Cardiovascular System: Biology Homework Assignment Solution

This document presents a comprehensive solution to a homework assignment focusing on the human cardiovascular system. The assignment delves into key aspects such as the sinoatrial (SA) node's role as the heart's pacemaker, the electrical network within the ventricles (Purkinje fibers), and the concept of depolarization in cardiac muscle cells. It explores autorhythmicity, the sequential steps of the cardiac cycle, and the distinct functions of arteries, veins, and capillaries. The assignment also addresses vasoconstriction and vasodilation, and the role of the muscle pump in venous return. Detailed answers and explanations are provided for each question, referencing relevant physiological principles and processes.

Running head: CARDIOVASCULAR SYSTEM
Cardiovascular System
Name of the Student
Name of the University
Author Note

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Answer to Question 1.
a) Sinoatrial node is the heart’s pace maker.
The SA node or the Sinoatrial node is named as the natural pace maker of the heart as it
sends the natural signals or electrical impulses from one cardiac muscle to another and as a
consequence of this the con contraction relaxation process of the cardiac muscles take place.
Firstly the electrical impulse generated from the SA node contracts the atrium and the blood
is transferred to the ventricle. Then the electrical impulses conduct through the AV nodes and
the ventricle contracts eventually (Boron and Boulpaep 2016).
Answer to Question 1.
b) The name of the electrical network within ventricular myocardium is parkinje fibres.
The contraction of this Parkinje fibres is associated with the presence of QRS complex of the
ECG. It is reported that the two bundle branches taper out to form multiple numbers of
parkinje fibres and they are responsible for stimulating individual groups of myocardial cells
and those cells then contract. The spreading of the electrical impulses through the ventricular
myocardium is associated with the QRS complex formation in ECG.
Answer to Question 1.
c) Discharge of electrical impulse is called depolarization.
The electrical impulse discharge in the cardiac cells is named as depolarization; however
changes of the electrical impulse of all the cells are also named as depolarization. In case of
cardiac muscle cell the cell maintain a resting current at -70 mv and during the contraction
phase the concept of depolarization comes into play. During the depolarization the electrical
impulse of the cells gradually changes and goes up to a value of +35 mv and this stage is

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known as the state of depolarization. This stage is followed by a repolarization and
hyperpolarization. After that the cardiac muscle cell again maintain the resting state or the
resting membrane potential (Mitchell 2014).
Answer to Question 1.
d) SA node initiates an excitatory impulse in every 0.8 seconds.
The different phase of the muscle contraction is conducted by the excitatory responses of the
SA nodes and it is reported that the due to the auto-rthythmic nature of the card iac muscle
the SA node conducted impulses in such way (Hall 2015).
Answer to Question 2.
The concept of autorhythmicity is closely related to the properties of the cardiac muscle cells
and it is mainly characterized by the property of initiating the electrical impulses by its own.
As a consequence of this property the mechanical stimulus of the cardiac muscle takes place
and it can pump the blood at a fixed pace. This unique property of the cardiac muscle cells is
completely related to the conduction of SA nodes and AV nodes. However, it is also very
important to mention that this property is not observed in skeletal or smooth muscle cells
(Boron and Boulpaep 2016).
Answer to Question 3.
1) Complete Cardiac diastole- ventricular filling (A)
2) The aortic and Pulmonary valves are forced open (B)
3) Atrial Contraction take place (C)
4) The back pressure of blood closes the tricuspid and mitral valves (G)

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5) Ventricular Contraction takes place (D)
6) Blood is forced into systematic and pulmonary circulation (E)
7) Semilunar valve snap shut (F)
8) Complete cardiac diastole –passive ventricular filling (H)
Answer to Question 6.
The contraction and relaxation process of heart is a very complex and interesting thing, At
first the deoxygenated blood comes to the right atria through pulmonary artery and the atria
fills. After that, when the atrial pressure is enhanced due to accumulated blood volume the
dicaspid valve opens towards the right ventricles and the blood fills into the right ventricle.
After that the blood goes to the lungs through opening of the semilunar valves. On the other
hand , the left atria fills with oxygenated blood and those oxygenated bloods is transferred to
left ventricle through tricuspid valve. After the filling process, the ventricle contracts and the
oxygenated blood is circulated to whole body. By this mechanism the atria and ventricle do
not contract simultaneously (Hall 2015).
Answer to Question 8.
The two key features of veins and arteries are as follows-
(i) Vein carries deoxygenated blood from whole body to heart and the artery carries
oxygenated blood from heart to whole body.
(ii) Arteries have small rounder lumen and on the other hand the veins have larger rounder
lumen (Hall 2015).

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Answer to Question 9.
Artery Vein Capillary
Carries blood from heart to
body
Carries blood from body to
heart
Connects arteries and vein
Carries oxygenated blood
mostly
Carries deoxygenated blood
mostly
Carries deoxygenated blood
and oxygenated blood
Presence of thicker walls Presence of thinner walls Walls are only one cell thick.
Pressure is comparatively
high than that of the veins
Pressure is comparatively
low than that of the arteries
Pressure is less than other
two
Valves are absent Valves are present Valves are absent
Speed of blood is faster than
other two
Speed of blood is slower than
other two
Blood speed is very very
less.
Answer to Question 11.
a) The contraction of the smooth muscle in vessels is called vasoconstriction.
The process of vasoconstriction takes place in the vascular smooth muscles in order to
regulate the process of blood flow in to the internal organs of the body and this mechanism is
mainly associated with the redistribution of bloods into the different organs of the body.
Whenever, reduced blood supply is required in a particular region of the body , then the blood
vessels of that region is vasoconstricted and the blood supply is regulated or reduced (Boron
and Boulpaep 2016).
Answer to Question 11.
b) The relaxation of the smooth muscle in vessels is called vasodialation.
The process of vasodialation takes place in the vascular smooth muscles in order to
regulate the process of blood flow in to the internal organs of the body and this mechanism is
mainly associated with the redistribution of bloods into the different organs of the body.
Whenever, enhanced blood supply is required in a particular region of the body , then the

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blood vessels of that region is vasodialated and the blood supply is increased in that
particular region or organ (Boron and Boulpaep, 2016).
Answer to Question 12.
The concept of muscle pump in relation to the vein in mainly associated with the issue
of blood circulation to the hearts or to the concept of venous returns of the body. One of the
major function of vein is to return the blood to the heart for redistribution and thus it can be
stated that this huge amount of blood must be returned to the heart. The muscle pump mainly
helps the veins in this return process of blood to the heart. For example, during the upright
position a huge amount of blood is accumulated in the leg muscles and when the individual
sits that particular muscle act as muscle pump and sends the blood to the heart. No, the
arteries and the capillaries do not use the muscle pump (Mitchell 2014).

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References
Boron, W.F. and Boulpaep, E.L., 2016. Medical physiology E-book. Elsevier Health
Sciences.
Hall, J.E., 2015. Guyton & Hall Physiology Review E-Book. Elsevier Health Sciences.
Mitchell, G., 2014. Medical physiology: objectives and multiple choice questions.
Butterworth-Heinemann.

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