Download Notes: Digestion

Digestion – EEWWWWW!
EQ: What is the purpose of digestion? What are three types
of digestion? Where does chemical digestion of
carbohydrates, lipids, and protein start and finish? Why do
we have to release inactive forms of enzymes for protein
digestion?
Purpose: Need to break apart the polymers of food into the
monomers that make them up so our cells can use these monomers
for their specific purposes.
 3 types of digestion:
1. Mechanical – breaking food down into smaller pieces
2. Chemical – food is broken down into simpler molecules
3. Absorption – simple molecules/monomers from chemical
digestion are absorbed into the cells.
Let’s start digesting!
 Oral cavity – Mechanical and Chemical digestion
- M: mastication (chewing) of food with the help of tongue,
lips, cheeks, and teeth.
- C: Salivary amylase breaks down starches (carbs) into less
complex sugars (smaller polymers)
***WHERE CARBOHYDRATE DIGESTION STARTS!
 The bolus, or ball of food, is pushed back into the pharynx
(throat) with the help of swallowing using skeletal muscle.
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 The bolus moves down esophagus by peristalsis
- Esophagus = “food tube”; smooth muscle; leads to
stomach.
- Peristalsis = wave of smooth muscle contractions
 When the bolus reaches the bottom of the esophagus, it
stimulates the esophageal sphincter to open
 Esophageal sphincter = separates acidic contents of the
stomach from the esophagus
 Stomach – Mechanical and Chemical digestion
- M: smooth muscle contractions churn food; helps to break
food up into even smaller pieces.
- C: enzymes break bonds of protein …see details below
***WHERE PROTEIN DIGESTION BEGINS!
 Glands in the stomach secrete (produce), mucus, hydrochloric
acid (HCl), and digestive enzymes
- Mucus = protects stomach lining from HCl
- HCl =
1. Kills bacteria on food
2. Unfolds large proteins to expose the bonds for
enzymes
- C: pepsinogen (inactive form of an enzyme)
o is released into the acidic environment
3. acid (HCl) activates pepsinogen into the enzyme =
pepsin
o pepsin starts to break bonds of proteins.
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 Why do we need to release an inactive form of an enzyme
first?
- Our cells are made of mostly protein
- So we don’t digest our own stomach cells when the
enzyme for protein digestion is secreted into the
stomach
- Once pepsinogen is activated into pepsin by acid, mucus
protects the stomach epithelial cells (lining).
 Rugae = folds in the stomach lining to increase surface area
for more efficient secretion and expansion.
- Chyme = fluid contents of stomach; contains partially
digested food, fluids, and enzymes.
- Chyme enters the small intestine, one squirt at a time,
controlled by the pyloric sphincter.
 Pyloric sphincter = separates the contents of the stomach
from the small intestine; regulates the amount of chyme
entering small intestine
 Small intestine – Mechanical, Chemical, and Absorption
 Separated into 3 sections; 1st part = duodenum
*** WHERE LIPID DIGESTION BEGINS AND ENDS!
*** WHERE CARB. AND PROTEIN DIGESTION END!
 1ST PLACE WHERE NUTRIENTS FROM FOOD ARE ABSORBED INTO YOUR
BLOOD SO THEY CAN BE CARRIED TO CELLS FOR USE
a)Liver has many functions:
1. Detoxifies blood – breaks toxins into safer molecules
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2. Makes bile
- Stored in the gall bladder; secretes bile into
duodenum to…
Job of bile:
- M: emulsify fat; breaks fat globs into smaller
globlets
3. Stores and releases sugars to keep blood sugar levels
at homeostasis
- See your endocrine notes = Negative feedback loop
of glucose levels in the blood!
b) Pancreas has many functions
1. Secretes sodium bicarbonate/baking soda (base) to
neutralize the acidic chyme coming from the
stomach
2. C: Pancreatic amylase – further digestion of
carbs into disaccharides …see (b) for what happens
to these
3. C: Other digestive enzymes to finish protein
digestion
- Proteins
amino acids (monomers)
4. A: Secretes insulin to absorb monosaccharides
into blood when they are fully digested. [see blood
glucose neg. feedback loop]
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5. C: Secretes lipase to finish lipid digestion
c) C: cells of duodenum - secrete sucrase, maltase, and
lactase to break apart sucrose, maltose, and lactose (all
disaccharides) into their monomer.
 A: Large intestine/colon
- Helps maintain homeostasis of water balance by removing
90% of the water from waste = back into to blood – then
back into cells.
o Vitamins and minerals are reabsorbed with the water
What’s left is solid waste
 Rectum – storage of waste before removal
 Anal sphincter/Anus – holds waste back until a nerve signal
stimulates it to open = = to potty!
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