Digestion and Digestive Systems

• Digestion involves breaking down large molecules into smaller ones through hydrolysis
• It occurs in the gastrointestinal tract by enzymes, bile, and hydrochloric acid
• Proteins are digested into amino acids
• Fats are digested into fatty acids and monoglycerides
• Starch is digested into glucose
• Digestion is controlled by the nervous system and hormones
• There are four basic types of digestive systems: monogastric, avian, ruminant, and pseudo-ruminant
• Mouth: Food is chewed, and saliva dilutes it, dissolving water-soluble constituents; saliva contains a-amylase
• Stomach: It is a temporary food storage, producing chyme (mixture of food and gastric secretion) which contains hydrochloric acid and pepsin
• Small intestine: Digestion and absorption of food mainly occurs here
• Liver: Produces bile and excretes cholesterol and bile pigments
• Pancreas: Synthesizes enzymes (digests fat, starch, protein, RNA, and DNA) and insulin and glucagon hormones

Pancreatic Enzymes

• Trypsin breaks down protein into smaller fragments
• Chymotrypsin also breaks down protein into smaller fragments
• Carboxypeptidases break down protein into smaller fragments
• Pancreatic lipase digests fats into fatty acids and monoglycerides
• Phospholipases break down lecithin into free fatty acids
• a-amylase digests starch into maltose and glucose
• Ribonuclease digests RNA into smaller fragments
• Deoxynuclease digests DNA into smaller fragments
• Collagenase digests connective tissue into smaller fragments
• Elastase digests elastin into smaller fragments
• Metabolism comprises all chemical reactions in the body
• Anabolism involves synthesizing glycogen, fat, and proteins.
• Catabolism involves breaking down substances to provide energy or for normal turnover.

Energy Sources

• Amino acids (from proteins)
• Fatty acids (from fats)
• Monosaccharides (from starch and sugars)

Catabolism

• Catabolic pathways release energy by breaking down complex molecules into simpler compounds
• Carbohydrates become glucose via enzymes
• Glucose becomes pyruvate, ATP via enzymes
• Organic acids, ATP become CO2; NH3, H2O, and ATP via enzymes
• Anabolic pathways consume energy to build complex molecules from simpler ones
• Protein synthesis from amino acids exemplifies anabolism.
• Energy is stored during catabolic processes as ATP, NADH, NADPH, and FADH2, eventually it dissipates as heat
• Synthesis requires energy in the form of ATP and the reducing agent NADPH, both generated during catabolism

ATP Synthesis

• Substrate-level phosphorylation involves ATP production during substrate hydrolysis with phosphoryl group transfer
• Oxidative phosphorylation forms ATP through electron transfers from NADH or FADH2 to O2, facilitated by electron carriers, in oxidation-reduction reactions

Catabolism

• Breakdown of proteins, carbohydrates, and fats occurs in stages
• Polymeric materials are hydrolyzed into monomers
• Hydrolysis products are converted to AcetylCoA
• Glucose is oxidized to pyruvate during glycolysis and then converted to acetyl CoA
• Fatty acids undergo β-oxidation to acetyl-CoA, and amino acids break down into compounds, including acetyl CoA
• Acetyl-CoA is oxidized to CO2 in the tricarboxylic acid cycle
• Reduced nucleotides NADH and FADH2 are formed alongside substrate-level phosphorylation
• Reduced nucleotides are oxidized during oxidative phosphorylation, forming water and releasing energy

Carbohydrate Digestion

• Occurs in ruminants (microbial), non-ruminants (enzymes), herbivores, omnivores, and carnivores.

Digestion of Dietary Carbohydrates (Non-Ruminant)

• Digestion is rapid
• It is catalyzed by glycoside hydrolases (glycosidases)
• Final products are glucose, galactose, and fructose, absorbed by small intestine cells
• Digestion begins in the mouth

Ruminant Digestion

• In ruminants, microbes attach to and colonize fiber to secrete enzymes
• Host animals provide microbes with continuous fermentation conditions, i.e. nutrients, water, and waste removal.
• Microbes ferment fiber and starch, producing energy, building blocks for new cells, volatile fatty acids (VFAs), CO2 and methane
• VFAs are absorbed and supply energy or are used for fat or glucose synthesis
• Ingested carbohydrates undergo extensive pregastric fermentation
• Rumen fermentation is efficient given the ingested feedstuffs
• Microbes ferment most carbohydrates
• No salivary amylase is present, but there is plenty of pancreatic amylase to digest starch
• Cellulose and hemicellulose from cell walls, are digested by cellulases and hemicellulases
• Complex polysaccharides are digested to yield sugars fermented to produce VFAs
• Starches and simple sugars are more rapidly fermented to VFAs

Bacteria Types

• Cellulolytic bacteria (fiber digesters): produce cellulase (cleaves β1→4 linkages), prefer cellulose and hemicellulose; Prefer pH 6-7 Produce acetate, propionate, little butyrate, CO2; They predominate in animals consuming roughage diets
• Amylolytic bacteria (starch, sugar digesters): digest starches and sugars, prefer pH 5-6; produce propionate, butyrate, and sometimes lactate; predominate in animals consuming grain diets
• Small intestine secretes digestive enzymes for carbohydrate digestion and absorbs H2O, minerals, amino acids, glucose, and fatty acids
• The cecum and large intestine contain bacterial colonies which ferments unabsorbed digestion products . They also absorb H2O, VFAs and form feces

Volatile Fatty Acids (VFAs)

• Acetate: Provides energy and is used for fatty acid synthesis
• Propionate : provides energy
• Gluconeogenic: Involved In glucose synthesis
• Butyrate: energy source converted by rumen epithelial cells into ketone (beta hydroxybutyrate)
• VFA production ratios depend on the diet
• VFAs are primarily produced in the rumen and result from the breakdown of carbohydrates
• Absorption occurs passively from rumen to portal blood. They provide 70-80% of a ruminant animal's energy needs.

Major Dietary Polysaccharides

• Starch (from plants)
• Glycogen (from animals)
• Salivary a-amylase hydrolyzes a(1→4) bonds of dietary starch and glycogen during mastication.
• Branched amylopectin and glycogen contain a(1→6) bonds, which are not able hydrolyzed by a-amylase.
• Digestion yields a mixture of short, branched, and unbranched oligosaccharides (dextrins)
• Carb digestion halts in the stomach temporarily due to a-amylase inactivation

Carbohydrate Digestion - Pancreas

• Pancreatic amylase (Hydrolyzes a 1-4 linkages)
• Remaining polysaccharides and oligosaccharides are digested in the small intestine via pancreatic amylase
• Produces monosaccharides and disaccharides
• Major importance in hydrolyzing starch and glycogen to maltose

Small Intestine Digestion

• Polysaccharides become disaccharides via amylase
• Sucrose becomes Glucose + Fructose via sucrase (Note: Ruminants lack sucrase)
• Lactose becomes Glucose + Galactose via lactase (Note: Poultry lack lactase)
• Maltose becomes Glucose + Glucose via maltase
• Isomaltose (a(1→6)) becomes Glucose + Glucose via isomaltase

Carbohydrate Summary - Monogastric

• Polysaccharides are broken down to monosaccharides, then taken up by active transport or facilitated diffusion and carried to the liver
• Glucose is transported to cells needing energy
• Insulin influences the rate of cellular glucose uptake
• In ruminants, the host animal provides the microbes the ideal conditions for continuous fermentation, e.g.. nutrients, water, waste product removal

Bacterial Digestion of Carbohydrates

• Bacterial microbes attach to (colonize) fiber components and secrete enzymes which digest plant cell walls
• Cellulose and hemicellulose are ultimately utilized by the animal

Microbial Populations

• Cellulolytic bacteria (fiber digesters): Produce cellulase Primary substrates include cellulose and hemicellulose; Prefer pH 6 Produce acetate, propionate, little butyrate and CO2; They predominate in animals fed roughage diets.
• Amylolytic bacteria (starch, sugar digesters): Digest starches and sugars Prefer pH 5; Produce propionate, butyrate, and sometimes lactate.; Predominate in animals fed grain diets.

Triglycerides (TGs)

• Major constituents of dietary fat
• Lesser amounts include cholesterol (CH), cholesterol esters (CEs), phospholipids (PLs), and fat-soluble vitamins

Regulation of Lipolysis

• Regulated by cholecystokinin (CKK) and secretin (secreted by duodenum endocrine cells)
• Cholecystokinin activates bile release from the gallbladder
• Bile salts and lecithin provided by gallbladder bile are important emulsifying agents
• Secretin triggers biliary and pancreatic cells to release NaHCO3 to neutralize acidic chyme from the stomach to the small intestine

Emulsification

• Fat globules entering the small intestine are too large for effective enzyme hydrolysis, and are emulsified by detergent action of biliary bile acids
• Provides a large surface area for pancreatic digestive enzymes to operate on

Conjugated Bile Salts

• Increases concentration
• Bile salts form micelles or spherical aggregates (33 bile salts per micelle, 3-10 nm diameter)

Primary Bile Acids/Salts

• They are good emulsifying agents
• Oh groups are on the same side, and pKa=6

Conjugated Bile Salts

• Have Amide bonds with glycine and taurine – They are good emulsifiers with lower pKa than bile acids

Enzymatic Hydrolysis of Dietary Lipids

• Small amounts of TGs are hydrolyzed to fatty acids and diglycerides by lingual lipase secreted by salivary glands, then swallowed into the stomach
• Lingual lipase and gastric lipase are both acid stable and have an optimum pH of 4
• Fat hydrolysis in the mouth and stomach is normally slow since it has not been emulsified: TG hydrolysis approx. 10% in adult animals vs approx. 40-50% in infants consuming milk lipase
• Homogenized milk contains highly emulsified TG, yet homogenization inactivates milk lipase
• Pancreatic lipase is secreted in an active form and has a pH optimum of 8. It is denatured by pH below 3
• Colipase peptide is required to bind lipase to small lipid particles. Colipase alters the pH optimum for lipase from 8 to 6.
• Pancreatic lipase hydrolyzes fatty acids from positions 1 and 3 of triacylglycerols. This produces free fatty acids (FA) and 2-monoacylglycerols.

Hydrolysis of Phospholipids by Phospholipases

• Pancreatic juice contains proenzyme of phospholipase A2 (activated by trypsin) and requires bile salts.
• The main products generated by phospholipase Al and A2 comprise free fatty acids and Product of hydrolysis under action of phospholipase C and D is choline, ethanolamine, serine, and or inositol.
• Cholesterol esterase releases FA from Cholesterol ester, forming Cholesterol and FFA

Lipid Degradation in Ruminants' Digestive Tract

• It is different from that in non-ruminants due to microbial processes in the large rumen. Microbes contain concentrated feedingstuffs, oilseeds, and animal fats provide triacylglycerides and small amounts of phospholipids to animals.
• In the large rumen, fats are hydrolysed into fatty acids, sugars, alcohols and or glycerol via bacteria
• The large rumen is where fat breakdown is initiated & glycerol and carbohydrates are immediately fermented into volatile fatty acids
• Micro-organisms also synthesize fatty acids, incorporated into membrane phospholipids
• About 85% of lipids entering the small intestine are free fatty acids absorbed as nutrients
• Most fatty acids present in the large rumen are in calcium, potassium and sodium salt form.
• About 15% reaching the duodenum are bacterial phospholipids.
• The end-products of lipid digestion are delivered to the luminal surface of jenula mucosal cells by mixed micelles, micelles dissociate as lipid-incorporated products diffuse
• Both short and MCFAs do not depend upon mixed micelles for mucosal uptake because of their relatively high water solubility
• Whole proteins are not absorbed due to their large size.
• Protein are hydrolyzed by digestive enzymes – these enzymes are secreted as inactive pre-enzymes to prevent self-digestion

Digestion - Monogastrics

• The enzyme pepsin (activated from pepsinogen by HCl) initiates protein digestion in the stomach
• Pepsin breaks the peptide bond between tyrosine and phenylalanine amino acids, creating peptide fragments and a few individual amino acids
• Proteins leave the stomach and enter the small intestine for enzymatic breakdown
• There are Major pancreatic proteases (optimal pH ~7).
• Trypsin (activated from trypsinogen), Chymotrypsin (activated from chymotrypsinogen), Carboxypeptidase and Aminopeptidase
• Trypsin and chymotrypsin split proteins into smaller peptides and some single amino acids
• Carboxypeptidase splits single amino acids from the carboxyl end of proteins
• Aminopeptidase and dipeptidase continue the digestion of peptides
• Not active enzymes must be converted to active form: Trypsinogen generates Trypsin, Chymotrypsinogen generates chymotrypsin, Procarboxypeptidase generates Carboxypeptidase, Proaminopeptidase generates Aminopeptidase

Endopeptidases cleave internal peptide bonds

• Trypsin cleaves on carboxy of Lys & Arg, Chymotrypsin cleaves carboxy terminal Phenyalanine, Tyrosine and Tryptophan

Exopeptidases cleave terminal amino acids

• Procarboxypeptidase removes carbody terminal residues from proteins
• Proaminopeptidase removes amino terminal residue from proteins
• Dipeptidase splits dipeptides
• Protein Digestion: Ruminants
• Single amino acids, dipeptides, and tripeptides are absorbed through the small intestine
• Amino acids use carrier systems for absorption
• Can be neutral, basic, acidic, and imino acids

Monoglyceride Protein Digestion

• Proteins are hydrolyzed by digestive enzymes which hydrolyze peptide bonds. They are secreted as inactive pre-enzymes to prevent self-digestion.
• Protein digestion begins in the stomach. Entering small intestine, polypeptides from stomach by pepsin are cleaved to oligopeptides and amino acids by pancreatic proteases.
• Free amino acids enter enterocytes (intestinal cells) via Na+-linked secondary transport system. Peptides are then hydrolyzed into amino acids. The digestion then proceeds by the same patterns as monogastric

Protein Digestion - Ruminants

• Protein digestion in ruminant animals is divided into two phases:1) digestion degradation in the reticulorumen or 2) digestion in abomasum and small intestine Since dietary proteins are classified as rumen degradable and rumen undegradable, proteins provide a source of nitrogen for the rumen microbes to make their own microbial protein Ruminant microbes use nonprotein nitrogenous substances such as urea for microbial protein synthesis in order to increase the urea levels, in the rumen
• Bacteria and protozoa degrade proteins that produce proteolytic enzymes
• Rumen microbes provide proteases and peptidases to cleave peptide bonds in polypeptides to release free amino acids from proteins
• Rumen-related amino acids release NH3 and the C skeleton by a process from which rumen microbes synthesize their own microbial protein, serving as a nitrogen source to the host ruminant animal
• The amount of microbial protein produced is adequate for maintenance and survival but not for high-producing animals
• Non-degraded rumen proteins are considered, i.e., bypass proteins and RUP
• Amino acid requirements of the host are met by RUP and microbial proteins, or both
• Both, ruminants and monogastrics require essential amino acids since amino acids cannot be stored

Some of the Similarities and Differences in Monogastric

• The amino acid profile in in small intestine reflects the diet
• No upgrading of low-quality dietary protein occurs
• Quality nor downgraded occurs
• They cannot use not protein
• A constant supply of amino acids is needed
• Ruminant differences:
• Amino acid profile differs from dieters
• Low-quality dietary protein is upgraded
• High quality diet is degraded
• able to use non protein nitrogen (e.g. urea)

Carbohydrates

• They are a major source of energy from The elements - C, H, and OAlso called saccharides
• Occurs in all plants and animals are essential to life.They Are produced by photosynthesis in plants
• The elements of glucose, are synthesized in plants from CO2, and H Are oxidized in living cells to produce energy
• Glucuse, C6H12O6 = C6(H2O)6Carbohydrates are – polyhydroxyaldehydes, polyhydroxyketones, or substances that give such compounds on hydrolysis.
• Monosaccharides, cannot be hydrolyzed to simpler compounds.Disaccharides are with two monosaccharides
• Polysaccharides that with many monosaccharides (from hundred to thousands)
• The number of carbon atoms present the carbonyl group is present as an aldehyde or ketone

Chirality in Monosaccharides/Fischer Projections

• Fischer projection Is used to represent carbohydrates D- Glucose- In fruit, corn syrup, and honeyAn aldohexose with the formula CKnown as blood sugar in the body.The monosaccharide polymers of starch,cellulose,and glycogen withNormal blood level of 4-6 mmol. A tolerance test measures blood glucose for several hours after ingestion.

D-glucose, D-fructose, and D- Ribose

• A ketohexose that Is the sweetest carbohydrate.
• Is found in fruit juices and honey.
• Converts to glucose in the body.Not found free in nature.
• Obtained from lactose, a disaccharide (after hydrolysis)Ribose and deoxyribose are the most important of pentose
• Important in: ATP, cyclicAMP and monomeric units of RNR

Synthesis of hemiacetals

• The aldehyde and alcohol approach each other because of the attraction of opposite charges (C=O is partially positive / negative and O-H is partially negative / positive) The hemiacetal is unstable and reverts back to the original aldehyde or alcohol1) The alcohol oxygen becomes bonded to the carbonyl carbon to form the ether
• Stabilize cyclic hemiacetals cyclic - They form when hydroxyl group on C-5 reacts with aldehyde group or ketone group.Disaccharide + H2O = two monosaccharide units
• Polysaccharide * table sugar = sucrose in sugar cane.Has an a,a - 1,2 - Glycoside bond
• *The Rings cannot be open! so NOT a reducing sugar

Lactose

• Made of glucose & Galactose (B1-4 glycosidic bond is unique); Only found in milk, is also the reducing monosaccharide.

Characteristics of Starch, Amylose, and Amylopectin

• Long chains of glucose; Is found in roots, tubers and seeds; Starch is made Amylose and amylopectin
• Is polymer of á-D-glucose unit; with a-1,4 Glycoside Band and continuos a; chain (helix)Is a polymer of glucose unit; branch chain polysaccharide

Carbohydrates - Glycogen Characteristics

• Glycogen, the primary storage form for Glucose in animal liver and muscle.The glycosidic bonds are formed from a-D-glucose and Has A14 and and a 16 glycosidic bounds
• Cellulose – B 1-4glycosidic bond -cannot de digested by human

Gylcolysis

• Glycolysis is a sequence (10) of reaction that metabolizes of glucose to two molecules of pyruvates and generating 8 molecule of ATP. under anaerobic (No O2) until, pyruvate process. Pruvate can processed either anaerobollicly (fermentation) , or completed oxidization Glucose -1. GLUCOSE 6 PHOPHATE- -2 FrUCTUSE 6 PHOSPHATE-3 FrUCTUSE-3 diphosphate to dihydroxy Acetel Phsphate to glyceraldehyde 3 phosphate =2ATP &2 NADH =

Pyruvate

• Occurs through phosphoglyverate kinase & Piruvate kinase. Two complex, are 1 ATP synthase 2 the lectern transpirat
• Membranes are flexible, self sealing and selected permeable to polar, their flexibility per minute shape changes company’s cell growth, and more

Sodium-potassium (Na+-K+) pump

• Active transport mechanism. 3 NA+ OUt and 2 K in
• Energy comes from ADP to change configuration of carrier.ATP powers work by coupling exagonic reactions with endodontics reactions

###ATP composition

1. Adenine, of niterogenous gas 2 ) Ribose five carbon 3) chain of three phosphate groups

• With no membrane potential H+ gradient to make the reaction, reverse occurs = ATP hydrolysis
• As of electrons moves through to three of ADP phosphate, a respiratory chain
• The transferal NADPH, will reduce an o2 of ETC
• NADH H +/2 2 +1 3 ADP to NAD, 2-HP // fADH & ADP = FAO H22 THE OPP IS IN An Alt route, A cyroplamic rouse 6 po4 that does not produce to SUBSTANCE LEVEPHOSHPO . it 2 functions - NAPDH function & provide
• the ppp is oxide non PPP, PPP = hi in adipose & liver = reduced a of Amino and of C.

Body PH

• All Living things are dependedon the life and action in series of mediums is are fluids
• Acid/Base is 7.35 and/or 7.25; respiratory arises in pulmonary unable to eliminate, also caused by activities.