YR 1 - HUMAN PHYSIOLOGY CHPTR 20-21 Flashcards
(41 cards)
Briefly explain heart circulation
The right side of the heart pumps blood through the pulmonary circulation which carries blood to the lungs where CO2 diffuses from the blood into the lungs and O2 diffuses from the lungs into the blood.
The pulmonary circulation returns the blood to the left side of the heart. The left side of the heart then pumps blood through the systemic circulation, which delivers O2 and nutrients to all the remaining tissues of the body.
From those tissues, CO2 and other waste products are carried back to the right side of the heart.
What are the functions of the heart?
- Generating blood pressure - The contractions make sure that the blood flows, this is responsible for the blood to move through the vessels
- Routing blood - Ensuring that the blood flowing to the tissues has adequate levels of O2
- Ensuring one-way blood flow - the valves of the heart ensure a one-way flow of blood through the heart and blood vessels
- Regulating blood supply - the rate and force of heart contractions change to meet the metabolic needs of the tissues, such as exercise, change in body position, and rest.
How is the heart shaped?
An adult heart is shaped like a blunt cone and is approx the size of a closed fist.
(heart mass)
Females average mass is 250g
Males average mass is 300g
Where is the heart located?
The heart is located in the mediastinum, a midline partition of the thoracic cavity that also contains the trachea, the esophagus, the thymus, and other associated structures.
What is the pericardium?
The pericardium is a double-layered, closed sac that surrounds the heart.it consists of two layers:
- the outer fibrous pericardium - this is a tough, fibrous connective tissue layer that prevents overdistension of the heart and anchors it within the mediastinum
- the inner serous pericardium - this is a layer of simple squamous epithelium
What three layers of tissue are the heart wall composed of?
- The epicardium - this is the superficial layer of the heart wall. It is a thin serous membrane that constitutes the smooth outer surface of the heart.
- The myocardium - this is the thick middle layer of the heart. it is composed of cardiac muscle cells and is responsible for the heart’s ability to contract.
- The endocardium - this is deep into the myocardium. it consists of simple squamous epithelium over a layer of connective tissue. The endocardium forms the smooth, inner surface of the heart chambers, which allows blood to move easily through the heart.
The endocardium also covers the surfaces of the heart valves.
What are the 4 chambers that the heart consists of?
The heart consists of four chambers: two atria and two ventricles.
The thin-walled atria form the superior and posterior parts of the heart, and the thick-walled ventricles form the anterior and inferior portions.
What are the 3 major right atrium openings?
- An opening from the superior vena cava
- An opening from the inferior vena cava
- An opening from the coronary sinus
The openings from the superior vena cava and the inferior vena cava receive blood from the body and the opening of the coronary sinus receives blood from the heart itself.
The left atrium has 4 relatively uniform openings from the 4 pulmonary veins that receive blood from the lungs.
Describe the blood flow through the heart
Blood flows through both sides simultaneously. Both atria contract at about the same time and both ventricles contract at about the same time, therefore blood is moving through both the pulmonary and the systemic circulations with each heartbeat.
Describe the structure and function of the heart skeleton
The heart skeleton consists of a plate of fibrous connective tissue between the atria and the ventricles.
This connective tissue plate forms fibrous rings around the atrioventricular and semilunar valves and provides solid support for them, reinforcing the valve openings.
What are the cardiac muscle cells?
+ their electrical properties
Cardiac muscle cells are elongated, branching cells that have one or occasionally two centrally located nuclei.
They contain actin and myosin myofilaments organised to form sarcomeres.
Cardiac muscle cells like other electrically excitable cells, such as neurons and skeletal muscle fibers have a resting membrane potential.
The resting membrane potential depends on a low permeability of the plasma membrane to Na+ and Ca2+ and a higher permeability to K+.
Autorhythmicity of Cardiac muscle
The heart is said to be autorhythmic because it stimulates itself (auto) to contract at regular intervals (rhythmic).
If the heart is removed from the body and maintained under physiological conditions with the proper nutrients and temperature it will continue to beat autorhythmically for a long time.
What are refractory periods of cardiac muscle?
Cardiac muscle like the skeletal muscle has refractory periods associated with its action potential.
The refractory period can be subdivided into the absolute refractory period and the relative refractory period.
During the absolute refractory period, the cardiac muscle cell is completely insensitive to further stimulation. The cell is sensitive to the stimulation but a greater stimulation than normal is required to cause an action potential.
Talk about Electrocardiogram
Action potentials conducted through the myocardium during the cardiac cycle produce electrical currents that can be measured at the body surface.
Electrodes placed on the body surface and attached to an appropriate recording device can detect small voltage changes resulting from action potentials in the cardiac muscle.
The electrodes do not detect individual action potentials: rather they detect a summation of all the action potentials transmitted by the cardiac muscle cells through the heart at a given time.
The summated record of the cardiac action potentials is an electrocardiogram.
What does a normal ECG consist of?
Waves and complex
- The P wave; which is the result of action potentials that cause depolarisation of the atrial myocardium, signals the onset of atrial contraction
- The QRS complex; composed of 3 individual waves- the Q, R, and S waves results from ventricular depolarisation and signals the onset of ventricular contraction
- The T wave; represents repolarisation of the ventricles and precedes ventricular relaxation. A wave representing repolarisation of the atria cannot be seen because it occurs during the QRS complex
Describe the cardiac cycle
The cardiac cycle refers to the repetitive pumping process that begins with the onset of cardiac muscle contraction and ends with the beginning of the next contraction.
The right and left halves of the heart can be viewed as two separate pumps that work together.
Each pump consists of a “primer pump” which is the atrium and a “power pump” which is the ventricle.
Atrial primer pumps complete the filling of the ventricles with blood, ventricular power pumps produce the major force that causes blood to flow through the pulmonary and systemic arteries.
Blood moves from an area of higher pressure to an area of lower pressure. Pressure changes produced within the heart chambers as a result of cardiac muscle contraction and relaxation move blood along the previously described routes of the pulmonary and systemic circulations.
What does systole and diastole mean?
Systole- means to contract
Diastole- means to dilate
Describe the heart sounds
The pumping heart produces different sounds and this is revealed using a stethoscope. The sounds are best heard by applying the stethoscope at particular sites in relation to the heart valves.
The lubb sound (first heart sound)- this sound is a low pitched sound. It occurs at the beginning of ventricular systole and is caused by vibration of the atrioventricular valves and surrounding fluid as the valves close.
The dupp sound(second heart sound)- this sound is a high pitched sound. it occurs at the beginning of ventricular diastole and results from the closure of the aortic and pulmonary semilunar valves.
A third heart sound can be heard in some normal people, particularly those who are thin and young.
Systole is therefore approx the time between the first and the second heart sound.
Diastole which lasts somewhat longer is approx the time between the second heart sound and the next first heart sound.
What is the Aortic pressure curve?
The elastic walls of the aorta are stretched as blood is ejected into the aorta from the left ventricle. Aortic pressure remains slightly below ventricular pressure during this period of ejection.
The pressure in the ventricles begins to decrease and so does the aortas. As ventricular pressure drops below that in the aorta, blood flows back toward the ventricle because of the elastic recoil of the aorta.
When the recoil has an increase in pressure it leads to a dicrotic notch which means double beating.
What does mean arterial pressure, cardiac output, and peripheral resistance mean?
Mean arterial pressure- is slightly less than the average of the systolic and diastolic pressures in the aorta. It is proportional to cardiac output x peripheral resistance.
Cardiac output- is the amount of blood pumped by the heart per minute,
Peripheral resistance- is the total resistance against which blood must be pumped.
What is cardiac output formula?
Cardiac Output = Heart Rate x Stroke Volume
CO = HR X SV
What is intrinsic regulation?
Tissues and organs within the body are able to intrinsically regulate, to a varying degree, their own blood supply in order to meet their metabolic and functional needs. This is termed local or intrinsic regulation of blood flow.
What are the pulmonary vessels?
Pulmonary vessels transport blood from the right ventricle, through the lungs, and back to the left atrium.
What are the systemic vessels?
Systemic vessels transport blood from the left ventricle through all parts of the body and back to the right atrium.
