CARDIOVASCULAR SYSTEM & BLOOD LBBBIO7
FIRST TRIMESTER | 2025-2026
○ Since the liver detoxifies substances, toxins
SYNCHRONOUS SESSION removed from the liver pass through the
sinusoids into the veins.
CIRCULATORY SYSTEM
FUNDAMENTAL PLAN OF THE BLOOD VESSELS
● We’ll talk about the circulatory system first — not
cardiovascular — because when we say circulatory, we’re ● L is the lumen, and the innermost layer is termed the tunica
talking about body structures that have vessels or tubes that intima, which has the endothelial lining—said to be a simple
transport fluid. squamous epithelium.
● Actually, there are two circulatory systems: ● The middle portion is the tunica media, made up of smooth
○ Major Circulatory System – the Cardiovascular muscles, and the outermost layer is the tunica adventitia
System, which includes the heart and blood (formerly called tunica externa).
vessels: arteries, veins, and capillaries.
○ Minor Circulatory System – the Lymphatic
System, which includes lymphatic tissues,
lymphatic structures, and lymphatic vessels.
CARDIOVASCULAR SYSTEM
● We have here a picture of an artery and a vein. Note the
differences in structure regarding those layers.
● Tunica Intima
○ The intima has an endothelial lining. In both
the artery and the vein, it’s the same—simple
● Blood is the circulating fluid in the cardiovascular system. squamous.
○ Liquid component: plasma ○ However, look at the lumen:
○ Cellular component: erythrocytes, leukocytes, ■ The lumen of the artery is circular,
and thrombocytes rounded, and narrower.
● Blood vessels include: ■ The lumen of the vein is bigger,
○ Arteries wider, and irregular.
○ Veins ○ This is because veins have thinner walls, while
○ Capillaries arteries have thicker walls. Their functions
● The pumping organ is the heart. differ:
● Sinusoids ■ Veins are said to be capacitance
○ Sinusoids are highly specialized capillaries vessels—they hold the greatest
found in organs like the liver and spleen. volume of blood at any given point in
○ They are tiny canals between cells that serve circulation.
as channels for fluid, especially blood. ■ Arteries are pressure
○ Their function is similar to ordinary capillaries reservoirs—they can withstand high
— exchange of materials. pressures because they receive
LBBBIO7: Histology Laboratory LESSON 8 1
FIRST TRIMESTER | 2025-2026
○ Since the liver detoxifies substances, toxins
SYNCHRONOUS SESSION removed from the liver pass through the
sinusoids into the veins.
CIRCULATORY SYSTEM
FUNDAMENTAL PLAN OF THE BLOOD VESSELS
● We’ll talk about the circulatory system first — not
cardiovascular — because when we say circulatory, we’re ● L is the lumen, and the innermost layer is termed the tunica
talking about body structures that have vessels or tubes that intima, which has the endothelial lining—said to be a simple
transport fluid. squamous epithelium.
● Actually, there are two circulatory systems: ● The middle portion is the tunica media, made up of smooth
○ Major Circulatory System – the Cardiovascular muscles, and the outermost layer is the tunica adventitia
System, which includes the heart and blood (formerly called tunica externa).
vessels: arteries, veins, and capillaries.
○ Minor Circulatory System – the Lymphatic
System, which includes lymphatic tissues,
lymphatic structures, and lymphatic vessels.
CARDIOVASCULAR SYSTEM
● We have here a picture of an artery and a vein. Note the
differences in structure regarding those layers.
● Tunica Intima
○ The intima has an endothelial lining. In both
the artery and the vein, it’s the same—simple
● Blood is the circulating fluid in the cardiovascular system. squamous.
○ Liquid component: plasma ○ However, look at the lumen:
○ Cellular component: erythrocytes, leukocytes, ■ The lumen of the artery is circular,
and thrombocytes rounded, and narrower.
● Blood vessels include: ■ The lumen of the vein is bigger,
○ Arteries wider, and irregular.
○ Veins ○ This is because veins have thinner walls, while
○ Capillaries arteries have thicker walls. Their functions
● The pumping organ is the heart. differ:
● Sinusoids ■ Veins are said to be capacitance
○ Sinusoids are highly specialized capillaries vessels—they hold the greatest
found in organs like the liver and spleen. volume of blood at any given point in
○ They are tiny canals between cells that serve circulation.
as channels for fluid, especially blood. ■ Arteries are pressure
○ Their function is similar to ordinary capillaries reservoirs—they can withstand high
— exchange of materials. pressures because they receive
LBBBIO7: Histology Laboratory LESSON 8 1
