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Digestion
Involves the degradation of large molecules in to smaller molecules that are absorbed directly by cells
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Protozoan Digestion
- Utilize intracelular digestion
- surround and engulf food via phagocytosis and enclose food in vacuole
- Lysosomes digest food and unusable exits in a vacuole
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Paramecium Digestion
- Cillia sweep microscopic food into oral grove where food vacuole forms around food
- Enzymes enter vacuole and products diffuse into cytoplasm, solid waste exits vis anal pore
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Cnidaria Digestion
- Employ both intracellular and extracellular digestion
- Tentacles bring food into the mouth and release the particles into a cuplike sac (gastrovascular cavity)
- Endodermal cells lining the cavity secrete enzymes
- Thus digestion principally occurs outside th cells
- However, once in small particles the gastrodermal calls engulf the nutrients and digestion is completed internally
- Undigested food is expelled through the mouth
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Annelida: Earthworms
- Body is many cells thick: requires a more advanced digestion
- Allows for specialization for mechincal and chemical digestion and absorption of the food
- Parts include mouth, pharynx, esophagus, crop (stores food), gizard (grinds food), intestine (doral fold for increased surface area and absorption) and anus
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Arthopods Digestion
Similar to annelida but with the addition of complex appendages and salivary glands
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Mammalian Digestion
Involves the regulation of a physical parameter that maintains normal cell homeostasis via negative feedback loop
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Negative Feedback Loop
Control signals feed into certain cells and cause the measured parameter to change direction
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Digestion Overview
- Mechanical and Chemical
- Saliva digests carbs and lubricates food
- Stretch receptors in the stomach cause release of juices that are very acidic and breaks down H bonds and 3D structure
- Stomach contents separete (lipids on tome, then proteins, then carbs)
- stomach pushes carbs and proteins first, easiest to derive E from
- Pancreatic fluids rich in Bicarbonate ions that neutralized stomach acids (in small intestine)
- Bile is secreted by liver to help absorb fat vis emulsification
- Smooth muscle of small intestine moves chyme down intestine
- Products are absorbed as they travel through small intestine
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Chyme
Partially digested food, enters small intestine
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Pancreatic Fluid
- Rich in Bicarbonate ions that neutralized stomach acids (in small intestine)
- Endocrine and exocrine
- Release bicarbonate to neutralize pH in small intestine
- Also secretes amylases, lipase, protease (breakdown proteins)
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Illeum
- Third part of small intestine
- All food is absorbed here
- Bile salts from liver are reabsorbed and recycled back to liver
- Unabsorbed material is excreted
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Mouth/Salva
- Chemical and mech digestion
- Salvia contains salivary amylase secreted from salivary glads starts digestion
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Amylase
- Is inactivated by low pH in stomach
- Amylase in center of food bolus can stay active longer (digests 50% of starch)
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Esophagus
Passageway from mouth to stomach
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UES upper esophageal spincter
- Prevents air from entering GI system
- Band of muscle at top of esophagus
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LES Lower esophegeal Sphicter
- Prevents food from backing up when chest pressure lowers (lungs inflate)
- Heart burn protection
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Stomach
- PH1-2
- Stores food as digested and absorbed
- Protein digestion starts here with low pH an enzyme pepson
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Pepsinogen
- Inactive form of pepsin
- HCL in stomach activates pepsin
- Pepsin usually remains inactive because it shreds proteins and will shred the proteins that produce it
- Mucous stops strong acids and protects stomach
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Small Intestine
- Duodenum First segment
- Jejunum second segment
- Ileum Third segment
- Lots of surface area
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Pyloric Sphincter
Regulates passageway of chyme into small intesting
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CK (Chloecystikinin)
- Hormone released by small intestine cells in duodenum
- Hormone stimulates release of amylase, lipase (fat digestion), bile (fatty acid emulsification)
- Also stimulates contraction of pyloricn sphincter
- CCk controls negative feedback loop for fat breakdown, is released due to fat digestion products
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Secretin
- Hormone that stimulates the release of bicarbonate ions from pancreas if too much chyme enters the duodenum and one time
- Causes contraction of pyloric sphincter
- Faster cyhme movement, faster pH control chyme
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Gastrin
- Stimulates the release of HCL and pepsinogen to further breakdown proteins and amino acid chains in stomach before enters duodenum
- Negative feedback look for protein breakdow gats released if stomach empties too fast, pyloric sphinter shuts
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Exocrine and Endocrine Organs
- Secrete into intestine vs blood stream
- Pancreas is both
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Vili
- Large circular folds the protrude into interior of intestine
- Made of epithelial cells that have microvilli which increase surface area
- Core of each villi lie a blood capillaries that drain villus into hepatic portal vein --> liver or further packaging and storage biomolecules
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Large Intestine
- Also known as colon
- Reabsorbed water and salts
- Bacteria here help digest other material that enzymes cannot breakdown
- ex: vitamin K and cellulose
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Bile Salts
- Are ampatipatic and will stabilize fat droplets in solution via emulsification allows for absorption of fats
- Secreted by liver stored in gull bladder
- Bile Pigments and salts act as emulsifies
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Evolutionary Adaptations
- Differences in vertebrates are from dietary differences
- Involve shape of teeth
- Length alimentary canal (how long tract is)
- Presence of enlarged/multi-chambered stomach called ruminants
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Ruminants
chambers of stomach
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