Homeostasis: The Foundation of Physiology

Prepared by Dr.Mohammed Sharique Ahmed Quadri

Assistant prof. PhysiologyAl Maarefa College

Physiology• Study of Functions of Living Things

• Two approaches to explain body functions

– Emphasis on purpose of body process (Why)• Explanations are in terms of meeting a bodily need

– Emphasis on Mechanism (How)• Explanations are in terms of cause and effect

sequences– Body is viewed as a machine

Organization of the Body

Levels of organization• Chemical

– Molecules composed

of atoms

• Cellular– Cells are basic unit

of life

• Tissue• Organ• Body system• Organism

Basic Cell Functions• Obtain nutrients and oxygen from

surrounding environment

• Perform chemical reactions that provide energy for the cell

• Eliminate carbon dioxide and other wastes to surrounding environment

• Synthesize needed cellular components

Basic Cell Functions• Control exchange of materials between

cell and its surrounding environment

• Sensing and responding to changes in surrounding environment

• Reproduction– Exception

• Nerve cells and muscle cells lose their ability to reproduce during their early development

Tissues

• Groups of cells with similar structure and specialized function

• Four primary types of tissues– Muscle tissue

– Nervous tissue

– Epithelial tissue

– Connective tissue

Tissues• Muscle tissue

– Specialized for contracting which generate tension and produce movement

– Three types of muscle tissue• Skeletal muscle

– Moves the skeleton

• Cardiac muscle– Pumps blood out of the heart

• Smooth muscle– Encloses and controls movement of contents through

hollow tubes and organs

Tissues• Nervous tissue

– Consists of cells specialized for initiating and transmitting electrical impulses

– Found in brain, spinal cord, and nerves

• Epithelial tissue– Consists of cells specialized for exchanging

materials between the cell and its environment

– Organized into two general types of structures• Epithelial sheets

• Secretory glands

Tissues• Connective tissue

– Connects, supports, and anchors various body parts

– Distinguished by having relatively few cells dispersed within an abundance of extracellular material

– Examples• Tendons

• Bone

• Blood

Organs• Consist of two or more types of primary

tissues that function together to perform a particular function or functions

• Example– Stomach

• Inside of stomach lined with epithelial tissue

• Wall of stomach contains smooth muscle

• Nervous tissue in stomach controls muscle contraction and gland secretion

• Connective tissue binds all the above tissues together

Body Systems

• Groups of organs that perform related functions and interact to accomplish a common activity essential to survival of the whole body

• Do not act in isolation from one another

• Human body has 11 systems

Body Systems

Body Systems

Homeostasis• Defined as maintenance of a relatively

stable internal environment– Does not mean that composition, temperature,

and other characteristics are absolutely unchanging

• Homeostasis is essential for survival and function of all cells

• Each cell contributes to maintenance of a relatively stable internal environment

Components of the extracelluar fluid ( internal environment)

Homeostasis• Body cells are contained in watery internal

environment through which life-sustaining exchanges are made

• Extracellular fluid (ECF)– Fluid environment in which the cells live (fluid

outside the cells)

– Two components• Plasma, interstitial fluid

• Intracellular fluid (ICF)– Fluid contained within all body cells

Homeostasis

HomeostasisFactors homeostatically regulated include

• Concentration of nutrient molecules

• Concentration of O2 and CO2

• Concentration of waste products

• pH

• Concentration of water, salt, and other electrolytes

• Volume and pressure

• Temperature

Role of Body Systems in Homeostasis

Homeostatic Control Systems

• In order to maintain homeostasis, control system must be able to– Detect deviations from normal in the internal

environment that need to be held within narrow limits

– Integrate this information with other relevant information

– Make appropriate adjustments in order to restore factor to its desired value

Homeostatic Control Systems

• Control systems are grouped into two classes

– Intrinsic controls• Local controls that are inherent in an organ

– Extrinsic controls• Regulatory mechanisms initiated outside an organ

• Accomplished by nervous and endocrine systems

Homeostatic Control Systems

• Feedforward – Term used for responses made in anticipation of

a change

• Feedback – Refers to responses made after change has been

detected

– Types of feedback systems• Negative

• Positive

Homeostatic Control Systems

• Negative feedback system– Primary type of homeostatic control

– Opposes initial change

– Components• Sensor

– Monitors magnitude of a controlled variable

• Control center– Compares sensor’s input with a set point

• Effector – Makes a response to produce a desired effect

– Example

Blood pressure regulation

Temperature regulation

Homeostatic Control Systems

• Positive feedback system– Amplifies an initial change

– Do not occur as often as negative feedback system

– Example• Uterine contractions become increasingly stronger until

the birth of the baby

Disruptions in Homeostasis

• Can lead to illness and death

• Pathophysiology – Abnormal functioning of the body associated with

disease

References

• Human physiology by Lauralee Sherwood, seventh edition

• Text book physiology by Guyton &Hall,11th edition

• Text book of physiology by Linda .s contanzo,third edition