Animal Nutrition and Digestion

Introduction to diet and digestive systems 

• A. types of diets

  • 1. Herbivore 

  • 2. Carnivore 

  • 3. Omnivore 

  • 4. Detritivores 

• B. types of digestive systems 

  • 1. Gastrovascular cavity *(flatworms): present in diploblastic organisms 

  • 2. Alimentary canal (hollow tubes): present in triploblastic organisms 

    • A. monogastric: one stomach cavity 

    • Plant material= cellulose/fiber

      • Coprophagy: Some animals eat their own poop to digestive it more

    • B. birds have three stomach chambers, the crop, proventriculus, and gizzard 

      • Crop: stores food

      • Proventriculus: produces gastric chemicals

      • Gizzard: contains stones that birds swallow; food mixes with chemicals and stones to grind it  up 

  • 3. Ruminants: are herbivores. Cows, sheep, goats. They eat lots of plant material that contains cellulose/fiber 

    • Reticulum 

    • rumen 

    • Food gets regurgitate and rechew

    • Abomasum

Digestion- the big picture 

1. Ingestion

2. Digestion

3. Abseroption

4. Elimination 

Human digestive system

• A. oral cavity: ingestion, physical and initial chemical digestion. 

  • 1. Saliva (protection)

    • Projects mouth from abrasion  

    • antibacterial 

    • Buffers acid produced by dental caries to reduce tooth decay 

    • Salivary amylase, the initial chemical digestion of carbs and helps swallow/lubrication 

  • 2. Mastication: mechanical breaking down of food by teeth, chewing

  • 3. Tongue: assists with forming food for chewing 

  • 4. Bolus: ball of food

• B. pharynx intersection of the digestive and respiratory systems 

  • Esophagus (DRAW THE SWALLOWING DIAGRAM)

  • Trachea 

  • Glottis: entrance of the trachea (windpipe- leads to lungs) 

  • Epiglottis: flap of tissue that covers the glottis when swallowing, preventing food from blocking the trachea 

• C. esophagus: connects pharynx to stomach 

  • 1. Sphincters: when contacted they close off openings (DRAW THE DIAGRAMS)

    • Esophageal sphincter: connects pharynx to esophagus 

    • Lower esophageal sphincter: connects esophagus to stomach 

  • 2. Peristalsis: smooth muscle moving in a wave/contrat to move bolus of food down esophagus down to stomach 

• D. stomach and sphincters 

• Stomach is bordered by two sphincter 

  • Lower esophageal sphincter (also known as the cardiac sphincter 

  • Pyloric sphincter 

• Stomach functions 

  • 1. Food storage- rugae. Can expand to hold 2 L of food and liquid 

  • 2. churning - peristalsis: contraction of smooth muscle surrounding stomach to mix food particles with chemical secretions 

  • 3. Secretion

    • Lumen: stomach cavity 

    • A. HCl (hydrochloric acid): strong acid H+ plus Cl-. parietal calls. It denatures proteins. 

    • B. pepsin (protease= protein digesting enzyme): produced by chief cells in inactive form (Stored as an insert form- pepsinogen) then is activated by HCL (acidic envit). (DRAW DIAGRAM)

    • Mucus: contains glycoprotein called mucin. Coats lining of stomach, prevents direct contact of HCl + pepsin (DRAW DIAGRAM)

  • 4. Protein digestion

    • 1) HCL unfold protein, exposing peptide binds

    • 2) HCL activates pepsinogen -> pepsin

    • 3) pepsin breaks peptide bonds.  polypeptide chain turns into smaller peptide fragments

  • 5. Chyme: liquid combination of food, HCL, pepsin, and water. It moves through the pyloric sphincter into the duodenum (beginning)  of the small intestine. 

• Stomach pH is 1.5 to 2

• E. small intestine 

  • 1. Accessory glands

    • Salivary glands

    • A. pancreas: secretes digestive enzyme also secretes bicarbonate (basic ph) which neutralizes HCL

    • B. liver: produces bile, contains salts which emulsify lipids (not an enzyme)

    • C, gallbladder: stores and releases bile salts into the duodenum

• Digestion- the duodenum- where all the action is (DRAW THE DUODENUM DIAGRAM) 

  • Chyme mixes with digestive enzymes, bile, salts and bicarbonate in duodenum 

  • (LOOK AT THE FLOWCHART)

  • A. carbohydrate digestion (green section flow chart)

    • Begins in oral cavity with exposure to salivary amylase (breaks down polysaccharides like starch into smaller polysaccharides or disaccharides)

    • Continues in small intestine with exposure to pancreatic amylase breaks down smaller polysaccharides into disaccharides 

  • B. proteins digestion (purple section of flow chart) (draw diagram)

    • Begins in stomach: 1. HCL unfolds proteins 2. Pepsin breaks peptide bonds making smaller polypeptides

    • Continues in small intestine with exposure to trypsin and chymotrypsin (proteases produced by pancreas) breaking down smaa;; polypeptides in chyme into even smaller polypeptides 

    • Smaller polypeptides are also exposed to carboxypeptidase which breaks them down into amino acids 

    • Epithelium of small intestine exposes any remaining small polypeptides to more proteases breaking them down into amino acids 

  • C. nucleic acids (DNA, RNA)

    • Happens in small intestine with exposure to nuc;ease produced by pancreas which break them down into nucleotides

    • Then nucleotidase and phosphatase (digestive enzymes in epithelium of small intestine) breaks nucleotides down into sugar, phostae, and nitrogenuos base

  • D. lipids 

    • Emulsification of fats by bile salts (made in liver, stored in gallbladder)

    • Digestion by lipases 

    • Lipids are nonpolar and hydrophobic 

    • Bile salts emulsify fat globules into small droplets (increase surface area that digestive enzyme access) 

    • Pancreatic lipase (an enzyme) separates fatty acid chains from carbon 

  • 3. Absorption- jejunum and ileum of small intestine (DIAGRAM)

    • Jejunum: middle portion of small intestine; 2.5 m long

    • Ileum: last portion of small intestine; 3 m long 

    • Surface area= 300 m^2

    •  4. Water reabsorption (DIAGRAM)

      • Ingest about 2 L of water

      • We secrete about 7 L water 

      • We absorb about 8.5 L of water in small intestine and 0.5 L in large intestine 

  • F. large intestine 

    • 1. Cecum 

      • Appendix

      • Appendicitis 

    • 2. Colon 

    • 3. Rectum