Physiology

Blood composition

Plasma (55%) and formed elements (45%) such as erythrocytes, leukocytes, and thrombocytes

Erythrocytes

Red blood cells

Leukocytes

White blood cells

Thrombocytes

Platelets

Heart structure

A powerful dual pump network organised into four chambers. The right atrium which receives oxygen poor blood from body, the left atrium which receives oxygen rich blood from lungs, the right ventricle which pumps oxygen poor blood to lungs, and the thick walled left ventricle which pumps oxygen rich blood to entire body

Blood vessels

A network of tubes that deliver oxygen and nutrients to tissues as well as removes wastes. They’re regulated by the nervous system and hormones.

Arteries

Strong muscular vessels that carry oxygen rich blood away from the heart at high pressure

Capillaries

Tiny vessels connecting arteries and veins for rapid exchange with surrounding system via diffusion

Veins

Vessels carrying oxygen poor blood back to heart which work under low pressure to ensure blood doesn’t flow backward against gravity

Cardiovascular system regulation

Autonomic nervous system

Exercise blood flow

Rapidly increases blood flow to working muscles by increasing heart rate and pump strength while constricting blood flow to non-essential organs

Blood pressure measurements

Measured with two numbers to track active pumping and resting phases of heartbeat

Functions of Blood

Transport dissolved substances, regulate pH and ions, restricting fluid losses at injury sites, defence against toxins/pathogens, and stabilizing body temperature

Dissolved substances transported in blood

Oxygen, carbon dioxide, waste products, & hormones

Blood stabilization of body temperature

Absorbs heat from active muscles & distributes to other tissue

Blood cell formation

Formed elements are developed by hematopoiesis. Hemocytoblasts differentiate into myeloid stem cells and lymphoid stem cells

Myeloid stem cells

Give rise to RBC/erythrocytes, platelets, eosinophils, basophils, neutrophils, and monocytes

Lymphoid stem cells

Gives rise to lymphocytes which migrate to lymphatic system to complete maturation

Erythrocytes characteristics

High surface to volume ratio, biconcave discs (7-8um diameter), lots of haemoglobin molecules, no mitochondria, anucleate (no nucleus), live 120 days, and discs bend and flex entering small capillaries

Leukocytes characteristics

Nucleated cells, no haemoglobin, lives hours to weeks (memory cells last longer), roles in inflammation and infection with granular leukocytes, and agranular leukocytes

Functions of leukocytes

WBC’s accumulate at sites of infection/inflammation with lymphocytes recirculating between blood and tissues. WBC’s emigrate from blood compartment with adhesion molecules on WBC and endothelial cells allowing WBC’s to stick to endothelium then move to site of infection/inflammation via chemotaxis. Once at infection site WBCs carry out functions in response such as phagocytosis or further histamine release.

Granular leukocytes

Neutrophil/phagocytic, eosinophil/allergic reaction, and basophil/histamine

Agranular leukocytes

Monocyte and lymphocytes/immune (B cells, T cells, and NK cells)

Haemoglobin molecules

Transport oxygen and carbon dioxide

Blood typing

Cell surface proteins that identify cells to immune system with normal cells ignored and foreign cells attacked. For example, blood type A would attack B antigens but ignore A antigens.

Blood type difference

Genetically determined by presence/absence of RBC surface antigens, A, B or none, and Rh

Blood types

Type A has surface antigen A and antibodies to B

Type B has surface antigen B and antibodies to A

Type AB has surface antigens A and B with neither antibody

Type O has neither A or B surface antigens with antibodies to both A and B

Rhesus (Rh) factor

There are 5 Rh antigens with Rh factor only referring to D antigen. Rh positive has presence of D surface antigen, and Rh negative has abidance of D. RBC has surface antigen A and Rh antigen A positive

Cross reactions

Normal cells are ignored and foreign cells are attacked. Plasma antibody meets its specific antigen and blood will agglutinate and hemolyze

Cardiovascular system

A circulating transport system that involves the heart (a pump), blood vessels (conducting system), and blood (fluid medium). It functions to transport materials to and from cells.

Erythropoietin release

Released with anaemia, low blood flow to kidney, and damage to respiratory surface of lung

Blood doping

Packed red blood cells are separated from plasma. Increases haematocrit and viscosity. Problems include heart strain, blood clots, strokes, kidney damage, and heart attacks

Erythropoiesis

Production of new RBC’s

1.      RBC’s and WBCs ratio

RBC’s outnumber WBCs 1000:1

Thrombocytes/platelets characteristics

Cell fragments involved in human clotting system, dis shaped structures (2-4um diameter), no nuclei, circulate for 9-12 days, and removed by spleen

Thrombocytes/platelets functions

Release important clotting chemicals, temporarily patch damaged vessel walls, and actively contract tissue after cloth for formation

Platelet production

Thrombocytopoesis, occurs in bone marrow, and megakaryocytes break into 2000-3000 cell fragments in red bone marrow

Hemostasis

The cessation of bleeding, occurs in 3 phrases which are the vascular phase, platelet phase, and coagulation phase

Vascular phase

Lasts up to 30 minutes, contraction of smooth muscle of damaged blood vessel wall caused by damage to smooth muscle and endothelial cells, activation of platelets (release vasoconstrictors), and reflexes initiated by pain receptors

Platelet phase

Begins within 15 seconds of injury with platelets contacting and adhering to damaged tissue in blood vessel wall. They work through a positive feedback loop of aggregation with activated platelets releasing clotting compounds.

Platelet phase restrictions

Plug size restricted by inhibitory compounds, negative feedback and formation of blood clot isolation

Coagulation phase

Begins 30 seconds or more after injury with clotting factors promoting formation of prothrombinase. This converts prothrombin (enzyme produced by liver) into thrombin

Clotting factors

Liver enzymes, substances from platelets and damaged tissues

Thrombin

Thrombin converts soluble fibrinogen into fibrin which forms threats that trap formed elements forming the clot

Clot retraction and repair

Platelets pull on fibrin threads which results in the clot contracting drawing wound edges closer together. Fibroblasts form connective tissue and new endothelial cells repair vessel lining with clot eventually dissolved through action of plasmin (plasma enzyme)

Granular leukocytes

Neutrophils, eosinophils and basophils

Cardiovascular system organisation

Pulmonary circuit which carries blood to and from gas exchange surfaces of lungs. Systemic circuit which carries blood to and from the rest of body

Pulmonary circulation

Veins, liver, superior/inferior vena cava, pulmonary arteries, and right artium/ventricle

Systemic circulation

Arteries, digestive tract, abdominal aorta, pulmonary veins, left atrium/ventricle, and coronary

Heart location

Rests on diaphragm, situated in the mediastinum, with two thirds lying to the left of midline

Pericardium

Heart is enclosed and stabilised by pericardium, which is a fibrous network of collagen fibres that’s lined by a serous membrane. The pericardial cavity is filled with fluid to reduce friction.

Serous membrane layers

Outer layer is parietal pericardium which lines inner surface of tough pericardial sac. Inner layer is visceral layer (epicardium) which is attached to outer surface of heart

Heart wall

Has 3 layers which are the epicardium, myocardium, and endocardium

Endocardium

Continues with endothelial lining of great vessels

Myocardium

Cardiac muscle (cardiomyocytes) tissue which is the middle layer of heart wall ad bulk of heart tissue. It also provides the pumping action and contains cardiac muscle fibres, intercalated discs, and functions of intercalated discs.

Myocardium muscle fibres

Contain single central nucleus, connected via gap junctions and have very high aerobic capacity

Myocardium intercalated discs

Specialized contact points between cardiomyocytes which join cells via gap junction and desmosomes

Myocardium intercalated discs functions

Maintain structure, conduct action potentials, and enhance molecular and electrical connections which transfer force of contraction

Superficial heart anatomy

Great veins and arteries at the base. Pointed tip is apex. Coronary sulcus which divides atria from ventricles. Interventricular sulcus which separates left and right ventricles

Heart chambers separation

Muscles of atria and ventricles are separated by connective tissue, skeleton

Atria

Left and right atria separated by interatrial septum with septum having fossa ovalis which are shallow depressions in the wall where foramen ovale of foetal heart was which closes over at birth. The auricle is a flap of expandable atrium which is visible when not filled

Ventricles

Right ventricle pumps blood to pulmonary circulation and has a thinner wall with less pressure than left ventricle. Left ventricle pumps blood to systemic circulation and has a thicker wall with greater pressure and rounder in shape

Blood flow 1

Right atrium receives blood from systemic circulation via superior/inferior vena cava and coronary sinus. Right atrium to right ventricle through AV valve. Right ventricle to pulmonary trunk and pulmonary arteries then into pulmonary circulation

Blood flow 2

Blood passes through lungs and returns to heart through 4 pulmonary veins. Pulmonary veins to left atrium to left clavicle through AV valve then into systemic circulation via aorta.

Heart valves

Direct blood flow through and out of the heart with the valves preventing backflow of blood. It’s composed of dense connective tissue covered by endothelium.

Atrioventricular (AV) valves

Lie between atria and ventricles with the right AV tricuspid and the left AV bicuspid/mitral. Cusps linked to chordae tendinae to papillary muscle. Valves open and blood flows into ventricles when pressure in atria is greater than ventricles. Valves close and blood flows into aorta or PA when pressure in ventricles is greater than atria.

Semilunar valves

Between ventricles and major arteries (aorta and PA) and they prevent blood flowing back into heart. The pulmonary semilunar valve is at base of pulmonary arterial trunk and the aortic semilunar valve is at the base of the aorta. There’s no valves between veins and atria.

Coronary arteries

Branch from ascending aorta and fill upon diastole. They carry oxygenated blood to the myocardium through pulsatile blood flow and little flow during systole

Coronary sinus

Carries deoxygenated blood back to right atrium through a thin walled vein with no smooth muscle to alter diameter

Myocardial infarction

Blockage of coronary artery due to lack of oxygen to muscle resulting in muscle death and potentially a heart attack. It can be caused by atherosclerosis due to plaque build up in coronary arteries which can be increased with smoking, high BP and diabetes. Symptoms can be chest pain (arm, jaw), tightness, shortness of breath, nausea and sweating

Cardiac muscle fibre types

Autorhythmic fibres and contractile fibres. Excitable tissue to rapid spread of action potentials (gap junctions) to contract as a unit (syncytium).

Autorhythmic fibres

Specialised muscle fibres that initiate and conduct AP to from conduction system

Contractile fibres

99% of all muscle fibres that provide mechanical work of the pump.

Conducting system components

Sinoatrial (SA) node (peacemaker), atrioventricular (AV) node, AV bundle, right/left bindle branches, and Purkinje fibres

Sinoatrial (SA) Node

Spontaneously depolarises (80-100 times/min) with the rate of depolarisation modified by neurotransmitters from ANS.

Atrioventricular (AV) node

Spontaneously depolarises (40-60 times/min) with conduction slowing at AV node due to AV nodal delay. This delay allows atria time to contract and fill the ventricles.

Cardiac action potential

Resting membrane potential is -90MV with excitation (neighbouring cell) causing MP to go toward firing threshold (-75mV) to action potential to rapid depolarisation, plateau, and repolarisation.

Rapid depolarisation

Voltage gated sodium channels open and there’s a rapid influx of Na+

Plateau

Na+ channels close rapidly (+30mV) to NA+ efflux. Voltage gated slow Ca2+ channels open slowly for a long time to Ca2+ influx. This then balances slow Na+ outflow (0mV)

Repolarisation

Voltage gated slow Ca2+ channels close and voltage gated slow K+ channels open to cause a K+ efflux

Electrical events sequence

SA node mass of cells (peacemaker) spontaneously generates AP. Stimulus then spreads across atria and reaches AV node. AV nodal delay (100 msec) then causes atrial contraction to begin. AP spreads along AV bundle to bundle fibres and Purkinje fibres. AP then relays across ventricles with muscles of ventricles contracting.

Heart pumping efficiently criteria

Atria must contract before ventricles, coordinate excitation so that each heart chamber contracts as a syncitium. Two atria should contract together with two ventricles also contracting together. It’s achieved via interatrial and internodal pathways as well as AV nodal delay.

Cardiac cycle

The period between the start of one heartbeat and the beginning of the next including both contraction and relaxation. The phases are within any one chamber and are systole (contraction) and diastole (relaxation).

Electrocardiogram

Represents summed electrical activity of all cardiac cells recorded from skins surface. Each peak represents a different component of electrical events during cardiac cycle with mechanical events taking place in between peak segments.

Electrocardiogram sections

P wave (atrial depolarisation), PR segment (AV nodal delay with atria contracted and emptying), QRS wave (ventricular depolarisation), ST segment (ventricles contracting and emptying), T wave (ventricular repolarisation), and TP segment (heart at rest and ventricles (and atria) are filling

Action potentials

Specialised autorhythmic cells of the heart generate their own action potentials

Cardiac myocytes

Stimulated electrically to contract through cardiac action potential using calcium. It’s long length prevents summation and tetany.

Heart conducting system

Ensures coordinated distribution of electrical activity through sequence of electrical and mechanical events with atria contracting together and ventricles contracting together

Cardiodynamics

Movements of blood and forces generated during cardiac contractions

End-diastolic volume (EDV)

Volume of blood in each ventricle at end of ventricular diastole

End-systolic volume (ESV)

Volume of blood remaining in each ventricle at the end of ventricular systole (=40% of EDV)

Stroke volume (SV)

Volume of blood pumped out of each ventricle during single beat. SV=EDV-ESV. Most important factor in single cardiac cycle.

Ejection fraction

The percentage of EDV represented by SV (=60% of EDV)

Cardiac output

The volume pumped by left ventricle in one minute. Cardiac output is equal to Heart rate times by stroke volume. Cardiac output is adjusted by ANS and hormones depending on needs

Factors affecting cardiac output

Heart rate is affected by autonomic innervation and hormones. Stroke volume is affected by end-diastolic volume and end-systolic volume

Autonomic innervation

Both SNS and PNS innervate the SA and AV nodes and atrial and ventricular muscle cells. It’s controlled by cardiac centres in medulla oblongata. Reflex pathways regulate cardiac centres through baroreceptors and chemoreceptors (carbon dioxide/oxygen) and higher order CNS

Cardioacceleratory centre

SNS increases heart rate

Cardioinhibitory centre

PNS decreases heart rate

Autonomic innervation of the heart

Cardioinhibitory centre, vagal nucleus, cardioacceleratory centre, medulla oblongata, vagus, spinal cord and sympathetic/parasympathetic

Sympathetic autonomic innervation of the heart

Sympathetic preganglionic fibre, sympathetic ganglia, sympathetic postganglionic fiver, and cardiac nerve