By: A. Riasi (PhD in Animal Nutrition & Physiology) Advanced Digestive Physiology (part 1) Isfahan University of Technology Isfahan, Iran

 The properties of ruminant 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 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 refl ex 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

The fermentor animals  Cranial fermentors (or ruminants)  Caudal fermentors (or cecal digestors)

FunctionRuminantsCecal fermentors Ability to efficiently digest and extract energy from celluloseYes Ability to utilize dietary hexose sources directlyNoYes Ability to utilize the protein from fermentative microbesYesNO Remember: The small intestine is the only site where simple sugars and amino acids can be absorbed in all animals!? Adapted from: Animal Nutrition Handbook Section 3: Rumen Microbiology & Fermentation The fermentor animals

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 Adapted from: Animal Nutrition Handbook Section 3: Rumen Microbiology & Fermentation  Substances detoxified in the rumen:

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

Adapted from: Animal Nutrition Handbook Section 3: Rumen Microbiology & Fermentation  Toxic substances produced in the rumen: Disadvantages of pregastric fermentation

 The wall of digestive tract as a hollow organ consisting of several layers:  Mucosa  Submucosa  Muscularis externa  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 tract 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

Schematic diagram of typical salivary gland. A, Serous endpiece; A’, in cross section. B, Seromucous demilune; B’, in cross section. C, Mucous endpiece; C’, in cross section. D, Intercalated duct; D’, in cross section. E, Striated duct; E’, in cross section. F, Terminal excretory duct. (Modified from Ten Cate AR: Oral histology, ed 2, St Louis, 1985, Mosby.)

Salivary gland and salivation A myoepithelial cell can be seen with its processes surrounding an acinus. (From Nanci A: Ten cate’s oral histology, ed 8, St. Louis, 2013, Mosby)

 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  g total N  1100 g NaHCO 3  350 g Na 2 HPO 4  100 g 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 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

Saliva as a source of systemic biomarker Adapted from: E. Lamya, and M. Maud, 2012

Mastication  Chewing of food is fast and irregular with variable amplitude.  The differences of chewing and rumination: Rumination is much more slowly and evenly Rumination is usually on one side Rumination occasionally changed to the opposite side

 Direct and indirect effects of mastication: Break the stem and leaf fragments of food and to cud solids into small particles. Movements of the teeth excite sensory buccal mechanoreceptors. Mastication

 The swallowing has three phases: Oral Phase Pharyngeal phase Esophageal pahse Swallowing