Assignment on Homeostasis (doc)

Homeostasis 1
HOMEOSTASIS
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Homeostasis 2
Homeostasis
Task 1
Question 1: Negative Feedback
Negative feedback can be described as the mechanism that the body uses to maintain conditions
within specific limits by opposing any changes that tend to deviate from the normal.
Thermoregulation is one of the ways the body uses to maintain a normal temperature range.
When there is a significant change in the temperature of the body, the hypothalamus is notified
via the receptors that detect this change. The hypothalamus responds by initiating the process
that resets the temperature back to normal (Pitoni, Sinclair and Andrews, 2011, p. 118). In
thermoregulation, when the temperatures are too high, the arterioles undergo vasodilation where
they enlarge to enable more blood to flow to the skin surfaces so heat can be lost (González‐
Alonso, 2012, p. 342). Additionally, the sweat glands secrete sweat that which helps in cooling
the body. Furthermore, the hairs undergo pilorelaxation where they flatten to allow heat loss. On
the other hand, when the temperatures drop too low, the arterioles undergo vasoconstriction
where they become smaller to reduce the amount of blood flowing into the skin surface thus
limiting heat loss. The body additionally shivers and the skeletal muscles rapidly relax and
contract to produce more heat through respiration (Pitoni, Sinclair and Andrews, 2011, p. 119).
The hairs on the skin also stand up to trap a layer of insulating warm air over the skin.
Question 2
The steroids hormones effect changes within cells when they first pass through the target cell’s
cell membrane. Once inside the cell, the hormones bind to specific receptors that are present
within the target cell’s cytoplasm. The steroid, bound to the receptor then travels to the nucleus

Homeostasis 3
where it links with another receptor found in the chromatin. After binding to the chromatin, the
hormone-receptor initiates the production of messenger RNA through a process known as
transcription (Melmed, 2016, p. 42). The messenger RNA is then modified and transported to the
cytoplasm where they code for the production of proteins through a process called translation.
The target cells for protein and steroid hormones have specific receptors on their membranes or
within the cells that enable them to respond to exposure. The extent to which a target cell is
activated depends on several factors that include the levels of hormones present in the blood, the
number of receptors for a particular hormone, and the affinity of the receptor to the hormone.
This mechanism can be described by the picture below (Melmed, 2016, p. 43).
Task 2
The insulin hormone regulates blood glucose by allowing the cells of the body to absorb and use
glucose thus reducing the level of blood glucose. Glucagon, on the other hand, stimulates the
cells to release blood glucose into the bloodstream (D’Alessio, 2013, p. 59). At around 9:15 am,
Mandy takes sweet biscuits with coffee. This food is digested and converted into glucose that is
sent into the bloodstream thus raising the level of blood glucose. As a result, insulin hormone is
produced by the pancreas that stimulates the body cells to absorb glucose, some of which is used
as energy while excess is stored in form of glycogen (Thorens, 2011, p. 83). By around 2:00 pm,

Homeostasis 4
the level of blood glucose in Mandy’s bloodstream will have dropped thus triggering the release
of glucagon hormone from the pancreas. The glucagon hormone helps in converting the stored
glycogen back into glucose that is then released into the bloodstream (Thorens, 2011, p. 84).
This reduction in the blood glucose level is the reason she feels hungry at 2:00 pm.
Task 3
The liver plays a very important role in the regulation of amino acids. The body does not store
excess amino acids and therefore once the body’s daily proteins needs have been met, the liver
has to deal with the excess. The liver breaks down excess amino acids to produce urea that is
released through urine. This explains the reason for David’s yellow urine. Excess protein that is
not converted into muscles is sent into the liver where they are converted into either urea or
glucose (Schiaffino et al., 2013, p. 4301). When turned into urea, it is excreted in urine. The
amino acids are oxidized in the presence of an enzyme that acts as a catalyst to form ammonia.
At the same time, the amine group is converted into ammonia through deamination. This product
is then released in the form of urine. This process can be explained by the photo shown below
(Sandri, 2013, p. 2124).

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Task 4
Question 1: Nephron (Kriz and Kaissling, 2013, p. 596)

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Question 2: Crossword Puzzle
Across
1. Pituitary hormone that regulates water reabsorption: abbreviation
4. Where maximum reabsorption of water takes place: abbreviation
7. Cluster of capillaries in Bowman capsule
10. Leads to the collecting ducts: abbreviation
14. The fluid excreted by the kidneys
Down
2. Painful or difficult urination
3. Substance produced in response to renin that increases blood pressure
4. Renal pelvis: combining form
5. Excessive urination at night

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8. Tube that carries urine from the kidney to the bladder
12. Kidney: combining form
13. Maximum amount of a substance that can be reabsorbed: abbreviation
Task 5
Question 1
Component Before Filtration After Filtration
Urea/gdm-3 0.3 0.3
Glucose/gdm-3 1.0 1.0
Water/gdm-3 900 900
Cells Red blood cells, platelets and
white blood cells
No cells
Plasma proteins/gdm-3 45 0
Inorganic ions/gdm-3 7 7
Question 2: Ultrafiltration
Ultrafiltration is the process by which blood is filtered in the glomerulus under high pressure to
form a glomerular filtrate. Blood enters into the kidney through the renal artery that separates
into afferent arterioles that deliver blood into to the kidney nephrons. The high pressure that
enhances the filtration results from the afferent arteriole being wider in diameter as compared to
the efferent arteriole (Pavlovic, M., 2015, p. 173). The afferent arteriole is the incoming arteriole
while the efferent arteriole is where blood leaves the renal glomerulus. The increase in the blood
pressure forces most of the water, almost all salts, glucose, and urea out of the capillaries. Water
and solutes are filtered out due to their relative molecular mass that is less than 68000. Plasma

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proteins and blood cells are however not filtered out via the glomerular capillaries due to their
relatively large physical size (Tojo and Kinugasa, 2012).
Task 6
Once the glomerular filtrate has been formed, not all the components filtered out are eliminated
out of the body. A process known as selective reabsorption takes place in the proximal
convoluted tubule whereby glucose is reabsorbed back into the blood. The reabsorption of
glucose is by the process of active transport using energy obtained from respiration (Mather and
Pollock, 2010, p. 307). Normally, the concentration of sodium ions is normally high in the
filtrate, almost in the same proportion as the concentration in the blood plasma. The sodium ions,
therefore, move from the tubular fluid into the proximal convoluted tubule in the company of
glucose molecules. This movement is aided by symporters that facilitate the passage of both the
sodium ions and glucose through the proximal convoluted tubule. It is important to note that the
cells of the proximal convoluted tubule have a huge number of mitochondria that provide the
energy used for the active transport of glucose. This process can be described by the diagram as
shown below (Mather and Pollock, 2010, p. 307).

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Task 7
It is important to maintain the amount of water in the body at a normal range to avoid the
damage of cells that may result from osmosis. As we are informed, David sweats a lot while
exercising on his trade mill. His body must, therefore, find a balance between the amount of
water that he gains and the amount of water that he losses through sweating. This balance in
water is aided by the action of the anti-diuretic hormone (Esteva-Font, Ballarin and Fernández-
Llama, 2012, p. 687). As David has been sweating, the hypothalamus detects a drop in water
levels in the blood and sends a signal to the pituitary glands to release the anti-diuretic hormone.
The hormone then travels to the kidney and triggers the tubules to reabsorb more water into the
blood thus reducing the loss of more water as urine. The result is that David excretes a small
quantity of very concentrated urine. Additionally, a reduction in the volume of water leads to a
drop in the blood volume. This change in the volume of blood stimulates the adrenal glands to
release the aldosterone hormone that helps in reducing sodium thus lowering the rate of excretion
through the kidney. The aldosterone hormone additionally enhances the retention of water.

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References
Esteva-Font, C., Ballarin, J. and Fernández-Llama, P., 2012. Molecular biology of water and salt
regulation in the kidney. Cellular and Molecular Life Sciences, 69(5), pp.683-695.
González‐Alonso, J., 2012. Human thermoregulation and the cardiovascular
system. Experimental physiology, 97(3), pp.340-346.
Kriz, W. and Kaissling, B., 2013. Structural organization of the mammalian kidney. In Seldin
and Giebisch's The Kidney (Fifth Edition) (pp. 595-691).
Mather, A. and Pollock, C., 2010. Renal glucose transporters: novel targets for hyperglycemia
management. Nature reviews Nephrology, 6(5), p.307.
Melmed, S., 2016. Williams textbook of endocrinology. Elsevier Health Sciences.
Pavlovic, M., 2015. Waste Disposal from the Body. In Bioengineering (pp. 169-185). Springer,
Cham.
Pitoni, S., Sinclair, H.L. and Andrews, P.J., 2011. Aspects of thermoregulation
physiology. Current opinion in critical care, 17(2), pp.115-121.
Sandri, M., 2013. Protein breakdown in muscle wasting: role of autophagy-lysosome and
ubiquitin-proteasome. The international journal of biochemistry & cell biology, 45(10), pp.2121-
2129.
Schiaffino, S., Dyar, K.A., Ciciliot, S., Blaauw, B. and Sandri, M., 2013. Mechanisms regulating
skeletal muscle growth and atrophy. The FEBS journal, 280(17), pp.4294-4314.
Schwartz, M.W., Seeley, R.J., Tschöp, M.H., Woods, S.C., Morton, G.J., Myers, M.G. and
D’Alessio, D., 2013. Cooperation between brain and islet in glucose homeostasis and
diabetes. Nature, 503(7474), p.59.