GI secretions and non-fermentative digestion Flashcards
what are the 4 major salivary glands
- parotid salivary gland
- mandibular salivary gland
- sublingual salivary gland
- zygomatic salivary gland
what is mumps
- highly contagious viral infection
- fever, swelling, swelling of salivary gland
- not life threatening
- zoonotic
salivary mucocele
- collection of saliva that has leaked from a damaged salivary gland or salivary duct and accumulated in the tissues
- common in dogs
what are the types of saliva
- serous (parotid)
- mucus (buccal)
- both (mandibular and sublingual)
what is the composition of saliva
mucins, water, electrolytes
what is unique about ruminant saliva
high amounts of HCO3 (bicarbonate)
hypotonic saliva
- non-ruminants
- less electrolyte compared to blood
isotonic saliva
- ruminants
- osomotic pressure/electrolytes is similar to blood/plasma
what enzyme digests starch
alpha-amylase
what enzyme digests fat
lingual lipase and present in all species
what enzyme is associated with lysozymes
antimicrobial enzymes
what are the functions of saliva
- moisten and lubricate food
- antimicrobial activity (oral hygiene)
- evaporative cooling - cat and dog
- buffering forestomach digestion in ruminants
- partial digestion of starch/fat
what is important about salivary ducts
- anatomy same to glomerulus and collecting ducts in kidney
- ion transporters
- respond to aldosterone (Na conc.)
what does electrolytes in saliva depend on
flow rate
what is the parasympathetic regulation of salivary secretion
- primary mode
- pavlov’s dog - conditioned reflex
- cholinergic receptors
- atropine suppresses salivary secretion
what is sympathetic regulation of salivary secretion
- B-adrenergic receptors
- salivation and drooling in carnivores preparing to attack
what are the two functionally separate secretions of the pancreas
- exocrine - digestion
- endocrine - insulin
what does the acinar secrete
- lipase (active)
- amylase (active)
- zymogens (inactive)
what does the duct cells secrete
HCO3
what does enterokinase do to trypsinogen
cleave it into trypsin
what does trypsin activate
trypsinogen
where are the inactive enzymes
pancreas
where are the active enzymes and what are they and what did they get activates by
- SI (duodenum)
- chymotryspin
- elastase
- carboxypeptidase A
- carboxypeptidase B
- trypsin
where is enterokinase located and released
- located on brush border of duodenal enterocytes
- released from brush border by bile salts
what is enterokinase stimulated by
trypsinogen
what is enterokinase
- 41% carb
- protease
what does premature activation of the pancreatic enzymes in the pancrease cause
acute pancreatitis
what is a risk factor for acute pancreatitis
big fat meals
what are the three phases of pancreatic secretion
- cephalic
- gastric
- intestinal
what is the cephalic phase
vagal stimulation (sight and smell of food)
what is the gastric phase
vagovagal reflex (stomach distention)
what is the intestinal phase
- intestinal distension (Ach)
- chemical stimulation (CCK, secretin)
what stimulates CCK secretion
fat and protein
what stimulates secretin secretion
H+
what do acinar, centroacinar and duct cells have receptors for
CCK, Secretin, and Ach
what is the function of secretin
increases production of HCO3
what do sinusoids contain
blood cells
what is in bile
- bile salts
- phospholipids and chlosterol
- electrolytes (HCO3-)
what is the pharmacologic importance of bile
- bile pigments (bilirubin) - jaundice
- metabolites of drugs and toxins
what does jaundice indicate
liver diseases
cholesterol is a ____ molecule
hydrophobic
cholic acid is a ____ molecule
amphiphilic
bile is stored and concentrated in ____
gallbladder
what are the two functions of CCK
gallbladder
- contracts the gallbladder
- CCK relaxes sphincter of Oddi
CCK from duodenum to blood stream in response to ____ and ____
fat; protein
what is the function of the gallbladder in dogs and cats
- bile is stored in gallbladder and modified
- CCK contracts gallbladder and relaxes the sphincter of Oddi
what is the function of the gallbladder in ruminants and pigs
- sphincter of Oddi poorly defined
- continuous secretion of bile
what is the function of the gallbladder in horses and rats
- no gallbladder
- continuous secretion
how is bile released
- initiated by the presence of food in the duodenum
- CCK
how is bile synthesized
- recirculation of bile from intestine
- de novo synthesis of bile salts from cholesterol
how is bile modified
- effects of secretin on HCO3-
- water
what are the functions of biliary secretion
- provides a source of bile acids for fat digestion and absorption and absorption of fat-soluble vitamins
- provides an excretory route for metabolites and drugs
- provides additional buffer (HCO3-) to neutralize H+ in the duodenum
enterohepatic circulation of bile salts
- re-absorption of ~94% of bile salts
- absorption occurs in distal ileum
- re-absorption from hepatic portal blood
- re-secretion into bile by hepatocytes
secretion of bile salts by hepatocytes is proportional to what
hepatic portal vein concentration of bile salts
what are the physical actions of digestion
- mastication
- grinding in the distal stomach
what are the purposes of physical actions of digestion
- physical reduction of food particle size
- increased surface area of food particles
what is chemical digestion
- hydrolysis
- splitting chemical bonds
what are the three chemical bonds that are broken
chemical digestion
- glycosidic linkages
- peptide bonds
- ester bonds
what are the two phases of chemical digestion
luminal and membranous
what is the luminal phase of chemical digestion
- enzymes active in lumen of gut
- large polymers (starch and protein)
what happens in the membranous phase of chemical digestion
- enzymes active at surface of gut
- small polymers digested to monomeric molecules suitable for absorption
where are the digestive enzymes from in the luminal phase
salivary, gastric, and pancreatic glands
where are the digestive enzymes from in the membranous phase
enterocytes (SI)
what occurs during carb digestion
- luminal digestion (starch)
- brush border oligosaccharidases
- only monomers are absorbed
what kind of bonds do amylase break
1-4 glycosidic
what happens in protein digestion
- luminal digestion
- brush border peptidases
- intracellular peptidases
- absorbed as small peptides and amino acids
what are the two groups of enzymes of protein digestion
endpeptidases and exopeptidases
how is the zymogen - chymotrypsiogen turned into chymotrupsin (active)
by trypsin
process of lipid assimilation
- emulsification
- luminal lipolysis
- micelle formation
- absorption of fatty acids
- formation of chylomicrons
- chylomicrons enter lymphatics
- lipid-soluble vitamins
what are dietary lipids
- triglyceride
- cholesterol ester
- phospholipids
lipase
- secreted in active form
- inhibited by bile acids
co-lipase
- secreted as pro-colipase
- activated by bile acids
- binds to lipase and bile acids
lipase/co-lipase are in a what ratio
1:1
how are absorbed lipids packaged
into chylomicrons
what is a micelle
bile-coated, emulsified fat droplet
where do chylomicrons enter
extracellular space and then into the lymphatics
what does a fatty meal occur in
chylomicrons
lipemia (chylomicronemia)
- lymphatics turn milky white
describe lipid absorption
- absorbed through the apical membrane by carrier proteins and simple diffusion in the jejunum
- absorbed lipids are re-esterified and re-packaged into chylomicrons in the enterocyte
- chylomicrons enter lymphatics
- bile acids are re-absorbed in the ileum by a sodium co-transport system
what are the 3 benefits of digestion
- nutritional
- toxicologic - breakdown of toxic proteins
- allergic - breakdown of allergenic proteins
how are proteins absorbed in the neonate
- proteins are not digested but absorbed intact
- in most livestock, no antibodies are passed from dam to fetus
- antibodies are acquired through colostum
what are there delays in, in protein absorption in the neonate
- delay in acid secretion from stomach
- delay in pancreatic function
what is present at birth
protein absorption
specialized intestinal epithelium
* special enterocytes engulf soluble proteins
* lost after 24 hrs
what receptor is on the enterocyte in neonates to take in Ig
Fc receptor and Ig is absorbed by pinocytosis
what is the major dietary carb for neonate
lactose from milk
what does lactase switch to with maturity
maltase
what is malassimilation and what is it caused by
- weight loss and diarrhea
- maldigestion and malabsorption
