Cardiovascular Flashcards
where is most of the blood volume located in the circulatory system
in the venous system
how do veins differ from arteries in terms of blood flow resistance
unlike arteries, which provide resistance to the flow of blood from the heart, veins are able to expand as they accumulate additional amounts of blood
what is the average pressure in veins compared to arteries
veins - 2mmHg
arteries - 100mmHg
why is venous pressure insufficient to return blood to the heart
- Venous pressure is low and unable to overcome gravity.
- Veins rely on muscle contractions, respiratory movements, and one-way valves to help return blood to the heart
how do veins in the lower limbs help return blood to the heart
the veins pass between skeletal muscle groups, which provide contractions that help move blood back to the heart
- skeletal muscle pump
what role does the diaphragm play in venous blood return
the diaphragms contraction creates pressure in the abdomen, which helps squeeze the veins and promote blood return to the heart
what is the role of elastin fibers in the aorta and larger arteries
elastin fibers between the smooth muscle cells in the tunica media of large arteries allow them to expand when blood pressure rises during ventricular contraction and recoil when blood pressure falls during ventricular relaxation
how do large elastic arteries respond to changes in blood pressure
large elastic arteries expand when blood pressure rises during ventricular contraction and recoil like a stretched rubber band when blood pressure falls during ventricular relaxation
what happens during the systolic phase of the heart
the ventricles contract, pumping blood into the arteries. this phase correspond to the highest blood pressure - systolic pressure
what happens during the diastolic phase of the heart
the ventricles relax and fill with blood from the atria. this phase corresponds to the lowest blood pressure - diastolic pressure
vasoconstriction vs vasodilation
vasoconstriction - decreases blood flow to the capillary bed
vasodilation - increases blood flow to the capillary bed
What is unique about the walls of capillaries compared to arteries and venules?
capillary walls are composed of just one cell layer, lacking smooth muscle and connective tissue, which makes it easier to exchange materials between blood and tissues
at the arterial end of a capillary…
blood pressure forces fluid out of the capillary to the fluid surrounding tissues
at the venous end of a capillary…
fluid is drawn back into the capillary by osmotic pressure
What is the function of the pharynx and larynx in the respiratory and digestive systems?
The pharynx is a muscular passage connecting the nasal cavity to the larynx. The larynx directs air toward the lungs and food toward the esophagus, and it also contains the vocal cords, which are folds in the lining tissue.
what are the functions of the larynx
the larynx diverts air to the lungs and food to the esophagus, and it also houses the vocal cords
What does lung compliance refer to, and how does it affect inspiration?
Lung compliance refers to the ease with which the lungs expand under pressure. High compliance means the lungs stretch easily during inspiration. Lung disease can reduce compliance, making it harder for the lungs to expand.
What is the role of elasticity in the lungs, and how does it contribute to expiration?
Elasticity is the ability of the lungs to return to their original size after being stretched. During expiration, the elastic recoil of the lungs helps them shrink back to their resting size, pushing air out of the lungs.
What gives the lungs their elasticity, and how does it affect lung function?
The high content of elastin proteins in the lungs provides elasticity, allowing them to resist over-expansion and return to their original size after stretching. This elastic recoil is essential for normal expiration.
How does the chest wall affect lung elasticity during breathing?
The lungs are normally stuck to the chest wall, keeping them in a state of elastic tension. This tension increases during inspiration as the lungs stretch, and is reduced during expiration as the lungs recoil back to their resting size.
why can’t the lungs inflate if the chest is wounded, even if ventilation continues
because they rely on being attached to the inner chest wall via pleural membranes. without this attachment, the lungs cannot expand properly during breathing
what role do pleural membranes play in lung inflation
pleural membranes attach the outer surface of the lungs to the inner wall of the chest cavity. this attachment allows the lungs to expand when the chest cavity volume increases during inspiration. without this connection, the lungs cannot inflate
what are the two layers of the pleural membranes
- one layer is attached to the surface of the lung
- the other is attached to the inner wall of the chest cavity
what is the function of the pleural fluid produced by the pleural membranes
the pleural fluid, which is mucous-rich, acts as a lubricant between the 2 pleural membranes. it reduces friction as the lungs expand and contract during breathing, ensuring smooth movement
What is the role of pleural fluid in lung expansion and contraction?
The pleural fluid acts as both a “glue” holding the two pleural membranes together and a lubricant, allowing the lungs to move smoothly within the thoracic cavity. This connection allows the volume of the lungs to change as the size of the thoracic cavity changes during breathing.
What is the role of surfactant in the alveoli?
Surfactant, a mixture of phospholipids and hydrophobic surfactant proteins secreted by type II alveolar cells, lowers surface tension in the alveoli. This prevents the alveoli from collapsing during expiration.
Why are premature babies sometimes born with collapsed alveoli?
Premature babies may lack sufficient surfactant, which is produced late in fetal life. Without enough surfactant, surface tension in the alveoli is not reduced, causing them to collapse.
tidal volume
volume of gas inspired or expired in an unforced respiratory cycle
inspiratory reserve
max volume of gas that can be inspired during forced breathing in addition to tidal volume
expiratory reserve
max volume of gas that can be expired during forced breathing in addition to tidal volume
residual volume
volume of gas remaining in lungs after max expiration
total lung capacity
total amount of gas in the lungs after a max inspiration
vital capacity
max amount of gas expired after a max inspiration
inspiratory capacity
max amount of gas that can be inspired after a normal tidal expiration
functional residual capacity
amount of gas remaining in the lungs after a normal tidal expiration
functional residual capacity
amount of gas remaining in the lungs after a normal tidal expiration
anatomical dead space - dead volume
nose, mouth, larynx, trachea, bronchi, bronchioles - where no gas exchange occurs
What is the percentage of fresh air reaching the alveoli, if …
i) the anatomical dead space is 150 mls, and
ii) tidal volume is 500mls?
500-150 = 350
350/500 x 100% = 70%
What is the role of hemoglobin in oxygen transport?
Hemoglobin acts as an oxygen shuttle, binding to O2 in the lungs and carrying it through the bloodstream to tissues, where it releases the oxygen when needed.
What makes hemoglobin special in terms of oxygen binding?
Hemoglobin not only binds to oxygen (O2) in the lungs, but it also has the ability to release oxygen when body tissues require it.
How does CO2 affect the binding of oxygen to hemoglobin?
In the lungs, low CO2 levels reduce blood acidity (higher pH), promoting oxygen binding to hemoglobin. In the tissues, high CO2 levels increase blood acidity (lower pH), which facilitates the release of oxygen from hemoglobin.
What happens to blood pH in the lungs versus the tissues in relation to CO2?
In the lungs, CO2 diffuses out of the blood, lowering its concentration and increasing blood pH (less acidic). In the tissues, CO2 levels rise as it’s produced by cells, decreasing blood pH (more acidic).
How does plasma acidity (related to CO2 content) influence hemoglobin’s ability to bind or release oxygen?
In the lungs, low plasma acidity (higher pH) promotes the binding of O2 to hemoglobin, forming oxyhemoglobin. In the tissues, high plasma acidity (lower pH) promotes the release of O2 from oxyhemoglobin.
What role does hemoglobin play in CO2 transport?
Hemoglobin also binds CO2 and acts as a CO2 shuttle, carrying CO2 from the body tissues to the lungs for exhalation.
What happens to oxygen in the lungs during gas exchange?
Oxygen dissolves in the alveolar lining fluid, diffuses through the alveolar and capillary walls into plasma, then into RBCs where it combines with hemoglobin to form oxyhemoglobin. This occurs because blood CO2 levels are low in the lungs.
How does oxygen bind to hemoglobin in the lungs?
Oxygen diffuses into RBCs in the lungs and binds chemically with hemoglobin to form oxyhemoglobin, a process facilitated by low CO2 levels in the blood.
What happens to oxygen in body tissues where it is being used?
In body tissues, oxygen is released from oxyhemoglobin and diffuses into the cells. This dissociation occurs because CO2 levels in the tissues are high, lowering the pH and making the blood more acidic.
How is CO2 transported in the blood?
CO2 diffuses from body cells into plasma and RBCs. Inside RBCs, it is converted into bicarbonate (HCO3-) by the enzyme carbonic anhydrase. A small amount of CO2 also binds chemically to hemoglobin, forming carbamino compounds.
What happens to CO2 once it enters RBCs and binds with hemoglobin?
Once CO2 enters RBCs, it is partially carried as carbamino compounds (attached to hemoglobin) and converted into bicarbonate ions (HCO3-) in the plasma. This helps regulate blood pH by buffering excess acidity.
How does CO2 affect the bicarbonate equation in the body tissues?
In the body tissues, constant CO2 production causes the bicarbonate equation to shift to the right, resulting in the production of bicarbonate ions (HCO3-) and hydrogen ions (H+), which lowers pH and promotes O2 release from hemoglobin.
What happens to CO2 in the lungs regarding the bicarbonate equation?
In the lungs, CO2 is exhaled and lost to the alveolar air sacs. The bicarbonate equation shifts to the left, converting bicarbonate ions (HCO3-) and hydrogen ions (H+) back into CO2 and water, allowing CO2 to be exhaled. This process is enzyme-regulated and works in both directions.
Why is the left ventricle wall thicker than the right ventricle wall?
The left ventricle (LV) performs much more work than the right ventricle (RV), as it pumps blood to the entire body, while the RV only pumps blood to the lungs. As a result, the LV wall is thicker (8-10 mm) compared to the RV wall (2-3 mm).
What is the function of the atrioventricular (AV) valves
The atrioventricular (AV) valves prevent the backflow of blood into the atria
tricuspid valve
the AV value between the right atrium and the right ventricle
- 3 flaps
bicuspid valve (mitral value)
the AV value between the left atrium and the left ventricle - 2 flaps
where are the one-way semilunr valves located
the origin of the pulmonary artery and the aorta
pulmonary artery
pumps deoxygenated blood to the lungs
aorta
pumps oxygenated blood to the body
What happens during ventricular contraction and relaxation in relation to the semilunar valves?
During ventricular contraction, the semilunar valves open, allowing blood to be pumped through them into the arteries. During ventricular relaxation, the semilunar valves snap shut, preventing blood from flowing back into the ventricles.
What happens during the contraction of the atria and ventricles in the cardiac cycle?
Both atria fill with blood and contract simultaneously, sending blood to the ventricles. About 0.1-0.2 seconds later, both ventricles contract simultaneously. One ventricle sends blood to the lungs (pulmonary system) and the other to the body (systemic system).
What is stroke volume and end-systolic volume?
During ventricular contraction (systole), about 2/3 of the blood is ejected from the ventricles, called stroke volume. - stroke volume is the amount of blood coming from the ventricle in 1 heart beat
The remaining 1/3 stays in the ventricles as the end-systolic volume.
equation for cardiac output
CO = HR x SV
heart rate x stroke volume
out of the 0.8 second cycle, how much is diastole and how much is systole
-diastole = 0.5sec
- systole = 0.3sec
What are the three regions of the heart that can spontaneously generate action potentials?
- Sinoatrial node (SA node) - Functions as the pacemaker, located in the right atrium near the superior vena cava.
- AV Node
- Purkinje fibers
How does the vagus nerve affect the heart’s electrical activity?
The vagus nerve innervates the SA node and can adjust the heart rate by influencing the pacemaker’s activity.
how do action potentials spread from the SA node
Action potentials originate at the SA node and spread to adjacent myocytes in the right atrium (RA) and left atrium (LA) through gap junctions between these cells.
Why are specialized myocardial cells needed in the AV node?
Specialized myocardial cells in the AV node are needed to move the impulse from the atria to the ventricles, as the atria and ventricles are separated.
What is the pathway of the heart’s electrical impulse?
- SA node
- AV node
- Continues through AV bundle
- Decends downthe intraventricular septum
- Spreads from endocardium to epicardium
- causes both ventricles to contract
How does the impulse lead to ventricular contraction?
The impulse spreads from the endocardium to the epicardium, causing both ventricles to contract simultaneously.
SA node
sinoatrial node
AV node
atrioventricular node
How does the conduction speed vary throughout the heart’s electrical pathway?
- SA Node: Impulse spreads quickly (0.8-1.0 m/sec)
- AV Node: Conduction rate slows (0.03 to 0.05 m/sec)
- AV Bundle (Bundle of His): Conduction rate increases
- Purkinje Fibers in the Ventricle Wall: Conduction rate peaks at 5 m/sec
Where does the impulse travel after the AV node?
After the AV node, the impulse continues through the AV bundle (bundle of His), descends down the intraventricular septum, divides into right and left branches, and spreads through the Purkinje fibers in the ventricle walls.
Where does the electrical impulse start and how does it move through the atria?
- The impulse starts at the SA node and spreads directly to atrial muscle cells.
- It travels through the right atrium and left atrium.
- Next, it moves to the AV node, located in the posterior septal wall of the right atrium.
What happens at the AV node and AV bundle?
At the AV node, the conduction rate slows, allowing the atria to contract and fill the ventricles.
The AV bundle (Bundle of His) is the only connection between the atria and ventricles.
Conduction rate begins to increase as the impulse moves to the AV bundle.
How does the impulse move through the ventricles?
- After the AV bundle, the impulse moves to the left and right bundle branches.
- The conduction speed increases at the Purkinje fibers, where the resting membrane potential is more positive, and there are lots of gap junctions for quick signaling.
- The Purkinje fibers connect directly to the ventricular muscle cells (myocytes) to trigger contraction.
What is an electrocardiogram (ECG), and how is it generated?
An ECG is the recording of potential differences generated by the heart, conducted to the body’s surface.
Electrodes placed on the skin record these potentials.
what is coronary artery disease
- Condition where coronary arteries become narrowed/blocked due to plaque buildup (atherosclerosis).
- Reduces blood flow to the heart, causing chest pain (angina) or heart attack (myocardial infarction).
bradycardia
slow heart rate - less than 60 bpm
tachycardia
fast heart rate - 100bpm
How do myocytes in the heart function together?
- Myocytes are connected by gap junctions at their ends.
- These gap junctions allow electrical impulses to pass cell to cell, ensuring synchronized heart contractions.
- The gap junctions appear as “intercalated discs.”
What are the 2 major organelles of myocytes in the heart?
Myocytes are organized into fibers (groups of myocytes).
Two major organelles:
Mitochondria: Provide energy for muscle contraction.
Sarcoplasmic Reticulum (SR): Handles calcium (Ca2+) for muscle contraction and relaxation.
How does an electrical signal cause a heart muscle cell to contract?
- Action potential originates in the SA node (pacemaker).
- Electrical signal causes Ca2+ to enter the myocyte cytoplasm through voltage-gated channels.
- Ca2+ then stimulates the release of more Ca2+ from the sarcoplasmic reticulum (SR).
- This release of Ca2+ triggers muscle contraction.
- For muscle relaxation, Ca2+ is pumped back into the SR.
Excitation-Contraction Coupling in Cardiac Muscle
- Voltage gated calcium channels open…
- Ca2+ diffuses from ECF to cytoplasm
- Ca2+ release channels on SR open
- Ca2+ released from SR binds to sarcomere,
stimulates contraction - Ca2+ ATPase pumps calcium back into SR
- Myocardial cell relaxes
Microanatomy of the muscle fibers in the heart
- Cells are arranged into long, rod-shaped organelles called myofibrils.
- Myofibrils have a striated pattern of alternating light and dark bands.
- Z-discs act as anchors for thin protein filaments, primarily actin
Myofibril Structure and Muscle Contraction
- Z-discs separate each myofibril into sections called sarcomeres.
- Thin filaments (actin) and thick filaments (myosin) lie between Z-discs.
- Muscle contraction occurs when the thin and thick filaments slide past each other, causing Z-discs to move closer together, resulting in the striated pattern.
Bands and Zones in Muscle Fibers
- I-bands: Light bands in the myofibril.
- A-bands: Dark bands in the myofibril.
- Z-discs: Located in the middle of the I-bands.
- H-zone: A narrow light band in the center of the A-band.
tropomyosin
attached to the actin
troponin complex
complex of 3 subunits attached to tropomyosin
How do thick filaments contribute to muscle contraction?
- Thick filaments (TF): Made up of rod-shaped proteins with angular heads.
- Muscle contraction is caused by the swiveling of the heads of the thick filaments.
How does the myosin head function in muscle contraction?
- The myosin head has both an actin-binding site and an ATP-binding site.
- When ATP is hydrolyzed to ADP, the myosin head activates and changes orientation.
- Ca2+ binds to troponin, moving the troponin-tropomyosin complex, exposing actin’s binding sites.
- Myosin attaches to actin and undergo a power stroke to contract the muscle.
How do skeletal and cardiac muscles differ in their stimulation for contraction?
- Skeletal muscles: Require external stimulation by somatic motor nerves to contract.
- Cardiac muscle: Automatically produces action potentials through the SA node, without needing external nerve stimulation.
How do skeletal muscles and myocardial cells differ in structure?
- Skeletal muscles: Long and fibrous, not interconnected.
- Myocardial cells: Short, branched, and interconnected. Cells are tubular and joined by gap junctions (electrical synapses).
How does excitation-contraction coupling differ between skeletal muscles and cardiac cells?
- Skeletal muscles: Direct excitation-contraction communication between transverse tubules and SR.
- Cardiac cells: Ca2+-induced Ca2+ release; voltage-gated channels release Ca2+ which stimulate SR to release MORE Ca2+ to start contraction
