Cardiovascular system
Brno, May 2024
• Overall concept of blood circulation
• Vessels
• Arteries
• Microcirculation
• Veins
• Lymphatics
• Heart
Lecture
Blood cardiovascular
Lymphatic vascular system
Cardiovascular system
= part of circulatory system
Circulatory s. = Closed tubular system
(carries fluids (blood, lymph) in tubes
Cardiovascular system – overall composition
Heart
PUMP
• moves bloood with all its elements
through the body
Blood vessels
TUBES
• distribute the blood to the cells
throughout the body and then
back to the heart
Three major types
Arteries
• deliver blood from the heart
to the capillaries
Capillaries
• intimate with body cells – place
of exchange between blood
and tissues
Veins
• carry blood from body to the heart
Blood vessels – several different flavours
Veins
ALWAYS return the blood to the heart
(contain about 2/3 body's blood at any given time)
Arteries
ALWAYS carry blood from the
heart to the periphery
LARGE
MEDIUM + SMALL
Microvasculature–<0.1mmMacrovasculature–diameter>0.1mm
Capillaries
Anastomosing tubules among
arteries and veins
= microvascular bed
For example
At ventricular diastole:
•the semilunar valves are closed
•no blood enters the arteries
•the blood moves forward due to the action of arteries
Blood vessels – flow of blood
Pulsatile to continuous
Due to specific
morphologies
of the vessels
Vessel type Diameter
(mm)
Blood velocity
(mm/sec)
Aorta 25 1 200 (systolic)
Arterioles 0.02-0.05 15
Capillaries 0.005-0.009 0.4
Venules 0.02 5
Inferior vena cava 30 80
…reflected by uneven distribution of blood
65 – 70% in veins
• Reservoir
• Lumens are larger than
in corresponding arteries
Capillaries
~ 100 thousand km (estimate)
&
only 5% of blood volume
&
largest surface area (~ 600 m2)
&
most of the cells are no farther
than 50 mm from a capillary.
Blood vessels – common building plan
(three-layered)
Lumen
Endothelium
Basement membrane +
Subendothelial connective tis.
Internal elastic lamina
External elastic lamina
Muscle layer
Adventitia
Tunica intima
Endothelial cells:
• polygonal, squamous, elongated
• covered by negatively charged glycocalyx (0.5 mm)
• provide repellent surface for cell elements
• glycocalyx - binding site for various regulators
• regulate permeability
• secrete regulators (e.g. interleukins,
Tunica media
• mainly smooth muscle (circularly arranged in layers)
• collagen and elastic fibers (lamelae), reticular fibers
• proteoglycans
• strenghten the vessels
• provide vasomotion
Tunica externa
• connective tissue (collagen 1 + elastin)
• home for vasa vasorum and nerve fibers
• continuos with stroma of the surrounding tissues
Arteries
Several categories accoriding to their: size + structure + function
Large = conducting = elastic artery
(aorta, common carotid, sabclavian a., common iliac a., pulmonary trunk)
Medium-sized = distributing = muscular artery (D > 1 mm)
(brachial, ulnar, femoral, renal, …)
Small artery (D = 0.1 -1 mm)
Arteriole (D < 0.1 mm)
Large = elastic = conducting arteries
Conducting
• their major function is to transport blood away from the heart
Elastic
• they absorb and store the contractile energy of the left ventricle and
transform the pulsatile flow of blood in smooth out
• during ventricular contraction (systole), the elastic laminae of conducting
arteries are stretched and reduce the pressure change
• during ventricular relaxation (diastole) ventricular pressure drops to a low
level but the elastic rebound of conducting arteries helps to maintain arterial
pressure
• as a consequence, arterial pressure and blood flow decrease and become
less variable as the distance from the heart increases
Large = elastic = conducting arteries
Lumen
Endothelium
Nerve
Basement membrane +
Subendothelium
Tunica media
Vasa
vasorum
Tunica adventitia
Tunica intima
100 mm
0.15mm2mm
Endothelium
• elongated cells - along the long axis
Subendothelial layer
• loose connective tissue
• contains many fine longitudinal elastic
fibres - these gradually merge into the
elastic components of t. media
• some smooth muscle cells near the
boundary with t. media - longitudinally
arranged
• place of atherosclerotic changes
Internal elastic lamina
• not clearly demarcated
• elastic fibers arranged circularly as
discontinuous fenestrated membranes
about 2.5 mm thick - about 50 lamellae
• smooth muscle cells - circularly
oriented, interspersed between elastic
membranes
• relatively thin
• loose connective tissue
• some elastic fibers – longitudinally
arranged, next to the t. media
• vasa vasorum and lyphatics (some into
t. media)
• nerves
Relatively thin wall as compared to their wide lumen (1/10 of the vessel diameter).
Large = elastic = conducting arteries
Tunica intima
Tunica media
Large = elastic = conducting arteries
Tunica intima
Monkey
H & E
x540
Tunica media
transition
Artery - Endothelium
Weibel-Palade bodies
• organelles that are unique to endothelial cells
• contain von Willebrand factor (activates coagulation factor VIII) + P-selectin
Arteries - Atherosclerotic changes
Endothelial injury
(upon predispozing factors)
Production of ROS Oxidizing of LDL Entry of monocytes Plaque formation
(conversion to foam cells) (necrosis + lipid accumulation)
subendothelium
Arteries - Atherosclerotic changes
Atheromatous plaque
Artery clogging
Muscular arteries = distributing arteries
Distributing
• distribute blood to specific destinations/organs
• size varies from centimeter down to just visibility by unaided eye
Muscular
• they regulate the perfusion of different parts of the body under
physiological conditions
Muscle arteries = distributing arteries
Endothelium
• elongated cells along the long axis
• well developed adhesion, tight, and gap
junctions
• Glycocalyx
Subendothelial layer
• thickness increases with age
• loose connective tissue
• many fine longitudinal elastic fibres
• some smooth muscle cells
Internal elastic lamina
• well developed
• relatively thíck (~ ½ of the tunica media)
• collagen and elastic fibers
• some fibroblasts and adipocytes
• vasa vasorum and lyphatics (some into t.
media)
• nerves – efferent – maximal in small caliber
arteries
• very thick
• concentrically arranged smooth muscle cells
• up to 50 layers of smc
• ECM with elastic, collagen and reticular
fibers
• GAP junctions between smc (coordination)
External elastic lamina
• well demarkated only in large caliber arteries
Lumen
Endothelium
Subendothelium
Tunica media
Tunica adventitia
Tunica intima
Internal elastic lamina
External elastic lamina
Muscular artery
Muscular arteries = distributing arteries
Muscle arteries = distributing arteries
Undulation - Artefact
(due to postmortem contraction of smooth muscle cells)
Muscle arteries = distributing arteries
Elastic stain
Muscle arteries = distributing arteries – small sized
- peripheral resistance vessel (along with arterioles)
- internal elastic lamina is clear x external elastic lamina is not distinguished
-
the tunica media contains 3 to 10 layers of smooth muscles
Muscle arteries = distributing arteries – small sized
Muscle arteries x Elastic arteries
Elastic elements predominate in their wallsSmooth muscle cells predominate in their media
Arterioles
- peripheral resistance vessel (along with small-sized arteries)
- part of the microcirculation (terminal circulation)
- internal diameter < 0.1 mm
- they regulate the flow of blood through capillary bed
Endothelium
• elongated cells along the long axis
Subendothelial layer
• non-developed
Internal elastic lamina
• non-developed
• reduced to only sheeth of collagen fibers
• NO vasa vasorum
• thin (still the major part of the wall)
• 1 to 2 layers of smooth muscle cells
External elastic lamina
• non-developed
Lumen
Endothelium
Subendothelium
Tunica media
Tunica adventitia
Tunica intima
Internal elastic lamina
External elastic lamina
Muscular artery
Arterioles
Capillaries
- are the site where materials carried in the blood are unloaded and other materials are loaded into the blood
- are the thinnest, simplest, largest, longest, and most widely distributed functional unit of the blood vascular system
- are inserted between arterial and venous limbs of the circulation
- branch extensively to form elaborate networks, the extent of which reflects the activity of an organ or tissue
- are the largest part of the microcirculation (along with arterioles and venules)
The total length of all the capillaries of
the human body =
about 100 000 km
Maximal distance of tissue cell from
the capillary =
about 50 mm
The length of the capillaries usually
varies between
about 0.25 and 1 mm
The total cross-sectional area of
capillaries =
about 800 x
greater than of the aorta
Capillaries
Extensive vasculature of renal cortex (perfused by red dye)
Paritubular capillaries
Scarse in: tendons, ligaments
Absent from: cartilage, epidermis, cornea
Capillaries
Capillary wall
Endothelium
• single layer, squamous
• serrated (wavy) cell borders
• zonulae occludentes + desmosomes + GAP junctions
Basal lamina
„Envelope“
• pericytes (+ reticular fibers and macrophages)
average diameter about 8 mm
Basal lamina
Endothelium
Pericyte
Capillaries
Rabbit mesentery (H+E; 600x)
Arteriole
Precapillary
sphincter
Capillary
Only about 25 - 50 % of capillary volume is actively
moving (containing) blood under normal conditions.
20-30
Capillaries – Regulation of blood flow
Capillaries
Pericyte
Striated muscle
Cerebellum (monkey)
Capillaries
According to the integrity of the endothelium and basement membrane – by TEM:
• Continuous capillary
• Fenestrated capillary
• Sinusoidal
Capillaries - Continuous
How ?
• non-interrupted lining
• no defects in the wall (endothelium + basal
lamina
Where ?
• most common type
• muscle, connective tissue, nerve tissue
(blood-brain barrier), exocrine glands
Capillaries - Fenestrated
How ?
• endothelial cells perforated (diameter ~60-80
nm; diphragm 4-6 nm)
• continuous basal lamina
Where ?
• in tissues where rapid interchange of
substances occurs between the tissue and
the blood
• intestinal mucosa, some endocrine glands,
pankreas, choroid plexus, ciliary body, …
• kidney glomeruli(no diaphragm over fenestrae)
Fenestrae with diaphragm
Fenestrated capillary - kidney
Diaphragm
Capillaries – Sinusoidal - Discontinuos
How ?
• enlarged diameter (up to 40 mm)
• endothelial cells with large pores without
diaphragm
• large clefts between endothelial cells
• discontinous basal membrane
(or even absent)
• pericytes are absent (macrophages instead)
Where ?
• liver (pores 100 nm)
• hematopoietic regions (bone marrow)
• endocrine glands (adenohypophysis, islets
of Langerhans)
Sinusoid
Capillaries – Sinusoidal - Discontinuos
Bone marrow
Blood vessels – several different flavours
Veins
ALWAYS return the blood to the heart
(contain about 2/3 body's blood at any given time)
Arteries
ALWAYS carry blood from the
heart to the periphery
LARGE
MEDIUM + SMALL
Microvasculature–<0.1mmMacrovasculature–diameter>0.1mm
Capillaries
Anastomosing tubules among
arteries and veins
= microvascular bed
Veins – capacitance vessels
- they function as blood reservoir - greater capacity for blood containment than arteries due to thinner wall
- lower blood pressure (10 mm Hg with little fluctuation)
- valves aid skeletal muscles in upward blood flow (typically in lower limbs – veins with diameter > 2 mm)
Three layered bulding plan
= paired duplication
of t. intima
Endothelium
• very thin
Subendothelial layer
• very thin
Internal elastic lamina
• missing or only very thin
• well developed – thickest layer
• often with longitudinally arranged
bundles of smooth muscle cells
• robust vasa vasorum (often penetrate
deep to t. media)
• relatively thin (except for lower limbs)
• Little bundles of smooth muscle cells
• collagen fibers – considerable amount
External elastic lamina
• non-developed
General features
Veins – Categories according to their diameter
Postcapillary venules
• endothelial cells + some pericytes
• receive blood from capillaries
• more porous than capillaries
• larger diameter than capillaries (15-20 mm)
Small- & Medium-sized veins
• most have individual names
• run parallel with corresponding arteries
• many have valves
Large veins
• close to the heart
• (v.cavae, pulmonary veins, internal jugular veins)
• paired with elastic arteries
• diameter > 10 mm
• with valves
• t. media is thin (muscle cells+connective tissue)
• thick t. externa (with longitudinal bundles of
smc; myocardial sleeves)
Collecting & Muscular venules
• increasing number of contractile cells
• tunica media is defined in muscular venules
Artery Vein
Veins – Middle-sized
Veins - Large
Vena cava
Bundles of smooth muscle cells
Veins – Valves
Appearence of internal surface Histological view
- bag-like protrusion of tunica intima, which prevent the blood flow
from running to opposite direction
- only in the veins that has low position or far away from heart
Lymphatic vessels
Thoracic duct
Right lymphatic
duct
- return fluid from tissues to the circulatiory system
- depend on skeletal muscles to move fluid
Lymphatic capillaries
•blunt ended
•very simple structure
•endothelial cells + fine reticular fibres of circular orientation
•the basal lamina is not developed
Lymphatic vessels and ducts
•thin walled tubes
•resemble veins in their structure (intima+media+adventitia)
•have valves
Lymphatic vessels
Heart - Anatomy
- a hollow organ that contracts rhytmically
- it functions as a pump
- it is composed of two sets of chambers:
Receiving atria
Right Left
Discharging ventricles
Right Left
- it is equipped by four valves
(blood can travel in only one direction)
Aortic semilunar
Pulmonary semilunar
Atrioventricular tricuspid
(right)
Atrioventricular bicuspid
(left)
Heart - Wall
Endocardium
• endothelium
• subendothelial layer
• subendocardial layer
Myocardium
Epicardium
• mesothelium
• submesothelial layer
inner surface
outer surface
Heart - Endocardium
inner surface
- is continuous with the tunica intima of the large vessels entering and leaving the heart
- the endocardium of the left half of the heart is not continuous with the one on the right
half as it is separated by a heart septum
- valves are derivatives of endocardium
Subendothelial layer
• connective tissue
• collagen, elastics, solitary smc, small blood vessels, nerves
Subendocardial layer
• loose connective tissue
• continuous with endomysium of the myocardium
• nerve fibers, vessels, impuls-conducting system
Purkinje fibers
Endothelium
• with continuous basal membrane
Heart - Myocardium
- its thickness varies in different parts (thickest – left ventrikle; thin in atria)
- has rich blood supply (many capillaries)
- has no regenerative capacity
- muscle fibers are arranged circularly around chambers
- masses of connective tissue in between the muscles – cardiac skeleton
(anuli fibrosi in valves, trigonum, septum membranaceum)
inner surface
left
ventricle
wall
right
ventricle
wall
interventricular
septum
Intercalated discs
Atrial natriuretic peptide
(endocrine function of contractile cells; acts on kidney)
Heart - Epicardium
- represents visceral layer of the pericardium
inner surface
Mesothelium
Mesothelium
• simple squamous epithelium
• basal lamina
• secretes pericardial fluid
Submesothelial layer
• loose connective tissue
• elastic fibers
• nerves
• blood and lymphatic vessels
• home of coronary vessels
• adipocytes (high in obese individuals)
Pericardium
Fibroserous sac enveloping heart
• mesothelium with basal lamina (faces epicardium)
• fibrous layer (dense connective t. with vessels and nerves)
Heart - Valves
- composed of connective tissue layers covered by endothelium on each side
Fibrosa
• dense core of connective tissue
Ventricularis
• dense connective tissue with
many elastic and collagen fibers
Spongiosa
• loose collagen
Atrial side
Ventricular side
Heart – Conducting system
- specially modified cardiac muscle cells (non-contracting, less myofibrils, abundant GA junctions)
- generate and conduct impulses of heart contraction to various parts of myocardium
- assure proper succession of beat of atria and ventricles
Sinoatrial node (node of Keith-Flack)
• it lies on the medial wall of the right atrium near the
entrance of the superior vena cava
• PRIMARY PACEMAKER
Atrioventricular bundle (bundle of Hiss)
• it divides into 2 branches (for the left and right
ventricles)
Purkinje fibres
• terminal ramifications of the AV bundle
Atrioventricular node (node of Ascoff and Tawara)
•it runs on the right side of the interatrial septum
•SECONDARY PACEMAKER
Purkinje fibers
Sinoatrial
node
Atrioventricular
node
Atrioventricular
bundle
Heart – Conducting system
Contractile cardiomyocytes
Signal-conducting Purkinje cells
Heart – Coronary circulation
- blood in the heart chambers does not nourish the myocardium
- the heart has its own nourishing circulatory system: Coronary arteries & veins
- 5-7% of blood flows through the coronary arteries
- blood empties into the right atrium via the coronary sinus
Thank you for your attention !
Questions and comments at:
ahampl@med.muni.cz