Anatomy and Physiology of the GIT Flashcards
Elements of the digestive system?
- mouth
- pharynx
- esophagus
- stomach
- small intestine
- large intestine
- rectum
- accessory glands (salivary, liver, pancreas)
What is the role of the pharynx?
defines whether going from larynx –> trachea or esophagus
What animal is similar to horse?
rabbit
What is the anatomical location of the GIT?
caudal to diaphragm
What is the upper lip useful for?
food selection (separating particles) and grazing
Tongue anatomy
apex, body, root
What is the structure of the tongue?
keratinized stratified squamous epithelium
- papillae to help sense food
Why do animals perform flehmen response?
- to detect smells (that humans cannot)
- could be nutritive
What is the purpose of saliva?
~20L per day
- more than other non-ruminant counterparts - ket higher dry matter food
- secrete more in the winter (dryer food)
- dehydration limits saliva secretion
What are the functions of the mouth?
- grasp feed
- moistening feed with saliva
- chew food –> reduce particle size
Mouth anatomy
- Diastema
- gaps between teeth (very large between incisors and molars) - diphyodont
- deciduous (baby teeth)
- permanent - Hypsodont
- pattern of dentition - ever growing/high crowned teeth (enamel extends past gum line) - Heterodonts
- incisors
- canine
- premolars
- molars –> grinding
Anatomy of the tooth
- crown
- root
- alveolus = socket where the tooth sits
- peridontium = connective tissue that holds tooth in place in jaw
- cementum = thin bone layer that covers entire tooth
- dentin = mineral deposition; vast majority of tooth
- enamel = superficial part of tooth; hardest part
- dental pulp/infundibulum = middle part that has all the innervation and nutrition for tooth
What gland secretes 90% of equine saliva?
Parotid gland
- also the sublingual and submaxillary glands
What is in saliva to buffer and lubricate feed?
bicarbonate = H,C, O
- makes sure its the right pH for amylase to start carb digestion
What is the pharynx a junction between?
- nasal cavity
- mouth
- trachea
- esophagus
Can horses breath through their mouths?
no
What are tonsils
aggregations of lymphatic nodules associated with mucous membranes
- lingual –> base of tongue, pharyngeal
What is the guttural pouch?
more dorsal and bigger in horses
- food can get caught here
What is the esophagus?
Muscular tube extending from the pharynx to the stomach
What aids in swallowing?
Tunica muscularis
What is the mesentery?
Anchors small intestine to back of intestinal wall
- attached to pelvis
- SI not attache to each other –> more flexibility
- LI is attached to each other but not back of intestinal wall
The walls of the digestive tract consist of?
- tunica mucosa
- stratified squamous epithelium - secretes enzymes, buffers, absorbs and secretes nutrients - tunica submucosa
- loose connective tissue - tunica muscularis
- striated vs. smooth - tunica serosa
- visceral peritoneum and connective tissue
What is the role of the cardiac sphincter?
Very strong –> forces food from esophagus into stomach and prevents stuff from coming back up
- prevents vomiting
What does fast emptying mean in terms of managing their feeding programs?
more frequent, smaller meals to match stomach size and gastric emptying rate
What regulates the pyloric region
Pylorus
- sphincter which controls gastric emptying into small intestine
How much acid is secreted per day? And what kind?
10-30 L per day
HCl - breaks down quaternary structures
Pepsin - converts tertiary to secondary
- partially controlled by the amount of protein a horse eats and how much water it consumes
Functional anatomy of the stomach
Non-glandular
- squamous
Glandular
- secretion of HCl and pepsinogen –> lower pH –> activates pepsin –> degradation of protein
Functions of the stomach
- small amount of fermentation
- digestion facilitated by HCl
- gastric lipase is also present –> emulsification of fat for digestion
What is the most metabolically active tissue in the body?
the gut
Role of the gut
- enzyme secretion
- first absorptive unit - absorb nutrients through transporters and metabolize nutrients
what is responsible for triggering peristalsis?
under the mucosa is the sub-mucosa –> connects circular and longitudinal muscles –> movement –> peristalsis
What is secreted by the pancreas?
Bicarbonate
- changes pH of digesta
- leaves stomach very acidic
Pancreatic amylase
- CHO digestion
- long polysaccharides –> short
Pancreatic lipase
- lipid digestion/emulsification
Components making up the small intestine
- duodenum
- receives ducts from pancreas and liver
- shortest part on small intestine - jejunum
- longest part of the small intestine (28m)
- high absorptive capacity (dipeptides, CHO, vitamins, minerals, amino acids - ileum
- contains many goblet cells (mucus) and aggregates of lymph nodes - great mesentery
- holds small intestine together
What organ secretes bile?
liver
What organ typically stores bile?
the gall bladder
- but the horse lacks this
Which components leave the small intestine and enter the colon?
cellulose, fiber, phosphorus
What are the functions of the small intestine?
- significant site of enzymatic hydrolysis of nutrients (pancreas and intestinal secretions)
- emulsification of lipids promoted by bile
- majority of absorption occurs in jejunum and duodenum
What make up the large intestine?
cecum, colon, rectum, anal canal
What is the cecum?
blind same
- equivalent to our appendix
- ~30L capacity
What makes up the colon?
ascending (“great” colon), transverse, descending (small colon)
~100L
What are the products of cellulytic fermentation?
volatile fatty acids or short chain fatty acids
- can provide 75% of horses energy
- vitamin K (blood clotting) and B vitamins (peripheral energy)
amino acids
What shot is commonly given to foals after birth?
vitamin K
- under developed cecum and colon - so little bacteria to produce enough vitamin K
- develops when hay/grain are introduced
What is the major site of water absorption?
cecum
Is microbial synthesis of vitamins adequate to meet requirements?
No, especially vitamin B in performance horses
What is undigested protein degraded to in the large intestine?
ammonia
Why are amino acids synthesized from protein in the large intestine of little nutritional significance?
There is little active transport of amino acids in the large intestine
- this means the horse is less able to improve amino acid profile of low quality dietary sources
- may benefit from AA supplement
When is the small intestine completely grown?
4 weeks of age
What promotes growth of the LI?
bulky, fibrous diet
When does the large intestine continuing growing until?
> 20 years
When does the cecum become fully functional?
15-24 months
What are the accessory glands?
Salivary, pancreatic, liver
What are the salivary glands?
parotid
mandibular
sublingual
Describe the pancreas
endocrine:
- pancreatic islets
- glucagon
- insulin
exocrine:
- sodium bicarbonate
- digestive enzymes (e.g. amylase, lipase)
Describe the livers role?
- largest gland in the body
- 1-2% adult body’s weight
- immediately caudal to diaphragm
- soothing organ (looks at all incoming nutrients from digestion/absorption and organizes accordingly)
- very metabolically active
- size stays stable (unless a big flux in meal size)
2 blood supplies:
- Hepatic artery = nutrient blood supply
- Portal vein = functional blood supply
when would horses benefit from Lys supp?
growth phase
- lys is limiting in grain and hay
How are carbohydrates absorbed/digested?
- starches and soluble carbs are digested and actively absorbed as simple sugars in SI or fermented to VFA (acetate, propionate, butyrate)
- insoluble carbohydrates are metabolized to VFAs
How are lipids absorbed/digested?
- predominantly absorbed in small intestine
- similar to other mammals
- no gall bladder, but high fat diets tolerated well (continuously secrete bile no matter the amount of fat consumed)
- fatty acid composition of body fat in horse similar to dietary fat
How are minerals absorbed/digested?
- major site of absorption of P in large intestine
- major site of absorption of Ca in small intestine
- excess P reduced Ca absorption (phytate binding)
- why horse can handle higher Ca:P ratio
What is the most unique feature of the equine digestive tract?
very large and functional cecum
- allows horse to function as a herbivore with mechanical agility not seen in ruminants (with a rumen)
SCFA production in ruminants vs. horses
ruminants are better at harvesting SCFA compared to horses
- to compensate, rather than eating more, horses chew more
- cattle and sheep eat >4x the amount or horses but nurses chew up to 4x more than cattle
Relative capacities (Pig, cow, horse)
Stomach:
cow>pig>horse
SI:
pig>horse>cow
Cecum:
horse>pig>cow
Colon/rectum:
horse>pig> cow
Total volume:
cow>horse>pig
Rate of passage in the horse
stomach = 3-9 h Si = 5-6 h cecum = 15-20h colon = 18-24h
List 3 major functions of the mesentery of the SI/
- supplies blood to the intestinal wall
- anchors the small intestine to the back of the intestinal cavity
- contains lymphatic ducts
List 3 functions of saliva?
- lubricate feed
- contains bicarbonate buffers that adjust pH of ingest to optimal levels
- contains amylase to aid in CHO digestion
What is the absorptive unit of the SI?
enterocyte
Why is even grinding of teeth important?
Imperative to health of horse - prevents proper chewing –> colic, weight loss
If you were wanting to increase the amount of fat in a horse’s diet, what is the consideration you should make before doing so?
The horse lacks a gall bladder
- continuous release of bile independent of the fat in diet
- done gradually to allow the body time to gradually adjust accordingly
Is it best to feed horses many small meals or discrete large meals throughout the day, and why?
Small, frequent meals
- small stomach that empty quickly
- continuous secretion of HCl (empty stomach + HCl –> ulcers)
- increased starch in cecum/colon –> rapid fermentation and alters bacterial population –> colic
What is the main role of the glandular portion of the stomach?
Secrete HCl and pepsinogen (activated to pepsin)
List 3 large intestine idiosyncracies
- cecum contains bacteria and protozoa for fermentation of undigested feedstuff
- microbial action synthesizes vitamins, VFAs, AAs
- VFAs produced this way can provide 75% energy requirement
- cecum is main site of water absorption
- microbial synthesis of vitamins isn’t enough to meet daily requirements
- undigested protein is degraded to ammonia
- microbial AA synthesized from protein is not significant because there is little active AA transport in LI
- horses less able to improve the AA profile of low quality protein
Why do foals need a vitamin K sot when they are born?
They have underdeveloped cecum & colon and thus do not have the bacteria present in order to produce sufficient vitamin K
Why is there increased absorption of nutrients in the duodenum and jejunum compared to the ileum?
The duodenum receives ducts from the pancreas and liver, which releases bile containing starch digesting amylases and fat emulsifying lipases. Therefore, nutrients are small enough to be absorbed in the duodenum and jejunum. The ileum contains more immune tissue than the duodenum and jejunum.
