HK 3940 Final Exam Prep
1. What is the functional significance of local vs. central regulation? (3 examples)
Brain and Spinal cord (CNS) monitor the interaction of our many bodily systems ensuring our overall survival and
coordinate the whole body system, However they don’t have the capacity to maintain/monitor everything at all times
(too much traffic). Therefore we have local tissue control systems present in a variety of systems which work both
independently and in cooperation or competition (override) with the CNS.
1) Local and central regulation of testosterone release
At tissue level, estradiol(-), activin(-), inhibin(+) from sertoli cell works on leydig cells to control testosterone
release. LH and FSH from brain (hypothalamus GnRH Anterior pituitary LH and FSH) also controls the
2) Local and central regulation of pepsinogen release
Chemo Rc in stomach senses the low pH and sends signals to chief cells to release pepsinogen which then is
converted to pepsin. Also central nervous system sends signals down via vagus nerve to enteric plexus
neurons and to chief cells to release pepsinogen.
3) Local and central regulation of contractility
Direct nervous innervation (both PNS & SNS) controls the cardiac myocyte contraction by dephosphorylation
and phosphorylation, respectively. Endothelial cells lining the heart also release endothelin to increase
contractility of the heart.
4) Active skeletal muscle
Active skeletal muscle releases vasoactive metabolites that help the arterioles of that skeletal muscle to
dilate to get more blood flow in to carry out further metabolism. Centrally, SNS innervation causes
vasoconstriction of arterioles in general to decrease blood flow through those arterioles. As a result, inactive
skeletal muscle will constrict while active skeletal muscle will be dilated.
2. What is the functional significance of negative feedback? (3 examples)
Negative feedback is a control mechanism in which is initiated if some factor becomes excessive or deficient, and
it will perform a series of changes which will return the altered factor back to normal, in order to maintain
1) Ca2+ level and PTH
Plasma Ca2+decrease induce the release of PTH from parathyroid gland. The release in PTH works on various
sites of body (bone, kidney, and small intestine) to increase Ca2+ back to normal range. The increased
plasma Ca2+ level negatively feedback on parathyroid to decrease PTH release.
2) Respiratory system central pattern generator
A neuron is a spontaneous depolarizer which sends AP down to alpha motor neuron pool to cause inspiration.
A neuron also stimulates B neuron and B neuron stimulates C neuron which will inhibit A neuron to alter the
duration or rate of respiration.
A +B +C -A change the rate of respiration
alpha motor neuron inspiration
3) Gastric acid secretion
To stop the positive feedback of acid secretion, you have negative feedback loop starting from D cell.
Decreased pH (lower than pH of 2) is sensed by chemo Rc and signal is sent to D cells to secrete somatostatin
which inhibits acid secretion (G cells and ECL cells).
1 3. What is the functional significance of positive feedback? (3 examples)
Positive feedback enables body system to amplify the signal to cause explosive changes. You need negative
system to shut this down so that the system wouldn’t go out of control. Positive feedback is not as common in
physiological processes. Once positive feedback is initiated an event will be stimulated which will increasingly
repeat and repeat till a final result has been achieved and the body can return back to homeostatic conditions.
1) Oxytocin release
Oxytocin is the posterior pituitary hormone that aid in delivery of baby by inducing uteral smooth muscle
contraction. When the baby drops lower in uterus, it stimulates the stretch receptor in cervix which sends info
to hypothalamus for more oxytocin release. Oxytocin binds to its Rc in uterus and cause uterine contraction
and increase membrane Rc for Oxytocin (increase sensitivity to oxytocin). It helps with the further push
against the cervix, and more cervix stretch for more oxytocin release. This is a positive feedback, because it
amplifies the signal. This is then shut down when baby is removed from uterus.
2) Gastric acid & enzyme release
To maximize the acidity, you have positive feedback loop from G cells (gastrin), ECL cells (histamine), and to
parietal cells (HCl). Increased acidity will be sensed by chemo receptor in stomach and this will increase more
pepsinogen release from chief cell which works to digest protein in stomach. In presence of low pH,
pepsinogen is converted to active form, pepsin which works to digest protein to amino acid. Amino acid
stimulates G cells to release more gastrin to stimulate parietal cells.
3) Neuron-Neuron junction in brain area associated with learning and memory
AP from presynaptic neuron opens V-gated Ca2+ channel to cause fusion of Glu vesicle to membrane.
Released Glu binds AMPA, NMDA, and metabotropic Rc on post synaptic cell to cause various changes in post
synaptic cell. More AMPA Rc will be added to the membrane to increase the sensitivity, and NO will diffuse out
to presynaptic cell to promote more release of Glu, As a result of series of actions, post synaptic cell maintain
depolarized. (Long term potentiation)
4. What is the functional significance of updating feedback? (3 examples)
In order to coordinate and correct the response, you need a mechanism to integrate everything. Sensors and
effectors update the coordinating center to keep track of what’s really happening and what’s needed to be
corrected. It allows the brain center to know what’s the body is doing at all times and to make the necessary
adjustment and performing a needed tasks
1) Cerebellum as a huge integrator in motor control
Cerebellum receives inputs from primary motor cortex, supplementary motor cortex, sensory organs and
alpha motor neuron so that it can compare what’s really happening and what has been meant to happen.
Cerebellum the correct problem, if there is, by sending output to basal ganglia or thalamus. This cycle of info
continues, and it’s all neurally connected. Cerebral cortex being updated to maintain and mature
spermatozoa in male reproductive system
2) Cerebral cortex being updated to maintain and mature ovum and endometrium
Changed estrogen level will be detected and the signal will be sent to cerebral cortex to update the change.
Cerebral cortex will coordinate the hypothalamic and anterior pituitary activity to accommodate the change
3) Digestive system
Central nervous system sends SNS and PNS to enteric plexus and to effectors (smooth muscle, endocrine cells,
secretory cells, vessels) to cause changes directly. The change in effector will be sensed by Rc (chemo, osmo,
mechano) and sensory afferent will be sent back to CNS to update the brain
5. What is the functional significance of functional segregation/compartmentalization? (3 examples)
2 Living organisms are compartmentalized in not only in cellular level but also in tissue, and organ levels. Functions
are segregated to each compartment, so that each part will be specialized to the function that is assigned to it. In
the human body, due to the complexity of different tasks that need to be carried out, various systems are
separated into functionally distinct areas performing different functions, instead of one area doing the entire
1) Gastrointestinal tract
GIT is a tube specialized along its length for sequential processing of food. In order to achieve sequential
digestion, it needs compartmentalization. It is achieved by sphincter that is barrier to flow of food being
transferred o the next GI component. For example, pyloric sphincter separates stomach from small intestine,
so that acidic chyme cannot enter duodenum until it is fully digested. Because stomach and small intestine is
compartmentalized by pyloric sphincter, it makes sure that stomach comes before small intestine so that
digestion will occur in sequence.
2) Cardiovascular system
Cardiovascular system is a closed system which is made up of 2 pumps and different pipes. It is
compartmentalized based on its function. Veins and arteries are composed of different cell types to give
different characteristics to the pipes. Vein is more compliant, so it doesn’t change its pressure as much with
the increased volume, therefore suitable for storage. Artery is less compliant, so it changes its pressure a lot
with the small increase in volume, therefore suitable for transport. Also each pump ejects blood into different
systems (systemic or pulmonary).
3) Respiratory system
Respiratory system’s primary function is to bring blood in very close proximity to atmospheric gases so that
gas exchange would occur. Inspired air goes to trachea and bronchi which have epithelial cells, cartilage
(prevent it from collapsing), smooth muscle and goblet cells. Bronchi and trachea works as an airway. Air gets
warmed and saturated with water, and enters alveoli where there’s only a single layer of elongated epithelial
cells. Alveoli have no muscle because presence of muscle disrupts gas exchange. Alveoli are the main site of
6. What is the functional significance of cell asymmetry? (3 examples)
Cells are asymmetrical in their distribution of transporters, channels and other cellular characteristics to create
directionality of movement of various substances
1) Parietal cells
The main function of parietal cell is to secrete HCl to increase acidity of the stomach. It has H+/K+ ATPase
and Cl- protein channels on luminal side, and bicarb/Cl- exchanger on basolateral side. CO2 and H2O are
brought into the cell via passive diffusion and form carbonic acid which dissociates to form bicarb and
hydrogen ion within the parietal cell. Hydrogen ion then diffuses out through H+/K+ ATPase on luminal side
and bicarb moves to ISS via bicarb/Cl- exchanger on basolateral side.
An AP can propagate in both directions, but to ensure we don’t get the propagation in the wrong direction,
neurons have specific transporters and pumps on each sides. Axons have voltage gated Ca2+ cahnnels to
cause release of Ach into synaptic cleft while, dendrites have Ach gated Na+ channel to open Na+ channel
and continue the signal down the neuronal cell. AP which is propagated towards the cell body will not be
transferred across synaptic clefct because there’s no Ca2+ channels located in the cell body, therefore no
Ach released. While Axon ends do not have any ligand gated Na2+ channel to propagate signals backwards
3) Late distal tubule in Kidney
3 Principle cells have Na+ and K+ channels on luminal side and Na+/K+ ATPase on basolateral side to regulate
Na+, K+ ionic balance. Intercalated cells have H+ pump (actively excreting H+ions) on luminal side and
Na+/K+ ATPase on basolateral side to regulate H+ ion.
7. What is the functional significance of time dependence? (3 examples)
During physiological situations, not all reflexes respond at the same time, in the same timeframe due to the
variability of response time in body (hormonal vs. neuronal). Some (neurons) may take very short periods of time
(ms-s) while others (hormone) take long periods of time (hrs-days). Each response has its own time scale which
fits in with the overall response. Ms-sec time, sec to min, & min-hour time scale action only minimize the impact
of disturbance in physiological system in short term, so that the organism will stay alive until it commences the
hours-days time scale action to fix the problem (have longer lasting effect)
1) Increased Mean Arterial Pressure is sensed by high pressure baro Rc on carotid artery or aortic arch. It sends
AP to brain stem to decrease SNS and increase PNS activity. Direction neural innervation to heart then
decreases heart rate, contractility, stroke volume, cardiac output, and eventually decreases MAP. Increased
MAP is adjusted within ms-sec time scale. Also signals from high (and Low) pressure baro Rc sends signals to
brain stem hypothalamus to decrease ADH release. Decreased ADH vasodilates vasculature to decrease
total peripheral resistance (then MAP decreases) –min-hour time scale and increase water loss at kidney to
decrease blood volume (then MAP decreases). This adjustment occurs in hours to days time scale.
2) Regulating free H+ ions
Buffer action is in ms- sec time scale, because buffers (bicarb, protein, and phosphate) in plasma simply bind
the free H+ ion to minimize the impact from acidosis. Lung’s action takes mins-hours to regulate [H+]. It
changes CO2 concentration by changing ventilation rates. It’s still a temporary solution to problem, because it
lacks the power to return system to normal (only stabilization). Kidney acts on hours-days time scale, and it’s
a powerful regulator due to its ability to excrete H+ and bicarb from the body. It actually fixes the problem of
∴this process ↑’s efficiency since each stage of compensation, can attempt to correct the problem while
minimizing change in pH long enough for the next successive system to take effect ∴ never leaves the body
3) Growth hormone
Within minutes, GH works on liver to increase the production of IGF and increase gluconeogenesis. At skeletal
muscle, you increase lean body mass while you decrease adiposity to increase fuel for growth overall. In days
and months timescale, you increase protein synthesis to increase organ size and function. Also you increase
the number and the size of chondrocytes to cause linear growth.
8. What is the functional significance of Flow (Q) = (P1- P2)/R
Flow in the body has directionality which depends on the pressure gradient and resistance of the cavity which it
flows in. Flow occurs from higher pressure to lower pressure, and with greater resistance you have decreased
1) Food flow within GIT
If P1 is greater than P2, digesta flows from previous compartment to the next, but when P2 is greater than P1,
flow doesn’t occur. Sphincter increases pressure of the next compartment to prevent the food flow
2) Blood flow within cardiovascular system
4 In order for the ventricle filling to occur, atrial pressure should be greater than ventricular pressure. Also to
pump blood out of left ventricle, ventricular pressure should be greater than aortic pressure so that aortic
valve will open.
3) Air flow into the respiratory system
In this case, P1 is atmospheric pressure, and P2 is alveolar pressure. Since atmospheric pressure is constant
unless the altitude changes, you can physiologically modify alveolar pressure. To bring the air in, you should
make P Alveoli more negative (since Patm is set to 0) or decrease resistance.
9. Compare inspired volume in the lung standing vs. lying down (draw the diagram)
The pleural pressure is negative and pulls open the alveoli. By pulling open the alveoli, we create a negative
pressure within the alveoli which is designated as P2 ("driving force" that pulls air into the alveoli). Because of
that sequence of events, we can directly relate pleural pressure to the volume within the alveoli. So a more
negative pleural pressure will result in greater stretch on the alveoli and therefore a great drive to pull air into the
alveoli. Therefore we can relate Ppl to stretch on the lung (ie how expanded the alveoli are) and this stretch is
then directly associated with volume within the alveoli.
Lying down (prone) – Because gravitational force is applied to across the lung equally, pleural pressure is -
4cmH2O over the entire lung. When skeletal muscle (intercostals moves rib cages or diaphragm moves down)
contracts, we change pleural pressure by 4cmH2O across entire lung, therefore every alveoli fills equally
throughout the lung (all -8cmH2O)
Standing up – Before inspiration occurs, the top of our lungs have the Ppl of -10, because gravity pulls the lungs
away from the chest wall even more and the bottom of the lung has a Ppl of -2, because gravity pushes the lung
against the diaphragm/bottom of the chest cavity resulting in a less negative pressure. When we contract our
skeletal muscles (intercostals, and diaphragm), we change Ppl by -4 across the entire lung. Since the alveoli at
the top of the lung started at -10 and go to -14, and we know from our graph that that change in Ppl doesn't result
in much increase of volume, because the alveoli are already stretched open/full of air. Therefore they won't add
much air to them when we inspire. At the bottom of the lung where we start with a Ppl of -2 and change it to -6,
this change in Ppl results in a large increase in volume due to the fact that these alveoli are starting in a non-
expanded state and have a greater potential to expand and therefore take in more air. So the majority of the air
that we breath in during a single breath while standing up will go to the bottom of the lung because the alveoli
there are able to accommodate that air, whereas the alveoli at the top of the lung are already full so can't take in
any more air. For that reason, we get the uneven distribution of ventilation when we are standing up. For each
breath we draw in, the majority of the air from that breath is going to go to the bottom of the lung because the
alveoli there are able to accommodate the incoming air whereas the alveoli at the top of the lung are already
expanded/full before inspiration occurs that not much more air can go there.
10. Describe the difference types of buffers in the blood, and how they function. Discuss similarities and
differences in buffers in the ISS and tissue and vascular circulation
The primary function of buffer is to minimize the impact from pH disturbance. There are protein buffer, bicarb,
and phosphate buffer to regulate hydrogen ion concentration. CA catalyzes the reaction (CO + H O ↔H CO ).2∴ 2 2 3
Greater capacity to hide H+ in a form of water.
ISS- no proteins, bicarb, phosphate; CA
Tissue – protein, bicarb, and phosphate; CA
Plasma – proteins, bicarb and phosphate there is no CA, therefore the reaction is much slower
RBC – Hemoglobin, bicarb and phosphate; CA
Protein- + H+ ↔ Protein –H; HPO4 +2H ↔ H PO2-; 4O + 2 O ↔H2CO ↔H +2HCO3 + 3-
5 All buffers work in ms- sec time scale to minimize impact form pH disturbance. Non bicarb system (phosphate
and proteins) is closed system (all components of acid base reaction remain in the system), while bicarb system is
open system (all components do not stay in the system), because CO2 is readily removed at lung. Without open
bicarb system, you suffer greater pH change (Letting CO2 escape has huge power in regulating pH)
11. What would happen in respiration when you increase dead space by using snorkeling?
Because tidal volume is alveolar volume + dead space volume, increasing dead space volume decreases your
alveolar volume. With decreased alveolar volume, you are decreasing alveolar ventilation. (Blood flow removes O2
and adds CO2 to alveolar space, while ventilation removes CO2 and adds O2 to alveolar space) With decreased
ventilation, you will decrease alveolar oxygen and increase alveolar CO2 (equilibration) increased PaCO2 and PaO2.
The change of this blood gas will be sensed by chemo receptor, and this chemo receptor(central – medulla, peripheral
– carotid and aortic) sends signals to coordinating center to increase ventilation (by increasing breathing frequency
and the depth of breathing) to bring oxygen and CO2 level back to normal. Because you have increased CO2, you are
shifting CO 2 H O 2H CO ↔H2+ 3CO to the rig3t. As a result of the equation shift, you have increased H+ and
HCO3-. Increased H+ is also detected by chemo Rc and signal sent to coordinating center increases ventilation. There
is no ms- sect time scale regulation on oxygen and CO2 level because of the respiration apparatus that we use to get
the air in.
12. What would happen if you have increased CO2 in the environment?
Because the air you are breathing in has higher PCO2, you will have increased alveolar CO2, therefore increased
arterial CO2 (challenge). With increased CO2, shift in CO + H O ↔H CO ↔H + HCO to the right occurs to increase
2 2 2 3 3
H+ and HCO3- (decrease in pH). Increased H+ ion and CO2 will be sensed by chemo Rc, and signal is sent to
coordinating center to increase ventilation (by increasing the breathing frequency and tidal volume). Decreased O2 is
also sensed by chemo Rc and increases ventilation (not as sensitive as CO2). Increasing ventilation to remove CO2
from the system doesn’t do much but minimizing the impact because the problem is outsideAlso at kidney, you are
excreting H+ (decreased urine pH).
13. What would happen if you go up to higher altitude?
As you go up to higher altitude, atmospheric pressure in general goes down, therefore partial pressure of Oxygen also
goes down. The challenge in this situation is decreased PO2 available for inspiring. Because you have less PO2 to
breathe in, you suffer decreased PaO2. The decreased PaO2 is sensed by chemo Rc at medullar and aortic & carotid
bodies, and signal is sent to coordinating center to increase ventilation. Increased ventilation would decrease CO2
and increase O2 in the system (ventilation removes CO2 and adds O2 to the alveolar space, while blood removes O2
and adds CO2 to the alveolar space). Decreased PaCO2 will be sensed by chemo Rc and this will work to decrease
ventilation. The competition between two Rc stimulation enable the body to maintain its ventilation rate at stable but
lower than normal level. We are not really fixing problem by breathing more air in, because there is a problem outside
air, and also stabilization at lower level occurs (body is not normalized yet). After a week, body accommodate to
scarce Oxygen situation by increasing RBC (hematocrit).
14. Snorkeling increases dead space. How does the body regulate this change after the first hour?
Dead space is where there is no gas exchange occurs. V tidal = V alveoli– V dead space. As dead space increases,
alveolar volume decreases, therefore alveolar ventilation decrease. Since ventilation removes CO2 from alveoli
and add O2 to alveoli, decreased ventilation would result in increased PACO2 and decreased PAO2 (because blood
will add more CO2 than removed by ventilation, and remove more O2 than added by ventilation). Because
6 equilibration (btwn alveolar space and capillary bed) occurs, you will have decreased PaO2 and increased PaCO2
going into systemic system.
The increased CO2 will shift the equation (CO + H O2↔H CO 2H + HCO2), 3ou will incre3se hydrogen ions
(therefore decreased pH), HCO3- (not renal compensation), and decreased protein buffer. Increased bicarb will
minimize the impact from decreased pH(ms- sec time scale).
Within the body there are ChemoRc which are found in the aortic arch(also carotid) and the medulla which detect
both O2 and CO2. Since there is an ↑ in CO2 and a ↓ in O2 there will be an ↑ in AP frequency to the coordinating
centre in order to ↑ ventilation. With an ↑ in AP frequency it will be able to stimulate the A neuron at the
Coordinating centre in order to initiate respiration. This happens in minute to hour time scale
In order to fix the problem renal compensation will be used. (hours to day time scale). After an hour, body can
finally work to at kidney level.
- Since there is ↑ acidity in the intracellular fluid in the proximal tubule there will be an ↑ in glutamine breakdown
which will breakdown into NH4 and HCO