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BIOL 235 Human Anatomy and Physiology Assignment 3 Questions and correct Answers (Correctly Explained).

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BIOL 235 (BIOL235)

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Athabasca University (AU )

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biol 235 human anatomy and physiology assignment 3 questions and correct answers correctly explained
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BIOL 235 Human Anatomy and Physiology Assignment 3
Questions and correct Answers (Correctly Explained).
1. Some patients who suffer from hypertension (high blood pressure) are prescribed
medications that are in the category of angiotensin-converting enzyme (ACE) inhibitors.
Explain why these drugs are used to combat hypertension.

When blood volume falls or blood flow to the kidneys decreases, juxtaglomerular cells in
the kidneys secrete renin into the bloodstream. In sequence, renin and angiotensin-
converting enzyme (ACE) act on their substrates to produce the active hormone
angiotensin II, which raises blood pressure in two ways. First, angiotensin II is a potent
vasoconstrictor; it raises blood pressure by increasing systemic vascular resistance.
Second, it stimulates secretion of aldosterone, which increases reabsorption of sodium
ions (Na+) and water by the kidneys. The water reabsorption increases total blood
volume, which increases blood pressure.

ACE inhibitor prevents an enzyme in the body from producing angiotensin II, a substance
that increases blood pressure.

2. Describe the fate of an RBC traveling from the heart to the left elbow and back to the
heart.

Usually blood passes from the heart and then in sequence through arteries, arterioles,
capillaries, venules, and veins and then back to the heart. In some parts of the body,
however, blood passes from one capillary network into another through a vein called a
portal vein. Such a circulation of blood is called a portal system. The name of the portal
system gives the name of the second capillary location. For example, there are portal
systems associated with the liver (hepatic portal circulation; and the pituitary gland.

Unlike their thick-walled arterial counterparts, venules and veins have thin walls that do
not readily maintain their shape. Venules drain the capillary blood and begin the return
flow of blood back toward the heart.

Although veins are composed of essentially the same three layers as arteries, the relative
thicknesses of the layers are different. The tunica interna of veins is thinner than that of
arteries; the tunica media of veins is much thinner than in arteries, with relatively little
smooth muscle and elastic fibers. The tunica externa of veins is the thickest layer and
consists of collagen and elastic fibers. Veins lack the internal or external elastic laminae
found in arteries. They are distensible enough to adapt to variations in the volume and
pressure of blood passing through them, but are not designed to withstand high pressure.
The lumen of a vein is larger than that of a comparable artery, and veins oft en appear
collapsed (flattened) when sectioned.

, The pumping action of the heart is a major factor in moving venous blood back to the
heart. The contraction of skeletal muscles in the lower limbs also helps boost venous
return to the heart. The average blood pressure in veins is considerably lower than in
arteries. The difference in pressure can be noticed when blood flows from a cut vessel.
Blood leaves a cut vein in an even, slow flow but spurts rapidly from a cut artery. Most of
the structural differences between arteries and veins reflect this pressure difference. For
example, the walls of veins are not as strong as those of arteries.

Many veins, especially those in the limbs, also contain valves, thin folds of tunica interna
that form flaplike cusps. The valve cusps project into the lumen, pointing toward the
heart. The low blood pressure in veins allows blood returning to the heart to slow and
even back up; the valves aid in venous return by preventing the backflow of blood.

3. Explain the steps that result in antibody production and describe the process that results
in an activated B-cell.

An antibody (Ab) can combine specifically with the epitope on the antigen that triggered
its production. The antibody’s structure matches its antigen much as a lock accepts a
specific key. In theory, plasma cells could secrete as many different antibodies as there
are different B-cell receptors because the same recombined gene segments code for both
the BCR and the antibodies eventually secreted by plasma cells.

The body contains not only millions of different T cells but also millions of different B
cells, each capable of responding to a specific antigen. Cytotoxic T cells leave lymphatic
tissues to seek out and destroy a foreign antigen, but B cells stay put. In the presence of a
foreign antigen, a specific B cell in a lymph node, the spleen, or mucosa-associated
lymphatic tissue becomes activated. Then it undergoes clonal selection, forming a clone
of plasma cells and memory cells.

During activation of a B cell, an antigen binds to B-cell receptors (BCRs). These integral
transmembrane proteins are chemically similar to the antibodies that eventually are
secreted by plasma cells. Although B cells can respond to an unprocessed antigen present
in lymph or interstitial fluid, their response is much more intense when they process the
antigen. Antigen processing in a B cell occurs in the following way: The antigen is taken
into the B cell, broken down into peptide fragments and combined with MHC-II self-
antigens, and moved to the B cell plasma membrane. Helper T cells recognize the
antigen–MHC-II complex and deliver the costimulation needed for B cell proliferation
and differentiation. The helper T cell produces interleukin-2 and other cytokines that
function as costimulators to activate B cells.

Once activated, a B cell undergoes clonal selection. The result is the formation of a clone
of B cells that consists of plasma cells and memory B cells. Plasma cells secrete
antibodies. A few days after exposure to an antigen, a plasma cell secretes hundreds of
millions of antibodies each day for about 4 or 5 days, until the plasma cell dies. Most
antibodies travel in lymph and blood to the invasion site. Interleukin-4 and interleukin-6,
also produced by helper T cells, enhance B cell proliferation, B cell differentiation into

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