Lecture slides, lecture 2 - Control of the internal environment PDF

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Control of the internal environment...

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Exercise Physiology KIN 3305 Instructor: Dr. Eunhee Chung

Chapter 2. Control of the internal environment

Learning Goals: You should be able to…. • Define the terms homeostasis and steady state • List the general components of a biological control system. • Compare between negative

feedback and positive feedback

Learning Goal 1 • Define the terms homeostasis and steady state

Homeostasis: What does it mean? • The maintenance of a relatively constant internal environment • Monitoring/controlling internal conditions to keep them constant (or within safe limits) despite external changes • The term homeostasis is generally reserved for describing normal resting conditions

Homeostasis is dynamic Although arterial pressure oscillates over time, mean pressure remains constant

Homeostasis • Give me some examples of the internal environment that are homeostatically controlled (discuss your group)?

Some aspects of the internal environment that are homeostatically controlled • • • • • • •

Temperature- normally 36 to 38°C Fluid Volume- varies with individual body size Blood Glucose concentration –normally 75-95mg/dL Sodium Concentration-normally 138-145 mmol/L pH-normally 7.35-7.45 O2 tension- normally 95-105mmHg (at sea level) CO2 tension- normally 35-45 mmHg

Define the steady state

Steady State • Physiological variable is unchanging, but not necessarily “normal” • Balance between demands placed on body and the body’s response to those demands

Steady state • Changes in body core temperature during submaximal exercise

Body temperature reaches a plateau (steady state)

Figure 2.2

Homeostasis vs. Steadystate • Homeostasis – An active process whereby the value of a variable is controlled and defended by the body against change.

• Steady-state – A variable may be described as a steady-state if it remains fairly constant in value over the time period. – Variables that are not homeostatically regulated: Heart rate, respiratory rate

Learning Goal 2 • List the general components of a biological control system.

Control Systems of the Body

Biological control system • Series of interconnected components that maintain a physical or chemical parameter at a near constant value • Components • Sensor or receptor : • Detects changes in variable

• Control center or integrator: • Assesses input and initiates response

• Effector: organs that produce the desired effect • Changes internal environment back to normal

Components of a biological control system

Response reverses the initial disturbance in homeostasis

Figure 2.5

Learning Goal 3 • Compare between negative feedback

and positive feedback

Negative feedback • Response reverses the initial disturbance in homeostasis • Example: – Increase in extracellular CO2 triggers a receptor – Sends information to respiratory control center – Respiratory muscles are activated to increase breathing – CO2 concentration returns to normal

• Most control systems work via negative

feedback

Examples of homeostatic Control: Regulation of body temperature:

Can you think about other examples of Negative Feedback?

Examples of Homeostatic control The regulation of blood glucose concentration

Negative feedback

The pancreas acts as both the sensor and effector organ

Figure 2.7

Positive feedback • Response increases the original stimulus (want to go one direction) • Example: Enhancement of labor when a woman give s birth – Initiation of childbirth stimulates receptors in cervix – Sends message to brain – Release of oxytocin from pituitary gland – Oxytocin promotes increased uterine contractions

– Another examples?

Positive feedback • The process of blood clotting • The generation of nerve signals • In excitation-contraction coupling of the heart

A Test of Homeostatic Control during Exercise • Exercise disrupts homeostasis by changes in ___, ____, ___, and ____

A Test of Homeostatic Control during Exercise • Exercise disrupts homeostasis by changes in pH, O2, CO2, and temperature • Control systems are capable of maintaining steady state during submaximal exercise in a cool environment

Exercise Disturbs Homeostasis • Increased energy requirement-high glucose use • Increased heat generation • Increased oxygen use • Increased carbon dioxide production • Increased lactic acid production • Fluid loss due to sweating

A test of Homeostatic control during Exercise • Intense exercise or prolonged exercise in a hot/humid environment may exceed the ability to maintain steady state – May result in fatigue and cessation of exercise

Some environmental threats to the internal environment • • • • •

Temperature- cold or hot High altitude High pressure Injury, disease Mental Stress

Failure of Control System • Failure of any component of a control system results in a disturbance of homeostasis • Example: – Type 1 diabetes • Damage to beta cells in pancreas • Insulin is no longer released into blood • Hyperglycemia results

– This represents failure of “effector”

Exercise training and homeostasis

Exercise improves homeostatic control system • Adaptation – Change in structure or function of cell or organ system – Results in improved ability to maintain homeostasis • Acclimatization – Adaptation to environmental stresses • Heat stress in a hot environment • Cell signaling – Communication between cells using chemical messengers – Important for maintaining homeostasis

Learning Goal: • Define cell signaling and outline the five types of cell signaling mechanisms that participate in the regulation of homeostasis and cellular adaptation.

Cell signaling mechanisms • • • • •

Intracrine signaling Juxtacrine signaling Autocrine signaling Paracrine signaling Endocrine signaling

Cell Signaling Mechanisms

Cell signaling mechanisms  Intracrine signaling  Within the same cell

 Juxtacrine signaling  Cell to cell contact.

 Autocrine signaling  A cell secretes a hormone or chemical messenger that binds to autocrine receptors on the same cell, leading to changes in the cell

Cell signaling mechanisms  Paracrine signaling  Chemical messengers act on nearby cells: immune system, nervous system.

 Endocrine signaling – Chemical messengers released into blood – These hormones are then carried throughout the body. – Only affect cells with specific receptor

Stress Proteins Assist in the Regulation of Cellular Homeostasis

Stress Proteins • Cells synthesize “stress proteins” ” when homeostasis is disrupted – Heat shock proteins repair damaged proteins in cell • Stresses include: – High temperature – Low cellular energy levels – Abnormal pH – Alterations in cell calcium – Protein damage by free radicals • Exercise induces these stresses

A Closer Look 2.1

Overview of Cellular Protein Synthesis

Now, you are able to answer • Compare and contrast the terms homeostasis and steady state. Be able to denote the difference between the two if give physiological data (blood pressure, heart rate, etc.) • Compare between negative feedback and positive

feedback

• Identify the three main components of a biological control system. Give an example of a biological control system in our body....