Regulation of the heart Regulation of the heart and vessel activities and vessel activities Romana Šlamberová, MD PhD Romana Šlamberová, MD PhD Department of Normal, Pathological and Department of Normal, Pathological and Clinical Physiology Clinical Physiology
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Regulation of the heart and vessel activities Romana Šlamberová, MD PhD Department of Normal, Pathological and Clinical Physiology.
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Regulation of the heart and Regulation of the heart and vessel activitiesvessel activities
Romana Šlamberová, MD PhDRomana Šlamberová, MD PhDDepartment of Normal, Pathological and Department of Normal, Pathological and
Clinical PhysiologyClinical Physiology
Distribution of blood Distribution of blood circulationcirculation
Total volume of blood in all vessels (intravascular volume): man: 5.4 l (77 ml / kg) woman: 4.5 l (65 ml / kg)
from that veins 75% large arteries 15% small arteries 3% capilaries: 7%
Resistance of blood Resistance of blood circulationcirculation
Total peripheral resistance: of all paralel restistance in the body
Actual resistance is given based on the lumen of vessels and viscosity of blood
Percentage portion of resistance in different types of vessels: large arteries 19% small arteries 47% capillaries 27% veins 7%
Resistance depends not only on type of vessel, but also on the actual situation of blood need in organs
Regulation of blood Regulation of blood circulationcirculation
Mechanisms of regulation: Local
Humoral (chemical) – O2, CO2, H+
Nervous Enzymatic and hormonal
General Fast = short-term (regulate blood pressure) Slow = long-term (regulate blood volume) –
several days
Local chemical regulatory Local chemical regulatory mechanismsmechanisms
The most obvious in the heart and the brain Goal: autonomic regulation of resistance
by organ based on its metabolic needs Principal: accumulation of products of
metabolism (CO2, H+, lactacid ) or consumption of substances necessary for proper function (O2) directly affects smooth muscles of vessels and induce vasodilatation
Local nervous regulatory Local nervous regulatory mechanismsmechanisms
The most obvious in the skin and mucous Goal: central regulation of blood distribution Principal: Autonomic nervous system
Sympaticus Vasoconstriction – activation of α receptors in vessels-
noradrenalin (glands, GIT, skin, mucous, kidneys, other inner organs)
Vasodilatation – activation of β receptors in vessels – adrenalin (heart, brain, skeletal muscles)
Local enzymatic and Local enzymatic and hormonal regulatory hormonal regulatory
mechanismsmechanisms Kinin ↑ = vasodilatation
Cells of GIT glands contain kallikrein – changes kininogen to kinin → kallidin → bradykinin (vasodilatation)
Kinins are any of various structurally related polypeptides, such as bradykinin and kallikrein, that act locally to induce vasodilation and contraction of smooth muscle.
A role in inflammation, blood pressure control, coagulation and pain.
Hormones of adrenal medula: adrenalin (vasodilatation), noradrenalin (vasoconstriction)
General fast (short-term) General fast (short-term) regulatory mechanisms (1)regulatory mechanisms (1)
Nervous autonomic reflexes Baroreflex
glomus caroticum, glomus aorticum Afferentation: IX and X spinal nerve Centre: medulla oblongata, nucleus tracti solitarii Efferentation: X spinal nerve, sympatetic fibres Effector: heart (atriums), vessels Effect: After acute increase of blood pressure –
activation of receptors – decrease of blood pressure (vasodilatation, decrease of effect of sympaticus)
Baroreceptor Baroreceptor sensitivitysensitivity
Depends on the tonus of n. vagus
People with low vagotonus have higher incidence of unexpected death
The sensitivity of baroreceptor reflex corresponds with good prognosis of life length (lower probability of heart attack)
Association between Association between bbaaroreceptor sensitivity and roreceptor sensitivity and
hypercholesterolemiahypercholesterolemia
Koskinen et al. 1995
Persons with higher level of LDL cholesterol have lower baroreceptor sensitivity
General fast (short-term) General fast (short-term) regulatory mechanisms (2)regulatory mechanisms (2)
Receptors in the heart Reflex of atrial receptors – mechano- and volumoreceptors
– activated by increased blood flow through the heart A receptors – sensitive to ↑ of wall tension after systole of
atriums B receptors – sensitive to ↑ of wall tension after systole of
ventricles Ventricular receptors – mechano- and chemical receptors -
activated in pathological cases Hypoxia of myocardium → decrease of heart rate
(Bezold-Jarisch reflex) → protection of myocardium of larger damage
General fast (short-General fast (short-term) regulatory term) regulatory mechanisms (mechanisms (33))
Humoral mechanisms Adrenalin – β receptors →
vasodilatation → ↓ peripheral resistance → blood from skin and GIT to skeletal muscles, heart and brain → ↑ minute heart volume
Frank-Starling’s law = initial length of the fibers is determined by the degree of diastolic filling of the heart, and the pressure developed in the ventricle is proportionate to the total tension developed.
The developed tension increases as the diastolic volume increases until it reaches a maximum, then tends to decrease.
Inotrophy = ability of muscle contraction and its dependency on other factors, e.g. initial tension of muscle fiber.
Ionotropic effect of heart rhythm ↑ heart frequency → ↑ amount of Ca2+ that
goes into heart cells → ↑ Ca2+ available for tubules of sarkoplasmatic reticulum → ↑ Ca2+ that is freed by each contraction → ↑ strength of contraction
Cardiomotoric centers Inhibition – ncl. Ambiguus (beginning of n. vagus
in medulla oblongata) Excitation - Th1-3 beginning of sympathetic fibres
Vasomotoric centers In brain stem (medulla oblongata, Pons Varoli) In the hypothalamus (controls activity of
vasomotoric centers in brain stem) Brain cortex – control both the hypothalamus and
the brain stem
Midbrain regions of CV Midbrain regions of CV controlcontrol
Area postrema
Nucleus tractussolitarius
Nucleus ambiguousCardiac decelerator center
Rostralventrolateralmedulla Cardiac accelerator centerVasoconstrictor center
Caudal ventrolateralMedullaFibers from this neurons project to the vasoconstrictor area and inhibit it
Ackermann
Cerebral chemoreceptorsCerebral chemoreceptors
Chemoreceptors in the medulla are most sensitive to pCO2 and pH and less sensitive to pO2
Reflex during decreased cerebral blood flow: increase in pCO2 and decrease in pH activates
chemoreceptors Increase in both sympathetic and parasympathetic
outflow Increased contractility, increased total physical
response, but decreased heart rate Intense arteriolar vasoconstriction redirects blood
flow to the brain
Sympathetic nerveSympathetic nerve activityactivity and arterial pressureand arterial pressure
•Decreasing blood pressure is followed with increasing sympathetic nerve activity•Vasoconstriction increases blood pressure
Respiration arytmiaRespiration arytmia
Heard frequency = 72 pulses/min, = pulse interval 0.83 s
During relaxation the frequency changes based of the respiration (RESPIRATION ARYTMIA) inspiration - increased frequency expiration – decreased frequency
Bradycardia = fysiological = deep long-term inspiration, deep forward bend and knee band = reflex changes of vagal tonus.
Tachycardia = fysiological = swallow (decrease of vagal tonus), change of position from lying or sitting to standing (ORTHOSTATIC REACTION).
Orthostatic reactionOrthostatic reaction
Changes in posture from supine position to standing
Mechanisms Blood pools in the veins of lower extremities Venous return to the heart decreases, cardiac
output decreases (Frank-Starling law) Mean arterial pressure decreases Decreased activation of baroreceptors Increased sympathetic outflow to the heart
and blood vessels and decreased parasympathetic outflow
Specific circulatory Specific circulatory systemssystems
Pulmonary and systemic circulation differs in their pressure and resistence. Pressure in pulmonary circulation is about 4 – 5 times lower than in systemic one.
Different organs have Differences in vascular resistance Differences in metabolic demands
Local control (intrinsic) Hormonal control (extrinsic)
Cerebral circulationCerebral circulation
15 % of cardiac output Is controlled by local metabolites
pCO2 (H+) is the most important vasodilator CO2 diffuses to vascular cells, forms H2CO3 (H+) Intracellular H+causes vasodilatation Increase in blood flow, removal of excess CO2
Decrease in pO2 increases cerebral blood flow
Many vasoactive substances do not affect cerebral circulation, do not cross the blood-brain barrier
Coronary circulationCoronary circulation
5 % of cardiac output Local metabolic factors
Hypoxia: increase in myocardial contractility – increased O2 consumption – local hypoxia
Hypoxia causes vasodilatation of the coronary arterioles – compensatory increase in blood flow and O2 delivery
Adenosine (from ATP) causes vasodilatation Mechanical compression of the blood vessels
during systole in the cardiac cycle – brief period of occlusion and reduction of blood flow
Pulmonary circulationPulmonary circulation
100% of cardiac output Lower pressure and low resistance Controlled by local metabolites, primarily by
pO2 (bellow 70 mm Hg) Opposite effect than in other tissue – hypoxia
causes vasoconstriction Mechanism – inhibition of NO production in
endothelial cells of blood vessel walls Redistribution of blood from poorly ventilated areas
to well-ventilated areas
Renal circulationRenal circulation
25 % of cardiac output Renal blood flow is autoregulated
Constant blood flow even when renal perfusion pressure changes (80-200 mmHg)
Renal autoregulation is independent of sympathetic innervation (transplanted kidney)
Angiotensin II – vasoconstrictor for both afferent and efferent arterioles, but efferent arteriole is more sensitive
Prostaglandins (E2, I2 – produced locally) – vasodilatation of both arterioles
At rest: activation of 1 (noradrenaline) receptors causes vasoconstriction, increased resistance and decreased blood flow
Activation of 2 (adrenaline) receptors causes vasodilatation
Local metabolites During exercise: local vasodilator – lactate,
adenosine, K+
Skin circulationSkin circulation
5 % of cardiac output Dense sympathetic innervation – regulates
blood flow for regulation of body temperature Increase core body temperature – decrease
sympathetic tone to the smooth muscle sphincters controlling A-V anastomoses - increase skin blood flow
Arteriovenous anastomoses – permit bypass of the capillary vessels
Fetal circulation (1)Fetal circulation (1)
The circulatory system of a human fetus works differently from that of born humans, mainly because the lungs are not in use: the fetus obtains oxygen and nutrients from mother through the placenta and the umbilical cord.
Blood from the placenta is carried by the umbilical vein.
About half of this enters the ductus venosus and is carried to the inferior vena cava,
while the other half enters the liver proper from the inferior border of the liver.
Fetal circulation (2)Fetal circulation (2)
The blood then moves to the right atrium of the heart. In the fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows from the right into the left atrium, thus bypassing pulmonary circulation (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid).
The majority of blood flow is into the left ventricle from where it is pumped through the aorta into the body.
Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the mother's circulation.
Some of the blood from the right atrium does not enter the left atrium, but enters the right ventricle and is pumped into the pulmonary artery.
In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs.
Postnatal development of Postnatal development of circulationcirculation
With the first breath after birth, the pulmonary resistance is dramatically reduced. More blood moves from the right atrium to the right ventricle and into the pulmonary arteries, and less flows through the foramen ovale to the left atrium.
The blood from the lungs travels through the pulmonary veins to the left atrium, increasing the pressure there.
The decreased right atrial pressure and the increased left atrial pressure pushes the septum primum against the septum secundum, closing the foramen ovale, which now becomes the fosse ovalis. This completes the separation of the circulatory system into the left and the right.
The ductus arteriosus normally closes off within one or two days of birth, leaving behind the ligamentum arteriosum.
The umbilical vein and the ductus venosus closes off within two to five days after birth, leaving behind the ligamentum teres and the ligamentum venosus of the liver respectively.
Differences between fetal and Differences between fetal and adult circulatory systemsadult circulatory systems
The fetal foramen ovale - the adult fosse ovalis. The fetal ductus arteriosus - the adult ligamentum
arteriosum. The extra-hepatic portion of the fetal left umbilical vein -
the adult ligamentum teres hepatis (the "round ligament of the liver").
The intra-hepatic portion of the fetal left umbilical vein (the ductus venosus) - the adult ligamentum venosum.
The proximal portions of the fetal left and right umbilical arteries - the adult umbilical branches of the internal iliac arteries.
The distal portions of the fetal left and right umbilical arteries - the adult medial umbilical ligaments.
Fetal hemoglobin differs from adult hemoglobin.
Fetal hemoglobin (1)Fetal hemoglobin (1)
Fetal hemoglobin differs most from adult hemoglobin in that it is able to bind oxygen with greater affinity than the adult form, giving the developing fetus better access to oxygen from the mother's bloodstream.
The P50 value for fetal hemoglobin (i.e., the partial pressure of oxygen at which the protein is 50% saturated; lower values indicate greater affinity) is roughly 19 mmHg, whereas adult hemoglobin has a value of approximately 26.8 mmHg.
Fetal hemoglobin (2)Fetal hemoglobin (2)
At birth, fetal hemoglobin comprises 50-95% of the child's hemoglobin.
These levels decline after six months as adult hemoglobin synthesis is activated, while fetal hemoglobin synthesis is deactivated.
Soon after, adult hemoglobin (hemoglobin A) takes over as the predominant form of hemoglobin in normal children.
Neonatal jaundice tends to develop because of two factors
Decrease of the number of erythrocytes. The breakdown of fetal hemoglobin as it is replaced with
adult hemoglobin The relatively immature hepatic metabolic pathways, which
are unable to conjugate bilirubin as fast as an adult.