histo/phys exam 4

During the luminal phase of protein digestion, what’s the difference b/t endopeptidases vs exopeptidases in how they work?

• endopeptidase = break proteins w/i AA chains

  • cleave complex proteins into shorter peptides

• exopeptidase = cleave AAs from ends of peptide chains

Pepsin precursor, source, activator, and endopeptidase/exopeptidase?

• precursor: pepsinogen

• source: chief cells in stomach secrete pepsinogen

• activator: HCl in stomach acid activates pepsinogen into pepsin

• endopeptidase

Trypsin, chymotrypsin, elastase, carboxypeptidase A, and carboxypeptidase B precursor, source, activator, and endopeptidase/exopeptidase?

• precursor: trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A + B

• source: precursors secreted by into duodenal lumen by pancreatic acinar cells

• activator: trypsinogen is activated by enterokinases embedded in duodenal brush border into trypsin → trypsin is an autocatalytic agent that then can further activate more trypsinogen + other pancreatic protein-digesting zymogens

• all are endopeptidases except carboxypeptidase A + B

Where does the luminal phase of protein digestion begin?

• begins in stomach w/ chief cells secreting pepsinogen

• protein-digesting zymogens activation occurs in duodenal lumen

Describe the membranous phase of protein digestion

• occurs d/t action of hydrolytic enzymes that are synthesized w/i the enterocytes + chemically bound to the surface epi. = brush border enzymes

• products of luminal phase protein digestion must diffuse into glycocalyx

  • big peptides → hydrolyzed by brush border peptidases into free AAs or smaller peptides

  • smaller peptides → absorbed intact by enterocyte → hydrolyzed by intracellular peptidases into free AAs

  • free AAs taken up by enterocyte via Na+ cotransport

• free AAs w/i enterocyte can diffuse across basolateral mem. into lateral space → diffuse into bloodstream

What are the 3 primary alterations in a neonate’s digestive system compared to an adult’s?

1) acid secretion delayed for several days after birth → acid digestion of proteins avoided

2) pancreatic secretion of trypsinogen delayed → protein digestion of proteins avoided

3) specialized intestinal epi. that can absorb proteins whole + intact → fxnal proteins can enter bloodstream intact

• ingestion of colostrum is the only way baby can get maternal Ab (no placental transfer) in horse, rmt, and pig

• gut closure occurs w/i 24 hrs after birth → neonate loses intact protein absorption ability

• neonates also have more lactase + less maltase → rely on lactose as primary carb source

• adults have less lactase + more maltase → rely on starch as primary carb source

Why are active transport mechanisms required for small intestinal absorption?

active transport req. for:

• moving molecules against their concentration gradient

• moving big molecules

Describe the mechanism of primary active transport in small intestinal absorption

• Na+-K+ ATPase pump located on basolat. mem.

• hydrolyze 1 ATP to move 3 Na+ out + 2 K+ in

• maintains negative RMP + low intracellular Na+

Describe the mechanism of secondary active transport in small intestinal absorption w/ 3 examples

• naturally large Na+ gradient provided by Na+-K+ ATPase pump provides potential energy to pull cotransported molecules against their concentration gradient

  • helps enterocyte absorb glucose even when enterocyte has more glucose than lumen

• Na+ cotransport protein has 2 binding sites for Na+ + 1 binding site for glucose/galactose

  • when all 3 sites facing gut lumen are occupied → all 3 molecules pulled/absorbed into enterocyte

  • glucose then moves thru basolat. mem. into lateral space into blood via facilitated diffusion driven only by its own conc. gradient

• Na+-H+ antiport on enterocyte apical mem. transports 1 H+ into gut lumen + 1 Na+ into enterocyte

• Na+ cotransport of free AAs in gut lumen works like Na+-glucose cotransport

Describe the mechanism of tertiary active transport in small intestinal absorption w/ 1 example

• driven by electrochemical gradient est. by a secondary active transport mechanism

• Na+/K+ ATPase pump is primary active transport mechanism → provides gradient that drives secondary active transport mechanism Na+/H+ antiporter → provides gradient that drives tertiary active transport mechanism Cl-/HCO3- exchanger

  • end result: 1 Cl- from gut lumen gets pumped inside the enterocyte + 1 HCO3- from inside enterocyte gets pumped outside into gut lumen

T/F During membranous phase of peptide digestion, absorption of dipeptides + tripeptides are hydrolyzed by enterocyte intracellular peptidases yielding AAs.

T

Describe the 2 mechanisms of passive transport in small intestinal absorption

• transcellular = absorption across apical mem. using ion channels, diffusion, transporters

  • molecules: monosaccharides, free AAs, Na+, Cl-, HCO3-, K+, and water

• paracellular = absorption thru tight jxns b/t enterocytes

  • mvmt driven by osmotic + electrochem. gradients

  • molecules: water, Cl-, K+

List the types of dietary lipids

• TGs (primary dietary lipid)

• phospholipids

• cholesterols

• lipid soluble vitamins

• waxes

Name the 4 steps of lipid digestion + absorption in order

1) emulsification

2) hydrolysis

3) micelle formation

4) chylomicron formation + absorption

What is Step 1 of lipid digestion + absorption? Define it, where + how it is completed.

• emulsification = the process of reducing lipid droplets to a small enough size such that they can be suspended in water → reduces surface tension + increases SA of droplets for maximal lipase interaction

• begins in stomach

  • lipids warmed + mixed in pyloric antrum → forming liq. lipid globules

• process finishes in dd. once globules get exposed to bile salts + phospholipids

In Step 1 of lipid digestion + absorption: _____ the surface tension of the lipids and allows the droplets to become even further divided + reduced in size. This ______ the surface area for action of lipase, colipase, and bile acids for fat digestion.

Decreasing the surface tension of the lipids and allows the droplets to become even further divided + reduced in size. This increases the surface area for action of lipase, colipase, and bile acids for fat digestion.

What is Step 2 of lipid digestion + absorption? Define it, where + how it is completed.

• hydrolysis = TGs broken down by hydrolytic enzymes

  • colipase clears path thru bile salts to reveal underlying TGs for lipase

  • lipase cleaves 1 TG → prod. 2 FFAs + 1 MG

• occurs primarily in jj. lumen

In Step 2 of lipid digestion + absorption: _______ 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 TGs

Lipase cannot penetrate the coat of bile products surrounding the emulsified lipid droplets. Colipase clears a path through the bile products, giving lipase access to the underlying TGs

What is Step 3 of lipid digestion + absorption? Define it, where + how it is completed.

• micelle formation = FFAs + MGs combine w/ phospholipids + bile acids to form micelles

• micelles = water-soluble taxi that allow FFAs + MGs to diffuse thru gut lumen into water + glycocalyx layer over apical enterocyte mem.

  • all parts of micelle EXCEPT bile acids then get transported across apical mem. by special FA-binding proteins

    • bile acids get reabsorbed at ileum

• primarily occurs in jj. segment

In Step 3 of lipid digestion + absorption: _______ and ______ combine w/ bile acids + phospholipids to form ______. 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 w/ the absorptive surface of the apical enterocyte membrane.

FFAs and MGs combine w/ bile acids + phospholipids to form micelles. All components of the micelle diffuse into the enterocytes except bile acids. Soluble micelles allow the lipids to diffuse into the unstirred water layer and into close contact w/ the absorptive surface of the apical enterocyte membrane.

What is Step 4 of lipid digestion + absorption? Define it, where + how it is completed.

• chylomicron formation + absorption

• w/i enterocyte, FFAs + MGs turned into TG by smooth ER

• then Golgi packages that TG w/ cholesterol, lipoproteins, and other lipids forming chylomicron = smol water-soluble fat globule composed of lipids + proteins

• Golgi then packages chylomicrons into exocytic vesicles → chylomicrons exocytosed thru basolat. mem. into lat. space → chylomicrons diffuse into interstitial fluid → diffuse into lymphatic capillaries aka lacteals → eventually dumped into venous circulation → eventually making it to muscle + adipose tissue

• chylomicron core: TGs + cholesterol esters

• chylomicron surface: phospholipids + cholesterol + protein helpers w/ hydrophobic end facing inside + hydrophilic end facing outside

• primarily occurs in jj. segment

In Step 4 of lipid digestion + absorption: Within the enterocyte, FAs and MGs are transported to the smooth ER and used to synthesize _______. The TG is packed w/ ______, _______, and other lipids forming a _______. Chylomicrons are absorbed at _____.

Within the enterocyte, FAs and MGs are transported to the smooth ER and used to synthesize TGs. The TG is packed w/ cholesterol, lipoproteins, and other lipids forming a chylomicron. Chylomicrons are absorbed at lacteals.

The majority of GI disorders involve the loss of ______ and ______.

electrolytes + water

What are electrolytes? List the electrolytes. Where are they located? What type of blood test would you order to test [electrolyte]?

• electrolytes = dissolved ions

• Na+, Cl-, HCO3-, K+

• located in ECF (ISF + blood), ICF, and IV fluid bags

• order blood chem to test [electrolyte]

Where are water + electrolytes absorbed? Where are they reabsorbed? Why is absorption/reabsorption of water important? Why is absorption/reabsorption of electrolytes important?

• absorbed primarily in SI (specifically jj) + a little bit in LI

• reabsorbed by kidneys

• important bc water + electrolyte balance required for homeostasis

  • imbalance can lead to dehydration, decreased blood volume + BP, bad things uh oh

Why is Na+ important? What effect will hyponatremia have on HR + skeletal m.? Describe the 3 mechanisms of Na+ absorption

• Na+ req. for:

  • depolarization for APs

  • ECF + ICF balance

• hyponatremia → dec. HR + skeletal m. cramping

• 3 mechanisms of Na+ absorption

  • Na+/glucose or AA cotransport (secondary active transport)

  • Na+/H+ antiport (secondary active transport)

    • important driver for coupled Na+/Cl- absorption

    • carbonic anhydrase hydration rxn prod. HCO3- + H+ → intracellular HCO3- drives exchange for luminal Cl- → driving coupled Na+ absorption

  • simple diffusion (minimal impact on Na+ homeostasis)

A drug that blocks the activity of the Na+/K+ ATPase pump could have what effect on Na+/glucose cotransport?

• decreased Na+/glucose cotransport

• Na+/K+ ATPase pump provides large Na+ gradient that drives Na+/glucose cotransport

Why is Cl- important? Describe the 3 mechanisms of Cl- absorption

• Cl- req. for:

  • ECF + ICF balance

  • ionic balance b/t RBC + plasma

  • HCO3- mvmt

    • when HCO3- leaves cell → Cl- must enter cell

    • when HCO3- enters cell → Cl- must leave cell

• 3 mechanisms of Cl- absorption:

  • paracellular Cl- absorption (major mechanism)

    • Cl- diffuses thru tight jxns b/t enterocytes into lat. spaces

  • coupled Na+/Cl- absorption

  • HCO3- dependent Cl- absorption (tertiary active transport)

    • net mvmt of HCO

Why is HCO3- important? What are the 2 ways HCO3- is measured and how do they differ? Describe the mechanism of HCO3- absorption

Why is K+ important? What effect will hyperkalemia have on HR + skeletal m.? Why is a bright orange sticker used when K+ is added to an IV fluid bag? Describe the 2 mechanisms of K+ absorption

Where are the major mechanisms of electrolyte absorption located in the GI tract? Where is Na+ cotransport located? Where is HCO3- absorption located?

Water absorption in SI + LI occurs according to ______ Forces and via the ______ ______ system. Water moves in the direction necessary to keep ingesta ______. What are the 2 ______ forces responsible for water mvmt? Define them. The ______ ______ 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. What does the venous side of the capillary bed contain? What is the osmolarity on the venous side compared to the arterial side? Why? Water absorption begins at the tip of the villus at ______ mOsm. The osmolarity __creases as more water is absorbed along the venous side of the capillary bed twd the venule.

What are the fxns of the liver?

GI blood flows through 2 types of capillary beds. What are they and how do their arterial hydrostatic pressures differ from each other?

Where is a normal pressure gradient required for normal GI blood flow? Describe the hepatic venous pressure gradient (HVPG). How does R-sided heart failure + diffuse liver disease cause ascites?

All water secretion is ______.

Will hyperosmotic ingesta cause an increase or decrease in water secretion into the SI?

Describe the SI secretion pathway for electrolytes + water

What is the fxn of the SI crypt cells?

Define diarrhea + describe the 2 mechanisms of pathophysiology

What type of acid-base imbalance + compensatory response would you expect in a dog w/ chronic diarrhea?

Where is the largest portion of the gut microbiome located?

The gut microbiome contributes to overall _____ and _____.

What are some benefits of a balanced gut microbiome?

ID colon structures

List some fxns of the colon

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

The vast majority of gut bacteria belong to which 2 phyla?

Bacteroidetes + Actinobacteria can produce ______, the essential energy source for ______.

The healthy gut bacteria help w/: ______ tight jxns, regulating _____, and stimulating ______.

Describe how colonocyte metabolism fxns as a control switch, mediating a shift b/t homeostatic + dysbiotic microbial communities.

A balanced microbial ecosystem is crucial for host health + homeostasis. Changes in the gut microbiome are associated w/ _____. List pathological conditions associated w/ that.

Define prebiotic, probiotic, and postbiotic.

Why is using fecal microbiota transplant more effective than using a probiotic in a dog w/ diarrhea?

Fermentative digestion occurs in specialized compartments positioned either ______ or ______ to the stomach + SI

Foregut fermentation compartment name?

Hindgut fermentation compartment names?

Foregut + hindgut digestive structures support fermentative digestion by providing an environment for?

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

Under normal conditions, ruminal microbes are _____ w/ a markedly _____ redox potential, reflecting the absence of _____.

Why is a negative redox potential important?

Compare + contrast monogastric glandular digestion vs fermentative digestion

List the microbes of the microbial ecosystem required for fermentative digestion.

Why are protozoa beneficial for fermentative digestion?

Digestive process in the _____ or _____ involves the interplay among the many species of _____. The ecosystem of fermentative digestion is extremely complex, w/ the _____ of 1 microbe serving as the substrate for other _____.

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

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

All cell wall molecules that are carbohydrate will be digested w/ ______ases produced by the ______. These ______ases release ______ and _______ from the complex carbohydrates of cell walls. The released ______ are ______ available for absorption by the animal and are metabolized by ______.

Is lignin digestible or indigestible?

Why is fermentative digestion a slow process?

______ enters a glycolytic pathway to produce VFAs. VFAs produce __% energy for herbivores.

List the 3 major VFAs

The total amount of VFAs produced w/ a high _____ diet is usually much higher than that produced w/ a high _____ diet.

Rmts depend on ____ ____ protein produced by _____ as their main source of dietary protein. This ____ ____ protein reaches the abomasum + SI when microbes are washed out of the rumen. The majority of bac. have surface _____ which catabolize _____ to _____. _____ is a major source of _____ required for _____.

Describe how microbial crude protein can be synthesized in the rumen from nonprotein nitrogen sources

Describe the NPN sources that are used for microbial protein production

Describe the 2 sources of hepatic urea production

Describe nitrogen recycling in rmts

Compare + contrast monogastric + rmt NPN pathways

The microbial growth rate depends on the supply of nutrients + the rate at which microbes are washed out from the rumen. The overall rxn in the rumen can be evaluated using what equation?

What happens to MCP when glucose + peptide availability are optimally balanced?

What happens to MCP when glucose availability > peptide availability?

What happens to MCP when peptide availability > glucose availability?

Describe the properties + fxns of rmt saliva

Describe the structure of rumen epi.

The rumen is composed of numerous _____ that vary in _____ and _____. What is the fxn?

Describe VFA absorption from the lumen of the rumen to the blood capillaries located in the lamina propria.

Where do VFAs come from?

What happens if VFAs are allowed to accumulate?

Why are VFAs important for the rmt?

Which VFAs stimulate papillary growth?

Describe the requirements for foregut fermentation.

Describe the primary contractions + secondary contractions associated w/ reticulorumen motility.

primary → mixing

secondary → eructation

What are the 4 zones of the rumen? What type of material is in each zone? What happens w/ particle density (specific gravity) from dorsal to ventral?

How do physical characteristics of feed impact digestibility?

Describe the steps of secondary (eructation) contractions.

Describe the 4 phases of the rumination cycle.

The time spent ruminating depends on what?

What type of diet would cause an increase in rumination time? ______ also influences the amount of rumination time.

Describe the process of rumen water flow. The transit rate of _____ must be considerably greater than the transit rate of _____ through the rumen.