HHIS221: HUMAN HISTOLOGY
Lesson 8 | Circulatory System and Blood
Tissues of the Vascular Walls
(1) Endothelium
Topic Outline:
● Circulatory System ● Internal surface of all components of cardiovascular
● Heart and lymphatic system.
● Blood Vessels ● Simple squamous epithelium
(a) Artery ● maintain a selectively permeable, antithrombogenic
(b) Vein (inhibitory to clot formation) barrier
(c) Capillaries ● they also determine when and where white blood cells
● Blood leave the circulation for the interstitial space of tissues
(a) RBC ● secrete a variety of paracrine factors - signals vessel
(b) WBC dilation, constriction, and growth of adjacent cells
(c) Platelets (2) Smooth Muscle
● occur in the walls of all vessels larger than capillaries
Circulatory System and are arranged helically in layers.
● Function: ● permit regulated vasoconstriction and vasodilation
➔ Pumps and directs blood cells and substances carried (3) Connective Tissue
in blood to all tissues of the body. ● Collagen: found in subendothelial layer
➔ Transport: For transport of nutrients, hormones, ● Elastic Fibers: provide resiliency to blood vessel
oxygen and other needed substances in the cell.
➔ Excretory: It also moves waste, carbon dioxide and Components of the Cardiovascular System: Heart
secretory products to their disposal areas / organs. Heart
➔ Protection: Aids in fighting off pathogenic ● It is a hollow muscular organ, about the size of a
microorganism by providing and/or transporting the clenched fist, located in the central mediastinum of the
cells and substances needed for this purpose. thoracic cavity.
Division of Circulatory System ● Modified artery that has a pumping capacity that propels
(A) Cardiovascular System – Blood Vascular System blood to the arteries of both the systemic and pulmonary
(B) Lymph vascular System circulations.
Components of the Cardiovascular System ● Four chambers: the left atrium and right atrium (upper
(A) Heart chambers), and the left ventricle and right ventricle (lower
(B) Blood Vessels chambers)
(d) Artery Structures of the Heart
(e) Vein A. Layer of the Heart
(f) Capillaries (1) Endocardium / Tunica intima
(C) Blood ● endothelium and Fibroelastic tissue, smooth muscle
(d) RBC fibers and modified cardiac muscle fibers
(e) WBC (2) Myocardium / Tunica media
(f) Platelets ● contractile cardiac muscle fibers arranged spirally
around each heart chamber
Structure ● Much thicker in the walls of ventricles (particularly left
The whole circulatory system has a common basic structure: ventricle) compared to myocardium in atrium
(1) An inner lining, the tunica intima, comprises a single (3) Epicardium / Tunica serosa / Visceral pericardium
layer of extremely flattened epithelial cells called ● simple squamous mesothelium supported by a layer
endothelial cells supported by a basement membrane of loose connective tissue containing blood vessels
and delicate collagenous tissue. and nerves
(2) An intermediate predominantly muscular layer, the tunica ● corresponds to the visceral layer of pericardium - the
media. Contains alternating layers of smooth muscle and membrane surrounding the heart.
collagen called elastic lamellae
(3) An outer supporting tissue layer called the tunica B. Cardiac Skeleton
adventitia. Contains connective tissue, small vessels ● Forms base for all cardiac valves
and nerves and vasa vasorum. ● Separates atria from ventricles & provides points of
insertion for cardiac muscle in the atria and ventricles
● Dense Irregular Connective Tissue in composition
● Helps coordinate the heartbeat by acting as electrical
insulation between atria and ventricles
1
, C. Cardiac Conducting System the kidneys, intestine, choroid plexus, and endocrine
● specialized to generate and conduct waves of glands.
depolarization which stimulates rhythmic contractions (3) Discontinued Capillaries / Sinusoids
● Consists of modified cardiac muscle fibers – permit maximal exchange of macromolecules as
● Composition: well as allow easier movement of cells between
1. Sinoatrial Node (Pacemaker) – made up of cardiac tissues and blood.
muscle cells, with myofibrils and some intercalated – have highly discontinuous basement membranes
discs and much larger diameters, often 30-40 μm, which
2. Atrioventricular Node – located in the floor of right slows blood flow.
atrium, composed of cells similar to the sinoatrial – found in the liver, spleen, some endocrine organs,
node and bone marrow
3. Atrioventricular Bundle/ Bundle of His – connects the (2) Veins
atrial and ventricular chambers of the heart ● Carry blood back to the heart from microvasculature all
4. Purkinje Fibers over the body
- Contractile Bundles: trigger waves of contraction ● Most veins are classified as small or medium veins that
to both ventricles simultaneously are usually located close and parallel to corresponding
- Abundant Glycogen muscular arteries
- Sparse Bundles of Myofibrils
Components of the Cardiovascular System: Blood
Vessels
Blood vessels
● Forms closed circuit to and from the heart.
● Walls of all blood vessels except capillaries contain
smooth muscle and connective tissue in addition to the
endothelial lining.
(3) Arteries
● blood vessels that bring oxygen-rich blood from your
heart to all of your body’s cells
● Types of Arteries:
(1) Large Elastic Arteries
– aka Conducting Arteries
– with fenestrated elastic laminae in the thick tunica
media
– Contains Vasa Vasorum
(2) Muscular Arteries
Types of Blood Vessels – less elastic material than Elastic Artery
(1) Capillaries – Distribute blood to all organs and maintain steady
● Permit and regulate metabolic exchange between blood blood pressure and flow with vasodilation and
and surrounding tissues. constriction
● These smallest blood vessels always function in (3) Small Arteries
networks called capillary beds – no vasa vasorum
● Types of Capillaries (according to the size): – Distribute blood to arterioles, adjusting flow with
(1) Continuous Capillaries vasodilation and constriction
– This is the most common type of capillary and is
found in muscle, connective tissue, lungs, exocrine
glands, and nervous tissue.
– With well-developed occluding junctions; allow
cellular exchange
(2) Fenestrated Capillaries
– have a sieve-like structure that allows more
extensive molecular exchange across the
endothelium
– found in organs with rapid interchange of
substances between tissues and the blood, such as
2
Lesson 8 | Circulatory System and Blood
Tissues of the Vascular Walls
(1) Endothelium
Topic Outline:
● Circulatory System ● Internal surface of all components of cardiovascular
● Heart and lymphatic system.
● Blood Vessels ● Simple squamous epithelium
(a) Artery ● maintain a selectively permeable, antithrombogenic
(b) Vein (inhibitory to clot formation) barrier
(c) Capillaries ● they also determine when and where white blood cells
● Blood leave the circulation for the interstitial space of tissues
(a) RBC ● secrete a variety of paracrine factors - signals vessel
(b) WBC dilation, constriction, and growth of adjacent cells
(c) Platelets (2) Smooth Muscle
● occur in the walls of all vessels larger than capillaries
Circulatory System and are arranged helically in layers.
● Function: ● permit regulated vasoconstriction and vasodilation
➔ Pumps and directs blood cells and substances carried (3) Connective Tissue
in blood to all tissues of the body. ● Collagen: found in subendothelial layer
➔ Transport: For transport of nutrients, hormones, ● Elastic Fibers: provide resiliency to blood vessel
oxygen and other needed substances in the cell.
➔ Excretory: It also moves waste, carbon dioxide and Components of the Cardiovascular System: Heart
secretory products to their disposal areas / organs. Heart
➔ Protection: Aids in fighting off pathogenic ● It is a hollow muscular organ, about the size of a
microorganism by providing and/or transporting the clenched fist, located in the central mediastinum of the
cells and substances needed for this purpose. thoracic cavity.
Division of Circulatory System ● Modified artery that has a pumping capacity that propels
(A) Cardiovascular System – Blood Vascular System blood to the arteries of both the systemic and pulmonary
(B) Lymph vascular System circulations.
Components of the Cardiovascular System ● Four chambers: the left atrium and right atrium (upper
(A) Heart chambers), and the left ventricle and right ventricle (lower
(B) Blood Vessels chambers)
(d) Artery Structures of the Heart
(e) Vein A. Layer of the Heart
(f) Capillaries (1) Endocardium / Tunica intima
(C) Blood ● endothelium and Fibroelastic tissue, smooth muscle
(d) RBC fibers and modified cardiac muscle fibers
(e) WBC (2) Myocardium / Tunica media
(f) Platelets ● contractile cardiac muscle fibers arranged spirally
around each heart chamber
Structure ● Much thicker in the walls of ventricles (particularly left
The whole circulatory system has a common basic structure: ventricle) compared to myocardium in atrium
(1) An inner lining, the tunica intima, comprises a single (3) Epicardium / Tunica serosa / Visceral pericardium
layer of extremely flattened epithelial cells called ● simple squamous mesothelium supported by a layer
endothelial cells supported by a basement membrane of loose connective tissue containing blood vessels
and delicate collagenous tissue. and nerves
(2) An intermediate predominantly muscular layer, the tunica ● corresponds to the visceral layer of pericardium - the
media. Contains alternating layers of smooth muscle and membrane surrounding the heart.
collagen called elastic lamellae
(3) An outer supporting tissue layer called the tunica B. Cardiac Skeleton
adventitia. Contains connective tissue, small vessels ● Forms base for all cardiac valves
and nerves and vasa vasorum. ● Separates atria from ventricles & provides points of
insertion for cardiac muscle in the atria and ventricles
● Dense Irregular Connective Tissue in composition
● Helps coordinate the heartbeat by acting as electrical
insulation between atria and ventricles
1
, C. Cardiac Conducting System the kidneys, intestine, choroid plexus, and endocrine
● specialized to generate and conduct waves of glands.
depolarization which stimulates rhythmic contractions (3) Discontinued Capillaries / Sinusoids
● Consists of modified cardiac muscle fibers – permit maximal exchange of macromolecules as
● Composition: well as allow easier movement of cells between
1. Sinoatrial Node (Pacemaker) – made up of cardiac tissues and blood.
muscle cells, with myofibrils and some intercalated – have highly discontinuous basement membranes
discs and much larger diameters, often 30-40 μm, which
2. Atrioventricular Node – located in the floor of right slows blood flow.
atrium, composed of cells similar to the sinoatrial – found in the liver, spleen, some endocrine organs,
node and bone marrow
3. Atrioventricular Bundle/ Bundle of His – connects the (2) Veins
atrial and ventricular chambers of the heart ● Carry blood back to the heart from microvasculature all
4. Purkinje Fibers over the body
- Contractile Bundles: trigger waves of contraction ● Most veins are classified as small or medium veins that
to both ventricles simultaneously are usually located close and parallel to corresponding
- Abundant Glycogen muscular arteries
- Sparse Bundles of Myofibrils
Components of the Cardiovascular System: Blood
Vessels
Blood vessels
● Forms closed circuit to and from the heart.
● Walls of all blood vessels except capillaries contain
smooth muscle and connective tissue in addition to the
endothelial lining.
(3) Arteries
● blood vessels that bring oxygen-rich blood from your
heart to all of your body’s cells
● Types of Arteries:
(1) Large Elastic Arteries
– aka Conducting Arteries
– with fenestrated elastic laminae in the thick tunica
media
– Contains Vasa Vasorum
(2) Muscular Arteries
Types of Blood Vessels – less elastic material than Elastic Artery
(1) Capillaries – Distribute blood to all organs and maintain steady
● Permit and regulate metabolic exchange between blood blood pressure and flow with vasodilation and
and surrounding tissues. constriction
● These smallest blood vessels always function in (3) Small Arteries
networks called capillary beds – no vasa vasorum
● Types of Capillaries (according to the size): – Distribute blood to arterioles, adjusting flow with
(1) Continuous Capillaries vasodilation and constriction
– This is the most common type of capillary and is
found in muscle, connective tissue, lungs, exocrine
glands, and nervous tissue.
– With well-developed occluding junctions; allow
cellular exchange
(2) Fenestrated Capillaries
– have a sieve-like structure that allows more
extensive molecular exchange across the
endothelium
– found in organs with rapid interchange of
substances between tissues and the blood, such as
2
