functional histology of CVS Flashcards
what are the principal function of the cardiovascular system (5)
1.mediates continuous movement of all body fluids
2. transports oxygen and nutrients to tissues
3. transports carbon dioxide and other metabolic water products from tissue
4. involved in temperature regulation
5. distribution of molecules (hormones) and immune cells
what are the the two components of the circulatory system
blood vascular system; lymph vascular system
what are capillaries
a complex network of thin tubules where the interchange between blood and tissues takes place
tunica intima composition
a single layer of extremely flattened epithelial cells (the endothelium); supported by a subendothelial basement membrane (vessels >1mm) and delicate collagenous tissue
tunica media composition and function
smooth muscle and elastic fibres, regulated by the sympathetic nervous system; controls vasoconstriction/dilation
tunica externa composition
collagen fibres that protect and reinforce vessels; vasa vasorum in larger vessels
what is the vasa vasorum ?
a specialized microvasculature that play a major role in normal vessel wall biology and pathology - a vascular network (arterioles, capillaries, venules) that supplies the walls of large blood vessels; provides metabolites to the externa/outer media
functions of the endothelium (3)
- acts as a selective permeable antithrombotic barrier
- determines when/where WBCs leave the circulation for interstitial space of tissue
- secretes paracrine factors for vessel dilation, constriction and growth of adjacent cells
what arteries are large elastic arteries (6)
aorta and its large branches (innominate, subclavian, common carotid, iliac); pulmonary arteries
large elastic arteries (LEA) structure and how it helps function
tunica media elastic fibres allows expansion with systole and recoil during diastole,
thereby propelling blood forward; Alternating perforated layers of elastic laminae; High elastic fibres within artery wall ensures continuous UNIFORM blood flow; During systole blood is pushed through artery as media expands; Elastic recoil of vascular wall propels blood through distal vessels during diastole (maintaining blood flow)
elastic conducting arteries structure and function
large lumen which allows low-resistance conduction of blood and acts as a conduit; contains elastin in all 3 tunics; withstands and smooths out large BP fluctuations; allows continuous flow of blood through body
muscular arteries structure and function
intima consists of an endothelial lining and small amount of connective tissue; well developed internal elastic lamina separates the tunica intima from the media; thicker tunica media (than other similar sized vessels), narrower lumen and thickened elastic laminae; more smooth muscle than LEAs which allows for vasoconstriction/dilation; external lamina lies between the tunica media and externa; tunica externa composed of collagen, elastic fibres and vasa vasorum; diameter changes to regulate flow to organs as needed
examples of muscular arteries
coronary; renal
key structural feature of muscular artery (4)
intima has an internal elastic membrane; thick tunica media in proportion to lumen; elastic fibres generally in intima/externa; external elastic membrane in some t.externa layers
key structural features of elastic arteries
media has alternating layers of smooth muscles and elastic fibres; t.externa has collagen, elastic fibres and fibroblasts
structure of small arteries/arterioles
tunica intima - endothelium + basement membrane; thin subendothelial connective tissue; internal elastic lamina (small arteries only)
tunica media - between 3-8 layers of circularly arranged smooth muscle in small arteries (1/2 in aterioles); some collagen, elastic fibres and ground substance (little in arterioles)
tunica externa - thin layer of connective tissue that blends with the surrounding connective tissue
function of small arteries/arterioles
to regulate blood distribution to tissues/organs; modulation of blood flow and pressure by changing lumen size - pressure and velocity of blood flow are both sharply reduced making the flow steady rather than pulsitile
main role of arterioles
control point for regulation of physiological resistance to blood flow
fluid flow resistance equation and what it indicates
R ∝ 1/(d^4); i.e. small changes in the anteriolar lumen size has profound flow limiting effects
structure and function of capillaries
lumen just big enough for single erythrocytes; composed of a single layer of endothelial cells surrounded by basement membrane; nutrient/waste exchange in tissues - some have more specific functions
3 types of capillaries and where they are found
continuous - muscle, lungs, CNS
fenestrated - endocrine glands, sites of metabolic/fluid absorption e.g. kidney
discontinuous/sinusoidal - liver, spleen, bone marrow, lymphoid tissue
structure of skin/muscle continuous capillaries (3)
endothelial cells provide an uninterrupted lining; cells held together with tight junctions; intracellular clefts of un-joined membranes allow the passage of fluids
structure of brain continuous capillaries
make up the blood-brain barrier; have tight junctions completely around the endothelium (no intercellular clefts or un-joined membranes)
structure of fenestrated capillaries
endothelium riddled with pores (fenestrations); greater permeability to solutes/fluids than other capillaries; found wherever active capillary absorption/filtrate formation occurs
structure of sinusoid capillaries
highly modified, leaky, fenestrated capillaries with large lumens; endothelial cells form a discontinuous layer with wide spaces between them; multiple fenestrations without diaphragms; basal lamina is discontinuous; large molecules can pass between blood and surrounding tissue
vein classifications (3)
venules; medium sized veins; large veins
venule structure
endothelial layer backed by basal lamina (may have pericytes); may be supported by a thin layer of smooth muscle; large lumen compared to wall
capillaries -> muscular venules
gradual transition: capillary -> postcapillary venule -> converge into larger collecting venules (have contractile cells and recognisable tunica media) -> muscular venules (media composed of 2/3 layers of smooth muscles)
what occurs in post capillary venules
the primary site at which white blood cells leave the circulation at site of infection or tissue damage
how is blood pushed through the veins
by the contraction of the tunica media and external compressions from surrounding muscles and other organs
how is blood pushed through the veins
by the contraction of the tunica media and external compressions from surrounding muscles and other organs
how is blood pushed through the veins
by the contraction of the tunica media and external compressions from surrounding muscles and other organs
structure of veins
tunica intima - thin subendothelial layer, folded to form valves = no internal elastic lamina= prevent back
flow of blood
tunica media - small bundles of smooth muscle cells intermixed with reticular and elastic fibres
tunica externa - collagenous
large veins tunica externa structure
tick; frequently contrains longitudinal bundles of smooth muscle; elastic fibres but not laminae like in arteries
special features of veins
contain valves (most prominent in legs where blood has to travel against gravity); muscular contraction (aids the return of blood to the heart)
arteries vs veins
artery - narrow lumen, thicker tunica media, intima separated by internal elastic lamina
vein - larger lumen, tunica externa is thickest, tunica intima is folded to form valves
3 layers of the heart wall
endocardium; myocardium; pericardium
what hormone is produced by the heart and what does it do
atrial natriuretic factor; secreted in relation to atrial stress, acts on the kidney to increase sodium excretion and GFR, to antagonize renal vasoconstriction, and to inhibit renin secretion
what is the fibrous skeleton and its function
the fibrous central region of the heart; serves as the base of the valves and the site of origin/insertion of the cardiac muscles; it acts as an insulator between the atria and ventricles (insulating AV septum)
structure of fibrous skeleton
dense connective tissue rings surround the valves of the heart, fuse and merge with the intraventricular septum; sinospiral and bulbospinal muscles; plate of fibrous connective tissue between atria and ventricles
why is the insulation of the fibrous heart skeleton essential
allows for the delay of impulse conduction between atria and ventricles as well as for the upward contraction through the ventricles; ensures muscle impulses are not spread randomly throughout
endocardium structure
homologous with the intima of blood vessels - single layer of endothelial cells resting on a subendothelial layer (a layer of loose connective tissue that contains elastic and collagen fibres with some smooth muscle)
subendocardial layer structure
a layer of connective tissue which attaches the subendothelila layer to the myocardium; contains veins, nerves and branches of the impulse conducting system (Purkinje fibres)
myocardium structure
the thickest of the heart tunics; cardiac muscle cells arranged in layers that surround the heart chambers in a complex spiral
epicardium structure
simple squamous epithelium (mesothelium) supported by a thin layer of connective tissue; serous membrane (visceral pericardium)
what is the parietal pericardium
the serous membrane that forms the outer wall of the pericardial cavity - forms the pericardial sac alongside a dense fibrous sac
subepicardial layer structure
loose connective tissue which contains veins, nerves and nerve ganglia + adipose tissue that surrounds the heart
5 elements of the cardiac conduction system
- SAN (pacemaker)
- AVN (gatekeeper)
- bundle of His
- left and right bundle branches
- purkinje fibres
what does the bundle of His split into
left and right bundle branches
lymphatic vascular system
lymphatic capillaries -> closed ended tubules -> anastomose to form vessels of increasing size -> terminate in the blood vascular system -> empty in large veins near the heart
