Circulatory System Flashcards
Key roles of circulatory system
Transports nutrients, gases, and waste.
Regulates body temperature and acid-base balance.
Aids immune function by transporting blood cells and antibodies.
Blood flow through capillaries:
Oxygen exchange
Waste exchange
RBCs release oxygen through capillary walls into tissues.
Carbon dioxide moves from tissues into RBCs.
Pulmonary circulation steps
- Oxygen-poor blood enters the right atrium via the superior and inferior vena cava.
- Moves to right ventricle, then to lungs via pulmonary trunk and arteries.
- Gas exchange occurs in pulmonary capillaries surrounding alveoli.
- Oxygen-rich blood returns via pulmonary veins to the left atrium.
The Aorta and Systemic Circulation:
Aorta
Divisions
Largest artery, branches into systemic arteries.
- Ascending Aorta
- Aortic Arch
- Descending Aorta (branches into iliac arteries at abdominal level).
Coronary Circulation:
Coronary Arteries
Coronary Sinuses
First branches of the aorta, supplying oxygen to the heart.
Contain baroreceptors & chemoreceptors to regulate cardiac function.
Thoracic Aorta Branches supply…
Pericardium (pericardial artery)
Esophagus (esophageal artery)
Mediastinum (mediastinal artery)
Thoracic muscles & diaphragm (intercostal & phrenic arteries)
Blood vessels and composition:
Types
Wall structure
Arteries, arterioles, capillaries, veins.
- Fibrous tissue: Provides structure.
- Elastic tissue: Expands and contracts.
- Smooth muscle: Regulates diameter.
- Endothelium: Produces vasoactive substances for BP regulation.
Blood pressure and regulation:
Normal
Pulse Pressure
Control mechanisms
120/80 mmHg (systolic/diastolic).
Difference between systolic & diastolic pressure.
CM:
Vasoconstrictors: Catecholamines, Angiotensin II, Vasopressin.
Vasodilators: Prostacyclin, Nitric oxide.
Cardiac Output and Stroke Volume
Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV).
Stroke Volume (SV): Volume of blood ejected per beat (~70 mL in a healthy heart).
Regulation: Preload, contractility, afterload.
Electrical conduction of the heart pathway
- SA Node → Pacemaker (70-75 bpm)
- AV Node → Delays impulse
- Bundle of His → Conducts signal to ventricles
- Purkinje Fibers → Spreads impulse across ventricles
Blood volume and venous return
Venous return depends on…
Blood volume.
Sympathetic stimulation.
Skeletal muscle contractions.
Respiratory activity.
Veins act as blood reservoirs (~64% of blood volume).
Blood pressure disorders:
Hypertension (>140/90 mmHg) - causes and treatment
Hypotension (<90/60 mmHg) - causes and treatment
- Risk of heart failure, stroke, kidney disease.
C: Obesity, stress, diet, lifestyle.
T: Diet, exercise, medication. - Risk of fainting, organ damage.
C: Dehydration, heart conditions.
T: Increased salt/water intake, compression stockings, medication.
Capillary exchange mechanisms:
Diffusion
Transcytosis
Bulk Flow
Movement of gases and nutrients.
Large molecules transported in vesicles.
Fluid movement due to pressure gradients.
Blood Homeostasis and Haemostasis
Maintains equilibrium (e.g., temperature, pH).
Prevents excessive bleeding through:
1. Vasoconstriction (reduces blood loss).
2. Platelet plug formation (clotting response).
3. Coagulation (fibrin clot formation).
Blood components:
Plasma (55-60% blood volume)
Erythrocytes (RBCs)
Leukocytes (WBCs)
Platelets
90% water, 8% proteins (albumin, globulins, fibrinogen), 2% nutrients/gases.
Oxygen transport via haemoglobin.
Immune function (e.g., lymphocytes, neutrophils).
Blood clotting and vessel repair.
Antiplatelet and anticoagulant drugs:
Aspirin
Heparin
Warfarin
Blocks thromboxane A2 → prevents platelet aggregation.
Injectable, immediate anticoagulant.
Oral anticoagulant, inhibits Vitamin K-dependent clotting factors.
Where does blood return from the systemic circuit enter?
Right atrium
Through which vessels does blood enter the right atrium?
Inferior and superior vena cava
Where does the right ventricle pump blood to?
Lungs
What is the single vessel leaving the right ventricle called?
Pulmonary trunk
Which valve prevents backflow of blood into the right ventricle during diastole?
Semilunar valve
What does the pulmonary trunk branch into? What do pulmonary capillaries surround?
Left and right pulmonary artery
Lung alveoli
Descriptions of:
Pulmonary trunk
Pulmonary arteries
Pulmonary veins
- Single large vessel exiting right ventricle dividing into right and left pulmonary arteries
- Left and right vessels that form pulmonary trunk leading to smaller arterioles and then to pulmonary capillaries
- 2 sets of paired vessels (pair on each side) formed from small venules, leading away from pulmonary capillaries flowing into left atrium
Where does blood with high O2 conc. return from the pulmonary circuit?
Left atrium
Where does the left ventricle pump blood into?
Aorta
What is the function of aorta and its branches? Where does it rise from? What does aorta branch into at the abdominal part of the body? 3 components of the aorta
Send blood to all organs
Left ventricle
2 iliac arteries
Ascending aorta, aortic arch, descending aorta
What is the function of aorta branches (arteries)? Description of aorta
- Distribute blood to all body tissues
- Largest artery in the body, originating from left ventricle and descending to abdominal region (bifurcates into common iliac arteries) at level of 4th lumbar vertebra; arteries originating from aorta distribute blood to almost all body tissues
Description of:
Ascending aorta
Aortic arch
Descending aorta
- Initial portion of aorta, rising superiorly from left ventricle for distance of 5cm
- Graceful arc to the left connecting ascending aorta to descending; ends at intervertebral disk between 4th and 5th thoracic vertebrae
- Portion of aorta continues inferiorly past end of aortic arch; subdivided into thoracic and abdominal aorta
Description of:
Thoracic aorta
Abdominal aorta
- Portion of descending aorta superior to aortic hiatus
- Portion of aorta inferior to aortic hiatus and superior to common iliac arteries
What do the coronary arteries branch from and their function?
Ascending aorta
Feed heart with oxygenated blood
What do sinuses in the ascending aorta contain?
Aortic baro-receptors and chemo-receptors
What is the importance of aortic baro-receptors and chemo-receptors?
Maintain cardiac function
What is the function of systemic vessels in lung tissue? Where does mixed blood drain into from the lung tissue?
Deliver nutrients
Pulmonary veins
Where do bronchial artery branches drain into?
Bronchial veins
What does each pericardial artery provide blood to? What does the oesophageal artery supply blood to? What does the mediastinal artery supply blood to?
Pericardium
Oesophagus
Mediastinum
Which arteries are included in the parietal or somatic branches of thoracic aorta?
Intercostal and superior phrenic arteries
What do intercostal arteries supply blood to? What does the superior phrenic artery feed?
Muscles of thoracic cavity and vertebral column
Superior part of diaphragm
What tissues are the blood vessel walls made up of? What type of cell lines the blood vessels?
Fibrous, elastic tissue and smooth muscle
Single endothelial cell layer
What is the function of fibrous connective tissue in blood vessels? What is the function of elastic connective tissue in blood vessels?
Providing structural support
Expand and hold blood, apply pressure
How are smooth muscles arranged in blood vessels? What happens when smooth muscles in blood vessels contract? What happens when smooth muscles in blood vessels relax? What innervates the smooth muscles in blood vessels?
Circular layer
Reduce vessel diameter and decreases blood flow
Increases vessel diameter and increases blood flow
Autonomic NS
How is blood pressure regulated by endothelium? What other processes does the endothelium contribute to?
Production of vaso-constrictor and vaso-dilator materials
Vessel growth, materials exchange
Arteries:
Function
Structure of wall
Lumen
Valves (Y/N)
How structure fits function
- Carry blood away from heart at high pressure
- Thick, strong, contain muscles, elastic fibres and fibrous tissue
- Narrow, varies with heartbeat (increases as pulse of blood passes through)
- No
- Strength and elasticity needed to withstand pulsing of blood, prevent bursting and maintain pressure wave, helps maintain high BP, preventing backwards blood flow
Capillaries:
Function
Structure of wall
Lumen
Valves (Y/N)
How structure fits function
- Supply all cells with their requirements, take away waste products
- Very thin, only one cell thick
- Very narrow, just wide enough for a RBC to pass through
- No
- No need for strong walls, most of BP has been lost, thin walls and narrow lumen bring blood into close contact with body tissue, allowing diffusion of materials between capillary and surrounding tissue, WBCs can squeeze between cells of wall
Veins:
Function
Structure of wall
Lumen
Valves (Y/N)
How structure fits function
- Return blood to heart at low pressure
- Thin, mainly fibrous tissue, contain far less muscle and elastic tissue than arteries
- Wide
- Yes, prevent backflow
- No need for strong walls, as most of BP has been lost, wide lumen offers less resistance to blood flow
What is the typical pressure in aorta and large arteries? What is approx. systolic pressure? What is approx. diastolic pressure?
- 90-100 mmHg
- 120 mmHg
- 80 mmHg
How is pulse pressure calculated?
Difference between systolic and diastolic pressures
What occurs during systole? What occurs during diastole?
Chambers contract and eject blood into arteries
Chambers relax allowing blood to fill them
What determines blood flow through a vessel?
Pressure gradient and vascular resistance
According to Ohm’s law, what is the relationship among blood flow (Q), pressure gradient (ΔP), and vascular resistance (R)?
Q = ΔP/R
What are vasoactive substances? With examples
Agents that increase/decrease blood pressure and heart rate
Vasoconstrictors and vasodilators
Examples of vasoconstrictors
Endothelin, angiotensin, ADH (vasopressin), CAs, PGI2, TXA2
Examples of vasodilators
ANP, histamine, 5-hydroxytyptamine, NO, bradykinin, PGE2, β-endorphin
Where are vasoactive substances released from?
Endothelium, endocrine glands, and myocytes
What is the formula for cardiac output (CO)? What is the approximate stroke volume (SV) in a healthy heart at rest?
CO = heart rate (HR) X Stroke volume (SV)
~70ml
What is cardiac reserve?
Difference between resting and maximum cardiac output
What happens during ventricular contraction?
Rapid pressure increase in the chamber
What are the components of the electrical conduction system in the heart?
Sino-atrial node (SA node)
Inter-atrial pathway
Inter-nodal pathway
Atrio-ventricular node
Bundle of His
Bundle branches
Purkinje fibres
Where is the SA node located? How many heart beats/min do the cells of the SA node generate?
Wall of right atrium
70-75
What are the three factors that control heart rate?
Autonomic NS influence
Catecholamines
Body temperature
What effect does sympathetic stimulation have on heart rate? What neurotransmitter is released from sympathetic nerves? What effect does parasympathetic stimulation have on heart rate? What neurotransmitter is released during parasympathetic stimulation?
Increase heart rate
Noradrenaline
Decreases heart rate
Acetylcholine
What receptor does noradrenaline bind to? What receptor does acetylcholine bind to?
Beta-adrenergic receptors
Muscarinic receptors
What are the effects of noradrenaline binding to beta-adrenergic receptors? What are the effects of acetylcholine binding to muscarinic receptors?
Increased discharge of SA node, conduction through AV node and Bundle of His
Decreased discharge of SA node, conduction through AV node
What is the definition of stroke volume?
Volume of blood pumped from left ventricle per beat
What phases are included in the heartbeat? What principle applies to the heart’s pumping ability?
Systole and diastole
Heart can pump what it receives
What factors contribute to regulation of stroke volume?
- Length of diastole
- Venous return (pre-load)
- Contractility of myocardium
- After-load
Heart rate
What is venous return?
Volume of blood returned to right atrium/minute
Why is the distensibility of arteries important? Which vessels are most distensible in circulatory system?
Maintains blood flow to tissues during the cardiac cycle
Veins
What is the physiological importance of veins being distensible? What percentage of blood volume is contained within veins at rest?
Allows them to serve as blood reservoirs
64%
What is the formula for compliance (C)? What is the relationship between cardiac output (CO) and venous return (VR)?
C = V/P
To increase CO, VR must increase
How does resistance vary in veins of different sizes?
Smaller veins offer low resistance, large veins offer more
What factors influence venous return (VR)?
- Blood volume
- Sympathetic stimulation of the veins
- Skeletal muscle activity
- Respiratory activity
How does blood volume affect BP? What does low blood volume lead to? What does an increase in blood volume lead to?
Direct effect on BP
Low venous pressure and low venous return
Increased venous pressure and venous return
What happens when blood pressure puts too much stress on artery walls?
Heart works harder, leading to unhealthy growth
What are contributing factors to hypertension?
- Obesity and a sedentary lifestyle
- Stress and Smoking
- Too much alcohol or salt in the food
What are complications of hypertension?
- Increase the risk of atherosclerosis
- Stroke
- Aneurysm
- Heart failure
- Heart attack
- Kidney damage
What are the treatments for mild hypertension?
- Reducing alcohol and sodium intake
- Recommending fruits and vegetables
- Exercise
- Lose weight if overweight
What happens when arterial pressure and blood flow decrease?
Low BP occurs
What are the symptoms of hypotension?
- Dizziness, fainting, lack of concentration
- Blurred vision, nausea, cold and pale skin
- Rapid breathing, fatigue, thirst and depression
What can very low BP damage?
Heart and brain
What are the risk factors for hypotension?
- Pregnancy
- Heart problems (heart attack, and heart failure…)
- Endocrine problems
- Dehydration
- Lack of nutrients
- Shock
- Haemorrhage
- Toxins
- Certain medications
- Eating disorders (like anorexia nervosa)
What are the treatments for hypotension?
- Doctors usually try to address the underlying problem
- Consuming more salt and drinking more water if there is no underlying issue
- Wearing compression stockings
- Drug medications such as fludrocortisone and midodrine
What chemical changes mediate metabolic vasodilation in a certain tissue?
- Decreased oxygen
- Increased carbon dioxide
- Increased hydrogen ions
- Increased potassium ions
- Increased adenosine
What are the three main mechanisms substances are exchanged across the capillary wall?
- Diffusion
- Trans-cytosis
- Bulk flow
What four forces determine the movement of fluid into or out of the capillary?
- Interstitial fluid hydrostatic pressure (Pi)
- Plasma colloid osmotic pressure (pp)
- Interstitial fluid colloid
- Osmotic pressure (pi)
What are the three mechanisms that contribute to haemostasis?
- Vascular constriction
- Formation of platelet plug
- Blood coagulation
What is the purpose of vascular constriction? What happens immediately after a blood vessel is injured?
Decrease flow of blood through vessel
Vascular smooth muscle constricts
What causes vasoconstriction?
- Sympathetic nerve reflexes as a response to pain
- Myogenic vasospasm as a response to injury
- Vasoconstrictors released from damaged tissue and platelets
What percentage of total blood volume does plasma form? What is the primary component of plasma? How much of plasma is water? How much of plasma is proteins? What are the three major plasma proteins?
55-60%
Water
About 90%
About 8%
Albumin, globulins and fibrinogen
What is the function of albumin? What percentage of plasma proteins does albumin make up? What percentage of plasma proteins do globulins make up? What do alpha and beta globulins transport? What do gamma globulins function as?
Binds with various molecules in the blood
About 55%
About 38%
Substances in the blood
Antibodies
Where is fibrinogen synthesised? What role does fibrinogen play?
Liver
Coagulation and thrombosis
What are erythrocytes? What cellular structure do erythrocytes lack? What is the primary function of erythrocytes?
RBCs
Nucleus and membranous organs
Transport oxygen to tissues
How many heme groups are there per haemoglobin molecule? What does each heme group contain? What is the average blood content of haemoglobin?
4
Iron atom which binds to oxygen
About 15g/100ml
How many oxygen molecules can each RBC transport?
Blood types: A, B, AB and O
More than 1 billion
Type A = antigen A
Type B = antigen B
Type AB = both antigen A and B
Type O = neither A nor B antigens
What is the normal range of leukocytes (WBCs) per μlitter of blood?
4000 to 11,000
What are the important inflammatory and immune functions of leukocytes?
- Destruction of pathogens (bacteria or viruses)
- Fighting cancer cells
- Phagocytosis of tissue wastes and dead cells
- Produced in large numbers in patients with parasitic infections
What percentage of total number of WBCs are lymphocytes? What are the 2 types of lymphocytes?
About 30%
B lymphocytes (secrete antibodies) and T lymphocytes (immune response and produced by thymus gland)
What are platelets? Where are platelets formed? What cellular structure do platelets lack? What do platelets contribute to? What are platelets involved in?
Small, round or oval cell fragments
Red bone marrow
Nuclei
Stop bleeding
Clot growth and repair of blood vessels
What do antiplatelet drugs inhibit? What do antiplatelet drugs prevent?
Platelet function
Development of atherosclerosis and arterial thrombi
Aspirin:
Inhibits what?
Blocks the synthesis of?
Effective low dose of aspirin for antithrombotic effect
Cyclo-oxygenase (aspirin-induced inhibition lasts 7-10 days due to life span of platelet)
Thromboxane A2 (TXA2) - vasoconstriction and platelet aggregation
81-325mg per day
What factors contribute to the prevention of blood clotting in the vascular system?
- Smoothness of the endothelial layer (prevents intrinsic mechanism activation)
- A layer of glyco-calyx on the endothelium (avoids platelets and prevent blood clotting)
- Plasmin dissolving fibrin continuously
What are anticoagulant drugs like heparin and warfarin used to prevent? What are anticoagulant drugs also used to prevent?
Deep vein thrombosis
Emboli formation due to cardiac disorders
Heparin:
Administration
Why administered this way?
What effect does it have?
- Injection
- Not absorbed via GI tract
- Immediate
How does warfarin act? What does vitamin K participate in? Which coagulation factors does vitamin K synthesise?
Deactivating vitamin K
Coagulation factor synthesis
II, VII, IX and X
