Animal Nutrition (Chapter 41)

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Animal Nutrition (Chapter 41)
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4 Common Materials to be Digested

• Starches/Polysaccharides ? Monosaccharides ?
  Cellular Resp.
• Lipids ? F.A. Glycerol ? Mem. Phospholipids.
• Protein ? Amino Acids
• Nucleic Acids ? Nucleotides

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Vitamins vs. Minerals

• Vitamins
• organic nutrients
• 13 essential to humans
• grouped into water-soluble (B Vitamins function
  as coenzymes and to build connective tissue) and
  fat-soluble (Vitamin A,D,E,K function in bone
  formation, color vision, blood clotting, etc)
• Minerals
• inorganic nutrients
• examples include Calcium (for bone formation),
  Iron (component of hemoglobin) and Magnesium
  (important in nervous system)

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Malnourished diet missing one or more essential
nutrients. Undernourished insufficient caloric
intake. Not a national problem in US!
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• Dont forget to take your Flintstones!

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Stages of Food Processing

• Ingestion
• Mechanical Digestion
• Enzymatic Digestion Enzymatic hydrolysis breaks
  down food into monomers that can then be used.
• Absorption cells absorb monomers.
• Elimination/Defecation undigested material
  leaves the body.

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The Mammalian Digestive System
About 30 ft!
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The Oral Cavity
Lips and Cheeks, composed of skeletal muscle,
form boundary.

• Teeth cut, smash, and grind food into smaller
  pieces with a larger surface area.
• Salivary Glands release saliva (more than one
  liter per day!) after being stimulated.
• Parotid
• Submandibular
• Sublingual
• Saliva contains mucin (a slippery glycoprotein),
  antibacterial agents, and salivary amylase
  (breaks down starch and glycogen)
• Tongue is responsible for tasting and shaping
  food into a ball shape called a bolus. Also a
  skeletal muscle!

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The Pharynx and Esophagus

• The Pharynx
• - Opens to Esophagus and Trachea (windpipe)
• - The Glottis, visible as the Adams Apple, is
  covered by a flap (epiglottis) to prevent passing
  food from going down the wrong pipe.
• The Esophagus (25 cm long). Lined with
  stratified squamous
• - controls the passage of food from the pharynx
  to the stomach by Peristalsis, rhythmic waves
  caused by muscle contractions
• - Esophageal Sphincter is a ring shaped stopper
  between the pharynx and esophagus.

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Solid foods 4 - 8 seconds Fluids 1 2 seconds
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The Stomach

• Folded, elastic and can hold about two liters of
  food and fluid!
• Gastric juices 1. Secreted by epithelium lining
  on the stomach wall 2. High in hydrochloric
  acid 3. Pepsin- an enzyme that begins hydrolysis
  of proteins
• - Smooth muscles of stomach churn, and help to
  create acid chyme.
• - Has two openings from the esophagus, the
  cardiac orifice, and to the small intestine, the
  pyloric sphincter

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Parietal Cells secrete HCl making stomach
contents pH 1.5 3.5 Chief Cells secrete
pepsinogen which become activated (by removal of
small peptide, exposing active site) by HCl to
become pepsin. Can also be activated by
pepsin. Mucus coats the stomach wall for
protection, prevent leakage of
chyme between cells, damaged cells quickly shed
and replaced. Surface epithelium renewed every
3-6 days!
Gastric Pits
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Functions of Hydrochloric Acid in Gastric Juices

• Acid disrupts extracellular matrix that keeps
  cells together in meat and plant material
• Kills most bacteria swallowed with food
• Activates pepsinogen
• Gastric secretions controlled by hormone ?
  Gastrin.
• Gastrin released by aroma, sight, thought of food
  and by food reaching the stomach

3 Liters/day!
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Passing through the Stomach

• A bolus will come to the stomach from the
  esophagus by way of peristalisis
• The stomach churns and mixes, and in cooperation
  with enzymes, creates acid chyme
• From here, the chyme goes through the pyloric
  sphincter into the small intestine.

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Digestive Juices in the Duodenum

• The duodenum is the first 25 cm or so of the
  small intestine
• Chyme mixes with three different digestive juices
  introduced in the small intestine
• Pancreatic juice
• Bile
• Intestinal juice

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The Duodenum
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Important Accessory Glands

• Pancreas
• - secretes pancreatic juice 1.2 1.5 L/day
  into the duodenum and chemicals (i.e. insulin)
  into the bloodstream. Produces most of the
  digestive enzymes used in the small intestine.
  Trypsinogen, carboxypeptidase, chymotrpsin,
  amylase, lipases, nucleases, bicarbonate
• Liver 3 lbs
• - production of bile, a fat emulsifier.
  Primarily cholesterol derivatives. Pigmented
  from bilirubin (formed during rbc recycling in
  liver) creating brownish color.
• Gallbladder
• - storage organ for bile. Excess cholesterol
  dissolved in bile salts can for gallstones which
  can obstruct flow of bile. Contraction of g.b.
  during bile release causes abdominal pain.
  Release of bile controlled by CCK.

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Carbohydrate Digestion in the Small Intestine

• Amylases from pancreas hydrolyze polysaccharides
  into maltose and other disaccharides
• The enzyme maltase splits maltose into two
  molecules of glucose
• Each family of disaccharides is hydrolyzed by a
  specific enzyme for that family- maltase
  hydrolyzes maltose, sucrase hydrolyzes sucrose

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Protein and Nucleic Acid Digestion
Remember that pepsin starts breaking down protein
into smaller polypeptides in the stomach

• Trypsin and chymotrypsin are enzymes that find
  bonds adjacent to specific amino acids and break
  those bonds.
• Dipeptidases split small peptides 1.
  Carboxypeptidase breaks off one a.a. at a time
  starting on side of the free carboxyl group 2.
  Aminopeptidase works in the opposite direction
  of carboxypeptidase.
• Enteropeptidase triggers the activation of these
  enzymes
• Nucleases break down DNA and RNA into sugars,
  nucleosides, nitrogenous bases, and phosphates

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Fat Digestion in the Small Intestine

• Since fats are insoluble in water, bile salts
  coat small droplets and keep the droplets from
  coalescing (emulsification)
• The droplets now have a larger surface area and
  provide more room for enzymes to work
• Lipase hydrolyzes the fat molecules

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Absorption of Nutrients

• Mainly absorbed in parts of the small intestine
  called jejunum and ileum
• In the intestine, there are many folds and little
  projections to increase surface area
• Villi- Lacteal absorb fats and then converge
  with larger vessels of the lymph system-
  Transport of sugars is usually passive, while
  transport of amino acids and vitamins is usually
  against a concentration gradient.- Capillaries
  and veins all converge to hepatic portal vessel,
  which leads to liver
• 2. Microvilli- Cost of digestion may be as high
  as 30 of the energy in the meal

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Site of Nutrient Absorption
3-6 hrs for chyme to travel through sm. intestine
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Hormones Role in Digestion

• Secretin is released by small intestine due to
  HCl from chyme. Prompts release of bicarb. from
  pancreas.
• Cholecystokinin is released in the presence of
  amino or fatty acids into sm. intestine and calls
  for pancreatic digestive enzymes to be released
  and bile release from gall bladder

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The Large Intestine

• Is connected to small intestine at a pouch called
  the cecum (aka. Appendix)
• As the wastes move along the colon, water is
  absorbed. Primary Function.
• Feces get increasingly more solid as it goes
  through the colon, we hope.
• Bacterial flora consume cellulose and produce
  about 500 ml of dimethyl sulfide, H2, N2, CH4,
  and CO2 aka flatus. Also synthesize vitamin K
  to be used by liver.

Exits at the rectum

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Structural Adaptations Due to Diet

• - Dentition 1. Carnivores have large canines
  and incisors 2. Herbivores have small
  canines 3. Omnivores have medium sized
  everything

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Structural Adaptations Due to Diet

• Length of digestive system 1. Carnivore is
  smaller 2. Herbivore is longer due to cell
  walls
• - Ruminant digestion