Digestion Flashcards
What are the primary functions of the digestive tract?
Digestion of consumed foods
Absorption of nutrients produced by digestion
Digestion
hydrolysis reactions that break ingested polymers (large molecules) into their smaller subunits (monomers)
Absorption
transfer of monomer subunits across wall of small intestine into blood or lymph
Motility
movement of food through tract includes ingestion, mastication, deglutition, and peristalsis
Peristalsis
(rhythmic contractions along GI tract that propel food)
Deglutition
Swallowing
Mastication
(chewing food and mixing with saliva)
Secretion (Endocrine)
(secretion of hormones that regulate digestive process)
Additional Functions of the Digestive Tract
Motility
Secretion
Storage and Elimination
Sections of the Small Intestine
Duodenum
Jejunum
ileum
Length of the Duodenum
12 inches (1 foot)
Sections of the Large Intestine
Colon
Cecum
Rectum
Organs of the GI Tract
Oral (Buccal Cavity) Esophagus Stomach Small Intestine Large Intestine
Accessory organs of the GI Tract
Teeth, Toungue, Salivary Glands
Liver and Gall Bladder
Pancreas
What are the two nerve nets (Plexuses)
Submucosa
Myenteric
What are the two nerve nets (Plexuses)
Submucosa
Myenteric
The activity of the Plexuses can be modified by
central nervous system and the autonomic nervous system
Neural Regulation of the GI Tract is done by
The Autonomic Nervous System
Both Sympathetic and Parasympathetic Innervation
Parasympathetic regulation of the GI Tract is done by
vagus nerve and spinal nerves in sacral region (to lower portion of large intestine)
What does the parasympathetic regulation of the GI Tract do?
Stimulates motility and secretion; favors digestion
Sympathetic regulation of the GI Tract
Reduces motility and secretory activity and stimulates sphincter contraction
What are the sphincters in the digestive system?
Oral Sphincter Cardiac Sphincter Pyloric Sphincter Ileocecal Sphincter Anal Sphincter
What are the sphincters in the digestive system?
Oral Cardiac Pyloric Ileocecal Anal
Function of teeth in the GI Tract
increases surface area upon which digestive enzymes work
Salivary Glands’ function in the GI Tract
secrete saliva
lubricates and softens food; aids in swallowing
contains salivary amylase
Salivary Amylase breaks down what macromolecules
Starches/Polysaccharides
Salivary Amylase breaks down what macromolecules
Starches/Polysaccharides
What are the three salivary glands
parotid, submaxillary, sublingual
What is the Parasympathetic system’s role in salivary secretion?
Stimulates secretion
What is the sympathetic NS’ role in Salivary Secretion?
Inhibits secretion (dry mouth when nervous)
Anticipation of food’s role in salivary secretion
(sight, smell, taste, or thought of food can trigger nervous system) and trigger salivary secretion
the physical presence of food in the mouth
induces salivary secretion
When Salivary Amylase breaks down starch, it is converted into
Maltose
Malitrose
Short Branched Oligosaccharides
Maltose Structure
glucose-Glucose
Malitrose Structure
Glucose-Glucose-Glucose
What sugars does Salivary Amylase not work on?
Sucrose
Lactose
Sucrose Structure
Glucose-Fructose (Table Sugar)
Glucose-Galactose (Milk Sugar)
Pharynx
Throat
Epiglottis
Flap that covers the trachea when ingesting food and drinks to ensure it gets to the esophagus
Esophagus
Involuntary contractions and relaxations propel food from pharynx to stomach
Stomach Function
Temporary storage of ingested material
Sphincters prevent backward flow of materials into esophagus and regulate release of stomach contents into small intestine
Stomach Function
Mechanical and chemical breakdown of ingested material
Churning of stomach mechanically disrupts foods
What active hormones in the stomach chemically break down foods?
Pepsin and HCl
How are stomach contents sterilized?
By the acid present
Where is protein digestion initiated?
In the stomach
What are the two types of mucous secreted in the stomach?
Soluble Form
Insoluble form
Soluble stomach mucous
mixes with other stomach juices
Insoluble Stomach Mucous
forms protective gel-like barrier over cells that line the stomach
Function of Insoluble Stomach Mucous
Traps dead cells
Traps bicarbonate ions (HCO3-)
Goblet Cells
Mucous-Producing cells in the stomach
Parietal Cells
Secrete Hydrochloric Acid
How are Parietal Cells stimulated to secrete HCl
Gastrin stimulates it
Chief Cells
Secrete Pepsinogen
Pepsinogen
Inactive Pepsin Hormone
How is Pepsinogen converted into pepsin
Acidic pH converts Pepsinogen into Pepsin
What is the function of Pepsin
Breaks down large proteins into smaller peptides
G Cells
Secrete Gastrin
Target Tissues of Gastrin
chief cells and parietal cells in stomach
Function of Gastrin
Stimulate Gastric Juice Production
- HCl from parietal Cells
- Pepsinogen from chief cells
What increases the pH of the stomach?
Gastrin
Promotes conversion of Pepsinogen to Pepsin
Parasympathetic Regulation of Gastrin Secretion
Stimulates secretion
How is gastrin secretion regulated by the contents in the stomach?
Stimulated by presence of proteins and especially the presence of certain amino acids (phenylalanine and tryptophan)
How does a very acidic pH affect Gastrin secretion?
Secretion inhibited when pH = 3
D Cells
Secrete Somatostatin
Shut down Gastrin secretion
What is the pH of the stomach when empty
2
What is the pH of the stomach when full?
6
The Presence of proteins and polypeptides in the stomach functions as
a Buffer to somewhat neutralize pH
True or False: The stomach is constantly secreting acid
False: The Stomach doesn’t produce acid unless it needs to
Cephalic phase of Gastric Secretion
stimuli come from central nervous system (triggered by thought, smell, sight, taste of food)
Gastric Phase of Gastric Secretion
primarily local stimuli
stretch of stomach wall when food enters
presence of protein and amino acids
hormonal stimulation by gastrin
Intestinal Phase of Gastric Secretion
Signals come from intestine and have inhibitory effect i.e. slow the rate of gastric secretion
Stretch of duodenum stimulate nerve reflex that inhibits gastric motility and secretion
Presence of fat in duodenum stimulates secretion of inhibitory hormones = enterogastrones
Enterogastrones
Inhibitory hormones stimulated by presence of fat in the duodenum
Almost all products of digestion are absorbed where?
In the small Intestine
Alcohol and Aspirin are absorbed where?
absorbed directly through stomach wall due to their lipid solubility
Absorption of aspirin through the stomach wall is associated with
absorbed directly through stomach wall due to their lipid solubility
Chyme
Liquefied Food; Passed from stomach to the small intestine
Small Intestine Functions
CHO digestion resumes and is completed here
Protein digestion continues and completes here
Fat digestion is initiated and completed here
Also functions to absorb nutrients, fluids, and electrolytes
How Long is the small intestine
16 feet
How Long is the Duodenum
1 foot long
Hormones important in Small Intestine Digestive Activity
Secretin Cholecyctokinin (CCK) Enterokinase Pancreatic enzymes Lipase, Amylase, Peptidases, Trypsinogen, Trypsin
What are the Pancreatic Enzymes?
Lipase, Amylase, Peptidases, Trypsinogen, Trypsin
S Cells Secrete
Secretin
What is Secretin’s target tissue
Pancreatic Ducts and liver
Secretion is Nature’s
Antacid
Stimuli for secretin Secretion
Acid (pH less than 4.5 stimulates secretion)
I Cells Secrete
cholecystokinin (CCK)
CCK (Cholecytokinin) target tissues
pancreatic acinar cells and gall bladder
I Cell Function
Induces secretion of digestive enzymes from pancreatic cells
Induces contraction of gall bladder, which releases bile into small intestine
Stimuli for CCK Secretion
Presence of protein and/or fat in chyme
Pancreatic Amylase
breaks CHO starch to maltose, maltriose, and small branched structures
Lipase
breaks down triglycerides into fatty acids and glycerol
Proteolytic Enzyme function
enzymes break peptides down to amino acids and dipeptide fragments
Trypsinogen
Converted to trypsin by enzyme (enterokinase) located along inner wall of small intestine
Enterokinase
Located along inner wall of small intestine. Converts Trypsinogen to Trypsin
Pancreatic Zygomens
Inactive Enzymes
Trypsin function in Pancreatic Zygomens
Trypsin converts other pancreatic zymogens (inactive forms) to their active forms within the small intestine
Most Pancreatic Enzymes are produced as
inactive molecules (Zygomens)
What is the purpose/function of Zygomens?
Protects the pancreas from self-digestion
Pancreatic Amylase is secreted into the duodenum in response to
Secretin
Pancreatic Amylase is active in the intestine because:
the acidic chyme is neutralized by HCO3- also secreted from pancreas in response to secretin
Is considerably more potent than amylase in saliva
Pancreatic Amylase function
converts complex CHOs to maltriose, maltose, and short branched sugars
Inner Surface of the Small Intestine
(epithelial layer) extensively folded and covered with smaller folds (villi) and even smaller folds (microvilli) increase surface area for absorption to occur
Function of Microvilli
Increase surface area for absorption
The small intestine is the site of absorption for:
carbohydrates, lipids, amino acids, calcium and iron in duodenum and jejunum
Bile salts, Vit B12, water, and electrolytes mainly in ileum
Monosaccharides move through the cells lining the sm. intestine and into the
Interstitium
After Monosaccharides enter the Interstitium, what occurs?
Monosaccharides then enter hepatic portal vein and are transported to liver first, and the rest of the body afterwards
The Hepatic portal vein role in CHO absorption in the Small Intestine
Monosaccharides then enter hepatic portal vein and are transported to liver first, and the rest of the body afterwards
conveys blood from capillaries in the intestine, stomach, and pancreas to capillaries in the liver
Fat Digestion prior to the small intestine
Limited. Some lipases in Saliva and Gastric Secretions contribute
Lipase
Enzyme important in fat digestion
Lipase is secreted into the Small Intestine from the
Pancreas
Lipase is secreted into the Small Intestine from the Pancreas in response to
Secretin
Lipase Function
Breaks down triglycerides to free fatty acids and monoglycerides
Lipase activity is dependent upon
the amount of surface area on which it can work
In Lipid digestion and Absorption in the Small intestine, Fats stimulate
I Cells to release CCK
In the Small intestine, CCK triggers
The release of Bile from the gall bladder
Blile Function
Fat Emulsification
True or False: Bile breaks bond between glycerol and fatty acids
False: The Bonds are not broken
Fat emulsification
Breaks Large Fat gobules into smaller fat gobules
Bile increases surface area available for what to act?
Pancreatic Lipase
The Hepatic Artery delivers oxygenated blood to
The Liver
The Hepatic Portal Vein function
receives absorbed nutrients first, then the rest of the body gets it. This does not include fat.
Liver’s Digestive functions
Secretes bile - essential for digestion and absorption of fats
Liver’s circulatory functions
destroys aged or abnormal blood cells and produces clotting factors
What converts protein metabolites into urea for elimination by the kidneys?
The Liver
Liver Immune Functions
(Kupffer cells)
The Liver functions as a blood reservior in regulation of
Blood Volume
Bile
Product of the liver cells
Bile contains
bile pigment, bile salts, phospholipids, cholesterol, and inorganic ions
Bile Pigment contains
bilirubin = breakdown product of hemoglobin
Bile Salts
lipid aggregates with non-polar parts in central region and polar regions toward water
What is essential for the absorption of fat from the digestive tract?
Bile
Gallbladder location
On the underside of the liver
Gallbladder function
Concentrates and stores the bile produced in liver
Gallbladder contraction forces
bile into small intestine
Cholecystokinin (CCK)
hormone released by ‘I’ cells of small intestine
Cholecystokinin (CCK) function
Stimulates release of digestive enzymes from pancreas and bile from gall bladder
Micelles
Aggregates of bile salts, free fatty acids, monoglycerides, and fat-soluble vitamins
Micelle arrangement and function
Arranged with non-polar regions to center, polar, water-soluble portions to outside
Makes lipids more water soluble in lumen of intestine
Micelle Transport
transported to epithelial cells lining small intestine
Importance of Micelle Formation
Intestinal epithelial layer is covered by an ‘unstirred’ water layer
Fats are nonpolar, and insoluble in water
Micelle Structure
outer borders are polar, but whose inner segments are nonpolar
Outer Polar Portion of Micelles
can dissolve in the unstirred water layer and be transported to epithelial cell surfaces
Nonpolar Portion of Micelles
can then be removed from micelle and absorbed individually, or in some cases the micelle itself may be absorbed
Chylomicrons
Inside epithelial cells, triglycerides and phospholipids are re-synthesized
Resynthesized triglycerides and phospholipids are combined with cholesterol and protein inside the cell to form chylomicrons
Chlylomicrons are released into
the lymphatic system - NOT INTO HEPATIC PORTAL VEIN
Liver does not get ‘first crack’ at lipids
Proteolytic enzymes are released in inactive form (Zygomens)
from the pancreas in response to secretin
Trypsinogen
inactive precursor that is converted (by enterokinase) to trypsin in the brush border of the small intestine
True or False: Trypsin converts other zymogens to their active forms
True
Collectively, the proteolytic enzymes break proteins and peptides into
single amino acids, or di- and tripeptides
Amino Acids are absorbed by
the epithelial cells of the small intestine by active co-transport with sodium
Di- and tripeptides are also absorbed by
epithelial cells of the small intestine and then broken down into amino acids within the epithelial cells
Epithelial cells release amino acids into portal blood
which is transported first to the liver, then to rest of the body
The Large Intestine is separated from the small intestine by
ileocecal valve
Large Intestine Function
Collects food residue (indigestible) material
Site of final water reabsorption - causes chyme to become solid (forms feces)
Stores feces until eliminated from body
Large Intestine Divsions
Cecum Colon -ascending -transverse -descending -Sigmoid
Divisions of the Colon
Ascending
Transverse
Descending
Sigmoid (leads to rectum)
Cecum
section nearest small intestine (appendix attached in this region)
What is the major portion of the Small Intestine
Colon
98% of water that enters the gut is
reabsorbed
How much water is reabsorbed in the small intestine?
85%
How much water is reabsorbed in the large intestine
13%
Absorption of water is a passive process
Osmotic gradient created by active transport of ions
Water moves according to its gradient