The Digestive System Flashcards
What are the 6 steps of digestive processing?
- Ingestion
- Mechanical Breakdown
- Propulsion
- Digestion
- Absorption
- Defecation
Describe peristalsis:
Adjacent segments of alimentary tract organs alternately contract and relax, moving the food along the tract distally.
Think squeeze then pull
Describe segmentation:
Nonadjacent segments of alimentary tract organs alternatively contract and relax, moving food forward then backward.
Think pushing and continually rubbing up against the wall
The alimentary canal is inside the body right?
While it might be “inside the body” it is technically one big tunnel that is considered to be outside the body.
Why is it important to regulate the alimentary canal?
To ensure effective breakdown and absorption.
What do the sensors located in the walls of the alimentary organs sense?
Stretch
Osmolarity
Ph
Substrates
End Products
What do the sensors in the walls of the organs cause?
- Initiate reflexes that activate or inhibit glands that secrete into the tube or into the blood
- Cause muscle contractions or cause the muscle to relax
What are the intrinsic controls of the alimentary canal?
Nerve plexuses and hormone producing cells within the tube itself that cause short reflexes.
What are long reflexes initiated by?
Initiated outside of the gut by the CNS
What line the abdominal cavity?
A serous membrane called the peritoneum
Describe the visceral layer of the abdominal cavity:
It covers most digestive organs and is continuous with the parietal layer
What is between the two layers?
The peritoneal cavity which is filled with serous fluid
What attached the transverse colon to the body wall?
Transverse mesocolon
What connects the small intestine to the body wall?
The mesentery
What is the stomach attached to?
The lesser curvature of the stomach is attached to the liver
Describe the greater omentum?
It is an apron of fat for protection that is attached to the greater curvature of the stomach where it then comes down to cover the organs before flipping up an attaching to the transverse mesocolon
Starting at the stomach, in order from deep to superficial, what are the fours layers of the alimentary canal?
- Mucosa
- Sub Mucosa
- Muscularis Externa
- Serosa
Starting at the stomach, in order from deep to superficial, what are the fours layers of the alimentary canal?
- Mucosa
- Sub Mucosa
- Muscularis Externa
- Serosa
What are the three functions of the mucosa?
- Secretes mucus, digestive enzymes, and hormones
- Absorbs nutrients
- Protects against disease
What are the three layers of the Mucosa starting at the deepest layer?
- Epithelium
- Lamina Propria
- Muscularis Mucosae
Describe the epithelial layer of the mucosa:
stratified squamous or simple columnar
Describe the Lamina Propria layer of the mucosa:
loose areolar CT, blood supple, and malt
Describe the muscularis mucosae
It determines the size of the lumen
When it is contracted it is wrinkled and when it is relaxed it is open
Describe the submucosa layer of the alimentary canal:
It is a much thicker layer of lose areolar CT than the Lamina propria and t contains blood vessels, nerves, and lymphatic vessels
Describe the muscularis externa layer of the alimentary canal:
It is comprised of smooth muscle in an outer longitudinal layer and an inner circular layer.
It also makes the sphincters
Describe the serosa layer of the alimentary canal:
It is the visceral peritoneum and the adventitia on the esophagus
What is the enteric nervous system?
It is the in house nerve supply that control motility and secretions
The On/Off Switch of the Alimentary Canal
(what are we secreting and what do we have to stop secreting
What are the two plexuses of the enteric nervous system and where are they locate
Submucosal plexus - Located in the submucosa
Myenteric Plexus - Located between the layers of the muscularis externa
What is another name for the oral cavity?
Buccal cavity
Describe the oral cavity:
Contained by the lips, cheeks, palate, tongue, and oropharynx
Comprised of stratifies squamous epithelium
Describe the lips and cheeks
Made of the skeletal muscles orbicularis oris and buccinator
Oral vestibule
What four structures comprise the mouth?
- Buccal cavity
- Lips and cheeks
- Palate
- Tongue
Describe the palate:
Made up of the hard palate and the soft palate
Describe the hard palate:
Comprised of the maxilla and palatine bones
Describe the soft palate:
Comprised of skeletal muscle, spongy tissue, and the uvula
Describe the tongue:
It is extremely strong, sensitive, and agile
Takes up most of the room in your mouth when it is closed
It is intrinsic muscles that work within the mouth and extrinsic muscles that actually do the visible movement
How can a person have no palate?
During fetal development, if the maxilla and palatine bones do not fuse properly then the person will be born without a palate.
What are the consequences of being born without a palate?
there is the risk of food or drink being aspirated into the respiratory system
What type of receptor are taste buds?
chemoreceptors
What is the rule regarding the variations in thinking something tastes good?
Everyone feels the same sensation but the individual nuanced perceptions are different.
What type of joint holds teeth in their correct position?
Gomphosis joint
What are the purpose of teeth?
Function in mastication
What are the four type of teeth?
- Incisors
- Canine
- Pre-molars
- Molars
How many deciduous teeth and how many adult teeth?
20 deciduous teeth
32 adult teeth
How are teeth generally replaced and at what age are most deciduous teeth replaced by adult teeth?
Generally replaced front to back
by age 12-13
What might explain why so many people have trouble with their wisdom teeth?
A slightly smaller jaw along with the fact that we are keeping our teeth for longer.
What is the largest gland of your mouth and overlies the masseter muscle?
Parotid gland
Which gland produces the majority of the saliva?
Submandibular gland
Describe intrinsic glands:
Produce saliva at a slow but constant rate
Describe extrinsic glands:
They produce the majority of saliva
What are the three salivary glands?
- Parotid
- Submandibular
- Sublingual
Describe the roles of the mucous and serous cells in the salivary glands:
Serous cells secrete a kind of watery component
Mucous cells secrete a thicker mucin protein that’s going to make mucous
Together they form functioning digestive saliva
What are three properties of saliva?
- Mostly water > 97%
- Hypotonic
- Slightly acidic - pH 6.75-7.0
What are 6 constituents of saliva:
- Electrolytes
- Salivary Amylase
- Lingual lipase
- IgA
- Lysozyme
- Mucin
What is the function of salivary amylase?
Works at the pH of the mouth to break down carbs immediately.
What is the function of lingual lipase?
Break down fats but not until the stomach
What is a lysozyme?
General antimicrobial enzyme in your saliva
About how much saliva do you secrete a day?
1.5 L/day
What cause the feeling of tightness in front of your ears when you consume something sour?
Your parotid glands contracting as hard as they can to get as much saliva as possible into your mouth
What two parts of the pharynx are a part of the digestive system?
- Oropharynx
- Laryngopharynx
What tissue makes up the pharynx and why?
Stratified squamous epithelium with many mucous glands in order to provide protections from swallowing
What makes up the walls of the pharynx?
Skeletal muscles
What does the pharynx lead into?
Esphagus
Describe the esophagus:
A 25 cm muscular tube that travels straight down the mediastinum and goes through the diaphragm at the esophageal line
Where does the esophagus join the stomach at?
At the cardia, lower esophageal (cardia, gastroesophageal) sphincter
What is the esophageal comprised of?
The top 1/3 if purely skeletal muscle
The bottom 1/3 is purely smooth muscle
The middle 1/3 is a mix of skeletal and smooth muscle
What is a fancy term for swallowing?
Deglutition
What are the three phases of deglutition?
- Oral phase
- Pharyngeal phase
- Esophageal phase
What happens during the oral phase of deglutition?
The tongue form a food bolus and pushes it into the laryngopharynx
What happens during the pharyngeal phase of deglutition?
The palate, tongue, vocal cords, and epiglottis block the oral and nasal cavities and airway while pharyngeal constrictors push the bolus into the esophagus
What happens during the esophageal phase of deglutition?
Peristalsis drives the bolus downward, and relaxation of the lower esophageal sphincter admits it into the stomach
How much gastric secretions are released due to neuronal and hormonal stimulation?
About 3L/day
What are the two neural controls of gastric secretions?
Parasympathetic activation increases secretions
Sympathetic activation decreases secretions
What is the hormonal control of gastric secretions?
Gastrin, which increases enzyme and HCl secretion
However, intestinal hormones can antagonize (stop) it
What are the three phases of gastric control?
- Cephalic (brain)
- Gastric (stomach)
- Intestinal (small intestine controlling the stomach)
Is the stomach a vital organ?
No
What are the four regions of the stomach?
- Cardia
- Fundus
- Body
- Pylorus
What is the role of the lower esophageal sphincter?
To make sure that the contents of the stomach stay in the stomach and don’t plash back into the esophagus.
What is the job of the pyloric sphincter?
Controls the release of chyme into the duodenum
What occurs when the stomach is empty?
it shrinks down by folding the mucosa into rugae
What is the function of the stomach?
It is a temporary food storage tank where food is converted to chyme
What is chyme?
A mixture of partially digested proteins, partially digested fats, some carbs, and some gastric juice
Describe the gross anatomy of the stomach including where it lies in tall and short people:
It is located in the upper left quadrant of the abdomen
It lies vertically in tall people and more horizontally in shorter people
It is 15-25 cm long and can hold 50mL to 4L of stuff
What is it innervated by?
Both the sympathetic and parasympathetic systems
What is the blood supply of the liver and where is its blood drained?
Bloody Supply: Celiac trunk
Blood drained: Via the hepatic portal system
What additional layer does the stomach have that is unique to the rest of the alimentary canal?
An oblique muscle layer to the muscularis externa
What is the epithelium lining the stomach?
Simple columnar epithelium
Describe the inner lining of the stomach:
It invaginates to form gastric pits, which lead to gastric glands which secrete gastric juice
What are the five unique cell types in the gastric glands
- Parietal cells
- Enteroendocrine (G) cells
- Stem cells
- Chief cells
- Mucous Neck cells
What do mucous neck cells do?
They release an acidic mucous
What do Parietal cells do?
They release HCl and intrinsic factor
What is the vital job of intrinsic factor?
Absorption of B12
What do chief cells do?
Secrete pepsinogen and lipases
What do enteroendocrine cells do?
They release chemical messengers such as histamine and gastrin
Why are there so many stem cells?
Since the environment is so caustic, the average life of a cell is only 3-6 days
What are the two types of glands in the stomach?
- Pyloric
- Gastric
What cells are in the pyloric glands?
- Parietal
- Mucous
- Enteroendocrine
What cells are in the gastric glands?
- Parietal cells
- Chief cells
- Enteroendocrine cells
What serves has protection for the stomach from the harsh environment?
Mucosal barrier
What does breakdown of the mucosal barrier cause?
Gastritis - inflammation of the stomach that can lead to an ulcer
What common type of medication interferes with the mucosal barrier making it more likely you will get gastritis and form an ulcer?
NSAIDS
What are the three factors of the mucosal barrier?
- A thick coating of bicarbonate rich mucous like a big smear of Vaseline
- Tight junctions between the epithelial cells of the mucosa
- High cell turnover rate
What two processes of digestion is the stomach not involved in?
ingestion and defecation
What is the only vital function of the stomach?
to secrete intrinsic factor to facilitate vitamin B12 absorption in the intestine
What is the only vital function of the stomach?
to secrete intrinsic factor to facilitate vitamin B12 absorption in the intestine
What is the stomach basically doing?
Continues mechanical breakdown and propulsion
What chemical digestion is occurring in the stomach
pepsin - proteins
Lingual lipase - triglycerides
What few things can the stomach absorb?
Water, alcohol, and lipid soluble drugs like aspirin
Describe the cephalic phase for the control of gastric secretions:
-It is triggered before eating food by site, smell, and thought
-Essentially it prepares the stomach for food by increasing the secretion of gastric juice
Explain the gastric phase for the control of gastric secretions:
-Neural stimulation by distension of the walls and partially digested proteins that have increased the pH of the stomach stimulate G cells to secrete gastrin which then causes more HCl production and enzyme release
Explain the positive feed back loop in the stomach starting from food and partially digested protein buffering the stomach acid and the oligopeptides directly stimulating the G cells:
- The partially digested proteins cause the pH to rise
- The elevated pH causes enteroendocrine cells (G cells) to secrete gastrin
- The gastrin stimulates the chief cells and parietal cells to secrete pepsinogen and HCl respectively.
- The HCl converts pepsinogen to pepsin which breaks down proteins into the the oligopeptides and partially digested proteins causing more gastrin to be secreted and the process continues
Explain the intestinal phase?
-It is both stimulatory and inhibitory
-Presence of chyme in the duodenum causes the release of intestinal gastrin which increase gastrin secretion in the stomach allowing the stomach to continue breaking things down
-Once filling is complete, the stomach is inhibited by the enterogastric reflex.
How does vomiting occur>
It occurs the contents of the stomach push on the lower esophageal sphincter until the pressure is so great it opens and then peristalsis runs in reverse.
The stomach stretches to accommodate incoming food but at what volume does it actually start to increase pressure?
1.5 L of food
Where is contractility of the stomach greatest at?
The pyloric region
While intensity of the stomachs contractions can vary, what is the rate it roughly contracts at?
3X/min
How much chyme does the pyloric sphincter release per contraction?
3-5mL
When do muscle relax?
When swallowing is initiated
Do carbs digest in the stomach?
No, only from salivary amylase and the intestine.
Satiety is based off of the volume of the stomach. True or false, why?
False because satiety is based on pressure. You have to raise the pressure high enough that you feel full.
What is the largest organ in the body?
Liver
How is the liver anchored to the stomach?
Via the lesser omentum
What are the four primary lobes of the liver?
- Right lobe
- Left lobe
- Caudate
- Quadrate
What does the port hepatis allow?
It allows entry and exit of the hepatic artery, hepatic portal vein, and the common hepatic duct?
What two ducts fuse to form the bile duct?
The common hepatic duct and the cystic duct coming from the gallbladder
What is the major digestive function of the liver?
To produce bile
Why does the liver have a high regenerative capacity?
The hepatocytes have the ability to regenerate if the are properly stimulated; however, if they are damaged by sclerosis, scarring, then they lose that ability
Why do drugs and alcohol damage the liver?
the liver breaks down alcohol and other drugs into something that can be secreted.
What ligament holds the inferior vena cava
Falciform
What shapes are the lobules?
Hexagonal
What are between the hepatocytes?
Liver sinusoids that empty into the central vein
What do the lobules consist of?
Hepatocytes radiating outward from the central vein which are in the middle of each lobule
What does each corner have?
A portal triad consisting of a branch the hepatic artery, hepatic portal vein, and bile duct.
What do hepatic macrophages do?
remove debris - filtering function
Where does the bile synthesized by the liver go?
It is secreted into bile canaliculi where it goes into the bile duct, then the left and right hepatic bile duct, into the common hepatic duct, and eventually through the duct work and ending in the gallbladder
Are hepatocytes important for detoxification?
Yes, they pull stuff out of the blood
What can hepatocytes store?
They can store glycogen, AA, and fat-soluble vitamins that they have pulled out of the digestive blood coming out of the stomach and small intestine
What are bile salts good for?
Lipid digestion
Where do bile pigments come from?
They exist from the breakdown of red blood cells
What is bile?
Bile is a yellow greenish alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids and electrolytes
What happens to the blood once it reaches the central vein in the liver?
All of the central veins connect together in a network that leads lead the venous blood out of liver into the hepatic vein which feeds into the inferior vena cava
What is unique about the blood in the liver?
Oxygenated blood and deoxygenated blood come together
What happens to all the blood from the stomach and the small intestine and large intestine that have absorbed all the nutrients?
It is going to go to the hepatic portal vein which will open into sinusoids where hepatocytes will absorb the nutrients such as AA, vitamins, and Glucose
What is the gallbladder?
A green muscular sac on the inferior side of the liver
What is the function of the gallbladder?
to store bile not immediately needed for digestion and to concentrate the bile
How does the gallbladder concentrate the bile?
I concentrates the bile by first reabsorbing H2O. This occurs by actively transporting sodium out and then H2O follows
Where does the gallbladder release the bile into to and then where does it go?
It is released from the cystic duct into the bile duct which meets up with the pancreatic duct at the hepatopancreatic ampulla
How does the gallbladder accidentally form gall stones?
Since cholesterol and fats are hydrophobic, they glom up in the presence of H2O, so if we reabsorb to much H2O, and we have to much cholesterol and fat in the bile, they can form gall stones
What can gallstones cause?
They can black the hepatopancreatic ampulla
What forms the common hepatic duct?
The left and right hepatic duct
What does the pancreas look like?
A tadpole shaped organ with its head siting in the curve of the duodenum
What do we need to digest our nutrients?
Pancreatic juice
What is the function of the pancreas?
To produce all of the enzymes required to breakdown all major macromolecules - collectively called pancreatic juice
Where is pancreatic juice released?
Via the main pancreatic duct
If the chyme entering the duodenum from the stomach has a pH of 2, how does the duodenum have a pH of 8?
The pancreatic juice has a lot of bicarb which is going to buffer the HCl in the chyme.
What is the pancreatic juice comprised of?
Water, enzymes, electrolytes, but primarily bicarbonate
What pH is pancreatic juice?
Ph of 8
What can happen if the gallstones block the hepatopancreatic ampulla sphincter?
If the gall stones block the hepatopancreatic ampulla, then pancreatitis can occur which can lead to auto-digestion
What does pancreatitis cause?
The pancreatic enzymes become activated in the pancreas itself and you begin to auto-digest the pancreas which eventually shuts off digestion all together.
What does secretin cause?
It causes the e
What does chyme entering the duodenum cause?
Causes duodenal enteroendocrine cells to secrete secretin, and cholecystokinin (CCK) into the bloodstream
What happens during the gastric and cephalic phases in the presence of CCK and secretin
the vagal nerve stimulates gallbladder to contract weakly.
What do secretin and Cholecystokinin immediately cause?
Secretin causes the pancreas to secrete bicarbonate pancreatic rich juice, by far the majority, while cholecystokinin causes the pancreas to secrete the enzyme rich portion of the pancreatic juice.
What does cholecystokinin cause further up the blood stream?
It causes the gallbladder to contract in the the presence of fatty chyme and the hepatopancreatic ampulla sphincter to relax. Bile then enters the duodenum
What do bile salts and to a lesser extent secretin cause further up the bloodstream?
They stimulate the liver to produce bile more rapidly.
