Use the video clip: CH 19 - Anatomy of the Blood Vessels for a review of vessel structure

1. Chapter 19 The Cardiovascular System: Blood VesselsG.R. Pitts, J.R. Schiller, and J. F. Thompson Use the video clip: CH 19 - Anatomy of the Blood Vessels for a review of vessel structure

2. Vessel Structure • Structure/function relationships change as one moves through the cardiovascular tree • Tunic thickness and composition of the three layers are variable

3. Capillary Beds • Flow regulated by smooth muscle “valves” • Metarterioles • from arterioles to venules through capillary bed • allows flow through capillary bed w/out flow through caps • True capillaries • pre-capillary sphincter • ring of smooth muscle • open/close to control flow • regulated by chemicals • intermittent vasomotion, open for flow 5-10 times each minute

4. Capillaries • Allow exchange of nutrients and wastes between the blood and the tissue cells • Capillary structure – simple squamous epithelium • basal lamina - connective tissue • endothelial cells • Details of structure determine specific functions • 3 types: continuous, fenestrated, sinusoidal

5. Vascular Anastomoses • Arterial Anastomoses - provide collateral supply to some organs and tissues, e.g., skeletal muscles • Arteriovenous Anastomoses - thoroughfare channels • Venous Anastomoses - most common, e.g., deep and superficial veins in limbs and head

6. Vessel Structure - Histology Vein Artery Vein Artery

7. Varicose Veins

8. Vessel Structure/Function • At rest • 60% of blood volume is located in veins and venules • venous system serves as reservoirs for blood • particularly veins of the abdominal organs and the skin • ANS regulates volume distribution • vasoconstriction • vasodilation • diverts blood to areas with increased metabolic needs Spleen ~1L Compare to Cardiac Output figures

9. Blood Distribution at Rest  0.75 L/min Rest CO = 5 L/min

10. Blood Distribution -- Exercise Using cardiac reserve CO = 25 L/min Heavy Exercise  20 L/min  0.75 L/min Rest CO = 5 L/min

11. Physiology of Circulation • Flow = ΔP/R • or CO = MAP/R • MAP = mean arterial pressure • higher pressure to lower pressure with decreasing resistance (R) • Blood pressure • pressure of the blood on the vessel wall • measure the pressure of a volume in a space • systole/diastole - 120/80 (mm Hg) • BP falls progressively from the aorta to essentially 0.0 mm Hg at the right atrium (RA)

12. Physiology of Circulation • Resistance - opposes blood flow because of the friction produced by the vessel walls • Factors that affect resistance (R) • (1) resistance (R) is proportional to viscosity: V R • “thickness” of the blood • e.g., dehydration, elevated plasma proteins, polycythemia (RBCs), leukemias (WBCs) • (2) resistance (R) is proportional to vessel length • obesity increases the route lengths within connective tissue • (3) resistance (R) is inversely proport. to vessel width • decrease the radius by 1/2 and R increases by 16X • most important in vessels that can change their size actively • changes in diameter affect flow • vessel wall drag – blood cells dragging against the wall • laminar flow – layers of flow

13. Physiology of Circulation • Systemic Vascular Resistance (SVR) =Total Peripheral Resistance (TPR) • all vascular resistance is offered by the systemic vessels • which vessels change size? • resistance is highest in arterioles • largest pressure drop is in the arterioles • Relationship of the radius to resistance in the arterioles is due to smooth muscle contraction/relaxation

14. Systemic Blood Pressure Arterial Blood Pressure • Pulsatile in arteries due to the pumping of the heart • Systolic/diastolic values • Pulse pressure = systolic (minus) diastolic Q- What does the Windkessel effect have on pulse pressure? Q- What is the effect of hardening of the arteries on pulse pressure?

15. Systemic Blood Pressure • Capillary Blood Pressure • relatively low blood pressure • low pressure is good design for capillaries because: • capillaries are fragile - high pressure would tears them • capillaries are very permeable - high pressure forces a lot of fluid out

16. Systemic Blood Pressure • Venous return • the volume of blood flowing back to heart from systemic veins • depends on pressure difference from beginning of venules (16 mmHg) to heart (0 mmHg) • any change in right atrial (RA) pressure changes venous return

17. Venous Return/Valves • Assistance for venous return • skeletal muscles act as pumps • contracting muscles squeeze veins • force blood back to the heart • valves prevent back flow • respiratory pump • inhaling causes a lowered pressure in the thoracic cavity • primarily to pull air into the lungs • helps to draw blood into thorax via pulmonary circulation

18. Velocity of Blood Flow • Velocity of blood flow - inversely proportional to the total cross sectional area (CSA) of vessels • Aorta • total CSA = 3-5 cm2 • velocity = 40 cm/sec • Capillaries • total CSA = 4500-6000 cm2 • velocity = 0.1 cm/sec • Vena Cava • total CSA = 14 cm2 • velocity = 5-20 cm/sec

19. Capillary Function • Capillary Function • site of exchange between blood and tissues • delivery of nutrients and removal of wastes • slow flow allows time for molecules to diffuse • Mechanisms of nutrient exchange • diffusion - O2, CO2, glucose, AA's, hormones, electrolytes -- diffuse down [ ] gradients • lipid soluble molecules can pass through cell membrane easily • water soluble molecules generally require transport mechanisms to enter/exit cells

20. Capillary Function • Forces driving the movement of fluid • Hydrostatic pressure capillary (HPc) • Hydrostatic pressure interstitial fluid (HPif) • Osmotic pressure capillary (OPc) • Osmotic pressure interstitial fluid (OPif) • Net filtration pressure (NFP) is the net effect of all four forces at any point along the capillary • Fluid movement • Fluid diffuses out and is reabsorbed across the capillary walls • Starling’s law of the capillaries

21. Net Filtration Pressure (NFP) • NFP = (HPC - HPIF) - (OPC - OPIF)        = Pushing forces - Pulling forces • On average, 85% of fluid entering the tissues on the arteriole side is reabsorbed on venous end

22. Maintaining Blood Pressure: Short Term Mechanisms - CNS • Neural Control - Cardiac Centers in medulla • Vasomotor center • medullary area dedicated to control of blood vessels • sends sympathetic output to blood vessels • Vasoconstricts or vasodilates as needed • Vasomotor tone - normal amount of vasoconstriction or vasodilation • ANS can vary the vasomotor tone which varies the delivery of blood to particular regional capillary beds • receives sensory input from different sources • baroreceptors (blood pressure) • chemoreceptors (O2, CO2, H+, HCO3-)

23. Maintaining Blood Pressure: Short Term Mechanisms - CNS • Baroreceptor initiated reflex • located at carotid sinuses and aortic arch • monitors blood pressure • regulates the activity of the sympathetic nervous system (vascular tone)

24. Maintaining Blood Pressure: Short Term Mechanisms - CNS • Chemoreceptor initiated reflexes • Carotid bodies, aortic bodies • Monitor changes in indicator chemicals (O2, CO2, H+, HCO3-) •  CO2,  H+, O2 (stresses) result in  sympathetic activity and  BP

25. Maintaining Blood Pressure: Short Term Mechanisms - CNS • Influence of higher brain centers (areas above medulla) - cortex and hypothalamus • not involved in minute-to-minute regulation • influence vasomotor center depending on conditions • temperature changes • stressful emotional situations

26. Maintaining Blood Pressure: Short Term Mechanisms - Chemicals • Renin - Angiotensin - Aldosterone • Renin/ACE • enzymes from kidney/lung • catalyze formation of Angiotensin I/II • Angiotensin II • vasoconstrictor • stimulates ADH, thirst • stimulates aldosterone release for Na+ & H2O reabsorption • why/how would these things affect blood pressure?

27. Maintaining Blood Pressure: Short Term Mechanisms - Chemicals • diverts blood from the skin and abdominal organs to the skeletal muscles • increases heart rate, stroke volume and, therefore, cardiac output & blood pressure • Adrenal medulla releases epinephrine and norepinephrine in coordination with activity from the Sympathetic Division of the ANS

28. Maintaining Blood Pressure:Short Term Mechanisms - Chemicals • Antidiuretic Hormone (ADH) or Vasopressin • osmoreceptors in hypothalamus trigger release from the neurohypophysis • ADH targets kidneys to retain water (ADH action is inhibited by alcohol) • ADH also stimulates vasoconstriction at high levels • why/how would this affect blood volume and pressure?

29. Maintaining Blood Pressure:Short Term Mechanisms - Chemicals Atrial Natriuretic Peptide (ANP) released from atrial cells in response to blood vol &  BP stimulates vasodilation, Na+ and water loss, antagonizes Aldosterone, inhibits thirst why/how would this affect blood volume and pressure?

30. Maintaining Blood Pressure: Long Term Regulation • Renal mechanism • control blood volume • nervous control - ANS • hormones • regulation in the short term by adjusting blood pressure and adjusting blood flow to different capillary beds • regulation in the long term by adjusting blood volume • target the kidneys •  BP,  urine flow to  BP •  BP,  urine flow to  BP

31. Control of Blood Flow • Autoregulation (local control) - local automatic adjustment of blood flow to match specific local tissue metabolic needs • Physical changes • Warming -  vasodilation • Cooling -  vasoconstriction • Chemical changes in local tissues generate metabolic byproducts • vasodilators or vasoconstrictors • Myogenic control • smooth muscle controls resistance •  stretch  contraction;  stretch  contraction

32. Blood Flow in Special Areas • Skeletal Muscle • fine tuned control with wide variation in rate of flow • brain directs the sympathetic division for NE release in response to the degree of muscular activity • α receptors - vasoconstriction • β receptors - vasodilation • metabolic regulation in tissue • low O2causes vasodilation, increasing flow • high O2cause vasoconstriction, decreasing flow • Brain • minimal variation in rate of flow • minimal nutrient storage, so adequate flow must be maintained! • local metabolic changes adjust local autoregulation

33. Blood Flow in Special Areas • Skin • adjusting rate of flow aids in temperature regulation • controls skin’s capacity as a blood reservoir • sympathetic and local metabolic regulation • Lungs • low pressure (25/10 mm Hg), low resistance system • flow regulated by O2 availability in the lungs • high O2 vasodilation to increase flow – opposite of muscle • low O2 vasoconstriction to decrease flow – opposite of muscle • Heart • variable flow depending on metabolic/pumping activity • sympathetic and local metabolic regulation

34. Regulation of Blood Pressure CO = MABP/R MABP = CO x R

35. The CirculationLearn specific vessels and routes in lab

36. The CirculationLearn specific vessels and routes in lab

37. Hepatic Portal System • HPS collects venous blood from five abdominal organs and routes the blood to the liver for specific processing of transported molecules - stomach: toxins (ethanol) - small intestine: nutrients, toxins - large intestine: nutrients, toxins - pancreas: insulin, glucagon - spleen: RBC breakdown products a portal system transfers venous blood from one capillary bed to another capillary bed before the blood is returned to the heart

38. Fetal Circulation Umbilical veins bring oxygen and nutrients from the placenta to the liver and then to the heart of the fetus

39. Fetal Circulation • ductus venosus bypasses liver • 3 Right  Left shunts • because oxygenated blood is derived from the placenta • ductus arterious  ligametum arteriosum • foramen ovale  fossa ovalis • interventricular shunt  no remnant

40. Circulatory Shocksudden dramatic loss in blood pressureor sudden decrease in circulatory flow • Hypovolemic Shock • Acute hemorrhage (or other sudden fluid loss as from vomiting or diarrhea) • Vascular Shock • Loss of vasomotor tone as from anaphylaxis, neural malfunction, or poisons (septicemia) • Cardiogenic Shock • Loss of cardiac output due to heart failure

41. End Chapter 19