Physio 2

• Functions of the gastrointestinal system of animals include; digestion in forestomachs, digestion in the intestine, absorption, and excretion
• The content covered includes digestion in ruminant forestomachs, organs that secrete substances into the small intestine, digestion in the small and large intestine, elimination of waste material, and digestion in birds

Digestion in the Ruminant Forestomachs

• Ruminants (cattle, deer, etc.) cannot directly digest plant material due to a lack of enzymes to break down cellulose in cell walls.
• Digestion occurs sequentially in a four-chambered stomach consisting of the non-glandular forestomach (rumen, reticulum, omasum) and terminal glandular stomach, the abomasum.

The Reticulum

• Acts as a flask-shaped compartment with a "honeycomb" appearance.
• It moves ingested food into the rumen and omasum and causes the regurgitation of ingesta during rumination.
• It also acts as a collection compartment for foreign objects.

The Rumen

• The largest compartment by volume in the ruminant forestomach.
• The mucosa varies regionally but forms variably pronounced leaf-like papillae.
• Primary function is as a storage compartment to facilitate microbial (bacterial and protozoal) fermentation of ingesta.
• Volatile fatty acids (VFAs like acetic, propionic, and butyric acids) are by-products of this fermentation.
• VFAs are readily absorbed across the ruminal mucosa into the circulation, serving as a directly accessible energy source.

Carbohydrate Digestion in Rumen

• Occurs through microbial fermentation.
• Dietary carbohydrates are degraded (fermented) by rumen microbes.
• The purpose of rumen fermentation is to produce energy as ATP for bacteria to use for protein synthesis and growth.
• VFAs (short-chain fatty acids) are produced as a product of rumen fermentation.
• VFAs are absorbed through the rumen wall into the portal vein and carried to the liver.

Microorganisms in the Rumen

• Bacteria, protozoa, and fungi are necessary for cellulose digestion and other plant materials.
• Rapid feed changes affect the microflora in the forestomachs.

Rumen Bacteria

• Play a major role in fermentation, converting cellulose from plants into usable energy products.
• Many different kinds of bacteria that are found only in the rumen.
• Some rumen bacterial species also digest starch, sugars, and other plant materials.
• Some bacteria can utilize gases and acidic by-products from other rumen bacteria and even destroy competing bacteria.
• They are strictly anaerobic (obligate anaerobes).
• Bacteria produce all necessary B vitamins
• Large amounts end up in the abomasum.
• Rumen bacteria are classified based on the nutrients they metabolize:
  • Cellulolytic: degrade cellulose and other carbohydrates in plant cell walls.
  • Hemicellulolytic: degrades hemicellulose.
  • Amylolytic: degrades starch and other soluble carbohydrates, but not cellulose.
  • Proteolytic: breaks down proteins.
  • Sugar utilizers: simple saccharides.
  • Ammonia producers.
  • Vitamin synthesizers.
  • Methane producers (Produce CO2, H2, formate, CH4).

Rumen Protozoa

• They are large, and single-celled organisms.
• They come in different shapes and sizes.
• They usually have microscopic hairs called cilia which help them move food to their mouth.
• They are obligatory or facultative anaerobic, meaning they can survive with or without oxygen.
• The rumen protozoa are able to use the low levels of oxygen that enter the rumen.
• This helps maintain anaerobic conditions important for the survival of rumen bacteria.
• They eat large amounts of starch at one time and store it, which may help slow down the production of acids, benefiting the rumen.
• Also eat bacteria as a source of nutrients, preventing bacterial overgrowth.
• As much as 50% of the microbial mass in the rumen can be protozoa.
• They are about 40 times the size of rumen bacteria
• The rumen protozoa produce fermentation end-products similar to bacteria, particularly acetate, butyrate, and hydrogen.
• Rumen methane bacteria attach and live on the surface of rumen protozoa for immediate access to hydrogen.
• Rumen protozoa multiply slowly, taking 15-24 hours, and hide in the slower-moving fiber mat of the rumen to avoid being washed out.
• Low roughage diets reduce retention of fiber in the rumen and decrease the number of protozoa in a cow's rumen.

Rumen Fungi

• Most are strictly anaerobic, but some can degrade lignin under aerobic conditions.
• They attach to feed particles and reproduce very slowly.
• Rumen fungi help fiber-digesting bacteria by splitting fibrous material apart.
• They need nutrition and vitamins from rumen bacteria.
• Contribute to fermentation.

The Omasum

• Contains numerous laminae (tissue leaves) that help grind down ingesta.
• The folds assist in the removal of fluid from the ingesta on their way to the abomasum.
• Reduces particle size and they allow for absorption of water and VFAs.
• Prevents buffering of the abomasum.

The Abomasum

• Serves as the true gastric stomach with three regions: cardiac, fundic, and pyloric.
• Here, digestive secretions like proteolytic enzymes and HCl are added, which leads to a pH decrease from 6 to 2.5.
• It denatures proteins, kills bacteria and pathogens, dissolves minerals, and allows for gastric digestion.

Layering of the rumen content of cows:

• Gas Layer
• Fiber Mat (Intense Fermentation)
• Intermediate Zone (Intense Fermentation)
• Liquid Zone (Moderate Fermentation)

Contractions of the Reticulum and Rumen

• There are three types of contractions in the reticulorumen the following:

  • Mixing Contractions (Primary Contractions)
  • Contractions related to eructation of gas (Secondary Contractions)
  • Contractions related to Rumination
    • The forestomach content is transported to the oral cavity for additional chewing where they will reduce the size of feed particles, thereby exposing new surfaces for fermentation
    • Animals that consume fiber-rich forage, ruminate longer

• High-yielding dairy cows produce 2000-4000 L of gas in the forestomachs each 24-h period

Organs That Secrete Substances Into Small Intestine

• The small intestine and near organs are protected from digestive enzymes by producing inactive forms that are only activated in the duodenum.
• Acid food from the stomach mixes with digestive juices from accessory glands like the pancreas, liver and gallbladder -The liver releases Bile
  • The pancreas releases pancreatic juice

Functions of the Pancreas

• Exocrine functions include:

  • Secreting pancreatic juice into the small intestine which breaks down all categories of foodstuff
  • Ductile cells produce Sodium bicarbonate which neutralizes the acidic gastric contents in the Duodenum
  • Acinar secretory cells contain zymogen granules which produce a variety of digestive enzymes to break down food substances into smaller absorbable molecules

• Endocrine functions include:

  • Secretes insulin and glucagons, hormones that regulate blood sugar and carbohydrate metabolism (they have opposite effects)

Major pancreatic Enzymes

• Pancreatic amylase digests polysaccharides into disaccharides.
• Pancreatic lipases digest triglycerides into fatty acids.
• Pancreatic nucleases digest nucleic acids into nuceotides
• Pancreatic proteinases digest peptides into amino acids
• Trypsinogen is activated by enterokinase into trypsin, activating chemotrypsinoges to chemotrypisn, proaminopeptidase to aminopeptidase, and procarboxypeptidase to carboxypeptidase

Regulation of pancreatic proteases in the small intestine

• CCK induces secretion of enzyme-rich pancreatic juice and secretin causes secretion of HCO₃--rich pancreatic juice
• Acidic, fatty chyme entering the duodenum causes release of cholecystokinin and secretin from duodenal wall enteroendocrine cells
• Bile salts and secretin transported via produce bile more rapidly.
• During Cephalic and gastric phases, vagal stimulation causes weak contractions of the gallbladder.

Functions of the Liver

• Liver is critical in lipid metabolism where hepatic cells produce bile (for fat emulsification), oxidize fatty acids including lipogenesis (fatty acids to glucose)
• Liver is important in carbohydrate metabolism where hepatic cells conduct glycogenesis (glucose to glycogen) and glycogenolysis (breakdown of glycogen to glucose)
• The liver stores glycogen, iron, and vitamins A,D,B12
• The liver contains phagocytes to destroy damaged erythrocytes and foreign substances with phagocytosis.
• The liver stores glycogen, iron, and vitamins A,D,B12
• Contains phagocytes to destroy damaged erythrocytes and foreign substances using phagocytosis
• Serves as a blood reservoir

Additional Liver Functions

• Converts and inactivates hormones, toxins, and drugs while converting lipid-soluble substances to water-soluble metabolites
• Excretes endogenous and exogenous substances via the bile and facilitates the excretion through urine of bile through soluble metabolites
• Liver produces most plasma proteins and blood coagulation factors
• Liver excretes bile piments
• Liver produces cholesterol, which is transferred to the blood or the bile

Composition of Bile

• Bile has bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes
• Is a yellow-green, alkaline solution
• Bile salts are cholesterol derivatives that emulsify fat, facilitate fat and cholesterol absorption, and help solubilize cholesterol
• Chief bile pigment is bilirubin, a waste product of heme

The Gallbladder

• Located on the inferior, visceral surface of the liver which stores and concentrates secreted bile
• Present in animal species such as dogs, cats, and humans where fat digestion is intermittent for periodic storage of bile
• Absent, or poorly developed in continuous fat digesting animals such as horses and ruminants

Regulation of Bile Release

• Vagal stimulation causes weak contractions from the gallbladder
• Cholecystokinin causes contractions from the gallbladder, is stimulated through bile acid presence in the duodenum

Digestive Tracts Adaptations to Varying Feed Sources

• Small intestine is less variable among species than stomach and hind gut, but generally shorter in carnivores than in herbivores;
• Large intestine Important of hind gut fermentation dictates variation in structure and size; Some hind gut fermentation occurs in most species;

Digestion in the Small Intestine

• A long tube, with a small diameter, extending from pyloric sphincter to the ileocecal valve.
• The small intestine Contains villi which secrete sucrase, maltase, lactase and peptidates to further breakdown proteins, lipids and minerals
• Small intestine Divided into Duodenum, Jejunum, and Ileum
• Active intestinal enzymes include maltase (digests maltose), sucrase (digests sucrose), and, lactase (digests lactose)
• Bile and acid chyme in the duodenum causes release of secretin and CCK

Digestion & Regulation

• Digestive enzymes embedded in the surfaces of microvilli split molecules of sugars, proteins and fats.
• Small intestine secretions are stimulated by gastric juice, chyme, and reflex stimulated by distension of the small intestinal wall.
• Each villus contains blood capillaries (for water, glucose, amino acids, vitamin etc) and lymphatic capillaries called lacteals to absorb long chained fats the forms of micelles
• Water is absorbed by osmosis, fatty acids by diffusion-passive transport (since fats are soluble), and other nutrients by active transport. Active transport requires energy (ATP).

Nutrient Absorption in Small Intestine

• Intestinal absorption transfers various substances from the digestive tract lumen to blood or lymph capillaries, through epithelium to the intestine, transporting blood (lymph) through the extracellular fluid and away from the intestine
• Absorption includes to the surface, between the cells and with blood (lymph)
• The dominance is the intestine' size to absorb to through intestinal villi and microvilli
• Duodenum (amino acids, vitamins, minerals, lipids, glucose and sugars in mogasatrics), Jejunum (carbohydrates/proteins), Ileum (VitB12 + bile salts)

Small Intestine Motility

• Muscle Contractions assist with mixing content, contacts cells and slowly move chyme
• Mixing Movements are contractions for intestinal content mixing
• Propulsive peristalsis moves chyme

Motility of the Small Intestine

• Segmentation is the most movement in the small intestine
• Contractions divide the intestinal content into many small segments
• It moves the content that causes mixing and brings new content to contact

Additional motility Facts

• Peristalsis contractions move from one section to to the next
• Is initiated when a segments receives chyme with expansion of the intestine
• the receptive relaxation then facilitates forwars displacement This wave is initiated down

Small Intestine Regulation

• The Enteric nervous system, automated nervous system and hormones regulate strength
• parasympathetic vagal fibers increase activity of sympathetic = contraction increases
• Enteric nervous system regulates peristaltics and contractions
• Food comp, emotions have influence on Motility
• Activation Gastrin, Motilin,CCK, Serotonin, activates for motility as inactivation is peptide and nerotension

Emptying of the Small Intestine

• There is an ileocecal spincter between small and large intestine that regulates in one way gate direction
• When relaxed causes transit relaxation due to the allowance to enter colon and prevent back flow

Digestion in the Large Intestine

• It’s the section through the terminal ileum and Anus Depending is species, the ingest will enter to large intestine through ileoocecal or ilecolic valves
• Consists of cecum, colon and rectum and depends on type of species and animals
• large intestine are for water and mineral absorption with microbial digestion
• All digestion is through microbial enzymes
• Goblet cells protects epithelia and contains HCO3’and mucus
• In carnivores, process is complete in in the large intestine where little if none significance
• Microbal Degradation is most important in energy supplied (Herbivores/omnivore)

Herbivores and omnivores: • Process takes place in Cecum (Rabbit) and colon (horses) • It provides fermentation which provide energy for them • Horses, absorption of VFA assists with excess acid and maintains pancreas and HOC2-Rich

Motility of the Large Intestine

• Segmentations, Peristalsis, Antiperistalsis, Mass Movements

Large Intestine Contractions:

• Segmentations contractions that chops and divides where absorption occurs
• Antiperistalsis contractions moves towards ileum to allow absorption of water and electrolyte
• Peristaltics Contractions add influx
• Mass Movements contains mortality not for digestivetube and contraction to clear intestinė

Elimination of Waste Material

• Rectum: Terminal, stores mucus and trigger distension when needed
• Anus has inter. and external Sphincters with controls
• Afferent travels to expanded rectum and motor back.Parasympathetic signal initiate
• Defecation

Birds: Mouth

• Begins from beak ends at the cloaca Food travel from ; beak, phayrn, stomach, etc, crop, proventriculus, small intestine ceca, colaca
• Birds have diet in high concentration with simple Digestive track Birds are adapted to what they eat and digestive tract • The more fiber, ceca large:
• Use Beaks to obtann feed
• Have no teeth
• Taste Bud back of toungue
• Can sense temperate
• Can feed to mouth for food

The Bird Esophagus, Crop, & Proventriculus

• The "Esophagus," is a flexible tube that connects the mouth with the digestive tract.

• The "crop" is a pouch-like enlargement of the esophagus where temporary food storing.

• The "proventriculus," also know as true stomach, is where the digestion occur

• HCI and digestive enzymes ( e.g., pepsin) Are added to the feed

Avian Gizzard

• Is a strong set of muscle which acts as birds mechanical teeth
• Food and juice from proventriculus travels here
• Thick Ligning to protect muscle
• Gastric Motitaltiy is synchronized and the chyme traveles the duodenum

Bird Small Intestine, Ceca & Large Intestine

• Made od duodenum and lower small in intestine
• The Duodenum has the digestive enzymes and bicarbonate for secretion
• Digestive enzy,es is prdominately for protein
• Secretes hormone in regulatory blood sugar
• Bile helps with absorption

Ceca and Large Intestine (Plural vs singular)

• Found near the end
• Help the body absorb water
• Fecal Matter is voided
• Has water absorption
• Has Fiber Fermentation by bacteria
• H2O soluble vitamin synthesis

Waste Elimination

• most posterior segment that extends from cecum
• Considerable water and ions absorption
• Fences white crystals
• Are transported through urine to colloidal

Explore ruminant digestion in forestomachs covering reticulum and rumen functions. Learn about cellulose breakdown and digestion flow through the four-chambered stomach including regurgitation and waste management.