Blood and the Cardiovascular System Flashcards
Blood
Blood transports everything that must be carried from one place to another, such as: o Nutrients o Wastes o Hormones o Body heat
- Regulates acid-base balance and fluid and electrolyte balance
- Prevents infection and excessive bleeding
Components of Blood
Blood is the only fluid tissue, a type of connective tissue, in the human body
- Components of blood
o Formed elements (living cells)
o Plasma (nonliving fluid matrix)
When blood is separated:
o Erythrocytes sink to the bottom (45 percent of blood, a percentage known as the haematocrit)
o Buffy coat contains leukocytes and platelets (less than 1 percent of blood)
Buffy coat is a thin, whitish layer between the erythrocytes and plasma
o Plasma rises to the top (55 percent of blood)
Blood Volume
o About 5–6 liters, or about 6 quarts, of blood are found in a healthy adult
o Blood makes up 8 percent of body weight
o Athletes have higher blood volumes
Blood Characteristics
o Sticky, opaque fluid
o Heavier and thicker than water
o Color range
Oxygen-rich blood is scarlet red
Oxygen-poor blood is dull red or purple
o Metallic, salty taste
o Blood pH is slightly alkaline, between 7.35 and 7.45
o Blood temperature is slightly higher than body temperature, at 38ºC or 100.4ºF
Blood Viscosity
Viscosity 5 times greater than that of water because blood contains elements
• Plasma proteins and electrolytes
• Contributes to blood flow resistance
• Thicker blood –> harder the heart has to work to pump
• Decreased blood temperature, prolonged exposure to high altitude, increased proportion of RBC’s –> increase viscosity
Plasma
- 90 percent water
- Straw-coloured fluid
Includes many dissolved substances (2%) o Nutrients Salts (electrolytes) Respiratory gases Hormones Plasma proteins Waste products (e.g., carbon dioxide)
Plasma Proteins - Examples
o Albumin—an important blood buffer and contributes to osmotic pressure
o Clotting proteins—help to stem blood loss when a blood vessel is injured
o Antibodies—help protect the body from pathogens
o Fibrinogen
o Globulin
Plasma Proteins - Functions
o Transporting lipids and fat-soluble vitamins, regulating blood pressure and volume, assisting in blood clot formation
Plasma Proteins - General
- Most abundant solutes in plasma
- Most are made by the liver
Contains a mixture of electrolytes and buffers
o Electrolytes –> sodium, potassium, chloride, magnesium and calcium
Help maintain fluid and electrolyte balance
o Buffers –> bicarbonate phosphate and sulphate
Regulate blood pH
Plasma - Blood Composition
Blood composition varies as cells exchange substances with the blood
o Liver makes more proteins when levels drop
o Respiratory and urinary systems restore blood pH to normal when blood becomes too acidic or alkaline
- Plasma composition is constant –> due to various homeostatic mechanisms of the body
- Plasma helps distribute body heat –> by-product of cellular metabolism
Forced Elements
- Haematopoiesis –> the formation of new blood cells within red bone marrow
- Formed elements begins as a haematopoietic stem cell –> another form of stem cell –> blast cell
Includes:
o Erythrocytes
Red blood cells (RBCs)
o Leukocytes
White blood cells (WBCs)
o Platelets
Cell fragments
- As blood cells develop from the stem cell –> enter bloodstream by seeping into blood as it enters the bone
Erythrocytes
Main function is to carry oxygen to living cells and carbon dioxide away (gas exchange)
RBCs differ from other blood cells
o Anucleate (no nucleus)
During development nucleus is forced out of the cell
• Increases surface area of the cell –> larger binding area
• Increases flexibility of the cell –> can change shape
• Restricts the cell lifespan –> 120 days as it cannot replicate
o Contain few organelles; lack mitochondria
o Essentially bags of hemoglobin (Hb)
o Shaped like biconcave discs
- Normal count is 5 million RBCs per cubic millimeter (mm3 ) of blood (most abundant)
Erythrocytes - Haemoglobin
o Binds oxygen –> known as the binding site
o Each hemoglobin molecule has 4 haem binding sites which can bind 4 oxygen molecules
o Each erythrocyte has 250 million hemoglobin molecules
o Normal blood contains 12–18 g of hemoglobin per 100 milliliters (ml) of blood
o Oxygen binds to haemoglobin –> forming oxy-haemoglobin molecule in the capillary of the lungs –> travel to tissue capillaries –> oxygen is unloaded and diffused from blood into oxygen deprived tissues
o Globin protein is binding site for carbon dioxide
o Composed of two molecules
Large protein –> Globin
Iron molecule –> Haem
Leukocytes
Crucial in body’s defense against disease
o Some WBCs engulf and digest bacteria (phagocytosis)
o Others produce antibodies, intensify inflammatory response, involved in allergic reactions
- Complete cells, with nucleus and organelles
- Able to move into and out of blood vessels (diapedesis)
o Slip through spaces in capillary walls to infection site - Respond to chemicals released by damaged tissues (known as positive chemotaxis)
- Move by amoeboid motion
- 4,800 to 10,800 WBCs per mm3 of blood
Platelets (Thrombocytes)
- Fragments of megakaryocytes (multinucleate cells)
o Specialised bone marrow cells - Needed for the clotting process
- Normal platelet count is 300,000 platelets per mm3 of blood
- Part of the formed element of the blood
- Do not have a nucleus
- Develop from a haemopoietic stem cell
Cardiovascular System (Circulatory System)
A closed system of the heart and blood vessels
o The heart pumps blood
o Blood vessels allow blood to circulate to all parts of the body
Functions of the cardiovascular system
o Transport oxygen, nutrients, cell wastes, hormones to and from cells, regulation of acid-base balance, regulation of temperature, assists immune function
Anatomy of the Heart
- Size of a human fist, weighing less than a pound
- Located in the thoracic cavity, between the lungs in the inferior mediastinum
Orientation
o Apex is directed toward left hip and rests on the diaphragm
o Base points toward right shoulder
- Adult heart beats approximately 70 times every minute
Coverings of the Heart
Pericardium—a double-walled sac
Fibrous pericardium is loose and superficial
Anchors heart to the sternum, diaphragm and lungs
Serous membrane is deep to the fibrous pericardium and composed of two layers
Parietal pericardium: outside layer that lines the inner surface of the fibrous pericardium
Visceral pericardium: next to heart; also known as the epicardium
Serous fluid fills the space between the layers of pericardium, called the pericardial cavity
Allows heart to beat in a frictionless environment
Walls of the Heart
Epicardium
o Outside layer; the visceral pericardium
Myocardium
o Middle layer (2/3 of the heart wall)
o Mostly cardiac muscle
Endocardium
o Inner layer known as endothelium
o Covers valves of the heart and allows blood to flow smoothly
Four Chambers of the Heart
Atria (right and left)
Low pressure receiving chambers
Assist with filling the ventricles
Blood enters under low pressure
Ventricles (right and left)
Discharging chambers
Thick-walled pumps of the heart
During contraction, blood is propelled into circulation
Great Vessels
Interatrial septum
Separates the two atria longitudinally
Interventricular septum
Separates the two ventricles longitudinally
Both prevent oxygen-rich blood from mixing with oxygen poor blood
Heart - Double Pump
Heart functions as a double pump
o Arteries carry blood away from the heart
o Veins carry blood toward the heart
Double pump
o Right side works as the pulmonary circuit pump
o Left side works as the systemic circuit pump
Pulmonary Circulation
Blood flows from the right side of the heart to the lungs and back to the left side of the heart
o Blood is pumped out of right side through the pulmonary trunk, which splits into pulmonary arteries and takes oxygen-poor blood to lungs
Carbon dioxide is removed at the lungs
o Oxygen-rich blood returns to the heart from the lungs via 4 pulmonary veins
Systemic Circulation
Oxygen-rich blood returned to the left side of the heart is pumped out into the aorta
o Blood circulates to systemic arteries and to all body tissues
o LV has thicker walls because it pumps blood to the body through the systemic circuit
- Oxygen-poor blood returns to the right atrium via systemic veins, which empty blood into the superior or inferior vena cava
Heart Valves
Allow blood to flow in only one direction, to prevent backflow
o Atrioventricular (AV) valves—between atria and ventricles
Left AV valve: bicuspid (mitral) valve
Right AV valve: tricuspid valve
o Semilunar valves—between ventricle and artery
Pulmonary semilunar valve
• Located at beginning of pulmonary artery
Aortic semilunar valve
• Located at beginning of aorta
AV Valves
Cusps anchored in place by chordae tendineae to the walls of the ventricles
o Thin, fibrous cords attached to the papillary muscles
o When ventricles contract –> papillary muscles contract –> prevent valve cusps swinging into the atria
- Open during heart relaxation when blood passively fills the chambers
- Closed during ventricular contraction
- Open and close in response to pressure changes in the heart
Semilunar Valves
- Closed during heart relaxation
- Open during ventricular contraction
- Open and close in response to pressure change in the heart
- Allows blood to flow from the ventricles to the lungs and the rest of the body
Operation of the AV Valves
- Deoxygenated blood enters the right atrium from both IVC and SVC
- Heart relaxes –> AV valve cusps hang limply into ventricles
- Collecting blood increases pressure against tricuspid valve causing the valve to open
- As tricuspid valve is open –> right ventricle fills passively –> right atrium contract and forces blood into ventricle –> right ventricle contracts and pressure increases in the chamber –> tricuspid valve closes, and pulmonary valve opens –> forces blood into the pulmonary artery
Operation of the Semilunar Valves
- Ventricles contract and force blood out of the heart –> cusps are forced open and flattened against the walls of the artery –> ventricles relax –> blood flows backward toward the heart –> cusps are filled with blood and closes the valves –> prevents arterial blood from re-entering the heart
Cardiac Circulation
- Blood in the heart chambers does not nourish the myocardium
o Coronary arteries provide functional blood supply for the myocardium - The heart has its own nourishing circulatory system consisting of:
o Coronary arteries—branch from the aorta to supply the heart muscle with oxygenated blood
o Cardiac veins—drain the myocardium of blood
o Coronary sinus—a large vein on the posterior of the heart; receives blood from cardiac veins - Blood empties into the right atrium via the coronary sinus
Intrinsic Circulation System of the Heart
- Cardiac muscle contracts spontaneously and independently of nerve impulses
- Conduction system transmits impulses which control HR and contraction strength of muscle tissue
- Spontaneous contractions occur in a regular and continuous way
o Atrial cells beat 60 times per minute
o Ventricular cells beat 20−40 times per minute
o Need a unifying control system—the intrinsic conduction system (nodal system)
Two Systems Regulating Heart Activity
o Autonomic nervous system
Decrease or increase HR depending on the system activated
o Intrinsic conduction system, or the nodal system
Sets the heart rhythm
Composed of special nervous tissue
Ensures heart muscle depolarization in one direction only (atria to ventricles)
Enforces a heart rate of 75 beats per minute
Intrinsic Conduction System Components
o Sinoatrial (SA) node
Located in the right atrium
Serves as the heart’s pacemaker (between 60-100 bpm)
o Atrioventricular (AV) node is at the junction of the atria and ventricles o AV bundle (bundle of His) and bundle branches are in the interventricular septum o Purkinje fibers spread within the ventricle wall muscles
Intrinsic Conduction System Impulse Distribution
- The sinoatrial node (SA node) starts each heartbeat
- Impulse spreads through the atria to the AV node –> atria contract
- At the AV node, the impulse is delayed briefly (for approx. 1/10th of a second)
- Impulse travels through the AV bundle, bundle branches, and Purkinje fibers
- Purkinjie fibres stimulate ventricular contraction –> blood is ejected from the heart
Tachycardia and Bradycardia
Tachycardia
o Rapid heart rate, over 100 beats per minute
o If prolonged, may progress to fibrillation
Bradycardia
o Slow heart rate, less than 60 beats per minutes
Electrocardiogram
- Recording of electrical activity of the heart
- Illustrates what is happening electrically in the atria and ventricles when the depolarize (contract) and relax (repolarize)
Three Main Waves
o P wave –> signals depolarisation of the atria immediately before contraction
o QRS Complex –> results from depolarisation of ventricles, precedes contraction of ventricles
o T wave –> results from currents flowing from repolarisation of ventricles as they relax
Atrial repolarisation is generally hidden by the QRS complex as its recorded at the same time
Cardiac Cycle Overview
The cardiac cycle refers to one complete heartbeat, in which both atria and ventricles contract and then relax
o Systole = contraction (chambers pump blood out of the heart)
o Diastole = relaxation (chambers are filling with blood)
- Average heart rate is approximately 75 beats per minute
- Cardiac cycle length is normally 0.8 second
- In a healthy heart –> when atria contract, ventricles are relaxed
Atrial Diastole (ventricular filling)
o Heart is relaxed and pressure is low
o Atrioventricular valves are open
o Blood flows passively into the atria and into ventricles
o Semilunar valves are closed
Atrial Systole
o Ventricles remain in diastole
o Atria contract
o Blood is forced into the ventricles to complete ventricular filling
Isovolumetric Contraction
o Atrial systole ends; ventricular systole begins
Intraventricular pressure rises
AV valves close –> prevents backflow of blood into the atria
For a moment, the ventricles are completely closed chambers
Ventricular Systole (Ejection Phase)
o Ventricles continue to contract
o Intraventricular pressure now surpasses the pressure in the major arteries leaving the heart
o Semilunar valves open
o Blood is ejected from the ventricles
o Atria are relaxed and filling with blood
Isovolumetric Relaxation
o Ventricular systole begins
o Pressure falls below that in the major arteries
o Semilunar valves close –> to prevent backflow of blood into the ventricles
o For another moment, the ventricles are completely closed chambers
o Meanwhile, atria been going through diastole (filling with blood)
o When atrial pressure increases above intraventricular pressure, the AV valves open –> cardiac cycle repeats
Cardiac Cycle (Order)
Atrial Diastole –> Atrial Systole –> Isovolumetric Contraction –> Ventricular Systole –> Isovolumetric Relaxation
Heart Sounds
- Correspond with closing of heart valves
- Heart murmurs are abnormal or unusual heart sounds
o Reflect turbulent blood flow
Lub
o Longer, louder heart sound caused by the closing of the AV valves
Dup
o Short, sharp heart sound caused by the closing of the semilunar valves at the end of ventricular systole
Cardiac Output
- Amount of blood pumped by each side (ventricle) of the heart in 1 minute#
- CO = HR × SV
- CO = HR (75 beats/min) × SV (70 ml/beat)
- CO = 5250 ml/min = 5.25 L/min
Varies due to body demands
o Rises when SV increases and/or when the heart beats faster
o Drops when either/both factors decrease
Stroke Volume
- Volume of blood pumped by each ventricle in one contraction (each heartbeat)
- About 70 ml of blood is pumped out of the left ventricle with each heartbeat
- Increases as force of ventricular contraction increases
Heart Rate
- Typically 75 beats per minute
Regulation of Stroke Volume
- 60 percent of blood in ventricles (about 70 ml) is pumped with each heartbeat
- Starling’s law of the heart
o The critical factor controlling SV is how much cardiac muscle is stretched
o The more the cardiac muscle is stretched, the stronger the contraction - Venous return is the important factor influencing the stretch of heart muscle
o Amount of blood entering the heart and stretching the ventricles
Factors Modifying Basic Heart Rate - Neural (ANS) Controls
Sympathetic nervous system speeds heart rate
Can temporarily change heart rate
During times of stress more strongly stimulate the SA and AV nodes and cardiac muscle itself –> heart beats faster –> more glucose and oxygen is made available
o Parasympathetic nervous system, primarily vagus nerve fibers, slow and steady the heart rate
o Most important external influence on HR
Factors Modifying Basic Heart Rate - Hormones and Ions
Epinephrine (adrenaline) and thyroxine speed heart rate
Excess or lack of calcium, sodium, and potassium ions also modify heart activity
Reduced level of ionic calcium –> decreases HR
Increased level of ionic calcium –> prolonged contractions may stop heart
Excess/lack of needed ions (sodium and potassium) modifies heart activity
Factors Modifying Basic Heart Rate - Physical Factors
Age, gender, exercise, body temperature influence heart rate
Exercise increases heart by activating skeletal muscle and respiratory pumps
Factors combine to increase cardiac output
Blood Vessels
Blood vessels form a closed vascular system that transports blood to the tissues and back to the heart
o Vessels that carry blood away from the heart
Arteries and arterioles
o Vessels that play a role in exchanges between tissues and blood
Capillary beds
o Vessels that return blood toward the heart
Venules and veins
Microscopic Anatomy of Blood Vessels
Three layers (tunics) in blood vessels surround opening called lumen (except the capillaries)
Tunica intima forms a friction-reducing lining (inner-most)
Flattened Epithelial Cells over a sheet of CT
Allows blood to flow smoothly through the vessel
Tunica media
Thick layer containing smooth muscle and elastic tissue
Controlled by sympathetic nervous system
• Vasodilation and Vasoconstriction
Tunica externa forms protective outermost covering
Mostly fibrous connective tissue
Supports and protects the vessel
Structural Difference in Arteries and Veins
- Arteries have a heavier, stronger, stretchier tunica media than veins to withstand large changes in pressure
Veins have a thinner tunica media than arteries and operate under low pressure
o Veins also have valves to prevent backflow of blood
o Lumen of veins is larger than that of arteries
o Skeletal muscle “milks” blood in veins toward the heart when they contract
o Changes in abdominal and thoracic pressure also help to pump blood
Capillaries - Structure
o Only one cell layer thick (tunica intima)
Allow for exchanges between blood and tissue
O2 and C02 gas exchange occurs between capillaries and tissues
Therefore, known as gas exchange vessels
Form networks called capillary beds that consist of:
A vascular shunt
True capillaries
o Blood flow through a capillary bed is known as microcirculation
o RBCs must pass through in a single file
o Those in kidney, liver, small intestine and endocrine glands have microscopic pores
Allow passage of small molecules such as hormones and WBCs
Capillary –> Capillary Bed –> Venule –> Veins –> Heart
True Capillaries
o Branch off a terminal arteriole
o Empty directly into a postcapillary venule
Entrances to capillary beds are guarded by precapillary sphincters
Contraction –> stops blood flow
Relaxation –> allows blood flow
Determined by the pH, oxygen, carbon dioxide and temperature in tissue
Major Arteries of Systemic Circulation: Aorta
o Largest artery in the body
o Leaves from the left ventricle of the heart
Regions
Ascending aorta—leaves the left ventricle
Aortic arch—arches to the left
Thoracic aorta—travels downward through the thorax
Abdominal aorta—passes through the diaphragm into the abdominopelvic cavity
Arterial Branches of the Ascending Aorta
o Right and left coronary arteries serve the heart
Arterial Branches of the Aortic Arch
Brachiocephalic trunk splits into the:
Right common carotid artery
Right subclavian artery
Left common carotid artery splits into the:
Left internal and external carotid arteries
• Internal –> serves the brain
• External –> serves skin and muscle of the head and neck
Left subclavian artery branches into the:
Vertebral artery –> serves part of the brain
In the axilla, the subclavian artery becomes the axillary artery → brachial artery → radial and ulnar arteries
Arterial Branches of the Thoracic Aorta
o Intercostal arteries supply the muscles of the thorax wall
o Other branches of the thoracic aorta (not illustrated) supply the:
Lungs (bronchial arteries)
Esophagus (esophageal arteries)
Diaphragm (phrenic arteries)
Arterial Branches of the Abdominal Aorta
o Celiac trunk is the first branch of the abdominal aorta.
Three branches are:
Left gastric artery (stomach)
Splenic artery (spleen)
Common hepatic artery (liver)
o Superior mesenteric artery supplies most of the small intestine and first half of the large intestine or colon
o Inferior mesenteric artery serves the second half of the large intestine
o Left and right renal arteries (kidney) –> supply kidneys
o Left and right gonadal arteries –> supply gonads
Ovarian arteries in females serve the ovaries
Testicular arteries in males serve the testes
o Lumbar arteries serve muscles of the abdomen and trunk
o Left and right common iliac arteries are the final branches of the aorta
Internal iliac arteries serve the pelvic organs
External iliac arteries enter the thigh → femoral artery → popliteal artery → anterior and posterior tibial arteries (supply the leg and foot)
Anterior tibial artery terminates in the dorsalis pedis artery which through the arcuate artery supplies the foot
Major Veins of the Systemic Circulation - SVC and IVC
- Superior vena cava and inferior vena cava enter the right atrium of the heart
o Superior vena cava drains the head and arms
o Inferior vena cava drains the lower body
Veins Draining into the SVC q
o Radial and ulnar veins → brachial vein (drains blood from arm) → axillary vein
o Cephalic vein drains the lateral aspect of the arm and empties into the axillary vein
o Basilic vein drains the medial aspect of the arm and empties into the brachial vein proximally
o Basilic and cephalic veins are joined at the median cubital vein (elbow area)
o Subclavian vein receives:
Venous blood from the arm via the axillary vein
Venous blood from skin and muscles of the head via external jugular vein
o Vertebral vein drains the posterior part of the head
o Internal jugular vein drains the dural sinuses of the brain
o Left and right brachiocephalic veins receive venous blood from the:
Subclavian veins
Vertebral veins
Internal jugular veins
o Brachiocephalic veins join to form the superior vena cava → right atrium of heart
o Inferior Vena Cava returns blood from all body regions below the diaphragm
o Azygos vein drains the thorax
Veins Draining into the IVC
o Anterior and posterior tibial veins and fibial veins drain the legs
o Posterior tibial vein → popliteal vein → femoral vein → external iliac vein
o Great saphenous veins (longest veins of the body) receive superficial drainage of the legs
o Each common iliac vein (left and right) is formed by the union of the internal and external iliac vein on its own side
Common iliac veins join to form the IVC
o Right gonadal vein drains the right ovary in females and right testicle in males
o Left gonadal vein empties into the left renal vein
o Left and right renal veins drain the kidneys
o Hepatic portal vein drains the digestive organs and travels through the liver before it enters systemic circulation
o Left and right hepatic veins drain the liver
Arterial Supply of the Brain and the Circle of Willis
Internal carotid arteries (branches of the common carotid arteries) divide into:
o Anterior and middle cerebral arteries
These arteries supply most of the cerebrum
- Vertebral arteries join once within the skull to form the single basilar artery
o Basilar artery serves the brain stem and cerebellum - Posterior cerebral arteries form from the division of the basilar artery
o These arteries supply the posterior cerebrum
Anterior and posterior blood supplies are united by small communicating arterial branches
Result
o Complete circle of connecting blood vessels called cerebral arterial circle, or circle of Willis
Surrounds the base of the brain
Provides more than one route for blood to reach brain tissue
• Can reduce effects of clots or impaired blood flow
Hepatic Portal Circulation: Overview
- Formed by veins draining the digestive organs, which empty into the liver via the hepatic portal vein
o Digestive Organs
o Spleen
o Pancreas - Following eating –> blood contains numerous nutrients
o As blood flows through liver –> nutrients can be removed and stored in previous ways
Hepatic Portal Circulation: Liver
Liver can detoxify toxins absorbed the stomach and intestines
o Drained by veins entering the IVC
Hepatic Portal Circulation: Major Vessels
Inferior and superior mesenteric veins, splenic vein, gastric veins
Inferior Mesenteric –> drains terminal segment of large intestine
Splenic Vein –> drains spleen, pancreas and left side of stomach
Superior Mesenteric –> Joins with splenic to form Hepatic Portal Vein
Left Gastric Vein –> drains right side of stomach
- Hepatic portal vein carries this blood to the liver, where it is processed before returning to systemic circulation
Vital Signs
- Measurements of arterial pulse, blood pressure, respiratory rate, and body temperature
Arterial Pulse
- Alternate expansion and recoil of a blood vessel wall (the pressure wave) that occurs as the heart beats
- Monitored at pressure points in superficial arteries, where pulse is easily palpated
- Pulse averages 70 to 76 beats per minute at rest, in a healthy person
o Influenced by activity, postural changes and emotions - As some pulse points are compressed to stop blood flow into distal tissues during significant blood loss or haemorrhage
o They are also called pressure points
Blood Pressure
- The pressure the blood exerts against the inner walls of the blood vessels
- The force that causes blood to continue to flow in the blood vessels
Blood Pressure Gradient
- When the ventricles contract:
o Blood is forced into elastic arteries close to the heart
o Blood flows along a descending pressure gradient - Pressure decreases in blood vessels as distance from the heart increases
- Pressure is high in the arteries, lower in the capillaries, and lowest in the veins
Measuring Blood Pressure
Two arterial blood pressures are measured
o Systolic –> pressure in the arteries at the peak of ventricular contraction
o Diastolic –> pressure when ventricles relax –> arterial pressure drops
- Expressed as systolic pressure over diastolic pressure in millimetres of mercury (mm Hg)
o For example, 120/80 mm Hg (S = 120, D = 80) - Auscultatory method is an indirect method of measuring systemic arterial blood pressure, most often in the brachial artery
- Continuous blood flow depends on the stretchiness of the larger artery and their ability to recoil and exert pressure on blood as it flows into vascular system
- Valves in large veins, milking activity of skeletal muscles, pressure changes in thorax
o Ensure blood flows back to the heart
Effects of Various Factors On Blood Pressure
Arterial blood pressure (BP) is directly related to cardiac output, blood volume, blood viscosity and peripheral resistance
o Cardiac output (CO; the amount of blood pumped out of the left ventricle per minute)
o Peripheral resistance (PR; the amount of friction blood encounters as it flows through vessels) –> BP = CO × PR
o Dependent on Stroke Volume and Heart Rate
o Blood must overcome peripheral resistance to continue flowing
o Constriction of smooth muscle in arteriole walls –> increases peripheral resistance –> blood backs up in arteries –> arterial pressure rises
o Dilation of smooth muscles –> has opposite effect
Factors on Blood Pressure: Neural Factors
o Parasympathetic nervous system has little to no effect on blood pressure
o Sympathetic nervous system promotes vasoconstriction (narrowing of vessels), which increases blood pressure
Sympathetic centre in the medulla oblongata is activated to cause vasoconstriction
When we stand up suddenly –> BP drops due to gravity –> activates pressure receptors (baroreceptors) in large arteries of neck and chest
• Send warning signals which result in vasoconstriction –>increases blood pressure back to normal
When blood volume suddenly decreases –> blood pressure drops –> heart beats more rapidly –> heart beats weakly and inefficiently –> vasoconstriction to increase venous return
Factors on Blood Pressure: Renal Factors
o Kidneys regulate blood pressure by altering blood volume
o If blood pressure is too high, the kidneys release water in the urine
As water is found in blood –> blood volume decreases –> blood pressure decreases
o If blood pressure is too low, the kidneys release renin to trigger formation of angiotensin II, a vasoconstrictor
o Angiotensin II stimulates release of aldosterone, which enhances sodium (and water) reabsorption by kidneys
Factors on Blood Pressure: Temperature
o Heat has a vasodilating effect
o Cold has a vasoconstricting effect
Factors on Blood Pressure: Chemicals
o Various substances can cause increases or decreases in blood pressure
o Epinephrine increases heart rate and blood pressure
o Nicotine increases blood pressure by causing vasoconstriction
o Alcohol causes vasodilation and reduces blood pressure
Factors on Blood Pressure: Diet
o Commonly believed that a diet low in salt, saturated fats, and cholesterol prevents hypertension (high blood pressure)
Variation in Blood Pressure
Normal human range is variable
o Systolic pressure ranges from 110 to 140 mm Hg
o Diastolic pressure ranges from 70 to 80 mm Hg
Hypotension (low blood pressure)
o Low systolic (below 100 mm Hg)
o Often associated with illness
o Acute hypotension is a warning sign for circulatory shock
o Expected result of physical conditioning
Hypertension (high blood pressure)
o Sustained elevated arterial pressure of 140/90 mm Hg
o Warns of increased peripheral resistance
o Brief rise in blood pressure is normal response to fever and emotional response
o Persistent hypertension is pathological
Capillary Exchange of Gases and Nutrients
- Interstitial fluid (tissue fluid) is found between cells
- Substances move to and from the blood and tissue cells through capillary walls
o Exchange is due to concentration gradients
Oxygen and nutrients leave the blood and move into tissue cells
Carbon dioxide and other wastes exit tissue cells and enter the blood
Substances take various routes entering or leaving the blood
o Direct diffusion through membranes
o Diffusion through intercellular clefts (gaps between cells in the capillary wall)
o Diffusion through pores of fenestrated capillaries (small solids and fluids)
Found where absorption is a priority or where filtration occurs
o Transport via vesicles (lipid insoluble materials) (endocytosis or exocytosis)
Substances not able to use these processes protein, plasma, blood cells
Fluid Movement at Capillary Beds
Fluid movement out of or into a capillary depends on the difference between the two pressures
o Blood pressure forces fluid and solutes out of capillaries
o Osmotic pressure draws fluid into capillaries
Blood has higher solute concentration due to plasma proteins than plasma
- Blood pressure is higher than osmotic pressure at the arterial end of the capillary bed
- Blood pressure is lower than osmotic pressure at the venous end of the capillary bed
- Thus, fluid moves out of the capillary at the beginning of the bed and is reclaimed at the opposite (venule) end
o Not all fluid forced out is reclaimed at the venule end
o Returning fluid back to the blood is the lymphatic system
Heart Murmurs
- Heart murmurs
o Caused by one of the heart valves not closing properly
o Common in young children and usually do not require special treatment
o Can be introduced as a result of aging, rheumatic fever or other disease
Diseases ending in itis
Pericarditis
May occur due to inflammation of the pericardial sac
Causes heart to rub against sac as it contracts –> produces stabbing pain in chest
Myocarditis
Inflammation of the myocardium
Can cause symptoms like pericarditis
Endocarditis
Inflammation of the inner lining –> includes inner surface of chambers and valves
Can be life-threatening and damage valves if left untreated
Heart Failure
o Occurs when the heart cannot adequately pump blood to meet oxygen needs of the body
o Heart muscle becomes stiff and has difficulty filling the blood
o Can be caused by disease or infection
Diseases of the Arteries: Aneurysms
- Abnormal ballooning of a vessel
Due to weakness in a wall of vessel
Smoking, High BP and high cholesterol increase risk
Pain and swelling are common symptoms
Diseases of the Arteries: Coronary Artery Disease
Narrowing of one or more coronary arteries due to the build up of plaque
Atherosclerosis
Build-up usually starts with an injury in the tunica media or inner most lining of artery
Can be caused by smoking, high blood pressure, high blood glucose from insulin resistance (diabetes) or high levels of fat or cholesterol in blood
Heart Attack
Myocardial infarction –> can occur if artery becomes completely blocked
Warning signs –> chest pain or shortness of breath
o May cause angina pectoris (chest pain)
Due to lack of oxygen or blood flow to heart
