1.2 Histology of the cardiovascular system

Question 1

What is the function of the serous fluid?

Answer 1

To prevent friction when the heart is contracting within the thoracic cavity - lubricate

Question 2

What is the structure & function of the fibrous pericardium?

Answer 2

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

Question 3

Where is the Transverse pericardial sinus?

Answer 3

posterior to ASCENDING aorta & pulmonary trunk
anterior to superior vena cava
superior to left atrium

Question 4

What is cardiac tamponade?

Answer 4

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

Question 5

Function of arteries & how they are classified?

Answer 5

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

Question 6

Name the groups of arteries from largest to smallest

Answer 6

arteries > arterioles > metarterioles > capillaries (smallest vessels in body)

Question 7

Why does blood flow around body?

Answer 7

due to systolic pressure

Question 8

Describe the structure of capillary walls

Answer 8

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

Question 9

What are pericytes?

Answer 9

branching network on the outermost surface of capillaries (endothelium), capable of dividing into muscle cells / fibroblasts during angiogenesis, tumour growth & wound healing

Question 10

What is contained within the endothelium?

Answer 10

pericyte > basement membrane > endothelial cells

Question 11

Which arteries tended to be elastic and which are muscular?

Answer 11

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

Question 12

Describe continuous capillaries

Answer 12

no gaps
in nervous, muscle & CT, lungs & secretory glands (don’t want leakage!)
joined by occluding (closed up) junctions

Question 13

Describe fenestrated capillaries

Answer 13

small gaps in capillaries
in gut, endocrine glands & renal glomerulus
little ‘windows’ interrupt the endothelium

Question 14

Describe sinusoid capillaries

Answer 14

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)

Question 15

What do capillaries merge into?

Answer 15

capillaries merge to large vessels - venules

venules merge to form larger vessels - veins

Question 16

Describe veins

Answer 16

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)

Question 17

What happens to veins when blood pressure not maintained? What is it determined by?

Answer 17

veins collapse

determined by ‘muscle-pump’ action in the leg (venous return) & pressure factors in abdominal & thoracic cavity

Question 18

Describe postcapillary venules

Answer 18

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

Question 19

Describe venules

Answer 19

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

Question 20

Describe Veins

Answer 20

Larger diameter (lower BP), thinner wall, more CT & fewer elastic & muscle fibres than accompanying arteries

Question 21

Describe small & medium veins

Answer 21

developed adventitia (outermost), thin media & intima layers

Question 22

Describe large veins

Answer 22

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)

Question 23

What are venae comitantes? (vena comitans - singular)

Answer 23

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

Question 24

Describe all the different vessels blood travel through from capillaries to the heart

Answer 24

capillaries

Question 25

are arteries & veins oxygenated or deoxygenated?

Answer 25

``` arteries oxygenated (apart from pulmonary artery - deoxygenated to lungs) veins deoxygenated (apart from pulmonary vein - oxygenated from lungs to heart) ```

Question 26

What are the sections that vessel walls are split into?

Answer 26

tunica adventitia > tunica media > tunica intima

Question 27

Describe the structure of tunica intima

Answer 27

endothelium, subendothelial layer, thick elastic lamina

Question 28

What are end arteries?

Answer 28

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

Question 29

What are examples of end arteries?

Answer 29

coronary artery, splenic (spleen) artery, renal (kidneys) artery

Question 30

what happens if end arteries are occluded?

Answer 30

insufficient blood supply to dependent tissues

Question 31

What are examples of absolute end arteries?

Answer 31

central artery to retina, labyrinthine artery to internal ear

Question 32

What is bridging (coronary artery)

Answer 32

compression of a segment of coronary artery during systole, results in narrowing of artery, opens up again in diastole

Question 33

Describe the structure of arterioles

Answer 33

carries blood fro muscular arteries to metarterioles

Question 34

Describe structures of tunica intima, media & adventitia

Answer 34

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

Question 35

Describe metarterioles

Answer 35

supply blood to capillary beds non-continous smooth muscle layer, individual muscle cells spaced apart contains precapillary sphincter

Question 36

What are precapillary sphincters and where are they located?

Answer 36

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?)

Question 37

How are capillary beds like when muscles are working hard?

Answer 37

capillary beds should be flooded to provide max oxygen & nutrients

Question 38

What happens to the vessels in strenous exercise?

Answer 38

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

Question 39

Describe the structure of capillaries

Answer 39

largest SA for gas & nutrients exchange passing RBC nearly fills entire lumen - short diffusion distance structure: single layer of endothelium & basement membrane

Question 40

Gaps in capillaries

Answer 40

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)

Question 41

Describe the purpose of lymphatic capillaries

Answer 41

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

Question 42

Inflammation & postcapillary venules

Answer 42

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

Question 43

Name the layers of the heart muscle

Answer 43

endocardium --> myocardium --> visceral pericardium --> (serous fluid) --> parietal pericardium --> fibrous pericardium visceral + parietal = serous pericardium