Co-ordination and Regulation:

• Aims:

• Must be able to outline the main forms of fluid in the body how substances are transferred.

• Should be able to outline what homeostasis is and how it occurs.

• Could be able to able to explain how negative feedback works in homeostasis.

Internal and External Environments• Cells in a multi-cellular organism need to maintain a

relatively constant internal environment for normal function.

• Internal and external environments refer to the organism as a whole and for the individual cells.

• There internal environment is made up of four main fluids:– Plasma– Lymph– Tissue Fluid– Cytosol

Intra-cellular Fluid

• All fluid found within the cells (Cytosol)

• Cytosol consists mostly of:– Water– dissolved ions– Small molecules– Large water-soluble molecules

• Cytosol has a high concentration of K+ ions and a low concentration of Na+ ions.

White blood cell (lymphocyte) in capillary  (TEM x16,210)

Extra-cellular Fluid• Extra-cellular fluid surround the outside of the cell.

• In some animals, including mammals, the extra-cellular fluid can be divided into two major sub-compartments:

• Interstitial fluid (including Lymph)• Blood plasma.

• Composition of extracellular fluid depends upon the exchanges between the cells in the tissue and the blood.

• Generally consists of a water solvent containing amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts, as well as waste products from the cells.

Extra-cellular Fluid• Tissue (interstitial)

fluid bathes the cells of the tissues.

• Provides:– Means of delivering

materials to the cells

– Intercellular communication

– Removal of metabolic waste

Exchange Between Fluids• Plasma and tissue fluid (extra-cellular fluids) are separated by cells

lining the capillaries.

• Extra-cellular fluids are separated from intracellular fluids by cell membranes.

• Substances within these fluids are exchanged via three mechanisms:

• Vesicular transport• Diffusion• Bulk flow

• Vesicular transport and diffusion are associated with the movement of solutes.

• Bulk flow is the most important process for the maintenance of relative volumes of blood and tissue fluid

Exchange Between Fluids

• Many substances move between cells and fluids, and between fluids including:

– Waste products (CO2, urea)– Glucose and amino acids– Oxygen

• Not all of the contents of the blood pass into the tissue, which means that tissue fluid and blood are not the same.

• Red blood cells, platelets and plasma proteins cannot pass through the walls of the capillaries.

Homeostasis• In order for cells to function properly, they require an

environment in which their requirements are met and conditions remain stable.

• Despite changes in the external environment, the internal environment of an organism remains fairly constant.

• Homeostasis is defined as the maintenance of a constant internal environment, maintained within narrow limits

Variables that are Subject to Homeostasis

• Body Temperature• Water balance• Nutrient balance (eg: Blood glucose)• Ions• pH (Hydrogen ion concentration)• Blood volume• Blood pressure• Oxygen• Carbon Dioxide• Red Blood Cells

A Homeostasis System Needs:

• Sensors (receptors) to detect changes in the internal environment (Stimulus).

• A comparator which fixes the set point of the system (e.g. body temperature). The set point will be the optimum condition under which the system operates.

• Effectors which bring the system back to the set point.

• Feedback control. Negative feedback stops the system over compensating (going too far).

• A communication system to link the different parts together (e.g. Central nervous system)

Negative Feedback• The maintenance of a stable

internal environment relies on Negative Feedback systems.

• “Negative” because the response to the stimulus reduces the effect of the original stimulus.

• Three Components:– Receptor: Monitors value of

variable.– Control Centre: Establishes set

point around which the variable is maintained.

– Effector: Changes the value of the variable. Gets orders from the Control Centre.

Control Center

Effectors

Feedback

Receptors

ResponseStimulus

In all homeostatic mechanisms a receptor detects a disturbance or misalignment in the levels of an important factor. The control center orders a response in an effectors. The response alters the original stimulus providing negative feedback to the control center. It then either stops the original response or produces an opposite response

Negative Feedback

Negative Feedback E.g. Raised CO2 Levels

Receptors

Medulla and aortic and carotid bodies

EffectorsDiaphragm and intercostal mucles

Control CenterBrain

Transmission

Transmission

Negative FeedbackLower CO2 levels

ResponseFaster, deeperbreathing

StimulusHigh CO2 levels in blood

Questions

• Answer the questions from pages 55 to 58 in the Biozone books.