digestion Flashcards
Why do animals need food?
Energy (Metabolic fuel and heat), Growth (raw materials), and reproduction
major aspects of food are
Feeding, digestion, and nutrition
how much of the body is made up of water
60%
principal body components other than water
Proteins
– ~half of the organic matter of mammals
* Lipids
– Diverse, some are essential fatty acids
* Minerals
– Many are metalloproteins
* Nucleic Acids
* Carbohydrates
– Usually low in abundance, but more abundant
when play structural roles (cellulose)
How much energy is transferred to each trophic level
10% pass down to predators and 90% is used as heat
Mid- and Hindgut Fermeters
- Midgut fermeters
– Mostly fish (tilapia, carp, catfish) - Hindgut fermenters
– Have enlarged colon or cecum
– Rabbits, horses, rhinos, elephants, apes,
rodents, birds, lizards, and turtles - Can absorb SCFA, but must re-ingest feces
(coprophagia) to absorb vitamins and amino
acids
Insects
- Use proventriculus as a gizzard (grinding)
– Malpighian tubules enter in midgut (excretory)
Crustaceans
-have hepatopancreas
– Sequesters toxins
– Stores lipids and glycogen
– Secretes digestive enzymes
– Digestion of food particles
– Absorption of nutrients
Bivalves
- Rely on ciliary, not muscular contraction
– Allows sorting of food particles by size - Crystalline style made up of amylases
– Aid in digestion as it breaks down on shield - Digestive diverticula- blind-ended sacs
– Food taken into cells where it is digested - Intracellular digestion
Wood eaters
Termites require protista and bacteria to digest
cellulose into usable acetic acid
Blood feeders
Symbiotic bacteria help digest blood and preserve it
during breakdown
Batch reactor
pulsed output, pulsed input, contents mixed, composition changes with time, occurs in the Hydra.
Continuous-flow stirred-tank reactor
continuous input, contents mixed, continuous output, composition unchanging with time at steady state, occurs in the ruminant forestomach.
plug-flow reactor
continuous input, axial gradient in composition, continuous output, composition uniform in cross-section at steady state, unchanging with time at any point along the reactor.
Foregut fermenters have a combination of continuous flow models
-continuous flow without mixing reactor devoted to enzymatic digestion
-continuous flow with mixing reactor devoted to microbial fermentation
Structure and function of the parts in the Vertebrate Alimentary Canal
ingestion occurs
headgut-receiving
Foregut-conducting storage digestion
midgut-digestion
hindgut-storage of waste
Muscle action
- Smooth Muscle
– Tonic- Sphinctors regulate passage
– Gut Motility - Muscular contractions that move food
forward along the digestive tract and serve
to mix contents
- Sphinctors regulate passage
Gut motility
Two types of movements:
* Peristalsis- Propulsive movements propel
contents forward along the digestive tract
* Segmentation- Mixing movements mix food
with digestive enzymes and promote
absorption
segmentation
segmental contractions are responsible for mixing, but there is no net forward movement
Mouth
- Ingestion
- Teeth and Tongue
– Mechanical Digestion
– Form Bolus - Saliva
– Moisten Food
– Chemical Digestion - Amylase, Lipase (minor role)
Oral cavity
§ Mouth
* Grinding of food into smaller pieces and mixing with saliva
§ Salivary glands
* Located outside oral cavity
* Saliva is 99.5% water, 0.5% electrolytes and proteins
* Saliva begins digestion of carbohydrates (amylase),
facilitates swallowing (mucous), has antibacterial properties
(lysozyme), solvent for molecules that stimulate taste buds,
facilitates speech (moistens oral cavity), maintains oral
hygiene
Salivary secretion is a two-stage process
1) Acini (glandular portion)
* Produces a primary secretion similar to plasma
* Amylase, peroxidase, lysozyme, and mucin are
secreted
* Na + , Cl - , K + , water and some HCO 3- are added
to the saliva
2) Duct cells
* Reabsorb Na + and Cl - from primary saliva and
addition of HCO 3- and K +
Formation of saliva
-acinar cells pump NaCl
into the acinar lumen and
water follows passively
-mucous cells secrete mucin
and serous cells secrete
enzymes (amylase, lysozyme)
-at the duct, NaCl is reabsorbed
and most of the bicarbonate
is produced
Salivary proteins
§ Amylase- breaks down polysaccharides into
disaccharides (serous secretion)
§ Mucus- facilitates swallowing and provides
lubrication for food (mucous secretion)
§ Lysozyme- antibacterial function
Regulation of salivary secretion
§ Continuous low level of salivary secretion due to
parasympathetic stimulation
§ Salivary secretion rate is enhanced by:
1) Unconditioned (simple) reflex pathway
2) Conditioned (acquired) reflex pathway
§ Both sympathetic and parasympathetic
(dominant) input to salivary glands enhance
secretion
§ Entirely under nervous control
Regulation of Digestion
- Involves neural & hormonal regulation
- Cephalic Phase; “thought of food”
– secretion of saliva/gastric/pancreatic - Gastric Phase- chyme in the stomach
– Distension, short peptides, acidity
– Gastrin – From G Cells
– ̄ pH
3 stomach layers
longitudinal layer, circular layer, oblique layer
GI tract 4 layers
Serosa-mesentery
Muscle layers-circular muscle, longitudinal muscle, myenteric plexus
Submucosa-gland in submucosa, submucous plexus
Mucosa-gland in mucous membrane, villi, lymph node, muscularis mucosa, epithelium, lamina propria
Stomach – Secretion and Digestion
- Mucous (Goblet) cells: mucus, HCO 3-
- Parietal cells: HCl (gastric acid),
intrinsic factor - Chief cells: pepsinogen (protease) &
gastric lipase - Enteroendocrine cells: Gastrin and
other hormones
Zymogen
inactive enzyme form
Small Intestine
- Folds of Kerckring
(circular folds) - Villi
- Crypts of Lieberkühn
- Central Lacteal
Absorption
- Diffusion
– Simple
– Facilitated - Active
- Endocytosis
Pancreas
- Exocrine & Endocrine Gland
- Digestive enzymes
– Many secreted as Zymogens - Trypsinogen ® Trypsin (by enterokinase)
- Procarboxypeptidase ® Carboxypeptidase
- Chymotripsinogen ® Chymotripsin
– Amylases, lipases, nucleases - Regulatory Hormones
Pancreatic Zymogens
- Trypsinogen
- Chymotrypsinogen
- Procarboxypetidase
Bile serves as
“detergent”
- Biliverdin, Biliruben
- Functions
– Buffer, basic
– Emulsify fats
– Waste removal
– Vitamin absorption - Reabsorbed by Liver
Bile salts break down fat droplets
Large Intestine
10,000 mills of fluid are absorbed, and most are coming back out in the small intestine.
* Storage
* Water Absorption
– Fluid intake
– Secretions
* Digestion
– Hindgut fermenters
* Waste Excretion
parts in the Large Intestine
- Haustra
– Formed by teniae coli- smooth muscle - Blind sacs
– cecum and appendix - Colon
- Rectum, Anal Canal
Basic Electrical Rhythm
stomach has stimulation and pause, and during the pause, the food is broken down.
Small intestine stimulations are caused by segmentation.
Regulation of Digestion
– Phases
* Cephalic
* Gastric
* Intestinal (Duodenal)
– Growth
* Raw Materials
– Reproduction
Mechanisms of
Regulation of Digestion
– CNS (Long Reflexes)
– Enteric NS (Short
Reflexes)
– Endocrine Mechanisms
* Endocrine
* Paracrine
* Peptidergic NS
Neural Regulation of Digestion
- Short Reflexes
– originate in enteric nervous system
– integrated w/o any CNS input; e.g. - gastroileal reflex: gastric activity -> ileum motility
- ileogastric reflex: ileum distension -> ̄ gastric motility
- intestino-intestinal reflex: distension of segment of SI –> relaxation of
remainder - Long Reflexes
– digestive reflexes integrated with CNS - Defecation Reflex, Salivary response etc
More Regulation of Digestion
- Intestinal Phase; chyme in duodenum
– Ileogastric Reflex ̄ gastric activity
– Chemical nature of chyme determines which
hormones are secreted - Acid à secretin à bicarbonate
- Fats/proteins à Cholecystokinin (CCK) à
pancreatic enz. and bile - Secretin & gastric inhibitory polypeptide (GIP)
also ̄ gastric activity (motility & enzyme
production)
