Cardiovascular physiology

Einstein diffusion vs time

Time is proportional to distance squared, meaning that small changes in distance result in large changes in tiMe. Therefore diffusion over long distances is far too slow.

Neuromuscular gap junction

0\.1 micrometer distance over which neurotransmitters diffuse, taking only 5 millionths of a second.

Cardiac infarct

Condition characterised by the formation of a dense wedge -shaped block of dead tissue in the heart muscle following an interruption to its blood supply

Ischaemia

Muscle that dies due to lack of oxygenated blood supply. The irony being that the adjacent cavity has copious amounts of richly oxygenated blood that cannot diffuse a few millimetres at an adequate rate.

Blood clot blockage/ ‘heart attack’

Thrombus (clot) → Ischaemia → Hypoxia → Necrosis

Ischaemia vs hypoxia

Lack of blood flow vs lack of oxygen

Primary function

Overcome the problem of moving chemicals long distances at a reasonably high speed. Using a pump and bulk flow.

Advantages of circulatory system

1. Organism can get bigger
2. Sustain a higher metabolic rate
3. Direct flow of metabolites between organs
4. Regulation of organ function

Disadvantages of circulatory system

1. Circulatory failure can be fatal
2. High pressure and flow requires control
3. High pressure = stress on vessels
4. Metabolically expensive

Hormones

Chemicals produced and secreted into the bloodstream by an endocrine gland. Carried to distant target organs to interact with receptors.

Adrenal glands

Endocrine organ situated on top of the kidney. Has two distinct zones: inner adrenal medulla and outer cortex.

Adrenal medulla

Makes and secretes adrenaline, a hormone which acts on the heart to increase heart rate and force of contraction.

Thermoregulatory control

A rise in core temp of 0.5°C causes blood vessels close to the skin to dilate, allowing heat loss. E.g. heat loss from rabbit ears.

Adaptation to hot environment

Desert mammals have disproportionately large ears to maximise the heat loss due to dilatation of peripheral circulation.

Immune system

Ciculatory system supports another key system by transporting white blood cells, platelets and red blood cells.

Open circulatory system

The heart pumps fluid through arteries that empty into a haemocoel, which bathes the organs, and return to the heart via veins.

Haemolymph

Fluid which has no distinction between blood and tissue fluid.

Disadvantages of open circulation

Limited control over velocity and distribution of blood flow. (However is usually not needed

Closed circulatory system

Blood does not leave the blood vessels and is sepearate from tissue fluid. Have relatively high blood pressure enabling quick transport to support high metabolic rate.

Squid

Organism with a closed circulatory system containing three hearts, one for each gill and one for the rest of the body.

Single circulation

FISH: Blood flows from the heart to the gills for gas exchange, then to the rest of the body and then back to the heart.≥

Double circulation

Amphibians, reptiles, birds and mammals. Blood flows from heart to lungs, then back to the heart to be repressurised, flow around the body.

Branchial cicuit

Vessels that serve the gills (respiratory organs)

Pulmonary circuit

Vessels that serve the lungs (respiratory organ)

Systemic circuit

Vessels that serve the rest of the body.

Trout dissection

Remove the **isthmus** (triangle of skin between the gills and pectoral fins), allows access to **pericardial cavity** (a sac). The triangular ventricle can be seen leadin to the **bulbous arteriosus** which represents the beginning of the **ventral aorta**, into which the ventricle ejects blood. Blood flows through the gills, becoming oxygenated and is taken to tissues via the **dorsal aorta**.

Amphibians

2 atria, 1 ventricle. Compensate for inefficiency by having rich vascular beds just beneath the surface of their moist skins, so blood returns to the heart already partially oxidised.

Birds and mammals

Septum separates atria and ventricles into two seperate chambers.

Aorta

Artery that takes blood from heart to systemic circulation

Arterioles

Small vessels connecting arteries and capillaries.

Capillaries

Tiny, 1-cell-thick walled vessels, that act as a bridge between arteries and veins. Thins walls allows oxygen and nutrients to pass from blood to tissues, and waste products vice versa.

Venules

Small vessels that connect veins to capillaries

Superior and inferior vena cava

Veins through which blood returns to the right side of the heart.

Pulmonary artery

Vessel that carries blood from the right ventricle to the lungs for oxygenation.

Pulmonary veins

Vessels that return oxygenated pulmonary blood to the left atrium.

Pericardial sac

Location of the heart, lower surface connected to the diaphragm.

Annulus fibrosus

Connective rings that surround the valves of the heart- the atria-ventricular (AV) valves and the semi-lunar/arterial valves.

Chordae tendinae

Collagenous tendons connected to the thin flaps of tissue of the AV valves. Tethered to papillary muscle, providing stability .

AV closing mechanism

Ventricle contracts, blood pushes against the underside of the valve forcing it into its closed position.

Tricuspid valve

AV valve that separates the right atrium from the right ventricle (R-S-T)

Mitral valve

AV valve that separates left atrium from left ventricle.

Semi-lunar valves

Separate the ventricles from the main arteries. Do not need connective tissues.

Aortic valve

Valve between left ventricle and AORTA

Pulmonary valve

Valve between right ventricle and PULMONARY artery

Tunica intima

Endothelium and its elastic connective tissue

10 micrometers

Nearly all cells in the body are within at least … of a capillary

Tunica media

Dense population of smooth muscle cells organised cocentrically with bands of elastic tissue. Varied thickness between vessels, e.g. thick layer in large elastic arteries to smooth pressure changed.

Tunica adventitia

Collagenous extracellular matrix containing fibroblasts, blood vessels and nerves. Functions to add rigidity and form.

Veins

Vessels that have relatively thin walls and large cross-sectional areas. Hold about 2/3 of the body’s blood.

Delayed compliance

Within tenths of a second, the pressure in a vessel returns to normal following a sudden increase or decrease. Result from smooth muscle cells changing length allowing the volume of the circulatory to inc or dec. (occurs in veins)

Darcy’s law

Q= ∆P/R i.e. liquids flow down pressure gradients from high pressure to low pressure against resistance

Perfusion pressure

Pressure difference between the arteries that supply a region and the veins that drain it.

Blood flow

= perfusion pressure / vascular resistance

Cardiac output

= blood pressure / vascular resistance

(because perfusion and blood pressure are almost equal as pressure in the venous system is only a few mmHg)

Stroke volume

Amount of blood pumped out of each ventricle per beat.

Heart rate

Speed of beating of ventricles

Determinants of blood pressure

Vascular resistance *x* cardiac output, where cardiac output = stroke volume x heart rate.

Laminar flow

A description of blood flow through a vessel where streams in the centre of the vessel travel the fastest, whilst those at the outside experience more pressure and are therefore slower. Forms a parabola shape.

Poiseuille’s Law

Shows how resistance is influenced by the length of the vessel, radius of the vessel and the viscocity of blood.

Haematocrit

Ratio of blood cells to plasma, indicative of blood viscocity.

Vasomotion

Change in vessel diameter, caused by nerves, hormones and local factors.

Vasodilatation- Increase

Vasoconstriction- decrease

Noradrenaline

Hormone that acts on receptors on blood vessels to increase vasoconstriction. Tonically active to maintain total peripheral resistance and arterial blood pressure.

Sympathetic tone

Vasoconstrictor which topically impose a squeezing tone on vessels to maintain total peripheral resistance. Withdrawing tone is the simplest way to dilate a blood vessel.

Dilation

Normally, adrenaline causes constriction, in skeletal muscle adrenaline can cause dilatation so that distribution of blood is to the areas.

Endothelium-derived relaxation factor (EDRF)

Term by which nitric oxide (NO) was first known by when it was released by vessel endothelium.

Nitric oxide (NO)

Chemical for which its formation is stimulated by substances that activate endothelial cells such as ACh. Produced via cleavage form the amino acid arginine by NO synthase.

Arginine

Amino acid from which NO is cleaved from

NO synthase

Enzyme that catalyses formation of NO, regulated by Ca²⁺ -calmodulin complex.

Ca²⁺-calmodulin complex

Intracellular complex that regulates NO synthase. Means that agents that promote extracellular calcium entry (ACh) increase the rate of NO synthase.

Sphygmomanometer

Used to estimate arterial blood pressure. Inflatable cuff encircles the upper arm and is inflated until pressure exerted is higher than the pressure driving arterial blood, causing blood flow to stop. Pressure is released until the Korotkoff sound is heard, representing highest artery pressure (shown on pressure gauge).

Korotkoff sound

Thumping sound with each wave of pressure.

Systolic pressure

Highest pressure at which the Korotkoff sound is first heard.

Diastolic pressure

Point at which the Korotkoff sound disappears, lowest arterial pressure.

120/80 mmHg

Average human arterial pressure, systolic/diastolic

Mean arterial blood pressure (MAP)

Diastolic plus a third of the difference between diastolic and systolic.

Arterial stiffness

Measure of the rigidity of blood vessels. Increases with age and cardiovascular disease. Vessels deposit calcium and collagen.

Increase in pulsality

Increase in systolic pressure relative to the diastolic pulse or an increase in the pulsality index (S-D/mean). Signify increased vascular resistance.

Exercise

NOT full body motion. But rather can be a single muscle/group of muscles. Doesn’t necessarily lead to changes in cardiac output, ventilation or adrenaline levels.

30-fold

Factor by which blood flow per unit of time in a rhythmically contracting muscle increases.

Local vasodilatation

Process caused primarily by local metabolites acting directly on the muscle arterioles. Explains the lag in return to normal blood flow once exercise has ended.

Metabolic autoregulation

More local metabolites, due to increased utilisation of oxygen. Therefore oxygen used=oxygen supplied, positive feedback loop.

Local metabolites

By-products of metabolism. E.g lactic acid and adenosine.

Dormant capillaries

Capillaries that have no blood flow at rest due to closed sphincters.

Recruitment of capillaries

Increased perfusion pressure during exercise opens dormant capillaries, shortening diffusion distance and contributing a 2-3 fold increase in surface area.

The cardiac cycle

Events associated with blood flow through the heart during one complete heartbeat. Systole, diastole, atria.

1. Atrial systole

Atria contract synchronously to provide the ventricles with last 20% of blood through the AV valves.

Atrial kick/boost

Additional blood forced into ventricles by atria

Jugular vein pulse

Seen due to the retrograde movement of blood into the venae cavae when the atria contract. (In the neck)

2. Isovolumetric contraction

Ventricular contraction without a change in ventricular volume. Forces the AV valves closed, pressure builds up.

3. Ventricular ejection

Pressure is generated by the ventricles, opening the semi-lunar valves (aortic valve on the left). High pressure blood is forced into the arteries, displacing low-pressure blood into the vasculature. Arterial pressure increases (blood enters faster than it can leave).

4. Isovolumetric relaxation

Ventricles begin to relax, rapid fall in ventricular pressure. Small amount of blood flows backwards closing the aortic valve, causes the dicrotic notch. Final third of ventricular blood flows away due to momentum.

Dicrotic notch

Brief rise in arterial pressure caused by closing of the aortic valve.

Stroke volume

Overall change in ventricular volume between ventricular ejection and Isovolumetric relaxation.

5. Late diastole

Both sets of chambers are relaxed and ventricles fill passively. End of cycle.

Phonocardiogram

Heard via auscultation through a stethoscope. First ‘lub’ is closure of AV valves. Second ‘dub’ is closure of semi-lunar valves.

Electrodes

Detect small changes in potential detected between different locations on the skin

Electromyogram

Recording of the burst of electrical activity taking place when the muscle is contracted.

Electroencephalogram

Electrodes are placed on the skull to record neuronal activity

Electrocardiogram

Process where small potentials (\~1mv) are recorded between different locations on the skin that reflect the underlying activity of the heart. The electrical events coupled to the mechanical events of the cardiac cycle.

Waves

Deflections above and below the baseline of an ECG.