CFR 5 Heart WT 2024-25

Cardiovascular System Overview

The Heart

• Function:

  • Responsible for blood circulation.

• Location:

  • Situated in the thorax within the pericardial cavity.

• Pericardium Structure:

  • Attached to the walls of the pericardium where major vessels enter/exit.

  • Lined by mesothelium, forming part of the pericardial membrane.

• Heart Layers:

  • Epicardium covered by mesothelium.

Blood Flow through the Heart

1. Deoxygenated blood enters the right atrium via superior and inferior vena cavae.

2. Blood moves to the right ventricle through the tricuspid valve.

3. Blood exits the right ventricle via pulmonary valve to pulmonary artery.

4. Blood travels to the lungs for gas exchange via left and right pulmonary arteries.

5. Oxygenated blood returns to the left atrium through pulmonary veins.

6. Blood enters the left ventricle via the mitral valve.

7. Blood exits the left ventricle through the aortic semilunar valve to the aorta.

8. Aorta distributes oxygenated blood to the body.

Circulatory System

• Types:

  • Systemic circulation (to body) and pulmonary circulation (to lungs).

• Relevant Vessels:

  • Carotid artery, aorta, pulmonary artery, jugular vein, vena cava.

Cardiac Muscle Physiology

• Importance of Coordination:

  • Proper muscle contraction timing is crucial.

• Cardiac Muscle Structure:

  • Striated muscle with individual cells connected by intercalated discs with gap junctions for ion diffusion.

• Myogenic Nature:

  • Can contract rhythmically without external stimulation and functions as a syncytium.

• Refractory Period:

  • Long refractory period (0.25 - 0.3 sec) prevents continuous contraction.

Nervous Control of the Heart

• Regulation:

  • Controlled by the cardiovascular center in the medulla oblongata.

  • Responds to pressure sensors and other stimuli.

Heart Rate

• Variability:

  • Lower in larger mammals (e.g., elephant: 25/min, mouse: 500/min).

  • Normal adult human heart rate: 72 beats/min, can rise to 195 bpm under stress.

  • Trained athletes may have resting rates as low as 50 bpm.

Heart Physiology

• Pacemaker Function:

  • SA node initiates contraction; mixes cardiac muscle with autonomic nerve fibers.

  • Located in the right atrium near the superior vena cava entry.

• Contraction and Electrical Impulse:

  • Fires at 100 beats/min but the autonomic nervous system adjusts.

  • Sympathetic nerves can double the heart rate, while parasympathetic nerves can reduce it by 30%.

  • Atria contract as one unit due to intercellular connections in cardiac muscle.

Excitatory and Conductive System of the Heart

• Contraction Mechanism:

  • Atria contract simultaneously; connected to ventricles by AV node, the only electrical route.

  • Delay (0.11 sec) in signal transmission allows for coordinated contraction.

• His-Purkinje System:

  • Conducts impulses quickly, ensuring simultaneous ventricle contraction.

Cardiac Cycle

• Definitions:

  • Systole: contraction phase; Diastole: relaxation phase.

  • Cardiac cycle duration: ~0.8 seconds, occurring 70 times/min on average.

  • Heart beats about 2.6 trillion times over a lifespan.

• Mechanics:

  • Atria contract and blood systematically fills ventricles; 70% flows passively, 30% actively.

• Ventricular Dynamics:

  • During ventricular diastole, chambers fill to 120-130 ml; during systole, the pressure closes the AV valves and opens semilunar valves, ejecting 70 ml blood (stroke volume).

Cardiac Output

• Definition:

  • Volume of blood ejected by the left ventricle per minute, also applicable to right ventricle's output.

• Calculation:

  • Cardiac output = Stroke volume x Heart rate (e.g., 70 ml x 72 bpm = 5040 ml/min).

• Variability:

  • Output changes in response to factors like stroke volume and heart rate; can spike under stress (up to 25 liters/min).

Frank-Starling Law of the Heart

• Principle:

  • Stroke volume linked to venous return; the heart adapts to varying inflow.

  • Ventricles expand to accommodate extra blood, enhancing contraction force.

• Physiological Limit:

  • Heart pumps all incoming blood without excessive venous buildup.

Heart Failure

• Understanding:

  • Cardiac output decreases; blood remains in heart post-contraction, causing systemic issues like dyspnea and edema due to congestion.

Electrocardiogram (ECG)

• Use:

  • Records electrical activities of the heart.

Heart Sounds

• Sounds:

  • 'Lub' indicates closure of AV valves; 'Dub' signifies closure of semilunar valves.

  • Abnormal sounds can indicate valve issues (murmurs).

Measurement of Blood Pressure

• Mechanism:

  • Sphygmomanometer is used to assess arterial pressure.

  • Normal resting adult: 120 mmHg systolic, 80 mmHg diastolic.

  • Variability exists among mammals and across body systems.

Blood Pressure Levels

• Systemic Dynamics:

  • Mean arterial pressure is approximately 100 mmHg in aorta.

  • Resistance causes significant pressure drops across the circulatory system (e.g., aortic pressure to 85 mmHg at arterioles).

Learning Resources

• Text References:

  • Sherwood. Human Physiology, Chapters 9 and 10.

  • Solomon. Biology, Chapter 44.

  • Chiras. Human Biology, 6th Edition, Chapters 5 and 6.

The eye has three main layers theres the avascular fibrous layer there the outer layer protects and is the place in where the muscles are attached to the sclera, which provides structure and support. The middle layer, known as the uvea, contains the choroid, ciliary body, and iris, playing crucial roles in nourishing the eye and regulating light entry. Finally, the inner layer, or retina, is responsible for converting light into neural signals, which are then transmitted to the brain for processing.

Fibrous layer ( has sclera and cornea) ( structure and strength)

Colour is better seen in the daytime because of the use of cones which have trid—- and it is also because of the connections with the cones and ganglion its a 6:1 ratio making it more high resolution while rods have a ratio of 1:20 making it ( shapes of both) ( theory of the 3 rods and light waves) ( rhodopsin) ( the order of how it happens as light goes through the lens the The photoreceptors then go into the cones which the through the horizontal cells go to the ganglia and through the ganglia then go to amcrine cells and then the optic nerve.

Sotopic & photopic

the location of the fovea

Monochramatic

Vitamin A,11-Trans retinol, retinol dehydrogenase, 11 trans retinal , 11 cis retinal, rhodopsin

Presbyopia is the loss of elasticity from making it more difficult for the eye to focus on nearby objects, typically occurring with age. this reults in a converging lense and because the fovea has been degraded

Astigmimatisim is due to a more oval shaped cornea it results in the blurring in one direction correction blindness

myopia results in seeing past the 25 cm mark diverging lenses

hypermiopia is a result in not being able to see within a 25 cm range .

1/25+ 1/1.25=0.84 converging

b-Horizontal cell ( interneurons have phtoroceptors)

a-ganglion

c- cone cells

Negative or positive Stimulus- afferent—set point—-contercenter—-efferent—-response

these are maintained doring homeostasis through feedback mechanisms that regulate physiological processes. and factors are external or internal.

+ive= out and -ive=in

the ospmotic pressure

the collidal osmotic pressure

,,

Lymphocytes ( second most common )

Monocytes(Largest in the blood, important for immune defense and phagocytosis).

• Neutrophils 62% (pus is dead guys of this)

• Eosinophils (5) ( parasites)Lysosomes

• Basophils (0.4%)( histamine and herian)

Stroke volume is the left ventricels release in pressure of blood during each heartbeat, which is crucial for determining cardiac output and overall heart function.

Frank starling is the the connects the stroke volume to the venous return and this then depends on the the stretch anything past a specific point results in dyspenea and eventually edema

90% is blood 10% is recycled to lymphs

uses muscles to faceliated return

lymphocytes

fluid recovery