combined asci 112 and 229 gastrointestinal flashcards

goal of digestion

to reduce macromolecules into simple monomers that can be absorbed by the body

mechanical digestion

• mastication

• mixing

• rumination

chemical digestion

the enzymatic breakdown of food molecules into smaller units

autoenzymatic digestion

• endogeneous enzymes

  • pepsin

  • lipase

  • amylase

alloenzymatic digestion (fermentation)

• exogeneous enzymes

  • cellulase

  • hemicellulase

• microbiome

  • bacteria

absorption

the process by which nutrients from digested food are taken up into the bloodstream or cells

oral cavity

• significant mechanical reduction

  • chemical: initiate carbohydrate and lipid reduction

• salivary amylase: carbohydrates

• salivary lipase: lipids

  • water

  • electrolytes

  • mucus

  • buffers (bicarbonate, phosphate buffers)

pharynx

• common passage for food and air

• lined by mucus membrane

• surrounded by muscle - plays a role in swallowing

esophagus

• muscular tube extending from the pharynx to the cardia (cardiac sphincter) of the stomach

stomach

• minor mechanical digestion

• chemical: initiate protein digestion

  • gastric lipase → lipids

  • pepsin → proteins

• HCL → activate protein digesting enzymes

cells that line the stomach

chief cells and parietal cells

chief cells

release pepsinogen

parietal cells

release HCL

• the release of HCL is a catalyst to break down pepsinogen into pepsin

• a precursor is always needed for protein digesting enzymes

small intestine

• major organ of digestion and absorption

• chemical digestion

  • digestive enzymes

• absorption through lining

  • over 6 meters

  • has a large SA

3 sections of small intestine

• duodenum

• jejunum

• ileum

duodenum

• most digestion

• acid and food from stomach mixes with digestive juices from:

  1. pancreas

  2. liver

  3. gallblader

accessory organs

1. pancreas

2. liver

3. gallbladder

absorption by SI

• through villi & microvilli

  • finger-like projections

  • increase SA

carbohydrate - digestion

______________ → pancreatic amylase → maltase → glucose → blood capillary

protein - digestion

__________ → trypsin → peptides → peptidase → amino acids → blood capillary

fat - digestion

bile salts + ___ globules → emulsification droplets → lipase → monoglycerides and free fatty acids → chylomicron → lymphatic capillary

pancreatic enzymes

• pancreatic amylase

• trypsin

• lipase

bile

• digestive fluid produced by liver

• stored in gallblader

• disperses fat droplets

large intestine

• little to no mechanical reduction

• no secretions to aid in chemical digestion

• major site of water absorption (monogastrics)

• site of fermentation

accessory glands

• salivary

• pancreas

• liver

salivary gland

• parotid

• mandibular

• sublingual

  • secretion of saliva is a reflex stimulated by presence of food or anticipation of food

    • under neural control

saliva contains

• water

• electrolytes

• mucus

• bicarbonate

• phosphate buffers

• enzymes

salivary enzymes

• amylase → carbohydrates

• lipase → lipids

pancreas

• secretes pancreatic juice from acinar cells filled w/ enzymes for nutrient digestion into SI

  • amylase: CHO

  • lipase: lipids

  • trypsinogen: inactive enzyme for protein digestion

• secretes sodium bicarbonate from duct cells

  • buffers acid from stomach

acinar cells

pancreatic secretion cells

hormones that signal to pancreas

1. secretin → bicarbonate digestion

2. CCK → enzyme and bile secretion

   • hormones produced by cells lining duodenum

digestive process

1. food flows: stomach → duodenum

   • acidic

   • triggers cells in duodenum to produce secretin and CCK into blood

2. hormones go to pancreas

   • signals pancreas to release enzymes and sodium bicarbonate

liver

• glandular organ in abdomen

  • regulates glycogen storage

  • detoxification of metabolites

  • protein synthesis

  • produces bile

  • gluconeogenesis

dual blood supply

• hepatic portal system: collects blood

• hepatic artery system: provides O2

hepatic portal system

• collects blood from GI

  • ¾ of total blood flow

hepatic artery system

• provides 30-40% of O2 needed for liver

  • ¼ of total blood flow

bile ducts

• collect bile produced by liver cells → sends to gallbladder

• critical to fat digestion

gallbladder

organ that stores bile

emulsification

the mixing of contents of the stomach for digestion

chylomicron

package of absorbed lipids that pass into lymphatic system

emulsified fat droplets

• bile salts will embed their heads in the fat droplets, repulsive action of the tail breaks droplet into smaller pieces

salivary glands

parotid, mandibular, sublingual

pancreatic enzymes

amylase, lipase, trypsinogen

sodium bicarbonate

comes from pancreatic duct cells

the liver

• organ that produces bile

• site of gluconeogenesis

prehension

grasping or ripping or tearing the food with the lips and teeth

mechanical digestion

mastication: chewing and grinding with the teeth

• mixing and breaking up via muscular contractions

chemical digestion

enzymatic and fermentation

mouth

• prehension

• taste

• chewing: teeth

carnivores

large canine teeth; for tearing rather than chewing

herbivores

molars and premolars flattened for grinding plant material

location of teeth

hypsodont

• teeth that are continuously erupting

• in horses and cows, not growing continuously

  • fully formed but emerging from gumline over time

brachydont

once tooth is fully erupted, will not emerge any further

functions of oral cavity

• first steps in digestion

• prehension of food

  • picking it up

• mastication

  • increases surface area of food for chemical digestion

  • mixes food with saliva

• saliva production

  • lubricates food

  • contains digestive enzymes

    • amylase: breaks down starch

layers of GI tract

mucosa, submucosa, muscularis layer, serosa

mucosa

• innermost layer

  • subdivided into 3 layers

    • simple columnar epithelium

    • lamina propria

    • muscularis mucosae

submucosa

2nd innermost layer

muscularis layer

• two layers of smooth muscle

• layers run perpendicular to each other

serosa

• connective tissue

• outermost layer

esophagus

• long, muscular tube

• moves food from mouth → stomach

• lined with non-cornified stratified squamous epithelium

• enters stomach at cardiac sphincter

• goblet cells

choke

• esophageal obstruction

  • cattle and horses

• esophagus is blocked by something

  • dry feed

  • large, chunky food items

  • masses of grass

monogastric stomach

• horses, pigs, humans, dogs, cats, etc. are monogastric

  • single chamber stomach

• subdivided into regions

  • cardia

  • fundus

  • body

• pyloric antrum

• pylorus

• lesser curvature

• greater curvature

margo plicatus

in horses, visible dividing line between fundus and body

absorption

• in monogastric stomachs:

  • limited _________ compared to intestines

  • water and some small molecules absorbed

gastric glands

• epithelium invaginates, creating gastric pits

• lead into ______ _____

• comprised of several cell types

  • each cell type secretes something different

parietal cells

• secrete hydrogen ions (H+) and chloride ions (Cl-)

  • via an active pump

  • together form hydrochloric acid

  • functions of HCl

    • killing of pathogens

    • protein digestion: denatures proteins

    • H+ converts pepsinogen to pepsin

chief cells

• secrete pepsinogen

• precursor to pepsin

  • pepsinogen → pepsin in presence of H+

• breaks down protein

gastric function

• food (ingesta) passes from esophagus through cardiac sphincter into stomach

• muscular action of stomach mixes food with gastric secretions

  • mucus

  • pepsin and HCl begin process of protein digestion

• when mixing, turns into chyme

  • pylorus acts to keep ingesta in stomach

  • when chyme is liquid enough, pyloric antrum contracts

  • chyme is squirted through pylorus into duodenum

ruminant stomachs

• rumen

• reticulum

• omasum

• abomasum

  • true stomach

    • don’t secrete digestive enzymes/ HCl

rumen

• the largest compartment

  • fills up majority of the LEFT side of the abdomen, from diaphragm to pelvis

  • may hold up to 40 gallons in adult cow

• fermentation via microbes

  • break down cellulose

  • bacteria, protozoa, and fungi

• convert cellulose → simple carbohydrates → volatile fatty acids (VFAs)

• convert proteins → peptides and amino acids

  • the microbes use some

  • convert others to ammonia and VFAs

types of VFAs

propionic acid, butyric acid, acetic acid

VFAs are

• absorbed across rumen wall

• transported to liver

  • propionic acid → glucose

  • butyric + propionic → used for energy in tissues

• 70% of cow’s total energy requirement

reticulum

• located between rumen and heart

• fermentation occurs here as well

• honeycomb appearance increases surface area

• receives denser materials

hardware disease

• heavy items that are ingested go to reticulum

• reticulum is in close contact w/ heart

• curious eaters

• metals can end up sitting in reticulum

  • can pierce wall of reticulum and into pericardium

  • infection/ abscess around the heart

omasum

• ingesta travels from rumen to omasum

• muscular and filled with leaf-like folds

  • breaks down particulate matter further

  • continues to absorb VFAs

  • leaves allow absorption of large quantities of H₂O

abomasum

• “true” stomach

• highly acidic

  • normal cow rumen pH is between 5.5-7 (depending on if grain or grass fed)

  • abomasum pH is normally around 2

• rugal folds like the monogastric stomach

• contents flow through pylorus into small intestine

esophageal groove

• rumen not a good destination for milk

  • fermentation won’t occur until microflora have established

  • rumen doesn’t have appropriate enzymes for milk digestion

• esophageal groove: fold of tissue between esophagus and omasum

  • creates a tube

  • conveys milk directly into omasum so it can be digested in abomasum and small intestine

intestinal segments

• small intestine

  • duodenum

  • jejunum

  • ileum

• large intestine

  • cecum

  • large colon (ascending, transverse, and descending segments)

  • rectum

duodenum

• receives contents from stomach

• cholecystokinin (CCK)

  • increases release of digestive enzymes

  • triggers gallbladder contraction (bile release)

  • multitude of other functions

• bicarbonate is secreted into lumen to neutralize chyme

• jejunum = largest portion

• ileum = shortest portion at end

absorption in SI

• maximized SA

  • mucosal folds

  • villi

  • microvilli: hairlike extensions

• each villus contains arterial vessel, venous vessel, and a lacteal

  • most nutrients taken up into venous vessel

  • facts go into the lacteal

pancreatic enzymes

• amylase: breaks down starch

• lipase: breaks down fat

• protease: breaks down protein/ peptides

bile

• released into duodenum from gallbladder

  • breaks down fat into smaller droplets

columnar

once nutrients have been broken down into component parts, transport proteins move them into _________ epithelial cells that line the small intestine

• then taken to liver via blood vessels

large intestine

• ileum deposits digesta into large colon (most species) or cecum (horse)

  • cecum is a sac-like structure

    • opens into colon

    • highly enlarged in horses

  • ruminants and pigs: spiral colon

• water absorption occurs throughout _____ _________

  • electrolytes

  • vitamins

mesentery

• suspends intestines in abdominal cavity

• veins and arteries supplying the GI tract run through it in a spider-web like pattern

pancreas

• secretes digestive enzymes

  • exocrine function

  • also has endocrine functions (insulin)

• located between duodenum and stomach

• lipase, amylase, protease, bicarbonate

liver

• all blood that went to GI tract goes to liver

  • through portal vein

  • liver “cleans” blood and modifies nutrients for use

  • produces bile

• cleaning function

  • filters toxins

  • infectious agents

• metabolism function

  • turns glucose → glycogen

  • synthesizes proteins from AAs

bile production

• hepatocytes

• stored in gallbladder

  • balloon like structure attached to liver

    • drains into duodenum

• bile salts emulsify fat

  • break into smaller droplets

  • surround each droplet with hydrophilic layer

  • increases surface area for digestion

mucin

• highly viscous glycoprotein secretion

• produced in cardiac + pyloric regions

• protects mucosa

gastrin

• released from pyloric cells

• due to stomach distension/ presence of proteins

• stimulates HCl and pepsinogen release, gastric motility

rennin

• proteolytic enzyme produced by gastric region cells

• only produced in young mammals

• coagulates milk to reduce rate of passage

  • causes casein protein to curd

pancreatic juice

• clear, watery

• enters duodenum via pancreatic duct

• contains digestive enzymes (ex. trypsin + amylase)

• stimulated by secretin and CCK

gastric inhibitory protein

• from duodenum wall cells

• released in response to lipid + protein in duodenum

• decrease stomach acid, decrease motility

secretin

• produced from walls of duodenum

• (+) production of pancreatic juice

succus entericus

• intestinal juice

• secreted from glands between villi

• made of:

  • sucrase

  • maltase

  • lactase

  • enzymes active to epithelial membrane absorption site

  • continues digestion of enzymes that escaped pancreatic digestion

coprophagy/ cecatrophy

• consumption of one’s own feces

80

horses get __% of energy from VFAs

microbes produce

• protein

• vitamin K

• production of heat

• detoxify

batch reactor

• discontinuous input

• well mixed, uniform

• composition changes with time

• discontinuous output

• ex:

  • glandular stomach (carnivores)

  • ceca (birds, rabbits)