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