Flashcards in The Gastrointestinal System Deck (113):
What does the gastrointestinal tract consist of?
- Oral Cavity
- Small Intestine
- Large Intestine
What is the gastrointestinal tract associated with?
- Gall Bladder
Throughout its length the GI tract is lined with different types of ___1___. Each functionally distinct area is lined with a type that reflects its function in the processing of ___2___.
Describe the following epithelium: Simple.
= 1 layer
Describe the following epithelium: Stratified.
= >1 layer
Describe the following epithelium: Pseudostratified.
= 1 layer that pretends to be 2
Describe the following epithelium: Squamous.
= Flat cells
Describe the following epithelium: Columnar.
= Column like cells
The mouth is the gateway to the ___1___, it is the access point not only for food but also for ___2___. The mechanisms of the mouth are designed to deal with both digestion and pathogen defence.
1. GI tract
What type of epithelium are the mouth and tongue covered by?
Stratified squamous epithelium.
Below the epithelia of the mouth and tongue there is an underlying submucosa containing what?
Food must be broken down into smaller pieces to increase its ____ 1 ____ for the action of digestive enzymes.
In the mouth the ___2___ divide up food. The muscles of the tongue and ___3___ aid pulverisation and bolus formation.
The muscles of mastication move the ___ 4 ___, bringing its teeth into contact with the teeth of the ____ 5 ____.
All the muscles elevate the jaw but ___6___ is the major effector.
___7___ elevates and protrudes the lower jaw.
The pterygoids create ___8___ movement of the lower jaw.
1. Surface area
4. Lower jaw
5. Upper jaw
Name the 3 main salivary glands.
What do the submandibular glands secrete?
Both serous and mucous saliva.
What do the parotid glands secrete?
What do the sublingual glands secrete?
Saliva is produced in the ___1___ of saliva glands by ____ 2 ____ of ions from blood and has a similar composition to extracellular fluid.
2. Active filtration
Where and why is the composition of saliva modified?
In the ducts within a gland. To make it appropriate for requirements.
Autonomic stimulation of the glands changes the composition and volume of saliva secreted.
Describe what sympathetic and parasympathetic stimulation does.
- Sympathetic stimulation produces a small amount of mucous saliva
- Parasympathetic stimulation produces a large volume of watery saliva.
List the functions of saliva.
- Lubrication due to mucin content
- Digestion due to presence of α-amylase
- Protection of oral mucosa through lubrication, rinsing action and alkaline pH
- Antibacterial through actions of antimicrobial thiocyanate.
- Thirst stimulation
- Absorption in the mouth
Name and describe the 3 layers of mucosa.
Epithelium - This thin layer lines the lumen of the tube, it may be simple or stratified, squamous or columnar. It forms a selective barrier that digested molecules must cross. It may contain mucous secreting goblet cells and endocrine cells secreting digestive hormones.
Lamina propria - This is a layer of loose connective tissue. It has a good blood supply and as it often contains lymphatics and numerous white blood cells, it is the first immunological barrier to pathogens in the GI system.
Muscularis mucosa - A thin layer of smooth muscle cells. This causes localised contractions in the mucosa.
The walls of the digestive tract consists of the same 4 layers throughout its length. Name them.
- Muscularis externa
What is the submucosa?
A layer of dense connective tissue that contains the submucosal plexus.
What controls secretion and blood flow and also relays information from the gut epithelium and stretch receptors in the wall, in the submucosa?
The submucosal plexus.
The submucosal plexus is a part of the ______ nervous system
The enteric nervous system is a branch of the ___1___ nervous system.
It is not part of the sympathetic or parasympathetic nervous systems but entirely separate.
Unlike the other ___1___ systems, the enteric system can operate independently of the ___2___.
2. Cental Nervous System
The enteric nervous system consists mostly of two major plexi within the GI wall. Name them and give their old names in brackets.
- Myenteric plexus (Meissner’s plexus)
- Submucosal plexus (Auerbach’s plexus)
What does the Muscularis externa consist of?
2 layers of smooth muscle; an inner circular and outer longitudinal layer.
Waves of contraction and relaxation along the layers of the Muscularis externa force food along the digestive tract, an action known as what?
Which nerve plexus of the enteric NS lies between the 2 layers of the Muscularis externa? What is this plexus involved in?
The myenteric plexus.
This plexus is involved mainly with the control of GI motility.
Which layer of GI epithelium forms part of the peritoneum?
Describe the function of the peritoneum.
The peritoneum lines the abdominal cavity and covers all the abdominal organs, anchoring them to the body wall.
The act of transferring a food bolus from the mouth to the oesophagus.
Name the 2 stages of swallowing.
- Pharyngeal Stage
- Oesophageal Stage
Describe the pharyngeal stage of swallowing.
The initiation of swallowing is voluntary. The tongue pushes the bolus backwards. When it contacts the back of the pharynx the swallow reflex is triggered. The soft palate rises to block off the nasopharynx and elevation of the larynx moves the epiglottis over the trachea.
Describe the oesophageal stage of swallowing.
Once food has entered the oesophagus, the involuntary action of the smooth muscle pushes the food towards the stomach.
Name the muscles of the tongue that initiate the swallow.
Which muscles lift the soft palate?
Which muscles lift the larynx to close off the trachea during the pharyngeal stage of swallowing?
Muscles of the throat (infrahyoid muscle).
Which muscles contract sequentially to push the food down the pharynx and into the oesophagus during the pharyngeal stage of swallowing?
The pharyngeal constrictors.
What type of epithelium lines the oesophagus?
Stratified squamous epithelium.
The muscularis externa of the upper third of the oesophagus consists of ___1___ muscle, the lower two thirds of ___2___ muscle.
Where in the oesophagus are mucus secreting glands present?
In the lamina propria and the submucosa.
Which nerve innervates the oesophagus?
The vagus nerve.
The GI tract is supplied by branches of the abdominal aorta. There are three branches of the abdominal aorta that supply the GI tract. Name them and describe their location.
The coeliac trunk - the most superior branch, arising level with the upper border of L1.
The superior mesenteric artery - leaves the abdominal aorta level with the lower border of L1, inferior to the coeliac trunk.
The inferior mesenteric artery - the most inferior of these three branches, leaving the aorta level with L3.
What do the branches of the coeliac trunk supply and what specific vessels supply them?
- Stomach - The stomach is supplied by the left and right gastric arteries and the left and right gastroepiploic arteries.
- Superior duodenum - The superior duodenum is supplied by the superior pancreaticoduodenal artery.
- Liver - The liver is supplied by the hepatic artery.
- Pancreas - The pancreas is supplied by the superior pancreaticoduodenal artery and the splenic artery.
What does the superior mesenteric artery supply?
Also describe what parts the specific vessels that originate from the superior mesenteric artery supply.
The small and large intestines from the inferior duodenum to the left colic flexure of the colon.
- The inferior pancreaticoduodenal artery arises from the superior mesenteric. It supplies the inferior part of the duodenum and pancreas and anastomoses with its superior counterpart.
- Numerous branches of the superior mesenteric artery form large loops, known as arcades, in the mesentery (the peritoneum that attaches the small intestines to the body wall). These supply the jejunum and ileum.
- The ileocolic artery supplies the terminal ileum, vermiform appendix and inferior ascending colon.
- The right colic artery supplies the superior ascending colon.
- The middle colic artery supplies the transverse colon
What do the branches of the inferior mesenteric artery supply? Also describe what parts the specific vessels that originate from the inferior mesenteric artery supply.
The large intestines distal to the right colic flexure, to the rectum.
- The left colic artery supplies the descending colon. This artery also anastomoses with the middle colic artery of the superior mesenteric artery.
- The sigmoid colon is supplied by the sigmoid arteries.
- The superior rectal artery supplies the proximal rectum. The distal rectum is not supplied by the abdominal aorta.
What are arcades?
Arcades in the GI tract are blood vessels that take the form of a series of arches. They form the blood supply to the jejunum and ileum. The arcades run from the aorta to the small intestine between the layers of peritoneum attaching the small intestines to the posterior body wall (the mesentery).
It is the most dilated part of the GI tract and acts as a food blender and reservoir.
What is it?
The low pH environment provided by ____ 1 ____ aids digestion and provides an important physiological barrier against ___2___.
1. Gastric secretions
Parietal cells in the fundus and body of the stomach secrete what?
Peptic/Chief cells in the fundus and body of the stomach secrete what?
- Pepsin precursor
What does the antral region of the stomach produce and what does this do?
Endocrine secretions - which control gastric secretion itself as well as gastric motility.
In addition to the circular and longitudinal layers of smooth muscle, the stomach has an ___1___ layer of smooth muscle that allows ___2___ of the stomach.
The lining of the stomach is protected from acid by a combination of factors.
The epithelium of the stomach consists of columnar epithelia. Tight junctions in this layer prevent damage to underlying tissues from acid secretions.
Constitutive secretion of the alkaline mucus layer by mucous cells (not goblet cells) in the gastric mucosa provides a mechanical barrier to acid secretions and pathogens.
What is the Peritoneum?
The peritoneum is a layer of connective tissue that covers all the organs of the abdomen.
Name the part of the Peritoneum that covers the stomach.
Name the part of the Peritoneum that covers the intestines.
What is the Peritoneum often compared to?
An inflated but malleable balloon that fills the abdominal cavity.
What is the Peritoneal cavity?
The potential space created by the peritoneum which is continuous around all the abdominal organs.
What are the functions of the Peritoneum?
- The peritoneum acts to anchor floppy abdominal organs to the posterior body wall so that they don’t squash each other or move around too much when we jump.
- It also carries the blood supply to the organs.
Anatomically describe where the 4 parts of the duodenum travel.
- The superior part travels slightly superiorly and posteriorly to the level of L1
- The descending part travels inferiorly, over part of the kidney to L3.
- The horizontal part travels medially to the left, crossing the aorta at L3.
- The ascending part travels superiorly on the left of the aorta to L2 where it becomes the jejunum.
The ___1___ duodenum receives further digestive secretions from the liver and gall bladder via the ____ 2 ____ and the pancreas via the ___3___ duct.
2. Bile duct
Where does the jejunum begin?
The Jejunum begins at the duodenojejunal junction, to the left of the L2 vertebrae.
The jejunum and ___1___ are anchored to the posterior body wall by the ___2___ and are the primary site of ___3___ absorption.
What are villi?
Finger-like projections that are present throughout the small intestine.
What do you call the recessions between villi?
What type of epithelium is the epithelial surface of villi?
There are numerous ___1___ on the surface of villi that form a ‘____ 2 ____’.
2. Brush border
Each villus contains a ___1___ network that transports absorbed amino acids and ___2___, plus a blind-ended ___3___ vessel (or lacteal) that transports absorbed ___4___. The capillary network drains eventually into the ___5____ vein.
What is considered to be the functional unit of absorption?
Four specialised cells are present within the epithelium of the villi. They arise from undifferentiated cells at the base of the crypts.
Name them and their functions.
Absorptive cells - They secrete digestive enzymes and absorb nutrients.
Goblet cells - Produce mucus that lubricates and protects the epithelium from mechanical damage.
Granular cells - Secrete enzymes and protect epithelium from bacteria.
APUD cells - Produce endocrine secretions that regulate secretion and motility of the GI tract and associated glands.
Which villi cells ascend the villi from the base of the crypts?
Absorptive & Goblet cells.
How often are the absorptive and goblet cells of villi shed and renewed?
Where are mature absorptive and goblet cells usually located?
At the tip of the villus.
Which villi cells remain at the base of the crypts?
Granular and APUD cells.
What characteristic of villi and microvilli improves their absorption ability dramatically?
Large surface area.
The blood that has flowed through the intestines is now full of amino acids and monosaccharides as well as any poisons and toxins that may have been absorbed.
Before it can be returned to the heart and lungs, what happens to this blood in the liver?
The blood is filtered by the liver to remove, process and if necessary excrete or store absorbed molecules.
Blood drains from the capillaries of the intestines into the ___1___ veins, which join to form the ___2___ vein.
What does the portal vein carry? And where to and from?
De-oxygenated blood, full of absorbed molecules from the intestines to the liver.
Where does the hepatic artery originate from and what organ does it supply?
The hepatic artery originates from the abdominal aorta and supplies the liver with oxygen.
What are hepatocytes/liver cells?
Epithelial cells that are arranged to form a 3D lattice.
What are sinusoids? (In the liver).
In the liver sinusoids run between each layer of hepatocytes. These allow close contact between the hepatocytes and the portal blood supply.
The products of hepatocyte function are removed via small channels between the cells, called what? What do these channels drain into?
The canaliculi then drain into the bile ducts.
Bile drains from the liver via the right and left ___1___ ducts which join to form the common ___1___ duct.
The common ___1___ duct is joined by the ___2___ duct that drains bile from the ___3___. Bile from the hepatic duct can travel up the ___2___ duct to be stored in the ___3___ or carry on to the descending ___4___.
The presence of food in the ___4___ stimulates the ___3___ to contract. Bile travels down the ___2___ duct to the common bile duct and then to the ___4___.
All of these ducts combine to form the ___5___ tract.
Bile stored in the gallbladder between meals is concentrated by the actions of the _______.
Name some of the functions of the liver.
- Glucose storage
- Synthesis of proteins, lipoproteins and cholesterol
- Digestion (bile salt production)
- Fat soluble vitamin storage
- Toxin and drug metabolism and excretion
Describe glucose storage.
- Glucose conversion
- Energy store release
- The liver (and muscles) store glucose as glycogen.
- The conversion of glucose to glycogen is stimulated by insulin.
- Glycogen is an energy store that is released when blood sugar levels fall.
Describe synthesis of proteins, lipoproteins and cholesterol.
- The liver synthesises most blood proteins and lipoproteins that act as transporters (except antibodies), the most abundant of which is albumin.
- Albumin acts as a transporter for many molecules and also helps maintain reabsorption of fluid from tissues into the blood. Lack of albumin causes oedema.
- The liver also synthesises proteins that act as clotting factors in the blood.
- Cholesterol is synthesised by the liver, this is used directly in cell membranes or converted into sex-hormones. Excess cholesterol is excreted in the bile.
Describe bile salts.
Bile salts are detergents that emulsify fats (facilitated by decreased pH) in the intestines, increasing their surface area and facilitating their absorbtion.
Describe fat soluble vitamins.
- Vitamin types
- Vitamins A,D,E and K are ‘fat soluble’ vitamins.
- Unlike water soluble vitamins, A,D,E and K can be stored in fat reserves in the liver, around organs or under the skin.
- Therefore if these vitamins are removed from the diet, the human body can utilise its stores. The diet must be low in these vitamins for some time before deficiencies appear.
Describe toxin and drug metabolism and excretion.
- Liver enzyme metabolism
- Liver enzymes metabolise many pharmacological and recreational drugs, the by-products of which are excreted in the bile or released into the bloodstream to be excreted by the kidneys.
- The liver metabolises the toxic by-product of metabolism, ammonia, into urea, which is released into the blood and excreted by the kidneys.
- Bilirubin, released by the spleen from breakdown of red blood cells, is modified by the liver so that it can be excreted in the bile.
- Other toxins and poisons absorbed by the intestines are metabolised and excreted by the liver.
What cells produce bile?
How does bile prevent damage to the intestines?
Its bicarbonate content produces an alkaline pH that serves to decrease the acidity of gastric contents released from the stomach. Thus preventing damage to the intestines.
___1___ in the liver breakdown ___2___ and other drugs producing toxic waste products, these may be excreted by the kidneys in the ___3___.
What is the pancreas and where does it lie?
An elongated gland, accessory to the GI tract that also has endocrine functions. It lies horizontally across the posterior abdominal wall.
Where is the ‘head’ of the pancreas located?
Within the curvature of the duodenum.
What do exocrine tissues of the pancreas release? And what is this?
Pancreatic juice - a major digestive secretion containing digestive enzymes.
Pancreatic enzymes are secreted in the ___1___ and modified in the ___2___.
Pacreatic juice is transported to the duodenum via the pancreatic duct, which joins the common bile duct to form the Ampulla of ___1___. Their entrance to the descending duodenum is controlled by the Sphincter of ___2___.
Pancreatic juice has two components.
Name and describe both.
- Has a high bicarbonate and low enzyme content.
- Helps neutralise the acidity of gastric contents.
Enzyme rich secretion:
- Contains the major enzymes involved in digestion
- Secreted as pre-enzymes that are activated in the gut so that they don’t digest the pancreas
The pancreas is partially under autonomic control.
What does sympathetic & parasympathetic stimulation do?
- Sympathetic stimulation decreases secretions
- Parasympathetic stimulation increases secretions
Apart from partial autonomic control, what else influences pancreatic secretion?
Other endocrine messengers of the digestive system.
What is more villous, the epithelium of the large intestine or the small intestine?
The small intestine.
Describe the epithelium of the large intestine.
The epithelium of the large intestine is simple columnar and contains crypts but not villi.
Goblet and absorptive cells are present. APUD cells are present but sparse.
Which has more goblet cells, the epithelium of the large intestine or the small intestine? Therefore what happens?
Goblet cells are more numerous in the large intestine than in the small intestine and therefore the amount of mucus in the large intestine is greater.
True or false? The lamina propria, muscularis mucosa and submucosa are similar in the large and small intestines.
The outer longitudinal layer of the smooth muscle surrounding the large intestine, except the rectum, is ___1___. It is divided into three separate bands that run the length of the colon, the ___2___.
2. Taeniae coli
True or false? The taeniae coli aid peristalsis.
Why is the taeniae coli a surgically useful feature?
They converge on the base of the vermiform appendix, a surgically useful feature as it can be used to identify a grossly infected appendix.
Where are the taeniae coli not present?
They are not present on the rectum, anal canal or vermiform appendix.