The Circulatory System: Systemic and Pulmonary

The Circulatory System

• As blood moves through the circulatory system, it passes through arteries (and arterioles), capillaries, and veins (and venules).
• The vascular system forms closed circuits consisting of the systemic and pulmonary circulations.

Systemic and Pulmonary Circulations

• The systemic circulation starts when the left ventricle ejects blood into the aorta.
• The aorta branches into arteries, which branch into smaller arteries and arterioles distributed to all body tissues, except the lungs.
• Arterioles lead to capillaries.
• Capillaries empty into venules, which merge into small veins, then larger veins. These eventually form the superior and inferior vena cava, which deliver blood back to the right atrium.
• The pulmonary circulation starts with the right ventricle ejecting blood into the pulmonary artery.
• The pulmonary artery branches into smaller arteries and then arterioles that lead to pulmonary capillaries.
• Blood then flows through pulmonary venules and pulmonary veins, which return the blood to the left atrium.

Arteries

• Arteries carry blood away from the heart to all tissues of the body.
• All arteries carry oxygenated blood except for the pulmonary arteries.
• Arteries have thick walls to transport blood under high pressure, resulting from the heart's pumping action.
• Arterial walls are composed of thick muscles and elastic fibers.
• Elastic fibers allow the artery to stretch under pressure.
• The thick muscle can contract to further push the blood away.

Capillaries

• Capillaries are the smallest blood vessels.
• Capillary walls are very thin, consisting of only one cell layer.
• They are very narrow.
• They are important for exchanging nutrients, gases, and waste products between tissues and blood.
• Half of the capillary length is supplied by arteries, and the other half by veins.

Veins

• After blood passes through capillary systems, it is returned to the heart by veins.
• Veins are the vessels that bring blood into the heart.
• All veins carry deoxygenated blood except the pulmonary veins.
• Vein walls are thin and contain connective tissue and smooth muscle, making them less elastic than arteries.
• Veins have valves that allow blood to flow in only one direction toward the heart, preventing backflow.
• Pressure in the veins is low.
• Blood is forced through veins by the contraction of surrounding skeletal muscles.

The Pulse

• The pulse is a wave caused by the expansion and recoil of the arteries.
• Arteries expand during systole and then recoil immediately due to their elastic tissue and muscle contraction.
• The pulse can be felt in many areas, but the radial and carotid artery pulses are the most important and easily accessible.

Blood Pressure

• Blood pressure is the force exerted by the blood on the walls of the arteries.
• During systole, the blood exerts pressure, known as systolic pressure, on the vessel walls (average 120 mmHg).
• During diastole, the vessel walls recoil to their original position, compressing the blood, resulting in diastolic pressure (average 70-80 mmHg).
• Blood pressure is measured using a (sphegmo-mono-meter).
• Blood pressure measurements are written as (systole/diastole), e.g., 120/80 mmHg.

The Blood

• Functions of blood include:
  • Transport: Delivering oxygen to every cell in the body and removing carbon dioxide from cells. Transporting nutrients to cells, removing waste products, transporting heat, and hormones.
  • Defense: Carried out by white blood cells (WBCs) and antibodies; reduced levels of these can lead to severe infections.
  • Hemostasis: Stoppage of bleeding.
  • Homeostasis: Maintaining a constant internal environment (ECF) for cells, including constant pH (7.4), osmotic pressure (290 mmHg), temperature (37°C), and consistent levels of nutrients, gases, and minerals.
• Composition of Blood:
  • Blood makes up 8% of body weight.
  • Plasma (55% of blood volume): Approximately 90% water. Solids (5%) include proteins (7g), crystalloids (NaCl 0.9%), and minimal gases.
  • Cells (45% of blood volume).

Blood Cells

- Erythrocytes: Red blood cells (4.5-5 million).
- Leukocytes: White blood cells (4000-8000 mm).
- Thrombocytes: Platelets (150,000-400,000).  NaCl 0.9% maintains osmotic pressure.

• Plasma Proteins:
  • Plasma contains proteins such as Albumin, Globulin, Fibrinogen, and Prothrombin

Cholesterol

• Cholesterol (lipid) is not found freely in blood to prevent precipitation in blood vessel walls and atherosclerosis; instead, it is bound to protein as a lipoprotein.
  • Types of cholesterol include low-density cholesterol (LDL) and high-density cholesterol (HDL), with HDL being better for the body.

Blood Groups

- To determine blood group, a drop of blood is tested with anti-A serum, anti-B serum, and anti-D serum. Lysis with anti-A indicates blood group A; lysis with anti-B indicates blood group B; lysis with anti-D indicates Rh-positive. Lysis with both anti-A and anti-B indicates blood group AB. If lysis occurs with neither anti-A nor anti-B, the blood group is O.

Additional Information

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Red Blood Cells

- Red blood cells are very small, have elastic membranes for flexibility, and are larger than capillaries. They are destructed after 4 months where gas and nutrient exchange occurs and destruction takes place in the spleen because it contains the smallest capillaries in the body.

Important Notes

- Carbon monoxide has a high affinity for hemoglobin.
- In the blood, iron is in the ferrous form.
- The main function of the respiratory system is to remove carbon dioxide.
- A person can survive with minimum oxygen but will die if carbon dioxide levels are too high due to acidosis.

Hemoglobin

• In the blood only the protein and HB has gram 7g Hb%12g
• The iron in the Hb% found in the form of ferrous not ferric and there are four polypeptides chains and each chain attached to iron