Homeostasis & intracellular signaling Flashcards
Who coined the word “homeostasis” in 1963?
Walter Cannon
What is the definition of homeostasis?
Self-regulating process by which biological systems maintain stability while adjusting to changing external conditions.
What is stability?
A particular physiologic parameter that is monitored and maintained within a relatively narrow range at all times.
When a process proceeds in a forwards and backwards direction at the same rate-no net change occurs
Equilibrium
When a process or system exerts energy to maintain a particular state:
Dynamic steady state
ex) Na+/K+ pump moves sodium out of cell to prevent swelling
What are the components that define homeostasis?
-Sensor
-Error detector
-Controller
-Effectors
A parameter that is measured in the body with sensors and is kept within a set of limits:
Regulated variable
-Limit = low and high range
-The “thing” that homeostasis is devoted to regulating
A process that can measure the regulated variable and deliver a signal about that variable:
Sensor
-Sometimes signals only happen when the regulated variable falls out of the “normal” range
Has a controller and error detector:
Control centre
“calculates” the difference between the set-point value of the regulated variable and the actual value of the regulated variable and sends an error signal to the controller:
Error detector
Sends output signals to effectors that can change the regulated variable depending on data:
Controller
The range of values of the regulated variable that the system tries to maintain:
Set Point
-very difficult to “find where the set point exists” in a biological system
How does the brainstem “know” what the normal pH is supposed to be?
No one has really figured this out
What the controller manipulates to “get the job done”:
Effector
-Effectors respond to information from the controller and change the value of the regulated variable
Effectors usually change values of the _______________________ in order to bring the regulated variable closer to the set-point.
Non-regulated variable
ex) if your pH drops, then your respiratory rate increases in order to get rid of excess carbon dioxide. Regulated variable = pH, Non-regulated variable = respiratory rate
Are homeostasis and negative feedback the same?
Homeostasis can and usually does use negative feedback loops, not all negative feedback loops are homeostatic.
(photo is an example of a simple negative feedback loop)
What products are created in this simple negative feedback loop?
A + B + C
What product inhibits the process?
“B” inhibits ABCase, reaction slows down
Output of a system is fed back in a manner that tends to reduce the fluctuations in the output:
Negative Feedback
-products tend to oscillate between low and high points, depending on how “fast” the product inhibits the process
What does the negative feedback loop lack that does not consider it to be homeostasis?
-Control centre
-Set point
-Error Signal
-Regulated Variable
What are the major baroreceptors?
-Carotid arteries
-Arch of the aorta
what happens when:
pressure drops -> message sent to the brainstem via nerves->
1) activation of the sympathetic nervous system -> release of epinephrine, norepinephrine
2) Epi and NE -> Elevation in HR and constriction of arterioles and increase stroke volume
The proprioceptor that senses muscle stretch:
Muscle spindle
As the muscle is stretched, what happens?
-Activates the muscle to contract against the stretch by stimulating the motor neuron in the ventral horn
-inhibits the antagonist muscle
(stretch is caused by hitting the tendon with a reflex hammer)
Is the stretch reflex a negative feedback system?
Yes
Is it a homeostatic system?
If not, what components of a homeostatic system are missing?
The stretch reflex is a rapid, short-loop reflex designed to protect muscles from overstretching. It is a local feedback mechanism that acts on a specific muscle in response to a sudden change in its length.
The component it’s missing is:
-set-point control
Homeostatic mechanisms only “turn on” when the regulated variable is outside the setpoint. (True/False)
False
-most sensors usually constantly deliver information to the control center
-The controller responds “more intensely” with a larger error signal, but it’s almost always sending input to the effectors at some basal rate
Is the sodium-potassium pump a regulated variable?
No, potassium is regulated but sodium is not
According to the chart, why does sodium stay in such a narrow range?
The body relies on various mechanisms, including the kidneys, hormones, and thirst regulation, to maintain the appropriate sodium balance. Sodium regulation is essential for overall health, and the body continually adjusts sodium levels to ensure proper functioning.
What is a typical feature of homeostatic systems?
Oscillations
ex) reading someone’s BP from standing to sitting; the diastolic pressures fluctuate continually, they are never constant
Systolic and diastolic pressures fluctuate continually, they are never constant:
Therefore, what features are always active at every moment?
controller, error detector, the sensor, and the effectors.
What is the normal range, sensor, control centre, effector, and effector response for core body temperature?
Normal range: 35.5-37.5 celcius
Sensor: Thermosensor
Control centre: Hypothalamus
Effector: blood vessels, sweat glands, skeletal muscle
Effector response: shivering, sweating, distribution of blood
What is the normal range, sensor, control centre, effector and effector response for mean arterial pressure?
Normal range: 85-100 mmHg
Sensor: Baroreceptor
Control centre: Brain stem
Effector: Heart & blood vessels
Effector response: change in heart rate, stroke volume, vascular tone
What is the normal range, sensor, control centre, effector and effector response for blood volume?
Normal range: 5 L
Sensor: Heart, Kidneys
Control Centre: Medulla
Effector: Heart and Kidneys
Effector response: Change in heart rate, stroke volume, vascular tone, and fluid/salt retention
Systems tend to overlap, rather than be isolated:
blood pressure regulation is interrelated with what other two regulation systems in the ECF?
Fluid volume regulation, and osmoregulation
Systems tend to overlap, rather than be isolated:
pH regulation is interrelated with what?
Arterial CO2
Effectors can be ___________ or __________ to achieve homeostasis, or different effectors can be called upon to control the regulated variable.
Turned up or Turned down
What happens to the effectors in BP regulation?
effectors are turned up or turned down
Separate metabolic pathways are activated in hyperglycemia vs. Hypoglycemia:
Glucose regulation
Disease states can cause ______________________ fluctuations
larger unstable
Disease states can sometimes be due to altered set points. (True/False)
True
ex) hypertension is partially a “set point error” disease
The more vital a parameter, the greater number of systems that regulate it. (True/False)
True
(redundancy is common)
The output of a system is fed back in a manner that tends to increase that system’s output.
Tends to result in an exponential “increase” in the output, until a limiting event is reached.
Positive feedback
What are the basics of the parturition reflex?
-Baby’s head presses on & thins the cervix ->
-Cervical thinning & stretch is detected by mechanoreceptors and transmitted to the brain ->
-The hypothalamus releases oxytocin in response->
-Oxytocin causes uterine contraction, forcing the baby against the cervix->
(back to the baby’s head presses on and thins the cervix)
This continues until the birth of the baby happens and decreases stretching of the cervix causing an interruption of the cycle.
System where changes in a regulated variable are anticipated, and the controller “pro-actively” activates an effector
Feed-forward loop
ex) visualizing performance prior to an athletic event (heart rate, stroke volume, BP, respiratory rate increase)
ex) muscle proprioceptors detect am increase in activity (signals to the respiratory center to increase ventilatory rate before any changes in blood gases occur.
Name the system/region or sensor for the following detail:
Voluntary control of respiratory rate
Cerebral Cortex
Name the system/region or sensor for the following detail:
Regulates respiratory rate based on emotional state, pain, body temperature set-points-> tells the brainstem to change ventilation
Hypothalamus
Name the system/region or sensor for the following detail:
When your muscles and joints move, send a signal to your brainstem-> your ventilation changes in anticipation of increased MSK oxygen and carbon dioxide exchange needs
Proprioceptors
Name the system/region or sensor for the following detail:
Increase ventilation when arterial oxygen drops and carbon dioxide increases-> very strong influence on ventilation
Chemoreceptors
-Peripheral
-Central
What is our body’s strategy?
keep the internal environment constant so that our cells aren’t in a “hostile environment” that’s difficult to regulate.
How do cells signal to each other?
Membrane receptors contact the ECM or another cell (ligand) -> an intracellular signal in one (or both) cells
Contact
How do cells signal to each other?
Cell “A” produces a soluble messenger which diffuses to a cell “B” -> binding to a membrane receptor on cell “B” -> an intracellular signal in cell “B”
Paracrine
How do cells signal to each other?
Cells in _________ organs release a chemical messenger into the bloodstream-> circulation of the messenger (hormone)-> an intracellular response in any cell that has a receptor for that hormone
Endocrine
How do cells signal to each other?
A __________ “A” sends an electrical signal along an axon to a synapse with cell “B”-> release of a neurotransmitter -> binding of neurotransmitter to a receptor on cell “B” -> an intracellular response
Neuron
(Cell “B” could be another neuron, a muscle cell(smooth, skeletal, cardiac), or an endocrine cell)
What are the four major types of intracellular signaling?
1) Contact-dependent
2) paracrine
3) synaptic
4) Endocrine
-Important for embryologic development, immune signaling, and for limiting/organizing growth
Contact-dependent (short distance signaling)
ex) epithelial cells contact the basement membrane via hemidesmosomes
-Integrins are part of the hemidesmosome complex- when they bind with the ECM, intracellular signals are generated
- These signals help determine polarity (which way is “up”)
-Very common signaling mechanism whereby cells signal locally to each other, via a soluble mediator.
-Wide ranges of use (immunological/defense, signals of local damage, regulation of growth/cell division/tissue repair, local regulation of blood flow)
Paracrine (short-distance signaling)
Example) Metabolically active tissue releases metabolites (H+, CO2, K+) that cause local vascular and endothelial cells to relax-> vasodilation and improve blood flow.
What are the mechanisms of the endocrine system?
-Organ secretes a messenger into the bloodstream
-Messenger is widely distributed throughout the body
-cells with receptors for the messenger respond
What are the two major structural (and strategic) branches of the endocrine system?
1) Hypothalamic-pituitary system
2) “other” endocrine glands
Describe the hypothalamic-pituitary system:
- The hypothalamus controls the endocrine secretions of the pituitary gland
-pituitary secretions act on another target gland or organ
Describe the “other” endocrine glands:
-Usually they directly sense a stimulus (they are the sensor and the control centre) and secrete a hormone in response to that stimulus
What are some examples of “other” endocrine glands?
-Pancreas and GI tract
-Parathyroid glands
-Adipose tissue
Which of these glands are under hypothalamic control?
-Pituitary
-Thyroid
-Adrenal
-Ovaries/testes
Where does the hypothalamus sit?
under the thalamus
What connects the hypothalamus to the pituitary gland?
Vascular stalk
The pituitary sits where?
Within the sella turcica. Located in the sphenoid bone, in the middle cranial fossa.
Name the structures:
1) Anterior Pituitary
2) Posterior pituitary
The anterior pituitary:
Place these functions in the correct order:
a) Anterior pituitary hormones control a number of other endocrine glands (thyroid, adrenal gland, gonads, liver)
b) The hypothalamus secretes releasing hormones into 1st set of capillaries
c) These travel down to the anterior pituitary and modulate hormone secretion from those cells
b, c, a
The posterior pituitary:
Place these functions in the correct order:
a) The axons of these neurons release hormones into the capillaries in the posterior pituitary
b) hypothalamic neurons project to the posterior aspect of the pituitary
c) Major hormones secreted: ADH & oxytocin, both of these act directly on target tissues, not on other glands
b, a, c
Name the hormone:
Controls water balance in the body
ADH ( antidiuretic hormone)
Which part of the pituitary secretes ADH?
Posterior pituitary
Oxytocin is secreted by the anterior or posterior pituitary gland?
Posterior
What is oxytocin?
Hormone that controls the positive feedback loop of childbirth
ADH secretion is controlled by what?
The osmolarity of the blood:
when the blood is more concentrated (less water), then ADH is secreted.
when ADH is secreted the water recovery by the kidneys increases and is kept in the bloodstream. When ADH decreases, more water is lost in the urine.
Blood osmolarity is detected by what in the hypothalamus?
Osmoreceptors
Thyroid hormone release is regulated by the hypothalamus in response to what?
Cardiovascular parameters and “metabolic” parameters (such as body temp)
Also released in a particular rhythm to help facilitate growth of the organism
Place these steps in order:
a) TRH stimulates ant. pituitary gland to release TSH
b) Thyroid hormone increases
c) decreased thyroid hormone
d) TSH stimulates thyroid gland to release thyroid
e) Stimulates hypothalamus to release TRH
c, e, a, d, b
The thyroid hormone negatively feeds back on the _______________ and __________________
anterior pituitary & the hypothalamus
TSH negatively feeds back on the ______________
hypothalamus
If you add Z to a system, then the same amount of Z has to leave the system to maintain a steady state (keep Z constant in the system)
If there’s an imbalance, then a new steady state will be reached
The volume of a fluid that has been completely “cleared” of a substance
Clearance
ex) Substance Z was removed from the pipe by the filtering system
Mass balance and clearance
What happens if you damage your clearance mechanism and clearance drops?
Kidneys: changing the rate of fluid filtration (glomerular filtration rate)
Lungs: changing the rate of ventilation (clearance mechanism for CO2)
Boyle’s law:
If you increase the pressure in a container with a gas in it, the volume of the gas will decrease.
The process by which we move atmospheric air into and out of the alveoli.
Ventilation
Which law is applied to pressure gradients in ventilation?
Poiseuille’s law
When gas moves into the lung during inspiration how does the pressure in the alveoli compare to atmospheric pressure?
The pressure in the alveoli decreases compared to the atmospheric pressure. The diaphragm contracts and moves downward, while the external intercostal muscles contract, causing the ribcage to move upward and outward.
During expiration, the pressure in the alveoli increases compared to the atmospheric pressure. The diaphragm relaxes and moves upward, while the external intercostal muscles relax, allowing the ribcage to move downward and inward due to its natural elasticity.
How does the pleural fluid help us transmit force from the muscles that change the volume of the thoracic cavity?
pleural fluid serves to reduce friction, create a continuous connection, and help transmit the forces generated by respiratory muscles to the lungs.
Laplace’s Law
Tension increases when:
-Radius increases
-Pressure increases
-Thickness does not have an effect on tension
A pathological increase in the diameter of a blood vessel
Aneurysm: due to high blood pressure or atherosclerosis
What impact does an increase in the diameter have on the tension/stress across the wall of this unhealthy (aneurysm) vessel?
When the diameter (or radius, as they are related) of the aneurysm increases, the radius term (r) in the equation becomes larger. Given that tension (T) is directly proportional to the radius, this means that the tension in the wall of the aneurysm also increases.
The diameter of the heart increases:
Dilated cardiomyopathy (genetic, uncommon infections, toxins, idiopathic)
As the radius of the ventricle increases, what happens to the tension?
Increases
