Human Kidney Anatomy
Kidney anatomy includes a number of inter-connected and inter-related structures that enable the kidneys to perform some very important functions. Some of these components or structures can be seen with the naked eye and are known as the gross anatomy. Others are microscopic and can only be observed under a microscope. These are referred to as the microscopic anatomy.
The various structures that form the kidney's anatomy are integrated and work together, to enable the kidneys to perform some complex but essential biological functions.
Some of these functions include 'removal of toxic waste', 'regulating blood pressure' and 'production of certain hormones'.
The human kidney anatomy is uniquely structured and equipped to perform these and other crucial functions, which are integral for homeostasis
and maintaining general good health.
Homeostasis (ho-me-oh-stay-sis) is basically the ability of the body to maintain internal stability, even when the environment around it changes. In a state of homeostasis, the body is able to detect harmful changes in its environment and activate mechanisms that counteract them. If the body loses its ability to maintain homeostasis, the result is usually disease or death.
The main components of the gross kidney anatomy are shown in the following diagram. This kidney diagram represents the structure of a kidney, sliced vertically.
KIDNEY DIAGRAM
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KIDNEY ANATOMY
Most humans are born with two kidneys, although one kidney is capable of performing the normal functions of both kidneys. In rare cases a person may be born with one kidney or may lose a kidney through injury, disease or surgery (for example when a person donates a kidney). Amazingly, such people are still able to lead normal lives, without any adverse effects to their health.
The external appearance of the kidneys is dark-red and bean-shaped (very similar to kidney beans). One side bulges outward (convex) and the other side is indented (concave).
Each Kidney is enclosed in a transparent membrane called the renal capsule... which helps to protect them against infections and trauma. The kidney is divided into two main areas... a light outer area called the renal cortex, and a darker inner area called the renal medulla. Within the medulla there are 8 or more cone-shaped sections known as renal pyramids. The renal papilla is located at the smaller end of the cone-shaped renal pyramids. The areas between the pyramids are called renal columns.
Each renal papilla is attached to a cup, or a small tube, called the minor calyx (CAY-lix), which collects urine for removal from the kidney, and eventually from the body. Two or three of these minor calices (plural of minor calyx) merge into what is called a major calyx.
The major calices then converge into a funnel-like cavity called the renal pelvis. The renal pelvis, which is attached to the indented side of the kidney, extends into the ureter. The ureter is a long narrow duct (tube) that conveys urine from the kidneys to the urinary bladder.
NORMAL KIDNEY SIZE
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It is approximately the size of a 'conventional computer mouse' or the 'size of your fist', if you prefer.
A kidney weighs approximately 150 to 160 grams and, together, both kidneys weigh about 0.5 percent of total body weight.
Obviously, these measures and weights are general approximations of a typical adult human kidney size. Depending on an individual's height, gender, age and BMI (body mass index), the size of their kidneys can be quite different from what is considered 'typical'.
Kidney disease is another important factor that may affect kidney size. In fact, the size of a kidney and changes in its size can provide indications of renal problems. For instance, polycystic disease and hydronephrosis (a condition where fluids accumulate inside the kidney) can cause distension (enlargement) of the kidneys.
Other chronic renal conditions can cause the kidney to decrease in size (known as atrophy), over a period of time (usually years). Alport Syndrome, Chronic Glomerulonephritis and Hypertensive Nephrosclerosis are examples of conditions which may cause atrophy.
It should be noted that the information provided about kidney anatomy and kidney size relates to adult humans, over the age of twenty (20) years. Generally, the kidneys are typically fully developed when an individual reaches their early twenties (about 23 to 25 years of age). There should be very little or no changes to the size of the kidneys, after this age.
Determining the normal kidney size of children could be quite challenging, given the wide variation in children's sizes and rate of development. Some studies have compared renal length with children's ages, to determine the typical kidney size of children. The results show the following average renal lengths, based on children's ages:
- Two (2) months and younger - 4.9 cm (2 inches);
- Three (3) months to one (1) year - 6.2 cm (2.5 inches);
- One to five (1-5) years - 7.3 cm (3 inches);
- Five to ten (5-10) years - 8.5 cm (3.5 inches);
- Ten to fifteen (10-15) years - 9.8 cm (3.9 inches); and
- Fifteen to nineteen (15-19) years - 10.6 cm (4.2 inches).
Again, it should be noted that these are just guidelines, based on averages. Actual lengths are likely to vary, based on individual body-weight and height.
KIDNEY LOCATION
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The kidney on the right side is usually slightly lower than the one on the left side of the abdominal cavity. The liver is located just above the right kidney and the spleen is located just above the left. The liver occupies more space in the abdominal cavity than the spleen, hence the reason why the right kidney is usually slightly lower than the left.
It should be noted, however, that there are exceptions and variations to the typical kidney location.
In rare cases, one or both kidneys may be located much lower in the abdomen or the pelvic cavity instead of higher in the abdominal cavity. In medical terms, when an organ is located in a non-typical location or position, this is referred to as situs perversus.
This is not necessarily a problem, once the kidney(s) is/ are functioning properly. In some cases, however, problems can arise in the case of pregnancy. As the fetus begins to develop in the womb this could sometimes place pressure on the kidney(s), which is/ are located in the lower abdomen, and cause acute renal failure.
Kidney Anatomy and Excretion
The most basic structures of the kidneys are nephrons. Inside each kidney there are about one million of these microscopic structures. They are responsible for filtering the blood... removing waste products.
The renal artery delivers blood to the kidneys each day. Over 180 liters (50 gallons) of blood pass through the kidneys every day. When this blood enters the kidneys it is filtered and returned to the heart via the renal vein.
The kidneys are full of blood vessels. Blood vessels are integral to efficient kidney function. Every function of the kidney involves blood; it therefore, requires a lot of blood vessels to facilitate these functions. Together, the two kidneys contain about 160 km of blood vessels.
The process of separating wastes from the body's fluids and eliminating them is known as excretion. The body has four organ systems that are responsible for excretion:
- The respiratory system - responsible for excretion of carbon dioxide and small amounts of water and other gases;
- The integumentary system - excretes water, lactic acid, inorganic salts and urea in the sweat;
- The digestive system - excretes water, salts, bile pigments, cholesterol, and other metabolic wastes;
- The urinary system.
The urinary system is one of the main organ systems responsible for excretion. It excretes a broad variety of metabolic wastes, toxins, drugs, hormones, salts, hydrogen irons and water. The kidneys are the main organs of the urinary system.
The human kidney anatomy is fascinating. These uniquely structured groups of tissues and cells (i.e. the kidney anatomy) effectively enable the kidneys to perform extremely complex but essential functions. Each structure within the kidney anatomy makes important contributions, on a daily basis, to keeping the body stable and healthy. If any area of the kidney is damaged or becomes diseased, this could significantly affect its ability to perform its crucial functions. It is, therefore, important to understand and appreciate the vital role of this organ and to take steps to protect and preserve it.
