DR.P.SUNITHA

The Vascular Pathways The cardiovascular system includes two circuits: 1)Pulmonary circuit which circulates blood through the lungs, and 2)Systemic circuit which circulates blood to the rest of the body. 3)Both circuits are vital to homeostasis.

Birds & mammals: 4 chambers Double circulation: 1) systemic 2) pulmonary complete septum eliminates mixing of oxygenated and deoxygenated blood separation greatly increases the efficiency of O 2 delivery to the cells

4-chambered heart 2 atria & 2 ventricles complete seperation of oxygenated and deoxygenated blood right heart drives pulmonary circulation left heart dives systemic circulation complete separation of oxygenation & deoxygenated blood

PULMONARY CIRCULATION With blood returning FROM the Body TO the Heart…(via the Vena Cava): Right Atrium  Tricuspid Valve  Right Ventricle  Pulmonary Semilunar Valve  Pulmonary Trunk  Pulmonary Arteries (2)  Alveoli in the Lungs   Capillaries in the Alveoli

ONCE BLOOD REACHES THE CAPILLARIES – GAS & NUTRIENT EXCHANGE OCCURS! In Pulmonary Circulation, this means that Carbon Dioxide is released to the alveoli in the lungs and Oxygen is picked up by the bloodstream.  Pulmonary Veins (4)  Left Atrium  Back to Systemic Circulation REMEMBER…the Left & Right sides of the heart pump blood SIMULTANEOSLY !

Pulmonary Pressures and Volumes Total 500 ml 60 – 200 ml Total 5000 ml

Path of blood through the heart

Pulmonary Circuit This loop oxygenates blood right pulmonary arteryleft pulmonary artery capillary bed of right lung pulmonary trunk capillary bed of left lung (to systemic circuit) pulmonary veins lungs (from systemic circuit) heart

The pulmonary circulation tissue CO2 O2 Pulmonary artery RV LA Pulmonary vein Pulmonary capillaries

The lung has low vascular resistance

The lung’s low vascular resistance is due to 1. Low vascular tone 2. Large capillary compliance

Pulmonary Circulation System

Pulmonary circulation is the part of the circulatory system that takes the blood from the heart to the lungs, where it is oxygenated, and returns it to the heart. The main parts of the pulmonary circulation system include the heart, pulmonary arteries, capillaries of the lungs, and pulmonary veins.

Blood that is low in oxygen returns to the heart through two large veins called the superior (or cranial) vena cava and the inferior (or caudal) vena cava. The un-oxygenated blood enters the right atrium of the heart. Flow of Blood in Pulmonary Circulation

The blood then passes through the right atrioventricular (tricuspid) valve into the right ventricle. The right ventricle pumps the blood through the pulmonary valve into the pulmonary trunk.

The pulmonary trunk quickly divides into two pulmonary arteries. Each artery carries blood to a lung. In the lungs the pulmonary arteries branch into capillaries that surround the alveoli.

Through diffusion, carbon dioxide moves from the blood into the alveoli and oxygen moves from the alveoli into the blood. The oxygenated blood then returns to the heart through the pulmonary vein into the left atrium.

From the left atrium, the blood flows through the left atrioventricular (bicuspid) valve into the left ventricle.

The thick-walled left ventricle pumps the blood through the aortic valve into the aorta. The amount of pressure that is required for pulmonary circulation is much less than what is required for systemic circulation. Therefore, the muscle mass developed in the right ventricle is much less that of the left ventricle.

Un-oxygenated blood is dark or brownish red, while oxygenated blood is bright red. In the pulmonary system, un- oxygenated blood is carried by the pulmonary arteries and oxygenated blood is carried by pulmonary veins. In the systemic system, arteries carry oxygenated blood and veins carry un- oxygenated blood.

SPECIAL FEATURES 1.Entire blood volume passes through the two lungs in one minute. Five litres of blood flows in one minute through the lungs whereas the rest of the body receives the same amount in one minute. 2.Pulmonary artery carries venous blood to the lungs. CO 2 is given up and O 2 is picked up. Pulmonary veins carry oxygenated blood to left atrium.

3.Capillary density is very high and the blood flow is referred to as sheet flow. This is useful for quick exchange of gases. 4.It is a low pressure system, mean pressure in the pulmonary artery is 15mmHg.mean pulmonary capillary pressure (6-8mmHg) is much lower compared to the systemic capillary blood pressure.

5.Blood flow through capillaries is much affected during different phases of respiration. 6.Arterioles and other vessels are sensitive to hypoxia. They show vasoconstriction to a low O 2 tension. This helps in diversion of the blood flow from a poorly ventilated region to a well ventilated region.

7.Pulmonary blood flow is always equal to cardiac output in all physiological conditions. 8.Regional variation blood flow to the lungs is not uniform. Due to gravitational influence basal regions receive more blood flow and apical regions receive less blood flow.

REGULATION OF PULMONARY BLOOD FLOW 1.Left ventricular performance. 2.Right ventricular performaance. 3.pulmonary vascular resistance. Hypoxia. Sympathetic nerve fibres Phase of respiration.

High capillary pressure Inflammation High surface tension Decreased plasma protein (starvation, liver disease, hemodilution) Impaired lymphatic drainage High altitude Drowning Potential causes of pulmonary edema

Pulmonary Edema normaledema

What’s it sound like? Pleural effusion

Diseases of the Lungs Chronic Obstructive Pulmonary Disease (COPD) Emphysema Reduction of the gas exchange area caused by break down of alveolar walls Alveolar walls seems to be destroyed by proteolytic enzymes released as a part of the inflammatory process.

Chronic Bronchitis Irritants reaching the bronchi and bronchioles stimulate inflamation and an increased secretion of mucus. The air passages become clogged with mucus, and this leads to a persistent cough. Chronic bronchitis is usually associated with cigarette smoking.

Asthma periodic constriction of the bronchi and bronchioles difficult to breathe in and, especially, out. Attacks of asthma can be triggered by airborne allergens and non specific irritants (chemical fumes, cigarette smoke) in susceptible individuals Pneumonia Pneumonia is an infection of the alveoli (bacterial or viral) Tissue fluids accumulate in the alveoli reducing the surface area exposed to air.

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