inhibits gastric secretions and motility
DIGESTION OF MACROMOLECULES DIAGRAM IMPORTANT**
Large intestine
◦ Relatively wide tube, much shorter than small intestine
◦ Absorbs water and electrolytes from remaining digested material
◦ Watery chyme compacted into feces
◦ Stores feces until eliminated through defecation
Cecum
first portion of large intestine
o Pouch in right lower abdominal quadrant
o Extends inferiorly from ileocecal valve, connected to ileum
Appendix
o Lined by lymphocyte-filled lymphatic nodules
o Attached to cecum
Colon, four segments
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Ascending colon
Originates at ileocecal valve, extends superiorly from cecum along right lateral abdominal cavity
transverse colon
Projects horizontally to left across abdominal cavity
