digestive anatomy & physiology

Question 1

digestion

Answer 1

chemical breakdown of feed

Question 2

types of stomach

Answer 2

monogastric/non-ruminants
1. simple: dog
2. complex: functional cecum to to break down fibrous feed

ruminants: 4 comparment stomach that can break down cellulose

Question 3

digestion mechanisms

Answer 3

physical/mechanical
* prehension: the way to get food into mouth
* mastication: chewing ➔ varies in length
* salivation: salivary glands produce saliva ➔ mixture of buffers & salts to mix & wet
* deglutation: swallowing (neuro controlled)
* peristalsis: contractions to move food down GI

chemical:
* acid (HCl) denatures protein
* bile: digests fat & acids in emulsion ➔ secreted from gallbladder

enzymatic: breaks bonds
* intestines: SI performs bulk of digestions
* pH changes ➔ buffering to neutralize stromach acids
* organs
* microbes live along length of GI
* vital ➔ can perform actions organs cannot
* pancreas produces digestive enzymes

Question 4

GI anatomy

Answer 4

headgut = mouth ➔ physical/mechanical ➔ receiving
foregut = stomach ➔ chemical ➔ acid breakdown & storage
midgut = SI ➔ digestion

1. duodenum: neutralizes stomach acid & enzymatic digestion
2. jejunum: digestion & absorption
3. ileum: absorption of AA, monosaccharides, & free fatty acids

hindgut = LI: absorption & elimination

1. colon: absorbs water & forms feces from everything not broken down & absorbed
2. cecum: blind pouch ➔ important in some species (horse) & unimportant than others
3. rectum: connects colon to anus

Question 5

salivary glands

Answer 5

saliva contains water, electrolytes, mucus, salts, & enzymes
* solubilizes dry food, mixes, & supplies buffers ➔ makes easier to swallow
* pigs have 5
1. parotid gland: largest ➔ under ear
2. submandibular gland: posterior base of mouth
3. sublingual gland: posterier to caudal madible

Question 6

monogastric GI

Answer 6

pigs:
* omnivore
* colon = largest segment of LI

chx:
* omnivore
* no teeth
1. beak
2. esophagus
3. crop: enlargement of esophagus ➔ storage
4. proventriculus = stomach ➔ acid digestion starts chemical breakdown
5. gizzard: muscular structure ➔ grinding
6. SI
7. LI w/ 2 cecum = colon
* cloaca = exit route for all ecretions
* vent = opening to cloaca

dog
* simple carnivore
* mainly eats protein ➔ easy to break down ➔ small SI
* pyloric sphincter: muscle ring to close stomach so acid doesn’t flow back into esophagus
* non-functional cecum
* ileocecal junction: where ilium meets cecum
* colon has 3 parts:
1. ascending colon
2. transverse colon
3. descending colon

horse
* herbivore but no rumen
* hind-gut fermenter: enzymes that break down cellulose located in cecum ∴ highly functional
* SI cannot break down cellulose
* coprophagy: feces is already broken down ➔ easily digestible
* 2 parts of colon ➔ large + small
* small analogous to normal

sturgeon
* eats clams/shellfish
1. esophagus
2. stomach
a. proximal
b. distal
3. gizzard ➔ no teeth
4. pyloric cecum: attached to stomach ➔ storage & digestion of fats
* pancreas in 1st loop of of SI
* gallbladder surrounded by & attached to liver
5. only 1 SI ➔ spiral to fit

Question 7

ruminants

Answer 7

herbivores cannot break down cellulose by enzymatic digestion ➔ microbes can

• esophageal groove = highly functional: express route to stomach for babies so milk bypasses other structures that don’t have enzymes to break down milk
• ruminant stomach = 4 compartments
  
  1. rumen: microbes produce enzymes as byproduct of rumen fermentation ➔ lined w/ papillae that ↑ SA ∴ ↑ absorption
  2. reticulum: catches large particles & sends back up for more chewing ➔ honeycomb texture
  3. omasum: dehydrator: hard ball with many folds ➔ condenses & dries
  4. abomasum: “true stomach” ➔ acid digestion starts chemical breakdown; smooth inner suface

Question 8

monogastric stomach anatomy & physiology

Answer 8

rugae: stretches to hold food

fundus: dome of stomach

cardia at base

mucous neck cells secrete mucus ➔ prevents degradation of proteins/nutrients

gastric pits: indentations = entry points

parietal cells secrete HCl

chief cells secrete enzymes: pepsinogen, rennin, gastric lipase

food is mized in stomach, then into membranes via gastric pits for digestive secretions, then back into stomach

Question 9

A

Answer 9

gastric pit: intendations in stomach membrane = entry points

Question 10

B

Answer 10

mucous cells: surface epithelium

Question 11

C

Answer 11

mucous neck cells: secrete mucous ➔ prevents degradation of proteins/nutrients by acid

Question 12

D

Answer 12

parietal cells: secrete HCl

Question 13

E

Answer 13

chief cells: secrete enzymes
* pepsinogen
* rennin
* gastric lipase

Question 14

G

Answer 14

gastric glands: synthesis & secretion of acids & enzymes

Question 15

liver

Answer 15

processes, metabolizes, filters out, & sorts nutrients

• makes bile: water, salts, cholesterol, pigments ➔ emulsifies fat & keeps in soln
• outgrowth of GI tract

Question 16

structure of SI

Answer 16

• nerves stimulate peristalsis: coordinated contractions of muscle facilitates digestion & absorption
• serosa: outermost layer
• longitudinal & circular muscles contract for peristalsis
• submucosa: connective tissue
• mucosa: innermost layer of SI ➞ performs all absorption
  
  • mesentery: attaches SI to abdominal wall
  • inner circular folds ↑ absorptive SA
  • lined with microvilli: finger-like projections that ↑ SA
• small intestine villi (small intestine epithelium)
• intestinal structure = key to functioning of animal
  
  • changing all the time
  • animal models can be used to mimic feeding conditions
  • malnourished from tight junctions letting nutrients flow being without being absorbed
• capillary bed: circulates feed components throughout body
• lacteal: lymph system
• crypt: immune surveillance & stem cells that will become enterocytes
• enterocytes: workforce of villi
• goblet cell: make mucus
• tight junction & desmosomes: cell junctions ➔ vary considerably along GI tract based on
• microvilli: final breakdown; inwards towards lumen ➞ ↑ SA
  
  • glycocalyx: thin layer of mucus that coats microvilli
    
    • layer of mucopolysaccharides & glycoproteins
    • contains digestive enzymes for final AA etc. not broken down
    • helps immune system recognize & attack foreign organism

Question 17

A

Answer 17

mucosa: innermost layer of SI ➔ performs all absorption
* mesentary attaches to abdomen wall
* lined w/ circular folds ➔ absorptive ↑SA
* lined w/ microvilli: finger-like projections that ↑SA
* capture as many nutrients as possible
* food interacts w/ villi & return to circulation

Question 18

B

Answer 18

submucosa: connective tissue

Question 19

C

Answer 19

serosa: outermost layer of SI

Question 20

D

Answer 20

longitudinal muscle layer: contract for peristalsis

Question 21

E

Answer 21

circular muscle layer: contract for peristalsis

Question 22

F

Answer 22

crypt: immune surveillance & stem cells that become enterocytes

Question 23

G

Answer 23

microvilli: final breakdown ➔ inward towards lumen, ↑SA
* glycocalyx: thin layer of mucous that coats microvilli
* contains digestive enzymes for AA not yet broken down
* pretection
* helps immune system recognize & attach foreign org

Question 24

H

Answer 24

lacteal: lymph system

Question 25

I

Answer 25

capillaries: circulate feed components throught body

Question 26

J

Answer 26

villus (intestinal epithelium): intestinal structure made of enterocytes & goblet cells with crypts, lacteal, & capillaries, lined with microvilli
* absorption structures

Question 27

K

Answer 27

enterocytes: workforce of villi ➔ perform bulk of absorption

Question 28

L

Answer 28

globlet cells: make mucous

Question 29

mol transport across SI epithelium

Answer 29

paracellular route across tight junctions btwn epithelial cells
* impermeable to large mol like AA & glucose
* passive

transcellular route across PM of epithelial cells (into cells)
* transporters

water can be absorbed by both routes

Question 30

gallbladder

Answer 30

secretes bile into duodenum to assist w/ lipid absorption

• absorbs & concentrates bile until needed
• not all animals have ➔ ex: horse feed constantly so bile use immediately after produced

Question 31

pancreas

Answer 31

secretes digestive enzymes
* trypsin, chymotripsin, & carboxypeptidase for AA
* lipase for fat
* amylase for carbs

Question 32

tight junctions & desmosomes

Answer 32

cell junctions
* diet & location have great impact ➔ nutrients can flow btwn cells quickly through faulty cell junctions which can severely ↓ absorption

Question 33

A

Answer 33

tight junctions

Question 34

B

Answer 34

desmosomes