Chapter 24 Flashcards
Digestive system
Consists of a group of organs that break down the food we eat into smaller molecules used by body cells grouped into two groups gastrointestinal tract and accessory digestive organs
Gastrointestinal tract
Also called the alimentary canal is a continuous tube that extends from the mouth to the anus including the mouth, most of the pharynx, oesophagus, stomach, small intestine, and large intestine
Tonus
A state of sustained contraction
Accessory digestive organs
Teeth, tongue, salivary glands, liver, gallbladder, and pancreas
What are the six basic processes performed by the digestive system?
- Ingestion
- Secreation
- Motility
- Digestion
- Absorption
- Defecation
What are the layers of the G.I. tract?
- Mucosa
- Submucosa
- Muscularis
- Serosa/adventitia
Mucosa
- Epithelium
- Lamina propria
- Muscularis mucosa
Epithelium of the mucosa in the G.I. tract
in the mouth, pharynx, esophagus, and anal canal is mainly nonkeratinized stratified squamous epithelium that serves a protective function
simple columnar epithelium which functions in secretion and absorption lines the stomach and intestines the tight junctions that firmly seal the neighbouring simple columnar epithelial cells to one another restrict leakage between the cells inside the epithelial cells are exocrine cells that secrete mucus and fluid into the lumen of the tract several Endocrine cells are called Enteroendocrine cells which secrete hormones
Lamina propria of the mucosa in the G.I. tract
Consist of areolar or connective tissue containing many blood and lymphatic vessels which are routes by which nutrients absorbed into the G.I. track reach other body tissues this layer supports the epithelium and binds it to the muscularis mucosae and contains most of the mucosa-associated lymphatic tissue and contains immune system cells
Mucosa associated lymphatic tissue (MALT)
Prominent lymphatic nodules that contain immune system cells that protect against disease present all along the G.I. tract especially in the tonsils, small intestine, appendix, and large intestine
Enteroendocrine
Secrete hormones
Muscularis mucosae layer of the mucosa in the G.I. tract?
A thin layer of smooth muscle fibres throws the mucous membrane of the stomach and small intestine into many small folds which increase the surface area for digestion and absorption
Submucosa of the G.I. tract
Consists of areolar connective tissue that binds the mucosa to the muscularis
contains many blood and lymphatic vessels that receive absorbed food molecules
also has an extensive network of neurons known as the submucosal plexus
Muscularis layer of the G.I. tract
The mouth, pharynx, superior and middle part of the esophagus contain skeletal muscle that produces voluntary swallowing. And the external anal sphincter which permits voluntary control of defecation
The rest of the G.I. tract muscularis consists of smooth muscle that is generally found in two sheets an inner sheet Of circular fibres and an outer sheet of longitudinal fibres involuntary contractions of the smooth muscle help break down food mix it with digestive secretions and propel it along the tract
Serosa layer of the G.I. tract
Portions of the G.I. tract that are suspended in the abdominal cavity have this layer
Composed of areolar connective tissue and simple squamous epithelium
Also called the visceral peritoneum because it forms a portion of the peritoneum
esophagus has no serosa and instead has a single layer of areolar connective tissue called adventitia
Enteric nervous system (ENS)
“Brain of the gut”
Arranged into two plexuses the myenteric plexus and the submucosal plexus
Myenteric plexus
Plexus of Auerbach
located between the longitudinal and circular smooth muscle layers of the muscularis
Mostly controls G.I. tract motility particularly the frequency and strength of contraction of the muscularis
Submucosal plexus
Plexus of Meissner
Found within the submucosa
Motor neurons of the submucosal plexus supply the Secretário cells of the mucosal epithelium controlling the secretions of the organs of the G.I. tract
What are the two major types of sensory receptors in the G.I. tract?
- Chemo receptors which respond to certain chemicals in the food present in the lumen
- Mecano receptors such a stretch receptors that are activated when food distends the wall of the G.I. Organ
Parasympathetic nerves that supply the G.I. tract?
The vagus nerve supplies parasympathetic fibres to most parts of the G.I. tract with the exception of the last half of the large intestine which is supplied by the parasympathetic fibres from the sacral spinal cord
Parasympathetic nerves that innervate the G.I. tract cause what?
Increase in G.I. secretion and motility by increasing the activity of the ENS neurons
Where did the sympathetic nerves that supply the G.I. tract arise from?
The thoracic and upper lumbar regions of the spinal cord
Sympathetic nerves that supply the G.I. tract cause what?
Cause a decrease in G.I. secretion and motility by inhibiting the neurons of the ENS
G.I. (gastrointestinal) reflux pathways
Regulate G.I. secretion and motility in response to stimuli present in the lumen of the G.I. tract
Retroperitoneal
Organs that are covered by peritoneum only on the anterior surfaces and are not in the peritoneal cavity
What are the five major peritoneal folds
- Greater omentum
- falciform ligament
- lesser omentum
- mesentery
- mesocolon
Greater omentum peritoneal fold
The longest peritoneal for drapes over the transverse colon and coils of the small intestine like a “fatty apron”
Falciform ligament of the peritoneal folds
Attaches the liver to the anterior abdominal wall and diaphragm
Lesser omentum of the peritoneal folds
Arises is an anterior fold in the serosa of the stomach and duodenum and it connects the stomach and duodenum to the liver it is the pathway for the blood vessels entering the liver and contains the hepatic portal vein, common hepatic artery, and common bile duct, along with some lymph nodes
Mesentery of the peritoneal folds
A fan shaped fold of the peritoneum Binds the jejunum and ileum of the small intestine to the posterior abdominal wall this is the most massive peritoneal fold and is typically laden with fat
Mesocolon peritoneal fold
Two separate folds of peritoneum bind the transverse colon and sigmoid colon of the large intestine to the posterior abdominal wall it also carries blood and lymphatic vessels to the intestine
together the mesentery and mesocolon hold intestines loosely In place
Mouth
Also referred to as the oral or buccal cavity
formed by the cheeks, hard and soft palate, and tongue
Cheeks
Form the lateral walls of the oral cavity
they are covered externally by skin and internally by mucous membrane which consists of nonkeratinized stratified squamous epithelium
Buccinator muscles and connective tissue lie between the skin and the mucous membranes of the cheeks
Lips
Also called labia
fleshy fold surrounding the opening of the mouth they contain the orbicularis muscle and are covered externally by skin and internally by mucus membrane attached to its corresponding gum by midline fold of mucus membrane called labial frenulum
Oral vestibule
The space in the oral cavity that is bounded externally by the cheeks and lips and internally by the gums and teeth
Oral cavity proper
The space that extends from the gums and teeth to the fauces
the opening between the oral cavity and the oropharynx
Palate
A wall or septum that separates the oral cavity from the nasal cavity
Forms the roof of the mouth making it possible to chew and breathe at the same time
Hard palate
The interior portion of the roof of the mouth formed by the maxillae and Palitine bones and is covered by mucus membrane
forms a boney partition between the oral and nasal cavities
Soft palatine
Forms the posterior portion of the roof of the mouth is an arch-shaped muscular partition between the oropharynx and nasopharynx that is lined with mucous membranes
Uvula
Hanging from the free border of the soft pallet and is a finger like muscular structure
During swallowing the soft palate and uvula are drawn superiorly closing off the nasal pharynx and preventing swallowed foods and liquids from entering the nasal cavity
Palatoglossal arch
Extends to the side of the base of the tongue anteriorly, A muscular fold that runs down the lateral side of the soft palate
Small salivary glands
Open directly or indirectly via short ducts to the oral cavity
the glands include labial, buccal, palatial glands in the lips, cheeks, and palate respectively and lingual glands in the tongue
Major salivary glands
Lie beyond the oral mucusa into ducks that lead to the oral cavity
the three major salivary glands are the parotid, submandibular, and sublingual glands
Parotid glands
Located inferior and anterior to the ears between the skin and the masseter muscle
secrete saliva into the oral cavity via a parotid duct that pierces buccinator muscle to open into the vestibule opposite the second maxillary molar tooth
Submandibular glands
Found in the floor of the mouth they are medial and partly inferior to the body of the mandible
their ducts the submandibular duct run under the mucosa on either side of the midline of the floor of the mouth and enter the oral cavity proper lateral to the lingual frenulum
Sublingual gland
Beneath the tongue is superior to the submandibular glands
their ducts the lesser sublingual ducts open into the floor of the mouth in the oral cavity proper
Composition and functions of saliva
Chemically saliva is 99.5% water and 0.5% solutes solutes including ions: sodium, potassium, chloride, bicarbonate, and phosphate
dissolved gases and various organic substances: including urea, and uric acid, mucus, immunoglobulin A, the bacteriolytic enzyme lysozyme, and salivary amylase and digestive enzymes that acts on starch
What is salivary amylase and how is it activated?
Chloride islands in the saliva activate salivary amylase
An enzyme that starts the breakdown of starch in the mouth into maltose, maltotriose, and a-dextrin
Salivation
Secretion of saliva
controlled by the autonomic nervous system
averages 1 to 1 1/2 L a day parasympathetic stimulation promotes continuous secretion of a moderate amount of saliva which keeps mucous membranes moist
Extrinsic muscles of the tongue
Extrinsic muscles of the tongue which originate outside the tongue and insert into connective tissues in the tongue
extrinsic muscles move the tongue from side to side an In and Out to maneuver food for chewing, shape the food into a round mass, and force the food to the back of the mouth for swallowing
Intrinsic muscles of the tongue
Originate in and insert into connective tissue within the tongue
they alter the shape and size of the tongue for speech and swallowing
Lingual frenulum
A fold of mucous membrane in the midline of the undersurface of the tongue is attached to the floor of the mouth and aids in limiting the movement of the tongue posteriorly
Lingual glands
In the lamina propria of the tongue secretes both mucus and a watery serious fluid that contains the enzyme lingual lipase
which acts on as much as 30% of dietary triglycerides and converts them to simpler fatty acids and diglycerdides
Teeth/dentes
Accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae the alveolar processes are covered by gingivae or gums which extends slightly into each socket the sockets are lined by the periodontal ligament or periodontal membrane which consists of dense fibrous connective tissue that anchors the teeth to the socket walls and acts as a shock absorber during chewing
A typical tooth has three major external regions: the crown; the visible portion, in bedded in the socket or one to three roots, and the neck is the constricted junction of the crown and root near the gumline
Dentin
Forms the majority of the tooth internally
consisting of a calcified connective tissue that gives the tooth its basic shape and rigidity
harder than bone because of its higher content of Hydroxyapatite
Pulp cavity
The space inside the tooth and is filled with pulp
Root canals
Narrow extensions of the pulp cavity run through the root of the tooth each root canal has an opening at its base the apical foramen
Endodontics
Branch of dentistry that is concerned with the prevention diagnosis and treatment of diseases that affect the pulp, root, periodontal ligament, and alveolar bone
Orthodontics
A branch of dentistry that is concerned with the prevention and correction of abnormally aligned teeth
Periodontics
A branch of dentistry concerned with the treatment of abnormal conditions of the tissues immediately surrounding the teeth such as gingivitis
What are the two dentitions called
Deciduous and permanent
Deciduous teeth
Also called primary teeth, milk teeth, or baby teeth
begin to erupt at about six months of age and approximately two teeth appear each month thereafter until all 20 are present
Incisor teeth
Closest to the midline are chisel shaped and adapted for cutting into food
There are central or lateral incisors based on their position
Canines
Next to the incisors moving posteriorly have appointed surface called the cusp canines are used to tear and shred food
First and second deciduous molars
Posterior to the canines
have four cusps
maxillary (upper) molars have three roots, mandibular (lower) molars have two roots
Permanent secondary teeth
32 teeth that are wrapped between ages six and adulthood the pattern resembles the deciduous dentition
What do enzymes contribute to the chemical digestion in the mouth
Salivary amylase and lingual lipase
Lingual lipase
Contained in saliva which is secreted by the lingual glands in the tongue becomes activated in the acidic environment of the stomach and thus starts to work after food is swallowed
Pharynx
Otherwise called the throat
Composed of skeletal muscle and lined by mucous membrane and is divided into three parts the nasal pharynx, the oropharynx, and the
Laryngopharynx
Muscular contractions of these areas help propels food into the oesophagus and then into the stomach
esophagus
Collapsible muscular tube that lies posterior to the trachea begins at the inferior end of the laryngopharynx passes through the inferior aspect of the neck and enters the mediastinum anterior to the vertebral column then it pierces the diaphragm through an opening called esophageal hiatus and ends in the superior portion of the stomach
Mucosa of the Esophagus
Consists of nonkeratinized stratified squamous epithelium, lamina propria, and a muscularis mucosae.
Mucosa also contains mucous glands
The muscularis of the superior third of the Esophagus is skeletal muscle the intermediate third is skeletal and smooth muscle and the inferior third is smooth muscle
The muscularis become slightly more prominent at both ends and forms the sphincters the upper esophageal sphincter which consists of skeletal muscle and the lower esophageal sphincter which consists of smooth muscle and is near the heart
Adventitia of the Esophagus
The superficial layer of the Esophagus
no serosa because the areolar connective tissue of this layer is not covered by mesothelium
Functions of the esophagus
Secretes mucus and transport food into the stomach
does not produce digestive enzymes and it does not carry on absorption
Deglutition
Swallowing
Occurs in three stages: voluntary stage in which the bolus is passed into the oropharynx, the pharyngeal stage the involuntary passage of the bolus through the pharynx into the esophagus, and the esophageal stage is the involuntary passage of the bolus through the Esophagus into the stomach
Peristalsis
A progression of coordinated contractions and relaxations
Stomach
J-shaped enlargement of the G.I. tract directly inferior to the diaphragm in the abdomen Connects the esophagus to the duodenum the first part of the small intestine
What are the four main regions of the stomach
- Cardia surrounds the opening of the Esophagus into the stomach
- Fundus is the rounded portion superior to and to the left of the cardia
- The body is inferior to the fundus, the large central portion of the stomach
- Pyloric part is divisible into three regions: the pyloric antrum connects to the body of the stomach, the pyloric canal leads to the third region, the pylorus which intern connects to the duodenum
How does the pylorus communicate with the duodenum of the small intestine?
Via a smooth muscle sphincter called the pyloric sphincter
Lesser curvature of the stomach
Concave medial border of the stomach
Greater curvature of the stomach
Convex lateral border of the stomach
What are the three types of exocrine gland cells that secrete their products into the stomach lumen?
Mucus neck cells, chief cells, and parietal cells
Gastric lipase
Splits triglycerides in fat molecules into fatty acids in monoglycerides
Pancreatic juice
A clear colourless liquid consisting mostly of water some salt sodium by carbonate and several enzymes
What are the enzymes in pancreatic juice?
Pancreatic amylase is starch digesting
Several enzymes that digest proteins into peptides called trypson, Chymotrypsin, carboxypeptidase, and elastase
