Circulatory system Flashcards
what does the blood vascular system consist of?
it consists of the heart, arteries, arterioles, capillaries, venules and veins.
describe generally the heart…
the heart is made up of 4 muscular chambers, two atria and two ventricles. the chambers are surrounded by a fibroserous sac - the pericardium.
the heart receives sympathetic and parasympathetic inervation, which modulate but do not initiate the rate of the heartbeat.
what hormone doe the heart produce to control blood pressure?
- how is this control executed?
the heart produces atrial natriuretic peptide
the hormone increases sodium and water secretion by the kidneys, and inhibits the release of renin, both of which decrease blood pressure.
what are the cardiac layers of the heart?
- endocardium
- myocardium
- epicardium
what is endocardium?
endocardium lines the lumen of the heart with simple squamous epithelium and a thin layer of loose connective tissue.
the subendocrdium underlies the endocardium and contains veins, nerves and purkuinje fibres in a connective tissue layer.
what is the myocardium?
derived from splanchnic mesoderm, the myocardium is the muscular layer of the heart.
the muscle cells are arranged in a spiral fashion about the hearts chamberes and inserted into the fibrous skeleton.
the myocardium contracts to expel blood from the heart into the arteries for distribution.
what hormones do the specialised cardiac cells of the atria of the heart produce?
atria natruretic polypeptide, atriopeptin, cardiodilatin,
all hormones that maintain flud and electrolyte balance and decrease blood pressure.
what is the epicardium?
the epicardium os the outermost lining of the heart - the visceral layer of the pericardium.
outer simple squamous epithelium (mesothelium) lines inner fibroelastic connective tissue containing nerves and coronary vessels as well as adipose tissue.
what is the fibrous skeleton of the heart?
the fibrous skeleton is made of thick bundles of collagn fibres orientated in various directions.
it is there for support and eshtablished electrically impermeable boundries to autonomic influence within the heart.
what are the two types of heart valves?
- AtrioVentricular valves (AV)
2. semilunar valves
what are the two AV valves formed from?
- function
the AV valves are composed of a skeleton of fibrous connective tissue arranged like aponeurosis and lined by endothelium on both sides.
they attach to the annuli fibrosi of the fibrous skeleton
the right has 3 cusps (tricuspid valve)
the left has 2 cusps (bicuspid mitral valve)
the valves prevent backflow of blood from the ventricles into the atria.
what are the semilunar valves composed of?
- function
the semilunar valves are found in the pulmonary trunk and the aortic trunk.
each is composed of 3 cusps that when filled pushed towards each other, closing the vessel.
they are lines by endothelium on both sides separated by sparse strands of connective tissue
the valves prevent regurgitation of blood back into the ventricles in which it came.
what is the impulse path that initiates and regulates heartbeat?
SA node generates impulses that initiates contraction of the atrial muscle.
impulses are conducted to the AV node
then down the AV bundle of His in the interventricular septum where it divides into branches and continues as purkinje fibres.
where is the SA node of the heart located?
the SA node is the pacemaker of the heart composed of specialised cardiac cells located in the wall of the right atrium.
where is the AV node of the heart?
the AV node is located in the wall of the right atrium, adjacent to the tricuspid valve.
what purkinje fibres?
purkinje fibres are large modified cardiac muscle cells that make contact with cardiac muscle cells in the apex of the heart via gap junctions, desmosomes and fasciae adherentes
what is the purfpose of the ANS in the regulation of the heart beat?
the ANS modulates but does not generate the impulse that controls the heart rate and stroke volume.
sympathetic innervation accelerates the heart rate
parasympathetic innervation slows heart rate.
what is the function of arteries?
arteries conduct blood away from the heart to organs and tissues of the body.
what are the layers the compose arteries?
- tunica intima - inner layer
- tunica media - middle layer
- tunica adventitia - outer layer
what are the types of arteries?
- elastic arteries (conducting arteries)
- muscular arteries (distributing arteries)
- arterioles
- metarterioles
what are elastic arteries?
elastic arteries are large conducting arteries. mostly aorta and its major branches.
- elastic arteries help reduce blood pressure associated with heartbeat.
- small vessels (vasa vasorum) and nerves run in their tunica adventitia and tunica media.
- thick, concentric sheets of elastic membrane (fenestrated) are found in their tunica media.
what are muscular arteries?
muscular arteries are distributing arteries. they include mostly the named arteries of the body.
- medium in size (between elastic arteries and arterioles)
- tunica adventitia contains vaso vasorum
- tunica media is thick, composed of layer of smooth muscle larger muscular arteries. and possesses an external lamina separating their boundry with the tunica adventitia.
what are arterioles?
arterioles regulate blood pressue and are terminal arterial vessels. they are the smallest of arteries with diameters of less that 0.1mm.
- they have narrow lumen
- lumen size = wall size - tunica adventitia is scant
- tunica media is composed of two layers of smooth muscle cells
- tunica intima consists of endothelium, a basal lamina and scant connective tissue
what are metarterioles?
metarterioles are narrow vessels arising from arterioles and give rise to capillaries.
- surrounded by incomplete sings of smooth muscle cells
- possess single smooth muscle cells that surround the origin to capillaries (precapillary sphincter)
- the precapillary sphincter prevents blood flow into the capillary bed.
what is vasocontriction?
vasoconstriction primarily involves arterioles and reduces flow to a local region.
- stimulated by sympathetic innervation via vasomotor nerves.
- nerves DO NOT synapse onto the smooth muscle cells, however discharge the neurotransmitter norepinephrine that diffuses through the smooth muscle layers and induces contration of cells via gap junctions - reducing the luminal diameter of the arteriole.
what is vasodilation?
vasodilation is accomplished via parasympathetic innervation.
- nerve terminals secrete acetylcholine, whcih stimulated the endothelium to release nitric oxide (EDRF)
- nitric oxide diffused across the smooth muscle cells in the vessel wal and activates their cGMP system, resulting in relaxation, which dilates the lumen
what is the general structure of a capillary?
capillaries consist of a single layer of endothelial cells arranged as a continuum to form a cylinder, surrounded by a basal lamina and occasional pericytes.
the endothelial cells:
- are nucleated, polygonal cells with attenuated cytoplasm
- posses golgi complex, ribosomes, mitochondria, and some RER
- contain IF (desmin and vimentin) supportive function
- joined by tight junctions
- luminal diameter may only hold 1 RBC at a time
how can capillaries be classified?
- continuous (somatic) capillaries
- fenestrated (visceral) capillaries
- sinusoidal (discontinuous) capillaries
what are continuous capillaries?
located in nervous tissue, muscle, connective tissue, exocrine glands and lungs continuous or somatic capillaries lack fenestrae and have a continuous basal lamina.
they contain numberous pinocytic vesicles (except in CNS)
what are fenestrated capillaries?
located in endocrine glands, intestine, pancreas and glomeruli of kidneys fenestrated or visceral capillaries contain an endothelial cells that are perforated with fenestrae.
- opening are 60-80nm and bridged by a diaphragm (except in glomeruli)
they have a continuous basal lamina
what are sinusoidal capillaried?
located in the liver, spleen, bone marrow, lymph nodes and adrenal cortex, sinusoidal or discontinuous capillaries possess many fenestrae that lack diaphragms.
sinusoidal capillaries are larger than continuous and fenestrated capillaries with a diameter of 30-40nm
these capillaries DO NOT have a continuous basal lamina.
what is diapedesis?
diapedesis is the process of leukocytes leaving capillaries via intercellular junctions to enter surrounding tissue.
what are the metabolic functions of capillaries? (7)
- conversion: angiotensin I to angiotensin II
- deactivation: bradykinin, serotonin, thrombin…
- breakdown of lipoproteins
- release of prostacyclin - potent vasodilator
- release of NO and Endothelin I
- regulation of transendothelial migration (neutrophils)
- release of tissue factors»_space; blood coagulation
what two ways can blood bypass a capillary bed from arterioles?
- contraction of precapillary sphincters prevent blood flow into the capilary bed from metarterioles, thus diverting the blood through a throughfare channel connected directly to a small venule
- AV anastomoses are small vessels that directly connects arterioles to venules.
what are veins?
veins conduct blood from tisuees towards to the heart.
veins contain ~70% of bodys blood at any one time.
the walls of veins are composed of 3 layers:
1. tunica intima
2. tunica media
3. tunica adventitia (thickest and most prominent)
vaso vasorum are more numerous in veins than arteries
no distinct elastic lamina in veins.
what does the lymphatic vascular system consist of?
it consists of peripheral lymphatic vessels, lymphatic vessels of gradually increasing size, and lymphatic ducts.
what is the purpose of the lymphatic vascularture?
it collects excess tissue fluid (lymph) and returns it to the venous portion of the cardiovascular system.
it drains most tissue (except the nervous system and bone marrow)
