Digestion and Nutrition - 2013

Overall Goal of Digestive Systems A. Obtain organic molecules from environment B. Reduce complex molecules such as proteins, polysaccharides, nucleic acids and lipids to absorbable sizes and C. Transport the molecules into the blood stream so that they may be assimilated into cells.

General Strategies for obtaining nutrientsA. Filter feeders - microorganisms, marine and freshwater crustaceans, baleen whales. (show whale video)http://videos.howstuffworks.com/discovery/428-corwins-quest-whales-video.htm

http://videos.howstuffworks.com/discovery/28113-assignment-discovery-baleen-whales-plates-video.htm

B. CarnivoresC. Herbivores 1. the problem with cellulose - requires bacteria or protozoa that produce cellulase 2. pregastric fermentation 3. postgastric fermentationD. OmnivoresE. Symbiotic nutritionchloroplasts from algae in the bodies of sea slugs - photo synthetic products feed slugshttp://www.newscientist.com/article/dn16124-solarpowered-sea-slug-harnesses-stolen-plant-genes-.html

bacteria in digestive tracks of ruminants (cows)http://www.teachersdomain.org/resource/nat08.living.str.living.digest

Perspectives on Digestion

OverviewMechanical - mastication, stomach, crop, and intestinal motilityChemical (secretions) - enzymes from saliva, pancreas and intestinesAbsorption - intestinal lumen o bloodAssimilation - blood into cells throughout the body.

MotilitySmooth musclePace setter potential - specialized cells in digestive tract produce electric impulses(potentials) that stimulate the gut to contract

Enteric (intrinsic) nervous control (responds to stretch, pH, hormones)Extrinsic = controlled by central nervous system (brain & spinal cord)

Fig. 14-5, p.619

Intrinsic Nerves of the Rat’s Stomach

Motility

Storage of waste

Defecation

Secretions

IngestionMouth

Pharynx Receiving

Foregut

Crop

ConductingStorageDigestion

Midgut (stomach)Digestion (acidic)

Hindgut

Digestion (basic)Absorption

Assimilation

Fig. 14-1, p.613

The enzyme “cellulase” is required to hydrolyze cellulose. This enzyme is only produced by microorganisms. Animals must provide organs that support the growth of these symbionts.

Starch is hydrolyzed to maltose by the enzyme “amylase” which is produced by the salivary glands and the pancreas.

Hydrolysis of a disaccharide (maltose) to two monosaccharides (glucose)

Maltase is the enzyme that performs this action. It is produced primarily by the cells that line the intestinal lumen.

Categories of Digestive Enzymes

Amylase: starch hydrolysis to maltose

Protease: proteins hydrolyzed to peptides

Lipase: triglycerides hydrolyzed to fatty acids and glycerol

Nucleotidases nucleic acids hydrolyzed to nucleotides

Gastrointestinal Tract (alimentary canal) mouth-anus

Accessory Organs Liver Gall Bladder Pancreas

Fig. 14-7a, p.624

Tongue

(a)

Trachea

Esophagus

Epiglottis

Pharynx

Uvula

Soft palate

Hard palate

Nasalpassages

Glottis at entrance of larynx

Bolus

Peristalsis - a local reflex

Fig. 14-8, p.627Duodenum

Smoothmuscle

FundusEsophagus

Gastroesophagealsphincter

Body

Stomachfolds

Oxynticmucosa

AntrumPyloricglandarea

Pyloricsphincter

Table 14-3b, p.632

Gastricpit

Mucosa

Submucosa

Table 14-3c, p.632

Gastric gland

Surface epithelial cells

Gastricpit

Chief cells

Mucous cells

Enterochromaffin-Like (ECL) cells

In oxyntic mucosa

Parietal cells

Produce pepsinogen

Produce HCl andIntrinsic Factor

Peptic Ulcers

Heliobacter pylori - bacterial infection responsible for 90%of all peptic ulcers

Treatment with antibiotics

Fig. 14-11, p.634

HCl, fats, osmo

CCK

Secretin

Intestinal Cross Section

Layers of the alimentary canalSerosa

Muscularis

Submucosa

Mucosa

Smooth muscle cells

Villus (Villi)

Microvilli

Mucosal cells

Fig. 14-20, p.647

Large fat droplet

Lipid emulsion

Small lipid (fat) droplet with bile salt moleculesadsorbed on its surface

Lipid-soluble portion(derived from cholesterol)

Negatively charged H2O-soluble portion (a carboxyl group at the end of a glycineor taurine chain)

Through action of bile salts

Fig. 14-17, p.644

Fig. 14-24a, p.654

Lipid Absorption

Fig. 14-14, p.641

Fig. 14-16, p.642

Block Diagram of Lipid Absorption

Lipids in Duodenum

Lipids combine with Bile and form Micelles

Micelles taken up by mucosal cells

Mucosal cells add proteins and extract fatty acids

Lipase begins to convert triglycerides to fatty acids

Lipids enter lymph capillaries as Chylomi ra

Chylomicra move through lymphatic system and enter the blood at subclavian veins.

Liver takes up Chylomicra and converts them to HDL’s and LDL’s

HDL’s and LDL’s re-enter blood and are distributed to other cells throughout the body.

Fig. 14-26, p.657

Transverse colon

Internal anal sphincter(smooth muscle)

Taeniae coli

Ileocecal valve

Ascending colon

RectumCecum

Appendix

Anal canal

External anal sphincter(skeletal muscle)

Sigmoid colon

Descending colon

Haustra

Fig. 14-27b, p.661

Reticulum

(b)

To smallintestine

Rumen

Abomasum

Omasum