Blood "connects" the various regions of the internal fluid environment by providing a flowing, circulating stream of liquid that transports, protects, and regulates

Blood stays within a closed system of tubes (= vessels) and chambers (of the heart)

EXCEPT: WBCs travel in and out of the blood stream Water and solutes diffuse in and out of blood stream

Cardiovascular disease is a major health concern     pp

Functional anatomy of the heart

General structure Four chambers: two upper atria (sing. atrium) and two lower ventricles Septum separates the "left heart" from the "right heart"     GA Located in mediastinum of thorax; about 2/3 of heart is left of median     GA  GA Apex is lower tip of heart; points somewhat to the left     pp  Base is broad top of heart     GA

Heart wall Endocardium = endothelial lining that is continuous with the endothelium (simple-squamous-like membrane) that lines the blood vessels Has valves (see below) as in veins Myocardium = cardiac muscle layer Very thick (thickest in chambers that pump harder [ventricles, esp. L ventricle]) Cardiac muscle of upper and lower heart each act as a syncytium Because fibers are branched and connected by gap junctions, they all contract together as if they were one giant cell     GA This means wall of upper chambers contract more or less at once; likewise for lower chambers Cardiac muscle is autorhythmic Cardiac muscle does not fatigue Cardiac muscle does not have tetanus instead,  cardiac muscle has single prolonged contractions peak of contraction in cardiac muscle is several times longer than in the twitch of a skeletal muscle

Pericardium = multilayer sac around heart

Fibrous pericardium is outermost covering

Serous pericardium     GA Visceral layer of serous pericardium is also called "epicardium" Note: in fig. 18-5 p.683, the label line for epicardium is several mm too far to your right in the first printing of the textbook; please check your copy Parietal layer of serous pericardium lines the inside of the fibrous pericardium Lubricating pericardial fluid between the two layers of the serous pericardium reduces friction

Chambers of the heart     GA  GA

	Two atria (sing. "atrium")  literally, "lobby" Heart's upper chambers (L and R atria divided by a septum) The auricle is the ear-like lateral out-pouching of each atrium Receiving chambers --receive blood from veins Pressurize blood, moving it to the lower chambers
	Two ventricles --literally, "little chambers" Heart's lower chambers (L and R ventricles divided by a septum) Pumping chambers --pressurize blood so it moves out of heart, maintaining a large enough pressure gradient to move blood most of the way around the circulatory loop
	Although ventricles (esp. L ventricle) have thicker walls, they all contain about the same volume of blood

Valves of the heart

Atrioventricular (AV) valves      GA Between each atrium and ventricle (R and L AV valves) Have two (L) or three (R) flaps (leaflets) held by stringy chordae tendinae (lit. "tendon cords") which are in turn attached to fingerlike projections inside the ventricles called papillary muscles The L AV valve, because it only has two leaflets, reminded early anatomists (who were apparently affected by fumes of formaldehyde and alcohol, or perhaps just alcohol) of a bishop's two-flapped, angled hat called a "miter" --for that reason the L AV valve is usually called the mitral valve When the ventricle contracts, blood pushes the leaflets into the atrium The leaflets stop at the point where they completely block blood flow back into the atrium because the chordae tendinae, held tightly by the papillary muscles, become taut

Skeleton of the heart

	Fibrous rings around the openings of the heart valves
	Give a more rigid support to the valve openings (like a door jamb)
	Provide electrical insulation between the atrial myocardium and the ventricular myocardium

Pathway of blood through heart and "circulatory routes"

Circulatory routes (AKA "circulatory loops" or "circuits") Pulmonary route From heart (right side) to gas-exchange tissues of lungs and back to heart (left side) Blood loses CO2 and gains O2 Systemic route From heart (left side) to "systemic" (non-pulmonary) tissues of body and back to heart (right side) Blood loses O2 and gains CO2 Systemic route is longer and more extensive than pulmonary route Blood goes through pulmonary route, then systemic, then pulmonary, and so on

R atrium 

Coronary circulation     GA

	Coronary is from "corona" meaning "crown" --referring to vessels encircling heart as a crown encircles the head
	Supply blood to the myocardium
	Anastomoses are critical when blockage occurs   ANIM

Fetal circulation     GA

	Special circulatory route prior to birth Umbilical cord Umbilical arteries (2) Umbilical vein Placenta     pp Ductus venosus  Foramen ovale Ductus arteriosus
	Changes to normal adult pattern at time of birth

Portal circulatory routes      pp

	Occurs when blood leaves a capillary bed and then moves through a "portal vein" to a second capillary network before returning to heart ("portal" means "gateway")
	Examples Hypophyseal portal circulation: heart --> hypothalamus --> anterior pituitary --> heart Hepatic portal circulation: heart --> digestive organs --> liver --> heart      GA

Types      pp

	Arteries - large vessels that conduct blood away from heart, toward Arterioles - small arteries that conduct blood way from larger arteries, toward
	Capillaries - microscopic, thin-walled vessels where water and solutes move in and out of blood ("exchange vessels") Sinusoids are like capillaries, except they are not tubular (instead, they are irregular, microscopic spaces)
	Veins - large vessels that conduct blood from venules toward the heart Sinuses are especially large veins where blood "pools" as a method of storing excess blood volume in the case of a sudden loss of blood (making veins and sinuses "reservoir vessels") Venules - small veins that collect blood from capillaries (and sinusoids), conducting blood toward

Wall of blood vessels

	Tunica intima ("intimate garment" = "underwear") Endothelium (similar to simple squamous epithelium) Smooth (for easy flow) and thin (for easy exchange) In veins (only), this layer has semilunar ("half-moon") valves (SL valves) Three "pockets" in the "underwear," all facing each other When blood goes "backward" pockets fill and press into each other, forming a barrier to further backflow When blood goes "forward" pockets are pushed flat against vessel wall and blood flows easily past them SL valves ensure one-way flow of blood
	Tunica media ("middle garment") Smooth muscle Supports wall (prevents rupture) by resisting pressure of blood Allows change in blood flow      pp Vasoconstriction = muscle contracts, reducing diameter Vasodilation = muscle relaxes, increasing diameter Regulated by nerves, hormones, and local regulators (e.g. prostaglandins) Elastic tissue Supports, but also allows recoil of an expanded vessel Absent in capillaries
	Tunica externa ("external garment;" also called tunica adventitia) Fibrous tissue, adding to flexible strength of wall Absent in capillaries
	Overall, arteries are thicker-walled than veins, with more muscle

Functional principles

	Arteries = "resistance vessels" can use their muscles to change resistance to blood flow, regulating where blood goes    pp
	Veins = "capacitance vessels" can increase their capacity (volume) by stretching and can thus act as blood reservoirs
	Capillaries = the primary "exchange vessels" can move substances easily into and out of the blood tissue     ANIM Microcirculation refers to blood flow through capillary networks A metarteriole is small connecting vessel from an arteriole that extends through a capillary bed (network) Precapillary sphincters are valve-like muscles of the metarteriole that regulate blood flow into capillary networks, just controlling exactly where in a tissue blood flows  Metarterioles can also allow blood to bypass a capillary bed, thus acting as a "thoroughfare channel"

Study/analysis of blood flow

Cardiac cycle

	Two-step cycle of contraction and relaxation Contraction = systole (SIS-toh-lee) Relaxation = diastole (dy-ASS-toh-lee)
	Cardiac cycle is alternate systole/diastole of atria, ventricles, atria, ventricles, and so on
	Five-step version of cardiac pumping cycle Atrial systole Isovolumetric ventricular contraction Ejection Isovolumetric ventricular relaxation Passive ventricular filling
	Heart sounds 1st heart sound = lubb = AV valves closing (and ventricular contraction noise) 2nd heart sound = dupp = SL valves closing

Electrical conducting system of the heart      GA     ANIM

	Three kinds of myocardial fibers Myocardial fibers (ordinary fibers) Conducting fibers (conduct action potentials more rapidly than ordinary fibers) Pacemaker fibers ("stronger" rhythm than ordinary fibers)
	Action potentials spread along entire atrial myocardium (triggering atrial systole) then entire ventricular myocardium (triggering ventricular systole) Must be sped up, to reach whole myocardium at about same time Must be coordinated/linked, so atria and ventricles stay "in time" with each other All cells within syncytium (atrial or ventricular myocardium) must follow the same pace (remember: each fiber has its own rhythm, which may be faster or slower than its neighbor)
	Sinoatrial (SA) node is primary "pacemaker" of heart, setting rhythm for atrial myocardium and for AV node See diagram for location of this and remaining structures
	Atrioventricular (AV) node is pacemaker for ventricular myocardium Follows signal from SA node, even though it COULD set its own pace
	Atrioventricular (AV) bundle rapidly conducts depolarization (action potential) through septum between ventricles to apex (bottom point) of heart
	Purkinje fibers rapidly conduction depolarization through lateral walls of ventricles
	Ectopic pacemakers are areas other than the SA node that "take over" (perhaps because the SA node is damaged)  "Ectopic" means "off place" or "out of place" Ectopic pacemakers are usually not as efficient as the SA node, so this creates a problem Can be treated by using artificial pacemakers

Electrocardiography (ECG or EKG)

	Baseline of the ECG wave shows no change (no depolarization, no repolarization)
	Deviations (waves) show depolarization OR repolarization P wave = depolarization of atrial myocardium QRS complex = repolarization of atrial myocardium AND depolarization of ventricular myocardium T wave = repolarization of ventricular myocardium U wave = "hump" on the T wave (not usually present) = repolarization of papillary muscles
	Oddities in the ECG show damage to myocardium or other problems Changes in intervals may mean a change in conduction velocity, which may mean a "heart block" or impairment of conduction  Fibrillation = asynchronous , uncoordinated contractions = no effective pumping FYI  Click here for a wonderful simulation of ECG tracing in several fictional patients.

Regulation of electrical activity

	Nervous regulation Sympathetic fibers (via cardiac nerve) increase heart rate Parasympathetic fibers (via vagus nerve) decrease heart rate Reflexes Baroreflexes (pressoreflexes) respond to changes in blood pressure Chemoreflexes respond to changes in CO2 or pH or O2 Carotid bodies and aortic bodies contain receptors for these reflexes
	Endocrine regulation (e.g. epinephrine, thyroid hormone)
	Misc. factors: blood temp, pain, ions (Ca++, Na+, K+), exercise
	Resting HR is about 65-80 beats/min

Measuring blood pressure

	Use a sphygmomanometer, which is simply a pressure gauge calibrated to mm Hg (how much a column of mercury [liquid metal] will rise in a tube as a result of a certain amount of pressure)
	Measures maximum and minimum pressures as the pulse wave passes by in an artery Maximum pressure = systolic pressure  (usually less than 120 mm Hg) Minimum pressure = diastolic pressure (usually less than 80 mm Hg)
	Reported as max/min or sys/dias, for example 120/80 or "one-twenty over eighty"
	Hypertension (HTN) is "high blood pressure"
	Circulatory shock results from extremely low blood pressure

Primary principle of circulation: blood flows down a pressure gradient

	That is, blood flows from  high pressure regions to lower pressure regions
	Highest pressure in heart (during contraction), then arteries, then capillaries, then veins, then heart (during relaxation)
	Perfusion pressure is the local pressure gradient needed to maintain blood flow through a tissue Perfusion means "flow through"

Anything that affects blood pressure affects blood flow

Cardiac output (CO)

	CO is the volume pumped out of the heart per unit of time
	ml/min or L/min (usually around 5 L/min for 70 kg adult male)
	CO = SV x HR   (SV = stroke volume)

Stroke volume (ml/beat)

Starling's law of the heart     pp Also called the Frank-Starling mechanism Cardiac muscle contraction increases in strength the more it is stretched (length-tension relationship) If end-diastolic volume (EDV; blood volume in ventricle just before it contracts) is large, this will stretch the myocardium and increase the strength of that heart stroke (beat) Thus, the heart pumps what it receives The higher the end-diastolic volume, the higher the stroke volume Affected by venous return of blood to the heart (in turn affected by total blood volume and operation of venous pumps --see below)

Changes in contractility (strength of contraction) Epinephrine, norepinephrine (NE) increase contractility Exercise

Heart rate (beats per minute; contractions per minute)

Affected by; autonomic nerves (chemoreflexes,  pressure reflexes, stress response), hormones, drugs, sex, violence, online tests, etc. (see above)

Total blood volume 

Affected by: dehydration, overhydration, hormones, kidney function, blood loss (hemorrhage, lit. "blood flow"), osmotic pressure (sufficient plasma proteins)

Peripheral resistance (PR; resistance to flow outside the heart)

	Vessel length (length directly proportional to resistance) Except during growth, doesn't change much
	Branching (number of branches directly proportional to resistance) May change over time with functional or structural changes in tissues
	Viscosity of blood Normally doesn't change much Could change when hematocrit (RBC%) changes; could also change with plasma protein fluctuations
	Diameter of vessels  Resistance inversely proportional diameter of vessel (by an exponent of 4)  Vasomotor mechanism: smooth muscle in wall of vessel changes diameter of vessel     pp This is the usual  way to regulate blood flow in local areas Microcirculation (blood flow in capillaries) RBCs must be deformable (bendable) or they won't fit through some capillaries Precapillary sphincters control flow locally These muscle "valves" are on arterioles NOT on capillaries
	Peripheral resistance can affect blood flow in local regions or the whole circulatory loop (total peripheral resistance; TPR)

Operation of venous pumps

	Orthostatic effect ("standing up" effect) Gravity causes blood to shift to the lowest venous reservoirs (legs)
	Skeletal muscle pump Skeletal muscles and SL valves of vein operate a "pump" that keeps pressure gradients up so that blood flows back to heart
	Respiratory pump Breathing movements and SL valves do the same thing as skeletal muscle pump

Pulse waves conserve energy and keep blood flowing continuously

	Pulse waves are created in arteries every time the heart contracts and pushes blood into the arteries    pp
	Stress-relaxation effect The arterial wall expands under the high pressure, absorbing some of the energy During heart relaxation, the arterial wall recoils and thus releases some of the energy it had absorbed Recoil of arterial walls thus keeps the pressure up, and thus keeps blood flowing, between heart contractions If vessel walls were instead stiff, blood would only flow in spurts --not continuously
	Pulse waves reflect heart rate and strength
	Pulse waves are best palpated (felt with your hand) at "pulse points" Areas where there is a large artery close to the skin and over a bone or other solid structure (so you can push it up against the bone and feel the pulse wave through the skin)    pp