Advance Digestive Physiology (part 1) By: A. Riasi (PhD in Animal Nutrition and Physiology) Isfahan University of Technology

 Development of digestive system  The properties of ruminant’s digestive tracts  Salivation  The receptors  The salivary glands  Control of salivation The topics

 Mastication and swallowing  Rumen and reticulum properties  Characteristics of the preruminant stomach  The wall structure  Development and control of forestomach motility  Blood circulation  Receptors The topics

 Rumination and its components  Attempts to control ruminoreticulum fermentation  Events associated with eructation  Absorption  Urea recycling  The role of thermodynamics in ruminant digestive The topics

 Omasum  Omasal motility  The properties of obomasum  Glands and secretions  Microscopic anatomy  Abomsal motility The topics

 Small intestine  Wall layers  Neuronal network  Blood circulation  Movements control  Transport systems in the epithelia  Entrogastric inhibitory reflex The topics

 Large intestine  Wall properties  Absorption  Motor activity of cecum  Evacuation contractions  Defecation The topics

 References  Ruminant Physiology, by Sejrsen et al (2006)  Ruminant Physiology, by Cronje (2000)  Farm Animal Metabolism and Nutrition, by D’Mello (2000)  Original and review papers

Advantages of pregastric fermentation  Make better use of alternative nutrients  Cellulose  NPN  Ability to detoxify some poisonous compounds  Oxalates, cyanide, alkaloids

Advantages of pregastric fermentation  More effective use of fermentation end products  Volatile fatty acids  Microbial protein  B vitamins  Decrease in handling undigested residues  In wild animals, it allows animals to eat and run

Disadvantages of pregastric fermentation  Fermentation is inefficient  Energy Loss Amount (% of total caloric value) Methane 5-8 Heat of fermentation 5-6

Disadvantages of pregastric fermentation  Fermentation is inefficient  Protein Some ammonia resulting from microbial degradation will be absorbed and excreted 20% of the nitrogen in microbes is in the form of nucleic acids

Disadvantages of pregastric fermentation  Ruminants are susceptible to ketosis  Ruminants are susceptible to toxins produced by rumen microbes  Nitrates Nitrites  Urea Ammonia  Nonstructural carbohydrates Lactic acid  Tryptophan Methyl indole  Isoflavonoid estrogens Estrogen

Development of digestive system Common Duiker, Deer Goats, Sheep, Moose Cattle, Bison

Development of digestive system Common Duiker, Deer Goats, Sheep, Moose Cattle, Bison

Development of digestive system Common Duiker, Deer Goats, Sheep, Moose Cattle, Bison

Development of digestive system Common Duiker, Deer Goats, Sheep, Moose Cattle, Bison

 The digestive system of animals has different function:  Ingestion (eating)  Chewing (mastication)  Swallowing (deglutition)  Absorption of nutrients  Elimination of solid wastes (defecation) The ruminant digestive tract

 The wall of digestive tract as a hollow organ consisting of several layers:  Mucosa,  Submucosa,  Muscularis externa and  Serosa/adventitia. The ruminant digestive tract

 The functions of mucosa:  Secretion of enzymes, acid, mucin, hormones and antibodies,  Absorption of the break down products of digestion, water, vitamins and etc,  Barrier to prevent the entry of antigens, pathogenic organisms, and immunologic protection. The ruminant digestive tract

 The digestive system of ruminant animals includes the different parts:  Oral cavity  Esophagus  Multi-chambered stomach  Small intestine  Large Intestine The ruminant digestive tract

 Salivary glands and salivation ◦ Secretions contain:  Enzymes (amylase and lipase)  Water  Glycoproteins Salivary gland and salivation

 Salivary glands and salivation ◦ Saliva has secretory IgA, lactoferrin and lysozyme. ◦ Saliva can serve a neutralizing function Salivary gland and salivation

 The salivary glands have different function ◦ Preparing enzymes ◦ Moistens and lubricates feed ◦ Water balance ◦ Bloat prevention ◦ Recycling of N and minerals including Na, P, and S ◦ Buffer secretion Salivary gland and salivation

 The architecture ◦ Secretory units  Serous  Mucous Salivary gland and salivation

◦ Ducts  Intercalated  Striated intralobular  Interlobular  Main excretory duct ◦ Myoepithelial cells ◦ Lymphocytes and plasma cells Salivary gland and salivation

In the left panel you see both serous and mucous secretory areas, in among the strands of skeletal muscle in the tongue. At right, a large serous gland is discharging via a duct (D) into the moat (M) around a vallate papilla. Salivary gland and salivation

 Different kinds of salivary galnds  Parotid  Mandibular  Sublingual  Some minor gland Salivary gland and salivation

 Salivary flow ◦ Saliva production occurring in 2 phases:  Primary secretion  Ductal secretion ◦ The salivary ducts rely heavily on the Na/K/2Cl cotransporter. Salivary gland and salivation

 Salivary flow ◦ The degree of modification of saliva in the ducts turns heavily on salivary flow rate.  Fast rates result in a salivary product more like the primary secretion.  Slow rates result in an increasingly hypotonic and potassium rich saliva. ◦ Effect of autonomic nervous system Salivary gland and salivation

 Salivary flow ◦ Ruminant produce a high daily output of saliva.  6 to 16 L/d in sheep  60 to 160 L/d in cattle Salivary gland and salivation

Salivary glandsTotal salivary volumes (L d) CharacteristicsSite of reflexogenic stimuli Parotids Inferior molars Palatine, buccal, pharyngeal Submaxillary Sublingual, labial Serous, isotonic, strongly buffered Isotonic, strongly buffered Mucous, hypotonic, weakly buffered Very mucous, hypotonic, weakly buffered Mouth, esophagus, ruminoreticulum Mouth during feeding, not cudding Mouth Total volume6-16 Salivary gland and salivation

 Salivary flow ◦ The secretions from the parotid glands are:  Isotonic with blood plasma,  Have no significant amylase content,  Change their composition in response to salt depletion,  Have a high alkalinity (pH 8.1)  Recycling the N and P Salivary gland and salivation

 Salivary flow ◦ A 700 kg dairy cow fed a hay-grain diet will secrete:  190 l saliva/day containing  gm total N  1100 gm NaHCO 3  350 gm Na 2 HPO 4  100 gm NaCl Salivary gland and salivation

 Control of salivary flow ◦ A basal level of parotid secretion occurs even in the totally denervated. ◦ Excitation of the secretory (acinar) cells by by the parasympathetic nerve endings. ◦ The increase in parotid blood flow does not exactly parallel the increase in parotid secretion. Salivary gland and salivation

◦ Salivary reflexs are integrated in salivary centers located in the hindbrain. ◦ The buccal mechanoreceptors located in or near the tooth sockets have major effect.  Chewing of ingesta in cattle may increase salivary secretion from 2 ml/min to 30 to 50 ml/min. Salivary gland and salivation

◦ The distension of the esophagus, reticulum, reticuloomasal orifice, and ruminoreticular ◦ Little increase is evoked by lightly stroking the ruminoreticular epithelium. ◦ Reflex increases in salivation may be inhibited by concurrent stresses and excitement. Salivary gland and salivation

◦ Some feeding factors may affect the saliva flow:  Dietary fiber concentration  Forage to grain ratio of the diet  Maturity of the forage ◦ Diet particle size  Grinding  Grain processing by-products  Diet moisture level Salivary gland and salivation