HOMEOSTATIC REGULATION

https://www.youtube.com/watch?v=XZxuQo3ylII&feature=youtu.be

Learning Objectives•Explain homeostasis• Discuss the relationship between external and internal environments •List the main body fluid compartments, their constituents and their relationship to each other •Define equilibrium and steady state •Give examples of homeostatic mechanisms •Explain negative feedback •Define controlled variable, sensor, comparator and set point and give examples of each in a negative feedback loop •Discuss factors that may change set points •Define redundancy and hierarchy with respect to hemoestatic control mechanisms •Explain positive feedback •Explain feed-forward regulation

Organ Systems in ReviewThe integration between systems of the body

Body Fluid Compartments

Intracellular Fluid,-28

(40%)

Interstitial Fluid- 11

Plasma- 3

Average Total Liters of Fluid-42(60%)

20%

Compartments and their Relationship

Blood Plasma 3 L

Interstitial 11 L

Intracellular 28 L

Transcellular 1 L

•most cases substances within the plasma must pass through the interstitial fluid before entering cells. •Therefore the interrelationships between these 4 compartments are crucial in underlying whole body homeostasis.

External and Internal Environments“all the vital mechanisms, however varied they may be, have only one object, that of preserving constant the conditions of life in the internal environment.” Claude Bernard (1857)

• The Basis of Physiological Regulation

• A Stable Internal Environment Is Essential for Normal Cell Function

Environments

pH 7.4

40 mm Hg0.23 mm HgPCO2

PaO2 95 mm Hg160 mm HgPO2

37 °C-10 and +40 °CTemperature

InsideOutsideVariable

.• stability of the internal environment is the primary

condition for a free and independent existence-By controlling its internal environment the organism is no longer at the mercy of the environment .

–

pH ?/variable

To summarize:

Homeostasis is the maintenance of a steady state of the internal environment of the body.

Body Fluid Constituents

[Na+] = 145 [K+] = 4.5 [Cl-] = 116

[Protein] = 0 mM Osmolality 290 mOsm

[Na+] = 142 [K+] = 4.4 [Cl-] = 102

[Protein] = 1 Osmolality 290 mOsm

[Na+] = 15 [K+] = 120 [Cl-] = 20

[Protein] = 4 Osmolality 290 mOsm

Plasma Interstitial Cellular

•substances aren’t in equilibrium, but there is a balancethere is a difference between the basic constituents of the body-fluid compartments. This means that homeostasis is not about reaching equilibrium, but about maintaining a steady-state. Since the system is not necessarily in equilibrium energy expenditure is required to maintain a steady state.

11

Homeostasis & Controls

•Successful compensation

•Homeostasis reestablished

•Failure to compensate

•Pathophysiology

• Illness

•Death

Feedback( flow of information along a closed loop )– Negative or Positive

• Negative – change is sensed and action taken to prevent further change e.g-regulation of secretion of hormones.

• Positive – change is sensed and action taken to amplify change (usually associated with a discrete end point, e.g. birth, ovulation)

Homeostatic Mechanisms

• Most homeostatic mechanisms are based on negative feedback

• specific terms that are used to describe the processes involved-

Controlled Variable SensorComparator, set point

Effectors

Blood Pressure Regulation

Blood Loss

Blood Pressure (controlled variable)

Baroreceptor (sensor)

Brain (comparitor)

Vasoconstriction ↑ Cardiac Output

(effectors)

Cardiovascular control

center – compares BP to

set point and adjusts

vascular tone and cardiac output

accordingly

Blood Glucose -ve Feedback

b-cell

Variable Blood Glucose

b-cellGlucose

Insulin secretion

Cells

Cutaneous Blood VesselsAnticipation of exercise and during exercise

Sympathetic outflow increases to maintain blood pressure

Cutaneous Blood VesselsAnticipation of strenous exerciseSympathetic outflow increases

to maintain blood pressure

Hypothalamus detects heat increase And inhibits sympathetic outflow

Vasodilation helps to divert blood flow to the skin For heat loss

Cutaneous Blood VesselsWith extreme exercise the need to control

Blood pressure takes priority and the Vessels constrict

Hypothalamus detects heat increase And inhibits sympathetic outflow

Vasodilation helps to divert blood flow to the skin For heat loss

Positive Feedback

Contraction

oxytocin

All steps in this process produce an increase in the next step leading to a loop of stimulation. The positive feedback loop is broken when the baby is expelled from the uterus and hence the step involving pressure against the cervix has been removed.

Feed-forward Control

• Anticipation of change – gets body ready for change

• e.g. heart rate and ventilation can increase even before exercise begins

• Or salivation and digestive enzyme production begins before a meal is eaten

Redundancy

• Homeostatic mechanisms are important – therefore often there is more than 1 control mechanism

• If 1 mechanism fails – then there is a backup system (e.g. ATP/adenosine in airway surface liquid secretion or control of cutaneous blood vessels by both cardiovascular control center and temperature control center)

• Or blood pressure (next slide)

Hypovolemic Shock

B.P. falls

Kidney Juxtaglomerular cells

Aortic arch Carotid sinusRenin

Activity drop

Hypothalamus Posterior Pituitary

Medulla oblongata

Angiotensinogen in blood

Angiotensin I

LUNG

Angiotenin II

ACE

Adrenal Cortex

Heart rate contractility

Blood Vessels

Kidney Salt water conservation

Aldosterone

ADHSympathetic output

Inc. volumeInc. vasc. resistance

Inc. B.P.

What is the normal pH value for body fluid?A) 7.15-7.25B) 7.35-7.45C) 7.55- 7.65D) 7.00-7.35E) 6.5-7.5

In response to a bacterial infection my body's thermostat is raised. I start to shiver and produce more body heat. When my body temperature reaches 101 degrees, I stop shivering and my body temperature stops going up. This is an example of:A) Negative feedbackB) A malfunctioning control systemC) Positive feedbackD) A negative impact

6. Which of the following is an example of a positive feedback?A) Shivering to warm up in a cold winter stormB) A cruise control set on your car applies more gas when going up a hillC) You sweat on a hot summer's day and the blood vessels in your skin vasodilateD) You get cut and platelets form a clot. This in turn activates the fibrin clotting system and more blood forms clots

Where is the body's "thermostat" found?A) Within the nervous system, in the HypothalamusB) Within the integumentary system, in the skinC) Within the brain, in the corpus callosumD) Within the Urinary system, in the kidneys

8. What system has little to contribute to the homeostasis of the organism?A) Urinary SystemB) Reproductive SystemC) Respiratory SystemD) Nervous System

Summary I

• Homeostasis – maintenance of a stable internal environment

• Steady state – unchanging with time • Equilibrium – when parameters are

maintained in an energetically favorable situation

• Redundancy – more than 1 system to control a variable (backup systems)

Summary II

• Negative feedback – feedback causes a perturbation to be minimized or reversed with view to keeping parameter at a set point

• Positive feedback – amplification of a deviation (usually defined end point)

Positive feed back