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Human Physiology: Organ Systems and Digestion
1. HUMAN PHYSIOLOGY
Research into human physiology is the foundation of
modern medicine. Body functions are carried out by
specialized organ systems. The structure of the wall
of the small intestine allows it to move, digest and
absorb food. The blood system continuously
transports substances to cells and simultaneously
collects waste product.
The skin and immune system resist the
continuous threat of invasion by pathogens. The
lungs are actively ventilated to ensure that gas
exchange can occur passively. Neurons transmit
the message, synapses modulate the message.
Hormones are used when signals need to be
widely distributed.
3. Understandings
Statement Guidance
6.1.U1
The contraction of circular and longitudinal
muscle of the small intestine mixes the food with
enzymes and moves it along the gut.
6.1.U2
The pancreas secretes enzymes into the lumen
of the small intestine.
Students should know that amylase, lipase and an
endopeptidase are secreted by the pancreas. The
name trypsin and the method used to activate it are
not required.
6.1.U3
Enzymes digest most macromolecules in food
into monomers in the small intestine.
Students should know that starch, glycogen, lipids and
nucleic acids are digested into monomers and that
cellulose remains undigested.
6.1.U4
Villi increase the surface area of epithelium over
which absorption is carried out.
6.1.U5
Villi absorb monomers formed by digestion as
well as mineral ions and vitamins.
6.1.U6
Different methods of membrane transport are
required to absorb different nutrients.
4. Applications and Skills
Statement Guidance
6.1.A1
Processes occurring in the small intestine that result
in the digestion of starch and transport of the
products of digestion to the liver.
6.1.A2
Use of dialysis tubing to model absorption of
digested food in the intestine.
6.1.S1
Production of an annotated diagram of the digestive
system.
6.1.S2
Identification of tissue layers in transverse sections
of the small intestine viewed with a microscope or in
a micrograph.
Tissue layers should include longitudinal and
circular muscles, mucosa and epithelium.
5. Digestive system
The part of the human body used for digestion
can be described in simple terms as a tube
through which food passes from the mouth to the
anus. (9 meter long)
The role of the digestive system is to break down
the diverse mixture of large carbon compounds in
food, to yield ions and smaller compounds that
can be absorbed.
For proteins, lipids and polysaccharides digestion
involves several stages that occur in different
parts of the gut.
6. 6.1.S1 Production of an annotated diagram of the digestive system.
Use the animation and video to learn about the digestive system
and how to draw it.
http://highered.mheducation.com/sites/0072495855/stu
dent_view0/chapter26/animation__organs_of_digestion.
html
https://youtu.be/Nm-pT7fk6gs
7. 6.1.S1 Production of an annotated diagram of the digestive system.
Plus add in the accessory
organs: the gall bladder,
liver and pancreas.
9. 6.1.S1 Production of an annotated diagram of the digestive system.
Now add the annotations to show what happens in digestion.
10.
11. 6.1.U1 The contraction of circular and longitudinal muscle of the small intestine mixes the food with
enzymes and moves it along the gut.
Peristalsis moves food through the alimentary canal
In the intestines the food is moved
only a few centimetres at a time so
the overall progression through the
intestine is much slower, allowing
time for digestion. The main function
of peristalsis in the intestine is
churning of the semi-digested food to
mix it with enzymes and thus
speed up the process of digestion.
1. Contraction of
longitudinal
muscle expand
the lumen in
front of the
food giving it
space to move
into.
2. Contraction of
circular muscles
behind the food
propels it
forwards.
n.b. The contractions are controlled unconsciously by the enteric nervous system. Peristalsis occur only in one
direction.
http://www.bbc.co.uk/schools/gcsebitesize/scie
nce/add_edexcel/common_systems/digestionre
v2.shtml
12. 6.1.U3 Enzymes digest most macromolecules in food into monomers in the small intestine.
13. Review: 2.5.U1 Enzymes have an active site to which specific substrates bind. AND 2.5.U2
Enzyme catalysis involves molecular motion and the collision of substrates with the active site.
Enzyme: A globular
protein that increases the
rate of a biochemical
reaction by lowering the
activation energy
threshold (i.e. a biological
catalyst)
http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf
Use the animation to find out more about enzymes and how they work.
A good alternative is How Enzymes Work from McGraw and Hill
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html
14. 6.1.U3 Enzymes digest most macromolecules in food into monomers in the small intestine.
Human Digestive Enzymes
Remember: enzymes are specific to their substrates and
each enzyme has its own optimum pH.
Three main types of enzymes in human digestion:
Amylases break down carbohydrates
Example: salivary amylase
Substrate: starch Product: maltose
Source: mouth (salivary glands)
Optimum pH: 7-7.8
Proteases break down polypeptides
Example: pepsin
Substrate: polypeptides Product: amino acids
Source: stomach
Optimum pH: 2
Lipases break down fats and lipids
Example: pancreatic lipase
Substrate: triglycerides Product: fatty acids & glycerol
Source: pancreas, delivered into small intestine
Optimum pH: 7.2 - 7.5
diagram from: http://www.teachervision.fen.com/digestive-system/printable/57730.html
15. Digestion in small intestine
Enzymes digest most macromolecules in food into
monomers in the small intestine.
The enzyme secreted by the pancreas into the lumen of the small intestine carry out
these hydrolysis reactions:
amylase
• Starch maltose
• lipase
• Lipids(fats and oil) fatty acid + glycerol
• phospholipase
• Phospholipids fatty acids + glycerol +phosphate
• protease
• Proteins and polypeptides shorter peptides
16. Digestion in small intestine
• This does not complete the process of digestion into
molecules small enough to be absorbed.
• The wall of small intestine produces variety of other
enzymes to digest more substances.
• nucleases
• DNA + RNA nucleotides
• maltase
• maltose glucose.
• lactase
• lactose glucose + galactose.
• sucrase
• sucrose glucose + fructose.
• Exopeptidases are proteases that digest peptides by
removing single amino acid either from the car boxy
or amino terminals of the chain until only a
dipeptide is left.
• dipeptides dipeptidases amino acids.
17. Digestion in Small intestine
Because of the great length of the small intestine, food takes hours to
pass through, allowing time for digestion of most macromolecules to be
completed
Some substances like cellulose is not digested because humans cannot
synthesize the necessary enzyme.
18. 6.1.U2 The pancreas secretes enzymes into the lumen of the small intestine.
https://commons.wikimedia.org/wiki/File:Diagram_showing_the_position_of_the_pancreas_CRUK_356.svg
The pancreas synthesises the three main types of digestive enzyme:
• amylase to digest carbohydrates, e.g. starch
• lipases to digest lipids, e.g. triglycerides
• proteases to digest polypeptides
Pancreatic juice containing
the enzymes is released into
the upper region of the small
intestine (duodenum) via the
pancreatic duct
The small intestine is where
the final stages of digestion
occur.
Pancreas contains two types of gland tissue
a. Secreting insulin and glucagon(small group of cell)
b. Secreting digestive enzymes(remainder of the pancreas)
Insulin and glucagon control blood glucose level
19. 6.1.S2 Identification of tissue layers in transverse sections of the small intestine viewed with a
microscope or in a micrograph.
The small intestine contains four distinct tissue
layers from the lumen
http://www.dartmouth.edu/~anatomy/Histo/lab_5/GI/DMS132/popup.html
Muscular layer
longitudinal
circular
Mucosa – inner lining, includes villi
Submucosa – connective tissue (between the
mucosa and muscle)
Muscular layer –
inner circular and
outer longitudinal
muscle perform
peristalsis
Serosa – protective
outer layer
Epithelial cells –
single outer layer of
cells on each villus
(see 6.1.U4)
20. Villi and surface area of absorption
The villi increases the surface area of epithelium over which absorption
is carried out.
The process of taking substances into cells and the
blood is called absorption.
In the human digestive system nutrients are absorbed
principally in the small intestine.
The rate of absorption depends on the surface area
of epithelium that carries out the process.
The small intestine in adult is approximately 7 meters
long and 25-30 mm wide and there are folds on its
inner surface, giving a large surface area.
The area is increased by the presence of villi.
Villi are small finger like projections of the mucosa on
the inside of intestine wall.
A villus is between 0.5 and 1.5mm long and there can
be as many as 40 of them per square mm of small
intestine
21. 6.1.U4 Villi increase the surface area of epithelium over which absorption is carried out.
Adaptations to Absorption Getting digested food molecules into the
blood from the lumen of the ileum.
Single-cell layer of epithelial cells
Short path for diffusion.
Capillaries close to epithelium
Short path for diffusion, rich supply of blood.
Lacteals (lymph vessels)
Allow for rapid absorption and transport of lipids.
Rich blood supply
Maintains concentration gradients between
lumen and blood.
Many villi protrude into the lumen, greatly
increasing the surface area for absorption.
Images from: http://en.wikipedia.org/wiki/Intestinal_villi
Microvilli on the surface of
each cell increase surface
area even further.
22. Absorption by villi
Villi absorb monomers formed by digestion as well as
mineral ions and vitamins.
The epithelium that covers the villi must form a barrier to harmful substances
The epithelium must also be permeable to the useful nutrients that pass through
The villus cells absorb these products
a. Glucose, fructose, and galactose
b.The 20 amino acids used to make proteins
c. Fatty acids, monoglycerides and glycerol
d. Bases from digestion of nucleotides
Villus also absorb substances required by the body, present in
food, but not in need of digestion
a. Mineral ions Ca2+, K+ and Na+
b. Vitamins A, B6, B12 or C
Some harmful substances pass through epithelium and are
subsequently removed from the blood and detoxified by the
liver.
Artificial flavor or colors pass out in the urine
Bacteria can be removed from the blood by phagocytic cells in
the liver
23. 6.1.U5 Villi absorb monomers formed by digestion as well as mineral ions and vitamins.
https://youtu.be/P1sDOJM65Bc
Along with vitamins and minerals all products
of digestion (monosaccharides,
amino acids, fatty acids & glycerol)
are absorbed by the villi
extra
24. To be absorbed into the body, nutrients must pass
from the lumen of the small intestine to the
capillaries or lacteals in the villi. The nutrients must
first be absorbed into epithelium cells through the
exposed part of the plasma membrane that has its
surface area enlarged with microvilli. The nutrients
must then pass out of this cell through the plasma
membrane where it faces inwards towards the
lacteal and blood capillaries of the villus.
Methods of absorption
Different methods of membrane transport are required to absorb different nutrients.
Many different mechanisms move
nutrients into and out of the villus
epithelium cells: simple diffusion,
facilitated diffusion, active transport
and exocytosis
25. 6.1.U6 Different methods of membrane transport are required to absorb different nutrients.
Method of
transport
Nutrients Outline
Simple
diffusion
Lipids
Fructose, vitamins Water-soluble (hydrophilic) molecules use channel
proteins to pass phospholipid bilayer
and enter the epithelial cells (down the
concentration gradient)
Active
Transport
Endocytosis
(Pinocytosis)
Antibodies from
breast milk
How is membrane transport involved in absorption of nutrients
from the small intestine?
26. 6.1.U6 Different methods of membrane transport are required to absorb different nutrients.
Method of
transport
Nutrients Outline
Simple
diffusion
Lipids
(fatty acids and
monoglycerides)
Lipids are non-polar and therefore can pass freely
through hydrophobic core of the plasma
membrane into the epithelial cells (down the
concentration gradient )
Facilitated
Diffusion
Fructose, vitamins Water-soluble (hydrophilic) molecules use channel
proteins to pass phospholipid bilayer
and enter the epithelial cells (down the
concentration gradient)
Active
Transport
Glucose, amino
acids and mineral
ions
Protein pumps use ATP to move molecules against
the concentration gradient into the epithelial cells
Endocytosis
(Pinocytosis)
Antibodies from
breast milk
The plasma membrane folds inward to form
vesicles to absorb larger molecules without
digesting them
How is membrane transport involved in absorption of nutrients
from the small intestine?
27. 6.1.A1 Processes occurring in the small intestine that result in the digestion of starch and transport of the
products of digestion to the liver.
Starch is an important component
of many human diets.
Starch occurs as amylose and
amylopectin, and most food
staples contain both forms.
Digestion of starch begins the
moment you start chewing your
food.
.
Once the saliva and the food have
been mixed, amylase starts
breaking down the α-1,4
glycosidic bonds that connect the
glucose monomers in amylose
and amylopectin.
The numbers 1 and 4 refer to
specific carbon atoms within the
two glucose molecules that are
joined by the bond
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Membranes/bauerp/co.gif
28. 6.1.A1 Processes occurring in the small intestine that result in the digestion of starch and transport of the
products of digestion to the liver.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Membranes/bauerp/co.gif
The end products are maltose, a dimer of
glucose connected by α-1,4 bonds, and
maltotriose, which is comprised of three
glucose molecules also connected by α-1,4
bonds.
Amylopectin also possesses a slightly different
type of bond, called α-1,6 glyosidic bonds,
however, these cannot be broken down by
amylase.
Even after the initial catalytic breakdown by amylase, the di- and tri-saccharides produced from
the starch molecules are too large to pass through membranes, so they need to be broken
down into monomers (monosaccharides) before they can be absorbed.
What enters the small intestine is a mixture of maltose, maltotriose and dextrins. Dextrins are
very small polymers still containing the α-1,6 glycosidic bond. Three enzymes that are
immobilised in the epithelial cells of the small intestine, maltase, glucosidase and dextrinase,
break down these molecules into glucose, which can then be absorbed by the villi.
All absorbed monomers from food are transported via the hepatic portal vein from the
small intestine to the liver, from there it enters the general circulation.
29. 6.1.A2 Use of dialysis tubing to model absorption of digested food in the intestine.
http://www.nuffieldfoundation.org/practical-
biology/evaluating-visking-tubing-model-gut
Dialysis (visking) tubing can be used to model absorption
The tubing is semi-permeable and contains pores
typically ranging 1 – 10 nm in diameter
Initially contains a
mixture of starch and
glucose
Test the solutions inside and outside the dialysis
tubing for starch and glucose before and after at
least 15 minutes have elapsed (see the Practical
Biology link for details).
Predict what will happen to the
glucose and starch after 15
minutes.
30. Nature of Science: Use models as representations of the real world - dialysis tubing can be used to model
absorption in the intestine. (1.10)
http://www.nuffieldfoundation.org/practical-
biology/evaluating-visking-tubing-model-gut
Dialysis (visking) tubing can be used to model absorption
The tubing is semi-permeable and contains pores
typically ranging 1 – 10 nm in diameter
Initially contains a
mixture of starch and
glucose
Test the solutions inside and outside the dialysis
tubing for starch and glucose before and after at
least 15 minutes have elapsed (see the Practical
Biology link for details).
Predict what will happen to the
glucose and starch after 15
minutes.
Physiology is the study of how the human body works. It describes the chemistry and physics behind basic body functions, from how molecules behave in cells to how systems of organs work together. It helps us understand what happens in a healthy body in everyday life and what goes wrong when someone gets sick
