the great serengeti migration: a quest for minerals
TRANSCRIPT
The great Serengeti migration: A quest for minerals
Digestive system
• Functions
• Organs
Figure 23.2
Organs of alimentary canal
Figure 23.1
MonthEsophagusStomachSmall intestineLarge intestineAccessory organsSalivary glands, liver, pancreas, gall bladder
Digestive tracts of various vertebrates
Digestive tracts of invertebrates and vertebrates
Figure 4.1 The composition of the adult human body
Nutrition
• Proteins
• Lipids
• Carbohydrates
• Vitamins and minerals
Figure 4.2 Amino acid chemistry (Part 1)
Figure 4.2 Amino acid chemistry (Part 2)
Figure 4.3 Fatty acids and triacylglycerols (Part 1)
Figure 4.3 Fatty acids and triacylglycerols (Part 2)
Figure 4.4 Carbohydrate chemistry
Figure 4.5 Vitamin structures
Feeding
Examples of feeding adaptations
Food chains
Figure 4.6 Some species feed by targeting and subduing individual food items (Part 1)
Figure 4.7 Specialization of a vertebrate feeding apparatus
Dentition
Figure 4.8 Specialization of an invertebrate feeding apparatus (Part 1)
Figure 4.8 Specialization of an invertebrate feeding apparatus (Part 2)
Figure 4.10 The feeding apparatus of a baleen whale
Figure 4.12 Reef-building corals of warm waters need light because they are symbiotic with algae (2)
Figure 4.9 Short food chains deplete energy less than long food chains do
Digestive systems of insects and crustaceans
• Crustaceans’ digestive system is separate from the excretory system
• Insects– the Malpighian tubules – excretory system is connected at the junction of the midgut and hindgut
Figure 4.16 The digestive systems of two types of arthropods: insects and crustaceans
Figure 23.1
Stomach (continued)
• Contractions of the stomach churn chyme.– Mix chyme
with gastric secretions.
– Push food into intestine.
Insert fig. 18.5
Small Intestine
• Each villus is a fold in the mucosa.
• Covered with columnar epithelial cells interspersed with goblet cells.
• Epithelial cells at the tips of villi are exfoliated and replaced by mitosis in crypt of Lieberkuhn.
• Lamina propria contain lymphocytes, capillaries, and central lacteal.
Insert fig. 18.12
Histology of the Alimentary Canal
Figure 23.6
Sensors of the GI tract– regulatory mechanisms
• Mechanoreceptors and chemoreceptors involved
• Located in the walls of the tract organs
• Sensors respond to– Stretching– Osmolarity– pH– Presence of substrates and end-products
Regulatory mechanisms (2)
• Receptors initiate reflexes
• Activate of inhibit glands that secrete digestive juices
• Stimulate smooth muscle of GI tract– Move food along the tract– Mix lumen content
Peristalsis and Segmentation
Figure 23.3
Adaptation associated with animal’s diet
• Microbe-assisted digestion –animals in hydrothermal vents-trophosomes
• Dentition/mouth parts• Length of digestive tract
– Herbivores– Carnivores– Omnivores– Sharks– Birds
Microbe-dependent digestion
• Digestion assisted by microbes
Animals maintain symbiosis with three categories of microbes
• Heterotrophic microbes– Organic compounds of external origin
• Autotrophic microbes– Synthesize organic molecules from inorganic
precursors• Chemosynthetic• Photosynthetic
Figure 4.13 Hydrothermal-vent worms are symbiotic with chemoautotrophic bacteria (Part 1)
Hydrothermal-vent worms
• Symbiotic with chemoautotrophic bacteria- trophosomes
• Worms have not mouth, gut, or anus
• Food comes from sulfur-oxidizing chemoautotrophic bacteria
• Organic molecules from bacteria meets nutritional needs
• Vents- source of H2S
Hydrothermal-vent worms
• Symbiotic with chemoautotrophic bacteria- trophosomes
• Worms have not mouth, gut, or anus
• Food comes from sulfur-oxidizing chemoautotrophic bacteria
• Organic molecules from bacteria meets nutritional needs
• Vents- source of H2S
Figure 4.13 Hydrothermal-vent worms are symbiotic with chemoautotrophic bacteria (Part 2)
Comparison of the digestive tracts of carnivores and herbivores
• Carnivores- foregut digestion
• Herbivores– Hindgut– Foregut
Figure 4.14 The digestive tract of ruminants (Part 1)
Stomach of ruminants
• Several chambers
• Rumen – first chamber/fermentation occurs
• Regurgitate fermenting materials from the rumen into mouth
• Further grinding and reswallow
• From rumen reticulum omasum abomasum (true stomach)
Functions of microbes in ruminants
• Synthesize B vitamins, essential amino acids
• Fermentative breakdown of compounds that animals cannot digest– cellulose
• Recycle waste nitrogen from animal metabolism
• Make ammonia so other microbes can use it as nitrogen source
Figure 4.14 The digestive tract of ruminants (Part 2)
Figure 4.15 The digestive tracts of two hindgut fermenters
Hind and midgut fermenters
• Enlarged cecum/colon– Rabbits, horses, zebras, rhinos, apes,
elephants
• Break down of cellulose and carbohydrates
• Forms short-chain fatty acid
• B vitamins- not utilized, lost in feces
• Coprophagy– rabbits eat special soft feces
A comparison of the digestive tracts of a carnivore (coyote) and a herbivore (koala)
Digestion and absorption
• Digestive enzymes in 3 spatial contexts
• Intraluminal enzymes
• Membrane-associated enzymes
• Intracellular enzymes
Intracellular and extracellular digestion
• Intraluminal and membrane-associated enzymes are responsible for extracellular digestion
• Intracellular enzymes are responsible for intracellular digestion
• Advantages and disadvantages of intra- and extracellular digestions?
Figure 4.17 The stomach of a clam (Part 2)
Carbohydrate digestion
Organ Substrate Enzyme End product(s)
Oral cavity Starch Sal1vary amylase Maltose
Stomach
Amylase denatured
Lumen of intestine
Undigested polysaccharides
Pancreatic amylase
Maltose
Brush border of small intestine
Disaacharides: maltoseSucroseLactose
MaltaseSucraseLactase
Monosaccharides
Figure 4.19 Absorption of monosaccharides in the vertebrate midgut (Part 2)
Protein digestion
Organ Substrate Enzyme End product(s)
Stomach
Polypeptides Pepsinogen +HCl = pepsin
Smaller peptides
Lumen of intestine
Polypeptides Trypsinogen, chymotrypsinogen (inactive enzymes released from the pancreas, transported to duodenum via pancreatic duct. These enzymes are activated by enterokinase from small intestine to trypsin and chymotrypsin
Smaller peptides
Smaller polypeptides
Aminopeptidase, carboxypeptidase
Amino acids
Brush border of small intestine
Dipeptides
Dipeptidase Amino acids
Figure 4.18 The digestion of a short protein by three pancreatic peptidases
Fat digestion
Organ Substrate Enzyme End product(s)
Oral cavity No enzyme to digest fat
Stomach
No enzyme to digest fat
Lumen of intestine Fat globules Fat globules
Bile salt from gallbladder lipase
Emulsified fat Glycerol, fatty acids
Brush border of small intestine
Chemical Digestion: Fats
Figure 23.35
Figure 4.19 Absorption of monosaccharides in the vertebrate midgut (Part 1)
Chemical Digestion: Carbohydrates
• Carbohydrates absorption: via cotransport with Na+, and facilitated diffusion– Enter the capillary bed in the villi– Transported to the liver via the hepatic portal
vein
Chemical Digestion: Proteins
• Absorption: similar to carbohydrates
• Enzymes used: pepsin in the stomach
• Enzymes acting in the small intestine
Chemical Digestion: Fats
• Absorption: Diffusion into intestinal cells where they:– Combine with proteins and extrude
chylomicrons– Enter lacteals and are transported to systemic
circulation via lymph
Coordination of digestion– neural and endocrine control
• Controls of digestive activity• Extrinsic
– Central nervous system and autonomic nervous system
• Intrinsic– Hormone-producing cells in stomach and
small intestine– Distributed via blood and interstitial fluid to
target cells
Endocrine control
• Endocrine control• Gastrin• Secretin• CCK• GIP
– Where?– When?– Why?– How?
Figure 4.20 GI function after a meal is coordinated in part by hormones secreted by cells in the gut