Understanding the Circulatory System……..

Transport Systems in
Mammals
Circulatory System
MVIMBI S 223111446

LESSON OBJECTIVES
Identify the main components of the mammalian circulatory system (heart, blood,
and blood vessels) and label them correctly on a diagram by the end of the lesson.
Explain how double circulation functions in mammals and compare it to single
circulation using at least two differences within the lesson.
Analyse the role of the circulatory system in transporting gases, nutrients, hormones,
and wastes, and demonstrate understanding by answering at least three application-
based questions in class by the end of the lesson

OPEN AND CLOSED SYSTEM
Open circulatory system
• Blood vessels lead into a cavity, which leads into a
network of interior channels and spaces. Blood
moves freely inside the body cavity in all directions.
Arthropods are a group of animals consisting mostly
of insects that have an open circulatory system
(Khonde, 2024).
Closed circulatory system
• Blood vessels lead from one type of vessel to another,
not into a body cavity. Blood flows in one direction,
continuously. Vertebrates have a closed circulatory
system
(Khonde, 2024).

External structure of the heart The heart:
→ has an apex which points to the left and is
covered by a double epithelium lining called
the pericardium; the space between the two
layers is filled with a fluid called the
pericardial fluid, which prevents friction and
allows space for movement as the heart
beats and is held in position by the large
blood vessels that enter and leave its
broader side (Khonde, 2024).

Internal structure of the heart
→ The heart:
→ is hollow with muscular walls made of striated cardiac muscle is lined
● ●
with a single epithelium layer called the endocardium (Soneeshah, 2023).
→ has four cavities called chambers: the upper chambers are the right and
left atria (singular: atrium), and the lower chambers are the right and left
ventricles; the atria are smaller and less muscular than the
ventricles(Soneeshah, 2023).
→ Valves separate each atrium from the ventricle below it; blood flows only
from an atrium to a ventricle; thin ligaments are attached to the valves and
the ventricle walls. Valves are found where the blood vessels attach to
● ●
the heart(Soneeshah, 2023).

The cardiac cycle
The cardiac cycle moves blood through the heart.
The heart distributes blood to all parts of the body
through two sets of muscular actions, called
contractions. (Ali7070, n.d.).
The cardiac cycle involves: systole – contraction of
the heart muscle diastole – relaxation of the heart
muscle. (Ali7070, n.d.).
The heart beats twice: atrial systole forces blood
through the heart into the ventricles ventricle
systole forces blood out of the heart(Ali7070, n.d.).

Control of the heart beat
MANY FACTORS AFFECT HEART BEAT AND CIRCULATION. SOME OF THESE ARE TEMPERATURE,
OXYGEN SUPPLY AND NERVOUS EXCITEMENT. THE STIMULUS THAT KEEPS THE HEART
● ●
BEAT GOING IS THE SINO-ATRIAL (SA) NODE – A PACEMAKER FOUND IN THE WALL OF THE
RIGHT ATRIUM. DURING THE ATRIAL SYSTOLE (0,1 SECONDS LONG): THE SINO-ATRIAL
● ●
NODE SENDS AN ELECTRICAL IMPULSE TO THE MUSCLE OF THE LEFT AND RIGHT ATRIA ● ●
THE TWO ATRIA CONTRACT TOGETHER THE TRICUSPID AND BICUSPID VALVES OPEN
● ● ●
BLOOD FLOWS INTO THE TWO VENTRICLES (ISHAQ, 2024).
●
● ELECTRICAL SIGNALS GO THROUGH THE MUSCLES OF THE ATRIA TO THE ATRIO-
VENTRICULAR (AV) NODE THIS SIGNAL GOES THROUGH THE ATRIO-VENTRICULAR
● ●
BUNDLE TO THE VENTRICLES THE TWO VENTRICLES CONTRACT TOGETHER BLOOD
● ● ● ●
IS FORCED INTO THE AORTA AND THE PULMONARY ARTERIES THE TRICUSPID AND
● ●
BICUSPID VALVES CLOSE(ISHAQ, 2024).

Exercise and heart beat
→ Strong exercise accelerates heart beat in two ways (Ishaq, 2024). ● ●
As cellular respiration increases: the level of carbon dioxide in
● ●
the blood increases receptors in the carotid arteries and aorta
● ●
are stimulated impulses are transmitted to the medulla (Ishaq,
● ●
2024). the accelerans nerve sends them to the heart heart beat
● ●
is increased. As muscular activity increases: muscle
● ● ● ●
movement drives more blood to the right atrium, which stretches ●
stretch receptors in its wall are stimulated impulses are sent
● ● ●
to the medulla the accelerans nerve sends them to the heart
● ● ●
heart beat is increased to cope with the extra volume (Ishaq,
●
2024).

Blood vessels
Structure and functions of the different blood vessels
Arteries: have walls that are three layers thick: one cell layer of squamous
● ●
epithelium, thick layer of smooth muscle to withstand pressure, surrounded by
connective tissue allowing them to stretch move blood away from the heart
● ● ● ●
connect to smaller arteries called arterioles have blood under high pressure being
● ●
pumped by the heart. Arteries that lie close to the skin are called pulse
points(AkinrotimiOluwadunsi, 2024).
Veins: have walls that are three layers thick: one cell layer of squamous
● ●
epithelium, thin layer of smooth muscle, surrounded by connective tissue allowing
them to stretch move blood to the heart have semilunar valves (one-way
● ● ● ●
valves), which keeps the blood moving towards the heart and prevents backflow under
gravity connect to smaller veins are called venules have blood under very low
● ● ● ●
pressure that flows against gravity (AkinrotimiOluwadunsi, 2024).
Capillaries: are microscopic blood vessels that connect arteries and veins
● ● ● ●
form branching networks that make a big surface area for diffusion have walls
● ●
that are only one cell layer thick – made of squamous epithelium interchange
● ●
nutrients, gases and waste(AkinrotimiOluwadunsi, 2024).

Cardiovascular diseases and disorders
→ Diseases that affect the cardiovascular system can be serious and are a major cause of death. Some
are genetic, but often they are due to an unhealthy lifestyle: smoking, eating too much fried, fatty
food, being overweight, doing little exercise, plus having high blood pressure and high cholesterol
(Khonde, 2024). These last two are also made worse by an unhealthy lifestyle. Anaemia: a
● ●
person has too few red blood cells due to a lack of iron (Khonde, 2024). The haemoglobin level is
low and the person is pale and has no energy. Leukaemia: a cancer that causes uncontrolled
● ●
production of some leucocytes. These cells gather in bone marrow, crowding out normal white
blood cells, red blood cells and platelets (Khonde, 2024).

High and low blood pressure: Hypertension is high
blood pressure, caused by salt and water being held in
tissues. The heart has to work harder and there is
increased pressure on the walls of blood
vessels(Soneeshah. 2023). This greatly increases the
risk of stroke, heart attack and kidney disease. Obesity
increases the risk. Hypotension is low blood pressure. If
the pressure drops too much, the person feels dizzy or
faints. However, hypotension is often linked to a long
life and an old age free of illness (Soneeshah. 2023).
Angina, atherosclerosis and strokes: Angina is chest
pain caused when too little blood and oxygen gets to
the heart muscle, due to a block or spasm of the
coronary arteries. It is caused by atherosclerosis of the
cardiac arteries. This can lead to a heart attack or a
brain-damaging stroke if a clot blocks a blood vessel to
the brain. (Soneeshah. 2023). Heart attack: When the
blood supply to part of the heart muscle (myocardium)
is greatly reduced or stopped, the person suffers
myocardial infarction. A blood clot or fatty deposit
blocks part of a coronary artery. A person can recover if
the heart muscle is undamaged and can still pump

REFERENCE LIST
AkinrotimiOluwadunsi. (2024, March 21). The Histology of the Cardiovascular System 2024
[PPTX]. SlideShare. Retrieved August 18, 2025, from
https://www.slideshare.net/slideshow/the-histology-of-the-cardiovascular-system-2024pptx/266
901896
Ali7070. (n.d.). Anatomy of blood vessels [PPTX]. SlideShare. Retrieved August 18, 2025, from
https://www.slideshare.net/slideshow/anatomy-of-blood-vessels-ppt/39958445
Ishaq, R. (2024, June 3). Introduction to Cardiovascular System [PPTX]. SlideShare. Retrieved
August 18, 2025, from
https://www.slideshare.net/slideshow/intoduction-to-cardiovascular-system_3-6-2024-pptx/273
207690
Khonde, S. (2024). 4-lecture Cardiovascular Pharmacy 2024 [PPTX]. SlideShare. Retrieved
August 18, 2025, from
https://www.slideshare.net/slideshow/4lecture-cardiovascular-pharmacy-2024pptx/266821840
Soneeshah. (2023). Cardiovascular System [PPTX]. SlideShare. Retrieved August 18, 2025, from
https://www.slideshare.net/slideshow/cardiovascular-systempptx-256741040/256741040
Toushiro, F. (n.d.). Cardiac cycle [PPTX]. SlideShare. Retrieved August 18, 2025, from

Understanding the Circulatory System……..

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