Chapter 8: Circulatory, lymphatic, and immune system (C7091185)

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1 Circulatory system

“I brought my stethoscope to school’s scripture once, and let my kids listen to their little hearts beating,” Jamie remarked, “I then told them, that in the same way, they should be attuned to listening to the Holy Spirit speaking to their little hearts .”

“That’s sooooo cute ,” Mandy said, “Here’s what I do-“

“To check for stigmata of infective endocarditis, I modify Schamroth’s window test, asking the patient to make a love heart… That’s so bad girl!” Mandy giggled.

Cardiovascular system delivers nutrients and oxygen to tissue, removes waste from tissue, transport hormones, and regulate body temperature. Images of the heart are usually visualized anteriorly (photo taken from the front) as 4 chambers, meaning your RHS is the patient’s LHS, and vice versa. So right atrium (RA) and right ventricle (RV) is on the LHS, and left atrium (LA) and left ventricle (LV) is on the RHS. Atrium is superior (higher) to the ventricle.


Frequently asked questions
What is the cardiovascular system used for?
Deliver nutrients and oxygen to tissue. Remove waste from tissue. Transport hormones. Regulate body temperature.

The heart anatomically looks veeeeery complicated. What exactly do I need to know?
Know what it looks like functionally. Divide the heart into four boxes: a top left, top right, bottom left, bottom right. The upper boxes are the atrium. The lower boxes are the ventricle.

I heard the left is called the right, and the right is called left. Why is this?
Because the patient is visualized from the front. So your right is their left, and vice versa.

Uh, that makes sense

Systemic circulation is the half of the cardiovascular system, which delivers oxygenated blood away [from the heart to the body’s tissue], and returns deoxygenated blood [from the body’s tissue toward the heart]. Systemic is contrasted with pulmonary circulation, which is the other half [of the cardiovascular system] which delivers deoxygenated blood away [from the heart] to the lungs, and returns oxygenated blood [back to the heart], notably the converse. At any instance, 75% of blood is in systemic circulation, and 25% in pulmonary circulation.

Frequently asked questions
What is the difference betwen systemic and pulmonary circulation?
There are 2 halves to the cardiovascular system: systemic, and pulmonary. The purpose of systemic is to deliver oxygenated body to the body [so its oxygen can be used]. The purpose of pulmonary is to re-oxygenate de-oxygenated blood.

So the pulmonary circulation is like a recharge? How does this occur?
The lungs. You breathe in oxygen, and that helps to oxygenate blood.

How much blood is in either circuit at any one time?
75% is in the systemic circulation, and 25% is in the pulmonary circulation.

In short, atrium leaks, and ventricle pumps. Left ventricle must pump blood throughout the entire systemic circulation, thus has a thicker wall, and is the strongest part of the heart.

  • RA: Deoxygenated blood [since oxygen is removed from blood/capillary into tissue, at the periphery] returns from [the superior and inferior] vena cava, emptying into the RA
  • RA⇒​RV: RA drips blood, and fills the RV with its blood
  • RV⇒(pulmonary circulation): RV pumps [with a stronger force than the atriums, but not as strong as the LV, as the LV pumps blood to the whole body, and the RV pumps blood only to the far closer lungs] the [deoxygenated] blood into the pulmonary artery. Note that the pulmonary artery is the only artery, which carries deoxygenated blood
  • Pulmonary circulation: Like systemic circulation, pulmonary circulation flows from the pulmonary artery into the arterioles, into capillaries, into venules, and into the pulmonary veins. Also analogous to systemic circulation, hydrostatic pressure decreases from pulmonary artery to pulmonary vein
  • (pulmonary circulation)⇒LA: Pulmonary vein returns blood (oxygenated, ever since the oxygen was added by the capillary of the lung) into the LA. Note that the pulmonary vein the only vein, which carries oxygenated blood
  • LALV: LA drips blood, and fills the LV with its blood
  • LV⇒(systemic circulation): LV pumps blood [out of the heart] into the aorta, which is the largest artery in the body
  • Systemic circulation: Artery carries blood away from the heart, and vein carries blood toward the heart. Note therefore that whereas arteries in systemic circulation carry oxygenated blood [away from the heart]; in arteries in pulmonary circulation carry deoxygenated blood [away from the heart]. Artery is elastic, stretching when filled. Blood moves from the arteries, into arterioles, into capillaries, into venules, into veins, and into the vena cava

Frequently asked questions
What is the difference between atrium and ventricle?
Atrium is higher, ventricle is lower. Atrium leaks, ventricles pump. For this reason, the ventricles have thicker walls.

Why is the left ventricle stronger than the right ventricle?
Whereas the left ventricle pumps into the systemic circulation [throughout the entire body], in contrast, the right ventricle only pumps into the pulmonary circulation [to the far closer lung]. Therefore, the left ventricle has to be far stronger than the right ventricle.

So what's the flow of blood? Starting from, deoxygenated blood.
After oxygenated is collected from blood throughout the body, blood finds it way back to the right atrium. This drips into the right ventricle. This pumps the blood through the pulmonary circulation, for re-oxygenation. Blood is then carried back to the left atrium. This drips into the left ventricle. Which then pumps throughout the body.

What are the different types of blood vessels?
Arteries, which carry blood away from the heart. And vein, which carries blood towards the heart. Smaller arteries are arterioles, and smaller veins are venules.

Does the artery always carry oxygenated blood, and vein always carry back deoxygenated blood?
No. This is only true in the systemic circulation. In the pulmonary circulation, the opposite is true. The pulmonary artery, as it moves away from the heart, carries deoxygenated blood [to be reoxygenated in the lungs]. In contrast, the pulmonary vein, as it moves towards the heart, carries the [now] reoxygenated blood.

Capillary are the smallest of the body’s blood vessels, the diameter of capillary is just smaller than the diameter of red blood cell, meaning red blood cells pass through in single file, and must bend slightly to do so. Capillary walls are only one cell thick, permitting the exchange of gas and nutrient between blood and surrounding tissue. Although the small diameter of capillary, the capillary network has the largest surface area in the vascular network. Since [latex]p=\dfrac{F}{A}[/latex], the greater the area, the lower the pressure [and therefore velocity]; and as capillary network has largest surface area, blood has the lowest velocity in the capillary network in the vascular network. Low velocity encourages increased gas and nutrient exchange.

Hydrostatic pressure (discussed ) is the pressure caused by the movement of blood, and therefore the pressure it exerts against the blood vessel wall. Hydrostatic pressure decreases along the systemic circulation pathway, as hydrostatic pressure is caused by the contracting LV, such that it is highest in the aorta [just exiting from the heart] and lowest in the vena cava [just reentering the heart]. Note therefore that the hydrostatic pressure decreases along the capillary, meaning hydrostatic pressure is greater on the arterial than venous side.

On the arterial end, as solute is exchanged [from the blood] into the surrounding tissue, osmotic pressure draws water to move [from blood] into the interstitium. However, as hydrostatic pressure decreases towards the venous end, and protein in bloodstream cannot easily cross the capillary wall, this osmotic pressure due to protein in bloodstream [which cannot easily cross the capillary wall] draws water [from interstitium] back into the bloodstream. Recovery however, is not complete; there a net loss of 10% of fluid to the interstitium, which is removed by surrounding lymph vessel.


Heart is a hollow muscle, about the size of a fist in kids, and the size of two fists in adults, which pumps blood out of the heart, through blood vessels to all the body, by rhythmic wave-like contractions. The wave first contracts the [superior] atrium, squeezing blood into the [inferior] ventricle. Contraction of heart is caused by action potential, expressed  as an electrical impulse. The impulse is started by the sinoatrial node (SA node), which is located in the right atrium (fills the right ventricle, as expressed ). SA node is composed of modified cardiac muscle cells, which spontaneously contracts at a rate faster than the normal heart rate. SA node is innervated by vagus nerve, which is parasympathetic, and carries about 75% of all parasympathetic neurons. Keeping in mind from  that parasympathetic is “rest and digest”, the vagus nerve thus slows down heart rate. Therefore, severing the vagus nerve, would lead to increase in heart rate. As applied earlier, and utilized also in neuron, gap junction permits action potential to spread from one cell to another, thereby permitting the impulse generated by SA node to excite both (right and left) atria. Gap junction is found within intercalated disc, which are the connections between muscle cells. The impulse is stayed at the atrioventricular node (AV node) for , before conducting through the bundle of His, located in the septum (wall) of the (lower) ventricles, and out across both ventricles via the Purkinje fibers.


Systole is the contraction of ventricles (pumping blood). In contrast, diastole is the period of time when the heart refills with blood after, involving relaxation of the heart followed by contraction of atria (squeezing blood into the inferior ventricle).

If blood is centrifuged, it separates into three layers:

  • Blood plasma is aqueous solution, containing plasma proteins such as albumin, immunoglobulin (aka antibody) and fibrinogen (a zymogen involved in blood clotting). Blood plasma with clotting factors removed, is known as blood serum
  • Buffy coat is a thin white layer between the plasma and red blood cells in the centrifuged test tube, and is the percentage volume of white blood cells. Thus, healthy blood has very few, only around , in a healthy adult
  • Hematocrit, which is the percentage volume of red blood cells, approximately 45% for men and 40% for women. Greater hematocrit increases blood viscosity, meaning blood flows less easily

All blood cells differentiate from a single type of stem cell in the bone marrow. Red blood cells (aka erythrocytes, RBC) are bags of hemoglobin and some enzymes. RBC do not have a cell nucleus nor organelles [so that the space available for hemoglobin is maximized, and there is reduced energy consumption]. RBC have a life span of up to approximately 120 days, before being phagocytized by Kupffer cells in the liver [to be iterated ], as well as the spleen. White blood cells (aka leukocytes, WBC) are cells involved in the immune system, and can be divided into various types, including:




Granulocyte, which have a cytoplasm that appears grainy under a light microscope. Granulocytes only stay in the blood for hours, before moving into the tissue, where it lasts  days. Granulocytes include:



Constitute up to 60% of leukocytes, which are phagocytes, which attack foreign invaders indiscriminately. Neutrophils also release antibiotic proteins. A far less proportion of leukocytes are eosinophils or basophils



Are also phagocytic, and are mediators of allergic response



(Analogous to mast cell, found in tissue) release histamine, which triggers the inflammatory response




Which circulate throughout the bloodstream, which mature at their destination tissue into macrophages

Macrophage (Greek for “big eater”)


They are the most voracious phagocytes



Which can be divided into B and T lymphocytes. Lymphocytes are involved in acquired immunity

Megakaryocyte in bone marrow, have fragments of cytoplasm pinched off, known as platelets. Thus, platelets are not cells, but fragments of cells.

Blood type is the classification of blood based on the type of antigen present on the surface of its RBC, into:

  • A blood, which has A antigen. Antibodies are normally made against foreign antigens. Therefore, because A blood has A antigen, it will not form A antibodies, but will form B antibodies. Therefore, if you have A blood, either A [which only has A antigen, which will not be attacked by B antibodies] or O blood [which has no antigens to be attacked] can be received [by transfusion]. Note therefore that O is the universal donor, as anybody can receive O blood
  • B blood, which has B antigen. Analogous to the reasoning for A blood, B blood can only receive either B or O blood
  • AB blood, which has both A and B antigen. AB blood has both A and B antigens, so will not form A nor B antibodies. Therefore, if you have AB blood, you can receive any blood, as there are no antibodies to create an immune response, known as a universal acceptor
  • O blood, which has neither A nor B antigen

The blood types are expressed in the same locus. Both A and B blood types are dominant, known as codominance. [Complete] dominance means expressed without blending. O blood is therefore homozygous (meaning either AA or aa) recessive (restricting the criteria further to only aa).

Blood can be further classified by the presence of the antigen Rh factor, such that Rh+ has the antigen, and Rh- doesn’t have the Rh antigen. Remember again that antibodies are normally made against foreign antigens. Therefore, because Rh+ has Rh factor antigen, it will not form Rh factor antibodies. As there are no antibodies to create an immune response, Rh+ can receive either Rh+ or Rh- blood. In contrast, because Rh- doesn’t have the Rh factor antigen, it will form Rh factor antibodies. Therefore, Rh- can only receive Rh- blood [which has no antigens to be attacked]. Rh factor is most important if a woman is Rh- and is pregnant, and the fetus has Rh+ blood, because blood can intermingle during delivery, causing the woman to make antibodies. This is not an issue for the first child, as the first child is already delivered [out] by the time the antibodies are made. However, in subsequent children, antibodies generated can migrate [from the mother] across the placental barrier [to the fetus] and cause destruction of the baby’s RBC. Anemia is a decrease in the number of RBC.

Formative learning activityMaps to RK8.A
What is the circulatory system?

2 Lymphatic system

As propounded , lymphatic system drains and recycles interstitial fluid [and therefore blood plasma], and also monitors blood for infection. Unlike the cardiovascular system, lymphatic system is an open system, meaning fluid can enter to and exit from the system, unlike blood which has no opening. Rather, the lymphatic system drains interstitial fluid into the blood, at two locations near the neck, the right lymphatic duct draining the right arm and the right side of the head into the right jugular vein of the neck, and the thoracic duct draining all other parts of the body into the left jugular vein of the neck. Note the CNS is not drained by the lymph system. Also unlike the cardiovascular system, lymphatic system has no pump, but skeletal muscle contraction and arterial pulse help fluid move through the lymph system.

Learning activity
What is the lymphatic system?

3 Immune system

The immune system can be either innate or acquired–

Innate immunity is non-specific, meaning it protects the host from foreign invaders indiscriminately. Apart from lymphocytes, all leukocytes are cells of the innate immune system. Also a part of the innate immune system, are physical barriers, such as skin; and chemical barriers, such as acid in stomach. Inflammation is an immune response to injured tissue, which may be caused by heat, chemicals, bacteria, trauma, etc. Inflammation can also be triggered by histamine (expressed ) released by basophils and mast cells, prostaglandins released by the cell membrane [of tissue], and lymphokine released by T cells. Some of these cells also activate macrophages, which start devouring tissue. Inflammation causes blood vessels to dilate, increasing blood flow to the inflamed area. Additionally, capillaries have increased permeability, resulting in leakage of fluid into the tissue, which is manifested as swelling. Leukocytes (except lymphocytes, as mentioned earlier) migrate to the infected area. Although neutrophil and macrophages directly kill infectious organisms, they eventually die. Pus consists of these dead leukocytes, along with dead tissue cells and fluid. The site of injury is sealed off, to confine the infectious organism.

Acquired immunity, which is the response if invaders successfully evade the innate response. As stated , the cells of acquired immunity are lymphocytes. Antigens are high molecular weight proteins or polysaccharides, which can elicit an [acquired] immune response. Hapten, a smaller molecule, can also elicit an immune response, but only if first attached to an antigen. Then, even if separated, [free] hapten is still recognized by the immune system. The acquired immunity [response] can be [further] divided into:

  • Humoral immunity, which involves the creation of antibodies by B lymphocytes. B lymphocytes develop in the liver, and matures in the bone marrow. The fact that B lymphocytes and bone both start with “B” is a coincidence, as that B is named after “Bursa of Fabricius”, an organ in birds in which B lymphocytes develop; mammals do not have an equivalent organ. After development, immature B lymphocytes migrate to the lymphoid tissue [which includes bone marrow]. B lymphocytes each have thousands of identical antibody-like proteins on its surface, with a variable region (on the proteins) that is specific for a particular kind of B lymphocyte. Each antibody-like protein matches to a specific antigen, or similar antigens. For example, as cowpox and chickenpox has similar antigens, exposure to cowpox will result in immunity from chickenpox. When an invader is phagocytized by a macrophage, after digestion, the macrophage presents the invader’s antigen on its surface. The macrophage [with a presented antigen] can thus be located by a B lymphocyte [with a matching antibody-like protein]. Helper T cells then release lymphokines (as stated ), which activate B lymphocytes. Upon activation, B lymphocytes differentiate into plasma [B] cells and memory [B] cells. Plasma cells are large B cells, which secrete antibodies analogous to the antibody-like protein on its surface. Mature plasma cells can secrete 2,000 antibodies per second for several days, before dying. As this response requires recruiting, it takes approximately 14 days to resolve, and is known as the primary response. Memory cells are clones of the original B lymphocyte, but have the advantage of persisting for long periods, just in case the antigen returns. Now with memory cells, subsequent exposures can be addressed far stronger and quicker, and is known as the secondary response, also known as being immune. Antibody (aka immunoglobulin) are proteins created in the lymph system, which circulate in blood, and attack foreign invaders that possess matching antigens directly. Antibodies can directly cause agglutination (defined ), precipitation [of the invader], lysis [of the invader], and neutralize toxins. Alternatively, antibody can attack invaders indirectly, by activating a protein complement cascade. Complement system achieves a number of functions, including:
    • Attracts macrophages and neutrophils to the infected area by marking the invaders for phagocytosis
    • Ruptures the cell membrane of foreign invaders, causing lysis
    • Clumps up invaders, known as agglutination, rendering them harmless
    • Activate basophil and mass cell, thereby triggering inflammation
  • (T-)Cell-mediated immunity, which involve T lymphocytes, named so because they mature in the thymus. Like B lymphocytes, T lymphocytes each have thousands of identical antibody-like proteins on its surface, with a variable region [on the proteins] that is specific for a particular kind of T lymphocyte. Again analogous to B lymphocytes, each antibody-like protein matches to a specific antigen, or similar antigens. T lymphocytes are unique however, in that they do not produce antibodies. Rather, they only differentiate into memory [T] cells and cytotoxic [T] cells. Memory T cells are analogous to memory B cells, mounting a faster and stronger response in subsequent encounters. Cytotoxic T cells, also known as killer T cells, kills cells by binding to foreign invaders that possess matching antigens, and secretes the protein perforin, which perforate the cell membrane, causing lysis. As T cells don’t phagocytize [which by its nature of digesting invaders, will have to eventually die], they can kill many cells without dying themselves. T cells are thus highly effective against cancer cells, and cells infected with a virus. There is also the regulatory T cell, which prevents T cells from destroying healthy cells

Formative learning activityMaps to RK8.C
What is the immune system, and what does it consist of?

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