3. Heart & Circulation Flashcards
2 factors determining whether an organism needs a transport system
- SA to volume ratio: could nutrients reach all parts of the organism by diffusion alone?
- How active is the organism?
6 important common features of transport systems
- Suitable medium to carry nutrients - usually a liquid (blood)
- Closed system of tubes (blood vessels)
- Form of mass transport in which liquid is moved in bulk over large distances/faster than diffusion (heart)
- Mechanisms to maintain movement in one direction (valves, maintaining a high pressure)
- Means of controlling the flow to different parts of the organisms (constriction/dilation of blood vessels)
- Mechanisms for gas exchange
What is meant by a closed circulatory system?
Blood stays/is contained within the blood vessels
What is the advantage of a double circulatory system?
Blood goes through the heart twice
Different pressures: high in systemic circuit, low in pulmonic circuit
What is the blood vessel going from the heart to the gut called?
Mesenteric artery
What does the hepatic portal vein do?
Blood goes to the liver so that excess glucose can be removed & stored as glycogen
Toxins can also be removed
All the layers of a blood vessel (innermost to outermost)
Lumen Endothelium Elastic tissue Muscle layer Tough fibrous outer layer
Describe the endothelium
Smooth & flat
Function of the tough fibrous outer layer
Prevents damage
Why do veins have a lower pressure than arteries?
Pressure comes from the heart, so by the time blood gets to the veins the pressure is much lower
Function of thick muscular layer in arteries
Allows them to constrict & dilate to control the volume of blood flowing to particular organs
Do veins need to constrict or dilate?
No
Function of thick elastic layer in arteries
Allows for stretch & recoil as the heart beats
Function of gaps between cells in capillary wall
Allows WBCs to leave capillaries and enter tissues (esp. phagocytes)
How thick is the endothelial cell wall in capillaries?
One cell thick; short diffusion distance!
Elaborate on the narrow lumen in capillaries?
- RBCs pushed up against the capillary wall: reducing diffusion distance
- Whole blood vessel is narrow: it can fit between cells in the tissue. No cell is far from a capillary.
What is tissue fluid?
Fluid that bathes the cells. Water with solutes such as glucose, amino acids etc dissolved in it.
How is tissue fluid formed?
High hydrostatic pressure in arteriole end of the capillary: water & small molecules are forced out of the capillaries through the small pores in the capillary walls (ultrafiltration).
Plasma forced out of capillaries to become tissue fluid.
What happens in the venules (tissue fluid)?
Lower hydrostatic pressure in venule end of capillary than in tissue fluid, so fluid moves back into capillaries.
Low WP in capillaries because lots of water was forced out at the arteriole end. This means water moves from the tissue fluid into the blood vessel by osmosis.
What is meant by excess tissue fluid, and where does it go?
Tissue fluid that didn’t move back into the capillaries
It drains into the lymphatic system
What do heartstrings do?
Stop the valves from opening the wrong way
Why is the wall of the left ventricle thicker than the right?
Needs to be able to contract with enough force to produce enough pressure to push blood around the body
Is the right AV valve the tricuspid or bicuspid?
Tricuspid
Do the left and right sides of the heart contract together or separately?
TOGETHER
What is diastole?
When the heart relaxes
What is systole?
When a particular chamber contracts (e.g. atrial/ventricular systole)
Ultimately, what does the cardiac cycle rely on?
Changes in PRESSURE!
What happens in diastole?
Blood flows in from the veins into the atria. Blood also starts to trickle down into the ventricles (due to gravity)
What are the semi-lunar valves doing in diastole?
They are closed!
Pressure in arteries > pressure in ventricles, preventing backflow of blood from arteries into ventricles
What happens in atrial systole?
- Atrial walls contract
- This increases atrial pressure
- Pressure in atria > pressure in ventricles
- This pushes the AV valves open and pushes blood into ventricles
What happens in ventricular systole?
- Ventricular walls contract, increasing the pressure in the ventricles
- Pressure in ventricles > pressure in atria
- This pushes AV valves closed
- This also pushes semi-lunar valves open, and pushes blood into arteries
In a heartbeat, what is the lub and what is the dub?
Lub = AV valves closing during ventricular systole Dub = semi-lunar valves closing
Valves open and close because of…
pressure differences!
Formula for cardiac output
Cardiac output = heart rate x stroke volume
Cardiac output
Volume of blood pumped by one ventricle per minute
Heart rate
Number of heartbeats per minute
Stroke volume
Volume of blood pumped by one ventricle per heartbeat
P wave on an EKG
Excitation of the atria
QRS complex on an EKG
Excitation of the ventricles
T wave on an EKG
Diastole
Heart muscle can be described as…
myogenic
What does myogenic mean?
Contractions of the heart muscle are initiated within the heart muscle itself, not the nervous system
The role of the nervous system is…
to speed up or slow down heart rate
Which contracts first: atria or ventricles?
Atria!
Where is the sinoatrial node (SAN)?
In the wall of the right atrium
What does the sinoatrial node do?
Initiates an impulse which spreads out through the atrial walls, stimulating them to contract
What does the atrioventricular node (AVN) do?
Conducts the impulse from the SAN into the ventricles (the only route for the ventricular walls to receive the impulse)
What does the non-conducting layer in the heart wall between the atria and ventricles do?
Stops the impulse spreading down into the ventricular walls
Where do the impulses go to after passing through the AVN?
Pass down the Purkinje fibres in the bundle of His to the heart apex
What happens after impulses pass down the Purkinje fibres?
They spread up through the ventricle walls causing contraction from the apex upwards. Blood is squeezed into the arteries.
What is the role of the coronary arteries?
Supply oxygen and glucose to the heart muscle for aerobic respiration
What is atherosclerosis?
Narrowing of the blood vessels
What can atherosclerosis lead to?
Angina: pain in the heart caused by lactic acid from anaerobic respiration
Heart attacks: part of the cardiac muscle stops respiring
What causes the lumen to have a reduced volume?
Build up of saturated fats & cholesterol in the blood vessel wall
What is an atheroma?
The buildup itself causing atherosclerosis
What is coronary heart disease (CHD)?
Disease caused by atherosclerosis in the coronary arteries
Risk factors for CHD
- Smoking
- Genetics
- Diet (high in saturated fats & cholesterol)
- Lack of exercise
- Age
- Gender (men more likely to get it)
- High blood pressure
- Blood cholesterol (HDLs & LDLs)
How is cholesterol transported around the body?
In lipoproteins
Types of lipoproteins
High or low density (HDL & LDL)
Is LDL bad or good?
Bad
- made of saturated fats
- transport cholesterol to the body, so much more likely to end up in a blood vessel & cause atherosclerosis
Is HDL bad or good?
Good
- made of unsaturated fats
- transports cholesterol to the liver which uses it in useful ways (e.g. making bile)
What is a thrombosis?
A blood clot that forms inside the blood vessels, and it can block blood flow
What can thrombosis in the brain do?
Cause a stroke
Link between atherosclerosis & thrombosis
- Atherosclerosis disrupts blood flow, so making thrombosis more likely
- Atherosclerosis narrows blood vessels: thrombosis could block the blood vessel/get stuck. Basically thrombosis becomes more of a problem.
