Digestive System Part 2. Two Types of Digestion Digestion is the process of breaking down nutrients...
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Transcript of Digestive System Part 2. Two Types of Digestion Digestion is the process of breaking down nutrients...
Digestive System Part 2
Two Types of Digestion• Digestion is the process of breaking
down nutrients so they can be absorbed– Undigested nutrients cannot be
absorbed and pass through the small intestine to the large intestine
– For more information, ask someone who is lactose-intolerant about drinking milk
• Mechanical (physical) digestion is the chewing and churning of food
• Chemical digestion is the breaking of chemical bonds in food
Mechanical Digestion
Chemical Digestion• The mouth and stomach also
initiate the process of chemical digestion– The mouth has salivary glands that
produce saliva, which begins chemical digestion
– The stomach has pepsin, an enzyme that denatures and breaks down protein
• Note chemical digestion of fats does not begin until the small intestine
Small Intestine Activity
• When food enters the stomach it still consists of starches, proteins and whole fats– These cannot be absorbed since
they are too large!• The small intestine can only
absorb the small molecules that make these up (simple sugars, amino acids, and fat molecules)– Large molecules that are not
digested cannot be absorbed!– Pancreas to the rescue!
Pancreatic Digestion• The pancreas secretes a huge battery
of chemicals to complete the breakdown of nutrients for absorption– Pancreatic lipase: for lipids– Pancreatic amylase: for starches– Trypsin (and others): for proteins– Pancreatic nucleases: for DNA and RNA
digestion– Bicarbonate (a base that cancels out
the acid of the stomach)• The small intestine itself also
expresses many enzymes that break two-part molecules apart
Small Intestine Absorption
• Since nutrients can only be absorbed through cell membrane, the small intestine epithelial tissue has adaptations for increasing surface area– The surface has many circular folds– The tissue is arranged into fingerlike villi
(singular villus) which create more surface area
– The individual cells have a brush border, or microvilli (singular microvillus)
• These cells expend ATP to actively transport nutrients into the blood
Small Intestine Microanatomy
Digestion Review
• Starches broken down to sugars by salivary amylase and pancreatic amylase
• Proteins broken down to amino acids by pepsin and trypsin
• Fat drops split apart with bile and broken down with pancreatic lipase
• DNA and RNA are broken apart and absorbed by pancreatic nucleases
Liver Function• Blood flows directly from the
small intestine to the liver– This is called hepatic portal
circulation– Protects the rest of the body
from whatever you just ate• The liver has metabolic enzymes
to process many nutrients after they are absorbed– Production of fat and glycogen– Storage of vitamins– Breakdown of toxins such as
alcohol
Large Intestine• The large intestine is filled with
colonies of bacteria that feast on our leftovers (often producing gas as a waste product)
• The large intestine is capable of absorbing water and vitamins, including those produced by bacteria– The large intestine is not actually
necessary for life and can be removed if needed
Normal Flora Redux
• Remember the concept of normal flora from immunology?– If you wipe out your normal
flora in your large intestine you are at risk for infection by a much nastier type of bacterium!
– Probiotics are foods that restock your large intestine with healthy bacteria• This is still a poorly understood
field of science
Lactose Intolerance• Lactose Intolerance is one of
many digestive disorders caused by a failure to absorb nutrients– Lactose (milk sugar) is made of a
molecule of glucose and galactose stuck together (too large to absorb)
– Most people express a small intestine enzyme called lactase that breaks them apart
• Failure to digest lactose (or other nutrients) results in the nutrients ending up in the large intestine– Bacteria metabolize it and release
gas and waste acids
Gastrointestinal Distress
• Inflammation of the intestines can also cause failure to absorb nutrients– These nutrients get to the large
intestine and bacteria call dibs at that point
– This results in diarrhea• Celiac disease is when inflammation
results from gluten (a wheat protein) exposure to the small intestine– If you do not have celiac disease,
gluten is NOT bad for you