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Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 1
Circulation/Transport
General two major transport systems in body: A. The Circulatory System B. The Lymphatic Sysem circulatory system works in conjunction with lymphatic system ! they are directly connected to each other A. Circulatory (cardiovascular) System circulatory system consists of “ plumbing ” and “ pumps ” & circulating fluid pump = the heart fluid = blood blood flows in closed system of vessels over 60,000 miles of vessels (mainly capillaries) >arteries! capillaries! veins heart< arteries & arterioles
- take blood away from heart to capillaries Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 2 capillaries - actual site of exchange venules & veins - bring blood from capillaries back to heart B. Lymphatic System an open system that returns excess materials in the tissue spaces back to the blood fluid = lymph no dedicated pump; muscle contractions move lymph along lymphatic vessels move lymph in one direction; lymph does not circulate
The Circulatory System
(Cardiovascular System) major connection between external and internal environment: everything going in or out of body must go through the circulatory system to get to where its going more than 60,000 miles of blood vessels with a pump that beats 100,000 times each day General Functions of Circulatory System: A. Transport B. Homeostasis C. Protection A. Transport functions:
- Pick up food and oxygen from digestive and respiratory systems and deliver them to cells
- pick up wastes and carbon dioxide from cells and deliver to kidneys and lungs
- Transport hormones & other chemicals, enzymes etc throughout the body B. Homeostasis functions:
- maintain fluid and electrolyte balances in tissues and cells
- maintain acid/base balances in tissues and cells
- help regulate temperature homeostasis transfers excess heat from core to skin for removal C. Protective Functions:
- Clotting and Inflammation prevent excessive fluid loss and limit the spread of infection
- Circulating cells and chemicals actively seek out and remove pathogens from the body = “ immune system ”
Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 5
The Heart – Anatomy
we are more aware of our heart than most other internal organs Some ancient Chinese, Egyptian, Greek and Roman scholars correctly surmised that the heart is a pump for filling vessels with blood Aristotle however thought the heart was the seat of emotion and a source of heat to aid digestion: excited! heart beats faster “heartache” of grief his thoughts predominated for over 2000 years before its true nature reemerged the heart is one of first organ systems to appear in developing embryo ! heart is beating by 4th^ week study of heart = cardiology no machine works as long or as hard as your heart beats: >100,000 x’s/day
30 Million times each year 3 Billion times in a lifetime to pump > 1 Million barrels of blood heart is about size and shape of closed fist heart lies behind sternum in mediastinum , broad superior border of heart = base Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 6 lower border of heart (= apex ) lies on diaphragm heart is enclosed in its own sac, = pericardium (=pericardial sac) (parietal pericardium) composed of tough fibrous outer layer and inner serous membrane outer surface of heart is also covered with serous membrane (= visceral pericardium) (= epicardium ) continuous with the pericardium between the 2 membranes is pericardial fluid !lubrication pericarditis = inflammation of pericardium, membranes become dry, each heartbeat becomes painful wall of heart: epicardium = visceral pericardium thin & transparent serous tissue myocardium = cardiac muscle cell most of heart branching, interlacing contractile tissue acts as single unit (gap junctions) endocardium = delicate layer of endothelial cells continuous with inner lining of blood vessels [endocarditis] Heart Chambers interior of heart is subdivided into 4 chambers : atria = two upper chambers with auricles smaller, thinner, weaker ventricles = two lower chambers larger, thicker, stronger left ventricle much larger and thicker than right ventricle left ventricle is at apex of heart Heart Vessels There are 4 major vessels attached to heart: 2 arteries (take blood away from heart): aorta
- from left ventricle pulmonary trunk
- from right ventricle 2 veins (bring blood back to heart): vena cava (superior & inferior)
- to right atrium pulmonary veins (4 in humans)
- to left atrium Heart Valves There are also 4 one-way valves that direct flow of blood through the heart in one direction: 2 Atrioventricular (AV) valves bicuspid (Mitral) valve
- separates left atrium and ventricle
- consists of two flaps of tissues tricuspid valve
- separates right atrium and ventricle
- consists of three flaps of tissues both held in place by chordae tendinae attached to papillary muscles ! prevent backflow (eversion) keeps valves pointed in direction of flow 2 Semilunar valves at beginning of arteries leaving the ventricles aortic SL valve at beginning of aorta pulmonary SL valve at beginning of pulmonary trunk
Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 13 Circuits of Bloodflow arteries, capillaries and veins are arranged into two circuits : pulmonary : heart! lungs! heart rt ventricle! pulmonary arteries (trunk)!lungs!pulmonary veins!left atrium systemic : heart! rest of body! heart left ventricle!aorta!body!vena cava!rt atrium heart is a double pump oxygen deficient blood in pulmonary artery and vena cava ! usually blue on models Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 14
Anatomy of Circulatory System
Major Arteries and Veins Pulmonary Circuit: Arteries pulmonary a. Veins pulmonary v. Systemic Circuit: Arteries aorta ascending aorta rt & lft coronary a. aortic arch brachiocephalic a. common carotid a. internal carotid a. external carotid a. subclavian a. axillary a. brachial a. lft common carotid a. lft subclavian a descending aorta celiac trunk superior mesenteric a. renal a. gonadal a. inferior mesenteric a. common iliac a. internal iliac a. external iliac a. femoral a. Veins: superior vena cava coronary v. brachiocephalic v. jugular v. subclavian v. axillary v. brachial v. inferior vena cava hepatic v. hepatic portal v. superior mesenteric v. inferior mesenteric v. renal v. gonadal v. common iliac v. internal iliac v. external iliac v. femoral v. Special Circulation Patterns
1. Coronary Circulation (or Cardiac Circulation) heart needs an abundant supply of oxygen and nutrients !myocardium has its own supply of vessels ~5% of blood goes to heart muscle tissue ~10-x’s its “fair share” based on weight alone any interruption of blood flow can cause necrosis within minutes = myocardial infarction R & L Coronary Artery branch from aorta just beyond aortic SL valve blood enters when Left Ventricle relaxes (most vessels receive blood when ventricles contract) most blood returns to heart through veins that drain into coronary sinus which empties into Right Atrium beneath entrance of Inferior Vena Cava 2. Circle of Willis 7 separate arteries
Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 17 branchig from the internal carotids and vertebral arteries arterial anastomosis interconnects them to form a circle of connecting arteries at base of brain ! more than one route for blood to get to brain
3. Hepatic Portal System veins from spleen, stomach, pancreas, gall bladder, and intestines superior and inferior mesenteric merge to form hepatic portal vein do not take blood directly to vena cava instead take it to liver for “inspection” - phagocytic cells remove toxins - vitamins and minerals are stored Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 18
Heart Physiology
for the heart to work properly contraction and relaxation of chambers must be coordinated Histology of Heart cardiac muscle fibers relatively short, thick branched cells striated! myofibrils are highly ordered usually 1 nucleus per cell rather than tapering cells are bluntly attached to each other by gap junctions = intercalated discs ! myocardium behaves as single unit but atrial muscles separated from ventricular muscles by conducting tissue sheath ! atria contract separately from ventricles cardiac muscle cells cannot stop contracting to build up glycogen stores for anaerobic metabolism ! need constant supply of oxygen & nutrients to remain aerobic ! greater dependence on oxygen than skeletal muscles have exceptionally large mitochondria comprise 25% of cell volume (vs skeletal mm!2%) cells are more adaptable in nutrient use; can use: glucose fatty acids (preferred) lactic acid Conducting System cardiac muscle cells are not individually innervated as are skeletal muscle cells !they are self stimulating the rhythmic beating of the heart is coordinated and maintained by the heart conducting system conducting system consists of: SA Node intrinsic rhythm 70 - 75 beats/min initiates stimulus that causes atria to contract (but not ventricles directly due to separation) AV Node picks up stimulus from SA Node if SA Node is not functioning it can act as a pacemaker =ectopic pacekmaker (usually slower intrinsic rhythm) AV Bundle (Bundle of His) connected to AV Node takes stimulus from AV Node to ventricles Purkinje Fibers takes impulse from AV Bundle out to cardiac mucscle fibers of ventricles causing ventricles to contract the heart conducting system generates a small electrical current that can be picked up by an electrocardiograph =electrocardiogram (ECG; EKG) ECG is a record of the electrical activity of the conducting system body is a good conductor of electricity (lots of salts) potential changes at body’s surface are picked up by 12 leads [ECG is NOT a record of heart contractions] R P T Q S P wave = passage of current through atria from SA Node conduction through atria is very rapid atrial depolarization QRS wave = passage of current through ventricles from AV Node – AV Bundle – Purkinje Fibers impulse slows as it passes to ventricles ventricular depolarization
Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 25
Physiology of Blood Vessels
Blood circulates in arteries and capillaries by going down a pressure gradient Blood Pressure =the force of the blood flowing through blood vessels measured as mmHg [ 100 mm Hg = 2 psi, tire ~35psi] changes in pressure are the driving force that moves blood through the circulatory system blood pressure is created by
1. the force of the heart beat previously discussed the heart maintains a high pressure on the arterial end of the circuit 2. peripheral resistance ! back pressure, resistance to flow mainly depends on diameter of a vessel and its compliance eg. vasoconstriction raises blood pressure Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 26 vasodilation lowers blood pressure eg. obesity leads to many additional vessels that blood must pass through! raises blood pressure [1lb of fat requires ~7 miles of blood vessels] eg. any blockage of the normal diameter of a vessel will increase resistance eg atherosclerosis inhibits flow! raises blood pressure Measuring Blood Pressure use sphygmomanometer usually measure pressure in the brachial artery procedure: a. increase pressure above systolic to completely cut off blood flow in artery b. gradually release pressure until 1st^ spurt (pulse) passes through cuff = systolic pressure c. continue to release until there is no obstruction of flow sounds disappear = diastolic pressure normal BP = 120/ range: 110-140 / 75- 80 [mm Hg] top number = systolic pressure; force of ventricular contraction bottom number = diastolic pressure; resistance of blood flow may be more important indicates strain to which vessels are continuously subjected also reflects condition of peripheral vessels Abnormal Blood Pressure Hypotension = low BP: systolic <100: usually not a cause for concern often associated with long healthy life but. in some may produce dizziness when standing up too quickly (esp in older patients) may be due to severe bleeding and lead to circulatory shock may hint at poor nutrition eg. <blood proteins Hypertension = 140/ if transient is normal: adaptation during fever, exercise, strong emotions if persistent is a cause for concern 30% of those >50 yrs old suffer from hypertension usually asymptomatic for first 10-20 yrs = silent killer prolonged hypertension is a major cause of: heart failure, vascular disease, kidney failurel stroke, aneuryisms high blood pressure affected by: heredity, gender (men at slightly higher risk of HBP), age (risk increases after age 35), race (African Americans at higher risk) Flow of Blood in Veins the blood pressure gradient is the main force that moves blood through arteries, arterioles and capillaries movement of blood through veins is not pressure driven by the heart veins have 1 - way valves prevent backflow most abundant in veins of limbs quiet standing can cause blood to pool in veins and may cause fainting varicose veins : “incompetent” valves esp. superficial veins may be due to; heredity, prolonged standing, obesity, pregnancy hemorrhoids: varicosities of anal veins due to excessive pressure from birthing or bowel movements
Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 29 venous pumps muscular pump (=skeletal muscle pump) during contraction veins running thru muscle are compressed and force blood in one direction (toward heart) respiratory pump inspiration: increases pressure in abdominopelvic cavity to push blood into thoracic cavity expiration: increasing pressure in chest cavity forces thoracic blood toward heart veins also act as blood reservoirs !with large lumens and thin walls they are compliant and can accommodate relatively large volumes of blood. (60-70% of all blood is in veins at any time) most organs are drained by >1 vein ! occlusion of veins rarely blocks blood flow as it does in arteries ! removal of veins during bypass surgery usually not traumatic Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 30 II. Blood Flow & Differential Distribution of Blood the overall flow of blood to and within a particular organ or tissue is related to blood pressure and peripheral resistance circulation also involves the differential distribution of blood to various body regions according to individual needs !active body parts receive more blood than inactive parts !blood volume must be shifted to parts as they become more active these shifts are regulated by Vasomotor System blood circulates because of pressure gradients individual arterioles can increase or decrease their resistance to blood flow by constricting or dilating mediated by autonomic nervous sytem vasomotor control center in medulla works in conjunction with cardiac centers Capillaries & Capillary Beds capillaries are the actual site of exchange of materials ! the rest is pumps and plumbing each capillary <1mm long thin walled - single cell layer thick extremely abundant in almost every tissue of body !most of 62,000 miles of vessels usually no cell >0.1 mm away from a capillary but only contains ~5% of blood in body variable pressure 35 – 15 mm Hg blood flows slowest in capillaries due to greater cross-sectional area of all capillaries combined ! blood flows 1000x’s faster in aorta than in capillaries provides greatest opportunity for exchange to occur Capillary Beds capillary beds are the functional units of circulatory system usually capillaries 10 – 100 capillaries are organized into each capillary bed arterioles and venules are joined directly by metarterioles (thoroughfare channels) capillaries branch from metarterioles cuff of smooth muscle surrounds origin of capillary branches = precapillary sphincter amount of blood entering a bed is regulated by: ! vasomotor nerve fibers ! local chemical conditions
Human Anatomy & Physiology: Circulatory System, Ziser Lecture Notes, 2013.11 37 cerebral atherosclerosis, thrombosis or hemorrhage of a cerebral aneurysm cuts off blood flow to part of the brain. effects range from unnoticeable to fatal depending on extent of tissue damage and function of affected tissue Varicose Veins can occur anywhere on body but most common on legs veins in legs are largest in body and must counteract gravity to get blood back to the heart veins become enlarged and valves fail to prevent backflow of blood often associated with tired, achy, or feeling of heavy limbs most common in superficial saphenous veins ! they are poorly supported by surrounding tissues many factors contribute to likelihood of varicose veins: heredity age esp occur betw 18 and 35 yrs, peaks betw 50 and 60 yrs gender women are 4 to 1 times more likely to get them pregnancy sometimes form during pregnancy (8-20% chance) then disappear afterwards lifestyle: prolonged sitting or standing daily Transposition of the Great Vessels the child will develop normally until they begin to walk the right ventricle wll be unable to pump enough blood through systemic circuit
