digestive 2

digestion

• breakdown of food groups into building blocks

  • can cross epithelial layer at the jejunum

• mechanical or physical

  • mechanical

    • oral cavity, stomach

    • mixing, chewing, grinding

  • chemical 

    • pepsin, amylase

    • breakdown into building blocks

esophagus

• Peristalsis

• Antiperistalsis

Peristalsis

• Moving food aboral (away from mouth, towards anus)

• Alternating contractions (longitudinal and circular muscle contractions)

• Propels food down caudally

Antiperistalsis

• Emesis (vomiting): 

  • emptying of the cranial part of the duodenum and stomach in an orad direction (toward the mouth)

  • Series of reflexes 

  • Protective mechanism (prevent ingestion of toxins, etc)

• Vs. regurgitation: 

  • emptying of contents of the esophagus

Stomach

• site of acid production

  • HCL produced

    • H flows into the lumen of the stomach

    • attracts negative Cl

    • forms HCL

• local mucus bicarbonate layer protect gastric mucosa

  • disruption of this layer

    • ulcers

stomach cells

• Mucous cells: 

• Chief cells:

• Parietal cells: 

• G-cells: 

Mucous cells:

• Mucous producing  

• protective barrier 

Chief cells:

• Pepsinogen (inactive) 

  •  cleaved 

  •  active pepsin  

  • breaks down proteins 

• Gastric lipase  

  • breaks down fat

• Rennin  

  • curdles milk in young animals  

  • solidifies  

  • slows down digestion of milk (more time to absorb)

Parietal cells:

• produce HCl

G-cells:

• produce gastrin  

• stimulates production of HCl

reminant stomach purpose

• Purpose is to make the size of the food smaller

  • Regurgitates undigested food into oral cavity (controlled)

  • Rechewed to make particles smaller

  • Re-salivate with buffer

  • Re-swallow 

rumen microbes

• Young calves do not have microbes  

  • introduced from environment, 4 to 6 weeks of age start chewing  

  • rumen papillae start to form

• Microbes attach to the fibrous mat  

  • breakdown of cellulose for energy

• Microbial fermentation produces  

  • Volatile fatty acids (VFA’s)  

    • absorbed via the rumen wall  

    • energy source

  • Vitamins

  • Gases (C02 and methane)  

  • burping/eructation to release from body

ruman activities

• Constantly mixing food

• Rhythmic contraction  

  • moves food between compartments

• Regurgitates from remastication and re-deglutition

• Ruminants will ruminate 8 to 10 hours a day  

  • “Chew their cud” around 40 times

Pancreatic products via pancreatic duct

• Bicarbonate  

• Inactive zymogens (precursors)

• Amylase  

• Lipase  

Bicarbonate

Inactive zymogens (precursors)

Amylase

Lipase

• Bicarbonate  

  • raises pH

• Inactive zymogens (precursors)

  • Protects the pancreas from autodigestion

  • Trypsinogen and chymotrypsinogen  

    • released into duodenum

    • Become trypsin and chymotrypsin

      • protein breakdown

• Amylase  

  • breaks down starch to maltose 

• Lipase  

  • breaks down fat 

Bile

• from liver

• Common bile duct enters SI near or with the pancreatic duct

• Greenish yellow fluid

• Bile: 

  • water + electrolytes + cholesterol + phospholipids + bilirubin

• Aids lipolytic (fat breaking) enzymes

• Stored in gallbladder 

animals w/o gallbladder

rats, horses

Bile salts

emulsify fats for digestion and absorption by the lacteals

Bilirubin:

• from red blood cell breakdown product 

Brush border of small intestines

• Brush border with microvilli increases surface area

• Enzymes for final digestion to subunits for absorption into blood for villi

• Proteins  

  • amino acids

• Fats 

  • fatty acids + glycerol

• Carbohydrates  

  • simple sugars

• Absorption of nutrients across the cells

DJU activities

• Duodenum 

  • (mostly digestion)  

• jejunum 

  • (mostly absorption + some digestion)   

• ilium 

  • (mostly absorption)

large intestine

• Cecum and colon

  • Fermentation

  • Less length for absorption

  • Water and vitamin absorption

  • Goblet cells 

    •  mucus 

  • Forms the feces 

basic nutrients

• Carbohydrates

• Proteins

• Lipids (fat)

• Water

• **Oxidizable carbon: this is the source of energy for the body. 

where does nurtient absorption happen

small intestine

carbohydrates

• simple sugars with five carbons and six carbons are found in tissues as

  • monosaccharides

    • single units

  • disaccharides

    • two units

• Complex sugars

  • formed by linking simple sugars to form polymers

  • Deposited as energy stores (amylose in starch granules)

  • Structures for support (cellulose in plant cell walls)

digestion of carbohydrates

• Starches are enzymatically broken down in duodenum

  • Salivary amylase 

    • destroyed in the acidity of the stomach

  • Pancreatic amylase 

    • released into the duodenum

  • Starch and glycogen 

    • broken down into shorter chains at the brush border

Brush border enzymes

• Enzymes cleave disaccharides to monosaccharides 

• Mucosal cells enzymes have multiple binding sites for substrates

  • One enzyme can bind maltose, iso-maltose, and sucrose

  • Further degrade maltose into glucose

transport into the bloodstream

• Once the carbohydrate has been broken down to its simplest unit 

  •  ready to be absorbed

• Glucose and fructose too big to diffuse; need transporter protein

• Transport requires ATP (active transport) or a concentration gradient (facilitated diffusion)

proteins

• Proteins are a sequence of amino acids linked by peptide bonds

• Over 300 amino acids known to exist  

  • only 20 amino acids are found in animal proteins

• digestion

  • Denaturation  

  • Peptidases break down proteins

  • Endopeptidases

absorption

• Mucosal cells absorb both amino acids and short peptides of two or three amino acid residues

• Amino acid transporters

  • Absorb amino acids into cells and secrete them into blood

  • Use ATP

  • Decrease in number as you reach the ileum

lipids 4

• Wax esters

• Triglycerides

• Phospholipids

• Sterols

• Entry of lipids into the duodenum  

  • release of cholecystokinin (CKK)

• CKK  

  • stimulates secretions from bile from liver + lipase/colipase from pancreas

water and electrolytes

• Water absorbed throughout by passive diffusion

  • ions dissolved in it

• Sodium linked to glucose and amino acid absorption 

  • countertransport

• Microbial fermentation products dissolved in water 

  • absorbed in large intestine

• Most water absorbed in large intestine 

  • recover that excreted with enzymes, etc.

Nucleases

• Nuclease – 

  • breaks down nucleotides/nucleic acids

• All living things have genetic material

  • Therefore must have mechanism to break it down in digestive tract