1. Digestion and Nutrition
Chapter 34

2. Digestion
mechanical/chemical breakdown of food  nutrients  absorbed into blood
mechanical
initial, physical breakdown of food into small pieces
does not change chemical make-up of food
mouth and stomach
chemical
breakdown of food into smaller chemical units (nutrients)
changes chemical make-up of food
mostly small intestine
nutrition
refers to the properties and functions of nutrients
absorption
nutrients transported into bloodstream across inner wall of small intestine
extracellular digestion
occurs outside of cells
may be within or outside of organism’s body
if inside, then in a digestive system
most common (incl. humans)
intracellular digestion
occurs within cells
less common
single-celled organisms

3. Intracellular digestion in Paramecium

4. Digestive Systems incomplete (sac-like)
lack separate openings for food entering and waste exiting
gastrovascular cavity
An incomplete digestive system in a gastrovascular cavity

5. Fig. 34.1 Incomplete digestive tract of a planarian

6. Fig. 34.2 Complete digestive tract of an earthworm
complete (tube-within-a-tube)
found in most animals (incl. humans)
separate openings for food entering and waste exiting
invertebrate examples
earthworm
mouth  pharynx  esophagus  crop  gizzard  long intestine (w/typhlosole)  anus
insects
mouthparts  foregut  midgut (w/glands)  hindgut  anus
Fig Complete digestive tract of an earthworm

7. Dentition among mammals
vertebrate examples
sharks and bony fishes
often very effective teeth
spiral valve and lengthy intestine
amphibians and reptiles
socketed teeth or fangs, Jacobson's organ
birds
beaks, feet, crop
two-part stomach
gizzard and proventriculus
mammals
teeth types
temporary and permanent
incisors, canines, premolars, molars
ruminants
animals with a 4-part stomach
rumen, reticulum, omasum, abomasum
able to digest cellulose
Fig. 34.4
Dentition among mammals

8. Ruminant digestion

9. Fig. 34.6 Swallowing Human Digestive System
oral cavity (mouth and throat)
taste buds, tongue, lips, teeth
salivary glands
secrete saliva and amylase
pharynx
back of throat
also contains nasopharynx and larynx (contains voice box)
swallowing
hard palate, soft palate (with uvula), epiglottis, and glottis
lips seal mouth  tongue presses food against soft palate
larynx raised  bends epiglottis over glottis  forces food down esophagus
Fig Swallowing

10. esophagus stomach transport tube with no digestive function
voluntary muscle at top
mostly involuntary smooth muscle
muscle contractions called peristalsis
lined with mucous
stomach
mostly mechanical breakdown
stores and mixes food
very high acidity (pH 1 or less)
rugae  mucin lining
muscular valves at both ends
pyloric and cardiac sphincters
some chemical breakdown
pepsin
gastric lipase
Fig Peristalsis in the digestive tract

11. Fig. 34.8 Anatomy of the stomach

12. small intestine functions
three portions, all composed of smooth muscle
duodenum  jejunum  ileum
functions
most chemical digestion
secretes and receives many digestive enzymes
all absorption
increased surface area for absorption
length
rugae
villi
finger-like projections lining the rugae
microvilli
fine hairs (cellular extensions) lining the villi
sends undigested waste material to large intestine

13. Fig. 34.9 Anatomy of the small intestine

14. large intestine (colon, bowel)
consists of several portions, mostly composed of smooth muscle
ascending colon  transverse colon  descending colon 
sigmoid colon  rectum  anal canal  anus
much voluntary skeletal muscle from rectum  anus
rectum contains rectal valves to hold waste in place
ileocecal valve
muscular valve at junction of small and large intestine
wider and shorter than small intestine
caecum
“dead end” pouch of tissue where small and large intestine meet
appendix
small extension of tissue projecting off of caecum
vestigial structure
functions
reabsorption of water
concentration of waste material (feces)
provide suitable habitat for beneficial, symbiotic bacteria

15. Fig. 34.5 The human digestive tract

16. Fig. 34.10 Some structures of the large intestine

17. three accessory organs
liver
secretes products into duodenum
many functions
detoxifies blood
stores glucose as glycogen
secretes many enzymes
produces bile
emulsification of fats
gall bladder
stores and secretes bile through the bile duct
pancreas
secretes many digestive enzymes
sodium bicarbonate and others
pancreatic ducts  duodenum
produces insulin and other hormones

18. Fig. 34.11 The liver, gall bladder, and pancreas

20. Chemistry of Digestion
mechanical breakdown
mouth (chewing) and stomach
chemical breakdown
mouth, stomach, and small intestine
hydrolysis reactions
absorption into the bloodstream
small intestine
nutrients distributed to body tissues
circulatory system
carbohydrate digestion (esp., starches and other polysaccharides)
salivary amylase  pancreatic amylase  disaccharides  maltase  monosaccharides (glucose)
lipid (fat) digestion
gastric lipase  emulsification (bile)  pancreatic lipase  fatty
acids/glycerol  reform as triglycerides  join w/cholesterol  chylomicrons
protein digestion
proteases
pepsin in stomach  shorter peptides  pancreatic proteases (trypsin) 
even smaller peptides  peptidases  individual amino acids
nucleic acid digestion
nucleases and nucleosidases
individual nucleotides absorbed into bloodstream

21. Fig. 34.12 Digestion and absorption of nutrients