Gastrointestinal System Flashcards
Key functions of the GI tract
Digestion - breaking down food & nutrients
Absorption - gets nutrients in the bloodstream
Excretion - Getting rid of digestive waste
Describe the layers of the Gastrointestinal tract from inner to outer layers
Mucosa
Muscularis mucosa
Submucosa
Submucosal plexus (Meissner plexus)
Circular layer of smooth muscle
Myenteric plexus
Longitudinal layer of muscle
Serosa
What does the mucosa layer consist of ?
Epithelium
Lamina propria
Muscularis mucosa
What does the submucosa consist of ?
Blood vessels and nerve bundles that form the submucosal plexus (Meissner plexus)
What is an integral part of the enteric nervous system ?
Meissner plexus
What is the function of the submucosal (Meissner) plexus ?
Regulates intestinal secretions and area specific absorption.
Interacts with blood vessels, circular and longitudinal muscle and muscularis mucosa.
What are the 2 layers in the muscularis externa ?
2 smooth muscle layers :
- Circular muscle
- Longitudinal muscle
What lies between the muscularis externa layers ?
Myenteric plexus
What is the function of the Myenteric plexus ?
Regulates intestinal smooth muscle that helps generate tonic and rhythmic contractions.
What does the serosa consist of ?
Connective tissue
Squamous epithelial cells
Describe the GI tract
Mouth
Oesophagus
Stomach
Small intestine
Large intestine
Anus
Role of the Upper GI tract
(Mouth, Oesophagus, Stomach)
Minimal role in nutrient absorption.
Transports and prepares food to be absorbed.
What are the 2 types of digestion ?
Physical (Mechanical) digestion
Chemical digestion
Mastication
Chewing on food to break it into smaller chunks.
Mechanical digestion
What happens during mastication ?
Tongue mixes food with saliva excreted by the salivary glands. This forms a bolus which is ready to be swallowed.
Where does swallowing take place ?
Through a muscular tube called the oesophagus.
What is the definition of peristalsis ?
Peristalsis is a type of involuntary muscle movement that occurs in your digestive system.
Describe peristalsis
Muscles of the oesophagus contract and PRODUCE A WAVE-LIKE MOVEMENT that pushes food downward into the stomach. This also continues throughout the GI tract.
What happens once food enters the stomach ?
It mixes with gastric juice, consisting of acids and gastric enzymes, which turns the bolus into a pulpy soup called CHYME.
What happens once chyme is produced in the stomach ?
The chyme moves to the 1st past of the small intestine called the DUODENUM , where bile secreted by the liver & pancreatic enzymes DIGEST IT EVEN FURTHER.
The end result is CHYLE, a milky fluid ready to be absorbed.
What is meant by segmentation ?
Mixing chyme with secretions and mucosa
What happens once chyle is produced in the 1st portion of the small intestine ?
The chyle moves to the 2nd portion of the small intestine called the JEJUNUM, which has a specialised mucosa that allows nutrients to be absorbed into the bloodstream by a network of local capillaries.
What happens once the nutrients are absorbed into the bloodstream in the 2nd part of the small intestine ?
The food residue keeps moving along the canal by PERISTALSIS.
It moves from the last part of the small intestine called the ILEUM into the large intestine or colon.
The ileum absorbs bile acids, fluid, and vitamin B-12.
What happens in the colon ?
The remaining nutrients and water get absorbed, leaving semi-solid materials, called excrements or feces.
What happens in the last segment of the large intestine (called the rectum) ?
Excrements collect in the rectum which is connected to the anus.
What happens when the rectum is full ?
It sends a message to the brain that triggers the need to defecate, called excretion.
As we get older, what happens to the efficiency of mastication ?
There is a greater risk of choking, as our GI system becomes less efficient and there is a reduction of saliva production as well as dental issues such as tooth loss.
Reduced peristalsis
What are the results of reduced production of gastric juice and bile ?
Reduced efficiency of chemical digestion
Name the 3 major arteries that supply blood to the gut.
Coeliac Artery
Superior mesenteric artery
Inferior mesenteric artery
Where does the coeliac artery deliver blood to ?
Liver
Stomach
Spleen
Gall Bladder
Pancreas
Where does the superior mesenteric artery deliver blood to ?
Small intestine
Most of the large intestine
Where does the inferior mesenteric artery deliver blood to ?
Terminal portions of the large intestine and rectum.
How is blood flow regulated ?
Autonomic Nervous System
Hormonal (endocrine) control
Local (paracrine) control
What does the parasympathetic system act as ?
Vasodilator
What does the sympathetic system act as ?
Vasoconstrictor
What does the enteric system act as ?
Vasodilator
What does gastrin act as ?
Vasodilator
What does adrenaline act as ?
Vasoconstrictor
What is the role of the sympathetic, parasympathetic and enteric nervous systems in the GI system ?
Regulates GI function
Role of the parasympathetic nervous system in the GI system
PSNS signals stimulate GI secretions and motility, facilitating digestion and absorption of nutrients. ‘rest and digest’
Where is innervation from in the PSNS ?
Vagus (medulla oblongata)
Pelvic splanchnic nerves
What nerves are part of the PSNS ?
CN 7
CN 9
CN 10
What are the primary neurotransmitters used in the PSNS ?
ACh
VIP
Gastric-releasing peptide substance B
Role of the sympathetic nervous system in the GI system
SNS decreases GI secretions and motility. ‘Fight or Flight’
What nerves are involved in the SNS ?
Nerves originating in T5-T12 and L1-L3
Where are the synapses in the SNS ?
Superior cervical
Celiac
Superior mesenteric
Inferior mesenteric
What is the upper GI tract innervated by ?
Nerves that synapse in the superior cervical ganglion
Define the 3 digestive phases
Cephalic phase
Gastric phase
Intestinal phase
What happens to the Enteric NS if the SNS and PSNS fibres are cut ?
It can still operate, so the ENS can function autonomously via intrinsic neural and sensory reflexes.
What is secreted during the gastric phase ?
Gastrin
What is secreted during the intestinal phase ?
Amino and fatty acids which stimulate I cells in duodenum to release CCK.
H+ stimulates S cells in duodenum to release secretin.
Gastrin function
Stimulation of gastric acid secretion
What are the 3 salivary glands ?
Parotid
Submandibular
Sublingual
Where is the parotid gland found ?
In the cheeks beside the ear
Where is the submandibular gland found ?
Under the jaw
Where is the sublingual glands found ?
Floor of the mouth
Function of the salivary glands
Lubrication
Protection
Digestion
Taste
In the voluntary phase of digestion, describe the structures
Epiglottis open
Nasopharynx open
Glottis open
In the pharyngeal phase of digestion, describe the structures
Epiglottis meets the larynx
Nasopharynx closed
Glottis contracts
In the phase after the pharyngeal phase of digestion, describe the structures
Trachea closed
Upper oesophageal sphincter opening
In the oesophageal phase of digestion, describe the structures
Upper oesophageal sphincter closed
What is the function of MMC’s in the stomach ?
Prevent bacterial overgrowth and keep stomach and intestine clean.
What is Migrating motor complexes stimulated by ?
Motilin
What do chief cells secrete ?
Pepsinogen and gastric lipase
Where are chief cells found ?
In the stomach
What is secretion stimulated by ?
Acetylcholine
Gastrin
Histamine
Somatostatin
Where does carbohydrate digestion begin ?
Mouth - by salivary amylase
Where is the main digestion of carbohydrates ?
Small intestine - pancreatic amylase
Where does protein digestion begin ?
Stomach - by pepsin
Where is the main digestion of proteins ?
Small intestine - pancreatic trypsin
Where does lipid (fat) digestion begin ?
Mouth - by lingual lipase
Stomach - by gastric lipase
Where is the main digestion of lipid (fats) ?
Small intestine - by pancreatic lipase
What is absorption of carbs and proteins dependent on ?
Sodium-dependent co-transport
