Midterm Flashcards
1
Q
What is a hormone and how does it act?
A
A hormone is a secretion from a gland.
It acts by travelling through the bloodstream to its target organ. Though it lands on several cells, it only binds to its own receptors where it is to be received.
2
Q
What is the role of negative feedback in controlling hormone secretion?
A
As hormone levels increase in the blood, the hormone exerts its effects, negative feedback inhibits the system and the hormone secretion decreases. Then, as hormone levels in the blood decrease and the hormones’ effects wane, inhibition of the system ceases and secretion of that hormones increases once again.
As a result of negative feedback, hormone levels in the BS remain relatively stable, fluctuating slight around an average value.
3
Q
What are paracrine hormones?
A
These hormones enter the interstitial fluid and affect only nearby cells.
4
Q
What are autocrine hormones?
A
These hormones affect only the cell secreting the substance.
5
Q
What is an endocrine gland?
A
Internal secretion (into the bloodstream)
6
Q
What is an exocrine gland?
A
Secretes chemical substances that enter ducts or tubes that lead to body surfaces.
7
Q
Where can the different endocrine glands be found on the body? (15)
A
- Anterior pituitary gland
- Posterior pituitary gland
- Thyroid gland
- Parathyroid gland
- Adrenal medulla
- Adrenal cortex
- Pancreas
- Pineal gland
- Thymus
- Testes
- Ovaries
- Digestive tract
- Heart
- Kidneys
- Liver
8
Q
What are the differences and similarities of glucagon and insulin?
A
Glucagon is a protein that stimulates the liver to break down glycogen into glucose through glycogenolysis and to convert noncarbohydrates into glucose through gluconeogenesis.
When blood glucoses levels drop, this hormone raises it (to prevent hypoglycemia) and raises it back to normal levels. Once the levels are back to normal, the hormone is inhibited.
Insulin stimulates the liver to form glycogen from glucose and inhibits the conversion of noncarbohydrates into glucose. It lowers blood glucose levels when they become too high. Once the glucose levels return to normal, the hormone secretion is decreased.
Both hormones play important roles in regulating blood glucose levels.
9
Q
How does stress response affect the body?
A
It causes increased activity in the sympathetic nervous system and an increase in secretion of adrenal hormones (epinephrine, norepinephrine).
The hypothalamus controls a general adaption syndrome. The responses to stress work to maintain homeostasis. Persistent stress can lead to an exhaustion phase that can be fatal.
10
Q
How does aging affect the endocrine system?
A
Endocrine glands shrink and accumulate connective tissue, fat, and lipofuscin, but actual hormone activity usually remains within normal range. Thymus has shrunken.
Biggest change is blood glucose regulation abilities. Possible insulin resistance.
11
Q
What are components of blood?
A
Formed elements (45%)
Plasma (55%)
Formed elements:
Platelets
RBCs (95%)
WBCs
Plasma:
Electrolytes
Water (92%)
Proteins
Wastes
Nutrients
Vitamins
Hormones
Gases
11
Q
What are components of blood?
A
Formed elements (45%)
Plasma (55%)
Formed elements:
Platelets
RBCs (95%)
WBCs
Plasma:
Electrolytes
Water (92%)
Proteins
Wastes
Nutrients
Vitamins
Hormones
Gases
12
Q
What are the normal levels and percentages of RBCs?
A
Adult males: 4,700,000 - 6,100,000 cells/mL, 38.3% - 48.6%
Adult women:
4,200,000 - 5,400,000 cells/mL, 35.5% - 44.9%
Children:
4,500,000 - 5,100,000
13
Q
How does the shape of a RBC important to its function?
A
Its shape enables it to readily squeeze through narrow capillaries, its shape helps it transport gas by increasing surface area where gasses can diffuse into and out of, and it places the cell membrane closer to the oxygen-carrying hemoglobin molecules in the cell (reduces distance for diffusion).
14
Q
What is a hematocrit?
A
A hematocrit (HCT) is a percentage of RBCs in whole blood. It separates the solid part (formed elements) from thw watery liquid portion (plasma).
The normal levels:
40% - 54% in men
35% - 46% in women
15
Q
What two categories do WBCs fall into? Why?
A
- Granulocytes
(have granular cytoplasm, lobed nucleus, and x2 the size of a RBC) - Agranulocytes
(lack specific granules)
16
Q
What are the WBCs that fall under the granulocytes category? (3)
A
- Neutrophils
- Eosinophils
- Basophiles
GRAN. N.E.B
17
Q
Describe the appearance of neutrophils
A
Fine, cytoplasmic granules that appear light purple to pink in a combo of acid and base stains
18
Q
Describe the function and role of neutrophils
A
They are the most abundant, accounting for 50%-70% of WBCs in an adult blood sample. They are mobile and phagocytic. They are also the first WBCs to arrive at the site of an infection. They kill bacteria by using something called a respiratory burst.
19
Q
Describe the appearance of eosinophils
A
Coarse, uniformly sized cytoplasmic granules that appear deep red in acid stains. 2 lobed nucleus.
20
Q
Describe the function and role of eosinophils
A
Weakly phagocytic. They are also attracted to and kill certain parasites. They also also help control inflammation and are involved in allergic reactions. They account for 1%-4% of circulating WBCs.
21
Q
Describe the appearance of basophils
A
Similar to eosinophils and shape of nuclei. There are fewer, more irregularly shaped cytoplasmic granules that appear deep blue in basic stain.
22
Q
Describe the function and role of basophils
A
Rarest of WBCs (<1% in circulating WBCs).
They migrate to damaged tissue to release heparin and histamine.
23
Q
What WBCs fall under the agranulocytes category?
A
- Monocytes
- Lymphocytes
24
Talk a bit about monocytes and lymphocytes
They are produced in the RBM, but some lymphocytes migrate to the thymus to mature.
25
Describe the appearance of monocytes
They are the largest of WBCs. Their nuclei is spherical, kidney shaped, oval or lobed.
26
Describe the function and role of monocytes.
They can engulf larger structures than neutrophils. They account for 3%-9% of circulating WBCs and can live for several weeks or months.
They leave the bloodstream and migrate to certain tissues where they transform into MACROPHAGES (highly phagocytic cells).
27
Describe the appearance of lymphocytes
Smallest of the WBCs, slightly larger than RBCs. Large, spherical nucleus surrounded by a thin layer of cytoplasm.
28
Describe the function and role of lymphocytes.
Account for 25%-33% of circulating WBCs. They can live for years. There are two major types of lymphocytes.
29
What are the major types of lymphocytes?
T-cells and B-cells
30
What is the function of T-cells?
Directly attack the pathogens
31
What is the function of B-cells?
They produce antibodies
32
What is the difference of serum and plasma?
Serum is plasma without all of its fibrinogen and most other clotting factors.
33
How are platelets involved in hemostasis?
Firstly, hemostasis is the stoppage of bleeding, which is important when the blood vessels are damaged. One of the mechanisms of hemostasis is a platelet plug form. When a blood vessel is damaged, platelets stick to any rough surface. Most notably, they stick to exposed collagen fibers. When they come into contact with that exposed collagen fibers, their shapes change. During this, the platelets also release serotonin and thromboxane A2. These platelets form a plug in the vascular break and creates a temporary hold to control the bleeding.
34
What happens if a clot forms within blood vessels?
A blood clot that forms in the blood vessel is called a thrombus. A clot that dislodges (or even a fragment of the clot) and is carried away by blood flow is called an embolus. If it becomes stuck in a narrow space, it is called an embolism.
If a blood clot in a blood vessel blocks blood flow from a vital area such as the heart or brain, it kills the tissues the vessel serves and this can be fatal. The same can happen with an embolism.
35
What is a edema?
Edema is excess fluid trapped in the tissue. As concentration of plasma proteins drops, so does the colloid osmotic pressure. Water leaves the blood vessels and accumulates in interstitial spaces, which causes swelling.
36
What antigens can be found on RBC? What antibodies can be found in the plasma? (2)
1. Antigen A
2. Antigen B
37
What are antibodies in the plasma? What antibodies does plasma have?
When an antigen is missing, an antibody is produced. For example, if antigen A is missing, the plasma produces Anti-A antibody.
38
What combo of the four antigen combinations do people have?
1. A
2. B
3. AB
4. Neither A nor B
39
How do antigens and antibodies create different blood types?
Individuals with type A blood have anti-B antibodies in their plasma; those with type B blood have anti-A antibodies; those with type AB blood have neither antibodies; those with type O blood have both anti-A and anti-B antibodies.
40
How does the Rh factor affect a developing fetus and its mother?
Problems can arise from a Rh-negative mother and a Rh-positive fetus. The first pregnancy will be uneventful and cause no problems. However, if during birth, the placental membrane that separated the maternal blood from the fetal blood tear and some of the baby's Rh positive blood cells enter the maternal circulation, the cells can stimulate that the mother's body produce anti-Rh antibodies.
During the second pregnancy, the anti-Rh antibodies (hemolysins) can cross the placental membrane and destroy the fetal red cells. The fetus would then develop a condition called erythroblastosis.
41
What are the functions of the cardiovascular system?
The heart is a muscular pump that generates the force required to move blood through the body's blood vessels. Along the way, oxygen and nutrients in the blood are distributed to tissue cells, while carbon dioxide and other waste products are removed and transported by the blood to various organs, such as the lungs and kidneys, for disposal.
42
Where is the heart found?
Located in the mediastinum of the thoracic cavity just superior to the diaphragm. Anterior by the sternum.
43
Describe the layers of the pericardium. (3)
1. Fibrous pericardium
Tough, protective outer fibrous bag that's made of dense connective tissue. Its attached to the central portion of the diaphragm, the posterior of the sternum, the vertebral column, and the large blood vessels associated with the heart. Surrounds a more delicate, double-layered serous membrane called the visceral pericardium.
2. Visceral pericardium (epicardium)
Covers the heart surface. At the base of the heart, it turns back upon itself and forms the outermost serous membrane which is called the parietal pericardium.
3. Parietal pericardium
Covers the inner surface of the fibrous pericardium.
44
What are the layers of the heart? (3 distinct layers)
1. Epicardium (outer)
Corresponds to the visceral pericardium and it protects the heart by reducing friction. A thin, serous membrane that consists of connective tissue covered by epithelium, and it includes capillaries and nerve fibers.
2. Myocardium (middle)
Thick, middle layer of the heart wall. Mostly consists of cardiac muscle tissue that pumps blood out of the heart chambers.
3. Endocardium (inner)
Innermost layers of the heart wall. Consists of epithelium and underlying connective tissue that contains many elastic and collagen fibers. Also contains blood vessels and covers some of the specialized cardiac cells called Purkinje fibers. The endocardium lines all of the heart chambers and covers the structures that project into them. All throughout the CV system.
45
Describe the pathway of blood into, through, and out of the heart.
Body cells --> RA --> right AV valve --> RV --> Pulmonary semilunar valve --> Lungs --> LA --> left AV valve --> LV --> aortic semilunar --> Body cells
46
Describe the pathway of the cardiac conduction system
SA node --> Atrial syncytium --> Junctional fibers --> AV node --> AV bundles --> Bundle branches --> Purkinje fibers --> Ventricular syncytium
47
Describe an EKG
An EKG is an electrocardiogram and it records and measures the patterns of the impulses that are generated, as well as the electrical impulses of the heart.
48
During the P wave in an EKG, what is happening in the heart?
This is when a deflection occurs.
SA node --> depolarization --> contractile cells in atrium --> leads to Atrial contraction
49
Describe the QRS complex in an EKG, what is happening in the heart?
This is when the cardiac impulse from the SA node reaches the ventricular cells and they quickly depolarize. (ELECTRICAL CHARGE AND IMPULSE ARE GREATER HERE BECAUSE OF THE THICKNESS OF THE MYOCARDIUM)
Depolarization --> contractile cells in ventricles --> Ventricular contraction
*Atrial repolarization occurs during ventricular depolarization but it's small and not seen in an EKG.
50
Describe what is happening in the heart during the T wave in an EKG.
End of cardiac cycle. Deflection that's produced by electrical changes here come with ventricular repolarization.
*Ventricular repolarization comes more slowly than depolarization so it's more spread out and has a lower ht wave.
51
Describe what's happening in the heart during atrial systole/ventricular diastole and atrial diastole/ventricular systole.
Systole - contraction of the heart chambers
Diastole - relaxation of the heart chambers
Atrial systole/ventricular diastole = atrial contraction/ventricular relaxation
Atrial diastole/ventricular systole = atrial relaxation/ventricular relaxation.
AS/VD
AD/VS (all valves stay closed)
a. Atria empties during atrial systole and ventricles fill during ventricular diastole
b. Atria fills with blood during atrial diastole, ventricles empty during ventricular systole.
52
How are heart sounds?
Heart sound --> lubb dupp
This is due to the vibrations in the heart tissues associated with blood turbulence when the heart valves close.
1 cardiac cycle = 2 heart sounds --> S1 and S2
First sound (S1, lubb):
VS starts, AV closes
Second sound (S2, dupp):
VD starts, SL close
Heart sounds indicate the condition of the heart valves.
53
What terms are used to described abnormal heart rhythms? (5)
1. Fibrillation
2. Tachycardia
3. Bradycardia
4. Flutters
5. Premature beat
54
What is fibrillation?
Small areas of the myocardium contract in an uncoordinated, chaotic fashion. Because of this, the myocardium fails to contract as a whole, and blood can no longer pump.
Atrial fibrillation isn't life threatening (because the ventricles can still pump blood), but ventricular fibrillation is often fatal. This can happen from an obstructed coronary artery, toxic drug exposure, or traumatic injury to heart or chest.
55
What is tachycardia?
Abnormally fast heartbeat (100+ bpm at rest). This can be caused by an increase in blood temperature, nodal stimulation by sympathetic fibers, certain drugs, or hormones, heart disease, excitement, exercise, anemia, or shock.
56
What is bradycardia?
Slow heart rate, usually fewer than 60 bpm. Can be caused by a decrease in body temperature, nodal stimulation by parasympathetic impulses, or certain drugs that cause bradycardia. Can also occur during sleep.
57
What are flutters?
When a heart chamber contracts regularly, but very rapidly (250 - 350 times/minute). Occasional flutters are normal, but this condition is more likely when there's damage to the myocardium.
58
What is premature beat?
Occurs before it is expected in a normal series of cardiac cycles. Cardiac impulses originating from unusual regions of the heart probably cause a premature beat. Impulses originate from a site other than the SA node. May arise from ischemic tissues or muscle cells irritated by disease or drugs.
59
What influences can affect heart rate and or BP? (10)
1. Cardiac output
2. Blood volume
3. Peripheral resistance
4. Blood viscosity
5. Epinephrine
6. Cardioaccelerator reflex
7. Fear
8. Anger
9. Physical exercise
10. Rise in BT
60
What is cardiac output?
Amount of blood your heart (ventricle) pump each minute. It calculated by using the following equation: Cardiac Output = Stroke Volume x Heart Rate
61
How does cardiac output related to BP?
BP varies with CO. If SV or HR increases, so does CO and BP and vice versa if it decreases.
62
What is blood volume?
The sum of formed elements and plasma volume in the vascular system.
63
How is blood volume related to BP?
BP is usually directly proportional to the BV in the CV system. If there's changes in the BV, it also alters the BP. The BV can also be altered if fluid balance is is upset (dehydration).
BV (and BP by extension) can be regulated by the release of hormones. ADH, RAAS, aldosterone.
64
What is peripheral resistance?
Friction between the blood and the walls of the blood vessels (impedes blood flow).
65
How is peripheral resistance related to BP?
BP must overcome PV if blood is to continue flowing. Factors that alter the PV change the BP.
66
What is blood viscosity?
Blood viscosity is the when the blood becomes thicker and is difficult to move through the blood vessels. The greater the viscosity, the greater the resistance to flow.
67
How is blood viscosity related to BP?
Formed elements and plasma proteins increase blood viscosity. The greater the blood's resistance to flowing, the greater the force needed to move it through the vascular system, so the BP rises.
+ blood viscosity = + BP
- blood viscosity = - BP
68
How does epinephrine affect the BP?
It increases the HR. Consequently, it alters the CO (and BP)
69
What is the cardioaccelerator reflex?
Decreasing the arterial BP initiates this and this sends sympathetic impulses to the SA node and because of these cardiostimulatory effects, the HR goes up and this increases the CO and arterial pressure.
70
What is stroke volume?
Volume of blood the ventricle discharges with each heartbeat
71
Where can a pulse be found in the body? (9)
1. Temporal
2. Carotid
3. Facial
4. Brachial
5. Radial
6. Femoral
7. Popliteal
8. Posterior tibial (side of foot)
9. Dorsalis pedis (where leg meets foot at top)
72
At any given moment, where can blood be found in the body?
Capillaries
73
What is arteriorsclerosis? How does it occur?
A condition when deposits of fatty material (particularly cholesterol, to form within and on the inner lining of the arterial walls. Plaque protrudes into the lumens of the vessels and interfere with blood flow. Plaque formation can initiate the formation of a blood clot (increasing risk of thrombi and emboli).
74
How does aging affect the CV system?
Aging takes a toll on the CV system. Incidence of disease of the heart and blood vessels increases exponentially with age.
Proportion of cardiac muscle declines, aging cells are more prominent in cardiac muscle cells, adipose accumulates in the ventricular walls and septum. Valvesthicken and become more rigid.
BP can increase, likely due to stiffening of arterial walls.
*Aging related changes most evident in the arteries.
75
What is the function of lymph?
Lymph acts as a filter against microbes, organic wastes, toxins and other debris. It carries lymphocytes throughout the body that fight against infections.
75
What is the function of lymph?
Lymph acts as a filter against microbes, organic wastes, toxins and other debris. It carries lymphocytes throughout the body that fight against infections.
76
Describe a lymphatic vessel
A lymphatic vessel is a thin tube that carries lymph (lymphatic fluid) and WBCs through the lymphatic system. These vessels have enlarged regions all throughout the body that are called "lymph nodes". The walls of lymphatic vessels are similar to veins, but thinner. They are composed of three layers:
1. Endothelial
2. Smooth muscle and elastic fibers (middle)
3. Connective tissue (outer)
They also have semilunar valves to prevent backflow of lymph.
77
Describe the pathway of lymph
1. Lymphatic capillary --> Afferent lymphatic vessels --> lymph nodes --> Efferent lymphatic vessel --> Lymphatic trunk --> Collecting duct --> Subclavian vein
78
Where can lymph nodes be found in the body? What is the structure of a lymph node? `
The structure of a lymph node can vary in size and shape, but they are usually less than 2.5 cm long and somewhat bean shaped. Lymph nodes can be found in groups or chains along the paths of the larger lymphatic vessels all throughout the body BUT NOT IN THE CNS
79
Major locations of lymph nodes?
1. Cervical region
(drains skin of scalp and face, as well as tissues of the nasal cavity and pharynx)
2. Axillary region
(drain upper limbs, wall of thorax, mammary glands, and upper wall of abdomen)
3. Supratrochlear region
(sides of elbow, enlarge in children in response to infections acquired through cuts and scrapes on the hand.)
4. Inguinal region
Receive lymph from lower limbs, external genital, and lower abdominal wall.
5. Pelvic cavity
Receive lymph from the lymphatic vessels of the pelvic viscera
6. Thoracic cavity
Receive lymph from the thoracic viscera and from the internal wall of the thorax.
6.
80
What type of cells provide our immunity? (3)
1. T-cells
2. B-cells
3. NK cells
81
How do T-cells function?
Major components of the adaptive immune system. Their roles include: directly killing infected host cells, activating other immune cells, producing cytokines, and regulating the immune response.
82
How do B-cells function?
Responsible for the humoral immunity component of the adaptive immune system. These WBCs produce antibodies, which play a key part in immunity. These antibodies bind to pathogens or to foreign substances, such as toxins, to neutralize them.
83
How do NK cells functions?
(part of innate defense) They express activation receptors that recognize virus infected cells. Highly related to receptors recognizing tumor cells. The activation receptors trigger cytotoxicity and cytokine production.
84
Compare an antigen to an antibody
Antigens react to antibodies. Antibodies have a binding site for specific antigens.
85
How do antibodies react to antigens? (3)
1. Antibodies bind to antigens in a direct attack against the antigens
2. To activate complement
3. Stimulate localized changes (inflammation) that help prevent spread of pathogens
86
Describe the thymus and its role in immunity.
The thymus is in the mediastinum. It varies in size (bigger in children and shrinks by age 20). It is a soft, bilobed gland that's enclosed in connective tissue capsule. The lobules have many T-cells that are developed from the progenitor cells in the RBM. Most are inactive, but some mature into T-cells.
87
What are the different glands associated with the lymphatic system?
1. Lymph nodes
2. Thymus
3. Spleen
88
Function of lymph nodes
Filter out potentially harmful particles from lymph before returning it to blood stream and monitor fluids (immune surveillance) through the actions of lymphocytes and macrophages.
88
Function of lymph nodes
Filter out potentially harmful particles from lymph before returning it to blood stream and monitor fluids (immune surveillance) through the actions of lymphocytes and macrophages.
89
Function of thymus
Lobules in thymus have many lymphocytes that are developed from the progenitor cells in the bone marrow. Most of them are inactive, but some mature into T-cells (those leave the thymus and provide immunity). Its role mainly lies in immunity.
90
Function of spleen
LARGEST LYMPH ORGAN.
Acts as a large lymph node. Instead of lymphatic sinuses, the spleen has venous spaces that are filled with blood instead of lymph.
91
Describe the tissue in the lobules of the spleen (2)
1. White pulp
2. Red pulp
92
Describe white pulp
It is distributed throughout the spleen in tiny islands. The tissue (tiny islands) is made of splenic nodules and is packed with lymphocytes.
93
Describe red pulp
This fills the remaining spaces of the lobules (includes the venous sinuses and the space around the sinuses). This pulp contains a lot of RBCs and many lymphocytes and macrophages.
94
What is the function of the spleen?
The spleen filters blood, much like the lymph nodes filter lymph.
95
How does stress affect immunity?
When we're stressed, the immune system's ability to fight off antigens is reduced. That is why we are more susceptible to infections. The stress hormone corticosteroid can suppress the effectiveness of the immune system.
96
What are the two immune responses?
1. Primary immune response
2. Secondary immune response
97
Describe the primary immune response
It happens when B-cells and T-cells become activated after first encountering the antigens that they're specialiazed to react to. Plasma cells release antibodies and they've carried throughout the body to help destroy the antigen-bearing agents that they're specialized to react to. Continues for several weeks to maintain a high amount of antibodies in the plasma. This occurs during the initial exposure to an infection.
98
Describe the secondary immune response
This occurs due to the primary immune response (the B-cells produced during proliferation will serve as memory cells and these memory B-cells combined with memory T-cells produce this secondary response.
This secondary immune response occurs when the same type of antigen is encountered again later on.
This response is long-lasting and though the antibodies remain in the body for several months or years, the memory cells live for much longer periods of time than those antibodies. Secondary immune response is more effective than the primary immune response.
99
What is interferon?
Interferons are proteins produced by lymphocytes and fibroblasts produce in response to viruses or tumor cells. These proteins bind to receptors on uninfected cells and stimulates them to synthesize proteins that block replication of a variety of viruses.
Its defense is nonspecific.
100
What is a complement?
A group of proteins (complement system) in plasma and other body fluids, that interact in an expanding series of reactions or cascades.
It binds to an antibody attached to its specific antigens or more slowly by an alternative pathway triggered by exposure to foreign antigens in the abscence of antibodies.
101
What are macrophages and what is their role in immunity?
Monocytes become macrophages when they leave the blood. They constitute the mononucleur phagocytic system.
Macrophages are part of innate (nonspecific) immunity and adaptive (specific) immunity. These cells play a role in both.
In innate (nonspecific) immunity, they play a role in phagocytosis (which removes foreign particles from lymph as it goes from IS spaces into the bloodstream). In phagocytosis, the most active phagocytic cells are neutrophils (engulf and digest the smaller particles) and monocytes (that phagocytize the larger ones).
Monocytes that leave the blood differentiate to become macrophages (free or fixed).
In inflammation (nonspecific/innate defenses):
White blood cells accumulate at the sites of inflammation, where some of them help control pathogens by phagocytosis. Neutrophils are the first to arrive at the site, followed by monocytes. Monocytes pass through capillary walls (diapedesis), becoming macrophages that remove pathogens from surrounding tissues.
In adaptive (specific) defenses:
Lymphocytes and macrophages that recognize specific nonself antigens carry out adaptive immune responses, which include the cellular immune response and humoral immune response.
102
Innate barriers vs. adaptive immunity
Nonspecific protective mechanisms repel all microorganisms equally, while the specific immune responses are tailored to particular types of invaders. Both systems work together to thwart organisms from entering and proliferating within the body.
Both defenses protect the body from pathogens and infection.
103
Describe differences between T-cells and B-cells
Thymocytes specialized T-cells. They account for 70% - 80% of lymphocytes in the bloodstream. Other lymphocytes remain in the RBM until they become B-cells.
B-cells are responsible for the humoral immunity component of the adaptive immune system. These WBCs produce antibodies.
T-cells are major components of the adaptive immune system. Their roles include directly killing infected host cells, activating other immune cells, producing cytokines, and regulating immune responses.
