Digestive System Flashcards
What is the digestive system?
The organ system that processes food, extracts nutrients, and eliminates residue
What are the five stages of digestion?
- Ingestion
- Digestion
- Absorption
- Compaction
- Defecation
What are the two types of digestion?
Mechanical and chemical
What is mechanical digestion? where is it done and what is its benifet
- The physical breakdown of food into smaller parts
- Teeth, stomach, small intestine
- Exposes food surface to enzymes
What is chemical digestion?
A series of hydrolysis reactions that break dietary macromolecules into monomers
What carries out chemical digestion?
Digestive enzymes
Where are digestive enzymes produced?
Salivary glands, stomach, pancreas, and small intestine
What are some nutrients that do not need to be digested and are available in usable form when ingested?
- Vitamins
- Amino acids
- minerals
- cholesterol
- Water
What are the two subdivisions of the digestive system?
The digestive tract and the accessory organs
The digestive tract is also know as the___
Alimentary canal
What is the digestive tract?
- 30 ft long tube
- from mouth to large intestins
What is the GI tract?
the stomach and intestines
What are accessory organs of the digestive system?
Teeth, tongue, salivary glands, liver,
gallbladder, and pancreas
Most of the digestive tract has a similar structural plan consisting of a layered _____
Wall
What are the general layers of the digestive tract organs? 4
- Mucosa
- submucosa
- muscularis externa
- serosa
What are the three layers of the mucosa?
- Epithelium
- Lamina propria
- Muscularis mucosae
What are the layers of the muscularis externa?
- the inner circular layer
- the outer longitudinal layer
What are the two layers of the serosa?
- Areolar tissue
- Mesothelium
What lymphatic tissue is found in the mucosa?
(MALT)
Mucosa-associated lymphatic tissue
Where does the serosa begin and end?
Begins in the lower esophagus ends just before the rectum
What is the enteric nervous system?
Nervous network in esophagus, stomach, and intestines that regulates digestive tract motility, secretion, and
blood flow
What are the two networks of neurons that make up the enteric nervous system?
- The submucosal plexus: glandular secretions and movment of mucosae
- Myenteric plexus: peristalsis and other contractions of muscularis externa
What are mesenteries?
connective tissue
sheets that suspend stomach and
intestines from abdominal wall
What is the function of the mesenteries?
To provide support, blood flow, and lymphatic flow to the abdominal digestive organs
What is the lesser omentum?
—a ventral
mesentery that extends from
the lesser curvature of the
stomach to the liver
What is the parietal peritoneum?
a serous membrane that lines the wall of the abdominal cavity
What is the Greater omentum?
A mesentery that hangs from the greater curvature of the stomach and covers the small intestine like an apron
What is the mesocolon?
an extention of the mesentery that anchors the colon to the abdominal wal
What are the three mechanisms that control motility and secretion of the digestive tract?
- Neural control
- Hormones
- Paracrine secretions
The oral/buccal cavity is composed of?
The mouth enclosed by cheeks, lips, palate, and tongue
What tissue lines the mouth?
Strat. squam. epithelium
The tongue is attached to the floor of the mouth at the?
Lingual frenulum
The border between the body and the root of the tongue is marked by?
Vallate papilae
What portion of the tongue produces saliva?
The lingual glands located amid the extrinsic muscles(muscles that attach tongue to mouth)
What are the four regions of a tooth?
- Crown
- Neck
- Root
- Gingival sulcus
What is the hard yellowish tissue that makes up most of the tooth?
Dentin
What is oral plaque?
a sticky residue on the teeth made up of bacteria and sugars
What is dental calculus?
calcified plaque
What is the first step in mechanical digestion?
Mastication
What are the main functions of saliva?
- Moisture to mouth and food(lubrication)
- Starch and fat digestion
- Dissolves molecules to activate taste buds
- Inhibits bacterial growth
Salivary glands are composed of ____ glands that are branched and end in a ___
- Tubuloacinar
- Acini
What are the different types of cells within a acini that secrete substances?
- Mucous cells: secrete mucous
- Serous cells: secrete thin fluid rich in enzymes and electrolytes
Where is the neural control for salivation located?
-The salivatory nuclei in the medulla oblongata and pons
What are some triggers of salivation?
- Tactile, pressure, and taste receptors
- odor, sight, though of food
How does parasympathetic stimulation effect salivation?
results in an abundance of thin enzyme rich saliva
how does sympathetic stimulation effect salivation?
results in less, thick saliva with more mucus
What is the function of the lower esophageal sphincter?
to prevent regurgitation
What is the swallowing center and where is it located?
-A pair of nuclei in the medulla oblongata that coordinates swallowing
What are the three phases of swallowing?
- Oral
- Pharyngeal
- esophageal
What are the empty, after meal, and full capacity of the stomach
- 50ml
- 1 to 1.5 L after meal
- up to 4L
What is chyme?
soupy or pasty mixture of semi-digested food in the stomach
What are the four regions of the stomach?
– Cardial part (cardia)—small area within about 3 cm of the cardial orifice
– Fundus (fundus)—dome-shaped portion superior to esophageal
attachment
– Body (corpus)–makes up the greatest part of stomach
– Pyloric part—narrower pouch at
the inferior end
What are the four subdivisions of the Pyloric portion of the stomach?
- Funnel like antrum
- Pyloric canal
- Pylorus
- Pyloric sphincter
Where does parasympathetic innervation of the stomach come from?
Vagus Nerve
Where does sympathetic innervation of the stomach come from?
Celiac ganglia
What is the path of blood to and from the stomach?
- Supplied by the celiac trunk
- drained blood from stomach and intestines filter through the liver via the hepatic portal circulation
The mucosa of the stomach is composed of ___ epithelium?
Simple columnar
The apical regions of the stomachs surface cells are filled with____
mucin
What is mucin?
a substance that swells with water and becomes mucus after it is secreted
The muscularis externa of the stomach has ___ layers instead of the normal 2
3
What are the three layers of the muscularis externa of the stomach?
- Outer longitudinal,
- middle circular
- inner oblique
What are gastric pits?
depressions in gastric mucosa that contain tubular glands at the bottom
What are the three types of tubular glands found in the gastric pits?
- Cardiac glands in the cardial part
- Pyloric glands in pyloric part
- Gastric glands in the rest
The cardial and pyloric glands of the gastric pits are primarily ___ cells
Mucous
What are parietal cells?
- Cells found mostly in the upper half of gastric pit glands
- They produce HCL, intrinsic factor, and ghrelin
What are cheif cells?
- The most numerous of the cells in the pits of the body of the stomach
- secrete gastric lipase and pepsinogen
What are enteroendocrine cells?
cells located in the lower end of the pit glands that produce paracrine messengers that regulate digestion
What is gastric juice and how much is produced each day?
- A mixture of water, HCl, and Pepsin
- 2 to 3L a day
- produced by gastric glands
How is HCl produced?
- Produced in the parietal cells using CAH
- CO2 is taken into the cell and turned into carbonic acid
- Carbonic acid is then split and H+ is transfered out of cell into lumin , K+ is pumped in
- Chloride is taken from blood through the cell and into lumin
- Hydrogen ion and chloride ion bond to form HCl
What are the functions of HCl in the stomach?
- Activates Pepsin and lingual lipase
- breaks down connective tissue and plant cell walls
- Converts iron into a digestable form
- Contributes to nonspecific immunity
What is Alkaline tide?
elevated bicarbonate levels when digestion occurs due to the production of HCl
What are zygomens?
Digestive enzymes secreted as inactive proteins
What is pepsinogen?
- the zymogen secreted by the chief cells
- inactive form of pepsin
How is pepsinogen converted to pepsin?
- HCl removes some of its amino acids
- It is also autocatalyic meaning that some of the pepsin from will convert more pepsinogen into pepsin
What is the function of pepsin?
To digest dietary protein into shorter peptides
Where is protein digestion completed?
in the small intestines
What are the functions of Gastric and lingual lipase?
They work to digest fats in the stomach
-only digest 10-15%
What is intrinsic factor?
- A glycoprotein produced by the parietal cells
- Essential for the absorption of B12 by its action of binding to B12 which allows it to be absorbed by the small intestine
How much chyme is passed into the small intestine at a time?
3mL
What are the three ways that the stomach is protected from its harsh environment?
- Mucous coat
- Tight junctions: prevent seeping gastric juice
- Epithelial cell replacement: replaced ever 3 to 6 days
How is gastric function regulated?
By a collaboration between the endocrine system and the nervous system
What are the three phases of gastric activity?
- Cephalic phase
- Gastric phase
- Intestinal phase
How does ingested food stimulate the gastric phase?
- By stretching
- By increase of pH
What three chemicals stimulate gastric secretion?
- Acetylcholine: parasympathetic nerve fibers
- Histamine: enteroendocrine cells in gastric glands
- Gastrin: g cells in pyloric glands
Explain the intestinal phase of gastric activity
- an inital increase in gastric activity
- Soon is inhibited by the enterogastric reflex
What are the four lobes of the liver?
Right, left, quadrate, and caudate
The ___ ligament separates the right and left lobe of the liver
falciform ligament
What are hepatic lobules?
tiny cylinders that fill the interior of the liver
What are hepatocytes?
Cuboidal cells surrounding the central vein forming plates up the lobule
What are hepatic sinusoids?
blood filled channels lined by fenestrated endothelium that fill up spaces between plates
Blood leaves the liver at its ____ surface
superior
Trace the flow of bile from the liver to the small intestine
- Flows from the liver via Bile canaliculi
- Passes into bile ductiles
- then to the right and left hepatic ducts which fomr the common hepatic duct
- passes the cystic duct or flows from the cyctic duct
- then down the bile duct
- combines with the duct of the pancreas and into the small intestine
When the bile duct and pancriatic duct converge it creates the___
Hepatopancreatic ampulla
What is the function of the gallbladder?
To store and concentrate bile
What is bile?
Yellow-green fluid containing minerals, cholesterol, neutral fats,
What is bilirubin?
The principal pigment derived from the decomposition of hemoglobin
Where is bilirubin metabolized into urobilinogen?
in the large intestine by bacteria
What are bile acids synthesized from?
cholesterol
___% of bile is reabsorbed in the ileum and returned to the liver
80%
What is the body’s only way of eliminating excess cholesterol
Bile acids that are excreted into the feces and more cholesterol is used to make more bile acids
How much pancreatic juice is secreted per day?
1200 to 1500 mL
___ release their secretions into small ducts that converge on pain pancreatic duct
Acini
The pancreatic duct joins the bile duct at the?
Heptopancreatic ampulla
What is pancreatic juice?
an alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and electrolytes
In the pancreas the ___ secrete enzymes and the ___ secrete sodium bicarb
Acini
Ducts
What are the three pancreatic zymogens?
- Trypsinogen
- Chymotrypsinogen
- Procarboxypeptidase
What converts trypsinogen?
- Converted to trypsin by enteropeptidase which is secreted by the mucosa of the small intestine
- trypsin is also autocatalytic, it converts trypsinogen into more trypsin
What converts chymotrypsinogen?
- is converted into trypsinogen by trypsin
What converts procarboxypeptidase?
-It is converted to carboxypeptidase by trypsin
What is the function of pancreatic amylase?
to digest starch
What is the function of pancreatic lipase?
to digest fats
What is the function of Ribonuclease? where is it found?
to digest RNA
-found in the small intestine from pancreas
What is the function of deoxyribonuclease? where is it found?
To digest DNA
-found in the small intestine from pancreas
What are the three stimuli that regulate the release of pancreatic juice and bile?
- Acetylcholine
- Cholecystokinin
- Secretin
What is the effect of Acetylcholine on pancreatic juice secretion? where does it come from?
- Comes from vagus and enteric nerves
- Stimulates acini to secrete enzymes during cephalic control
- DOES NOT STIMULATE RELEASE JUST PRODUCTION
What is the effect of Cholecystokinin on pancreatic juice secretion? where does it come from?
- Secreted by the mucosa of duodenum in responce to fat in the small intestines
- Stimulates acini to secrete enzymes
- Strong stimulation of gallbladder
- induces contractions of gallbladder and relaxation of hp sphincter
What is the effect of secretin on pancreatic juice secretion? where does it come from?
- Released from the duodenum in response to acidic chyme arriving from the stomach
- Stimulates liver and pancreas ducts to secrete more sodium bicarb
- raises pH to level required for enzyme activity in small intestines
What are the three main regions of the small intestine?
- Duodenum
- Jejunum
- ileum
Where does the duodenum begin?
At the pyloric valve
The duodenum ends in a sharp bend called the ___
Duodenojejunal flexure
What are the four major events of digestion that occur in the duodenum?
- Stomach acid neutralization
- Emulsification of fats via bile acids
- inactivation of pepsin
- Chemical digestion via pancreatic enzymes
Where does most of the nutrient absorption occur?
in the Jejunum
Why does the Jejunum have such a rich blood supply?
because it is the sight of most of the nutrient absorption in the body
list the regions of the small intestine’s in order
- Duodenum
- Jejunum
- Ileum
What is the ileocecal junction?
End of the small intestine where the ileum joins the cecum of the large intestine
What is the ileocecal valve and what forms it? its function?
- a sphincter formed by the thickened muscularis of the ileum
- functions to regulate the passage of waste into the large intestine
Where does the small intestine receive its blood supply from?
- The superior mesenteric artery
- leaves via the superior mesenteric vein
What is the form and function of the plicae circularis?
- Circular folds that increase the surface area of the small intestine
- involve only the mucosa and sub mucosa
- function to cause chyme to spiral through the intestine increasing its exposure to surface area
The plicae circulares increase surface area by a factor of___
2-3
Villi increase surface area by a factor of ___
10
Micro villi increase surface area by a factor of ___
20
the lumen of the small intestine is lined with___
simple columnar epithelium
What are the two types of cells that cover villi?
- Absorptive cells
- goblet cells
How does the epithelium of the digestive system protect itself from digestive enzymes?
Via tight junctions prevent the seeping of enzymes
What type of tissue makes of the core of a villi? What is this core called?
- Areolar tissue
- The lamina propria
The micro villi on the absorptive cells of the villi make up the ___ border
Brush
What is the function of the brush border?
To produce enzymes that carry out final parts of enzymatic digestion
How does the brush border deliver its enzymes?
via contact
What are intestinal crypts?
pores on the floor of the small intestine between villi that open into tubular glands
Absorptive cells as also called___
Enterocytes
What type of cells make up the surface of the intestinal crypts?
- Upper half is the same as villi (goblet and absorptive)
- Lower half is active stem cells
Other than stem cells, what other cells are found at the bottom of intestinal crypts? what are their functions
- Paneth cells
- Secrete defensive proteins to resist bacterial invasion
What are the duodenal glands and where are they found?
- Found in the submucosa of the duodenum
- Secrete bicarb rich mucus that neutralizes stomach acid
Where in the small intestine do a majority of the lymphocytes live
The lamina propria and the submucosa
What is the main secretion of intestinal crypts? how much per day is secreted?
Intestinal juice
1-2 L a day
What is intestinal juice and when is it released?
- A mixture of water, mucus, and a little enzyme
- pH of 7.4 to 7.8
- Released in response to acid, hypertonic chyme, and intestinal distension
What three functions does the contraction of the small intestines surve?
- To mix chyme with Intestinal hjuice, bile, and pancreatic juice
- To churn chyme
- to move residue towards large intestines
What is intestinal segmentation?
-The moment of stationary ring like contractions along the intestine
What are the beinfits of segmentation?
Variations in contraction times causes a random rhythm which allows chyme to reach maximum surface area contact before moving to large intestine
What controls the pace of segmentation?
Enteric pacemaker cells in the muscularis externa
When does segmentation decline and peristalsis begin?
When most nutrients have been absorbed
What is peristalsis? what hormone triggers it?
- A series of wave like contractions that move food from the small intestines to the colon
- Triggered by motilin
Where does peristalsis begin? how long does the process take?
- the duodenum
- 2 hours
When does the ileocecal valve open?
-When food in the stomach triggers the gastroileal reflex that triggers segmentation and the relaxation of the valve
When does the ileocecal valve close?
- It is normally closed
- Closes when the cecum fills with residue and the pressure pinches the valve shut
Where does the digestion of starch begin? what enzyme is at play?
in the mouth via salivary amylase
What is the chain of breakdown for a starch?
- Starch is digested into oligosaccharides
- then into the disaccharide maltose
- Maltose into glucose
What percentage of starch is broken down via salivary amylase?
50%
What happens to starch after the mouth?
- Salivary amylase is quickly denatured by the stomach (only functions at a pH of 6.8 to 7.0)
- Digestion is resumed in the small intestine via pancreatic amylase
what occurs After starch is broken down into oligosaccharides and maltose
Brush border enzymes continue digestion
What brush border enzymes hydrolyze oligosaccharides?
Dextrinase and Glucoamylase
What brush border enzymes hydrolyze maltose?
Maltase
What brush border enzymes hydrolyze the disaccharides sucrose and lactose?
Sucrase and lactase
What is the fate of monosaccharides in the small intestines?
They are immediately absorbed
What percentage of absorbed sugar is glucose?
80%
How is glucose absorbed at the brush border?
Via a sodium-glucose transport protein
What happens to the sugars once they are absorbed?
they are transported out of the cell via facilitated diffusion and absorbed into bloodstream to go to the liver
How is galactose absorbed?
Via the same Sodium-glucose transporter as glucose
How is fructose absorbed?
Via facilitated diffusion
What happens to fructose after it is absorbed and before it is transported out of the cell?
A majority of it is converted into glucose
Other than through the ICF how else is glucose absorbed at the brush border?
- Solvent drag caused by the increased osmolarity of the ECF due to sugars leaving the epithelial cells.
- Due to leaky tight junctions
What are the three main sources of Protein?
Exogenic -Dietary -Endogenic -Digested digestive enzymes -Sloughed epithelial cells
How many grams of amino acids come from endogenic routes?
30g/day
How many grams of amino acids come from exogenous routes?
about 60g/day
What types of enzymes digest proteins?
Proteases(peptidases)
Where does protein digestion begin?
in the stomach via pepsin
How does pepsin work?
it hydrolyzes any peptide bond between thyrosine and phenylalanine
What percentage of protein is digested via pepsin?
10-15%
What enzymes take over protein digestion after the stomach?
Trypsin and chymotrypsin
How do trypsin and chymotrypsin continue protein digestion?
- They hydrolyze polypeptides into shorter oligopeptides
- O-peptides are then taken apart one amin acid at a time
What are the three enzymes responsible for dismantling oligopeptides?
- Carboxypeptidase
- Aminopeptidase
- Dipeptidase
What is the role of Carboxypeptidase in protein digestion?
COmes from the pancreas
-Removes amino acids from the carboxyl end of the chain
What is the role of aminopeptidase in protein digestion?
- Brush border enzyme
- removes amino acids from the -NH2 end of the chain
What is the role of dipeptidase in protein digestion?
- brush border enzyme
- Splits dipeptides in the middle to release two free amino acids
How are proteins absorbed?
Once converted into free amino acids they are absorbed into the intestinal epithelial cells via sodium dependent amino acid cotransporters
How are absorbed amino acids transported into the bloodstream?
facilitated diffusion
why is lipid digestion complicated?
Because lipids are hydrophobic
What are lipases?
Fat digesting enzymes
Where does lipid digestion begin?
In the mouth via lingual lipase secreted by the intrinsic salivary glands
What % of lipids are digested before the small intestines?
10-15%
Before it reaches the duodenaum what does the stomach do the lipids to make digestion easier?
It emulsifies it through vigorous pumping in the antrum
What breaks down emulsification droplets once in the smal intestine? why is this benificial?
- Bile, Lecithin, and -agitation
- Exposes more fat surface to enzymes
Lipase acts specifically on ___
Triglycerides
How does lipase act on triglycerides?
-By removing the first and third fatty acids from the glycerol backbone
What is the product of lipase action?
Two free fatty acids and a mono glyceride
How are free fatty acids, monoglycerides, and other lipids absorbed?
- They are absorbed via Micelles in the bile
- after absorption they are transported and passed through the plasma membrane of the absorptive cells
What are micelles?
- 20-40 bile acids arranged with their hyydrophilic sides on the outside
- has a core of cholesterol and phospholipids
What happens to lipids once they are transported into the intestinal cells?
- They are transported to the ER and re-synthesized into triglycerides
- then given a coat of phospholipids and protein in the golgi
- Become chylomicrons at that point
What happens to chylomicrons?
They are taken up by lacteal into the lymph and eventually enters the bloodstream
What is chyle?
fatty intestinal lymph
What enzymes are responsible for digesting nucleic acids?
Nucleases (Deoxyribonuclease and ribonuclease)
How do nucleases work? and where?
- At the brush border
- Split nucleic acids into phosphate ions, sugar base, and nitrogenous bases
How are the products of nucleic acid digestion absorbed?
Membrane carriers
How are vitamins digested?
- the remain unchanged and are absorbed as is either with other lipids if lipid soluble
- absorbed via diffusion if water soluble
- b12 needs to be bound to intrinsic factor first
Where are minerals absorbed?
in the small intestines
How is sodium absorbed?
it is co-transported with sugars and amino acids
How is chloride absorbed?
It is exchanged for bicarb reversing chloride-bicarb exchange that occurs in the stomach
How is potassium absorbed?
Simple diffusion
How much iron and calcium is absorbed?
only what is needed
How is iron absorbed?
Active transport of ferrous ions (Fe2+)
How is calcium absorbed?
- Transcellular in the dupdenum
- Diffusion between cells in the jejunum and ileum
How does vitamin D effect calcium absorption?
It affects absorptive cells of the dupdenum by increasing the nummber of calcium channels
What does parathyroid
hormone stimulate when calcium levels are low?
The production of vit. D in the kidneys
How is water absorbed in the small intestines?
Via osmosis following the absorption of salts and organic nutrients
What causes diarrhea?
- When the large intestine absorbs too litter water.
- occurs when feces passes too quickly or there are high concentrations of solutes (Like undigested lactose)
What causes constipation?
When fecal movement is slow and too much water is absorbed.
What are the taeia coli?
Longitudinal fibers of the muscularis externa of the large intestine.
What are the haustra of the large intestine?
Pouches in the colon caused by the muscle tone of the teaniae coli
The internal anal sphincter is composed of___
the smooth muscle of the muscularis externa
The external anal sphincter is composed of?
Skeletal muscle of pelvic diaphragm
WHat are the omental appendages?
Club like fatty pouches of peritoneum adhering to the colon. Unknown function
The intestinal crypts of the large intestine have a high concentration of ____ cells
Goblet
The gut microbiome is responsible for the digestion of ___
- Cellulose, pectin, and other undigestable carbs
- help to synthesize b vitamins and K vits
The main function of the large intestine is to ____
reabsorb water and electrolytes.
What ar the two types of contractions within the large intestine?
- Haustral contractions-every 30 mins
- Mass movements- 1-3 times a day
What action stimulates the movment of the colon?
Gastrocolic and duodenocolic reflexes (Filling of stomic and duodenum)
What are the two defecation reflexes and what triggers them?
- triggered by the stretching of the rectum
- Intrinsic defecation reflex
- Parasympathetic defecation reflex
What is the intrinsic defecation reflex?
- A weak response to rectal stretching
- Relaxes the internal sphincter
What is the parasympathetic defecation reflex?
- rectal stretching causes sensory signal to spinal cord
- pelvic nerve returns signal and intensify’s peristalsis while also relaxing the internal anal sphincter
How is defecation controlled?
Through voulntary control of the external sphincter and puborectlis muscles
