Circulatory system

Respiratory and Circulatory systems

• Bring oxygen and nutrients to the cells

• Work together to maintain homeostasis

Circulatory system

• A transport system to supply all tissues with nutrients and to transport waste materials away from the tissues.

• Including the cardiovascular and lymphatic systems

• Transports nutrients, hormones, and metabolic wastes to different parts of the body

• Closed system

• Contains 2 fluids, blood and lymph

Components of Blood

• Plasma (55%)

• Platelets

• Blood cells:

  • Red blood cells (erythrocytes): 45%

  • White blood cells (leucocytes)

Plasma

• 55% of blood volume

• Pale yellow, clear liquid that is about 90% water

• Includes transporting nutrients, gases and vitamins

  => Functions:

  • Transport medium for blood

  • Regulates fluid and electrolyte (Na+, K+, Ca2+) balance and maintains pH

red blood cells (erythrocytes)

• Circular, flattened, biconcave discs with the centre of each cell thinner than its edge

• No nucleus and mitochondria

• Contain hemoglobin (T and R states)

• Transport oxygen from the lung to the other tissue

• From the stem cells in the red bone marrow of long bones

red blood cell production and its control

• Low blood oxygen causes the kidneys and the liver to release erythropoietin (EPO) which stimulates RBC production

• This is a negative feedback mechanism

White blood cells (leucocytes)

-White blood cells have nucleus, lack hemoglobin and colorless

-Protection against disease

• Phagocytes: protect the body by ingesting harmful foreign particles, bacteria and dead or dying cells

• Lymphocytes: eliminate the antigen by releasing antibodies (B cells) and cytotoxic granules (cytotoxic T cells)

• Signaling to other cells of the immune system

Platelets (thrombocytes)

• not true cells

• fragments of cytoplasm from bone marrow cells

• function in blood clotting.

Functions of blood

2 main functions:

• Transport: substances such as oxygen, carbon dioxide, nutrients, waste products, hormones

• Protection:

  • Ingest foreign particles through phagocytosis

  • Produce antibodies to combine with antigens from pathogen to destroy them

  • Clotting to protect humans from bleeding continuously

Hemostasis and Blood Coagulation

Following an injury, 4 events are available to stop the bleeding:

1) Blood Vessel Spasm: Vessels decrease in size to stop bleeding in small vessels.

2) Platelet Plug Formation: Inner torn layer of the vessels releases chemical signals that call platelets to the site of injury

3) Blood clotting: Requires the presence of certain clotting factors to form fibrin (Prothrombin + Ca²⁺→ Thrombin + Fibrinogen + Ca²⁺→ Fibrin)

4) Fibrinolysis: Begins the repair process

Agglutination

• Clumping of red blood cells in response to a reaction between an antibody and an antigen

Antigens

• A chemical that stimulates cells to produce antibody

Antibodies

• A protein that reacts against a specific antigen

Cardiovascular system

consists of the heart and all blood vessels

Heart

• The heart lies in the thoracic cavity

• coverings: pericardium

• 4 chambers (cavities):

  • Right and left atrium

  • Right and left ventricle

• An atrioventricular valve connects each atrium to the ventricle below it

  • For the right: Tricuspid valve

  • For the left: Bicuspid valve (Mitral valve)

• The septum: prevents mixing of blood from the 2 sides of the heart

• The valves ensure that blood flows in only one direction

Atrium

• Thin-walled, elastic

• Expands as it collects blood, only pump blood the short distance to the ventricle

Ventricle

• much thicker muscular wall, as it pumps blood either to the lungs or the rest of the body

The left-hand side of the heart

deals with the oxygenated blood from the lungs

The right-hand side of the heart

deals with the deoxygenated blood from the body

Blood vessels

make up 2 circuits:

+) Pulmonary circuit: eliminates carbon dioxide via lungs and oxygenates the blood

+) Systematic circuit: delivers oxygen to all body cells and carries away wastes

3 types of blood vessels:

• Artery ( 3 layers of tissue)

• Vein (3 layers of tissue)

• Capillary ( 1 layer of tissue)

Arteries carry blood away from the heart

Veins carry blood toward the heart

The capillaries are exchanging vessels located between the arterial and venous systems

=> allow the exchange of gases, nutrients, hormones, and other molecules in the blood.

• Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena Cava

Arteries

• Carry blood away from the heart

• Bright red due to high oxygen levels

• Thick muscle and elastic fibres:

  • the thick muscle can contract to push the blood along

  • the elastic fibres allow the artery to stretch under pressure

Veins

• Carry blood towards the heart

• Blood appears darker in color

• Have valves which prevent the blood from going in the wrong direction

• Thin muscle and elastic fibres

Capillaries

• Connect the smallest arteriole and the smallest venule

• Walls are very thin to exchange materials between the blood and other body cells.

• One thick and permeable wall

The flow of blood through the heart

• Blood travels to the heart through the superior vena cava (head, neck, and forelimbs) and inferior vena cava (trunk and hind limbs)

• The superior and inferior vena cava flow into the right atrium, moves into right ventricle, finally pushed into lungs in the pulmonary arteries.

• The blood then picks up oxygen and travels back to the heart into left atrium through the pulmonary veins

• The oxygen-rich blood travels through the left atrium to the left ventricle and exits to the body through the aorta

• The aorta provides blood to the heart through the coronary arteries

Initiating Contraction

• Contraction of the heart is initiated by a small cluster of cardiac muscle cells called the sinoatrial (SA) node

• In the upper wall of the right atrium

Contraction of the ventricle

• The electrical impulse initiated by the SA node subsequently reaches another special area of the heart, known as the atrioventricular (AV) node.

• The AV node is located in the septum between the atria

• The AV node relays the electrical impulse to the muscle cells that make up the ventricles

  => The ventricles contract a fraction of a second after the atria

  => Completing one full heartbeat

Cardiac cycle

• The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle

• Contains: systole and diastole

Systole

• The contraction (pumping) phase

• Occurs when the ventricles contract, closing the AV valves and opening the semilunar (SL) valves to pump blood into the 2 major vessels that exit the heart

Diastole

• The relaxation, or filling, phase

• Occurs when the ventricles relax, allowing the back pressure of the blood to close the SL valves and open the AV valves

In atrial systole and ventricular diastole

• Blood flows passively into the ventricles

• The remaining 30% of blood is pushed into the ventricles.

• The A-V valves open and the semilunar valves close

• The ventricles relax

• This causes an increase in ventricular pressure

In ventricular systole and atrial diastole:

• The A-V valves close and semilunar valves open

• The chordae tendineae prevent the cusps of the valves from bulging too far into the atria

• The atria relax

• The blood flows into atria

• The ventricular pressure increases

• The blood flows into pulmonary trunk and aorta

Electrocardiogram

In an average adult at rest, the heart beats about 70 times each minute.

The heart rate

Also called pulse, is the number of beats per minute

The stroke volume

the amount of blood pumped in a single contraction

The cardio output

• the volume of blood pumped into the systemic circulation per minute

• depends on both the heart rate and stroke volume

Regulation of the cardiac cycle

The SA node controls the heart rate

Factors that influence heart rate

• Physical exercise

• Body temperature

• Concentration of ions: K+, Ca2+

• Parasympathetic impulses decrease heart action

• Sympathetic impulses increase heart action

Blood pressure

force exerted by blood as it moves through blood vessels

Heart attack

• Occurs when an area of the heart muscle stops working and dies.

• When an area of the brain dies the result is a stroke

Lymphatic system

• Collects and recycles fluids leaked from the cardiovascular system, involved in fighting infections

• Made up of a network of vessels called lymphatic vessels and tiny bean-shaped structures called lymph nodes

• Lymph nodes may become swollen when they are fighting infection