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Homeostasis NPB Cheat Sheet (DRAFT) by

Understanding the mechanisms for bodily regulation under the concept of Homeostasis.

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Concept of Homeos­tasis

Homeos­tasis Defini­tion:
The mainte­nance of a dynamic steady state within the internal bodily envior­nemnt
Homeos­tasis Concept:
dynamic mechanisms are the factors that allow for a near-s­teady state by detecting and responding to deviations from the "set point" through effector responses

Factors in a Homeos­tatic Control System

Sensor
detects deviations from set point and relays inform­atory signal to the integr­ato­r/c­ontrol system
Control Center­/In­teg­rator
integrates inform­ation input from the sensor to allow for a response system to restore the set point back to normal
Effector
Response system that receives inform­ation on adjust­ments in order to restore the set point back to normal.

Homeos­tasis Conceptual Summary Figure

Intrinsic Control System

Definition
LOCAL control systems built INTO a tissue­/organ
Example:
Increased CO2 production by exercising skeletal muscle leads to --> relaxation of smooth muscle and dilation of blood vessels; increased blood flow brings more O2

Disrup­tions in Homeos­tasis

Pathop­hys­iology
abnormal bodily function associated with disease
Result
homeos­tatic disruption so severe that death results

Extrinsic Control System

Definition
Systems outside of an organ/­tissue allowing for the co-ord regulation of multiple organs­/ti­ssues.
Example 1
The nervous system detects LOW blood pressure leading to --> Increased Heart rate + constr­iction of blood vessels
Example 2
The endocrine system detects HIGH blood glucose leading to --> excretion of hormonal control

Homeos­tasis Mainte­nan­ce=Cell commun­ication

Direct Intrac­ellular commun­ication
Gap Junctions + Transient Direct linkup of Cells surface markers
Indirect Intrac­ellular commun­ication via Extrac­ellular messengers
Paracrine Secretion + Neurot­ran­smitter secretion
Endocrine Signaling
Hormonal + neuroh­ormonal secretion

Altera­tions in Homeos­tasis

Set points can change
1) In sickness temper­ature can change --> Fever
2) Throughout Aging --> BMR (basal metabolic rate can change
3) Throughout daily life --> Circadian rhythms can change

Thermo­reg­ulation

Shivering -->
when body temp is LOW, heat is produced to increase body temp back to normal through shivering
Sweating -->
when body temp is HIGH, heat is lost to reduce the body temp back to normal through sweating

Thermo­reg­ulation

Shivering -->
when body temp is LOW, heat is produced to increase body temp back to normal through shivering
Sweating -->
when body temp is HIGH, heat is lost to reduce the body temp back to normal through sweating
 

Important Regulatory Systems

Nervous System
brain, spinal cord, nerves, and sense organs
Endocrine System
all hormon­e-s­ecr­eting glands

Negative Feedback (NF)

Systems that operate under Negative Feedback
Intrinsic and Extrinsic control systems operate under the principle of negative feedback
Goal
Remediate an unwanted change
Definition
A change in a controlled variable triggers a response that drives the variable in the opposite direction of the initial change, thus opposing the change
Afferent Signal­/Path
Send info from Sensor to control center
Efferent Signal­/Path
Send info from Control Center to Effectors in order to help restore homeos­tasis
Example: Temper­ature Regulation
High body temp sensed by skin cells --> Send info to brain/­control center­--> send info to Sweat Glands­/Ef­fec­tor­-->­release Sweat --> Response: Lower Body temp back to normal levels

NF Ex: Regulating Glucose Concen­tration

Set point of glucose concen­tration of Plasma
~80mg/dL
Beta Cells
Release INSULIN from pancreas when glucose concen­tration INCREASES
Alpha Cells
Release GLUCAGON from pancreas when glucose concen­tration DECREASES
B-Cells Negative Feedback Mechanism
Beta cells SENSE glucose levels in blood (Incre­ase­/De­crease) and compare them to the set point glucose concen­tra­tion; Too high = send info to control center (afferent path) --> Control center sends info to effector (efferent path) --> Response: release INSULIN --> decrease glucose concen­tration back to set point

NF: Glucose Homeos­tasis Figure

Nervous system VS Endocrine system

Nervous System
Endocrine System
WIRED; specific structual arrangment between neurons + target cells
WIRELESS; widely dispersed endocrine glands that are unrelated to each other + target cells
Chemcial Messenger= Neurot­ran­smitter into --> synaptic cleft
Chemcial Messenger= Hormones releas­ed-­-> blood
SHORT distance (diffusion across synaptic cleft)
LONG distances (carried by blood)
RAPID response + BRIEF duration
SLOW response + LONG duration
Function= co-ords rapid + precise responses
Function= Control long duration activities
 

Feedfo­rward Mechanisms

Defini­tion:
System that operates without a detector by activating homeos­tatic mechs + predicting when a change is likely to occur
Potential Mech #1
In response to an antici­pat­ed/once in a lifetime (infre­quent) event
Ex 1:
The normal antici­patory regulation of heartbeat in advance of actual physical exertion
Potential Mech #2
Through Body Rhythms
Ex 2:
The rhythms are internally driven but entrained (timing is set) by enviro­nmental cues.

Non-Ho­meo­static Mech= Positive Feedback

Definiton:
System with no contri­bution to homeos­tatis BUT, contri­butes to specific physio­logical needs in which the INITIAL change is AMPLIFIED and moves AWAY from set point
Import­ance:
In processes such as childbirth or firing an action potential
Childbirth Example
During labor (stimu­lus), the the nerve receptors (sensors) detect cervical stretching and signal to the brain (control center) which allows for the release of oxytocin (effector) from the pituitary gland in order to stimulate more stretching and stronger contra­ctions and stimulate the olacenta to further make prosta­gla­ndins stimul­ating more oxytocin and more cervical stretc­h/c­ont­rac­tio­ns(­opp­osite of negative feedback which would end the contra­cti­ons­/st­ret­ching).

Homeos­tat­ic-ally maintained Factors

1. Nutrients
2. Oxygen + Carbon Dioxide
3. Waste Products
4. pH
5. Water, Salt, other electr­olytes
6. Volume + pressure
7. Temper­ature