Heart and Circulatory System Physiology

Physiological Measures of the Heart and Circulatory System

Heart Rate (HR)

• It is the number of heartbeats per minute
• The average HR in a healthy adult is about 70 beats/minute
• Increased heart rate is called tachycardia
• Decreased heart rate is called bradycardia
• Sympathetic effects increase HR
• Parasympathetic effects decrease HR
• Children usually have a higher HR than adults

Stroke Volume (SV)

• It is the amount of blood ejected from one ventricle during one systole
• The average SV in adults is about 70ml/systole
• Sympathetic stimulus increases SV
• Parasympathetic effects practically do not alter SV due to few parasympathetic nerves in the ventricles

Cardiac Output (CO)

• It is the volume of blood pumped by each ventricle per minute, usually expressed in liters
• It is the amount pumped by each ventricle, not the total amount pumped by both ventricles
• Calculated by multiplying heart rate (HR) and stroke volume (SV)
• CO = HR (70 beats/min) * SV (0.07L/beat) = 4900 ml/min = 5.0 L/min
• During exercise, the cardiac output may reach 20 to 30 L/minute
• Heart rate, stroke volume, the autonomic nervous system, and hormones influence the cardiac output

End Diastolic Volume (EDV) and Residual Volume (RV)

• End diastolic volume is the amount of blood in one ventricle at the end of diastole
• During diastole, more than 70ml of blood, often 140 ml, goes into each ventricle
• Stroke volume increase leads to EDV decreasing
• EDV - SV = RV (residual volume)
• 140 ml - 70 ml = 70ml
• Normally, 70 ml of blood remains in the ventricles in every systole, which is termed Residual volume
• Stroke volume can be increased during stress because of the presence of residual volume, which will result in increased cardiac output

Blood Flow

• It refers to the amount of liquid passing one point in a unit of time
• It is the movement of blood from arteries to capillaries and then to veins
• Blood flows from high-pressure areas to low-pressure areas, following the decreasing pressure gradient from arteries to capillaries to veins
• The rate, or velocity, of blood flow is inversely related to the total cross-sectional area of blood vessels
• Blood flow is slowest in the capillaries allowing time for gas and nutrient exchange
• Resistance opposes the flow of fluid

Resistance

• Vascular resistance's most important factor is the friction between the blood and vessel walls
• In blood vessels, the resistance is mostly due to vessel diameter
• Vessel diameter decrease leads to resistance increase and blood flow decrease
• Little pressure remains by the time blood leaves capillaries and enters venules
• Blood flow through the veins is not a direct result of ventricular contraction
• Venous return depends on skeletal muscle action, respiratory movements, and constriction of smooth muscle in venous walls
• Blood viscosity is 5 times greater than water and also impacts vascular resistance

Pulse

• Refers to the rhythmic expansion of an artery caused by the blood ejection from the ventricle
• Can be felt where an artery is close to the surface and rests on something firm
• Wave of distention (pulse wave) diminishes as it travels towards peripheral blood vessels
• Pulse is 15+ times more rapidly transmitted than blood flow
• A healthy, resting adult pulse rate ranges from 60 to 90 BPM
• Pulse can drop to 40 BPM during sleep
• Pulse can rise to 200-220 BPM during heavy exercise
• Younger people generally have higher pulse rates
• Resting heart rate for infants is as high as or higher than an adult's pulse rate during heavy exercise

Blood Pressure

• Measures the force blood exerts against vessel walls
• Refers to arterial blood pressure or pressure in the aorta and its branches
• Systolic pressure is due to ventricular contraction
• Diastolic pressure occurs during cardiac relaxation
• Pulse pressure is the difference between systolic and diastolic pressure
• It is recorded as the systolic pressure over the diastolic pressure using a sphygmomanometer
• Blood pressure increases when cardiac output, blood volume, peripheral resistance, and viscosity increase
• BP = CO * VR (vascular resistance)
• Arterial blood pressure is maintained within normal ranges by changes in cardiac output and peripheral resistance
• Pressure receptors (baroreceptors) in the arteries of the thorax and neck regulate short-term blood pressure

Hypertension

• Also termed high blood pressure
• It is a medical condition where blood pressure is chronically high
• Arterial hypertension refers to "hypertension" without qualifiers
• Persistent Hypertension leads to strokes, heart attacks, heart failure, and chronic renal failure

Diseases of the Heart

Acute Myocardial Infarction (MI)

• Commonly known as a heart attack
• Characterized by varying degrees of chest pain or discomfort, weakness, sweating, nausea, vomiting, and arrhythmias. Sometimes loss of conciseness occurs.
• The blood supply part of the heart is interrupted
• It leads to local heart tissue damage
• The severity of heart attacks varies
• Life-threatening medical emergency needing immediate attention
• Diagnosed using medical history, ECG, and blood tests for cardiac enzymes
• Treatment includes restoring blood flow via thrombolysis and/or angioplasty
• Close monitoring on a Coronary Care Unit is needed to observe complications and on secondary prevention

Blood Vessels

• A component of the circulatory system
• Transports blood throughout the body
• Arteries and veins move blood away from or towards the heart, respectively

Arteries

• Carry blood away from the heart
• Pulmonary arteries transport oxygen-low blood from the right ventricle to the lungs
• Systemic arteries transport oxygen-rich blood from the left ventricle to body tissues
• Blood proceeds from ventricles into large elastic arteries and then smaller arteries until they branch into microscopic arteries called arterioles
• Arterioles have a key role in regulating blood flow into tissue capillaries
• About 10% of blood volume is in the arterial systemic system at any given time
• Arterial walls consist of 3 layers, those are: tunica intima (interna), tunica media, and tunica externa:

Artery Walls

• Tunica intima (interna) consists of: simple squamous epithelium, a surrounding connective tissue basement membrane, and elastic fibers
• The tunica media layer consists of: the thickest layer, primarily smooth muscle, providing support for the vessel and change vessel diameter to regulate blood flow and blood pressure
• The tunica externa is the outermost layer made out of: connective tissue, varying amounts of elastic and collagenous fibers that are dense near the tunic media and loose near the vessel's periphery

Arterioles

• The blood vessel that extends and branches out from an artery and leads to capillaries
• Have muscular walls and primarily vascular resistance site
• Mean blood pressure in the arteries supplying the body is the result of interaction between cardiac output and vascular resistance, which is normally defined as total peripheral resistance (TPR)

Capillaries

• Connect arteries and veins
• Facilitates material exchange between blood and tissue cells
• The metabolic activity of the tissue impacts on capillary structure that provides nutrients and capillaries

Capillary Distribution

• Tissues such as skeletal muscle, liver, and kidney have extensive capillary networks because they are metabolically active and require an abundant supply of oxygen and nutrients
• Connective tissue has a less abundant supply of capillaries
• The epidermis of the skin and the lens and cornea lack a capillary network
• About 5% of blood volume is in systemic capillaries at any given time with 10% in lungs with 10% in arterial system
• Smooth muscle cells in arterioles regulate blood flow from arterioles into capillaries
• Composed of only one layer of cells
• Microcirculation happens through pores that pass between cells

Capillary makeup

• Depending on the tissue, capillaries may contain lots of pores (fenestras)
• Methods for capillary exchange include diffusion, osmosis, and endo + exocytosis

Veins

• Carry materials towards the heart
• Blood proceeds through capillaries and enters the smallest veins or venules, then it flows into larger veins until it reaches the heart
• In the pulmonary circuit the blood from the lungs contains: a high oxygen content in the pulmonary veins is transported to the left atrium of the heart
• In the systemic circuit the blood from the body tissues contains: a reduced oxygen content in the systemic veins is transported to the right atrium of the heart
• Walls consist of the same three layers as arteries but there is less smooth muscle and connective tissue which makes the walls thinner with less pressure

Vessels Walls

• The same three layers as arteries are present (tunica intima, tunica meida, and tunica externa)
• There is less smooth muscle and connective tissue compared to arteries
• Vein walls are thinner, with less pressure
• Can hold more blood (70% percent of total blood volume is contained at any given time)
• Medium and large veins have venous valves, similar to the semilunar valves in the heart, that assist in blood movement
• Important at arms in legs and to prevent backflow of blood in response to the pull of gravity

Vascular Diseases

Atherosclerosis

• Disease affecting arterial blood vessels, including surgically moved veins
• Athero - plaque with foamy appearance
• Sclerosis - outer hardening with wall stiffening
• Atherosclerosis refers to larger arteries, Arteriosclerosis refers to arterioles
• Commonly referred to as "hardening" or "furring" of blood vessels
• Atheromas develop in vessel walls, rupturing in late stages, reduced blood flow in vessel lumen leads to damage downstream that has lost blood flow

Blood

• A liquid connective tissue composed of plasma and formed elements

Plasma

• Liquid component of blood
• Mammalian blood consists of plasma (~60% of volume) and cellular components (~40%)
• 90% water and 10% dissolved materials like proteins, glucose, ions, hormones, and gases
• It has nutrients, waste, salts, proteins, etc.
• Proteins transport molecules like cholesterol

Albumin

• Most abundant, made in Liver (average amount is 70g/L), which is produced in the liver
• Albumin controls oncotic/osmotic-colloidal pressure of the blood
• Pressure produced by osmotic particles, like Na+, K+, Ca2+, Cl- ions, and colloidal particles like albumin
• The more particles, the higher the oncotic pressure
• Other plasma proteins include immunoglobulins, clotting factors (fibrinogen, prothrombin), transport proteins, and hormones like insulin and glucagon
• After clotting, blood plasma is called serum, does not contain clotting factors

Formed Elements

• They are the blood cells
• Hematocrit is the amount of formed elements in blood, precipitates when anticoagulants are added
• Hematocrit is different in men and women, men have more hematocrit, than women

Red blood cells

• Also termed erythrocytes
• Cells that are flattened, doubly concave, are about 7 µm in diameter, carry oxygen in hemoglobin, and lack a nucleus (mature)
• Humans have 25 trillion (1/3 of all cells in the body)
• They are continuously produced in the red bone marrow of long bones, ribs, skull, and vertebrae
• Erythrocytes are degraded by the liver/ spleen and contain a iron in their makeup
• Lifespan is approximately 120 day, the Liver degrades heme units and responsible for the color of feces
• Second 2M red blood cells replaced each second of circulation

White blood cells

• Leukocytes
• Larger than erythrocytes, they have nucleus
• Lacks hemoglobin, function is cellular immune response
• Leukocytes comprise less than 1% of the blood's volume
• Made of stem cells in bone marrow with 5 types

Types of Leukocytes

• Neutrophils - enter the tissue and perform phagocytosis on foreign substances
• Macrophages - release factors increasing WBC growth
• Lymphocytes - fight infections: include T-cells to fight cells containing viruses and B-cells to make antibodies
• Antigen-antibody complexes are phagocytized by a macrophage
• White blood cells can squeeze through the pores in the capillaries and fight diseases in interstitial areas

Platelets

• Result from cell fragmentation, involved with clotting
• Cell fragments from megakaryocytes
• Comprise essential blood elements
• Platelets survive for 10 days before being removed by the liver and spleen
• 150,000 and 300,000 platelets in each ml of blood
• Platelets adhere and stick to tears, and secrete clotting factors with clotting capabilities
• A hemophilic blood type cant blot without correct proteins-or clotting factors

Damage

• It's wall damage follows a series of processes that stop bleeding
• Contraction of the vessels (or Vasospasm ) occurs in minor injuries
• Hemostasis (stop of injury) via platelet plug and platelet injury formation of that prevents bleeding
• Lastly, coagulation occurs
• Thirteen coagulation factors involved in the process of coagulation, the factors are positive
• Certain chemicals such as Vit-k and Ca+ ions can stop Coagulation by binding

Blood groups

Blood type

• Reflect individuals characteristics that carry red material components and carbohydrates
• The classification types of blood are broken into ABO an Rh
• Antigen count = is 46 with a rare presence of AB0 an RH
• Incompatibility leads to anemia, shock and and death.

Blood group characteristics

• They are categorized by Antigens in certain cell types
• Lack of specific markers can leads to antibodies in certain types

ABO system makeup

• The human blood types (A, B, AB, O) possess unique antigens and are broken into two components.
• The individual cell has Antigens in its presence that are linked to anti-bodies
• A anti bodies that is neg or O neg that are only blood donors
• Each b antigen contains antibodes that may be pos or neg
• Combination of A and B are universal donor

Rhesus factor

• Rh-D factor inherited on first factor
• Factors are or are not are or not red cells

Blood factor

• Matched RH are very important
• MImatching leads to hemolysis
• The mothers of newborns in this factor causes ige anti bodies
• IgG antibodies can cross a placenta that may have an A and B

Blood disease

• The genetic disease, which is often hereditary, contains cell shape defects that deoxygenate and leads to ischemia

Sickle cell disease

• Anemia occurs, leading to an increase in blood count and tissues that form hemolysis
• Leukemia leads to function of the cell that leads to the spleen and other organs
• Lymphatic is a series of plasma cells that take form by diffusion

Lymph circulation

• The system is not closed that helps draw it in
• It then transports large lymph nodes