digestive anatomy & physiology Flashcards
digestion
chemical breakdown of feed
types of stomach
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
digestion mechanisms
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
GI anatomy
headgut = mouth ➔ physical/mechanical ➔ receiving
foregut = stomach ➔ chemical ➔ acid breakdown & storage
midgut = SI ➔ digestion
- duodenum: neutralizes stomach acid & enzymatic digestion
- jejunum: digestion & absorption
- ileum: absorption of AA, monosaccharides, & free fatty acids
hindgut = LI: absorption & elimination
- colon: absorbs water & forms feces from everything not broken down & absorbed
- cecum: blind pouch ➔ important in some species (horse) & unimportant than others
- rectum: connects colon to anus
salivary glands
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
monogastric GI
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
ruminants
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
- rumen: microbes produce enzymes as byproduct of rumen fermentation ➔ lined w/ papillae that ↑ SA ∴ ↑ absorption
- reticulum: catches large particles & sends back up for more chewing ➔ honeycomb texture
- omasum: dehydrator: hard ball with many folds ➔ condenses & dries
- abomasum: “true stomach” ➔ acid digestion starts chemical breakdown; smooth inner suface
monogastric stomach anatomy & physiology
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
A
gastric pit: intendations in stomach membrane = entry points
B
mucous cells: surface epithelium
C
mucous neck cells: secrete mucous ➔ prevents degradation of proteins/nutrients by acid
D
parietal cells: secrete HCl
E
chief cells: secrete enzymes
* pepsinogen
* rennin
* gastric lipase
G
gastric glands: synthesis & secretion of acids & enzymes
liver
processes, metabolizes, filters out, & sorts nutrients
- makes bile: water, salts, cholesterol, pigments ➔ emulsifies fat & keeps in soln
- outgrowth of GI tract
structure of SI
- 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
-
glycocalyx: thin layer of mucus that coats microvilli
A
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
B
submucosa: connective tissue
C
serosa: outermost layer of SI
D
longitudinal muscle layer: contract for peristalsis
E
circular muscle layer: contract for peristalsis
F
crypt: immune surveillance & stem cells that become enterocytes
G
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
H
lacteal: lymph system
I
capillaries: circulate feed components throught body
J
villus (intestinal epithelium): intestinal structure made of enterocytes & goblet cells with crypts, lacteal, & capillaries, lined with microvilli
* absorption structures
K
enterocytes: workforce of villi ➔ perform bulk of absorption
L
globlet cells: make mucous
mol transport across SI epithelium
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
gallbladder
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
pancreas
secretes digestive enzymes
* trypsin, chymotripsin, & carboxypeptidase for AA
* lipase for fat
* amylase for carbs
tight junctions & desmosomes
cell junctions
* diet & location have great impact ➔ nutrients can flow btwn cells quickly through faulty cell junctions which can severely ↓ absorption
A
tight junctions
B
desmosomes
