Download Digestion 2015

Digestion
and
absorption
Objectives
Understandings:
• The contraction of circular and longitudinal muscle of the small intestine mixes
the food with enzymes and moves it along the gut.
• The pancreas secretes enzymes into the lumen of the small intestine.
• Enzymes digest most macromolecules in food into monomers in the small
intestine.
• Villi increase the surface area of epithelium over which absorption is carried out.
• Villi absorb monomers formed by digestion as well as mineral ions and
vitamins.
• Different methods of membrane transport are required to absorb different
nutrients.
Applications and skills:
• Application: Processes occurring in the small intestine that result in the
digestion of starch and transport of the products of digestion to the liver.
• Application: Use of dialysis tubing to model absorption of digested food in the
intestine.
• Skill: Production of an annotated diagram of the digestive system.
• Skill: Identification of tissue layers in transverse sections of the small intestine
viewed with a microscope or in a micrograph.
Digestion
Metabolism
chemical reactions
breaking down food and
releasing energy from
nutrients
Digestion
mechanical & chemical
breakdown of food into
nutrients
Digestion
Prepares food for cellular intake because most food molecules are
large polymers and insoluble
They must first be digested to smaller soluble
molecules before they can be absorbed into the
blood
The Digestive Process
•
•
•
Mechanical processing
and
movement:
chewing, mixing
•
•
Secretion:
fluid,
digestive enzymes and
hormones, bile, acid,
alkali, mucus
•
Digestion:
breaking
down food to smallest
absorbable units
•
•
Absorption: through
mucosa, into blood or
lymph vessels
•
Elimination:
undigested material
eliminated
•
•
Ingestion
– Taking in food through
the mouth
Propulsion (movement of
food)
– Swallowing
– Peristalsis – propulsion
by alternate contraction
&relaxation
Mechanical digestion
– Chewing
– Churning in stomach
– Mixing by segmentation
Chemical digestion
– By secreted enzymes:
see later
Absorption
– Transport of digested
end products into blood
and lymph in wall of
canal
Defecation
– Elimination of
indigestible substances
from body as feces 6
Movement & Control
Peristalsis
push food along by
rhythmic waves of
smooth
muscle
contraction in walls of
digestive system
Sphincters
muscular
ring-like
valves, regulate the
passage of material
between sections of
digestive system
Chemistry of Digestion
Amylases
Enzymes are biological catalysts
that increase the rate of reaction
Lipases
Hydrolysis
molecules
products
of insoluble
to soluble
Nucleases
food
end
Proteases
The Digestive Enzymes
type of
enzyme
example of
enzyme
source
substrate
product
optimum
pH
Amylase
salivary
amylase
saliva
starch
maltose
pH 7
gastric juice
protein
shorter
polypeptid
e chains
pH 2
pancreatic
juice
lipids
(triglycerid
es)
glycerol
and fatty
acids
pH 8
Protease
Lipase
pepsin
pancreatic
lipase
The Digestive Enzymes
The Digestive Enzymes
Digestive System
Digestive System
 mouth - the first part of the digestive system, where food
enters the body. Chewing and salivary enzymes in the mouth
are the beginning of the digestive process (breaking down the
food).
 esophagus - the long tube between the mouth and the
stomach. It uses rhythmic muscle movements (called
peristalsis) to force food from the throat into the stomach.
 stomach - a sack-like, muscular organ that is attached to the
esophagus; food is mixed with acids & enzymes  chemical
digestion. Food remains for few hours; peristalsis mixes food
until almost fluid – called chyme; pyloric sphincter opens
allowing small amounts of acid chyme into duodenum;
repeated until stomach empty
Main function: storage; chemical digestion of proteins
Digestive System
 small intestine - the long, thin tube that food goes
through after it leaves the stomach. Main function:
chemical digestion of carbs, lipids, proteins & absorption.
 large intestine - the long, wide tube that food goes
through after it goes through the small intestine
 anus - the opening at the end of the digestive system from
which feces exit the body.
Digestive System
 pancreas - enzyme-producing gland located below the
stomach and above the intestines. Enzymes help in the
digestion of carbohydrates, fats and proteins in the small
intestine.
 liver - a large organ located above and in front of the
stomach. It filters toxins from the blood, and secretes bile
(which breaks down fats) and some blood proteins.
 gall bladder - a small, sac-like organ located by the
duodenum. It stores and releases bile (digestive chemical
produced in liver) into the small intestine
Accessory Organs
Absorption & Assimilation
Absorption
The soluble products are first taken up by various
mechanisms into the epithelial cells that line the gut. These
epithelial cells then load the absorbed molecules into the
blood stream.
Assimilation
The soluble products of digestion are then transported to the
various tissues by the circulatory system.
The cells of the tissues then absorb the molecules for use
within this tissues the broken down molecules actually
become part of the body
Structure of the Small Intestine
• Blood supply in the villus which absorb the end products
of digestion from the epithelial cells
• The lacteals (green) that receive the lipoproteins before
transporting them to the circulatory system.
• Muscular walls that maintain the movement of chyme by
peristalsis.
Structure of the Small Intestine
Structure of the Small Intestine
Structure of the villus
 The structure of the villus (villi) increases the
surface are for the absorption of digested food
molecules.
 folds increase SA:VOL ratio by X 3
 Villi project into the lumen of the gut
increasing the surface area by X 10
 Microvilli are outward folds of the plasma
membrane increasing the surface area another
X10
The Process of Digestion
A. Mouth –
1. teeth begin mechanical digestion (chewing,
grinding)
2. saliva (digestive enzyme) begins chemical
digestion,
breakdown of carbohydrates into
smaller sugar molecules
(amylase) and
breakdown of bacteria cell walls (lysozyme)
B. Esophagus – food tube
1. peristalsis – contractions of smooth muscle toward
the stomach
The Process of Digestion
C. Stomach
1. chemical digestion– pepsin breaks down proteins and needs
hydrochloric acid to work which stops amylase.
Mucus needed to protect stomach
2. mechanical digestion – churned stomach contents
become chyme.
D. Small Intestine
1. most chemical digestion and absorption of food
2. digestive fluids from pancreas, liver and lining of duodenum
a. pancreas – regulates blood sugar
1. breaks down carbohydrates, proteins,
lipids, and nucleic acids
2. produces sodium bicarbonate,
neutralizes acids
b. liver – makes bile for breaking down fats (stored in
gall bladder)
The Process of Digestion
E. Absorption in the Small Intestine
1. villi– folded surfaces, increase surface area for absorption
a. products of carbohydrates and proteins
(undigested fat and some fatty acids absorbed by
lymph)
F. Large Intestine
1. absorption of water
2. bacteria produce compounds (vitamin K)
a. massive antibiotic use can cause vitamin K
deficiency
3. undigested material leave body through rectum