Histo exam 4

Rumination time: what type of diet would cause an increase in rumination time? ____________ also influences the amount of rumination time

- less hours spent per day for high grain diets - more hours spent per day for high forage diets Feed intake level also influences the amount of rumination time - high intake stimulates greater rumination

List the requirements that must be met by the cow for normal fermentation to occur

- production of copious amounts of saliva - microbes- rate of removal of microbes must be compatible with regeneration times of the most favorable microbes - substrate for fermentation must be supplies - temperature must be maintained at or near 37 c - moisture - ionic strength of the rumen fluid must be kept within an optimal range - negative oxidation-reduction potential must be maintained - acid products of anaerobic fermentation must be buffered or absorbed - normal motility patterns of the reticulorumen - indigestable waste must be removed

GI blood flows through two capillary beds. List the two capillary beds. Is arterial hydrostatic pressure high or low in each capillary bed?

1. Blood capillaries in the lamina propria of small intestinal villi - arterial hydrostatic pressure is high- majority of tissues - forces fluid through the capillary beds into interstitial fluid 2. Sinusoidal capillaries of liver - arterial hydrostatic pressure is low - comparatively large and offer little resistance to blood flow

Describe the two sources of hepatic urea production

1. Nitrogen arising from the deamination of endogenous amino acids (occurs in liver) and converted to urea 2. Nitrogen absorbed as NH3 from the rumen - NH3 absorption from the rumen is proportional to the NH3 production rate in the rumen, which is subject to the influences of carbs and protein availability in the rumen - NH3 is toxic at moderate concentrations, is absorbed from the rumen and delivered to the liver through the hepatic portal blood vascular system - liver extracts NH3 from the portal blood efficiently; thus little of the potentially toxic NH3 reaches the systemic circulation

How do the physical characteristics of feed impact digestability?

Feed does not leave the rumen until it is broken down into small particles by microbes and remastication - rate of breakdown of fiber is based on digestability - poorly digestible fiber takes longer to be broken down sufficiently There are fixed limits to volume of rumen so rate of feed intake cannot exceed rate of ingeta outflow - Chopping or grinding of poorly digestible forages increases the rate of passage from the rumen because particle size reduction is necessary before pieces can pass into the omasum

Where are water and electrolytes absorbed? Where are the water and electrolytes reabsorbed? Why is absorption/reabsorption of water important? Why is absorption/reabsorption of electrolytes important?

Absorbed in the small and large intestine Reabsorbed in the kidneys Absorption/reabsorption of water- maintain normal blood volume and mean arterial pressure Absorption/reabsorption of electrolytes- vital for various physiological functions

Almost all ________ and ________ are subject to _____________ digestion. What do CHOs and proteins provide for the microbes?

CHOs and proteins, fermentative Provides substrates for energy and growth of microbes When CHO enters the rumen or cecum/large colon, hydrolytic microbial enzymes are activated

Foregut fermentation compartment name?

Cranial to the stomach - foregut fermentation occurs inside the rumen - cows, sheep, goats, giraffes

Describe the small intestine secretion pathway for electrolytes and water

Electrolytes and water from blood capillaries- lateral space into the basolateral membrane- enterocyte- lumen of small intestine Crypt cells of small intestine- (electrolytes) Secrete Cl with coupled Na/Cl transport mechanism on basolateral membrane - Na is quickly pumped out via Na/K ATPase pump - Cl is trapped and accumulates until Cl channels in apical membrane open and flows down the concentration gradient into the lumen of crypt - electrical attraction of Na created by Cl movement allows Na to flow from the lateral spaces in a paracellular route which water follows Na, Cl, and water are secreted from the crypt

Name the four phases of lipid digestion and absorption

Emulsification Hydrolysis Micelle formation Absorption

List the precursor, source, and activator for pepsin. Endopeptidase or Exopeptidase?

Endopeptidase Source- gastric glands Precursor- Pepsinogen Activator- Hydrochloric acid, pepsin

How do endopeptidases work? How do exopeptidases work?

Endopeptidase- Majority of proteolytic enzymes Break proteins at internal points along the amino acid chains Resulting in the production of short chain peptides from complex proteins Exopeptidase- release individual amino acids from ends of peptide chains

Describe what happens to MCP when glucose and peptide availability are well matched

Energy for cellular growth comes primarily from glucose, with peptides directed toward microbial protein synthesis Under these conditions, the products favor microbial protein synthesis, with little NH3 production

What is the function of the small intestine crypt cells?

Ensures the continual availability of water and Na in the gut lumen

Trypsinogen from the pancreas is activated by ________? Where is this enzyme produced?

Enterokinase Produced in duodenal mucosal cells

Phase 3- Micelle formation _________ and _______ combine with bile acid and phospholipids to form ________. What are micelles? All components of the micelle diffuse into the enterocytes except _______ Soluble micelles allow the lipids to ________ into the unstirred water layer and into close contact with the absorptive surface of the apical enterocyte membrane The majority of bile acids are recycled via _________ circulation. Briefly describe this type of circulation

Fatty acids and monoglycerides --- to form micelles Micelles- small water soluble aggregations of bile acids and lipids All components of the micelle diffuse except bile acids Diffuse through gut lumen Enterohepatic circulation- bile acids extracted by the liver are recycled into the bile -- liver extracts bile acids from portal blood so concentration of bile acids in the systemic circulation is minimal

Describe the microscopic anatomy of the rumen where VFA absorption occurs

Forestomach epithelium supplies such a system, absorbing a large portion of the VFAs - this absorptive process helps maintain rumen pH by removing acid from the forestomach ingesta and contributing bicarbonate in the process Cells of the stratum corneum/granulosum are tightly joined by tight junctions that may functionally resemble the tight junctions of the enterocytes - deeper in the epithelium, the cells of the stratum spinosum and stratum basale are separated by intercellular spaces that increase in size as the basement membrane is approached - these intercellular spaces are similar to the lateral spaces of small intestinal simple columnar absorptive epithelia look at slide

Is lignin (dietary fiber) digestable or indigestable?

Indigestable- resistant to the action of either mammalian or microbial enzymes

Protozoa are beneficial in the rumen because of the ingestion of? Why are protozoa beneficial in the rumen?

Ingestion of: - large numbers of bacteria to maintain bacterial numbers - smaller protozoa - particles of starch and protein Beneficial- - slows the digestion of rapidly fermentable substrates - protects from bacterial action

The microbial growth rate depends on the supply of nutrients and the rate at which microbes are washed from the rumen. The overall reaction in the rumen can be evaluated using what equation? Understand what the variables in the equation represent

Microbes require energy and nitrogen for growth and maintenance Energy is derived from either glucose or peptide Nitrogen is derived only from peptide Glucose + peptide = MCP + VFA + NH3 + CH4 + CO2 MCP= microbial crude protein; nitrogen containing product NH3= ammonia; nitrogen containing product VFAs, CH4, and CO2 are microbial cell products from glucose and peptide

Appreciate the microscopic anatomy of the colon (digestive histology lab iii). What are the functions of the colon?

Microbiome provides overall wealth Production of vitamins Fermentation of organic matter that escapes digestion and absorption in the small intestine Bile acids are reabsorbed via enterohepatic circulation, primary bile acids serve as substrates for bacterial biotransformation to secondary bile acids in the colon Absorption of water, vitamins, and electrolytes Storage of feces Defecation

Define probiotic

Microorganisms (usually bacteria) that are consumed for their health benefits Some probiotic produced marketed for cats and dogs may temporality improve diarrhea, but the bacteria they contain cant rebalance a disrupted microbiome

What are the functions of the liver?

Modifies nutrient rich blood Detoxifies (NH3----> urea) - measured a BUN Regulates nutrient concentration of blood reaching tissues

Briefly describe the steps of secondary (eructation) contractions

Occur in association with every second or third set of primary contractions Cranial moving wave that starts in the caudal ventral blind sac and continues over the dorsal blind sac Function- move gas toward the cranial portion of the rumen - begins with contraction of caudoventral blind sac to express trapped gas into dorsal sac while cranial sac relaxes and cranial pillar elevates allowing for liquid ingesta to move away from cardia so gas can enter esophagus and be eructated Forward moving contraction of dorsal sac moves gas towards cardia

Describe the membranous phase of protein digestion

Occurs due to action of hydrolytic enzymes Membranous phase enzymes are synthesized within the enterocyte and chemically bound to the surface epithelium Large and important part of the glycocalyx Substrates for these enzymes must diffuse into the glycocalyx before hydrolysis can occur Peptide digesting enzymes (peptidases) are present on the enterocyte surface membrane and extend into the glycocalyx and inside the enterocyte - peptidases hydrolyze oligopeptides yielding free amino acids - some of the longer chain peptides are incompletely digested, yielding dipeptides and tripeptides Dipeptides and tripeptides that are absorbed intact are subsequently hydrolyzed by the action of intracellular peptidases Results in the formation of free amino acids that are available for absorption into the blood

Starling's law- name the two pressures responsible for water movement

Oncotic and hydrostatic pressure Starlings law - determines distribution of water between the intravascular and extravascular fluid - Oncotic pressure and hydrostatic pressure

Define oncotic (osmotic) pressure

Osmotic force exerted by plasma proteins that draw water into the capillary lumen

Define prebiotic

Sources of dietary fiber that provide food for beneficial gut bacteria

Water absorption in small intestine and large intestine occurs via ......

Starlings law and villous vascular system

Describe VFA absorption from the rumen to the blood capillaries located in the lamina propria a. Vacuolated, keratinized cells of the stratified squamous epithelium of a papilla b. Where do VFAs come from? c. What happens if VFAs are allowed to accumulate? d. Why are VFAs important for the cow?

a- Do not appear to retain adequate metabolic machinery but are metabolically active b- bacterial waste produce c- suppression of fermentation-- lowers rumen pH d- provides 60-80% of the dietary energy

In normal conditions, ruminal microbes are ________ with a markedly ________ redox potential, reflecting the absence of _______

anaerobic, negative, oxygen

All cell wall molecules that are carbohydrate will be digested with _____ (hydrolytic enzymes) produced by the ___________. Cellulases release ________ and ____________ from the complex CHOs of cell walls. Released saccharides are ________ available for absorption by the animal and are metabolized by ______

cellulases produced by microbes monosaccharides and oligosaccharides not directly metabolized by microbes

Fermentative digestion occurs in specialized compartments positioned either ______ or ________ to the stomach and small intestine

cranial or caudal

A balanced microbial ecosystem is crucial for host health and homeostasis. Changes in the gut-microbiome are associated with _________. List the symptoms that can occur if there is an imbalanced microbiome

diseases Symptoms: Inflammation Obesity Metabolic syndromes Mood disorders Digestion Host metabolism Vitamin synthesis Biotransformation of bile acids Correct maturation of gastrointestinal cells

Define hydrostatic pressure

force exerted by fluid pressing against wall Forces water directly into capillaries

Water moves in direction necessary to keep ingesta ______

iso-osmotic

Briefly describe the steps of rumination Step 1- regurgitation Step 2- remastication (cud chewing)

1- occurs just before initiation of a primary rumen contraction - When it occurs, there is an extra contraction of the reticulum just before the regular biphasic reticular contraction - Simultaneous with the extra reticular contraction, the cardia relaxes, and there is an inspiratory excursion of the ribs with the glottis closed creating a negative pressure within the thorax favoring the movement of ingesta into the esophagus - When ingesta enter the esophagus, a reverse peristaltic wave propels the material cranially into the oral cavity - excess water is expressed by tongue and water is swallowed MATERIAL ORIGINATE FROM DORSAL PORTION OF RETICULUM AND ARE NOT THE COARSEST MATERIAL IN RUMEN Partially fermented material is then subjected to remastication - duration depends on character of diet- coarse materials will require more time than finely ground or highly digestible feeds - increasing surface area - exposing additional fermentable substrates not exposed to previous microbial action and assists with particle separation process - small particles will be re-swallowed and sink into reticulum for passage to omasum - large particles, when reswallowed, are ejected back into cranial portions of rumen

Three primary alterations of the neonatal digestion

1. Acid secretion from the stomach is delayed for several days after birth 2. Trypsinogen secretion from pancreas is delayed - acid and trypsin digestion of proteins is avoided 3. A specialized intestinal epithelium present at birth only is capable of engulfing soluble proteins in the intestinal lumen and discharging them into the lateral spaces The fetal intestinal epithelium has the same villous structure as the mature epithelium, but the villi are covered with enterocytes capable of protein absorption

Water absorption begins at the top of the villus at ______ mOsm. The osmolarity increases or decreases as more water is absorbed along the venous side of the capillary bed toward the venule

600 decreases

Describe how microbial crude protein (MCP) can be synthesized in the rumen from nonprotein nitrogen (NPN) sources

A- Absorbed peptides contribute to an intracellular pool of amino acids from which microbial proteins are synthesized B- Amino acids are also produced from intracellular synthesis using NH3 and VFAs C- Several types of bacteria do not have proteases for an amino acid source and are dependent on an extracellular source of NH3 for amino acid synthesis D- Amino acids not used for protein synthesis can be metabolized to NH3 and VFA

Pathophysiology of diarrhea a- Define diarrhea b- Define malabsorptive diarrhea c- Define hypersecretory diarrhea d- What type of acid-base imbalance would you expect in a dog with chronic diarrhea?

Amount of water in the feces is a balance between ingestion, secretion, and absorption Diarrhea- increase in frequency of defecation and increase in fecal water volume Malabsorptive diarrhea- occurs when absorption is inadequate to recover enough secreted water due to loss of GI epithelium, results in villus length, short villi will impair absorption of electrolytes Hypersecretory diarrhea- occurs when the rate of intestinal secretion increases and overwhelms the absorptive capacity Most causes of this result from inappropriate secretion from the small intestinal crypts Crypt epithelium is abnormally stimulated Metabolic acidosis due to loss of HCO3 in diarrhea

Describe what happens to MCP when the availability of glucose > peptide

Ample energy available to the microbes, but insufficient peptide to support rapid microbial protein synthesis Microbial energy utilization becomes inefficient as energy is used for the maintenance of nondividing cells rather than for the energy requiring processes of growing cells Maintenance energy needs of the microbes still drive some fermentation of glucose with moderate VFA production, but production of microbial cells is limited because of lack of N

Describe what happens to MCP when peptide > glucose

Ample peptide potentially to support rapid microbial protein synthesis and growth Growth potential cannot be achieved because of insufficient energy supplies Conditions force the microbes to use peptides to meet energy needs instead of for protein synthesis Microbial growth rate is slow and VFA production is moderate

165 rRNA gene sequencing demonstrates > 90% of bacteria belong to which two phyla?

Bacteroidetes, firmicutes

Where does luminal phase protein digestion begin?

Begins in the stomach

Where is a normal pressure gradient required for normal GI blood flow? Describe the HVPG (hepatic venous pressure gradient). How does right side heart failure and diffuse liver disease cause ascites (increased fluid accumulation in the abdomen)?

Between the caudal vena cava and the hepatic portal vein for normal GI blood flow HVPG - 3-6 mm Hg (small pressure gradient)- offsets the osmotic and hydrostatic forces, therefore inhibiting water absorption in the small intestine Right side heart failure - pumping capacity of the heart becomes reduced, unable to remove returning venous blood - accumulation of blood, increases blood volume which directly increases thoracic vena cava pressure - increase in pressure interferes with blood flow out of the liver, which reduces blood flow out of the intestines Diffuse liver disease - interferes with GI blood flow - increased sinusoidal capillary pressure - increased resistance to hepatic blood flow - slight increases in hepatic blood flow resistance have large effects on small intestinal blood flow

Which VFAs stimulate papillary growth?

Butyrate and propionate Diets with high digestibility result in high rumen VFA concentrations, which stimulate the growth of long papillae

Hindgut fermentation compartment names?

Caudal to stomach - hindgut fermentation occurs inside the cecum and large colon - horses, zebras, rhinos, donkeys

Where is the largest portion of the gut microbiome located?

Colon or large intestine

What is a protein made of? List the proteolytic enzymes. What are proteolytic enzymes required for?

Combo of up to 20 individual types of AA Various proteolytic enzymes are necessary for protein digestion Differ in efficiency in cleaving peptide bonds between specific types of AA Types- Endopeptidases Pepsin Chymosin Trypsin Chymotrypsin Elastase Exopeptidases Carboxypeptidase A Carboxypeptidase B

Where is luminal phase protein digestion completed?

Completed in the duodenum by the action of pancreatic enzymes

The villous vascular system arrangement provides direct ________ blood flow. This type of blood flow describes blood traveling _________ the __________ side of the capillary and blood traveling __________ the __________ side of the capillary

Consists of an arteriole extending up the central portion of the villi and dividing into many capillaries countercurrent up arterial down venous

What does the venous side of the capillary bed contain?

Contains absorbed nutrients

Why is digestion so slow?

Due to breaking down complex structures and organization of natural plant fibers

Describe how colonocyte metabolism functions as a control switch, mediating a shift between homeostatic and dysbiotic microbial communities

During homeostasis, colonocyte metabolism is directed towards oxidative phosphorylation, resulting in high epithelial oxygen consumption - epithelial hypoxia helps maintain microbial community dominated by obligate anaerobic bacteria Dysbiotic- increases in epithelial oxygenation causing expansion of facultative anaerobic bacteria

Draw and name the four zones in the rumen. What type of material is in each zone? What happens with particle density (specific gravity) from dorsal to ventral?

Gas zone - VFA, CO2, and CH4 Solid zone- fiber mat Slurry zone - medium density Liquid zone - high density Density increases from dorsal to ventral

____________ enters a glycolytic pathway to produce VFAs (volatile fatty acids). VFAs provide _______% energy for herbivores

Glucose 70%

The gut microbiome contributes to overall _______ and __________

Health and wellness Production of vitamins Fermentation of organic matter that escapes digestion and absorption in the small intestine Bile acids are reabsorbed via enterohepatic circulation, primary bile acids serve as substrates for bacterial biotransformation to secondary bile acids in the colon Absorption of water, vitamins, and electrolytes Storage of feces (rectum) Defecation

Where is vitamin K produced? What is vitamin K required for in the blood?

Large intestine Important for clotting factors

Phase 2- Hydrolysis Pancreatic lipase and colipase __________ cannot penetrate the coat of bile products surrounding the emulsified lipid droplets. _________ clears a path through the bile products, giving lipase access to the underlying triglycerides

Lipase cannot penetrate the coat Colipase clears a path Lipase cleaves the fatty acids off each of the triglyceride molecule but does not cleave the central fatty acid

Gut closure

Loss of the protein absorptive function in the neonate Lactose from milk is the major carbohydrate in the diets of neonatal and young mammals - all mammals are born with high intestinal lactase activity Maltase activity is necessary for digesting the products of luminal starch digestion- weak or absent for several weeks after both As animal progresses toward weaning, lactase activity wanes and maltase activity increases, allowing the animals to shift from lactose to starch as a CHO source Many species of adult animals - lactase activity is nonexistent - cartoons frequently feature kittens and cats drinking milk

Majority of GI disorders involved the loss of ______ and ______

Loss of water and electrolytes

Describe the absorption pathway for nutrients, water, and electrolytes

Lumen of small intestine- CHO3, glucose, galactose, fructose Proteins- amino acids Electrolytes Water -------> Brush border Simple columnar epithelial cell ---------> Enterocytes ---------> Basolateral membrane into the lateral space ------> Venous side of blood capillary within lamina propria -------> hepatic portal vein

Describe neonatal digestion

Major function of digestion is to break down proteins by hydrolysis Neonates- absorb whole proteins through their enterocytes without breaking them up No antibodies are passed through the placenta from the dam to the fetus - antibodies must be acquired through ingestion of colostrum 3 primary alterations are present in neonates; 1. Acid secretion from the stomach is delayed for several days after birth 2. Trypsinogen secretion from the pancreas is delayed -- acid and trypsin digestion of proteins is therefore avoided 3. A specialized intestinal epithelium is present at birth that is capable of engulfing soluble proteins in the intestinal lumen and discharging them into the lateral spaces for absorption by the body - the fetus has the same villous structure as mature epithelium- but it is covered with these modified epithelial cells - these epithelial cells disappear about a day after birth (gut closing)

Why is a negative redox potential important?

Major impact on the microbes influencing digestion, absorption, and metabolism of nutrients

Describe small intestinal absorption. Why are active transport mechanisms needed?

Movement of the digested products across enterocyte epithelium------ enterocyte----lateral space---- blood Molecules move across membrane barriers in response to chemical and electrical gradients When molecules can freely penetrate a membrane - movement across is determined by diffusion and differences in chemical and electrical gradients - molecules flow from areas of high to areas of lower concentration - charged particles move to areas of opposite charge Charged ions and most organic nutrient molecules cannot pass through the GI epithelium and are absorbed into the enterocyte through diffusion and transport proteins 1. there are three active transport protein mechanisms for absorption 2. there are two passive transport mechanisms for absorption

Describe the NPN sources that are used for microbial protein production

NH3- if sufficient glucose is available, most rumen microbes, even those capable of utilizing performed peptides, can synthesize microbial protein from NH3 Nitrates Urea - NH3--- urea occurs in the liver - nitrogenous waste of protein catabolism (end product of N metabolism)

Briefly describe how are VFAs absorbed

Sodium-hydrogen ion exchange by epithelial cells decreases local pH at absorptive surface Drop in pH leads to shift in VFAs form normal ionic form to free acid state Cell membranes are permeable to VFA free acids and absorption proceeds due to concentration gradient between lumen and cells When one VFA molecule is absorbed, one molecule of bicarb is generated in lumen; so VFA absorption helps buffer rumen pH

Describe the properties and functions of ruminant saliva

Parotid, mandibular, and sublingual salivary glands Isotonic, bicarbonate-phosphate buffer secreted in large quantities Alkaline pH is a well buffered solution necessary for neutralizing acids formed by fermentation in the rumen Majority of water and electrolytes secreted in saliva must be absorbed rapidly in the rumen and recirculated through the total body water Clinical correlation- esophageal blockage Flow of saliva is diverted from the GI tract, cow quickly becomes dehydrated and acidotic

Why is Cl important ? Describe the three mechanisms of Cl absorption

Required for 1. ECF and ICF balance Water follows Cl absorption 2. Maintains the ionic balance between the plasma and erythrocytes - internal respiration- conversion of CO2 to HCO3 with Cl shift - external respiration- conversion of HCO3 to CO2 with reverse shift CO2 to HCO3 and the related Cl shift maintains the ionic balance between plasma and erythrocytes Three mechanisms 1. Paracellular Cl absorption Cl from the gut lumen passes directly into the lateral spaces through the tight junctions 2. Coupled Na/Cl absorption Net movement of Cl and Na across the apical membrane 3. HCO3 dependent Cl absorption Net movement of HCO3 into the gut lumen, increasing luminal pH

What are electrolytes? List the electrolytes. Where are electrolytes located? What is the term used to describe an increase or decrease for each electrolyte? What type of blood test would you order to test (electrolytes)?

Positive or negative ions dissolved in solution - Na sodium - Cl chloride - HCO3 bicarbonate - K potassium Location- extracellular fluid --- interstitial fluid and blood intracellular fluid Iv fluid bags Na sodium - hypo and hypernatremia Cl chloride - hypo and hyperchloremia HCO3 bicarb - acidosis or alkalosis- metabolic K potassium - hypo and hyperkalemia Blood test- chemistry panel

Describe the two patterns of reticulorumen motility

Primary (mixing) contractions Secondary (eructation) contractions

List the three VFAs (dissociated ions)

Primary VFAs - acetic acid - propionic acid - butyric acid VFAs are often referred to as their dissociated ions - acetate - propionate - butyrate

Describe the following transport mechanisms: Active transport, secondary active transport, tertiary active transport, and passive transport

Primary active- Na-K-ATPase pump Two K in and 3 Na out Secondary active transport- Na/glucose exchanger-symport Na/H exchanger- antiport Na-K-ATPase pump establishes the gradient that drives the symport or antiport exchanger (secondary) Two Na enter for every glucose entering the cell Tertiary active transport- CL/HCO3 exchanger NA-K-ATPase pump (primary) establishes the gradient that drives the Na-H exchanger (secondary) Na/H exchanger establishes the gradient that drives the Cl/HCO3 exchanger Passive transport Transcellular and paracellular absorption Ion channels in apical membrane Tight junctions between enterocytes Transcellular- absorption through the apical membrane using ion channels Ion channels are proteins within enterocyte apical membrane No metabolic energy is directly required to effect ion movement Paracellular- Absorption through the tight junctions between enterocytes

Why is Na important? What effect will hyponatremia have on heart rate and skeletal muscles? Describe the three mechanisms of Na absorption

Required for 1. depolarization phase of action potential required for cardiac and skeletal muscle contraction - hyponatremia- heart rate and skeletal muscles ECF and ICF fluid balance 2. ECF (ISF and blood) and ICF fluid balance --- bradycardia ---- skeletal muscle cramping Three mechanisms of Na absorption 1. sodium cotransport proteins Secondary active transport pathway 2. Na/H antiport exchanger Intracellular H is exchanged for luminal Na across the apical membrane Most active in ileum and colon 3. Simple diffusion Na channels in apical membrane Smallest impact on Na homeostasis

Phase 1- Define emulsification. Where and how is the emulsification phase completed? __________ the surface tension of the lipids and allows the droplets to become even further divided and reduced in size. This _________ the surface area for action of lipase, colipase, and bile acids for fat digestion

Process of reducing lipid droplets to a size that form stable suspensions in water - breaking complex fat into smaller fat molecules so its easier for enzymes to break down The stomach starts the emulsification phase and the small intestine completes it 1. Stomach: lipids are warmed to body temperature and subjected to the intense mixing and sieving actions of the body/pyloric antrum 2. Small intestine: detergent action of bile acids from the liver Reduces the surface tension of the lipids and allows the droplets to become even further divided and reduced in size Increasing surface area for action of lipase, colipase, and bile acids

What do the Redox conditions in the digestive tract of animals determine?

Redox conditions in the digestive tract of animals determine whether aerobic oxidation or anaerobic fermentation of nutrients will occur Redox Eh= redox potential Anaerobic fermentation is preferred--- without oxygen

Define rumination

Remastication or chewing cud occurs when the animal is not actively eating - during times of rest, but not during sleep

Why is HCO3 important? How is HCO3 measured? How is TCO2 calculated? Describe the mechanism of HCO3 absorption

Required for 1. Acid-base balance and normal blood pH HCO3 partially absorbed by neutralization of HCl from the stomach but remains in the intestine after neutralization of stomach acid Measured on chemistry panel as HCO3 and TCO2 TCO2 is an indicator of HCO3 slightly overestimates value due to included dissolved CO2 - calculated value from the pCO2 and HCO3 H and HCO3 are produced within the enterocytes from water and CO using carbonic anhydrase- H is then exchanged for Na across the apical membrane using Na H antiport

Why is K important? What effect will hyperkalemia have on heart rate and skeletal muscles? Why is a bright orange sticker used when K is added to the IV fluid bag? Describe the two mechanisms of K absorption

Required for repolarization phase of action potentials causing cardiac and skeletal muscle relaxation Hyperkalemia due to chronic renal failure. Effect on heart rate and skeletal muscle - bradycardia - skeletal muscle weakness BRIGHT ORANGE STICKER WHEN K ADDED TO BAG - used to communicate to others that K has been added Mechanisms - Paracellular passive diffusion Primary mechanism of K absorption Movement of H2O out of the intestinal lumen results in increase in the luminal K concentration-- K absorption - H, K, ATPase pump exists in the caudal portion of the colon Transport pathway recovers remaining K from colonic ingesta of animals with diets low in K

Briefly describe Nitrogen recycling in ruminants

Ruminants - urea is secreted from kidneys and salivary glands - NH3 is absorbed in the rumen--- urea in the liver--- secreted into blood Urea can diffuse into rumen from rumen blood capillaries into rumen epitheium and then rumen lumen; urea will be quickly transformed to NH3 Urea diffuses into salivary glands from blood capillaries into salivary gland epithelium and then secreted into saliva

Where are the major mechanisms of electrolyte absorption located in the GI tract? a- Sodium cotransport? b- Bicarbonate absorption?

Sodium cotransport - duodenum and upper jejunum Bicarbonate absorption- ileum and colon

What are the benefits of a balanced gut microbiome?

Supports brain function Helps support immune system Maintains healthy skin and coat Maintains healthy weight Supports kidney function Supports longevity Protects heart

Why is using a fecal microbiota transplant (FMT) more effective than a probiotic in a dog with diarrhea

Supports well-formed and easy to pass poop Fast-acting and gentle Restores digestive and immune health Soothes the intestinal tract Improves clinical signs in 80% of dogs Promotes healthy skin and oat Veterinarian recommended Replaces the missing gut microbes that are specific to that animal

Describe the microbial ecosystem of fermentative digestion

Symbiotic microbes (microorganisms) produce enzymes- cellulase, amylase, and protease required for enzymatic hydrolysis Majority anaerobic - bacteria - fungi- small numbers - protozoa Major alteration of substrate molecules (CHOs and proteins) by the microbial environment Slow process

List the dietary lipids

Triglyceride- primary dietary lipid - Originates from either plant or animal sources Phospholipids from plant and animal sources Cholesterol and cholesterol ester from animal sources Waxes from plant sources

Phase 4- absorption Within the enterocyte, fatty acids and monoglycerides are transported to the smooth ER and used to synthesize ________. The TG is packaged with __________, __________, and other lipids forming a _________. Where are chylomicrons absorbed?

Triglycerides Cholesterol, lipoproteins, and other lipids forming a chylomicron - small fat globule composed of lipid and protein Chylomicrons are extruded from the golgi into exocytotic vesicles, which are transported to the basolateral aspect of the enterocyte Vesicles fuse with the plasma membrane and undergo exocytosis into the lateral space They are too large to pass through basement membrane of the intestinal blood capillaries so they are absorbed through lacteals (lymphatic capillaries)

List the precursor, source, and activator for trypsin, chymotrypsin, elastase, carboxypeptidase A, and carboxypeptidase B. Endopeptidase or exopeptidase?

Trypsin- endopeptidase Source- pancreas Precursor- trypsinogen Activator- enterokinase, trypsin Chymotrypsin- endopeptidase Source- pancreas Precursor- Chymotrypsinogen Activator- trypsin Elastase- endopeptidase Source- pancreas Precursor- proelastase Activator- proelastase Carboxypeptidase A- Exopeptidase Source- pancreas Precursor- Procarboxypeptidase A Activator- Trypsin Carboxypeptidase B- Exopeptidase Source- Pancreas Precursor- Procarboxypeptidase B Activator- trypsin

Describe the cascade of intraluminal zymogen activation in the duodenum

Zymogens are released into the small intestine lumen Trypsinogen--- trypsin through enterokinase from duodenal mucosal cells Trypsin serves as an autocatalytic agent to activate additional trypsinogen and other pancreatic protein digesting enzymes

Define postbiotic

When gut bacteria feed on prebiotics, they break down those probiotic fiber molecules through a process of fermentation Fermentation activity produces waste products, or byproducts, which are referred to as postbiotics Certain postbiotics have been found to support good gut health in several ways, especially by helping to reduce inflammation

Ruminants depend on ______ produced by __________ as the source of dietary protein. Microbial crude protein (MCP) reaches the abomasum and small intestine (absorption of protein) when microbes are washed out of the rumen. The majority of bacteria have surface _________ which catabolize __________ to _______-____________ is a major source of ______ required for ___________

microbial crude protein, microbes proteases, RDP to peptide NH3, non-protein nitrogen, microbial growth Rumen degradable protein to peptides---- amino acids and NH3 --- microbial crude protein NH3 is a major source of nitrogen required for microbial growth Microbes also convert NPN to NH3

What is the osmolarity on the venous side compared with the arterial side of the capillary? Why?

osmolarity is slightly higher than the arterial side of the capillary - slight difference in osmolarity can be multiplied by the countercurrent blood glow characteristics of the arterial and venous capillary blood supplies

All water secretion is ____________ a- Will hyperosmotic ingesta cause an increase or decrease in water secretion into the small intestine lumen? b- The ______ intestine provides more or less volume of secretions compared with the large intestine

osmotic a- increase b- small, more

The rumen is composed of numerous ____________ that vary in _______ and ________. What is the function?

papillae, shape and size Composed of numerous papillae that vary in shape and size from short and pointed to long and foliate for ruminal absorption

Insoluble CHOs require the __________ attachment of bacteria to the surface of the plant particle. Where are the enzymes located?

physical attachment enzymes located on the surface coating of the bacteria Enzymatic action liberates glucose, other monosaccharides, and short chain polysaccharides into the fluid phase, outside the microbes and then undergo further metabolism by the microbial mass

Bacteroidetes and Actinobacteria can produce _______ the essential energy source for ______________

short-chain fatty acids, colonocytes

Total amount of VFA produced with a high ________ diet is usually much higher than that produced with a high _______ diet

starch, fiber

The healthy gut bacteria help with: ________ tight junctions, regulating ___________, and stimulating ____________

strengthening, intestinal motility, the production of anti-inflammatory compounds Because of its important functions, the gut microbiota is frequently defined as a "forgotten organ"

Requirements for fermentative digestion: foregut and hindgut digestive structures support fermentative digestion by providing an environment for?

thriving microbial population pH 6.2 to 7 - slightly acidic to neutral Moisture (aqueous environment) Electrolytes within normal limits Negative redox (oxidation-reduction reactions) conditions are maintained

Time spent ruminating depends on the ?

type of diet