Digestive Flashcards
what is digestion
- breakdown of ingested food
- absorption of nutrients into the blood
- concentration and removal of waste products
what is metabolism
- production of cellular energy (ATP)
- regulation of cellular activities
what are the 2 main functional groups of organs
- alimentary canal (continuous hollow tube)
- accessory digestive organs
structures of the alimentary canal
- mouth
- pharynx
- esophagus
- stomach
-small intestine - large intestine
anus
functions of the salivary glands
- Lubrication/binding
- Solubilization of dry food
- Oral hygiene – flushes away debris
- Begins starch digestion (salivary amylases)
- Alkaline buffering
-Evaporative cooling (ie, important in dogs)
function of incisors
rip and cut
function of canines
tear and pierce
function of premolars
grind and shear
function of molars
grind
different types of teeth
- incisors
- canines
-premolars
-molars
how many primary and secondary teeth
20 primary
32 secondary
first step from mouth to stomach
mastication (chewing food)
- teeth
second step from mouth to stomach
deglutition (swallowing)
- oral, pharyngeal, esophageal
mouth, pharynx and upper esophagus are muscles innervated by what neurons
somatic motor neurons
middle and lower esophagus are muscles innervated by what neurons
autonomic neurons
what does the esophagus connect
connects pharynx to the stomach
what is peristalsis
food moves by a wake-like muscular contraction
- pushes bolus into the stomach
how do muscle layers in the stomach help with digestion
the smooth muscle layers in the stomach run along the length of the organ, around the organ and also in an oblique direction. these muscles help mix and mechanically break up food in the stomach
gastric pits
are the openings of the gastric glands
what cells make up the gastric glands
- mucous cells
- chief cells
- parietal cells
what does mucous cells secrete
mucus
what does parietal cells secrete
HCl, intrinsic factor (B12)
what do chief cells (zymogenic) secrete
secrete pepsinogen
what causes peptic ulcers and how are they related to helicobacter pylori
- erosions of the mucosa in the stomach can lead to peptic ulcers where the stomach digests itself
- is caused by the bacteria helicobacter pylori, which infects the GI tract of about 50% of adults worldwide
what do pepsinogen/HCl do
- in the presence of HCl, the inactive enzyme pepsinogen is activated to the pepsin form, which can digest proteins into smaller polypeptides
regions of the stomach
- duodenum
- jejunum
- illeum
Duodenum
- first 25cm
- mucous secretion, receives pancreatic secretions and bile from liver
Jejunum
- 1m in length
- numerous folds and villi
Ileum
- last 2m
- fewer folds/villi than jejunum
- absorbs primarily bile salts, water, electrolytes
- contains Peyer’s patches
- empties into large intestine via ileocecal valve
what type of cells cover the villi and what do they do?
villi are covered with columnar epithelial cells which are responsible for absorption
what do goblet cells in the small intestine do
they secrete mucus to lubricate and protect the epithelial lining
how are epithelial cells replaced in the small intestine
epithelial cells at the tip of the villi are continuously sloughed off and replaced by new cells that come from the intestinal crypts
what role do paneth cells play in the small intestine
paneth cells at the base of the crypts secrete antibacterial molecules (lysozyme, antimicrobial peptides) to protect the intestine from inflammation
sucrase functions
digests sucrose to glucose and fructose
- deficiency produces GI disturbances
maltase
digests maltose to glucose
lactase
digests lactose to glucose and galactose
- deficiency produces gastrointestinal disturbances (lactose intolerance)
peptidase - aminopeptidase
produces free AA, dipeptides, and tri peptides
peptidase - enterokinase
- activates trypsin (and indirectly other pancreatic juice enzymes)
- deficiency results in protein malnutrition
phosphatase - Ca2+, Mg2+, ATPase
needed for absorption of dietary calcium
- enzyme activity regulated by Vit D
phosphatase - alkaline phosphatase
- removed phosphate groups from organic molecules
- enzyme activity may be regulated by Vit D
access to food 24 hours a day vs 8 hours a day
24 hours:
higher:
- adiposity
- glucose intolerance
- leptin resistance
- liver pathology
- inflammation
lower:
- motor coordination
what role do the bacteria in the colon play in digestion
The “good” bacteria help with digestive processes and outcompete pathogenic bacteria.
what happens when pathogenic bacteria take over the colon
When pathogenic bacteria take over, the colon reacts by eliminating its contents and sloughing off the colon epithelium, leading to diarrhea.
What is the role of the appendix in the digestive system?
The appendix is thought to contain a reservoir of “good bacteria” that can help re-colonize the colon after diarrhea and the expulsion of colon contents.
What is the appendix, and what was its function previously thought to be?
The appendix is a small component of the colon, and until recently, no specific function was identified for it. It was often considered a vestigial organ.
Does the appendix function in digestion?
No, the appendix does not function in digestion, but like the tonsils, it contains lymph vessels.
What is appendicitis, and what symptoms does it cause?
Appendicitis is the inflammation of the appendix, causing pain in the lower right quadrant of the abdomen.
What can happen if the appendix ruptures?
If the appendix ruptures, it can lead to inflammation in the peritoneal cavity, a condition known as peritonitis.
what are the accessory organs of digestion
- pancreas
- liver
- galbladder
what is the structure of the liver in terms of its cells and sinusoids
The liver is made up of hepatic cells lining large capillaries called sinusoids. The sinusoids are also lined by endothelial cells and contain Kupffer cells, which are phagocytes.
What is remarkable about the liver’s regenerative abilities?
he liver has amazing regenerative capabilities. If 2/3rds of a rodent’s liver are surgically removed, the remaining tissue will regenerate to its original mass in just one week.
What are the two blood inputs to the liver?
- The portal vein (from the intestines, providing a major blood supply)
- The hepatic artery (from the heart to the liver).
What is the role of the liver’s endocrine function?
- Producing enzymes and hormones, and the output is sent into the hepatic vein, which returns blood to the heart.
- This allows nutrients to be pumped throughout the body.
What are the two exocrine regions of the liver, and what do they do?
The right and left hepatic ducts.
- These ducts carry bile produced by the liver. The bile is then stored in the gallbladder.
How does bile move from the liver to the intestines?
The right and left hepatic ducts merge with the cystic duct from the gallbladder to form the common bile duct, which then carries bile into the intestines.
How is bilirubin formed from the heme group?
A derivative of the heme group (minus the iron) is converted into bilirubin. This bilirubin is carried in the blood on albumin proteins and taken up by the liver.
How does the liver process bilirubin?
In the liver, bilirubin is mixed with glucuronic acid, making it water-soluble. It can then be secreted into bile and sent to the intestines.
What happens to bilirubin after it is converted in the intestines?
In the intestines, bilirubin is converted by bacteria into urobilinogen, which is then removed in feces. Some urobilinogen can re-enter circulation and be excreted by the kidneys.
what does the galbladder look like and what does it do
it is a sac-like organ attached to the inferior surface of the liver
- stores and concentrates bile from the liver
The pancreatic juice contains what digestive enzymes?
amylase - digests starch
trypsin - digests proteins
lipase - digests triglycerides
What is required for digestion to occur in the small intestine?
Digestion requires both pancreatic enzymes and brush border enzymes. The brush border enzymes activate the inactive form of the pancreatic enzyme trypsin.
How is trypsin activated, and what is its role?
Trypsin is activated by the brush border enzymes in the small intestine. Once active, trypsin is a protease that can activate other pancreatic enzymes involved in digestion
What endocrine functions does the pancreas perform?
Produces hormones such as insulin, glucagon, and somatostatin.
What digestive functions does the pancreas serve?
The pancreas also serves as a digestive organ by secreting digestive enzymes into the small intestine. These enzymes help digest chyme, including carbohydrates, proteins, and lipids.
what are the main functions of the digestive system
- Motility
- Secretion
- Digestion
- Absorption
2 types of herbivores
- Ruminants
- Simple stomach herbivores
2 types of digestion in animals
- Enzymatic digestion
- Microbial digestion: fermentation
what are the major steps of digestion in carbohydrates
- Starch (polysaccharides) - broken down by amylases
- Disaccharides - broken down by brush border enzymes
- Monosaccharides (simple sugars)
what are some brush border enzymes that break down disaccharides
- dextrinase
- glucoamylase
- lactase
- maltase
- sucrase
How are carbohydrates digested in the mouth?
- Chewing mixes food with salivary secretions containing ptyalin (an α-amylase)
- This hydrolyzes starch into maltose and other small glucose polymers.
What is the role of ptyalin (α-amylase) in carbohydrate digestion?
Ptyalin (α-amylase) hydrolyzes starch into maltose and other small glucose polymers, initiating the digestion of carbohydrates in the mouth and stomach.
Why is salivary amylase (ptyalin) not effective for long in the stomach?
Salivary amylase is inactivated by the acidic pH in the stomach, and since people don’t chew their food long enough, digestion of carbohydrates by this enzyme is limited.
How are complex carbohydrates further digested after the stomach?
Digesttion continues with the action of pancreatic amylase, which further breaks down starches into simpler sugars.
What role does pancreatic amylase play in carbohydrate digestion in the small intestine?
- Pancreatic amylase, is more potent than salivary amylase.
- Within 30 minutes, it hydrolyzes almost all carbohydrates to maltose
How does pancreatic amylase differ from salivary amylase in carbohydrate digestion?
Pancreatic amylase is more potent than salivary amylase, allowing it to more effectively break down carbohydrates into smaller sugars in the small intestine.
How are monosaccharides absorbed after being formed in the small intestine?
The monosaccharides (galactose, glucose, fructose) are internalized by the absorptive cells in the small intestine and then diffuse out into the capillaries of the intestinal villi for transport into the bloodstream.
What are the typical breakdown products of carbohydrates?
The typical breakdown products of carbohydrates are:
80% glucose
10% galactose
10% fructose
Where does blood from the villi of the small intestine drain, and why is this important?
Blood from the villi drains into the hepatic portal system, which leads directly to the liver. This is important for nutrient processing and regulation before the blood enters general circulation.
Why is it important for blood from the villi to be processed by the liver before entering general circulation?
Blood leaving the villi is rich in nutrients, and if this nutrient load entered general circulation directly, it could increase blood viscosity and potentially have adverse effects on blood pressure.
What is the “first pass effect” in the liver?
As blood passes through the liver after nutrient absorption, a lot of the nutrients are removed and processed from the blood before it enters the general circulation.
steps of the hepatic portal system
- small intestine absorbs products of digestion
- nutrient molecules travel in hepatic portal vein to liver
- liver monitors blood content
- blood enters general circulation by way of hepatic vein
why is glucose considered an essential nutrient
- for energy production by many cells
- serving as the primary fuel source for cellular activities
what happens to glucose in excess of immediate needs
excess glucose can be converted into glycogen, and stores in the liver and muscle for future energy use
How is cholesterol absorbed from food?
Cholesterol is a small molecule that is absorbed from food without being digested.
Where does most blood cholesterol come from?
Most blood cholesterol (85%) is produced by the liver, with only 15% coming from the diet.
how is cholesterol transported in the blood
with lipoproteins
What role does cholesterol play in cells?
- is a major component of cell membranes
- serves as the base substrate for the synthesis of steroid hormones
what are the major lipid groups in our diet
- triglycerides
-phospholipids - sterols
How much fat digestion occurs in the stomach?
A very small amount of fat digestion occurs in the stomach, accounting for less than 10% of total fat digestion.
What enzyme starts the digestion of fats in the stomach?
Lingual lipase, which is swallowed with saliva, begins the digestion of triglycerides in the stomach.
Why is lipid digestion more challenging than protein or carbohydrate digestion?
Lipids are not water-soluble, so the digestive enzymes have difficulty accessing and breaking them down.
What issue does the lack of water solubility cause for lipid digestion?
Because lipids are not water-soluble, enzymes have difficulty reaching and digesting them, making their digestion more complex than that of proteins and carbohydrates.
Why do enzymes have limited access to lipids during digestion?
Enzymes in solution have limited access to insoluble lipid molecules because lipids are not water-soluble, making it difficult for the enzymes to interact with them.
How do bile salts assist in lipid digestion?
Bile salts emulsify lipids by breaking them into small droplets, which greatly enhances the access of lipases to lipid molecules, facilitating their digestion.
Where are lipases found, and where does lipid digestion occur?
Lipases, which digest triglycerides and phospholipids, are only present in pancreatic juices. Therefore, lipid digestion can only occur in the small intestine, specifically after emulsification by bile salts.
What role do the pancreas and gallbladder play in lipid digestion in the small intestine?
The pancreas releases lipases to digest lipids, while the gallbladder releases bile to emulsify the lipids, allowing effective digestion in the small intestine (duodenum).
What is the most important enzyme responsible for digesting triglycerides?
The most important enzyme responsible for digesting triglycerides is pancreatic lipase, which is secreted in large quantities in pancreatic juice.
How efficient is pancreatic lipase in digesting triglycerides?
Pancreatic lipase is highly efficient; within 1 minute, it secretes enough to digest all triglycerides it comes into contact with.
What does pancreatic lipase do to triglycerides?
Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides.
major steps in digestion of lipids:
starts as a triglyceride and pancreatic lipase breaks them down into monoglycerides and fatty acids
steps of chemical digestion of lipids
- emulsification of fat droplets by bile salts
- hydrolysis of triglycerides in emulsified fat droplets into fatty acid and monoglycerides
- dissolving of fatty acids and monoglycerides into micelles to produce “mixed micelles”
What are the products of triglyceride and phospholipid digestion by lipase?
The products of triglyceride and phospholipid digestion are monoglycerides, fatty acids, and glycerol, which diffuse into the absorptive cells.
What happens to the monoglycerides and fatty acids inside absorptive cells?
Inside the absorptive cells, monoglycerides and fatty acids are re-synthesized into triglycerides. These triglyceride droplets leave the cells by exocytosis and enter the lacteals of the villi.
Where do triglyceride droplets go after leaving the absorptive cells?
Triglyceride droplets are transported into the lacteals of the villi, which are part of the lymphatic system.
Where are chylomicrons secreted, and how do they reach the blood?
Chylomicrons are secreted into the central lacteals of the intestinal villi, pass through the lymphatic system, and eventually reach the blood via the thoracic duct (TD).
What happens to chylomicrons in the blood?
In the blood, chylomicrons acquire ApoE protein, which helps them bind to capillaries in target tissues like muscles and adipose tissue.
How are fatty acids released from chylomicrons in target tissues?
Lipoprotein lipase in the target tissues (muscles and adipose tissue) breaks down the triglycerides in chylomicrons, releasing fatty acids for energy use in muscles or fat storage in adipose tissue.
What happens to the depleted chylomicron after it releases fatty acids?
After triglycerides are broken down, the depleted chylomicron returns to circulation and is eventually transported back to the liver.
What happens during protein digestion?
Proteases breaks proteins into large polypeptides
steps of chemical digestion of proteins
- proteases break down proteins into large polypeptides
- large polypeptides are broken down into small polypeptides and peptides by peptidases
- these are then broken down into amino acids by brush border enzymes
What is pepsin and where does it function and what pH does it function at?
Pepsin is an important protein enzyme in the stomach that functions effectively at a pH of 2.0-3.0 and is inhibited at pH > 5.0.
What unique role does pepsin play in digestion?
Pepsin is one of the only enzymes capable of digesting collagen, a key component of connective tissue found in meats.
Why is collagen breakdown necessary for meat digestion?
For meat digestion to occur, collagen must first be broken down by pepsin, as it is a major component of the connective tissue in meat.
What enzymes are found in pancreatic secretions for protein digestion?
- trypsin
- chymotrypsin
- carboxypeptidase
- proelastase
What stimulates the release of pancreatic proteolytic enzymes?
Partial breakdown products from the stomach stimulate the release of pancreatic proteolytic enzymes
What types of peptidases are found in enterocytes of the small intestine?
Enterocytes contain endopeptidases (like trypsin) that cleave internal bonds and exopeptidases that cleave amino acids from the ends of peptides.
How are di- and tri-peptides further digested in the small intestine?
Di- and tri-peptides are digested by enterocytes into single amino acids, completing the protein digestion process.
After the proteins are digested and hydrolyzed to AA, where do the AA go?
The AA can now enter the bloodstream
How are amino acids transported into absorptive cells?
By transport proteins through carrier-mediated transport.
What happens to peptides and amino acids in the absorptive cells?
Peptides are digested by brush border peptidases, and the resulting amino acids are transported into the absorptive cells by a transporter associated with the enzyme.
How are amino acids transported from absorptive cells to the bloodstream?
Transport proteins carry the amino acids out of the absorptive cells and into the capillaries of the villi, where they enter the bloodstream.
where and how does vitamin absorption mainly take place
by the passive process of diffusion in the jejunum and the ileum
How do water-soluble vitamins (like B1, B2, B3, B6, etc.) enter the bloodstream?
Most water-soluble vitamins diffuse directly into the blood, except for vitamin B12, which requires intrinsic factor for absorption.
How is vitamin B12 absorbed in the intestine?
Vitamin B12 combines with intrinsic factor produced by the stomach, and this complex is absorbed in the intestine via endocytosis.
What happens to excess water-soluble vitamins in the body?
Excess water-soluble vitamins pass into the urine when their concentration in plasma exceeds the renal capacity for reabsorption.
