GENERAL CONSIDERATIONS
CARDIOVASCULAR SYSTEM
- Mediates continuous flow of all body fluids.
- Transport oxygen and nutrients to the tissues.
- Transport carbon dioxide and metabolic waste products from the tissues.
- Thermoregulation.
- Distribution of hormones and cells (immune system cells).
COMPONENTS OF THE
CARDIOVASCULAR SYSTEM
- Heart
- Highly modified, muscular blood vessel pumps the blood.
- Closed circuit of vessels (as blood leaves the heart):
A. Elastic arteries (aorta and pulmonary arteries)
B. Muscular arteries
C. Small arteries and arterioles
D. Capillaries
E. Venules and small veins
F. Medium veins
G. Large veins (venae cava)
TYPES OF CIRCULATION
- PULMONARY
- SYSTEMIC
- LYMPHATIC
PULMONARY
CIRCULATION - right heart
Circuit of blood between the heart and the lungs.
* Blood leaves the right ventricle → pulmonary arteries → capillaries →pulmonary veins → left atrium.
* Deoxygenated blood gets sent to the lungs to get oxygenated.
SYSTEMIC
CIRCULATION - left heart pumps oxygenated blood
- Distributes blood from the
heart to the body tissues. - Blood leaves the left ventricle → aorta →systemic arteries →systemic capillaries - in all body tissues where gas exchange occurs →systemic veins → inferior and superior vena cavae → right atrium.
- For exchange of CO2 and O2, nutrients and metabolic wastes between blood and tissues, distribution of hormones
LYMPHATIC
CIRCULATION
- Outside of the heart – lymphatic system.
- A system of blind-ended lymph vessels located throughout the body that act as drainage without a pump.
- Returns the tissue fluid (lymph) to the venous circulation afterimmunological screening through the lymphatic system.
HEART CHAMBERS
- The heart as four chambers:
- Atria – receiving chambers
- Right atrium - upper right chamber - get blood from superior venae cavae and coronary sinus pumps blood into the right ventricle
- Left atrium - lower right - gets blood from RA via the 4 pulmonary veins and pumps into LV
- Ventricles – discharging chambers
- Right ventricle - upper left. Gets O2 blood from the RA and pumps into pulmonary trunk which carries blood to the lungs for O2 pickup
- Left ventricle- get blood from LA and pumps into the aortic arch (brachiocephalic artery, Left common carotid artery, Left subclavian artery) and to the tissues in the systemic circuit
- Right and left sides act as separate pumps.
- Right side – participates in the pulmonary circuit.
- Left side – participates in the systemic circulation.
HEART VALVES
- Allow blood to flow in only one direction (prevent backflow).
- Four heart valves:
A. Semilunar valves—between ventricle and artery; - Closed during heart relaxation
- Open during ventricular contraction
- Pulmonary semilunar valve
- Aortic semilunar valve
B. Atrioventricular (AV) valves—between atria and ventricles;
* Anchored in place by chordae tendineae (“heart strings”);
* Open during heart relaxation.
* Closed during ventricular contraction:
* Bicuspid (mitral) valve (left side of heart).
* Tricuspid valve (right side of heart).
LAYERS OF THE HEART WALL
PERICARDIUM (Heart sac)
* Two layers enveloping the heart:
* Outer fibrous pericardium.
* Inner serous pericardium
EPICARDIUM
* Outermost layer of the heart wall.
* Covers the heart and forms the visceral layer of serous pericardium – inner layer of pericardium.
MYOCARDIUM
* Middle layer of the heart.
* Contracts to pump blood into arteries
ENDOCARDIUM
* Innermost layer of the heart.
* Lines the interior chambers and covers the heart valves.
EPICARDIUM
Outer layer of the heart.
* Thin serous membrane that covers the heart and forms the visceral pericardium.
* mesothelial cells on the outer surface- squamous or cuboidal
* Morphology – Simple squamous / Simple cuboidal.
* Responsible for secretion of lubrication fluid.
* Morphology: DICT
* Adipose tissue ,Blood vessels and nerves present.
MYOCARDIUM
Middle layer of the heart.
* Morphology: Striated involuntary.
* Cardiac muscle fibers have striations. a single nucleus. involuntarily controlled. intercalated discs (ID):
* Attach adjacent cells to each other.
* Allow rapid transfer of electrical impulses between cells. with Purkinje fibers
- Connective tissue involvement:
- Endomysium – CT that supports individual muscle fibers.
- Perimysium – CT that supports bundles of muscle fibers (fascicle).
- Epimysium – CT that supports the entire heart muscle = epicardium.
ENDOCARDIUM
- Innermost layer of the heart.
- Endothelium:
- Thin epithelium lining the heart chamber
- Contains endothelial cells.
- Morphology: Simple squamous.
- Sub-endothelium:
- Fibrous connective tissue surrounding endothelium.
- Morphology: LOCT .
- Below endocardium:
- Conducting system of heart –conducting muscle fibers.
- Purkinje fibers – specialized type of cardiac muscle
INTRINSIC
CONDUCTING SYSTEM
- Heart muscle cells contract, without nerve impulses.
- Contraction regular, continuous way through sequential stimulation.
- Special tissues in the heart sets its pace:
- Sinoatrial node
- Atrioventricular (AV) node
- BUNDLE OF HIS
- Purkinje fibers
BASIC STRUCTURAL ORGANIZATION of the heart
Concentric layers of TUNICA (“coats”) that surrounds the lumen:
INNERMOST LAYER Tunica intima in blood vessels and the heart is the Endocardium
MIDDLE LAYER Tunica media in blood vessels and the heart is the Myocardium - thickest
OUTER LAYER Tunica externa/
adventitia (stretchy collagen fibers to prevent the vessels from bursting) in blood vessels and the heart is the Epicardium
Muscles involved:
* Smooth muscles in blood vessels; cardiac muscles in heart.
Nerves involved:
vasa vasorum and nervi vasorum- large blood vessels with their own blood supply and nervous stimulation
cardiac blood vessels and nerves have their own blood supply and nervous stimulation
capillary is the smallest and doesnt have the 3 tunics only the endothelium as the tunica since they are so thin
tunics in the blood vessels
TUNICA INTIMA
Endothelium + Subendothelium
ARTERIES: Smooth lining
VEINS: Smooth lining with valves to ensure one-way flow.
CAPILL: entire wall
INTERNAL ELASTIC LAMINA (IEL) Elastin fibers
ARTERIES: Separates Tunica intima from Tunica media
VEINS: Absent
CAPILL: Absent
TUNICA MEDIA Smooth muscles +elastic fibers
ARTERIES: constriction and dilation of vessels. THICK
VEINS: constriction and dilation of vessels. THIN
CAPILL: Absent
EXTERNAL ELASTIC LAMINA (EEL)
Elastin fibers
ARTERIES: Separates Tunica media from Tunica externa
VEINS: Absent
CAPILL: Absent
TUNICA EXTERNA /ADVENTITIA
COLLAGEN FIBERS- DICT
ARTERIES: flexible support that resists collapse and injury. THIN
VEINS: flexible support that resists collapse and injury. THICK
CAPILL: Absent
veins in tissue look more collapsed compared to the arteries because the arteries have more pressure in pumping than veins
ARTERIES
Transports blood away from the heart towards the capillary beds.
* Blood flows through large arteries → small arteries → arterioles → capillary beds → body tissues.
* Walls of arteries are muscular to accommodate changes in pressure.
*smooth muscle and elastic tissue.
* Thicker walls and smaller lumens than veins of similar size.
* Tunica media is the predominant layer
ELASTIC tissue
- Large arteries and thickest
- Tunica media contains sheets of elastic tissue (IEL and EEL).
- allow aorta and pulmonary
arteries to withstand pressure by distending and recoiling.
MUSCULAR tissue
- Medium arteries.
- Tunica media is composed of smooth muscles.
- The layer of smooth muscles is bounded by IEL and EEL.
- Regulate blood pressure, contraction and relaxation of smooth muscles. deliver blood to specific organs
SMALL ARTERIES &
ARTERIOLES
- Smooth muscle layer is thinner
+/- IEL. Disappears as the diameter becomes smaller. - Regulate blood pressure, deliver blood under low pressure to the capillary beds.
-distributes blood from the arteries
VEINS
Return blood from the capillary beds back to the heart.
* Lower blood pressure – further away from the pumping heart.
* Thinner walls and larger lumens than arteries of same size.
* Tunica adventitia predominant layer
* Large veins have valves that prevent backflow of blood.
* Skeletal muscle contractions aid in blood flow.
LARGE VEINS
- smooth muscles in the tunica adventitia.
- IEL and EEL absent.
- Tunica adventitia is the predominate tunic.
- Possess valves to prevent back-flow of blood.
MEDIUM VEINS
- Smooth muscle layer defined.
- IEL and EEL absent.
- Tunica adventitia is the predominate
tunic
SMALL VEINS &
VENULES
- Smooth muscles disappear as the
diameter of the veins decreases. - Tunica media and tunica adventitia is absent in venules.
- Walls lined by endothelium
CAPILLARIES types
CONTINUOUS capillaries
* Most common.
* Endothelium and basement membrane is continuous no pores
* Found in skin and muscle.
FENESTRATED capillaries
* Endothelium contains pores.
* Found in endocrine organs and portions of the GIT.
DISCONTINUOUS capillaries- Sinusoid
* Larger diameter.
* Slower blood flow.
* Endothelium has large pores.
* Found in liver and spleen.
