3.2 Flashcards
What are the external features of the heart?
- Main part of the heart consists of cardiac muscle
- Coronary arteries lying over the surface of the heart
What can happen when the coronary arteries become blocked?
- Angina
- Myocardial infarction
What is cardiac muscle?
Specialized muscle found in the walls of the heart
What is the structure of cardiac muscle?
- Consists of fibers that branch producing cross-bridges
- Numerous mitochondria between muscle fibrils (myofibrils)
- Muscle fibrils (myofibrils) are separated by intercalated discs
- Nucleus is divided into contractile units called sarcomeres
When does deoxygenated blood enter the heart?
When does deoxygenated blood enter the heart?
When does oxygenated blood enter the heart?
Through the PULMONARY VEIN into the LEFT ATRIUM
What are the atrioventricular valves?
Valves between the atria and the ventricles which ensure the blood flows in the correct direction
What is the role of the tendinous chords connected to the AV valves?
revent the valves from turning inside out when the ventricles wall contract
What prevents blood from flowing between the ventricles?
A wall of muscle called the septum separates the ventricles from each other.
This ensures that oxygenated blood in the left side of the heart and deoxygenated blood in the right side are kept separate
When does deoxygenated blood leave the heart?
Out of the RIGHT VENTRICLE into the PULMONARY ARTERY
When does oxygenated blood leave the heart?
Out of the LEFT VENTRICLE into the AORTA
What are semilunar valves?
Valves that prevent blood re-entering the heart from the arteries
How are the walls of the Atria adapted for blood pressure?
- Muscle of atrial walls are very thin
(chambers do not create much blood pressure)
How are the walls of the Right Ventricle adapted for blood pressure?
- Walls are thicker than that of the atria to enable it to pump blood out of the heart to the lungs
- Not at too high of a pressure as the lungs are close and the capillaries are fragile
How are the walls of the Left Ventricle adapted for blood pressure?
- Walls are two or three times thicker than that of the RV which enables it to overcome the resistance of systemic circulation and supply the body with oxygen
What is the cardiac cycle?
The sequence of events in one full beat of the heart
What is the role of the valves?
Ensure blood flows in the correct direction
What is systole?
Contraction of the heart
What events happens starting from after ventricular systole?
- The pressure in the ventricles rapidly drops
- Blood in the atria pushes the AV valves open
- Blood entering the heart flows straight through the atria and into the ventricles
- The pressure in the atria and ventricles rise slowly
- The valves remain open while the atria contract, but close when the atria begin to relax
- As the ventricles begin to contract (systole), the pressure increases which causes the blood to move upwards
What causes the closing of the AV valves?
- Swirling action in the blood around the valves when the ventricle is full
What prevents the AV valves opening during ventricular systole?
- Blood fills the valve pockets to keep them closed
- The tendinous chords attached to the valves
What events happens starting from before ventricular systole?
- The pressure in the major arteries is higher than the pressure in the ventricles
- This means the semilunar valves are closed
- Ventricular systole increases the pressure of the ventricles which forces the semilunar valves open
- Once the ventricles have finished contracting, the heart muscle begins to relax (diastole)
- This causes the pressure to drop which pushes the semilunar valves closed
What causes the semilunar valves to close?
The semilunar valves are pushed closed by the blood collecting in the pockets of the valves
Why can cardiac muscle be described as myogenic?
The heart is able to initiate its own contraction
What is fibrillation?
Uncoordinated contraction of the atria and ventricles
What is the Sino-atrial node?
A small patch of tissue that sends out waves of electrical excitation at regular intervals in order to initiate contractions.
The SAN is also known as the pacemaker
What causes the contraction of the atria?
- The wave of excitation spreads over the walls of both atria
- It travels along the membranes of the muscle tissue
- As the wave of excitation passes, it causes the cardiac muscle cells to contract
- This is atrial systole
Why does the excitation from the SAN spread to the ventricles?
The tissue at the base of the atria is unable to conduct the wave of excitation, and so it cannot spread down the ventricle walls.
What is the Atrial-ventricular node?
The only route which that can conduct the wave of excitation through to the ventricles. The wave of excitation is delayed in the node.
Why is there a delay at the AV node?
To allow time for the atria to finish contracting and for the blood to flow down into the ventricles before they begin to contract.
What causes the contraction of the ventricles?
- After the short delay, the wave of excitation is carried away from the AVN and down specialized conducting tissue called PURKYNE TISSYE.
- This runs down the interventricular septum
- At the base of the septum, the wave of excitation spreads out of the walls of the ventricles
- As the excitation spreads upwards from the base (apex) of the ventricles, it causes the muscles to contract
- This means that the ventricles contract from the base upwards
What is Purkyne tissue?
Consists of specially adapted muscle fibers that conduct the wave of excitation from the AVN down the septum to the ventricles
How do electrocardiograms work?
The sensors attached to the skin pick up the electrical excitations by the heart and convert this into a trace
ECG image
draw an ecg
What is Bradycardia?
A slow heart rhythm
What is Tachycardia?
A rapid heart rhythm
What is Atrial Fibrillation?
When the atria beats more frequently than the ventricles. No clear P wave seen.
The typical ECG pattern of AFib shows a chaotic, irregular baseline with no distinct P waves, which are the electrical signals generated by the atria. Instead, the baseline is often undulating and irregular, with a wavy or sawtooth appearance.
What is Ectopic Heartbeat?
An extra or early beat of the ventricles
On an electrocardiogram (ECG), an ectopic heartbeat can be seen as an early, extra QRS complex that occurs before the next expected sinus beat. The QRS complex will often look different from the normal sinus QRS complex, as the ventricular depolarization may be initiated from a different location in the ventricles.
What are the three main factors that influence the need for a transport system?
- Size
- Surface area: volume ratio
- Level of metabolic activity
How does size affect the need for a transport system?
The cells inside a large organism are further from its surface - the diffusion pathway is increased.
The diffusion rate is reduced, and diffusion is too slow to supply all the requirements.
How does the level of metabolic activity affect the need for a transport system?
active organisms need good supplies of nutrients and oxygen to supply the energy for movement
animals that keep themselves warm, such as mammals need even more energy
What are the features of a good transport system?
- A fluid or medium to carry nutrients, oxygen and waste products around the body
- A pump to create pressure that will push the fluid around the body
- Exchange surfaces that enbale substances to enter the blood and leave it again where they are needed.
- Tubes or vessels for mass flow
- Two circuits - one to pick up oxygen and one to deliver it
What is a single circulatory system?
One in which the blood flows through the heart once for eachh circuit of the body
What is a double circulatory system?
One in which the blood flows through the heart twice for each circuit of the body.
What is pulmonary circulation?
blood flow between heart and lungs
What is systematic circulation?
blood flow between the heart and the cells and tissues in the body
What are the disadvantages of single circulation within fish?
- Blood pressure drops as it flows towards the body, nd will not flow very quickly.
- The rate at which oxygen and nutrients are delivered to respiring tissues is limited.
What are the advantages of double circulation within humans?
- The heart can increase pressure after blood passes through the lungs so the blood can flow quickly to the rest of the body
What are the disadvantages of double circulation within humans?
- The blood can not be at a high pressure when going through the lungs otherwise it may damage the capillaries within the lungs
What is an open circulatory system?
One in which the blood is not held within vessels
How does an open circulatory system work?
- Tissues and cells are bathed directly in the blood
There is a muscular pumping organ like the heart. This is a long, muscular tube that lies just under the upper surface of the body. Blood from the body enters the heart through pores called Ostia. The heart then pumps the blood towards the head via peristalsis.
Some larger insects have open-ended tubes attached to the heart which direct the blood towards active parts of the body
What are the disadvantages of an open circulatory system?
- Blood pressure is low and blood flow is slow
- Circulation may be affected by body movements or lack of body movements.
What is a closed circulatory system?
One in which the blood is held within vessles
What are the advantages of an closed circulatory system?
- High pressure, so that blood flows more quickly
- More rapid delivery of oxygen and nutrients
- More rapid removal of Carbon dioide and other wastes
- Transport is independant of body movements
What do all blood vessels have?
A single layer of cells called the endothelium lining the inside of the vessel. It is particularly smooth in order to reduce friction with the flowing blood.
What does the Inner layer (tunica intima) consist of?
- Thin layer of elastic tissue which allows the wall to strecth and reocil to help maintain pressure
What does the Middle layer (tunica media) consist of?
- A thicker layer of smooth muscle
What does the Outer layer (tunica adventitia) consist of?
- Thicker layer of collagen and elastic tissue to withstand and main blood pressure
What are arteries?
Blood vessels that carry blood away from the heart
What are features of the arteries?
- Thick walls
- Narrow lumen
- Folded inner wall to allow lumen to expand as blood flow increases
What are arterioles?
Small blood vessels that distribute the blood from an artery to the capillaries
What are features of the arterioles?
- Wall contains a layer of smooth muscle.
Contraction of this muscle will constrict the blood flow to redirect blood flow to different parts of the body
What are capillaries?
Very small blood vessels with very thin walls
What are features of the capillaries?
- Very narrow lumen (size of RBC). This reduces diffusion distance.
- Single layer of flattened endothelial cells. This reduces diffusion distance.
- Leaky walls. They allow blood plasma and dissolved substances to leave the blood
What are venules?
Small blood vessels that collect blood from capillaries and lead into the veins.
What are veins?
Blood vessels that carry blood back to the heart
What are features of the veins?
- Thinner walls with less collagen and elastic tissue as they do not need to stretch and recoil due to the lower pressure
- Wider lumen to allow ease of blood flow.
- Contain valves to help the blood flow back to the heart and to prevent it flowing in the opposite direction.
What is blood?
The fluid used to transport materials around the body.
What does blood consist of?
- Plasma
- Dissolved substances (CO2, O2, minerals, glucose, amino acids, hormones and plasma proteins)
- Red blood cells
- White blood cells
- Platelets
What is tissue fluid?
The fluid surrounding the cells and tissues
What does tissue fluid consist of?
- Dissolved substances (O2 and nutrients)
- Neutrophils
- Few proteins or fats
How is tissue fluid formed?
At the arterial end of the capillary, the blood is under high hydrostatic pressure due to the contraction of the left ventricle in the heart.
- This means the fluid containing oxygen, glucose, and nutrients is forced out of tiny gaps between the cells in the capillary wall.
- Cells/platelets and plasma proteins are retained in the capillary as they are too big to fit through the gaps.
- The fluid is now known as tissue fluid and as it surrounds the cells allows the movement of substances across the plasma membranes.
What process moves blood out of capillaries?
Mass flow rather than diffusions
How is tissue fluid retuned to the capillaries?
- At the venous end of the capillary, the hydrostatic pressure is much lower.
- This allows some of the tissue fluid to return to the blood carrying CO2 and other waste substances into the blood.
Where else does tissue fluid move too?
- Some tissue fluid is directed into the lymphatic.
- This drains excess tissue fluid out of the tissues and returns it to the blood system in the subclavian vein in the chest.
What is lymph?
The fluid held in the lymphatic system.
It is similar in composition to the tissue fluid but contains lymphocytes, as these are produced in the lymph nodes
It also contains fats near the digestive system, but few proteins.
What is oncotic pressure?
The pressure created by the osmotic effects of the solutes
Compare oncotic pressure in Blood plasma, tissue fluid, and lymph?
- More negative, less negative, less negative
Compare hydrostatic pressure in Blood plasma, tissue fluid and lympth?
- High, low, low
What effect do the pressures in blood have?
Hydrostatic pushes fluid out in tissues
Oncotic pulls water back into the blood
What effect do the pressures in tissue fluid have?
Hydrostatic pushes fluid into the capillaries
Oncotics pulls water into the tissue fluid
What is formed when oxygen binds with hemoglobin?
Oxyhaemoglobin
What is hemoglobin?
The red pigment used to transport oxygen in the blood.
What is the basic structure of hemoglobin?
- 4 polypeptide chains
- A haem group attached to each polypeptide
- Each haem group contains a Fe2+ ion
What causes the affinity between oxygen and hemoglobin?
The iron ion can attract and hold a single oxygen molecule. The haem group is said to have a high affinity for oxygen
What is affinity?
A strong attraction
How many oxygen molecules can each hemoglobin molecules hold?
-4 Oxygen molecules
- 8 Oxygen atoms
What is oxygen association?
When hemoglobin combines with oxygen in the lungs to be transported around the body
What is oxygen dissociation?
When oxygen is released from oxyhemoglobin where it is needed for respiration
What is the partial pressure of oxygen/ oxygen tension?
The relative proportion that oxygen contributes to a mixture of glasses
What is the shape of the Oxygen Dissociation Curve?
An S-shape
What happens to hemoglobin saturation at a low oxygen tension?
At low oxygen tensions, the hemoglobin does not readily associate with oxygen molecules.
This is because the haem groups that attract the oxygen are in the center of the hemoglobin molecule.
This makes it difficult for the oxygen molecules to reach the haem group and associate with it.
The difficulty in combining with the first oxygen molecule accounts for the low saturation level of hemoglobin.
What happens to hemoglobin saturation at a 50% oxygen tension?
The diffusion gradient into the hemoglobin increases.
One molecule enters and associates with one of the haem groups.
This causes a conformational change in the hemoglobin molecule which allows more oxygen molecules to enter the hemoglobin and associate with the other haem groups.
This accounts for the steepness of the curve as the oxygen tension rises.
What happens to hemoglobin saturation at a 100% oxygen tension?
There is no more free haem groups for oxygen to attach too. Therefore the curve levels off.
How does fetal hemoglobin differ from adult hemoglobin?
Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.
Therefore, the fetal hemoglobin dissociation curve is to the left of the curve for adult hemoglobin.
Why does fetal hemoglobin need a higher affinity for oxygen?
Fetal hemoglobin must be able to associate with oxygen in an environment where oxygen tension is low enough to make adult hemoglobin release oxygen.
Where does fetal hemoglobin associate with oxygen?
Fetal hemoglobin absorbs oxygen from surrounding fluids. This reduces the oxygen tension even further.
As a result, oxygen diffuses from the mother’s blood fluid into the placenta. This reduces the oxygen tension within the mother’s blood, which in turn, makes the maternal hemoglobin release more oxygen.
What three ways is Carbon dioxide transported in the body?
5% is dissolved directly in the plasma
- 10% is combined with hemoglobin to form Carbaminohemoglobin
- 85% is transported as Hydrogencarbonate ions
How are Hydrogencarbonate ions formed?
- Carbon dioxide in the plasma combines with water to form a weak acid called Carbonic Acid
- The Carbonic Acid dissociates to release Hydrogen ions (H+) and Hydrogencarbonate ions (HCO3-)
How is Carbonic Acid formed?
CO2 + H20 -> H2CO3
Catalysed by Carbonic Anhydrase
What happens when the Hydrogencarbonate ions are formed?
The ions diffuse out of the RBC into the plasma.. This affects the charge inside the cell.
What is the Chloride Shift?
The movement of Chloride ions into the erythrocytes to balance the charge as Hydrogencarbonate ions leave the cell
What happens when the H+ ions build up in the red blood cell?
Cause the contents to become very acidic
What happens to counteract the increasing acidity in the RBC?
The hydrogen ions are taken out of the solution by associating with hemoglobin to form hemoglobonic acid.
The hemoglobin acts as a buffer
What is the Bohr Effect?
The effect that increasing carbon dioxide has on hemoglobin.
More CO2 = > H2CO3, > H+ > PH
The increased acidity affects the tertiary structure of the hemoglobin and reduces the affinity of the hemoglobin for oxygen.
The hemoglobin is unable to hold as much oxygen, and oxygen is released from the oxyhemoglobin to the tissues.
What is the Bohr Shift?
When more Carbon dioxide is present, hemoglobin becomes less saturated with oxygen.
This is reflected in a change to the hemoglobin dissociation curve, which shifts downwards and to the right.
