The blood system

• Arteries convey blood at high pressure from the heart's ventricles to the tissues of the organism
• Kidney - renal artery
• Liver - hepatic artery
• Heart - coronary arteries
• Elastic and muscular tissues contribute to the toughness of the arteries' walls, as they have to withstand constantly changing and intermittently high blood pressure without bulging outwards (back) or bursting.
• The elastic tissue is arranged into layers that can stretch when the artery expands during systole but then recoil back to their original shape once diastole begins again.
• Muscle fibers are also present within the tunica media layer, which allows them to contract and relax in response to changes in blood pressure.
• Veins carry deoxygenated blood away from the body’s organs and return it to the right side of the heart.
• Capillaries are tiny vessels where exchange between the bloodstream and surrounding cells occurs through diffusion.
• Arterioles are smaller than arteries and carry blood from an artery to a capillary bed.
• Veins return deoxygenated blood to the heart.
• Valves prevent backward flow of blood.
• Capillaries connect arterioles to venules and allow exchange between cells and blood.
• Arterioles are small branches off larger arteries that regulate blood flow to different parts of the body by constricting or dilating.
• Venules are smaller veins that collect blood from capillaries and merge together to form larger veins.
• Blood flow is controlled by valves located at intervals along the length of the vein.
• The circulatory system is responsible for transporting oxygen, nutrients, hormones, and waste products throughout the body.
• Arteries' walls are composed of three layers:

  • tunica externa - a though outer layer of connective tissue
  • tunica media - a thick layer of elastic and smooth muscle fibres
  • tunica intima (endothelium)
• Tunica intima consists of endothelial cells which line the lumen of the vessel
• The muscle and elastic fibres assist in maintaining blood pressure between pump cycles
• Peak pressure is called systolic pressure
• Pulmonary circulation - to and from lungs
• Systemic circulation - to and from all other organs in the body, including the heart
• Oxygenated blood flows into the left side of heart, through pulmonary veins from the lungs, and then out through the aorta
• Deoxygenated blood flows into the right side of heart through the vena cava and out through the pulmonary arteries
• Capillaries connect arteries with veins and allow exchange of substances between cells and blood
• Blood vessels are classified as arteries, capillaries or veins based on their structure and function
• Minimum pressure in the arteries is called diastolic pressure
• Circular muscles are localized in the wall of artery
• Blood flows through tissues in capillaries with permeable walls that allow exchange of materials between cells in the tissue and the blood in the capillary
• Capillaries have diameter of 10μm (micrometers) (width of one red blood cell - hemoglobin)
• Capillary wall consist of one layer of very thin endothelium cells, with pores between cells (permeable wall - transport through diffusion)
• Veins collect deoxygenated blood at low pressure from the tissues of the body and return it to the right atria of the heart
• Veins do not need to be thick-walled because they carry blood at low pressure. Their walls contain far fewer muscle and elastic tissue
• The veins have valves which prevent backflow of blood when the heart is not pumping.
• Arteries have thick muscular walls to maintain their shape and resist the high pressure exerted by the blood flowing through them
• Atriums (komory) collect blood from veins (vena cava and pulmonary vein) and passes it to ventricles
• Ventricles (przedsionki) pump blood into the arteries (aorta and pulmonary artery)
• The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla (móżdzek) of the brain
• Epinephrine (also called adrenaline) increases the heart rate to prepare for vigorous physical activity