Download The Heart - OnCourse

1) The circulatory system
a) Blood Vessels
i) Arteries
(1) Strong elastic vessels
(2) Adapted for carrying blood under high pressure
(3) Subdivide into progressively smaller tubes
(a) Arterioles
(b) Capillaries
ii) Arterioles
(1) Have same make up as arteries
(2) As they decrease in diameter
(3) They give rise to metarterioles
iii) Capillaries
(1) The smallest blood vessels
(2) Form connection between the smallest
(a) Arterioles
(b) Venules
(3) Make Up
(a) The thin walls form semipermeable membranes
(i) Substances in blood are exchanged here
(ii) with those in tissues/fluid
(4) Density of capillaries in tissue
(a) Varies depending upon tissues rate of metabolism
(i) High metabolic property tissue are richly supplied with capillaries
1. Muscle
2. Nerves
(ii) Low metabolic property tissue have little capillary supply
1. Articular cartilage
2. epidermis
(5) Exchanges in capillaries
(a) Materials exchanged
(i) Gases
(ii) Nutrients
(iii)Metabolic by products
iv) Veins
(1) Venules
(a) Microscopic veins continuing from capillaries
(b) Merge to form veins
(2) Veins
(a) Carry blood back to atria
(i) Pathways parallel arteries
(b) Valves
(i) Flaplike
(ii) Project inward
(iii)Composed of 2 leaflets that catch blood when blood backs up
(c) Function as blood reservoirs
(i) Aid in control of blood pressure by constricting (during Hemorrhage)
b) Blood pressure
i) Force exerted by the blood against the inner walls of the vessels
(1) Rises and falls consistent with the cardiac cycle
(a) Ventricles contract (systole) force blood into vessels
(i) Pressure rises sharply
(ii) Systolic pressure
(b) Ventricles relax
(i) Pressure drops
(ii) Diastolic pressure
(2) Physiologically
(a) As blood surges into arteries
(b) Elastic walls of arteries swell
(c) Walls recoil during relaxation
(d) The expansion and recoil of the arteries is the pulse
ii) Measurement
(1) Sphygmomanometer
(2) Cuff relays pressure to column of mercury standard (mm Mercury)
(a) Force exerted can move column x mm of Mercury
(b) 100 mm Hg = pressure moved column 100 mm Mercury
(3) Results of measurement are reported as a fraction
(a) Systolic / diastolic pressures
(4) Cuff is inflated so pressure exceeds arterial (brachial) pressure
(a) Effectively closes artery
(b) No blood flow
(5) Stethoscope is used to hear sounds of blood flow through artery
(a) Placed over brachial artery
(b) At distal end of cuff
c) Factors influencing BP
i) Heart action
(1) Determines how much blood enters the system
(2) Also determines rate of flow of blood
(a) Stroke volume
(i) Volume of blood discharged from ventricle
1. 70ml
(b) Cardiac output
(i) The volume discharged from the LV per minute
(ii) = SV x HR
(3) Blood pressure varies directly with CO
(a) If SV and/or HR increase than so does CO and BP
(b) If SV and or HR decrease than so does CO and BP
ii) Blood Volume
(1) 5 liters on average
(2) BP is directly proportional to BV
(a) If BV drops due to bleeding than BP drops
(3) on arterial side
(a) If SV and HR increase
(b) The arterial system may have to accept more blood than can flow
into the peripheral system
(c) This increase Arterial BV
iii) Peripheral resistance
(1) Created by friction of walls of vessels and blood
(a) During vasoconstriction PR increases
(b) In Vasodilation pressure drops
iv) Viscosity
(1) Ease in which molecules flow past one another
(2) Blood cells and plasma proteins increase viscosity
(a) Dehydration = Greater viscosity = greater resistance to flow = inc pressure
(b) When viscosity decreases then BP drops
(3) Normally viscosity is stable
(a) Anemia lowers viscosity
(b) Polycythemia (bone marrow abnormality) increases viscosity
d) Control of BP
i) Regulating cardiac output and peripheral resistance
(1) CO/PR
(a) Affected by mechanical, neural and chemical factors
(b) Mechanical (blood entering ventricle affects SV)
(i) Starling’s Law
1. when blood enters the ventricle
2. myocardial fibers are stretched
3. The greater the degree of stretch the greater the force of contraction
a. Within reason
(c) Neural Regulation
(i) Pressoreceptors (baroreceptors)
1. detect changes in pressure
2. located in the aortic arch and carotid sinus
(ii) Peripheral resistance
1. regulated by diameter of arterioles
a. if pressure is high message (vasodialation)
b. If pressure is low messages (vasoconstriction)
(d) Chemical
(i) Epinephrine & Norepinephrine
1. Increase both contractility and HR
2. influence peripheral resistance
a. causes vasoconstriction in many vessels
i. Epinephrine causes vasodialation in Skeletal Muscle
ii) Venous control of BP and flow
(1) Blood pressure decreases as it reaches the veins
(a) Blood flow is not a direct result of heart action
(b) Depends on other factors
(i) Skeletal muscle contraction - moves blood from one valve section to another
(ii) Respiratory movements Blood is squeezed from the abdominal veins into thoracics
(iii)Vasoconstriction - pressure is low Increased sympathetic impulses
e) Disorders of the circulatory system
i) Hypertension (High Blood Pressure)
(1) Persistently elevated arterial blood pressure
(a) Causes
(i) Some are unknown – essential (idiopathic) hypertension
(ii) Circulatory problems
1. Atherosclerosis, Arteriosclerosis
(iii)Kidney Disease
1. produces changes that interferes with blood flow to the kidneys
(2) Untreated can cause problems
(a) Thickening of left ventricle (heart enlargement)
ii)
iii)
iv)
v)
vi)
(i) Coronary arteries unable to supply blood to tissue
(ii) Angina pectoris
(b) Enhances the development of atherosclerosis
(i) In response to damage to vessels by HBP
(ii) Arteries injured accumulate plaque
1. May lead to vessel occlusions
2. Increase chances for
a. Embolisms
b. Thromboses
c. Stroke (brain)
Atherosclerosis
(1) Accumulation of lipids (cholesterol) inside the artery
(a) Formations called plaque
(b) Part of the repair process
(c) Goes haywire
(i) Gets large and protrudes into lumen (Opening of artery)
(ii) Allows clots to form (plaque gets sticky)
(iii)Occludes blood flow
Arteriosclerosis
(1) Continuation of atherosclerosis
(2) Degenerative changes to vessel wall
(3) Plaques calcify
(a) Vessels loose elasticity
(b) Vessel can rupture or hemorrhage
Phlebitis
(1) Inflammation of a vein
(2) Causes
(a) Trauma, Infection
(b) Unknown
Varicose Veins
(1) Abnormal and irregular dilations of superficial veins
(a) Particularly in legs
(b) Valve function may be lost
(c) Blood pools in distended areas
(2) Causes
(a) Increased back flow pressure distends veins
(b) Due to gravity
1. May increase venous pressure and can cause edema in associated tissue
Edema
(1) When too much fluid leave the capillary
(2) In response to trauma (Histamine is released)
(a) Lymph can’t handle the fluid
(b) Swelling occurs