1.2 Histology of the cardiovascular system Flashcards
What is the function of the serous fluid?
To prevent friction when the heart is contracting within the thoracic cavity - lubricate
What is the structure & function of the fibrous pericardium?
a tough layer of CT continuous with the central tendon of diaphragm, non-distensible, prevents rapid overfilling of the heart
serious consequence e.g. cardiac tamponade
Where is the Transverse pericardial sinus?
posterior to ASCENDING aorta & pulmonary trunk
anterior to superior vena cava
superior to left atrium
What is cardiac tamponade?
Pericardial effusion can occur when there is accumulation of fluid within the pericardial cavity
heart becomes subjected to increased pressure, chambers become compressed, compromising cardiac output
Function of arteries & how they are classified?
carry blood away from heart to rest of body
classified as elastic (conduction) or muscular (distributing)
elastic arteries stretch during systole
muscular arteries branch into arterioles - control amount of blood into an organ/tissue by regulating blood pressure (constrict/dilate) - controlled by ANS
Name the groups of arteries from largest to smallest
arteries > arterioles > metarterioles > capillaries (smallest vessels in body)
Why does blood flow around body?
due to systolic pressure
Describe the structure of capillary walls
1 cell thick, allows exchange of substances between blood & tissue
can be continuous (no opening) / fenestrated (small openings in structure) / sinusoidal (large openings in wall allowing whole cells to move
surrounded by pericyte
What are pericytes?
branching network on the outermost surface of capillaries (endothelium), capable of dividing into muscle cells / fibroblasts during angiogenesis, tumour growth & wound healing
What is contained within the endothelium?
pericyte > basement membrane > endothelial cells
Which arteries tended to be elastic and which are muscular?
large arteries - elastic e.g. aorta (spring back during diastole to smooth out pressure changes)
medium arteries - muscular as they distribute into arterioles
elastic arteries > muscular arteries > arterioles > metarterioles > capillaries
Describe continuous capillaries
no gaps
in nervous, muscle & CT, lungs & secretory glands (don’t want leakage!)
joined by occluding (closed up) junctions
Describe fenestrated capillaries
small gaps in capillaries
in gut, endocrine glands & renal glomerulus
little ‘windows’ interrupt the endothelium
Describe sinusoid capillaries
discontinuous capillaries, larges diameter, slowest flow
in liver, spleen & BM
whole cells can move between blood & tissues through gaps & incomplete basal lamina (of basement membrane)
What do capillaries merge into?
capillaries merge to large vessels - venules
venules merge to form larger vessels - veins
Describe veins
similar to arteries, thinner wall & wider lumen
has semi-lunar paired valves to allow 1D blood flow (towards heart)
narrower than 1mm (thoracic / abdominal cavities don’t have valves)
What happens to veins when blood pressure not maintained? What is it determined by?
veins collapse
determined by ‘muscle-pump’ action in the leg (venous return) & pressure factors in abdominal & thoracic cavity
Describe postcapillary venules
similar to capillary walls (endothelial lining with pericytes)
more permeable than capillaries, larger lumen, lower pressure, fluid drains in (down pressure gradient) apart from inflammatory response: fluid & leukocytes (WBC) emigrate (drain out)
receive blood from capillaries
Describe venules
Larger lumen, smooth muscle fibres begin to associate with endothelium, tunica media being to appear (intermediate layer after tunica intima)
endothelium associated with pericytes / smooth muscle cells (thin wall)
valves present to prevent backflow
Describe Veins
Larger diameter (lower BP), thinner wall, more CT & fewer elastic & muscle fibres than accompanying arteries
Describe small & medium veins
developed adventitia (outermost), thin media & intima layers
Describe large veins
thicker intima, thin media, thick adventitia APART FROM superficial veins of the legs (thick muscular walls to resist distension - enlargement by gravity)
valves act with surrounding muscle contraction to push blood towards heart (1D)
What are venae comitantes? (vena comitans - singular)
deep paired veins, accompanying each side of a smaller artery
(3) vessels wrapped around artery, all contained within 1 sheath
pulsing of artery promotes venous return within adjacent, parallel & paired veins
blood vessel reach all parts of body apart form cartilage, epithelia & cornea
Describe all the different vessels blood travel through from capillaries to the heart
capillaries
are arteries & veins oxygenated or deoxygenated?
arteries oxygenated (apart from pulmonary artery - deoxygenated to lungs) veins deoxygenated (apart from pulmonary vein - oxygenated from lungs to heart)
What are the sections that vessel walls are split into?
tunica adventitia > tunica media > tunica intima
Describe the structure of tunica intima
endothelium, subendothelial layer, thick elastic lamina
What are end arteries?
terminal artery supplying all or most of blood to a body part without significant collateral circulation
progressive branching without developing channels connecting to other arteries
What are examples of end arteries?
coronary artery, splenic (spleen) artery, renal (kidneys) artery
what happens if end arteries are occluded?
insufficient blood supply to dependent tissues
What are examples of absolute end arteries?
central artery to retina, labyrinthine artery to internal ear
What is bridging (coronary artery)
compression of a segment of coronary artery during systole, results in narrowing of artery, opens up again in diastole
Describe the structure of arterioles
carries blood fro muscular arteries to metarterioles
Describe structures of tunica intima, media & adventitia
TI: inner layer of endothelial cells, thin layer of subendothelial CT (outer)
TM: single smooth muscle cell layer, completely encircles TI
TA: barely sufficient layers of fibroblasts
Describe metarterioles
supply blood to capillary beds
non-continous smooth muscle layer, individual muscle cells spaced apart
contains precapillary sphincter
What are precapillary sphincters and where are they located?
precapillary sphincters are muscles at the neck of capillary
each muscle cell acts as a sphincter, contracting to control blood flow through capillary bed
when sphincters are contracted, blood flow to capillary beds significantly reduced (higher pressure?)
How are capillary beds like when muscles are working hard?
capillary beds should be flooded to provide max oxygen & nutrients
What happens to the vessels in strenous exercise?
arterioles dilate, precapillary sphincters relax, increase blood flow to skeletal muscles
reverse for digestion : divert blood to vital organs (brain & heart) - constriction of arterioles to intestine to decrease blood flow
Describe the structure of capillaries
largest SA for gas & nutrients exchange
passing RBC nearly fills entire lumen - short diffusion distance
structure: single layer of endothelium & basement membrane
Gaps in capillaries
controlling which molecules & structures can leave capillary
continuous: only water & certain ions can leave
sinusoidal: cells & proteins can leave (larger structures) e.g. liver (large gaps in basement membrane as well as endothelium)
Describe the purpose of lymphatic capillaries
drains away any excess fluid which isn’t drained by the capillary bed
returns the extracellular fluid to the body at junctions of the internal jugular (right side of neck) & subclavian veins (left side of neck) - a pair
Inflammation & postcapillary venules
surrounds interstitum - tissues
pressure in venules increase in inflammation, higher than surrounding tissues, allow fluid to leak to site of inflammation with inflammatory cytokines & WBC’s
Name the layers of the heart muscle
endocardium –> myocardium –> visceral pericardium –> (serous fluid) –> parietal pericardium –> fibrous pericardium
visceral + parietal = serous pericardium
