 Definition  Classification: three types:  1-Occluding junction: -tight junction  2- Communicating junction: - gap junction  - chemical synapse  3- Anchoring junction: - adherens junction  - focal adhesions  - desmosome  - hemidesmosome

 Mechanism of transport: -Passive transport-Active transport

passive transport: along the concentration gradient or electrical gradient or both. It is also called diffusion or downhill movement. Two types: 1- Simple diffusion : Two types: - Simple diffusion through protein layer - Simple diffusion through lipid layer

 Factors affecting rate of diffusion: Diffusion is directly proportional to: 1-permeability of the cell membrane 2-body temperature 3-concentration gradient 4-solubility of the substance Diffusion is inversely proportional to: 1-thickness of cell membrane 2-charge of the ions 3-size of the molecules

 1- Bulk flow: diffusion of large quantity of substances from a region of high pressure to a region of low presuure. E.g. Gases across the respiratory membrane in lunge

distilled water 10% sucrose solution 2% sucrose solution Hypotonic Conditions Hypertonic Conditions Isotonic Conditions

 Definition  Carrier protein: - uniport - symport or antiport  Substances transported by active transport  Types of active transport: 1- primary active transport 2- secondary active transport

 Sodium-Potasium pump:

 Two types: - Co-transport -Counter transport

simple diffusion facilitated diffusion active transport ATP

 I-Endocytosis: is the transport mechanism by which macromolecules enter the cell. Three types: 1- Pinocytosis:

phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

 Homeostasis: ability to maintain a constant internal environment in an ever-changing outside world  All body systems working together to maintain a stable internal environment, respond to external and internal changes to function within a normal range (body temperature, fluid balance)  The internal environment of the body is in a dynamic state of equilibrium  Failure to function within a normal range results in disease

 Variables produce a change in the body  The three interdependent components of control mechanisms:  Detector or sensor– monitors the environments and responds to changes (stimuli)  Control center – to which the information regarding the deviation is transmitted  Effector – receive the information from the control to correct the deviation.

Input: Information sent along afferent Pathway to Control center Output: Information sent along efferent pathway to Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis Stimulus: Produces change in variable Change detected by receptor EffectorReceptor (sensor) Imbalance Variable (in homeostasis)

 Most common way that homeostasis is maintained in the body  In negative feedback systems the response of the effector negates or opposes the stimulus (shuts off the original stimulus)  Example: Regulation of room temperature

 Rare in nature  The response of the effector output reinforces or exaggerates the stimulus (e.g. blood clotting, ovulation, action potential)  NOT a way to maintain homeostasis