Digestion and Absorption part 2
The mouth, salivary glands, and esophagus
● Mouth: is the initial grinding of feed
● Mastication: reduce feed particle size and mix feed with saliva
● Ruminant animals: complete mastication of regurgitated ruminal contents
● Saliva: moisture the feed
● Salivary glands: parotid, mandibular, sublingual, buccal
Ingestion and rumination
● Ingested feed is chewed to mix it with saliva and form a bolus
● The bolus is deposited in the anterior portion of the rumen
● Rumination:
○ Regurgitation of the digested from the reticulo-rumen
○ Swallowing of regurgitated liquids
○ Re-chewing of solids accompanied by further salivary secretion
○ Re-swallowing of the bolus
Saliva functions
● Moistens the feedstuffs: chewing and bolus formation
● Lubricates the bolus: easy swallowing and passage down
● Digestive action: enzymes (lipases and amylases)
● Water balance → a lot of recycling of water and saliva
● Buffering compounds
● contains recycled N and minerals (Na, K, Mg, P, Cl)
Note: Wave-like movements called peristalsis moves the bolus of food down the esophagus
The forestomach of the ruminant and the crop of poultry
The function of forestomach (rumen, reticulum, and omasum): store and delay passage of
ingested food, as well as sites of anaerobic microbial fermentation of plant materials and
absorption.
The Forestomach has three compartments which are the rumen, reticulum, and omasum
The reticulum or “honeycomb” absorbs most of the fatty acids.
, Omasum
The function of the omasum is the absorption of water and minerals.
The omasum is the third compartment of the stomach
Has a shag-like appearance
Abomasum (is the true stomach)
Abomasal mucosa
● The abomasum has a glandular gastric mucosa comparable to that of other mammals
● The wide initial portion of the abomasum contains proper gastric glands with HCl-
producing parietal cells and chief cells that produce proteases
Note: Proteases are enzymes that digest and degrade down proteins
The crop of poultry
The crop of a chicken is where food is stored
The proventriculus is the true stomach of the chicken
Proventriculus in chickens
Causes:
● HCl production
● Digestion of proteins
True stomach functions
Parietal cells: HCl secretion
Chief cells:
● Gastric lipase
● Pepsinogen → pepsin
● Prorennin → rennin/chymosin (curdle milk)
Chyme: a semi-fluid mixture of digestive secretions and partially digested feed material
Chymosin or rennin is produced by gastric chief cells in young ruminants and some other
newborn animals to curdle the milk they ingest, allowing a longer residence in the bowels and
better absorption.
Chymosin is also produced by gastric chief cells in human infants. Some other non-ruminant
species, including pigs, cats, and seals, produce it.
The gizzard or muscular stomach
The gizzard grinds the food with previously swallowed stones and passes it back to the true
stomach/proventriculus, and vice versa.
The mouth, salivary glands, and esophagus
● Mouth: is the initial grinding of feed
● Mastication: reduce feed particle size and mix feed with saliva
● Ruminant animals: complete mastication of regurgitated ruminal contents
● Saliva: moisture the feed
● Salivary glands: parotid, mandibular, sublingual, buccal
Ingestion and rumination
● Ingested feed is chewed to mix it with saliva and form a bolus
● The bolus is deposited in the anterior portion of the rumen
● Rumination:
○ Regurgitation of the digested from the reticulo-rumen
○ Swallowing of regurgitated liquids
○ Re-chewing of solids accompanied by further salivary secretion
○ Re-swallowing of the bolus
Saliva functions
● Moistens the feedstuffs: chewing and bolus formation
● Lubricates the bolus: easy swallowing and passage down
● Digestive action: enzymes (lipases and amylases)
● Water balance → a lot of recycling of water and saliva
● Buffering compounds
● contains recycled N and minerals (Na, K, Mg, P, Cl)
Note: Wave-like movements called peristalsis moves the bolus of food down the esophagus
The forestomach of the ruminant and the crop of poultry
The function of forestomach (rumen, reticulum, and omasum): store and delay passage of
ingested food, as well as sites of anaerobic microbial fermentation of plant materials and
absorption.
The Forestomach has three compartments which are the rumen, reticulum, and omasum
The reticulum or “honeycomb” absorbs most of the fatty acids.
, Omasum
The function of the omasum is the absorption of water and minerals.
The omasum is the third compartment of the stomach
Has a shag-like appearance
Abomasum (is the true stomach)
Abomasal mucosa
● The abomasum has a glandular gastric mucosa comparable to that of other mammals
● The wide initial portion of the abomasum contains proper gastric glands with HCl-
producing parietal cells and chief cells that produce proteases
Note: Proteases are enzymes that digest and degrade down proteins
The crop of poultry
The crop of a chicken is where food is stored
The proventriculus is the true stomach of the chicken
Proventriculus in chickens
Causes:
● HCl production
● Digestion of proteins
True stomach functions
Parietal cells: HCl secretion
Chief cells:
● Gastric lipase
● Pepsinogen → pepsin
● Prorennin → rennin/chymosin (curdle milk)
Chyme: a semi-fluid mixture of digestive secretions and partially digested feed material
Chymosin or rennin is produced by gastric chief cells in young ruminants and some other
newborn animals to curdle the milk they ingest, allowing a longer residence in the bowels and
better absorption.
Chymosin is also produced by gastric chief cells in human infants. Some other non-ruminant
species, including pigs, cats, and seals, produce it.
The gizzard or muscular stomach
The gizzard grinds the food with previously swallowed stones and passes it back to the true
stomach/proventriculus, and vice versa.
