Human Physiology II Notes-2 PDF

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Human Physiology II Notes...

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----------------------------------------------------------------------------------------------------------------------------------------Forces Influencing Bulk Flow 1. Capillary blood pressure (Pc) a. Fluid or hydrostatic pressure exerted by blood on the inside of capillary walls b. Tends to force fluid out of capillary 2. Plasma-colloid osmotic pressure (  P) a. Oncotic pressure caused by colloidal dispersion of plasma proteins b. Plasma has higher protein concentration but lower water concentration c. Encourages movement into the capillaries 3. Interstitial fluid hydrostatic pressure (PIF) a. Pressure exerted by interstitial fluid on the outside of capillary walls b. Tends to force fluid into capillaries 4. Interstitial fluid–colloid osmotic pressure (IF) a. Plasma proteins in interstitial fluid is extremely low b. Does not contribute significantly to bulk flow i. Very close to zero

PC = Capillary blood pressure P = Plasma-colloid osmotic pressure

PIF = Interstitial hydrostatic pressure IF = Interstitial-colloid osmotic pressure

Net filtration and net reabsorption along vessel length

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----------------------------------------------------------------------------------------------------------------------------------------The Lymphatic System • Extensive network of one-way vessels • Functions: 1. Return of excess filtered fluid 2. Defense against disease a. Lymph nodes have phagocytes that destroy bacteria filtered from interstitial fluid 3. Transport of absorbed fat 4. Return of filtered protein • Initial lymphatics o Small, blind-ended terminal lymph vessels o Permeate almost every tissue of the body • Lymph o Interstitial fluid that enters a lymphatic vessel • Lymph vessels o Formed from convergence of initial lymphatics o Eventually empty into venous system near where blood enters right atrium o One-way valves spaced at intervals direct flow of lymph toward venous outlet in chest • Lymph empties into the venous system at the junction of the jugular and subclavian veins o Veins later empty into the superior vena cava that leads into the right atrium of the heart • Lymph flow averages 3 L per day o Blood flow averages 7200 L per day • Oedema and Interstitial Fluid Accumulation • Swelling of tissues due to accumulation of excess interstitial fluid • Causes of oedema o Reduced concentration of plasma proteins e.g. in kidney disease, liver disease or loss of protein from burns o Increased permeability of capillary wall e.g. allergic reaction o Increased venous pressure e.g. swelling during pregnancy o Blockage of lymph vessels e.g. Elephantiasis Veins • Venous system transports blood back to heart o Capillaries drain into venules o Venules converge to form small veins that exit organs o Smaller veins merge to form larger vessels • Veins o Large radius offers little resistance to blood flow o Also serve as blood reservoir

----------------------------------------------------------------------------------------------------------------------------------------Factors influencing venous return • Cardiac activity o Driving pressure from cardiac contraction o Effect of cardiac suction • Sympathetically induced venous vasoconstriction • Skeletal muscle activity • Effect of venous valves • Respiratory activity

Blood Pressure • Blood pressure is monitored and regulated in the body • Primary determinants o Cardiac output o Total peripheral resistance o Mean arterial pressure = cardiac output × total peripheral resistance Determinants of Mean Arterial Blood Pressure are cardiac output and total peripheral resistance (1) • 2 – Determinants of cardiac output are heart rate and stroke volume • 3 – Parasympathetic activity decreases heart rate • 4, 5 – Sympathetic activity increases heart rate and stroke volume, and increase venous return by inducing venous vasoconstriction (7) • 6 – According to Frank-Starling law, stroke volume increases as venous return increase

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Other factors that enhance venous return are skeletal muscle pump (8), respiratory pump (9) and cardiac suction (10). How much blood returns to heart is influenced by the effective circulating blood volume (11), which depends on short-term (bulk flow, 12) or long-term (salt-water balance, 13) effects. Salt-water balance is hormonally controlled (14, 22) 15 – Total peripheral resistance is determined by arteriolar radius and blood viscosity. 16 – The number of red blood cells determines blood viscosity. Arteriolar radius depends on local metabolic control (17) that match blood flow to metabolic needs e.g. increased muscle contraction (18). Arteriolar radius is constricted (20) by sympathetic activity (19) and hormones (21)

The Baroreceptor Reflex • Any change in mean arterial pressure triggers an autonomic system response – the baroreceptor reflex o Influence heart rate and blood pressure to adjust cardiac output and total peripheral resistance to restore blood pressure to normal • Location of important baroreceptors o Carotid sinus o Aortic arch *Firing rate in afferent neuron from carotid sinus baroreceptor – provide moment-to-moment regulation of blood pressure*

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Short-term control adjustments o Occur within seconds o Adjustments made by alterations in cardiac output and total peripheral resistance o Mediated by means of autonomic nervous system influences on heart, veins, and arterioles Long-term control adjustments o Require minutes to days o Involve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst

Summary of the effects of the Autonomic Nervous system (Parasympathetic and Sympathetic Nervous Systems) on Mean Arterial Blood Pressure

----------------------------------------------------------------------------------------------------------------------------------------Baroreceptor Reflexes to Restore Blood Pressure to Normal

Other Reflexes and Responses • Left atrial receptors and hypothalamic osmoreceptors affect long-term regulation by controlling plasma volume • Chemoreceptors in carotid and aortic arteries are sensitive to low O2 or high acid levels in blood - reflexively increase respiratory activity • Certain behaviors and emotions mediated through cerebral-hypothalamic pathway • Exercise modifies cardiac responses • Hypothalamus controls skin arterioles for temperature regulation • Vasoactive substances released from endothelial cells control vessel diameter

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Blood Pressure Abnormalities • Hypertension (high blood pressure) o Blood pressure above 140/90 mmHg o Two broad classes ▪ Primary hypertension ▪ Secondary hypertension • Hypotension (low blood pressure) o Blood pressure below 100/60 mm Hg Primary Hypertension • Catchall category for blood pressure elevated by variety of unknown causes rather than by a single disease entity • Potential causes o Defects in salt management by the kidneys o Excessive salt intake o Diets low in K+ and Ca2+ o Plasma membrane abnormalities, e.g. defective Na+-K+ pumps o Variation in gene that encodes for angiotensinogen o Endogenous digitalis-like substances o Abnormalities in NO, endothelin, or other locally acting vasoactive chemicals o Excess vasopressin Secondary Hypertension • Accounts for ~10% of hypertension cases • Occurs secondary to another known primary problem • Examples of secondary hypertension o Renal hypertension – e.g. atherosclerotic plaque in renal artery

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Endocrine hypertension – e.g. Pheochromocytoma (adrenal medullary tumor cause excessive release of Epinephrine and Norepinephrine) Neurogenic hypertension – due to defect in cardiovascular control center (in the medulla oblongata)

Complications of Hypertension • Congestive heart failure • Stroke • Heart attack • Spontaneous haemorrhage • Renal failure • Retinal damage Hypotension • Hypotension is when blood pressure below 100/60 mmHg • Occurs when o There is too little blood to fill the vessels o Heart is too weak to drive the blood • Orthostatic (postural) hypotension o Transient hypotensive condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position Circulatory Shock • Occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained • Four main types o Hypovolemic (“low volume”) shock o Cardiogenic (“heart produced”) shock o Vasogenic (“vessel produced”) shock o Neurogenic (“nerve produced”) shock

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Consequences and Compensations of Haemorrhage Haemorrhage leads to fall of blood volume and ultimately arterial pressure Change in arterial pressure is detected by baroreceptors which initiates compensations through the cardiovascular center (2) Fall of arterial pressure also cause a fall in capillary blood pressure (12) that affects interstitial fluid and plasma flow – autotransfusion (13) Ultimately the adjustments are aimed at increasing plasma volume (17) to then increase cardiac output and increase arterial pressure (11) that had dropped due to haemorrhage

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– Introduction to Blood Blood represents about 8% of total body weight Average volume: ~5L in women, ~5.5L in men Consists of three types of cellular elements suspended in plasma o Erythrocytes (red blood cells, RBC) ▪ Important in O2 transport o Leukocytes (white blood cells, WBC) ▪ Immune system’s mobile defense units o Platelets (cell fragments) ▪ Important in hemostasis (blood clotting) Haematocrit definition of blood • Haematocrit (packed cell volume) o Represents the percentage of erythrocytes (RBCs) in the total blood volume • 99% of cells in centrifuged blood are erythrocytes o Haematocrit values ▪ Women ~42% and Men ~45% o Average plasma volume in blood ▪ Women ~58% and Men ~55% o WBCs and platelets are colorless and less dense ▪ Found in buffy coat ▪ Represent less than 1% of the total cell volume • • •

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