Chapter 24 - Digestive System Flashcards
What are the two groups of organs that make up the digestive system?
- Gastrointestinal (GI) tract
2. Accessory digestive organs
What are the organs of the gastrointestinal tract?
Mouth, most of the pharynx, esophagus, stomach, small intestine, large intestine
What are the organs of the accessory digestive organs?
Teeth, tongue, salivary glands, liver, gallbladder, pancreas
What are the six basic processes of digestion?
- Ingestion - eating
- Secretion - release of water, acid, buffers and enzymes into lumen of GI tract
- Mixing and propulsion - churning and propulsion of food through GI tract
- Digestion - mechanical and chemical breakdown
- Absorption - passage of digested products from GI tract into blood and lymph
- Defecation - elimination of feces
What is motility?
The capability of the GI tract to mix and move material along its length
What is mechanical digestion?
- teeth cut and grind food
- smooth muscles of stomach and small intestine churn food
What is chemical digestion?
Food is split into smaller molecules by hydrolysis
What are feces or stool?
Eliminated material
- wastes, indigestible substances, bacteria
What are the four layers of the GI tract?
from deep to superficial
- Mucosa
- Submucosa
- Muscularis
- Serosa/adventitia
What is the mucosa?
Inner lining of the GI tract
- mucous membrane
What is the mucosa composed of?
- Epithelium layer (direct contact with food)
- Connective tissue layer (lamina propria)
- Smooth muscle layer (muscularis mucosae)
Describe the structure and function of the epithelium layer of the mucosa?
Stratified squamous epithelium - serves a protective function (mouth, pharynx, esophagus, anal canal)
Columnar epithelium - functions in secretion and absorption (stomach and intestines)
- Tight junctions prevent leaks
What are enteroendocrine cells?
Secrete hormones into the GI tract
- regulate glucose levels, food intake, and stomach emptying
What is the lamina propria?
Connective tissue layer of GI tract (middle layer)
What does the lamina propria contain?
Blood and lymphatic vessels
- routes by which nutrients are absorbed to reach other tissues
What are mucosa-associated lymphatic tissues (MALT)?
What do they contain?
Lymphatic nodules
- contain immune system cells that protect against diseases
What is the muscularis mucosae?
Smooth muscle fibre layer of GI tract (superficial layer)
- creates folds in stomach and small intestine to increase surface area
What is contained in the submucosa layer?
- blood and lymphatic vessels (absorbed food molecules)
- extensive network of neurons (submuscosal plexus)
- glands and lymphatic tissue
Where is the muscularis skeletal muscle?
Mouth, pharynx, superior and middle parts of esophagus
- produces voluntary swallwoing
External anal sphincter
- voluntary control of defecation
Where is the muscularis smooth muscle?
The rest of the GI tract
- stomach, small intestine, large intestine
What is another name for the serosa?
Visceral peritoneum
- forms a portion of the peritoneum
What forms the superficial layer of the esophagus, since it lacks a serosa?
Adventitia
- single layer of areolar connective tissue
What is the enteric nervous syste, (ENS)?
“Brain of the gut”
- neurons that extend from esophagus to the anus
What two plexuses make up the ENS?
- Myenteric plexus
2. Submuscosal plexus
What does the myenteric plexus control?
Controls GI tract motility (movement)
- frequency and strength of contraction of the muscularis
What is the submuscosal plexus control?
Controls the secretions of the organs of the GI tract
What other nervous SYSTEM is the ENS subject to?
Autonomic nervous system
- sympathetic and parasympathetic fibres
What does the stimulation of parasympathetic nerves in the GI tract cause?
Increase in GI secretion and motility
- increases the activity of ENS neurons
What does the stimulation of sympathetic nerves in the GI tract cause?
Decrease in GI secretion and motility
- inhibits the neurons of the ENS
- fear, anxiety, anger - slow digestion
What do receptors in the gastrointestinal reflex pathways send information about?
Nature of the contents in GI tract and degree of distension (stretching) of the GI tract
What is the largest serous membrane in the body?
Peritoneum
How is the peritoneum divided?
- Parietal peritoneum - lines the wall of the abdominopelvic cavity
- Visceral peritoneum - covers organs
What is the peritoneal cavity?
Space between the parietal peritoneum and visceral peritoneum
- contains lubrication serous fluid
Where is the retroperitoneal located?
Situated or occurring behind the peritoneum
What organs are part of the retroperitoneal?
Kidneys, ascending and descending colons, duodenum of small intestine, pancreas
Describe the anatomy of the peritoneal.
- large folds that weave between the viscera
- binds the organs to one another
- contain blood vessels, lymphatic vessels, nerves
What are the five major peritoneal folds?
- Greater omentum
- Falciform ligament
- Lesser omentum
- Mesentery
- Mesocolon
Describe the greater omentum.
- largest peritoneal fold
- drapes over the transverse colon and coils of the small intestine like a “fatty apron”
- can cause “beer belly” with excessive weight gain
- contains many lymph nodes to combat GI infections
Describe the falciform ligament.
- attaches the liver to the anterior abdominal wall and diaphragm
- liver is the only digestive organ that is attached to the anterior abdomianl wall
- second peritoneal fold
Describe the lesser omentum.
- suspends the stomach and duodenum from the liver
- contains hepatic portal vein, common hepatic artery and common bile duct
- third peritoneal fold
Describe the mesentery.
- fan-shaped fold of the peritoneum
- binds the jejunum and ileum of the small intestine to the posterior abdominal wall
Describe the mesocolon.
- bind the transverse colon and sigmoid colon to the posterior abdominal wall
- hold intestines loosely in place
What is the mouth also referred to as?
Oral or buccal cavity
What are the cheeks?
Form the lateral walls of the oral cavity
- covered externally with skin
What are the lips or labia?
Fleshy folds surrounding the opening of the mouth
What is the oral vestibule?
The space bounded externally by the cheeks and lips and internally by the gums and teeth
What is the oral cavity proper?
Space that extends from the gums and teeth to the fauces
What are the fauces?
Opening between the oral cavity and the oropharynx (throat)
What is the function of the palate in the mouth?
Makes us able to chew and breathe at the same time
What is the hard palate?
Anterior portion of the roof of the mouth
- bony partition between the oral and nasal cavities
What is the soft palate?
Posterior portion of the roof of the mouth
- muscular partition betwwen oropharynx and nasopharynx
What is the uvula?
A fleshy extension at the back of the soft palate that hangs above the throat
What is the function of the salivary glands?
Releases saliva
- cleanses mouth and teeth
- lubricates, dissolves, and begins chemical breakdown of food
What are the three pairs of major salivary glands?
- Parotid glands
- Submandibular glands
- Sublingual glands
Where are the parotid glands located and what do they secrete?
Inferior and anterior to the ears
- watery (serous) liquid containing salivary amylase
How does saliva from the parotid glands reach the oral cavity?
Through the parotid duct
- pierces the buccinator muscle
Where are the submandibular glands located and what do they secrete?
Found in the floor of the mouth
- fluid that contains amylase but is thickened with mucous
Where are the sublingual glands located and what do they secrete?
Beneath the tongue and superior to the submandibular glands
- secrete a much thicker fluid, contributes a small amount of salivary amylase
Where do the sublingual glands open into?
Floor of the mouth in the oral cavity proper
Where do the submandibular glands open into?
Submandibular ducts
- “gleeking”
What is the chemical composition of saliva?
- 99.5% water
- .05% solutes
(sodium, potassium, chloride, bicarbonate, phosphate) - slightly acidic pH 6.35-6.85
What is salivary amylase?
An enzyme that starts the breakdown of starch in the mouth into maltose, maltotriose and a-dextrin
What are the functions of saliva?
- buffer acidic foods
- starts breakdown of starch
- help remove waste from the body
- lubricates food
What is salivation?
The secretion of saliva
- controlled by ANS
What is the tongue and what does it form?
Accessory digestive organ
- forms the floor of the oral cavity
How do the extrinsic muscles move the tongue?
- From side to side
- In and out
- Maneuver food for chewing, shape the food and force the food to the back of the mouth
How do the intrinsic muscles move the tongue?
Alter the size and shape
- for speech and swallowing
What is the lingual frenulum?
Fold of mucous membrane in the midline of the undersurface of the tongue
- attached to the floor of the mouth
- limits movement of tongue posteriorly
What are papillae?
Projections of the lamina propria that cover the upper and lateral surfaces of the tongue
- some contain taste buds
- some contain touch receptors
What is the function of lingual glands?
Secrete mucous and watery serous fluid that contains lingual lipase
What does lingual lipase do?
Acts on as much as 30% of dietary triglycerides (fats and oils), converts them to simpler fatty acids and diglycerides
What are teeth?
Dentes
- accessory digestive organs
- located in sockets of the alveolar processes of the mandible
What are gingivae?
Gums!
- extend slightly into each socket
What is the function of the periodontal ligament?
Anchors the teeth to the socket walls and acts as a shock absorber during chewing
- lines each socket
What are the three major external regions of a tooth?
- Crown
- Root
- Neck
What is the crown of a tooth?
Visible portion above the level of the gums
Where are the roots of a tooth located?
Embedded in the socket
- contains 1-3 roots
What is the neck of the tooth?
Constricted junction of the crown and root near the gum line
Internally, what forms the majority of the tooth?
Dentin
What is dentin?
Calcified connective tissue
- gives shape and rigidity
- harder than bone
Where can you find enamel?
Covering the dentin of the crown of a tooth
- hardest substance in the body
What is the function of enamel?
Protects the tooth from wear and tear of chewing
- protects against acids
What is cementum?
Bone-like substance
- attaches the root to the periodontal ligament
What is the pulp cavity?
Enlarged space that lies within the crown
- filled with pulp
What is pulp?
Connective tissue containing blood vessels, nerves and lymphatic vessels
What are root canals?
Extensions of the pulp cavity
- run through the root of the tooth
What are dentitions?
How many do humans have?
Sets of teeth
- 2!
What are the names of the two dentitions?
- Deciduous teeth
2. Permanet teeth
What are deciduous teeth?
Baby teeth (primary/milk teeth) - there are 20 deciduous teeth
What are incisors?
central or lateral incisors
Closest to the midline, chisel-shaped teeth
- adapted for cutting into food
- contain 1 root
What are cuspids?
Used to tear and shred food
- beside the incisors
- contain 1 root
What are the first and second molars?
Crush and grind food to prepare for swallowing
- beside the cuspids
- have 4 cusps
How many roots do upper molars have?
Lower molars?
Upper: 3 roots
Lower: 2 roots
What are permanent teeth?
Secondary teeth
- replace baby teeth
- contains 32 teeth
What are deciduous molars replaced with?
First and second premolars
- two cusps
- 1 root
- used for crushing and grinding
What do the permanent molars replace?
Nothing!
- erupt as the jaw grows to accomdate them
When do the first, second and third molars (permanent) appear?
First: at age 6
Second: at age 12
Third: after age 17 (wisdom teeth) - sometimes do not erupt
What is mastication?
Mechanical digestion in the mouth
- results from chewing
What is a bolus?
Soft, flexible, easily swallowed mass
- results from mastication
What two enzymes contribute to chemical digestion in the mouth?
- Salivary amylase - breakdowns starch
2. Lingual lipase - breakdowns lipids
How does lingual lipase become activated?
In the acidic environment of the stomach
- starts to work after food has been swallowed
What are the three parts of the pharynx?
- Nasopharynx - only in respiration
- Oroparynx - digestive and respiratory functions
- Laryngopharynx - digestive and respiratory functions
What is the pharynx?
The throat
What is the esophagus?
Food tube
- collapsible, muscular tube
- 25 cm long
- lies POSTERIOR to the trachea