ch. 11.2: steps of digestion pt. 2

what is the cardiac sphincter

connects the esophagus and the top of the stomach

what is the top section of the stomach called & what is secreted

the fundic/cardiac section

secretes mucus and HCL

what is the middle section of the stomach called & what is secreted

body/proper gastric

secretes HCL and pepsinogen

what is the bottom section of the stomach called & what is secreted

pyloric

secretes mucus and pepsinogen

what is pyloric sphincter

connects the stomach and the duodenum

go quiz yourself on the stomach parts using the diagram

yes ma’am

where are glands located in the stomach?

gastric pits

what is the purpose of neck, parietal, and chief cells

neck: produce mucus for the stomach lining

parietal: produce HCl through carbonic anhydrase

• H and Cl are separately pumped into lumen where they are they combined to make HCl

chief cells: pepsinogen

what is the name of the “true stomach” in monogastrics vs. avians vs. ruminants?

most monogastrics (pig, human dog): glandular stomach

avian (chicken): proventriculus

ruminants (cow, sheep): abomasum

what are the 3 types of digestion in the stomach

mechanical, chemical, and enzymatic

what happens in mechanical digestion

muscular contractions (churn digesta & break down) and mixing digesta w enzymes

what 2 things play a role in chemical digestion

gastric glands and HCl

what do gastric glands do in chemical digestion

parietal cells produce HCl

what does HCl do in chemical digestion

denatures proteins and activates enzymes

• activates pepsin by cleaving stuff from pepsinogen (produced by chief cells)

• pepsin begins the hydrolysis of protein

provides an optimal acidic environment for pepsin (pH of 2-2.5)

kills bacteria (minus food borne illnesses)

what plays a role in enzymatic digestion?

proteases

• pepsin:

  • produced by chief cells

  • cleaves proteins at specific sites to make shorter chains

  • (protein digestion)

• rennin: protease that acts on milk protein

  • important for baby animals

what are the 2 other functions of the stomach?

storage (esp. for monogastrics; allows us to eat quickly) and metering (limits movement of digesta and prevents the overloading of the intestines)

what’s the role of mucin in the stomach

secreted by cells lining the stomach

provides a protection coating against HCl

why can HCl not destroy our stomach normally, and what happens when it does?

mucus coat and HCl is diluted by saliva and digestion (raises the pH)

ulcers: HCl burns stomach lining

what is the role of urease in the stomach?

an enzyme that breaks down urea to act as a buffer

what is a zymogen

enzymes synthesized by cells as an inactive form

what are the 3 segments of the small intestine?

duodenum, jejunum, ileum (in that order)

where is & what is the function of the duodenum

where: extends from pyloric sphincter to jejunum

is the primary site for digestion

where is & what is the function of the jejunum

where: extends from duodenum to ileum

is the primary site for absorption

where is & what is the function of the ileum

the shortest segment

extends from the jejunum to the large intestine

secondary site of absorption

what are the 3 alkaline secretions (in the small intestine) made to increase the pH of the digestive tract from 2-2.5 to 7-7.5?

1) bile

2) pancreatic juices

3) duodenal juice

what is the function and source of bile?

made in the liver, stored in the gall bladder

functions:

• detergent that solubilizes fats

• forms a complex with fatty acids to aid in the absorption of fat

what are the 5 main enzymes in pancreatic juice and what do they help digest?

1 and 2) trypsin and chymotrypsin - protein

3) carboxypeptidases - protein

4) pancreatic lipase - fat

5) amylase - starch

what 2 buffers are also in pancreatic juice?

HCO3 (bicarbonate)

NaCO3 (sodium carbonate)

where and what is the function of duodenal juices?

where: secreted by the brush border of the S.I.

function: contains enzymes secreted by intestinal mucosa

• activates trypsin from trypsinogen (made by pancreas) using enterokinase

• activates enzymes for protein and CHO digestion

what 3 organisms are found in the large intestine?

bacteria, protozoa, and fungi

is there any enzyme secretion from the host in the large intestine?

no, digestion is limited to that performed by microorganisms

while absorption is limited in the LI, what things CAN be absorbed?

VFAs (produced by the digestion of fiber by microbes)

water

electrolytes

rank these in order of greatest digestive ability of the large intestine to the least: monogastric herbivores, omnivores, carnivores

monogastric herbivores » omnivores » carnivores

what part of a particular monogastric herbivore is said to be comparable in size to the rumen of ruminants?

the large intestine of an adult horse

why is the absorption of fiber in monogastric herbivores not as efficient as fermentation in ruminants?

much of the nutrient content has been removed by the small intestine, so we’re past the site of primary absorption (post-gastric fermentation in monogastrics)

what can be formed/digested by MCOs in the LI?

• cellulose can be degraded to VFAs & then absorbed

  • provide 40-90% of energy

• fermentation can result in the microbial production of B vitamins and bacterial protein, but these cannot be absorbed

how do rabbits differ from other species?

they practice coprophagy (feeding on excrement)

what percentage of crude fiber digestion occurs in omnivore large intestines?

18-20%

what are the 5 things that make up feces

1) mostly water (varies with species)

2) undigested feed

3) residues of digestive enzymes that were secreted in SI

4) sloughed cells (lining of brush border of SI that fell off and were replaced)

5) bacteria

what are the 4 components of urine

1) mostly water

2) minerals - Cl, K, P, Na (electrolytes)

3) nitrogen compounds

• animals: urea

• birds: uric acid

• fish: ammonia

4) small amount of glucose and small carbs