Chapter 10 Blood Vessels and Blood Pressure

Transcription

1 VI edit Pag Chapter 10 Blood Vessels and Blood Pressure V edit. Pag

2 Function of the Cardiovascular System: Transport of O 2, nutrients and waste

3 Cardiac Output at Rest Pulmonary circulation Parallel arrangement of blood vessels supplying different organs assure fresh blood supply to every organ Some organs received an excess of blood supply that can be adjusted according to the body s needs Systemic circulation

4 Flow through Blood Vessels Flow Rate= Pressure Gradient / Vessel s Resistance F = dp / R

5 Pressure Gradient (dp) Force that push blood through blood vessels

6 Resistance (R) Easiness by which blood flow through a blood vessel Resistance is determined by: 1) Vessels length 2) Vessel s diameter (opening) 3) Blood s viscosity R ~ (viscosity x length) / (diameter) 4

7 Organization of the Vascular System Vascular System consist of: 1) Arteries 2) Arterioles 3) Capillaries 4) Venules 5) Veins

8 Organization of the Vascular System Vascular System Arteries Arterioles Capillaries Venules Veins Pressure reservoir Resistance Vessels Substance Exchange, Volume reservoir Resistance Vessels

9 Arteries Function: Passageway Pressure reservoir Structure: Endothelium Smooth Muscle Connective tissue- elastin & collagen

10 Arteries as a Pressure Reservoir

11 Blood Pressure

12 Blood Pressure Gradient

13 Mean Arterial Pressure (MAP) is the average pressure driving blood forward into the tissue MAP = DP + (1/3) Pulse pressure Pulse Pressure= SP DP

14 Systemic Arterioles Function: Passageway Resistance control via regulation of diameter Structure: Endothelium Smooth Muscleinnervated by sympathetic NS Connective tissue- with little elastin

15 Control of Blood Flow through Arterioles Changes in the diameter of the arterioles can be used to regulate: 1) Arterial blood pressure 2) Distribution of blood between different organs (distribution of cardiac output)

16 Functional Consequences of Blood Flow Control in Arterioles

17 Factors that Regulate Blood Flow in Arterioles Intrinsic Factors Extrinsic Factors Vasoconstriction (increased contraction of circular smooth muscle in the arteriolar wall, which leads to increased resistance and decreased flow through the vessel) Caused by: Myogenic activity Oxygen 2 Carbon dioxide 2 and other metabolites Endothelin Sympathetic stimulation Vasopressin; angiotensin II Cold

18 Factors that Regulate Blood Flow in Arterioles Vasodilation (decreased contraction of circular smooth muscle in the arteriolar wall, which leads to decreased resistance and increased flow through the vessel) Caused by: Myogenic activity Oxygen (O 2 ) Carbon dioxide (CO 2 ) and other metabolites Nitric oxide Sympathetic stimulation Histamine release Heat

19 Regulation of Blood Pressure in Arterioles by Metabolic Activity Metabolic activity of skeletal muscle cells ( oxygen need) Adenosine Vasodilation of arterioles Blood flow to skeletal muscle cells Oxygen available to meet oxygen need

20 Sympathetic Regulation of Blood Pressure in Arterioles Alpha1 receptors: present in arterioles throughout the body (except brain). Mediate vasoconstriction Beta2 receptors: present in in arterioles of heart and skeletal muscles. Mediate vasodilation Functional Consequences?

21 Kidney Regulation of Blood Pressure Vasopressin-regulate amount of water that is reabsorbed in kidneys Angiotensin II-regulate amount of sodium that is reabsorbed in kidneys Increase blood volume Increase blood volume Vasoconstriction Vasoconstriction

22 Control of arteriolar diameter is important for blood pressure regulation Total peripheral resistance Arteriolar diameter Blood viscosity Number of red blood cells Concentration of plasma proteins Local (intrinsic) control Extrinsic control Myogenic responses to stretch Vasopressin Heat, cold application (therapeutic use) Angiotensin II Histamine release (involved with injuries and allergic responses) Local metabolic changes in O 2 CO 2, other metabolites Sympathetic activity (exerts generalized vasoconstrictor effect) Major factors affecting arteriolar radius Epinephrine and norepinephrine

23 Blood Pressure Blood flows through a series of blood vessels in the systemic circulation due to the development of a pressure gradient. The mean arterial pressure is the average driving force, propelling blood through the vessels of the cardiovascular system. Brooks/Cole - Thomson Learning

24 Influence of Total Peripheral Resistance on Mean Arterial Pressure MAP = Cardiac Output X Total Peripheral Resistance

25 Control of arteriolar diameter is important for blood pressure regulation Total peripheral resistance Arteriolar diameter Blood viscosity Number of red blood cells Concentration of plasma proteins Local (intrinsic) control Extrinsic control Myogenic responses to stretch Vasopressin Heat, cold application (therapeutic use) Angiotensin II Histamine release (involved with injuries and allergic responses) Local metabolic changes in O 2 CO 2, other metabolites Sympathetic activity (exerts generalized vasoconstrictor effect) Major factors affecting arteriolar radius Epinephrine and norepinephrine

26 Capillary Function: Passageway Substance exchange Structure: Endothelium Brooks/Cole - Thomson Learning

27 Diffusion in Capillaries Diffusion: movement of a substance down its concentration gradient. There is no carrier-mediated transport in capillaries. D ~ concentration/distance Diffusion is facilitated in capillaries because: 1) Thin walls 2) Narrow diameter 3) Extensive branching 4) Slow flow

28 The Blood-Brain Barrier Consist of tightly packed endothelial cells that prevent unregulated flow of substances into the CSF and the brain

29 Velocity of Blood Flow Substance exchange is facilitated in capillaries because of the slow velocity of the blood flow Velocity = Flow rate / Total of flow cross-sectional area Notice flow rate = cardiac output = 5 L/min

30 Large cross-sectional area of the capillary system result in a significant reduction in Flow Velocity to keep up with a constant Flow Rate

31 Histamine can regulate pore size Substance Exchange Across Capillary Wall Capillary pores allow substance exchange between blood and tissue In some tissue capillaries don t have pores (brain), whereas in others the pores are very large (liver)

32 Capillaries and Metarterioles Capillary sphincters consist of smooth muscle rings Intrinsic factors regulate the capillary sphincters, such as: 1) O 2 2) CO 2 3) Adenosine

33 Regulation of Capillary Sphincter

34 Interstitial Fluid Fluid surrounding every cell

35 Substance Exchange Substance exchange takes place between: 1) Blood and interstitial fluid 2) Interstitial fluid and intracellular space

36 Substance Exchange Mechanism of substance exchange across the capillary wall: 1) Simple diffusion: allow the passage of single substances (independent of each other) 2) Bulk flow: allow the passage of substances in bulk (filtration)

37 Diffusion Allow the movement of a single substance down its concentration gradient

38 Bulk Flow or Filtration Allows the movement of several substances in bulk and requires some external force In the capillaries, blood pressure acts as the driving force that push bulk substances into the interstitial fluid

39 Forces Influencing Bulk Flow Capillary blood pressure (P C )-fluid or hydrostatic pressure Capillary osmotic pressure (=25 mm Hg) Interstitial fluid hydrostatic pressure (P IF = 1 mm Hg) Interstitial fluid osmotic pressure (=0 mm Hg)

40 Osmotic Pressure Tendency of water to move down its concentration gradient Membrane (permeable to H 2 O but impermeable to solute) Side 1 Side 2 H 2 O H 2 O moves from side 1 to side 2 down its concentration gradient Solute unable to move from side 2 to side 1 down its concentration gradient Pure water Lower H 2 O concentration, higher solute concentration Water concentrations not equal Solute concentrations not equal Tendency for water to diffuse by osmosis into side 2 is exactly balanced by opposing tendency for hydrostatic pressure difference to push water into side 1 Osmosis ceases Opposing pressure necessary to completely stop osmosis is equal to osmotic pressure of solution = Water molecule = Solute molecule Side 1 Side 2 Hydrostatic (fluid) pressure difference Osmosis Hydrostatic pressure Original level of solutions

41 Osmotic Pressure The larger the amount of solute, the less water, the larger the tendency of water to move in, the greater the osmotic pressure Side 1 Side 2 Hydrostatic (fluid) pressure difference Original level of solutions Osmosis Hydrostatic pressure

42 Net Flow is determined by the interplay of all forces acting on plasma and interstitial fluid Net Pressure= (Capillary Blood P + IT osmotic P) (IF hydrostatic P + Plasma osmotic P) Interstitial Fluid From arteriole Blood capillary To venule

43 Differences in MAP Determines Direction of Bulk Flow (Ultrafiltration and Reabsorption)

44 Bulk Flow Ultrafiltration occurs at the beginning of the capillaries Reabsorption occurs at the end of the capillaries Initial lymphatic vessel Interstitial fluid 11 mm Hg (ultrafiltration) -9 mm Hg (reabsorption) From arteriole Blood capillary To venule

45 Forces at arteriolar end of capillary Forces at venular end of capillary Outward pressure Outward pressure Inward pressure Inward pressure From arteriole Net outward pressure of 11 mm Hg = Ultrafiltration pressure Net inward pressure of 9 mm Hg = Reabsorption pressure

46 Net Filtration and Net Absorption along the capillary

47 Functional role of bulk flow (Regulation of extracellular fluid volume distribution between interstitial and plasma fluids) Myogenic responses to stretch Heat, cold application (therapeutic use) Histamine release (involved with injuries and allergic responses) Local (intrinsic) control Arteriolar diameter Total peripheral resistance Extrinsic control Number of red blood cells Local metabolic Sympathetic activity changes in 2 O (exerts generalized CO 2, other vasoconstrictor metabolites effect) Major factors affecting arteriolar radius Blood viscosity Concentration of plasma proteins Vasopressin Angiotensin II Epinephrine and norepinephrine Bulk flow plays an important role in regulating blood volume and blood pressure in cases of blood loss (hemorrhage, increased blood plasma volume)

48 Functional role of bulk flow (Regulation of extracellular fluid volume distribution between interstitial and plasma fluids)

49 Lymphatic System Allow return of fluid from interstitial fluid to the blood

50 Lymphatic System Run in parallel to circulatory system The lymphatic system transport interstitial fluid as lymph back into the circulatory system

51 Function of Lymphatic System 1) Return excess filtered fluid (interstitial fluid) 2) Defense against disease 3) Transport of absorbed fat 4) Return of filtered proteins

52 Lymphatic Vessels

53 Movement of Lymph Movement of lymph in lymphatic vessels is facilitated by: 1) Contraction of smooth muscles (intrinsic myogenic activity) 2) Squeezing effect of skeletal muscles

54 Edema Disruption of lymphatic movements resulting in increased interstitial fluid Lymph Interstitial fluid Net exchange pressure= (Cap. blood Pressure+IF osmotic Pressure) - (IF hydrostatic Pressure+Plasma Osmotic Pressure) Edema is caused by: 1) Reduced concentration of plasma proteins 2) Increased protein permeability of capillaries 3) Increased venous pressure 4) Blockade of lymph vessels

55 Veins Function: Passageway Blood reservoir (capacitance vessels) Structure: Endothelium Thin layer of smooth muscles with little myogenic activity and elasticity

56 Veins as Capacitance Vessels Velocity of flow = Flow rate / Total crosssectional area Veins are highly stretchable with no elastic recoil: Thin walls with less smooth muscles than arteries (less myogenic activity) Little elastin, more collagen Veins control venous return by slowing down the flow of blood to the heart

57 Regulation of Venous Return Venous return to heart is facilitated by differential pressure b/ atria and venous system 17 mm Hg 0 mm Hg Extrinsic factors: Sympathetic activity Skeletal muscle, skeletal muscle pump Venous valves Respiratory activity, respiratory pump Cardiac suction

58 Regulation of Venous Return Cardiac output Stroke volume End-diastolic volume Passive bulk-flow shift of fluid from interstitial fluid into plasma Salt and water retention Venous valves (mechanically prevent backflow of blood) Venous return Blood volume ( venous pressure pressure gradient) Cardiac suction effect ( pressure in heart pressure gradient) Respiratory pump ( pressure in chest veins pressure gradient ) Pressure imparted to blood by cardiac contraction ( venous pressure pressure gradient) Sympathetic vasoconstrictor activity ( venous pressure pressure gradient; venous capacity) Skeletal muscle pump ( venous pressure pressure gradient) = Short -term control measures = Long -term control measures

59 Sympathetic Regulation of Venous Return Alpha1 receptors: present in arterioles/veins. Mediate vasoconstriction=increase resistance (in arterioles) and decrease venous capacity (blood volume that veins can accommodate) Sympathetic stimulation produce venous vasoconstriction, decrease venous capacity

60 Venous Valves Prevent Backflow of Venous Blood Malfunction of venous valves generate varicose veins

61 Skeletal Muscle Contractions Squeeze Venous Blood Toward Heart

62 Negative Thoracic Pressure (due to Respiration) Increase Flow of Venous Blood Toward Heart

63 Venous Pressure and Gravity Tendency of blood to accumulate in lower veins is counteract by: 1) Activation of sympathetic nervous system (vasoconstriction) 2) Squeezing effect of skeletal muscles

64 Blood Pooling in Lower Parts of the Body due to Gravity Induces Swelling of Ankles and Feet

65 Decreased Atrial Pressure Increases Flow of Venous Blood Toward Heart Ventricular contraction AV valves move downward, pressure in atria low

66 Blood Pressure Regulation MAP = CO x TPR CO = HR x SV, TPF~viscosity/radius Blood pressure need to be regulated to maintain proper blood flow to all organs, prevent extra work by the heart Blood pressure is regulated by controlling cardiac output, total peripheral resistance and blood volume

67 Control of Cardiac Output Cardiac output Heart rate Stroke volume Extrinsic control Intrinsic control Parasympathetic activity Sympathetic activity (and epinephrine) End-diastolic volume Intrinsic control Venous return

68 Factors that Regulate Total Peripheral Resistance Total peripheral resistance Arteriolar diameter Blood viscosity Number of red blood cells Concentration of plasma proteins Local (intrinsic) control Extrinsic control Myogenic responses to stretch Vasopressin Heat, cold application (therapeutic use) Angiotensin II Histamine release (involved with injuries and allergic responses) Local metabolic changes in O 2 CO 2, other metabolites Sympathetic activity (exerts generalized vasoconstrictor effect) Major factors affecting arteriolar radius Epinephrine and norepinephrine

69 Blood Pressure Regulation Short term regulation Baroreceptor reflex - alter cardiac output and total peripheral resistance Long term regulation Involve control of blood volume by regulating salt and water balance MAP = CO x TPR CO = HR x SV

70 Baroreceptor Reflex Involve activation of carotid sinus and aortic arch baroreceptors, transmission of information to cardiovascular center and stimulation of ANS

71 Changes in MAP Regulate Firing Rate of Baroreceptors

72 Baroreceptor Reflex Parasympathetic stimulation Heart Figure Heart rate Page 378 Cardiac output Blood pressure Sympathetic stimulation Heart Heart rate Contractile strength of heart Stroke volume Cardiac output Blood pressure Arterioles Vasoconstriction Total peripheral resistance Blood pressure Veins Vasoconstriction Venous return Stroke volume Cardiac output Blood pressure

73 Homeostatic Regulation of Blood Pressure by Baroreceptor Reflex When blood pressure becomes elevated above normal Carotid sinus and aortic arch receptor potential Rate of firing in afferent nerves Cardiovascular center Sympathetic cardiac nerve activity and sympathetic vasoconstrictor nerve activity and parasympathetic nerve activity Heart rate and stroke volume and arteriolar and venous vasodilation Cardiac output and total peripheral resistance Blood pressure decreased toward normal

74 Homeostatic Regulation of Blood Pressure by Baroreceptor Reflex When blood falls bellow normal Carotid sinus and aortic arch receptor potential Rate of firing in afferent nerves Cardiovascular center Sympathetic cardiac nerve activity and sympathetic vasoconstrictor nerve activity and parasympathetic nerve activity Heart rate and stroke volume and arteriolar and venous vasodilation Cardiac output and total peripheral resistance Blood pressure increase toward normal Fig (2) Page 379 Slide 52

75 5) Emotions Other Factors that Modulate BP 1) Osmoreceptors in hypothalamus 2) Chemoreceptors in aortic and carotid bodies 3) Increased load as a result of exercise 4) Hypothalamic control of cutaneous blood vessels

76 Changes in Blood-Pressure Control Mechanisms 1) Hypotension (Blood pressure less than 100/60) 2) Hypertension (Blood pressure more than 140/90)

77 Disruption of Blood Pressure Control Causes Hypertension 1) Primary hypertension Caused by a variety of factors like defect in salt regulation, drugs, local vasoactive substances 2) Secondary hypertension Caused by renal dysfunctions, atherosclerotic plaques and lack of elasticity in arteries, abnormal release of adrenaline