Homeostasis, Cells Flashcards
Homeostasis
-Conditions within the body, the internal environment, that are maintained at near constant conditions
-WALTER CANNON
-The internal environment refers to everything under our skin, which is about 35 trillion cells
-The body has sensors and feedback mechanisms to maintain homeostasis
Ex: Maintaining body temp of 37C. Shivering or sweating
Anesthesia & Homeostasis
-Anesthesia takes your feedback mechanisms and takes them completely offline
Ex: Paralyzing in the cold OR, body can no longer shiver to bring core temperature up
What do cells need to maintain homeostasis?
Forms of input and output
-Cells need reasonably constant conditions and a supply of energy;
-Input for energy is oxygen, food such as sugar, fats
-Output is energy (work, heat, potential energy) and waste products such as;
-CO2: byproduct of metabolism
-H+: Protons formed during a chemical rxn
-urea (not useful, body needs to get rid of it as it’s being produced)
and H2O, solid waste
Homeostasis Examples: Kidneys
-Responsible for maintaining BP at a normal level
-Responsible for the majority of our ECF buffering abilities
-Generate buffers and make sure that our buffer levels are w/in normal constraints in the body
Homeostasis Examples: GI
-Replaces nutrients in the blood as they’re being used or consumed by cells
Homeostasis Examples: Lungs, Heart
-Lungs: Helps regulate our blood gasses
-Heart: Essentially two pumps separated by a wall (septum)
- L & R heart pump are responsible for making sure that we get a decent amount of gas exchange happening w/in the lungs and that we peripheral cardiovascular system is supplied with the proper nutrients
Homeostasis: Peripheral Vascular Beds
-Blood flows into tissue through the arteries and into the arterials.
-The fluid being brought in by the CV system has the opportunity to deliver nutrients that the cells are going to be using, and removes wasteful byproducts via the venous system.
-The amount of blood that flows through a tissue is determined by the metabolic demand of that tissue
Homeostasis: Peripheral Vascular Beds, Arterial Side
- If the cells are really active, the composition of the ECF changes. Because the cell is pulling in oxygen and nutrients, there will be a deficiency in the ECF
- This change is picked up by sensors w/in the CV system–> increased blood flow to that area to bring levels back to normal
-This process is very tightly controlled and delivers only enough to meet tissue needs **
- This change is picked up by sensors w/in the CV system–> increased blood flow to that area to bring levels back to normal
Homeostasis: Peripheral Vascular Beds, Venous Side
-Because blood flow increases on the arterial end, it should also increase on the venous end to help remove wasteful byproducts at a faster rate because of the increased metabolic demand
Negative Feedback Mechanisms
-Major control system w/in the body. Almost all systems are managed via negative feedback
-Positive or negative changes are detected by a sensor somewhere out in the periphery and the body counteracts/opposes that change
-Change is always opposite or negative to the initial change
Ex: pH or CO2 levels are changing. The body responds to correct the change occurring. The sensor detects the change, feeds that information back to the “controller,” and the controller acts to correct the problem
Negative Feedback Example; BP change
-BP goes from 100mmHg to 50mmHg. Sensors in periphery send information back to the CNS, the CNS acts to bring the BP up by squeezing your blood vessels or making the heart pump harder.
-CNS increases sympathetic outflow (increased circulating norepinephrine)
-CNS decreases parasympathetic outflow
-Circulating compounds such as vasopressin (ADH) increase
-Atrial natriuretic peptide levels decreased
-This is a negative response to the original stimulus. We are counteracting it
Remember: Negative feedback works the same way a thermostat in a house does
Negative Feedback Example: CO2 Levels
-CO2 levels rising in the blood stream
–> brainstem senses–> ventilation increases
Positive Feedback Loop
-Stimuli in the body/outside the body causes some type of change
-The body responds by amplifying this change
-Good for some things
-Can be bad, potentially terrible, for other things
-Vicious cycles can happen with pathologic positive feedback loops (typically avoided w/ physiologic positive feedback loops)
-There are checkpoints in place that turn off the physiologic positive feedback loop
Physiologic Positive Feedback Loop Example; Oxytocin during L&D
-Uterus contracts–> pushes the fetus towards the cervix–> cevix stretches out after being exposed to pressure from the fetus
-In response to the cervical stretch, oxytocin is released from the brain. It acts on smooth muscle in the uterus and causes more contractions–> pushes fetus more–> cervix stretches more–> more oxytocin released
-Birth of the child is the “check point” that shuts this feedback loop off. Oxytocin levels decrease, contractions stop
Physiologic Positive Feedback Loop; Blood clotting
-Blood vessel is injured (scalpel in the OR?)–>it bleeds–> coagulation factors are liberated when the endothelial cells are damaged and those factors influence platelet plug formation
-In platelet plug formation & coagulation cascade activation, coagulation & platelet plug formation speeds up as more time passes
-Under normal circumstances, this continues until the bleeding stops
-The coagulation factors will either get covered up, put back into the cell, run out, and all of this signals for the coagulation to stop
-The checkpoint here should be that the bleeding has stopped. If coagulation didn’t stop, the blood vessel would become occluded
Pathologic Positive Feedback: Severe Hemorrhage
-We lose a significant amount of blood
–> BP is decreased–> coronary blood flow is reduced
-If our coronary blood flow is reduced while our BP is low, our heart is trying to correct the problem but coronary perfusion is insufficient to keep up with the metabolic demands of the heart –> cardiac output drops–> BP is reduced even more–> If allowed to progress unchecked, death with probably occur
Positive feedback loop that has run completely out of control
-We can typically handle a 20% blood loss if otherwise healthy. The pumping effectiveness of the heart is initially reduced and cardiac output is decreased; however, cardiac output should be back to normal w/in a few hours
-Blood vessels are going to squeeze, the heart is going to try and pump harder, and there will be massive fluid shifts that rearrange volume w/in the body (fluid shifted into cardiovascular system from out spaces)
-40% blood loss will likely result in death
Pathologic Positive Feedback: Sepsis/Necrosis
-Sepsis –> widespread infection –>cells in the body are dying at a rate faster than they can the body can manage
–> toxic, metabolic byproducts, potassium w/in dying cells are released into the internal environment surrounding the neighboring cells–> neighboring cells begin to die
Pathologic Positive Feedback: Severe Acidosis/CNS Effects
-Severe acidosis–> CNS is affected–> respiratory drive is reduced–> perpetuates the acidosis making us more acidotic
Pathologic Positive Feedback: Kidneys
-Each kidney has ~ a million nephrons
-As we age (45yrs +), nephrons begin to die and the remaining nephrons have to carry a larger load–> the larger the load placed on the remaining nephrons, the more likely those nephrons are to die
-The older we get, the faster this process happens–> some degree of renal failure
Cells: Basic Functional Unit
-Smallest living unit
-Specialized for specific tasks (skin cells, lung cells for gas exchange)
-Usually capable of replication
~35 trillion human cells per body, 25trillion of those being RBCs
-Cells are capable of sustaining their own lives because of everything that is contained w/in them (enzymatic machinery to create ATP –> energy for cell)
Groups of cells that are like-minded–> Tissues–> Organs–>Body
Cells; Replication
-Typically capable of replicating themselves
-If unable to replicate themselves, there is typically a progenitor cell nearby that can perform that task
-RBC’s cannot replicate themselves; however, there are progenitor stem cells within the bone marrow that are capable of producing RBCs
-Lifespan is ~90-120days
-RBCs do not have a nucleus or genetic material to create copies of themselves
-Neurons do not replicate very fast or very often
-Heart cells replicate at a very, very slow speed and low rate
Cells; Basic Borders/Internal Elements
-Internal contents of the cell typically dictates it’s function
-Cell Wall/Membrane is a phospholipid bilayer. This provides a large barrier because of the orientation of the cell wall. The fatty, oily middle layer is an obstacle
-The phosphate head is a charged region of the cell wall; charged compounds typically behave well in water.
-Lipid tails (uncharged) do not behave well in water. Fatty acid chain
-Cytoplasm: Fluid within the cell. The chemistry of the cytoplasm is very important; this is where the chemical reactions occur
-Nucleus: Barrier or protected internal environment that keeps our DNA/Genetic information packed up & secure from things like viruses and bacteria
Cells: Nuclear Compartments
-Nuclear Envelopment/membrane: A double phospholipid bilayer. Almost an entire cell wall creating a barrier between what’s inside and the cytoplasm of the cell
-The body does allow some things to come into contact w/ our DNA through pores within the nuclear membrane
Ex: Steroids- Can affect gene transcription to turn on stress response proteins
If the wrong things come into contact with our genetic information, terrible things such as cancer can happen
-DNA/Genes float inside of the nucleus and can be turned on and off to help the cell accomplish different tasks
-Endoplasmic reticulum: An extension of the nuclear wall and a storage place. Fats and proteins are produced here, calcium is stored here
Ex: Muscle cells need Ca+ to function
Cells: Protein & Fat Production
-As genes are read or turned on, they are encoded for protein or lipids. These instructions are then carried to various places where they can be turned into lipids and proteins
-Granular/Rough Endoplasmic Reticulum: Where proteins are synthesized. The rough ER is covered in ribosomes–> they take the genetic instructions from our DNA (transcription) –> RNA is formed
–> RNA spliced –> Transported out of the nucleus to ribosomes for translation–>Proteins are packaged into vesicles–> transported through cytoplasm to the Golgi apparatus
-95% of proteins are manufactured in the rough ER. The rest happens freely in cytoplasm
-Smooth Endoplasmic Reticulum: No ribosomes present; where lipids are created. Lipids are needed for our cells to survive
-Golgi apparatus: Used for post-translational processing; sometimes proteins need to be modified, folded differently, or altered in some way. Proteins are then packed into vesicles and are ready for use
Cells: Vesicles
-Transport vesicles transport proteins within the cell
-Active proteins or peptides are transported out of the cell by secretory vesicles (ADH or oxytocin)
-Secretory vesicles can move to the cell wall, fuse with the cell wall, and then dump their contents immediately outside the cell wall
Cell Wall: Proteins
-Proteins are able to position themselves in the cell wall and permit passage of charged compounds across the cell wall
Ex: Ion channel, Ion pump
-Proteins are made up of strings of AA
