Chapter24: Lecture Midterm II Flashcards
Digestive system
consists of a group of organs that break down the food we eat into smaller moelcules that can be used by body cells
The digestive canal (gastrointestinal tube)
a continuous tube that extends through the thoracic and abdominal cavities from the esophagus to the anus through the thoracic and abdominopelvic cavities
Organs of the digestive canal include
- esophagus
- stomach
- small intestine
- large intestine
- anal canal
The accessory digestive organs include
- mouth
- teeth
- tongue
- salivary glands
- pharynx
- liver
- gallbladder
- and pancreas
What helps to breakdown food in the stomach
muscular contractions in the wall of the digestive canal physically breakdown the food by churning it and propelling the food along the canal from the esophagus to the anus
6 Basic functions of the digestive system
- ingestion
- secretion
- mixing and propulsion
- digestion
- absorption
- defecation
What does the secretion phase of the digestive system do
releases water, acid, buffers and enzymes into the lumen of the digestive canal
What does the mixing and propulsion stage of the digestive system do
churns, and moves food through the digestive canal
Each day, cells within the wall of the digestive canal and accessory digestive organs secrete a total of
7 litres of water, acid, buffers and enzymes into the lumen of the digestive canal
From the esophagus to the anal canal there are 4 layers of tissues from deep to superficial:
- mucosa
- submucosa
- muscular layer
- serosa/adventitia
The mucosa
- inner lining of the digestive canal
- composed of epithelium, lamina propria and muscularis mucosae
The epithelium layer of the mucosa in the mouth, pharynx, esophagus and anal canal is
non keratinized stratified squamous epithelium that serves a protective function
The stomach and intestines epithelium layer is
simple columnar epithelium; functions in secretion and absorption
the type of exocrine cells that secrete mucus and fluid into the lumen of the digestive canal
enteroendocrine cells
The lamina propria
is areolar connective tissue containing many blood and lymphatic vessels, which are routes by which nutrients absorbed into the digestive canal reach other tissues of the body
The lamina propria supports the
epithelium and binds to the muscularis mucosa
The lamina propria contains what cells
MALT
- prominent lymph nodules contain immune system cells that protect against disease
Muscularis mucosae
thin layer of smooth muscle fibers
- throws the mucous membrane of the stomach and small intestine into many small folds, which increase the surface area for digestion and absorption
Movement of the muscularis mucosae ensures that
all absorptive cells are fully exposed to the contents of the digestive canal
The submucosa
consists of areolar connective tissue that binds the mucosa to the muscularis
- contains many blood and lymphatic vessels that recieve absorbed food molecules
- contains glands and lymphatic tissue
The submucosa also contains an extensive network of
neurons known as the submucosal neural plexus
Muscular layer of the mouth, pharynx, superior and middle parts of the esophagus contains
skeletal muscle that produces voluntary swallowing
- skeletal muscle also forms the external anal sphincter which permits voluntary control of defecation
Throughout the rest of the digestive canal the muscular layer consists of
smooth muscle that is found in two sheets;
- inner sheet: circular fibers
- outer sheet: longitudinal fibers
Involuntary contractions of smooth muscle in the digestive tract…
help break down food, mix it with digestive secretions and propel it along the digestive canal
Those portions of the digestive canal that are suspended in the abdominal cavity have a superficial layer called the
serosa
Serosa
serous membrane composed of areolar connective tissue and simple squamous epithelium
The esophagus lacks…
serosa; instead, only a single layer of areolar connective tissue called the adventitia forms the superficial layer of this organ
The digestive canal is regulated by an intrinsic set of nerves called
enteric nervous system
The enteric nervous system is known as the
brain of the gut
The neurons of the ENS are arranged in two neural plexuses;
- myenteric neural plexus
- submucosal neural plexus
Myenteric neural plexus
located between the longitudinal and circular smooth muscle layers
Submucosal neural plexus
found within the submucosa
The ENS consists of
motor neurons, interneurons, and sensory neurons
because the motor neurons of the myenteric neural plexus supply the longitudinal and circular smooth muscle layers of the muscular layer
this neural plexus mostly controls digestive canal motility (movement), particularly the frequency and strength of contraction of the muscular layer
The motor neurons of the submucosal neural plexus supplies the
secretory cells of the mucosal epithelium, controlling the secretions of the organs of the digestive canal
The interneurons of the ENS interconnect
the neurons of myenteric and submucosal neural plexuses
The sensory neurons of the ENS supply the
mucosal epithelium and contain receptors that detect stimuli in the lumen of the digestive canal
The wall of the digestive canal contains two types of sensory receptors
- chemoreceptors
- mechanoreceptors
What nerve supplies parasympathetic fibers to most parts of the digestive canal
the vagus nerve
The large intestine however, is supplied by
parasympathetic fibers from the sacral spinal cord
Parasympathetic preganglionic neurons of the vagus or pelvic splanchic nerves synapse withh
parasympathetic postganglionic neurons located in the myenteric and submucosal neural plexuses
Some of the parasympathetic posganglionic neurons synapse
directly with smooth muscle and glands within the wall of the digestive canal
In general, stimulation of the parasympathetic nerves that innervate the digestive canal causes an
increase in digestive canal secretion and motility by increasing the activity of ENS neurons
Sympathetic nerves that supply the digestive canal arise from
the thoracic and upper lumbar regions of the spinal cord
- make connections with the ENS
Sympathetic postganglionic neurons synapse with
neurons located in myenteric and submucosal neural plexus
In general the sympathetic nerves that supply the digestive canal
cause a decrease in digestive canal secretion and motility by inhibiting the neurons of the ENS
Emotions such as anger, fear and anxiety may
slow digestion because they stimulate sympathetic nerves that supply the digestive system
GI reflex pathways regulate
GI secretion and motility in response to stimuli within the GI tract
Peritoneum
largest serous membrane of the body;
- consists of a layer of simple squamous epithelium with an underlying supporting layer of areolar connective tissue
Parietal peritoneum
lines the wall of the abdominal cavity
Visceral peritoneum
covers some organs in the cavity and is their serosa
Peritoneal cavity
the slim space containing lubricating serous fluid between the parietal and visceral peritoneal cavity
Organs that are retroperitoneal
kidneys, ascending and descending colons of the large intestine, duodenum of the small intestine, and pancreas
Unlike the heart and lungs smooth surface, the peritoneum contains
large folds that weave between the viscera
The folds on the viscera contain
blood vessels, lymphatic vessels, and nerves that supply the abdominal organs
What are the 5 major peritoneal folds
- greater omentum
- falciform ligament
- lesser omentum
- mesentery
- mesocolon
The greater omentum
- drapes over from transverse colon like a fatty apron
- double sheet that folds back on itself (4 layers)
- contains adipose tissue that contributes to beer belly
- contains many lymph nodes that contain macrphages and antibody producing plasmocytes that help combat and contain infections of the digestive canal
The falciform ligament
attaches the liver to the anterior abdominal wall and diaphragm.
- The liver is the only digestive organ that is attached to the anterior abdominal wall
The lesser omentum
arises as an anterior fold in the serosa of the stomach and duodenum
- it connects the stomach and duodenum to the liver
- pathway for blood vessels entering the liver and contains the hepatic portal vein, common hepatic artery and bile duct, along with some lymph nodes
Mesentery
- fan shaped fold of the peritoneum
- binds the jejunum and ileum of the small intestine to the posterior abdominal wall
- forms a double-layered structure
Between the two layered folds of the mesentery, are the
blood and lymphatic vessels and lymph nodes
Mesocolon
- two separate folds of peritoneum
- bind the transverse colon and sigmoid colon of the large intestine to the posterior abdominal wall
What carries blood and lymphatic vessels to the intestines
mesocolon
Together the mesentery and mesocolon
hold the intestines loosely in place, allowing movement as muscular contractions mix and move the luminal contents along the digestive canal
The mouth is formed by
lips, cheeks, hard and soft palates, oral cavity, teeth, salivary glands and tongue
What attaches the lip to its corresponding gum
labial frenulum
What helps keep food between the upper and lower teeth when chewing
contraction of buccinator muscles
Fauces
opening of the mouth to the pharynx
hard palate
anterior portion of roof of the mouth- formed by maxillae and palatine bones
soft palate
posterior portion of roof of mouth - arch shaped muscular partition between oropharynx and nasopharynx
Uvula
during swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity
Salivary glands
releases a secretion called saliva into the oral cavity; to keep the mouth and pharynx moist and clean
When food enters the mouth,
secretion of saliva increases, and it lubricates, dissolves, and begins chemical breakdown of food
The mucosa and submucosa of the mouth contain
about 800-1000 small salivary glands that open directly and indirectly via short ducts into the oral cavity
- these include: ; labial, buccal, and palatal glands and lingual
All small glands located in the mucosa and submucosa are called
minor slaivary glands
Three main pairs of salivary glands
- parotid
- submandibular
- sublingual
Parotid glands
located inferior and anterior to the ears, between the skin and the masseter muscle
Submandibular glands
are found on the floor of the oral cavity proper; they are medial and partly inferior to the mandible
The submandibular glands are lateral to the
lingual frenulum
Sublingual glands
beneath the tongue, and superior to the submandibular glands
What is saliva composed of
99% water and 0.5% other solutes
- solutes include ions: sodium, potassium, chloride, bicarbonate and phosphate
Some dissolved gasses and various organic substances are also present such as
urea, uric acid, mucus, immunoglobulin A, the bacteriolytic enzyme, lysozyme, and salivary amylase (digestive enzyme that acts on starch)
All salivary glands supply the same ingredients; T or F
False
The parotid glands secrete;
watery (serous) liquid containing salivary amylase
Submandibular glands secrete
salivary amylase mixed with mucus
The sublingual glands secrete
mostly mucus and small amount of salivary amylase
The water in saliva provides a medium for
dissolving foods so that they can be tasted by gustatory receptors so that digestive reactions can begin
what activates salivary amylase
chloride ions
salivation is controlled by
the autonomic nervous system
average salivary secreted daily
1000 -1500 mL
Parasympathetic promotes salivation whereas
sympathetic does not
Tongue
accessory digestive organ composed of skeletal muscle covered with mucus membrane
The tongue participates in
chewing, swallowing, and speeth
The upper and lateral surfaces of the tongue are covered with
papillae, some of which contain taste buds
The extrinsic muscles of the tongue
move it from side to side and in and out to maneuver food for chewing
- form the floor of the mouth and hold the tongue in position
intrinsic muscles of the tongue
originate and insert into the connective tissue within the tongue
- alter the size and shape of the tongue for speech and swallowing
Lingual papillae
projections of the lamina propria covered with stratified squamous epithelium
- contain gustatory epithelial cells
some lingual papillae lack taste buds but contain
receptors for touch and increase friction between tongue and food, making it easier for the tongue to move
Lingual glands
in the lamina propria of the tongue
- secreye mucus and watery fluid that contains lingual lipase, which acts on as much as 30% of dietary glycerides
Teeth
accessory digestive organs located in dental alveoli in mandible and maxillae
enamel
consists of calcium phosphate and calcium carbonate
- harder than bone
incisors:
closest to midline
- chisel shaped and adapted for cutting into food
canines:
have a pointed surface called a cusp
- used to tear or shred food
molars;
have four cusps
- used to crush and grind food and prepare food for swallowing
When food is first swallowed, it passes from the mouth to the
pharynx
The pharynx is composed of
skeletal muscle and lined by mucus membrane
the pharynx is divided into 3 portions
- nasopharynx
- oropharynx
- laryngopharynx
Nasopharynx
functions only in respiration
Swallowed foods passes from the mouth to
the oropharynx and laryngopharynx; muscular contractions of these areas help propel food to the esophagus and then into the stomach
The mucosa of the esophagus consists of
non-keratinized stratified squamous epithelium, lamina propria, and musuclaris mucosae
Near the stomach, the mucosa of the esophagus contains
mucus glands
At the ends of the esophagus, the muscular layer
becomes slightly more prominent and forms the upper esophageal sphincter and the lower esophageal sphincter
The superficial layer of the esophagus is known as the
adventitia