Page 150 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
Definition An effect on cardiac conductivity
Dromotropism Positive Dromotropic effect Negative Dromotropic effect
Types
↑in Conduction velocity ↓ in Conduction velocity

3-Excitability

Definition Ability of muscle to Respond to an electrical stimulus (2nd stimuli) [If 2 Successive Stimulus ➔ Muscle
will respond to only one]
ف
Types of Refractory period ةحارلا تارت It is a period of rest ( ) contraction & contraction

Refractory Absolute Refractory Period Cannot respond to any stimuli (No matter how large a

period (ARP) stimulus) (because Na+ Chanel is closed)
The
Relative Refractory Period Can only respond to strong stimuli (> Normal).
cardiac
(RRP)
muscle
Can respond to Weaker stimuli (More excitable than
Other period Supra-Normal Period (SNP)
normal)

4-Contractility
Definition Electrical activation of the cardiac cells include contraction
Force of contraction is dependent on: Intracellular Ca Concentration that enter cardiac cell during the plateau phase

 The electrical activation (excitation) of cardiac cells induces  Contraction.  Contractile unit of the cardiac muscle is the
 Sarcomere.
factor

 Steps of Excitation-Contraction Coupling:
1. During the plateau phase: Ca2+ enters the cells through L-type Ca2+ channels.

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