Download Carbs

Digestion
3 types of digestion:
1. Mechanical – breaking food into smaller pieces; increases
surface area of food for…
2. Chemical – breaking bonds in food into smaller molecules
for…
3. Absorption – where nutrients enters blood stream
• villi: projections increasing surface area of organ many
times
• microvilli: microscopic projections of individual cells
• capillaries in villi absorb amino acids and sugars
• lacteal: extension of lymph system into villi =
absorption of fats
 Overview of digestive tract organs
 Oral Cavity (mouth):
 mastication of food = increases surface area - mechanical
digestion
 saliva = lubrication of food, protection from bacteria,
prevent tooth decay with buffers
 ball of saliva and partially digested food = bolus
…swallow using skeletal muscle
 Epiglottis = flap-like structure made of cartilage (connective
tissue)
 Covers wind pipe when swallowing directing food to the
correct tube – esophagus
 Before entering the esophagus proper, the bolus hits the
upper esophageal sphincter triggering it to open
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 Upper esophageal sphincter = stops contents of esophagus
from backing up into the pharynx
 Esophagus
 Lined with smooth muscle
 Peristalsis = smooth muscle contractions moves bolus to –
esophageal sphincter before entering stomach
 Lower esophageal sphincter (cardiac sphincter) = blocks
stomach contents from entering esophagus
 Stomach
 Lined with smooth muscle
 Contraction = churning of bolus = mechanical digestion
 HCl and enzymes released – enzymes = chemical digestion
 Partially digested food is liquid = chyme
 Acidic chyme triggers – pyloric sphincter to open as chyme
enters small intestine
 can take 2 to 4 hours for a meal to enter the small
intestine
– rugae = folds in stomach to increase surface area;
stomach can hold up to 2L of food and fluid! Wow!
 Pyloric sphincter
 Stops intestinal contents from backing up into the stomach
 regulates acid chyme entering into small intestine (one
squirt at a time)
 Small intestine
 1st part of the small intestine = duodenum
 Main site of digestion and absorption (when food comes in
contact with blood for the first time)
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– microvilli = brush border (looks like a shag carpet)
 most digestion occurs here
 mixes enzymes with acid chyme from stomach
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 pancreas release pancreatic juice – to duodenum via
pancreatic duct
 liver makes bile – stored in gall bladder – to duodenum via bile
duct.
– liver: first organ for digestive blood to enter (mostly)
– stores glucose as glycogen
– filters and detoxifies poisons and drugs
– other storage and conversion functions
 Cells of the duodenum itself = brush boarder cells
 Enzymes of brush boarder are bound to the surface of the
epithelial cells (chem. digest.)
 2nd part = jejunum - more absorption
 3rd part = ileum – even more absorption
 Ileocecal valve
 Separates small and large intestine; stops back flow
between these two organs.
 Large intestine (colon)
 Re-absorb water (about 90%) and maintains the fluid
balance of the body.
 vitamins and minerals are also absorbed
 Rectum
 stores waste before removal
 As the rectal walls expand due to the materials filling it
from within, stretch receptors from the nervous system
located in the rectal walls stimulate the desire to
defecate. If the urge is not acted upon, the material in the
rectum is often returned to the colon where more water is
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absorbed. If defecation is delayed for a prolonged period,
constipation and hardened feces results.
 Anal sphincter
 Defecation = removal of solid waste from body
Specific Macromolecule digestion
 Carbohydrate Digestion:
 Oral cavity
 Mastication = mech. digest.
 salivary amylase: hydrolysis of starch and glycogen from
other animals (chemical digest.)
 products = smaller polysaccharides
 Pancreas
 Pancreatic amylase secreted into duodenum
– Smaller disaccharides from starch = maltose (c.d.)
 Duodenum
 maltase: finishes hydrolysis of starch--maltose (glucose
+ glucose)
 sucrase = glucose + fructose
 lactase = glucose + galactose
– all chemical digest.
 After sugars from carbs are absorbed into blood stream from
the small intestine, blood moves to liver first and then to the
rest of the body via the circulatory system.
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 Lipid Digestion:
 Oral Cavity - mastication
 Small intestine
 Only site of lipid digestion
1. Liver – makes bile
 Bile salts aid in the digestion and absorption of lipids
 Emulsifies fat = mechanical digest.
– Separates globs into globlets
– Increases surface area
 How?
– Bile has polar and non-polar ends
– non-polar ends clings to lipid - - polar ends cling to
water = pulls globs apart.
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2. Pancreas – makes lipase
 Enters duodenum via pancreatic duct
 Hydrolyzes lipids into fatty acids and glycerol (chem.
digest.)
 After monomers are absorbed by small intestine, they move
directly to the lymphatic system and then to the circulatory
system. (Not to the liver first)
– lacteal: extension of lymph system into villi = absorption
of fats
Note: Lymph is the fluid that is formed when interstitial fluid
(between cells) enters the initial lymphatic vessels of the
lymphatic system. The lymph is then moved along the lymphatic
vessel network. Eventually, the lymph vessels empty into the
lymphatic ducts, which drain into specific veins.
 Protein Digestion:
 Oral cavity = mastication
 Stomach
 Churning of food
 HCl – secreted by parietal cells
– dissolves connective tissue of protein (mechanical)
– pepsinogen (a zymogen) is secreted by chief cell of
gastric pits in stomach
 Zymogen – an inactive enzyme precursor
– acid environment activates pepsinogen into pepsin
– pepsin: hydrolyzes proteins into smaller
polypeptides (chem. digest.)
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 Example of a positive feedback mechanism – when pepsin is
activated, it can also activate additional molecules of
pepsinogen—self accelerating process
 Mucus = secreted by goblet cells; protects stomach cells
from digestion (acidic environment and chem. digest. of
self-cellular protein)
 Into Duodenum (from pancreas)
**zymogen = inactive enzyme form
**proteases (from pancreas) = active form
Zymogen
a. Trypsinogen
b. Chymotrypsinogen
c. Procarboxypeptidase
Activated by
Enterokinase
(from small
intestine
Trypsin
Trypsin
all
chemical
digest.
Protease
from
Trypsin
pancreas
Chymotrypsin
Carboxypeptidase
pancreas
pancreas
a, b, and c all make peptide chains smaller and smaller
Aminopeptidase cleave off individual a.a.
Small
intestine
 After a.a. from protein are absorbed into blood stream from
the small intestine, blood moves to liver first and then to
the rest of the body via the circulatory system.
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