تقنيات التخدير - المحاضرة 9 و 10

Anesthesia Techniques

• Course: Physiology
• Stage: Second stage
• Instructor: Dr. Farah Altaay
• Lecture: 9 & 10

Starling's Law of the Heart

• Otto Frank observed that increasing the stretching of the ventricle before contraction increased its strength.
• Ernest Starling expanded on this, demonstrating that increased venous return to the heart increases filling pressure (LVEDP).
• This increased filling pressure in turn increases stroke volume (SV).
• Conversely, decreased venous return results in decreased stroke volume.
• This cardiac response to venous return changes and filling pressure is intrinsic to the heart (does not depend on extrinsic factors).
• This mechanism is known as the Frank-Starling mechanism or Starling's Law of the heart.
• Increased filling pressure leads to increased cardiac output.

Frank-Starling Curves

• These curves illustrate the relationship between ventricular preload (LVEDP) and stroke volume (SV).
• Increased venous return leads to increased LVEDP, which results in a proportionally greater SV.

Physiological Significance of Starling's Law

• Starling's Law explains how the heart adjusts to changes in venous return to maintain blood circulation effectively.
• Increased venous return results in greater filling of the heart chambers.
• This, in turn, stretches the heart muscle fibers, leading to a more forceful contraction and increased stroke volume.
• The greater the preload, the greater the stroke volume.
• It represents the relationship between contractility and afterload.

Autonomic Nervous System

• The ANS controls involuntary functions like heart rate, blood pressure, respiration, digestion, and glandular secretions.
• It has two interacting systems: sympathetic and parasympathetic.
• These systems have antagonistic effects on the heart.

Parasympathetic Nervous System

• The parasympathetic system is most active under restful conditions.
• It counteracts the sympathetic system after a stressful event and restores the body to a restful state using acetylcholine (ACh).
• Functions: Pupil Constriction, Stimulation of saliva, Constricts Bronchi, Slows heart rate, Stimulates Bile production, Stimulates digestion.
• Reduces blood flow.

Sympathetic Nervous System

• The sympathetic system prepares the body for increased energy expenditure, emergency, or stressful situations.
• It uses norepinephrine (NE).
• Functions: Dilated Pupils, Inhibits saliva, Relaxes Bronchi, Increases heart rate, Slows digestion, Stimulates glucose release, Reduces interstitial muscles
• Increases blood pressure.

Effect of Sympathetic Stimulation on Cardiovascular System

• Increased heart rate.
• Increased myocardial contractility.
• Constriction of blood vessels.
• Increased renin secretion by kidneys (increasing blood pressure).

Effect of Parasympathetic Stimulation on Cardiovascular System

• Decreased heart rate.
• Decreased cardiac output.
• Decreased blood pressure.
• Parasympathetic system does not cause vasodilation.

Neurotransmitters in Autonomic System

• Neurotransmitters are chemical substances that transmit signals from one neuron to another or to a target cell.

Sympathetic Neurotransmitters

• Sympathetic postganglionic fibers release norepinephrine (NE), which acts on adrenergic receptors in target tissues (e.g., cardiovascular system).

Parasympathetic Neurotransmitters

• Parasympathetic postganglionic fibers release acetylcholine (ACh).
• ACh acts on cholinergic receptors in target tissues (e.g., heart).

Receptors

• The sympathetic and parasympathetic nervous systems use different receptors.
• Sympathetic system primarily uses adrenergic receptors (α and β).
• Parasympathetic system primarily uses cholinergic receptors. (nicotinic and muscarinic)