Circulation and introduction to pulmonary system

Question 1

Arteries, capillaries Veins

Answer 1

For most blood vessels, the walls consist of three layers
Capillaries & sinusoids different to arteries & veins

Question 2

arteries

Answer 2

Transport blood away from the heart
Carry oxygenated blood, except the pulmonary and umbilical arteries
Have a narrow lumen
Have more elastic tissue
Do not have valves
Transport blood under pressure

Question 3

VEINS

Answer 3

Transport blood to the heart
Carry deoxygenated blood, except the pulmonary and umbilical veins
Have a wider lumen
Have less elastic tissue
Do have valves
Transport blood under low pressure

Question 4

Flow of blood

Answer 4

Arteries
* Arterioles
* Capillaries- sinusoids (special form of capillary that is very permeable, main relevance liver and pituitary gland)
* Venules
* Veins

Question 5

Lymphatics

Answer 5

Lymph vessels are drainage channels: drain interstitial fluid back into bloodstream.
* Lymph capillaries look like blood capillaries.
* Not part of cardiovascular system but lymphatics have slow pulsatile
mechanism that drains the lymph into the venous system via thoracic ducts.
* Function: Carry interstitial fluid and any leaked plasma proteins back into circulation.
* Also carry damaged cells or bacteria to local lymph nodes to start an immune response. (Will discuss further in session on immunity).
* They are also a major channel for the spread of cancer cells.

Question 6

Capillary Exchange

Answer 6

Osmolality in capillary is higher than interstitial fluid as it contains plasma proteins.
Capillary blood pressure > blood colloid osmotic pressure in first half of the length of a typical capillary. Thus, water and solutes flow out of blood capillary into surrounding interstitial fluid, a movement called filtration.
Capillary blood pressure decreases progressively so in second half of capillary the osmotic pressure < capillary pressure and reabsorption occurs

Question 7

capillary exchange pt 2

Answer 7

Pressure changes and flow of water in capillary exchange (1Kpa=7.5 mmHg).Lymphatics also improve movement of excess waste

Question 8

Control of Blood pressure

Answer 8

Blood pressure (BP), the pressure exerted by blood on walls of a blood vessel. Recorded in millimeters of mercury, (mm Hg).
BP is highest in aorta
Blood pressure falls progressively as distance from the left ventricle increases, to about 35 mm Hg as blood passes into systemic capillaries. At venous end of capillaries, blood pressure drops to about 16 mm Hg.
Blood pressure continues to drop as blood enters systemic venules and then veins, and is only a few mmHg as blood returns to right atrium

Question 9

Venous Return

Answer 9

Venous return is movement of blood from capillaries to venules to veins back to atria of the heart.
If you stand, venous pressure in lower limbs barely enough to overcome the force of gravity.
Effective venous return accomplished by two pumps:
1. The respiratory pump
2. The skeletal muscle pump,
-both depend on the one‐way valves in veins.

Question 10

Venous Return-respiratory pump

Answer 10

The respiratory pump is based on alternating compression and
decompression of veins.
During inhalation (breathing in) the diaphragm moves downward, causing a decrease in pressure in thoracic cavity and increased pressure in abdominal cavity.
Blood moves from compressed abdominal veins into decompressed thoracic veins and into right atrium.
When you breath out the valves in the veins stop the opposite occurring.

Question 11

Venous Return-skeletal muscle pump

Answer 11

The skeletal muscle pump is an important factor in promoting venous return, especially in the limbs.
When you contract leg muscles it pushes blood through the valve closer to the heart, an action called milking

Question 12

Local control of blood flow

Answer 12

The amount of blood that goes to a specific organ will depend on the overall blood pressure and tissue differences in vascular resistance- fluid will try and go through the easiest route
Local control of blood flow (vascular resistance) important in tissues that require variable amounts of oxygen/nutrients. These include –
* Skeletal muscles during exercise
* Gastrointestinal tract during digestion
* Sites of injury

Question 13

local control of blood flow pt2

Answer 13

Mechanisms involved in changes in local blood flow include-
* Release of metabolic waste products: CO2, lactic acid
* Tissue temperature
* Hypoxia (lack of oxygen)-vasodilation
* Local release of vasodilator chemicals like histamine and Nitric
oxide-tissue injury
* Changes in vasoconstrictor hormones like adrenalin and
angiotensin 2

Question 14

Control of overall blood pressure

Answer 14

Short term increase in blood pressure achieved by increasing vascular resistance through constriction of arteries by nerves & circulating chemical signallers e.g., adrenalin

Question 15

Control of blood pressure pt 2

Answer 15

Short term control through baroreceptors, chemoreceptors and circulating hormones
* Long term control through BLOOD VOLUME by kidneys and renin angiotensin system
* Baroreceptors in carotid artery and in first part of aorta (aortic arch)
* These sensors check what is happening with blood pressure and relay information to the brain stem to take restorative action

Question 16

Feedback loop for short term BP control

Answer 16

Chemoreceptors do similar thing to baroreceptors but only important when situation severe (systolic BP <80 mmHg, or pH decreased (more acid), pCO2 high or O2 low. They cause increased breathing, HR, stroke volume and Vasoconstriction.

Question 17

Long term pressure control-hormonal signals

Answer 17

Antidiuretic hormone (ADH) released by pituitary gland if osmolality too high, causes increased water absorption by kidneys
Atrial Natriuretic Peptide (ANP) is hormone released from heart if blood volume too high stimulated by stretch receptors
-causes decreased reabsorption of sodium (and water) and reduces blood pressure
Renin-angiotensin-aldosterone system (RAS)

Question 18

Long term pressure control (RAS)

Answer 18

Renin-angiotensin-aldosterone system (RAS)
Low blood volume flow to kidneys causes release of hormone renin.
* This causes angiotensin in blood to convert to angiotensin 1.
* This is converted to angiotensin 2 by angiotensin converting enzyme (ACE) in lungs and kidneys.
* Angiotensin 2 is a vasoconstrictor and with renin causes adrenal glands to release aldosterone that makes the kidneys reabsorb more sodium and water.
* Therefore, ADH and RAS increases blood volume. ANP decreases it

Question 19

Effect of aging on cardiovascular system

Answer 19

• Loss of cardiac muscular strength
• Reduced cardiac output
• Decline in maximum heart rate
• Increase in systolic blood pressure
• Increased stiffness of the heart chambers * Increased stiffness of the aorta
• Baroreceptor reflex is less fast: may suffer postural hypotension.

Question 20

Deep vein thrombosis & pulmonary embolus

Answer 20

• If venous blood is stagnant- prolonged bed rest
• Legs in plaster
• Blood thicker or increased tendency to clot (e.g., in cancer patients)
• Veins gets blood clot * Swollen leg
  If clot dislodges-travels to heart, passes through right side of heart and lodges in lungs causing Pulmonary embolus
• Fall in blood pressure, difficultly breathing.
• Prevention- movement, pressure stockings, aspirin, heparin, warfarin, * Treatment-blood clot dissolving medicines

Question 21

Hypertension

Answer 21

95% people with primary hypertension, no underlying cause
5% secondary hypertension due to diabetes, kidney disease, pituitary and adrenal gland tumors, and thyroid gland problems.
High blood pressure damages blood vessels, heart, brain, and kidneys before it causes pain or other symptoms. A major risk factor for heart disease and strokes.
In blood vessels, hypertension causes thickening of arterial muscle layer, speeds up development of atherosclerosis and coronary artery disease and increases systemic vascular resistance. In the heart, hypertension increases the work the ventricles need to do to eject blood.

Question 22

Lifestyle Treatment of Hypertension

Answer 22

Lose weight.
* Limit alcohol intake.
* Exercise. Engaging in moderate activity (e.g., brisk walking) several times a week for 30 minutes can lower systolic blood pressure by about 10 mm Hg.
* Reduce intake of sodium (salt). Half the people with hypertension are “salt sensitive.” For them, a high‐salt diet promotes hypertension, and a low‐salt diet can lower their blood pressure.
* Don’t smoke, quit or reduce smoking.
* Manage stress.

Question 23

Drug treatment of hypertension

Answer 23

Diuretics decrease BP by decreasing blood volume, because they increase elimination of water and salt in urine.
* ACE (angiotensin converting enzyme) inhibitors block formation of angiotensin II and cause vasodilation.
* Beta blockers reduce blood pressure by inhibiting the secretion of renin (affecting RAS system) and by decreasing heart rate and contractility.
* Vasodilators relax smooth muscle in arterial walls, causing vasodilation and lowering blood pressure by lowering systemic vascular resistance.
* Calcium channel blockers slow inflow of Ca2+ into vascular smooth muscle cells & reduce heart’s workload by slowing Ca2+ entry into heart pacemaker cells and regular myocardial cells decreasing heart rate and force of myocardial contraction.

Question 24

Angina, ischemia, Heart attack & arterial blockage

Answer 24

Changes occur to inner lining of large and medium sized arteries.
* In large arteries, elastic layer replaced by fibrous tissue and calcium. Although lumen may remain large, elasticity is reduced and systolic blood pressure increases
* Strength of vessel wall is weakened, may balloon out: an aneurysm
* In arterioles, lumen becomes narrowed as the wall gets deposits of fibrous material called hyalin .

Question 25

Angina, ischemia, Heart attack or arterial blockage pt2

Answer 25

Both large and smaller arteries may also get deposits of cholesterol and calcium, called plaques, narrowing lumen.
* Risk factors: obesity, smoking, diabetes, hypertension, hyperlipidaemia.

Question 26

Angina and limb ischemia

Answer 26

A relative lack of blood supply mainly becomes noticeable when the heart or limb needs extra energy/oxygen.
* If heart affected, chest pain may come on when person runs to catch a bus, having eaten a large meal.
* Symptoms generally resolve after stopping exertion.
* Treatment is with blood pressure control, stop smoking, aspirin, warfarin, cholesterol lowering agents

Question 27

Occlusion of artery

Answer 27

In coronary arteries, the plaque may break open into the lumen and cause a blood clot to form. Completely blocking the flow of blood to distal tissue. Angina pain will not go away and usually more severe.
* Similarly, lower limb is painful and in pale skinned people, may become very pale in appearance.
* Both conditions emergencies