Transcript Topic #6: Human Physiology

Topic #6: Human Physiology
I. Digestion and Absorption
A. Peristalsis
1. The contraction of circular and longitudinal
muscle layers of the small intestine mixes the
food with enzymes and moves it along the gut
2. The circular and longitudinal muscles are
smooth muscle fibers, not striated
3. Waves of muscle contraction are called
peristalsis  the two types of muscles work in
concert with each other
a. The tube lengthens and shortens in
response to the contracting and relaxing of
the continuous and longitudinal fibers
b. Similar to a drawstring in pants…lol…pants
I. Digestion and Absorption
4. Swallowed food moves quickly down the
esophagus to the stomach in one continuous
peristaltic wave
5. Peristalsis only occurs in one direction – away
from the mouth
6. Vomiting is reverse peristalsis and uses the
abdominal muscles are used instead of the
circular and longitudinal muscles
7. Food moves only a few centimeters at a time in
the intestines
8. Moves food along and mixes it with enzymes
to speed up the process of digestion
I. Digestion and Absorption
B. Pancreatic juice
1. The pancreas secretes enzymes into the lumen
of the small intestine
2. Pancreas contains two types of gland tissue
a. Secreting insulin and glucagon
b. Secreting digestive enzymes
3. Both sets of glands are regulated by hormones
4. Digestive enzymes are synthesized in
pancreatic gland cells on ribosomes on the ER
then sent to the Golgi and then sent out by
exocytosis
5. Pancreatic juices
a. Amylase to digest starch
I. Digestion and Absorption
C. Digestion in the small intestine
1. Enzymes digest most macromolecules in food
into monomers in the small intestine
2. The enzymes carry out these hydrolysis
reactions
a. Starch is digested to maltose by amylase
b. Triglycerides are digested to fatty acids and
glycerol or fatty acids and monoglycerides by
lipase
c. Phospholipids are digested to fatty acids,
glycerol and phosphate by phospholipase
d. Proteins and polypeptides are digested to
shorter polypeptides by protease
I. Digestion and Absorption
3. This does not complete the process of
digestion
4. The wall of the small intestine secrete enzymes
a. Nucleases digest DNA and RNA into
nucleotides
b. Maltase digests maltose into glucose
c. Lactase digests lactose into glucose and
galactose
d. Sucrase digests sucrose into glucose and
fructose
e. Exopeptidases are proteases that digest
peptides by removing single amino acids
f. Dipeptidases digest dipeptides into amino
acids
I. Digestion and Absorption
5. 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
6. Some substances remain largely undigested
a. Cellulose
b. We do not secrete cellulase
c. Main source of dietary fiber
D. Villi and the surface area for digestion
1. Villi increase the surface area of epithelium
over which absorption is carried out
2. Process of taking substances into cells and the
blood is called absorption
I. Digestion and Absorption
3. The rate of absorption depends on the sruface
area of the epithelium
4. Inner folds – villi – increase the surface area of
the lumen of the small intestine
I. Digestion and Absorption
5. A villus is between 0.5 – 1.5mm long and there
can be as many as 40 of them per square
millimeter of small intestine wall
6. They increase the surface area by a factor of 10
E. Absorption by villi
1. Villi absorb monomers formed by digestion as
well as mineral ions and vitamins
2. The epithelium that covers the villi must form a
barrier to harmful substances
3. The epithelium must also be permeable to the
useful nutrients that pass through
4. The villus cells absorb these products
a. Glucose, fructose, and galactose
I. Digestion and Absorption
b. The 20 amino acids used to make proteins
c. Fatty acids, monoglycerides and glycerol
d. Bases from digestion of nucleotides
5. 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
6. Some harmful substances get absorbed too
a. Removed and detoxified by the liver
b. Artificial flavor or colors
c. Pass out in the urine
d. Bacteria can be removed from the blood by
phagocytic cells in the liver
I. Digestion and Absorption
E. Methods of absorption
1. Different methods of membrane absorption
are
required to absorb different nutrients
2. To be absorbed into the body, nutrients must
pass from the lumen of the small intestine to the
capillaries
3. Mechanisms like simple diffusion, facilitated
diffusion, active transport and exocytosis
4. Illustrated well using triglycerides and glucose
as examples
a. Triglycerides must be digested before
absorbed
b. Products of digestion are fatty acids and
monoglycerides
I. Digestion and Absorption
c. Can be absorbed by simple diffusion
d. Fatty acids are absorbed by facilitated
diffusion  fatty acid transporters in the
membrane
e. Once inside epithelial cells, fatty acids are
combined with monoglycerides to produce
triglycerides, now it can’t diffuse back into the
lumen
f. Triglycerides coalesce with cholesterol to
form droplets with a diameter of about 0.2mm
and become coated in phospholipids and
protein
g. Lipoprotein particles are released by
exocytosis
I. Digestion and Absorption
h. Glucose cannot pass through the plasma
membrane by simple diffusion – it is polar and
hydrophilic
i. Na+/K+ pumps in the inside of the cell
membrane pumps Na+ from the cytoplasm to
the interstitial spaces inside the villus
 this creates a low concentration of sodium
ions inside villus epithelium cells
j. Sodium-glucose co-transporter proteins in
the microvilli transfer sodium and glucose
together from the intestinal lumen to the
cytoplasm of the epithelium cells
k. Glucose channels allow the glucose to move
by facilitated diffusion into the blood
II. The blood system
A. Arteries
1. Arteries convey blood at high pressure from
the ventricles to the tissues of the body
2. Arteries take blood from the heart to the
tissues of the body
3. Thick strong muscle in their walls work with
the heart to to control blood flow
4. Elastic tissue contains elastin fibers that store
the energy that stretches them at the peak of the
pumping cycle
5. The recoil will propel the blood down the
artery
6. Contraction of smooth muscle in the artery
determines the diameter of the lumen
II. The blood system
7. Both elastic and muscular tissues contribute to
the toughness of the walls which have to
withstand constantly changing blood pressure
8. Each organ of the body is supplied with blood
by the arteries
B. Artery walls
1. Arteries have muscle and elastic fibers in their
walls
2. Artery wall layers
a. Tunica externa – tough outer layer
b. Tunica media – thick layer with smooth and
elastic fibers
c. Tunica intima – smooth inner lining
II. The blood system
C. Arterial blood pressure
1. The muscle and elastic fibers assist in
maintaining blood pressure between pump cycles
2. Peak pressure is called systolic pressure
a. pushes the wall of the artery outwards
b. Widens the lumen
c. Stretches the elastic fibers
3. At the end of a heartbeat, the pressure falls
4. The resting pressure is called diastolic pressure
5. Vasoconstriction reduces the circumference of
the lumen and increases blood pressure
6. Vasoconstriction restricts blood flow to the
part of the body they supply and vasodilation
increases it
II. The blood system
D. Capillaries
1. Blood flows through tissues in capillaries with
permeable walls that allow exchange of materials
between cells in the tissue and the blood in the
capillary
2. Narrowest blood vessels with diameter of
about 10mm
3. They branch and rejoin repeatedly to form a
capillary network
4. Transport blood through every area of the
body, except…
a. Cornea
b. Lens
II. The blood system
5. Consists of one layer of very thin endothelium
cells
a. Coated by a filter-like protein gel
b. Contains pores between the cells
c. The wall allows part of the plasma to leak
out and form tissue fluid
d. Plasma is the fluid in which the blood cells
are suspended
e. Tissue fluid contains oxygen, glucose and all
other substances in blood plasma apart from
large protein molecules
f. The permeabilities of capillary walls differ
between tissues and change over time
II. The blood system
E. Veins
1. Veins collect blood at low pressure from tissues
of the body and return it to the atria of the heart
2. Veins bring blood back to the heart
3. The blood is at much lower pressure
4. Veins do not need as thick of walls as arteries
a. Fewer muscle fibers
b. Fewer elastic fibers
5. They can dilate to become wider and hold
more blood than arteries
6. 80% of a sedentary person’s blood is in the
veins (falls during exercise)
7. Blood flow in veins is assisted by gravity and
skeletal muscles
II. The blood system
8. Each part of the body is served by one or more
veins
G. Valves in veins
1. Valves in veins and the heart ensure circulation
of blood by preventing backflow
2. Sometimes, blood pressure in the veins is so
low there is danger of backflow into the
capillaries
3. If blood starts to flow backwards, it gets
caught in the flaps of a pocket valve
a. These valves fill with blood
b. Blocks the lumen of the vein
4. When blood flows toward the heart, it pushes
II. The blood system
the flaps to the sides of the vein
a. The pocket valves then open
b. Blood can flow freely
5. These valves allow blood to flow in one
direction only – ensure that blood circulates
F. The double circulation
1. There is a separate circulation for the lungs
2. There are valves in the veins and heart that
ensure a one-way flow
3. Blood capillaries in lungs can not withstand
high pressures so blood is pumped to them at
relatively low pressure
4. After passing through the capillaries,
II. The blood system
the pressure is very low, so the blood travels back
to the heart to be pumped with enough pressure
that it can travels to the rest of the organs of the
body
5. Humans have two separate circulations
a. Pulmonary circulation – to and from the
lungs
b. Systemic circulation – to and from all other
organs, including the heart muscles
G. Heart Structure (refer to coloring diagram)
1. The heart has two sides
a. Left and right side
b. Pump blood to the systemic and pulmonary
circulations
II. The blood system
2. Each side of the heart has two chambers
a. Ventricles that pump blood out into the
arteries
b. Atria that collect blood from veins and pass
it to the ventricle
3. Each side of the heart has two valves
a. An atrioventricular valve
 bt atrium and ventricle
b. A semilunar valve
 between ventricles and arteries
4. Oxygenated blood flows into the left side of
the heart from the pulmonary veins and then out
through the aorta
II. The blood system
5. deoxygenated blood flows through the right
side of the heart through the vena cava and out in
the pulmonary arteries
H. The sinoatrial node
1. The heartbeat is initiated by a group of
specialized muscle cells in the right atrium called
the sinoatrial node
2. The heart is unique because it has muscles that
contract without stimulation by motor neurons
3. Myogenic contraction – generated by the
muscle itself
4. The SA node is a small group of special muscle
cells in the wall of the right atrium
II. The blood system
I. Initiating the heartbeat
1. The sinoatrial node acts as pacemaker
2. Because the SA node initiates each heartbeat,
it sets the pace for the beating of the heart
3. If the SA node becomes defective, it can be
regulated or even completely replaced by an
artificial pacemaker
 an electronic device placed under the skin
 electrodes implanted in the wall of the heart
that that initiate each heartbeat in place of the
SA node
J. Atrial and ventricular contractions
1. the SA node sends out an electrical signal that
II. The blood system
stimulates contraction as it is propagated through
the walls of the atria and then the walls of the
ventricles
2. The SA node initiates a heartbeat by
contracting and simultaneously sends out an
electrical signal
3. The electrical signal spreads throughout the
walls of the atria
4. This happens because there are
interconnections between adjacent fibers
5. The fibers are branched so the signal passes to
many others so the signal propagates across the
entire heart
II. The blood system
6. After about 0.1 seconds, the electrical signal is
conveyed to the ventricles
a. The time delay allows time for the atria to
pump the blood that they are holding into the
ventricles
b. The signal is then propagated throughout
the walls of the ventricles
K. The Cardiac Cycle
1. Pressure changes in the left atrium, left
ventricle and aorta during the cardiac cycle
2. 0.0 – 0.1 seconds
a. Atria contract causing a small pressure
increase
II. The blood system
b. Semilunar valves are closed and blood
pressure in the arteries gradually drops to its
minimum
 blood continues to flow along them, but no
blood is pumped in
3. 0.1 – 0.15 seconds
a. Ventricles contract with rapid pressure build
up
b. Atrioventricular valves close
c. Semilunar valves remain closed
4. 0.15 – 0.4 seconds
a. The pressure in the ventricles rises above
the pressure in the arteries
II. The blood system
b. Pressure slowly rises in the atria as blood
drains into them from the veins and they fill
5. 0.4 – 0.45 seconds
a. The contraction of the ventricular muscles
wanes and pressure inside the ventricles
rapidly drops
b. The atrioventricular valves remain closed
6. 0.45 – 0.8 seconds
a. Pressure in the ventricles drops below the
pressure in the atria
b. Atrioventricular valves open
c. Blood from the veins drains into the atria
d. A slow increase in pressure results
II. The blood system
L. Changing the Heart Rate
1. The heart rate can be increased or decreased
by impulses brought to the heart through two
nerves from the medulla of the brain
2. One nerve will cause the pacemaker to increase
the frequency of heartbeats
3. Signals from the other nerve decrease the rate
4. Cardiovascular center
a. Inputs from receptors to monitor
i. Blood pressure
ii. pH  reflects CO2 concentration
iii. Oxygen concentration
II. The blood system
b. Low blood pressure, low oxygen
concentration and low pH all suggest the heart
needs to speed up
i. increases flow rate
ii. Delivers more oxygen
iii. Removes more carbon dioxide
c. High blood pressure, high oxygen
concentration and high pH are all indicators
that say the heart rate may need to slow down
M. Epinephrine
1. Epinephrine increases the heart rate to prepare
for vigorous physical activity
2. The SA node also responds to epinephrine
II. The blood system
3. Epinephrine is also known as adrenalin
4. Epinephrine is secreted by the adrenal gland
and its release is controlled by the brain
a. Rises when vigorous physical activity is
necessary
b. Flight or fight hormone
III. Gas Exchange
A. Ventilation
1. Ventilation maintains concentration gradients
of oxygen and carbon dioxide between air in
alveoli and blood flowing in adjacent
capillaries
2. All organisms absorb one gas from the
environment and release another one
III. Gas Exchange
3. This process is called gas exchange
4. Leaves absorb CO2 and release O2
5. Animals absorb O2 and release CO2
6. Gas exchange occurs in small air sacs called
alveoli inside the lungs
a. Happens by diffusion
b. Between the blood in the capillaries and the
air in the alveoli
7. Gases only diffuse because there is a
concentration gradient
a. More O2 in the alveoli than the blood
b. More CO2 in blood than the alveoli
8. Ventilation – pumps fresh air into the alveoli
III. Gas Exchange
and removes stale air
B. Type I pneumocytes
1. Type I pneumocytes are extremely thin alveolar
cells that are adapted to carry out gas exchange
2. The lungs contain huge numbers of alveoli
with a very large total surface area
3. The walls of each alveolus consists of a single
layer of cells – called the epithelium.
4. The cells in the epithelium are are the Type I
pneumocytes
5. They are flattened cells with the thickness of
0.15mm of cytoplasm
6. Adjacent capillary cells also consist of a single
III. Gas Exchange
layer of very thin cells
7. So…the air in the alveolus and the blood in the
alveolar capillaries are less than 0.5mm apart
8. The distance the oxygen and carbon dioxide
have to travel is very
C. Type II pneumocytes
1. Type II pneumocytes secrete a solution
containing surfactant that creates a moist surface
inside the alveoli to prevent the sides of the
alveolus adhering to each other by reducing
surface tension
2. These cells occupy about 5% of the alveolar
surface area
III. Gas Exchange
3. These cells secrete a fluid which coats the inner
surface of the alveoli
4. This fluid allows the oxygen to dissolve and
then diffuse into the blood
5. Provides an area for the carbon dioxide to
evaporate into the air
6. Pulmonary surfactant – the molecules are
similar to phospholipids
- hydrophilic heads facing the water
- hydrophobic tails facing the air
a. Forms a monolayer
b. Reduces surface tension
c. Prevents the collapse of the lung
III. Gas Exchange
7. Premies are often born with insufficient
pulmonary surfactant
a. Suffer from respiratory distress syndrome
b. Need oxygen and doses of surfactant
extracted from animal lungs
D. Airways for ventilation
1. Air is carried to the lungs in the trachea and
bronchi and then to the alveoli in the bronchioles
2. The trachea branches into two paths 
bronchi
3. The bronchi continue to branch, tree-like into
bronchioles
4. At the end of each branch is an alvelolus
III. Gas Exchange
E. Pressure changes during ventilation
1. Muscle contractions cause the pressure
changes inside the thorax that force air in and out
of the lungs to ventilate them
2. It’s basic physics…and kind of gas laws
3. As the volume inside the lungs increases,
pressure will decrease
4. When the pressure inside the lungs is lower
than atmospheric pressure, air will flow into the
lungs
5. As the volume inside the lungs decreases,
pressure will increase
6. This will cause air to flow out of the lungs
III. Gas Exchange
F. Antagonistic muscles
1. Different muscles are required for inspiration
and expiration because muscles only do work
when they contract
2. Muscles do work when they contract by
exerting a pulling force that causes a particular
movement
3. Muscles become shorter when they do this
4. Muscles lengthen while they are relaxing
- it happens passively, they do not lengthen
themselves
5. Muscles are pulled into an elongated state by
the contraction of another muscle
III. Gas Exchange
6. therefore, muscles can only cause movement
in one direction
7. When one muscle contracts, movement occurs
and the other muscle will relax
8. Therefore, muscles can only cause movement
in one direction
9. Muscles moving in this way are known as
antagonistic muscles
F. Antagonistic muscle action in ventilation
1. External and internal intercostal muscles, and
diaphragm and abdominal muscles as examples
of
antagonistic muscle action
Inspiration
Expiration
Diaphragm
Moves down and flattens
Moves up and becomes more
domed
Ribcage
Moves up and out
Moves down and in
Volume and pressure changes
Volume increases, pressure
decreases
Volume decreases, pressure
increases
Movement of the diagphragm
Diaphragm contracts and
moves down; pushes
abdomen wall out
Diaphragm relaxes and can be
pushed upward in dome
shape
Movement of the ribcage
(external intercostals)
External intercostal muscles
contract, pulling the ribs up
and out
External intercostal muscles
relax and are pulled back into
their elongated state
(internal intercostals)
Internal intercostals relax and
are pulled back into their
elongated state
Internal intercostal muscles
contract, pulling ribcage in
and down
III. Neurons and synapses
A. Neurons
1. Neurons transmit electrical impulses
2. Two systems are used for internal
communication within the body  endocrine and
nervous
3. Neurons are nerve cells
a. 85 billion of them in the nervous system
b. Transmit nerve impulses – electrical signals
c. Structures of the neuron
i. Cell body – nucleus and cytoplasm
ii. Dendrites – short, branched nerve fibers
iii. Axons – long nerve fibers
III. Neurons and synapses
B. Myelinated nerve fibers
1. The myelination of nerve fibers allows for
saltatory conduction
2. The fiber is a cylindrical shape with a 1mm
diameter
3. Conduct impulses at a rate of 1m/s  speedy
quick!
4. Some neurons are coated by a material called
myelin
a. Consists of many layers of phospholipid
bilayer
b. Schwann cells deposit the myelin by
growing round and round the nerve fiber
III. Neurons and synapses
c. There may be 20 or more layers when the
Schwann cell stops growing
d. There is a gap in myelin between adjacent
Schwann cells  the Node of Ranvier
i. Nerve impulses jump from node to node
along the axon  saltatory conduction
ii. Much quicker than continuous
transmission (100m/s)
C. Resting Potentials
1. Neurons pump sodium and potassium ions
across their membranes to generate a resting
potential
2. A neuron not transmitting a signal has a
III. Neurons and synapses
potential difference or voltage across its
membrane  resting potential
3. This potential is due to an imbalance of postive
and negative charges across the membrane
4. Na+/K+ pumps transfer sodium and potassium
ions across the membrane
a. Sodium is pumped out
b. Potassium is pumped in
c. The number of ions is unequal
i. 3 Na+ ions are pumped out
ii. 2 K+ ions are pumped in
d. Creates a concentration gradient for both
ions
III. Neurons and synapses
5. The membrane is about 50 times more
permeable to K+ ions than Na+ ions
a. K+ ions leak back across the membrane
faster than Na+
b. The Na+ concentration gradient across the
membrane is steeper than the K+ gradient
creating a charge imbalance
6. There are also large proteins inside the
membrane of the nerve fiber that are negatively
charged
7. gives the neuron a resting membrane potential
of about – 70mV
III. Neurons and synapses
D. Action Potentials
1. An action potential consists of depolarization
and repolarization of the neuron
2. depolarization  a change from negative to
positive
3. repolarization  a change back from positive
to negative
4. Depolarization is due to opening of Na+
channels allowing for Na+ to move IN to the
neuron (with the conc. gradient)
5. The movement of sodium reverses the charge
imbalance, so the inside charge is positive relative
to the outside
III. Neurons and synapses
6. Raises the membrane potential to a positive
value of about +30mV
7. Repolarization happens rapidly after
depolarization
a. Due to the closing of the sodium channels
b. Potassium channels open right after
c. Potassium diffuses out of the neuron
d. The membrane potential changes back to
-70mV
e. Does not restore resting potential until the
sodium and potassium concentration gradients
have been re-established
III. Neurons and synapses
E. Propagation of action potentials
1. Nerve impulses are action potentials
propagated the axons of neurons
2. A nerve impulse starts at one end of a neuron
and travels to the other end
3. Nerve impulses always move in one direction
F. Local currents
1. Propagation of nerve impulses is the result of
local currents that cause each successive part of
the axon to reach the threshold potential
2. Inside the axon there is a higher sodium ion
concentration in the depolarized part so sodium
diffuse along the inside of the axon to the neighboring
III. Neurons and synapses
part that is still polarized
3. Outside the axon the concentration gradient is
in the opposite direction so sodium ions diffuse
from the polarized part back to the part that has
just depolarized
4. These movements are called local currents
5. Local currents reduce the concentration
gradient in the part of the neuron that has not yet
depolarized
6. This makes the membrane potential rise from
the resting potential of -70mV to about -50mV
7. Sodium channels in the axon membrane are
voltage-gated and open at -50mV
III. Neurons and synapses
8. This is known as Threshold Potential
9. Thus, local currents cause a wave of
depolarization and then repolarization to be
propagated along the axon at a rate of between 1
and 100m/s
G. Synapses
1. Synapses are junctions between neurons and
between neurons and receptor or effector cells
2. In both the brain and spinal cord there are
immense numbers of synapses between neurons
3. In muscles and glands, there are synapses
between neurons and muscle fibers or secretory
glands
III. Neurons and synapses
4. Chemicals called neurotransmitters are used to
send signals across these synapses
H. Synaptic Transmission
1. Occurs very rapidly:
2. Nerve impulse reaches the end of the presynaptic neuron
3. Depolarization of the pre-synaptic neuron
causes Ca2+ ions to move into the neuron
4. Influx of Ca2+ ions causes synaptic vesicles to
move to the pre-synaptic membrane and fuse
with it
5. The neurotransmitter is released into the
synaptic cleft by exocytosis
III. Neurons and synapses
6. The neurotransmitter diffuses across the
synaptic cleft and binds to receptors on the postsynaptic membrane
7. The binding of the neurotransmitter to the
receptors causes sodium channels to open
8. Sodium ions diffuse down their concentration
gradient into the post-synaptic neuron causing
the post-synaptic membrane to reach threshold
potential
9. An action potential is triggered in the postsynaptic neuron and is propagated along the
neuron
10. The neurotransmitter is recycled and
reabsorbed
III. Neurons and synapses
I. Acetylcholine
1. Secretion and reabsorption of acetylcholine by
neurons at synapses
2. Acetylcholine is used at synapses between
neurons and muscles
3. It’s produced by combining choline (from food
we eat) and an acetyl group (from cell
respiration)
4. Acetylcholine is loaded into vesicles to be
released into the synaptic cleft during synaptic
transmission
J. Threshold Potentials
1. A nerve impulse is only initiated if the threshold
potential is reached
III. Neurons and synapses
2. Nerve impulses follow an all-or-nothing
principle
3. An action potential is only initiated if threshold
potential has been reached
4. At a synapse, the amount of neurotransmitter
secreted following depolarization of the presynaptic membrane may not be enough to cause
the threshold potential to be reached
5. A typical post-synaptic neuron in the brain or
spinal cord has synapses with not with just one,
but with many pre-synaptic neurons
6. Increases the likelihood that a threshold
potential will be reached…so you can think…get
out of the way…not get hit by a rubberband…