Biochemistry - Nephron Structure, Renal Tubules, Formation of Urine and Secretion, Hormonal Regulation of Kidneys, and Kidney Diseases

Running head: BIOCHEMISTRY 1
Biochemistry
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BIOCHEMISTRY 2
Nephron structure
The nephron is the microscopic structure of the kidney, made up of about one million
small tubes known as the tubulues. The nephrons confer both the functional as well as structural
unit of the kidneys. The nephron consists of two compartments: the malphagian body and the
renal tubes. The malphagian body is a double walled cup that surrounds several capillaries. This
cup is commonly known as the bowman’s capsule while the network of capillaries is known as
the glomerulus. The main parts of the nephron tubule are the proximal convoluted tubule, loop of
Henle, distal convoluted tubule and the collecting duct. It is worth noting that a substantial
amount of glucose, small proteins and other useful materials are reabsorbed in the proximal
convoluted tubule. The afferent arteriole which is a branch of the renal artery finds its way to the
glomerulus and ultimately divides into so many capillaries. These capillaries unite again to form
the efferent arterioles which leaves the glomerulus once more. The bore is the diameter of the
lumen in the afferent arteriole which is bigger than that of the efferent arteriole. Moreover, the
walls of the capillaries are made up of the squamous endothelial material which is found on the
basement membrane. The cells contain several tiny pores on the capillary walls to facilitate the
passage of materials. Moreover, the capillary walls on the Bowman’s capsule consist of the
squamous epithelium and rests in the basement membrane to be modified into special cells
known as the podocytes (Lasagni et al., 2015).
The renal tubules
This is a very crucial structure of the kidney since it contains the tube fluids which are
finally filtered into urine for excretion by the body. These tubules are part of the nephrons and
each normal kidney has about one million nephrons with each having the renal tubules. Thus
these structures are described as the end of the neuron because after the tubular fluids leave the

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renal tubules, they end up in the collecting ducts, which empties to the ureter. The tubular fluid
starts as the glomerular filtrate which consists of the fluids filtered from the body by the
glomerulus. Once the filtrate begins leaving the glomerulus, it enters into the proximal tubule
which is the first portion of the renal tubules. In the proximal tubules, there is the regulation of
the pH and secretion of organic acids which are not needed by the body into the filtrate.
Moreover, there is an increased reabsorption of water and sodium ions back into the body by the
capillaries. The midpoint of the renal tubules is known as the tube of Henle and functions to
create a concentrate of the sodium and chloride ions, urea and other wastes into the urine while at
the same time absorbing more water back to the body. Finally, the distal convoluted tubule is
farthest and enables the pH regulation through secretion of protons in form of hydrogen ions into
the urine and absorbing back the negatively charged bicarbonate ions (Subramanya & Ellison,
2014). This step is very important in the regulation of various ions in blood such as the calcium,
sodium, and potassium. When the filtrate is passing down the descending loop of Henle, it does
this in a contrary direction to the fluids inside the ascending limbs. The fluids are highly
concentrated when moving down and more dilute when moving upwards. This fashion is known
as the countercurrent flow thus allowing the production of the concentrated urine.
Formation of urine and secretion
Formation of urine occurs in three steps which involve various regulatory processes.
These are the glomerular filtration, reabsorption in the tubes and secretions. In glomerular
filtration, the glomerulus filters low molecular weight materials in blood and retains the high
molecular weight substances like proteins. This clearly means that the proteins will be retained in
the blood and not lost in urine. If during a test, proteins are found in urine, this is indicative of
kidney damage or any other disease which could be affecting the glomerular membrane. In the

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reabsorption stage, even though the filtrate in the glomerulus has the same concentration of
glucose as the plasma, none of it is found in urine (Dantzler, 2016). Therefore, glucose should be
completely reabsorbed inside the tubules when the sugar concentrations are normal. Basically,
reabsorption of materials is dependent on the renal threshold of the materials inside. Different
solid materials get reabsorbed at various sites of the renal tubules. Glucose, amino acids and
small proteins can pass through the glomerulus and hence their absorptions occurs in the first
portion of the proximal tubules. On the other hand, bicarbonates, sodium and chlorides get
absorbed in a uniform manner along all parts of the proximal and distal tubules. However,
potassium ions are reabsorbed in the proximal tubules and later get secreted in the distal tubules.
Even though majority of materials are reabsorbed in the tubules, there are others which
are actively transported and excreted in the lumen of the tubules. In the tubules of man, majority
of the materials which are secreted are creatinine and potassium ions. It is at these sites that the
foreign materials such as diagnostic and therapeutic that have been introduced get removed
through urine.
Hormonal regulation of the kidneys
For the kidneys to function well, the interplay of three hormones is needed. These
hormones include the adrenal cortex hormone, vasopressin and parathormone. The aldosterone
hormone is involved in the excretion of sodium ions and potassium ions. The parathormone
stimulates the secretion of phosphates while vasopressin is an antidiuretic hormone which
facilitates the reabsorption of water. In the vent that the vasopressin hormone is absent, then
there will be production of high amounts of dilute hormone.