Mass Transport in Humans Flashcards
Blood Flow through the Heart
- The function of the heart is to pump blood around the body.
- In mammals, the heart is part of a double circulatory system.
- The blood passes through the heart and is pumped to the lungs, returning back to the heart (pulmonary circulation).
- The blood now passes through the heart a second time (the blood is re-pressurised) and pumped round the body organs before returning to the heart (systemic circulation).
- Blood moves around the body due to the pressure difference between the pressure in the heart (high) and the pressure in the blood vessels (low). This is an example of mass flow.
Heart structure
The heart is two separate pumps, side by side, each consisting of an upper chamber (atrium) and a lower chamber (ventricle). The wall of the heart is made of cardiac muscle. (heart cells are cardiomyocytes)
- Deoxygenated blood returns from the body in the vena cava (vein) and enters the right atrium.
- The blood then passes, via an atrio-ventricular valve into the right ventricle and out, via the semi-lunar valve, into the pulmonary artery.
- The blood now passes through the lungs and returns to the left atrium via the pulmonary vein.
- The blood passes through a second atrio-ventricular valve into the left ventricle and then through the semi-lunar valve into the aorta and then onto the body tissues
What does the renal vein do?
carry blood from kidneys to the heart
What is the role of valves
Prevent back flow
Right Vs Left ventricle
The right ventricle of the heart is pumping blood through the pulmonary arteries only; the left ventricle is pumping blood through a much larger number of capillaries (branching off from the aorta) around the body. Therefore, the left ventricle requires more pressure and consequently, the wall of the left ventricle is much thicker than that of the right ventricle
Vessels entering and leaving
Right atrium- Vena cava brings blood from body (lowest pressure) (VE)
Right ventricle- Pulmonary artery takes blood to lungs (VL)
Left atrium- Pulmonary vein brings blood from lungs (VE)
Left ventricle- Aorta takes blood to body (VL)
Role of coronary arteries
The coronary arteries branch off from the aorta and supply the heart muscle with blood
What is pressure?
Pressure is the amount of force acting on a surface
What is the change in pressure in the heart chamber caused by?
The change in pressure in the heart chambers is as a result of both the changes in the volume of blood within the chambers and the contractions of the heart muscle.
Systole and Diastole definitions
systole- contraction of heart muscle
diastole- heart muscles relaxed
Pressure in the chambers
1) Blood enters atrium
- Blood volume increases pressure in atrium
- Pressure in atrium greater than in ventricle
- atrio ventricular valve opens.
Atrium muscles contract (atrial systole)
- Further increases pressure
- Remaining blood forced into ventricle from atrium
2) Blood enters ventricle
- increases pressure in ventricle due to volume of blood
- Pressure in ventricle greater than in atrium
- atrio ventricular valve closes.
3) Ventricle muscles contract (ventricular systole/ atrial diastole)
- Further increases pressure in ventricle until greater than in aorta/ pulmonary artery
- Semi Lunar valve opens.
Blood enters aorta / pulmonary artery
- Blood is pumped to body (left) or lungs (right)
4) Ventricle muscles relax (diastole)
- Pressure in ventricle is less than in aorta/ pulmonary artery
- Semi lunar valves close
Blood enters atrium
- Blood volume increases pressure in atrium
- (back to 1)
Heart Valves
The atrio-ventricular valves (AV) and the semi-lunar valves (SL) ensure that the blood flows in one direction only through the heart.
These valves will only open in one direction. Valves only open one way due to tendons that anchor the valve. These are sometimes referred to as ‘heart strings. They open and close due to pressure differences on either side of the valve.
Atrio-ventricular valves
Open: greater pressure in atria than ventricles.
Close: greater pressure in ventricles than atria.
Semi-lunar valves
Open: greater pressure in ventricle than arteries (pulmonary & Aorta).
Close: greater pressure in arteries than ventricles.
Pressure changes graph
A. pressure in ventricle rises above that in atria , AV valve close
B. pressure in ventricles rises above that in aorta, SL valve opens
C. pressure in ventricle falls below that in aorta. SL valve close
D. pressure in atrium rises above ventricles. AV valve open
The thickness of the aorta wall changes all the time during each cardiac cycle.
Explain why
- (Aorta wall) stretches;
- Because ventricle contracts
- (Aorta wall) recoils;
- Because ventricle relaxes
- Maintain smooth flow
Describe how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.
- Atrium has higher pressure than ventricle
- Atrioventricular valve opens;
- Ventricle has higher pressure than atrium
- Atrioventricular valve closes;
- Ventricle has higher pressure than aorta;
- Semilunar valve opens;
- Higher pressure in aorta than ventricle
- Semilunar valve closes;
- (Muscle / atrial / ventricular) contraction
Cardiac Output definition
the volume of blood expelled from the left ventricle per minute.
Cardiac Output
CO = SV x HR
Stroke Volume:
Volume of blood expelled from the left ventricle on one cardiac cycle
Heart Rate:
Number of cardiac cycles (beats) per minute.
Units: Volume per unit of time dm3 min -1
Coronary Heart Disease
refers to any interference with the coronary arteries, which supply blood to the heart muscle itself.
Two most common causes of blockage to the coronary arteries are:
* Atherosclerosis (heart attack)- usually occurs after damage has occurred to the artery wall for some reason (e.g. due to high blood pressure)
* Thrombosis (stroke)- clots builds up very rapidly causing further blockage
Risk factors in Coronary Heart Disease
high cholesterol diet, high lipid diet, lack of exercise, smoking
High blood pressure, Increase blood toxins, Increase cholesterol level in blood
=
Damage to endothelium wall, Increase in lipid uptake
age, gender, genetic predisposition
- Smoking increases blood pressure and therefore damage to endothelium. increases levels of cholesterol in blood
- Stressful lifestyle causes increased blood pressure
Mass Flow definition
is the bulk movement of liquids (and gases) due to a pressure difference.
Mass Flow
Closed systems are more efficient than open systems.
It is easier to generate and maintain a pressure gradient.
In most animals, the contraction of the LEFT VENTRICLE generates high hydrostatic pressure.
The pressure in the capillaries and veins is much lower, therefore blood moves down the pressure gradient…through the arteries, arterioles, capillaries, venules and into the veins.
The lower the surface area to volume ratio, and the more active the organism, the greater the need for a specialised transport system with a pump.
Artery
Transport of blood from heart to organ.
Blood is under high pressure. The wall is very thick to withstand this pressure
Structure:
Endothelial layer
- layer is only one cell thick (endothelial cells) - lumen
- Gives a smooth layer which reduces friction and gives smooth flow.
Middle (Elastic layer)
- Contains a large amount of elastic protein fibres.
- Allows wall to stretch as pulse of blood flows past. This stops pressure rising too high.
- Recoils once blood passes. This maintains hydrostatic pressure on the blood.
- Overall, variations in blood pressure partially smoothed (equalised) out.
- Also contains a muscle layer (smooth muscle).
- Muscle contractions constrict the vessel and reduce the volume of blood passing through vessel to increase blood pressure.
Outer layer
- Made of fibrous proteins and gives support and strength to wall, helping it to resist damage due to the high pressure of the blood inside.
Arteriole
Smaller vessels than arteries and connect artery to the capillaries.
As the vessel diameter is smaller than an artery, there is greater friction between the blood and the vessel wall. This causes a fall in blood pressure.
Structure as for an artery but there are two major differences:
-The elastic layer is thinner. As the blood pressure is lower, there is less need for the elasticity required to allow the pulse of blood to pass.
-The muscle layer is thicker. The muscle in the arterioles can be contracted to constrict the vessel. This reduces flow into the organ (to increase delivery of oxygen to actively respiring muscle cells).
Alternatively, the muscle can be relaxed which causes the vessel to dilate and allow more blood into the organ.
Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions
Elastic tissue
1 Elastic tissue stretches under pressure
2 Recoils
3 Evens out pressure
Muscle
4 Muscle contracts;
5 Reduces diameter of lumen constricts vessel;
6 Changes flow/pressure;
Epithelium
7 Epithelium smooth;
8 Reduces friction
Explain how an arteriole can reduce the blood flow into capillaries.
- Muscle contracts
- Constricts arteriole
Capillaries
- Wall only has the endothelial layer
- Involved in exchange of materials between blood and the tissue cells.
- Diameter is very small and there is a large number of capillaries. This creates greater friction and high surface area, reducing blood pressure and blood flow as the blood passes through the capillaries
Veins
These carry blood back to the heart from the tissues. The blood is under lower pressure, therefore the vein wall does not need to be thick.
Structure is similar to that in the artery. However,
- Muscle layer is thinner. There is no need for vaso-constriction as all the blood is going back to the heart
- Elastic layer is thin. Pressure is very low and the wall does not need to stretch or recoil.
The veins have valves. The residual blood pressure is very low. The blood is moved along the vein by the squeezing action of skeletal muscles when they contract. The valves only allow the blood to pass through in one direction to ensure that the blood goes back to the heart.
Pressure changes in the circulation
Pressure changes in the circulation as the blood flows around the circulation, the type of flow and the pressure varies.
In the arteries:
Flow is fast and pressure is high and fluctuating (pulsar) due to the contraction of the LEFT VENTRICLE.
In the capillaries:
increased CROSS-SECTIONAL AREA causes increased friction, which reduces blood pressure and flow changes from pulsar to smooth and speed of flow decreases.
In the veins:
pressure is low and flow is slow and non-pulsar
Adaptions of capillaries
Very thin walls- increases rate of diffusion
Numerous and branched- increases overall surface area for diffusion
Narrow diameter (lumen)- ensures RBC is in contact with wall (Increases effective surface area between RBC and capillary wall and reduces distance for diffusion)
Wall spaces / fenestrations- there are gaps between the cells of the endothelial cells which allow rapid formation of tissue fluid and WBC to pass tissue spaces.
Describe how tissue fluid is formed and how it is returned to the circulatory system
Formation
1. High hydrostatic pressure
2. Forces water / fluid out;
3. Large proteins remain in capillary;
Return
4. Lower water potential in capillary
5. Due to proteins;
6. Water enters capillary by osmosis
returns to lymphatic system
Explain the role of the heart in the formation of tissue fluid
left ventrilce contracts causing high hydrostatic pressure
forces water out
