2. GI Part 11

Question 1

what are the 2 motility patterns in the rumen and what kind of contractions do they have

Answer 1

1. mixing (primary contractions)

2. eructation (secondary contractions)

Question 2

steps of primary contractions (8)

Answer 2

1. bolus enters rumen and remains suspended in area near cardis (contains air bubbles)
2. biphasic (double) contractions of reticulum
3. caudal moving contraction of dorsal sac moves ingesta further back into dorsal sac
4. cranial moving contraction of dorsal sac mixes ingesta; ingesta now under bacterial fermentation and produces gas; gas accumulates in dorsal sac
5. smaller particles decant into ventral sac
6. contraction of ventral sac separates big and small particles; small material goes over cranial pillar into cranial sac
7. contraction of cranial sac which further separates material into big and small
8. reticulum contracts – reticulo-omasal orifice relaxes and small particles (dense material) are forced through opening into omasum

then a new cycle starts

Question 3

describe the biphasic contraction of the reticulum during the primary contractions

Answer 3

1. first contraction is weak

2. second is forceful, nearly obliterating reticulum lumen –> bigger particles pushed to dorsal sac

Question 4

what is the function of primary contractions

Answer 4

reduce particle size of forage

Question 5

what influences rate of particle passage from rumen and rate of feed intake

Answer 5

digestibility of feed

physical characteristics of feed

Question 6

how many reticulo-rumen contractions occur per minute

Answer 6

1-3

Question 7

when are reticulo-rumen contractions most frequent; when do they dissapear

Answer 7

most frequent 00 during eating

disappear – during sleep

Question 8

what do the rate and strength of contractions depend on

what stimulates the most frequent and strongest contractions

Answer 8

rate and strength depend on structure of the diet

coarse, fibrous feeds stimulate the most frequent and strongest contractions

Question 9

what is the function of secondary contractions

Answer 9

force gas toward cranial portion of rumen

Question 10

when do secondary contractions occur

Answer 10

at end of primary contraction cycle

Question 11

steps (?) of secondary contractions

Answer 11

1. cranial moving contraction starting in the caudal dorsal blind sac
2. forward moving contractions of the dorsal sac that moves gas toward the cardia; gas will enter the esophagus and can be eructed

Question 12

function of regurgitation reflex

Answer 12

bring large particles from rumen back to mouth so they can be chewed to reduce particle size

Question 13

steps (?) of regurgitation reflex

Answer 13

1. begins with contraction of mid dorsal rumen –> this pushes gas cap caudally and big particles toward cardia
2. lower esophageal sphincter relaxes and bolus enters esophagus and is propelled to mouth by antiperistalsis

Question 14

normal frequency of regurgitation

what % of cows should be chewing cud

Answer 14

1 regurgitation every 2-3 minutes

60% of cows in a herd should be actively chewing cud

Question 15

what are main gases produced during rumination and percentages

Answer 15

carbon dioxide – 60-70%

methane – 30-40%

Question 16

eructation frequency

Answer 16

1 per minute

Question 17

describe eructation center

Answer 17

localized in medulla

receives afferent fibers from mechanoreceptors placed in dorsal sac of rumen (where gas accumulates)

Question 18

where does gas accumulate in the rumen

Answer 18

dorsal sac

Question 19

what is tympanism and when does it occur

Answer 19

bloating

occurs when eructation mechanisms fail

Question 20

causes of tympanism (4)

Answer 20

1. blockage of esophagus
2. impaired vagal nerve function
3. rabies
4. mor typical due to ingestion of legumes

Question 21

describe legume bloat:
type of pasture that causes it and what they contain
how does gas accumulate
can gas be detected

Answer 21

when cattle feed on lush, rapidly growing alfalfa or clover pastures –> contain waxy saponins

gas becomes trapped in tiny bubbles and normal free gas bubble cannot accumulate on top of dorsal rumen sac

presence of gas is not detectable by mechanoreceptors of dorsal sac

Question 22

what controls the reticulorumen motility

Answer 22

ENS and vagus nerve

Question 23

what do stretch receptors and chemoreceptors monitor

Answer 23

distension, consistency of ingesta, pH, VFA concentration, ions

Question 24

where is the control center for reticulorumen motility located

type of fibers and where they go

Answer 24

located in the brainstem – dorsal vagal nucleus

efferent fibers go to rumen with the vagus nerve

Question 25

describe the esophageal groove (reticular groove)

Answer 25

a gutter like imagination traversing the wall of the reticulum from the cardia to the reticulo-omasal orifice

Question 26

function of the esophageal groove (reticular groove)

Answer 26

diverts milk away from the developing rumen and pas it directly to the abomasum

Question 27

describe esophageal groove (reticular groove) closure

Answer 27

reflex action (brainstem impulses arrive through vagus) afferent stimuli arise from centrally (anticipation of suckling --> cephalic phase) and from the pharynx (suckling) when stimulated, msucles of the groove contract causing it to twist --> lips of groove close together forming tube form cardia to omasal canal

Question 28

what happens in ruminant ketosis Normal: acetate and butyrate --> acetyl CoA --> citrate

Answer 28

if oxaloacetate is not enough or if acetyl CoA is excessive (excess fat oxidation) -- acetyl CoA accumulates as acetoacetyl CoA which is degraded to acetoacetate, beta-hydroxybutyrate, and acetone (ketone bodies)

Question 29

conditions for maintaining fermentation in the horse

Answer 29

similar to those of the rumen substrate supply, control of pH (buffers), osmolality, anaerobiosis, retention of fermenting material, removal of waste product and residue

Question 30

things to consider when talking about fermentation efficiency in horse (4)

Answer 30

1. ingesta passage through stomach and small intestine before arrival to large intestine --> exposure to gastric acids and digestive enzymes may increase digestion rate in hindgut 2. some proteins escape small intestine digestion and absorption and arrive to hindgut 3. there is an extensive urea recycling into the colon and cecum (similar to rumen) 4. in contrast to ruminant, horses do not have a mechanism to recover and utilize microbial proteins and most pass out in feces

Question 31

what helps rabbits recover microbial proteins

Answer 31

cecotrophy

Question 32

who is more efficient -- degradation of cellulose

Answer 32

ruminats

Question 33

who is more efficient -- absorption of VFA

Answer 33

ruminants

Question 34

who is more efficient -- utilization of microbial protein

Answer 34

ruminants

Question 35

who is more efficient -- poor food quality

Answer 35

horses -- eat more and have lower retention time

Question 36

who is more efficient -- food is scarce

Answer 36

ruminants -- more efficient at digesting and absorbing

Question 37

where does most carb digestion occur in ruminants and through what type of digestion how much digestible carbs enter intestine

Answer 37

occurs in forestomach through fermentative digestion almost no digestible carbs enter intestine

Question 38

where does glucose available to ruminants originate from what is most important precursor of glucose in ruminants

Answer 38

originates from gluconeogenesis precursor -- VFA propionate

Question 39

at what level does propionate enter Krebs cycle

Answer 39

succinate

Question 40

what is succinate and what can it lead to

Answer 40

4 carbon intermediate can lead to formation of oxaloacetate which is the entry metabolite for gluconeogenesis

Question 41

special considerations -- glucose homeostasis in ruminants (5)

Answer 41

1. ruminants exist in constant state of potential glucose deficiency 2. gluconeogenesis covers 85-100% of glucose needs 3. insulin levels are regulated by VFA concentrations 4. all glucose available to ruminants originates from gluconeogenesis 5. most important precursor of glucose in ruminants is VFA propionate

Question 42

where is most of propionate absorbed from rumen extracted from does it ever enter the systemic circualtion

Answer 42

almost all the propionate absorbed from the rumen is extracted from the portal blood by the liver and never enters the systemic circulation

Question 43

where are fatty acids synthesized in ruminants | what is used as a precursor

Answer 43

fatty acids are only synthesized in adipose tissue using acetate as a precursor -- never use glucose

Question 44

what does glucose go to in high producing dairy cows what do remaining tissues use

Answer 44

lactose -- milk sugar remaining tissues function on alternative fuels

Question 45

describe the mouth and esophagus of the bird (3)

Answer 45

no soft palate no teeth esophagus of large diameter

Question 46

describe the crop

Answer 46

storage function ingesta accumulates once gizzard is full epithelium is rich in mucus secreting cells

Question 47

describe the proventriculus

Answer 47

contains a glandular epithelium

Question 48

describe the gizzard

Answer 48

muscular organ for grinding and sieving ingesta ejection of bone, hair, indigestible material into oral cavity for elimination

Question 49

what do grain eating birds do to aid in grinding of food

Answer 49

swallow stones and gravel (grit)

Question 50

describe small intestines of bird

Answer 50

short in relation to body size

Question 51

describe ceca in birds

Answer 51

paired in some species in other species they are rudimentary

Question 52

describe rectum in birds

Answer 52

ends in cloaca -- where digestive, urinary, and reproductive discharges converge