Vasoconstriction if BP goes up. Vasodilation BP goes down. blood.. Vasodilation wastes detected, to move them away. None

Transcription

1 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics 15 Summary of Controls on Perfusion and Systemic BP (short version): 1. Autoregulation of perfusion Control Category Short Term Short Term Outcomes Longg Term Long Term Outcomes Autoregulation: Methods the tissues have to control their own available blood flow (Perfusion). In general, act to protect the tissues from high or low BP. High BP causes many problems; low BP causes wastes to build up and tissue death. Myogenic: Smooth muscle surrounding local arterioles dilate/contract to increase flow/decrease flow, depending on blood pressure. Local Metabolites: Presence of nutrients/wastes causes the precapillary sphincters to open or close, depending on need of tissues. Vasoconstriction if BP goes up. Vasodilation if BP goes down Vasodilation if wastes detected, to move them away. Vasoconstriction not discussed. Angiogenesis: Tissues can causee new blood vessels to grow, bring them more blood.. None Diverts blood flow to organ or tissue. Cancerous tumors mimic this, stealing blood from healthy tissues.

2 Anatomy & Physiology II Note Series 2. Nervous Controls of Systemic BP (Also see summary image at end of this section) CJ Shuster 16 Control Category Short Term Short Term Outcomes Long Term Long Term Outcomes Nervous System: Extrinsic control from the nervous system. In general, this is Systemic Control of BP - acts to protect the whole body, including the brain, from high or low BP. Often, opposite effects of the Autoregulation Control Methods. Only short-term (acute). Sympathetic control only! There seemss to be little influence from the parasympathetic system, allowing local controls (autoregulation) to determine blood flow. Baroreflexes mediated by pressure in the aorta & carotid bodies. Unfortunately, thesee homeostatic controls seem to be ignored in the case of chronic hypertension. That is, they tend to adapt, so blood pressure is not lowered properly. Vasodilate if need nutrients/get of wastes. rid No Vasoconstriction discussed. None Chemoreflexes Not discussed. None Monitor changes in ph and oxygen and carbon dioxide levels of the blood. Higher Brain influences, especially under stress/anxiety. Not discussed. None

3 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics 17 Summary Image for Neural Control of BP, including effects on CO: NOTE TO STUDENT: Everything talked about up to this point concerns a relatively normal cardiovascular system, meaning an average person at sea level. There are a number of changes that occur due to abnormal circumstances that are NOT pathological, such as responses to exercise and living at a higher elevation. We will not go through this in this series. Rather, if it is offered, it will come as an addendum.

4 Anatomy & Physiology II Note Series CJ Shuster Endocrine Controls of Systemic BP Control Category Short Term Short Term Outcomes Long Term Long Term Outcomes Endocrine system: Extrinsic control from via hormones In general, this is Systemic Control of BP - acts to protect the whole body, including the brain, from high or low BP. Often, opposite effects of the Autoregulation Control Methods. Slower than the neural methods, but longer lasting. We only discussed short term (acute) methods. If BP goes down, 3 hormones discussed: Renin & Angiotensin II hormonal complex Antidiuretic Hormone (ADH) Adrenal medulla hormones: Epinephrine & Norepinephrine (Epi & NE) Raises BP if it drops (in a lot of ways, including generalized vasoconstriction) Raises BP if it drops (increases blood volume by lowering urine production) Raises BP if it drops (in a lot of ways, including generalized vasoconstriction) If BP goes up, 1 hormone discussed; short-term effect only: Atrial Natriuretic Lowers BP, Peptide generalized vasodilationn (among other things) Exist, but we didn t discuss them.

5 Shuster s A&P Notes Series Blood Vessels, Perfusion & Capillary Dynamics 19 - For exam, know/define the following: Autoregulation, & what happens to vasoconstriction/dilation if BP drops or rises Define Myogenic Define Local metabolites Define Angiogenesis Neural Systemic Control, & what happens to vasoconstriction/dilation if BP drops or rises Sympathetic response Define chemoreceptors and baroreceptors Hormonal Systemic Control, & what happens to vasoconstriction/dilation if BP drops or rises Define Renin, Angiotensin, and ACE. Where are they produced? What does Renin do to angiotensin I? What does angiotensin II do to blood vessels? What do the adrenal medulla hormones do to BP, in general, and under what circumstance? What does ANF do to BP, and under what circumstance?

6 Anatomy & Physiology II Note Series CJ Shuster 20 D) CAPILLARY EXCHANGE & HOMEOSTASIS OF THE VOLUME OF BLOOD (Capillary Dynamics) 1) Exchange with the interstitial tissues: Microcirculation. - What are the forces driving the nutrients & wastes in/out of the capillaries? Movement in/out of capillaries, over the endothelial surface or between cells: 1. Passive means: (i) Diffusion & osmosis the vast majority! (ii) Filtration ( bulk flow ): Areas where filtration is important have lots of intracellular clefts. Special capillaries are called "Fenestrated capillaries". * Kidneys, intestines, etc. * Fenestrations. 2. Active means: exocytosis, endocytosis, pinocytosis. We will not be dealing with the active means, however. - For the most part: move water via filtration or osmosis, and let ions/dissolves substances follow! This is what we will be talking about here. * Filtration: moving substancess out of the bloodstream. * Reabsorption: moving substances back into the bloodstream. Later, we will be seeing important places where these processes are active: The digestive & urinary tracks But for most of the tissues, the cardiovascular system uses passive means. - Important Terms: Ischemia: insufficient blood flow. Hemorrhage: blood loss due to a broken vessel.

7 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics 21 - The process depends on the difference of gradients between the interstitium and blood, with molecules moving to low concentrated spaces from high concentrated ones. Wastes (such as CO2) move out of interstitial fluids into blood, nutrients such as glucose, amino acids, oxygen (O2) move opposite direction. Concentration gradients must be maintained, which is why blood flow is so important. * Diffusion through the capillary walls depends on the permeability of the wall to which exchange materials: 1. If charged, they need to be small. 2. Lipid-soluble molecules move freely (which is why lipid soluble toxins are so dangerous!). 2) Homeostasis of water movement between compartments (blood, interstitial fluids, intracellular fluids) - Since we wall. are dependent (mostly) on diffusion & osmosis, we must maintain concentration gradients across capillary - To maintain homeostasis of water levels in the bloodstream (Blood Volume): * Local Control: Some chemicals increase/decrease permeability of capillary walls. More about this as we use them during the semester! * Systemic Control: Lymphatics return water to the veins. More on this in the Lymphatics Chapter. - Homeostatic imbalances: 1. Increase movement of ions, water into tissues = edema. And, low BP. 2. Increase movement of ions/ /water into capillaries = dehydration (of the tissues). And, raises BP.

8 Anatomy & Physiology II Note Series - Detail of Capillary Dynamics - There are 4 pressures: 2 Hydrostatic and 2 Osmotic (Colloidal) Pressures There are two hydrostatic and two osmotic pressures that affect transcapillary fluid exchange. (but, only 2 are important under normal circumstances): 1. Capillary (plasma) hydrostatic pressure IMPORTANT pressure! An outward pressure. This is mostly due to blood pressure; therefore, Cardiac Output. This is filtration pressure. 2. Capillary (plasma) osmotic ( colloidal ) pressure IMPORTANT pressure! An inward pressure. Blood is hypertonic to the extracellular fluid. This pressure is principally determined by plasma proteins that are relatively impermeable. Thus, the term colloidal. Albumin generates about 70% of this pressure. 3. Tissue (interstitial) hydrostatic pressure. An inward pressure. Normally = zero! CJ Shuster Tissue (interstitial) osmotic ( colloidal ) pressure. An outward pressure. Water moves into tissues, due to thee presence of some large proteins. Only important in some pathologies. - We are going to ignore #3 & #4. So, from now on, Blood hydrostatic pressure ( filtration pressure ) and Blood colloidal pressure ( osmotic pressure ) are our only concerns.

9 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics 23 - In what direction will fluid move? Filtration versus Reabsorption 1. Capillary hydrostatic pressure on the capillary walls moves it out at the beginning of the capillary. Due to blood pressure. Theree is more pressure on the arteriole side because of friction in the capillary lowers P by the time it gets to the venule side. In a well-functioning cardiovascular system: on average, it is about +35 mmhg, giving us an outward pressure of about +10 mmhg, leading to filtration of waterr and any small ions and electrolytes dissolved in it. 2. Osmotic pressure moves it out at the end of the capillary. This pressure is also not constant throughoutt the capillary. This increasess as we get to the end of the capillary (venulee end), as we have moved water out of the capillary at the arterial end (making the blood more hypertonic). This pressure is typically mmhg, givingg us an average inward pressure of -7 to -10 mmhg, leading to the reabsorption of the water.

10 Anatomy & Physiology II Note Series CJ Shuster 24 Homeostasis of blood volume & pressure: Arteriole-end hydrostaticc pressure and venule-end osmotic pressure are equal. Imbalances: * If hydrostatic pressure (blood pressure) > osmotic pressure, we have edema. * If hydrostatic pressure (blood pressure) < osmotic pressure, we have dehydration. Congestive Heart Failure: Occurs when the heart is unable too provide sufficient pumpp action to maintain blood flow to meet the needs of the body. The term Congestive refers to fluid buildup in lungs. D) CIRCULATORY SHOCK - inadequate blood flow to tissuess causes series of events that leads to death. - Usually due to a loss of blood pressure. - There are many types, depending how BP was lost. Here are some common examples: 1. Hypovolemic Shock - loss of blood volume. * It may be due to Hemorrhage (blood loss due to a broken vessel) ), extreme dehydration, etc. 2. Cardiogenic shock - inadequate circulation due to insufficient heart contraction. This may be the result of heart attack or ectopic focus.

11 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics Distributive shock - shock due to uncontrolled vasodilation, in response to some chemical/toxin present. The chemicals are called vasodilators. - Distributive shock: when a vasodilator ends up in the entire bloodstream, causing this local vasodilation to occur throughout thee body, dropping BP. There are several causes of distributive shock: 1. Septic shock - vasodilation in response to chemicals/metabolites released by an infecting agent (usually a bacterium). Sepsis or Septicemia infection of the blood Recall that certain metabolites produced normally lead to vasodilation (seee Perfusion section); this is an unfortunate consequence. 2. Anaphylactic shock - reaction to an allergen, antigen, drug or foreign protein causing the release of histamine which causes widespread vasodilation. 3. Neurogenic shock - Caused by any traumatic injuries withh immense pain. Recall that epinephrine also causes vasodilation, for example. ** There are other types of shock, all with different causes of loss of BP

12 Anatomy & Physiology II Note Series CJ Shuster 26 - Pathophysiology How this kills: The patient enters a positive feedback loop that results in death. Example: Often, shock occurs when there is a conflict between perfusion needs of local tissues, and systemic needs to maintain BP: A heart attack kills enough cardiac tissue to lessen blood flow due to a lowered BP. The body's tissues become hypoxic (low oxygen), which results in local vasodilation. That leads to a further lowering of systemic BP. The cardiovascular system responds by trying to increase BP via all the mechanism described earlier. There is a sympathetic nervous response, but the damaged cardiac tissue cannot keep it up. This causes vasoconstriction in some places, but vasodilation in others. - Patient goes through several stages of shock: The first stage is called Compensated Shock: the patient's body is employing physiological mechanisms, including neural, hormonal and local chemical mechanisms in an attempt to reverse the condition. The symptoms are rapid heart rate, anxiousness, and other signs of Sympathetic output. Life can be saved during Compensated Shock. We will not name the other stages of shock in this series. Eventually, the tissues become acidic, and the cells starve from lack of oxygen and glucose. This includes the cardiac cells (lowering CO further), and the pre-capillary sphincter muscles (causing more blood to pool up). Blood pools up, tissues die, organs fail.

13 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics 27 E) MONITORING CIRCULATORY EFFICIENCY - VITAL SIGNS - circulatory + respiratory + body temperature. 1) PULSE - Put pressure against artery to feel pulse put out by each heartbeat. Must be an artery, as veins are not pulsatile. Also, arteries = large & close to the surface. * RADIAL - Most common. * Also act as PRESSURE POINTS to stop bleeding. * Normal = beats/min; but varies between lying down & sitting up, emotional states, etc. 2) BLOOD PRESSURE - AUSCULATORY METHOD - checking systemic BP using a Sphygmomanometer and a pressure cuff wrapped around arm.

14 Anatomy & Physiology II Note Series CJ Shuster Add air until P(cuff )> systolic pressure, at which point the artery is compressed and no blood can pass through. 2. Then, release air in cuff while listening to artery w/ a STETHESCOPE. When P(cuff) = P(systole), blood just barely can pass through artery. Can hear SOUNDS OF KOROTKOFF = blood squeezing through artery = SYSTOLIC PRESSURE = HIGHEST PRESSURE. 3. Keep releasing air until P(cuff) = P(diastole) - blood flows unobstructed through artery. SOUNDS OF KOROTKOFF disappear = DIASTOLIC PRESSURE = LOWEST PRESSURE OF SYSTEM. BP measured as SYSTOLE / DIASTOLE Normal = ( mmhg) / (75-80 mmhg). But, depends on age, race, weight, socioeconomic class, mood, physical activity, posture.

15 Shuster s A&P Notes Series Blood Vessels,, Perfusion & Capillary Dynamics 29 - Systolic and Diastolic blood pressure readings are variable in an individual,, and althoughh useful, are limited in their diagnostic use. Therefore, we use other measures of arterial efficiency: Pulse pressure is the difference between the systolic and diastolic pressure readings. It is measured in i millimeters of mercury (mmhg). It represents the force that the heart generates each time it contracts. If resting blood pressure is 120/80 mmhg, pulse pressure is 40. Mean arterial pressure (MAP) is a term used to describe an average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle. Do not worry about how to figure MAP pressure for this series. But, it is the number we use in the rest of this chapter while talking about the pressure of blood as it enters the arterioles & capillaries. Lower MAP results in ischemia, or insufficient blood flow. 3) ALTERATIONS IN BP (i) HYPOTENSION - low BP; systolic < 90 mmhg. Not common. Low blood pressuree can be caused by low blood volume, hormonal changes, widening of blood vessels, medicine side effects, anemia,, heart problems or endocrine problems. (a) ORTHOSTATIC HYPOTENSION - head rush or dizzy spell, person's blood pressure suddenly falls when standing up or stretching. Common in elderly people; lessened sympathetic nervous response leads to blood pooling in lower limbs, leads to fainting spellss when rising from bed. Cure: slow postural changes before rising. (b) CHRONIC HYPOTENSION Condition last more than a year or two. Most common reason: Heart problems. Another example: bad nutrition leads to anemia leads to low blood protein leads to low viscosity leads to low PR leads to low BP. Hypothyroidism also causes it. (c) ACUTE HYPOTENSION usually blood loss. (ii) HYPERTENSION - Strains the heart and vessels. Big range for systolic pressures, as it is age and sex related. Heree is a simplified chart that most

16 Anatomy & Physiology II Note Series medical peoplee use: CJ Shuster 30 Not curable; often = a symptom. Death from stroke, heart attack, renal failure. (a) PRIMARY HYPERTENSION: No identifiable cause. Most common (90-95%). Complex; due to many factors. * Diet, obesity, age, race, heredity, stress, smoking. 30% of all people over 50. (b) SECONDARY HYPERTENS SION: Identifiable cause. Kidney disease most common cause (we ll look at the kidney s role in blood volume in the Kidney Chapter). (c) ORTHOSTATIC HYPERTENSION: person's blood pressure suddenly rises when standing up or stretching. Common in elderly people; breakdown in normal sympathetic nervous response. Heart palpitations