Circulatory System and Blood, and Acid-Base Physiology

Question 1

What are the components of whole blood?

Answer 1

plasma and formed elements (blood cells/cell fragments). hematocrit is the ratio of rbc to total blood volume. in women it is around 37-48% and in men 45-52%. hematopoietic stem cells are 2 early branch points which form lymphoid progenitor cells for lymphocytes and natural killer cells, and myeloid progenitor cells for any other blood cell in the body.

Question 2

What are the major functions of the circulatory system?

Answer 2

it distributes dissolved gases and other molecules for nutrition, growth and repair to to tissues and removes metabolic wste products from tissues. it circulates hormones or neurotransmitters for fast chemical signalling. it dissipates heat by delivery of heat from the core to the surface of the body. it mediates the inflammatory and host defence responses against invading microorganisms. it supports detoxification and elimination roles of the liver and kidneys.

Question 3

What is the function of arteries, arterioles and capillaries in blood vessels.

Answer 3

arteries deliver oxygenated blood to tissues. they are made of extensive elastic tissue and smooth muscle, and under high pressure they have thick walls.

arterioles are the smallest branch of arteries

capillaries are the site of gas, nutrients and water exchange. it has the largest total cross sectional and surface area.

Question 4

What is the function of venules, arteriovenous anastomosis and veins in blood vessels.

Answer 4

venules are formed by merged capillaries.

arteriovenous anastomosis is a transitional muscuolar central vessel in a capillary bed where blood is shunted and allowed to bypass capillaries (fingers and toes)

veins are the site of return of blood to heart (from systemic circulation or lungs). they progressively combine to form larger veins. contain valves, have thin walls and under low pressure compared to arteries.

Question 5

What is the anatomy of an artery?

Answer 5

contained tunica which is a layered structure, categorised into externa, media and intima. they vary in diameter and proportion of smooth musculature and elastic tissue.

elastic arteries accomodate pressure changes from the cardiac cycle. muscular arteries regulate bp.

arterioles regulate local tissue perfusion and capillaries provide gas/nutrient exchange.

Question 6

What is the anatomy of a vein?

Answer 6

they contain tunica. they have thinner walls so the lumen of the vein is larger than the lumen of an artery of a comparable size. they contain valves to prevent blood backflow due to gravity, always directing blood back to the heart.

Question 7

What is the arterial system?

Answer 7

the vasodilation/constriction of arterioles significantly affects bp. slight vasodilation will significantly dec resistance in the vessel and increase blood flow. slight vasocontriction will significantly increase resistance in the vessel and decrease blood flow.

Question 8

What is the venous system?

Answer 8

vasoconstriction inc bp helping with venous return to the heart. it also causes the lumen to become rounder, decreasing resistance and increasing flow. it is a low pressure resevoir, and as blood moves from venule to veins, bp drops but blood velocity increases.

Question 9

What is venous return?

Answer 9

venous return occurs through muscle contractions, respiratory pump, and vasoconstriction.

in muscle contractions, pressure inc passively in veins forcing blood through the valves.

in the respiratory pump, as air pressure within the thorax drops, bp in thoracic vein also dec below pressure of abdominal veins, causing the blood to flow from outside thorax to inside thorax following the pressure gradient.

in vasoconstriction, the constriction of veins increases bp and flow and opens valves eg during exercise.

Question 10

What is flow characterisation?

Answer 10

blood flow is usually laminar, forward in a parabolic pathway. if flow becomes impeded or when there is a regularity, blood flow can become turbulent. this can be caused by a blood clot or occur near a valve, which can cause increased resistance and damage the wall of the blood vessel leading to an increased risk of disease. reynold’s number predicts the likelihood of flow being turbulent.

Question 11

How is bp measured?

Answer 11

bp is measured through a sphygmomanometer. turbular flow is accomponied by murmurs or bruits (in vasculature). a bruit reflects the commencement of turbulent blood flow when the pressure of the cuff dec below the arterial pressure. when obtaining manual bp, this is heard through a stethescope.

Question 12

What is blood perfusion?

Answer 12

it is the rate of blood flow into a tissue. perfusion rates at rest reflect metabolic activity, which differs dramatically during exercise.

Question 13

How is tissue perfusion regulated?

Answer 13

it is regulated by both local factors and autonomic sympathetic tone.

Question 14

What are the 3 main types of capillaries?

Answer 14

continuous capillary is the most common form, made of endothelial junctions 10-15nm wide and are found in skeletal muscle.

fenestrated capillary have thin endothelial cells and have many fenestrations, they surround epithelia and can be found in the small intestines and exocrine glands.

discontinuous (sinusoidal) capillary have large fenestrations and gaps and are found in sinusoids such as liver and marrow.

Question 15

What is capillary exchange?

Answer 15

capillary exchange provides surrounding tissues with oxygen, glucose, amino acids, and fluid exchange between blood and surrounding extracellular fluid. they are responsible for diffusion, trancytosis and bulk flow.

Question 16

What is the sterling hypothesis?

Answer 16

it states the flow of fluid across the capillary wall depends on the force of bp (hydrostatic pressure) on the walls, which tends to force fluids out, and osmotic pressure within the capillary, which tends to bring fluids in and has a greater conc of dissolved substances in blood. net filtration pressure is the combination of pressures inside the capillary. starling forces determind the volume and directionality of fluid movement (Jv).

Question 17

What is filtration and absorbtion?

Answer 17

filtration occurs from blood to ECF to cells, with O2, glucose, amino acids, and hormones.

absorption occurs from cells to ECF to blood, with CO2, waste and water.

Question 18

What are fluid dynamics?

Answer 18

approx 20L fluid filtered through the capillaries per day. 85% of fluid that is filtered along arteriole end is reabsorbed on venous end. fluid that doesn’t return are plasma proteins that leave capillary into the interstitial space. the remainder of fluid and proteins enter the lymphatic capillaries (3L/day) and is eventually returned to blood.

Question 19

How is blood flow regulated in the capillaries?

Answer 19

regulated by local factors through autoregulation. capillaries open and closed based on the requirements of a given tissue, with oxygen requirement being the most important. the terminal part of the arteriole (metarteriole) contains precapillary sphincters to control blood flow into the capillaries. local factors influence whether the sphincters are open or closed (vasomotion).

Question 20

How is blood flow regulated in skeletal muscle?

Answer 20

relies on autoregulation. this leads to hyperemia which increases blood flow into the vessels. active hyperemia is local vasodilation to deliver blood (and oxygen) to muscles more efficiently. reactive hyperemia is blood flow response to occlusion (eg increased flow following occulsion of the bronchial artery when measuring bp)

Question 21

How is blood flow regulated in the kidneys?

Answer 21

through autoregulation such as arteriole myogenic mechanism, or tubuloglomerular feedback.

through sympathetic tone, where the reduction of sympathetic stimulation results in vasodilation and increased flow at rest, and increase of sympathetic stimulation constricts arteriolar smooth muscle resulting in diminished glomerular filtration rate (GFR) and less demand for oxygen.

Question 22

Describe blood flow to the liver and how it is regulated.

Answer 22

blood flows to the liver through the hepatic system. it is regulated by hepatic arterial flow, portal venous inflow and the relationship between hepatic arterial and portal inflow circuits. the portal triad is the hepatic arteriole which delivers oxygenated blood to the liver, the portal venule which carries blood from the pancreas, stomach, spleen, small intestine and colon to the liver, and the bile duct which collects bile products secreted by hepatocytes. blood mixes with the microvessels (sinusoids) and drains into the central vein which leads to the vena cava and back to the right atrium of the heart.

Question 23

What is the lymphatic system?

Answer 23

it helps with fluid balance throughout the day, and drains interstitial fluid back into the venous system. it initiates an immune response by producing and transporting lymphocytes, and transports dietary lipids absorbed by GI into the blood.

it consists of the lymph which is a colourless fluid that floats in lymphatic vessels, and lymphatic tissues which have special capillaries that permit movement of lymphocytes from the blood into the lymphatic system throughout the body.

Question 24

How is fluid moved in the lymphatic system?

Answer 24

20L of fluid leave capillaries everyday, only 17L returned. the lymph helps return the other 3L to circulation from capillaries into the llymph system , passing through lymph nodes and lymphatic vessels and drains back into the venous system. the rate of lymph flow depends on interstitual fluid pressure and the activity of lymphatic pump (valves) being stretched and opening, continuously moving lymph through the system.

Question 25

How do changes in H+ affect the body?

Answer 25

changed can affect the charge of protons and compromise their function. it must be regulated at all times via homeostatic control. the concentration is maintained by kidneys, lungs and buffer systems.

Question 26

What is extracellular pH?

Answer 26

7.3-7.5, homeostasis important for enzymes to function and speed up chemical reactions, electrolyte balance and conc, and the function of certain hormones.

Question 27

What is blood pH?

Answer 27

7.35-7.45, maintained through the bicarbonate buffer system. it is dependent on kidneys reabsorbing bicarbonate and excreting non-volatile acids. pH<6.8 or >8 results in death.

Question 28

What are acid-base imbalances?

Answer 28

our bodies are slightly more alkalinic. out bodies produce more acids than bases due to food and metabolism, so our body compensates to restore pH back to normal. at partial compensation, the body is not in completely normal ranges, and then continues towards complete compensation.

Question 29

How does ion transport repspond to intracellular metabolic acidosis?

Answer 29

if HCl is injected into the cytoplasm, pH dec as H+ ions are freely floating. causes an inc uptake of HCO3- into cell and dec movement of HCO3- outside of cell. H+ is transported out of the cell and pH inc.

Question 30

How does ion transport repspond to intracellular metabolic alkalosis?

Answer 30

if KOH is injected into the cytoplasm, inc pH. dec uptake of HCO3- into cell and inc movement of HCO3- outside of cell. dec exchange of H+ and pH dec.

Question 31

What is the function of buffer systems?

Answer 31

a buffer maintains pH by resisting changes to pH. in blood and extracellular fluid there is the bicarbonate, phosphate and protein buffer systems. in the respiratory system it is the offloading of CO2, and in the renal system it is the excretion of phosphate and ammonium.

Question 32

What is the bicarbonate buffer system?

Answer 32

occurs in rneal and respiratory systems, can be extracellular or intracellular. weak acid H2CO3 and bicarbonate salt base NaHCO3. HCO3-:H2CO3 maintained at 20:1, continuous motion to keep the ratio.

Question 33

What is carbonic anhydrase?

Answer 33

it is a family of metalloenzymes that catalyse the reversible hydration of CO2 to HCO3- and H+. it is a primary enzyme in the bicarbonate buffer system and produces gastric acid in the stomach. it is found in many tissues and is involved in various systems such as CO2 transport for respiration, reabsorption of HCO3- in kidneys and maintenance of O2 binding in blood.

Question 34

What is the phosphate buffer system?

Answer 34

intracellular and renal tubule buffer, in proximal tubules, ascending loop of Henle and early distal tubules. consists of weak acid H2PO4 and base HPO4-.

Question 35

What are protein buffers?

Answer 35

hemaglobin and plasma proeteins during CO2–> HCO3- conversion, in rbc H+ buffered by hgb. zwitter ions. plasma cell proteins where carboxyl donates H+, amino accepts H+ and side chains buffer H+.

Question 36

What is the function of biological buffers?

Answer 36

they are located in the respiratory and renal systems for maintaining acid-base balance.

Question 37

How does the respiratory system maintain pH?

Answer 37

it maintains normal ECF pH by changing rate of breathing to maintain constant Pco2. relies on the bicarbonate buffer system for CO2 transport in blood. Exhaling CO2 from the system helps to maintain blood pH. a build up of CO2 results in increased H+ and greater acidosis. depletion of CO2 results in dec H+ and greater alkalosis.

respiratory compensation is when pH falls, there is an inc respiration rate to remove CO2, and if pH rises, there is a dec respiration rate to conserve HCO3-.

Question 38

How does the renal system maintain pH?

Answer 38

the kidneys are the most effective regulator of pH. to increase [H+], large amounts of acid can be eliminated through secretion of H+ at renal tubules, and H+ binds to NaHPO4- to form monosodium phosphate NaH2PO4- which is excreted in urine. H+ can be excreted in the form of NH4+ in the lumen of the proximal convoluted tub7ule, most H+ produced is secreted this way. it can reabsorb or create HCO3- to bind to H+, like the respiratory system, kidneys use bicarbonate buffering especially in the proximal convoluted tubule.

renal compensation is when pH calls, inc H+ sec and inc HCO3- reabsorbtion. if pH rises, dec H+ sec and HCO3- secreted.

Question 39

How is blood pH maintained?

Answer 39

it involved the coordinated responses of plasma bicarbonate buffering. blood pH depends on the ratio of [pCO2]/[HCO3-]. the lungs and kidneys compensate for dysfunction of the other to help maintain blood pH in the short term.

Question 40

How is acid-base balance measured?

Answer 40

arterial blood gases provide a measure of pH, Pco2 and Po2. dissolved gases are used to calculate [HCO3-].

Question 41

What are pH disturbances?

Answer 41

they can be respiratory or metabolic. 1 cause is simple ,may causes are mixed.

Question 42

What is an anion gap?

Answer 42

the anion gap measures unknown anions in blood plasma. it helps with the diagnosis of metabolic acidosis. it is calculated by measuring the difference between the major +ve and -ve ions found in plasme. acidosis is the excess production of a patholgic acid which becomes an unmeasured anion buffered by HCP3-. dec HCO3-, inc anion gap = inc in unknown ion.