Transcript Animal Physiology, Chapter 4

The great Serengeti migration: A quest for minerals
Digestive system
• Functions
• Organs
Organs of alimentary canal
Figure 23.2
Small intestine
Large intestine
Accessory organs
Salivary glands, liver, pancreas, gall bladder
Figure 23.1
Digestive tracts of various vertebrates
Digestive tracts of invertebrates and vertebrates
Figure 4.1 The composition of the adult human body
Nutrition
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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
Examples of feeding adaptations
Food chains
Feeding
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 bacteriatrophosomes
• 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 bacteriatrophosomes
• 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
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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 intraand 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:
maltose
Sucrose
Lactose
Maltase
Sucrase
Lactase
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
Dipeptides
Dipeptidase
Amino acids
Brush
border of
small
intestine
Figure 4.18 The digestion of a short protein by three pancreatic peptidases
Fat digestion
Organ
Substrate
Enzyme
Oral cavity
No enzyme to
digest fat
Stomach
No enzyme to
digest fat
Lumen of intestine
Brush border of
small intestine
End product(s)
Fat globules
Bile salt from
gallbladder
Emulsified fat
Fat globules
lipase
Glycerol, fatty acids
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
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Endocrine control
Gastrin
Secretin
CCK
GIP
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Where?
When?
Why?
How?
Figure 4.20 GI function after a meal is coordinated in part by hormones secreted by cells in the gut