Structure And Digestive Properties Flashcards
Jejunum
Enzymatic digestion and absorption
Duodenum
Site of entry of pancreatic and biliary secretions
Ileum
Reabsorption of bile salts
Hormone production
Digestion
Breakdown of food molecules by enzyme action
3 spatial categories of digestive enzymes
Intraluminal: secreted, work in the SI lumen
Membrane associated: apical membrane of epithelial cells
Intracellular: enzymes within the cells
Pancreas
Enzyme secretion : trysinogen, amylase,lipase
Bicarbonate secretion
Hormone secretion
Acinar cells
Exocrine secretion
Enzymes ( amylase,lipase)
Duct cells
Exocrine secretions
Bicarbonate
Trypsin
Activate the pancreatic zymogens
Liver
Produces bile
Gallbladder
Storage organ for bile
Bile salts
Made from cholesterol
Modified to have polar end
Non polar interacts with fat
Endocrine regulation of bile secretion
CCK: relaxes Sphincter of Oddi, gallbladder contractions
Secretin: bicarbonate secretion
Positive Feedback of bile secretion
Bile acids reabsorbed in ileum and return to liver
Increases bile production as long as CCK keeps gallbladder contracting and sphincter open
Absorption
Must cross apical and basolateral membrane
Monosaccharides, amino acids and water soluble vitamins absorption
Carrier-mediated transport (active or passive)
Electrolytes and mineral absorption
Through channels
Carrier mediated transport (active or passive)
Fats and fat soluble vitamins absorption
Lipid micelles diffuse through membrane
Chylomicron synthesis and release into lymph
Cecum
Blind sac Paired in birds Enlarged in hind guy fermenters Microbial fermentation (some species) and VFA absorption Water and electrolyte absorption
Colon
Microbial fermentation ( some species) and VFA absorption Water abs electrolyte absorption
Rectum
Not in birds, cloaca instead
Storage if feces prior to defecation
Microbes –>
Fiber (cellulose)–> glucose –>VFA
What does VFA stand for?
Volatile Fatty Acid
3 types of VFAs
Acetic
Propionic
Butyric
2 types of neurons in the enteric nervous system
Receptor and sensory neurons: mechanoreceptors and chemoreceptors
Motor neurons: innervate gut muscle, blood vessel muscle, glands
Release neurocrines
Neurocrines
Released from motor neurons in response to an action potential
ENS communicates with the CNS through autonomic nervous system
Parasympathetic motor neurons: stimulatory
Sympathetic motor neurons: inhibitory
Motility
Movement of gut wall
Roles of motility
Moves digesta along GIT
Retains digesta for digestion,absorption,storage
Physically breaks down food, mix it with secretions
Bring digesta in contact with absorptive surface
Peristalsis
Main propulsive motility pattern
Occurs from the esophagus to the end of the large intestine
Coordinated contraction of longitudinal and circular smooth muscles
Peristalsis behind the bolus
Circular muscles-contracted
Longitudinal muscles- relaxed
Peristalsis ahead of the bolus
Circular muscles-relaxed
Longitudinal muscles-contracted
Net effect of peristalsis
Bolus pushed down the GIT
Segmentation
Non propulsive motility pattern Allows digesta to be retained in a segment of the intestine Allows mixing with secretions Gives time for absorption to occur Small and large intestine
How does segmentation work?
Contraction of short segments of circular muscles creates areas of constricted and displayed lumen
Avian foregut digestion: Crop
Mucous secretion
Avian foregut digestion: proventriculus
Glands secrete acid, mucous and pepsinogen
Similar gastric,cephalic and intestinal phases as in mammals
Gizzard
Muscular contractions move digesta between proventriculus, gizzard and duodenum
Motility in the stomach: proximal region
Adaptive relaxation: stomach expands to accommodate digesta: storage
Keeps pressure in stomach constant
Motility in the stomach: distal region
Peristalsis: pushes digesta towards the pyloric sphincter (which is constricted) =mixing and grinding
Only small particles can leave the stomach
Small intestine motility: during digestion:
Peristalsis moves digesta for short distances, followed by cycles of segmentation contractions
Moves digesta down GIT
Allows for mixing and absorption
Small intestine motility: inter digestive phase:
Powerful waves of peristalsis
Covers large distances
Pushes remaining material out of SI
Large intestinal motility: segmentation
Allows for mixing, fermentation, and absorption (cecum and colon)
Large intestinal motility: retropulsion(antiperistalsis)
In the colon, waves of contraction that move in the direction of the cecum/small intestine
Retains digesta for longer, mixing
Opposed by the inflow of digesta from the ileum
In birds, moves material from cloaca back into LI
Cellulose
Fiber
β 1-4 linkages of glucose
Mammalians cannot digest
Starch
α 1-4 linkage
Ruminants
Herbivores that consume a high fiber diet
Examples of ruminants:
Cows sheep goats deer giraffes bison antelope oxen
Ruminants 4 chambers
Reticulum
Rumen
Omasum
Abomasum
Pseudo ruminants
Camels llamas and alpacas do not have omasum
Foregut fermenters
Microbes found in reticulum and rumen
What is the difference in non ruminants and ruminants?
Foregut
Mouth of a ruminant
No upper incisors
Chewing of a ruminant
Vertical and lateral motion
