This system is the way that blood is cleaned and returned to your body, while waste materials are sent out of your body as urine through tubules (tiny tubes). The blood pressure in the glomerulus (the glomerular blood hydrostatic pressure) helps to move the blood along. As the fluids are leaving, water and nutrients are reabsorbed.
The Kidneys
The kidneys are bilateral bean-shaped organs, reddish-brown in colour and located in the posterior abdomen. Their main function is to filter and excrete waste products from the blood. They are also responsible for water and electrolyte balance in the body.
Metabolic waste and excess electrolytes are excreted by the kidneys to form urine. Urine is transported from the kidneys to the bladder by the ureters. It leaves the body via the urethra, which opens out into the perineum in the female and passes through the penis in the male.
In this article we shall look at the anatomy of the kidneys – their anatomical position, internal structure and vasculature.
Anatomical Position
The kidneys lie retroperitoneally (behind the peritoneum) in the abdomen, either side of the vertebral column.
They typically extend from T12 to L3, although the right kidney is often situated slightly lower due to the presence of the liver. Each kidney is approximately three vertebrae in length.
The adrenal glands sit immediately superior to the kidneys within a separate envelope of the renal fascia.
Prosection of the kidneys in-situ within the abdominal cavity. Note how the renal veins are anterior to the renal arteries.
Kidney Structure
The kidneys are encased in complex layers of fascia and fat. They are arranged as follows (deep to superficial):
- Renal capsule – tough fibrous capsule.
- Perirenal fat – collection of extraperitoneal fat.
- Renal fascia (also known as Gerota’s fascia or perirenal fascia) – encloses the kidneys and the suprarenal glands.
- Pararenal fat – mainly located on the posterolateral aspect of the kidney.
Fig 2
The external coverings of the kidney.
Internally, the kidneys have an intricate and unique structure. The renal parenchyma can be divided into two main areas – the outer cortex and inner medulla. The cortex extends into the medulla, dividing it into triangular shapes – these are known as renal pyramids.
The apex of a renal pyramid is called a renal papilla. Each renal papilla is associated with a structure known as the minor calyx, which collects urine from the pyramids. Several minor calices merge to form a major calyx. Urine passes through the major calices into the renal pelvis, a flattened and funnel-shaped structure. From the renal pelvis, urine drains into the ureter, which transports it to the bladder for storage.
The medial margin of each kidney is marked by a deep fissure, known as the renal hilum. This acts as a gateway to the kidney – normally the renal vessels and ureter enter/exit the kidney via this structure.
Fig 3
The internal structure of the kidney.
Anatomical Relations
The kidneys sit in close proximity to many other abdominal structures which are important to be aware of clinically:
- Suprarenal gland
- Spleen
- Stomach
- Pancreas
- Left colic flexure
- Jejunum
- Diaphragm
- 11 th and 12 th ribs
- Psoas major, quadratus lumborum and transversus abdominis
- Subcostal, iliohypogastric and ilioinguinal nerves
- Suprarenal gland
- Liver
- Duodenum
- Right colic flexure
- Diaphragm
- 12 th rib
- Psoas major, quadratus lumborum and transversus abdominis
- Subcostal, iliohypogastric and ilioinguinal nerves
Arterial Supply
The kidneys are supplied with blood via the renal arteries, which arise directly from the abdominal aorta, immediately distal to the origin of the superior mesenteric artery. Due to the anatomical position of the abdominal aorta (slightly to the left of the midline), the right renal artery is longer, and crosses the vena cava posteriorly.
The renal artery enters the kidney via the renal hilum. At the hilum level, the renal artery forms an anterior and a posterior division, which carry 75% and 25% of the blood supply to the kidney, respectively. Five segmental arteries originate from these two divisions.
The avascular plane of the kidney (line of Brodel) is an imaginary line along the lateral and slightly posterior border of the kidney, which delineates the segments of the kidney supplied by the anterior and posterior divisions. It is an important access route for both open and endoscopic surgical access of the kidney, as it minimises the risk of damage to major arterial branches.
Note: The renal artery branches are anatomical end arteries – there is no communication between vessels. This is of crucial importance; as trauma or obstruction in one arterial branch will eventually lead to ischaemia and necrosis of the renal parenchyma supplied by this vessel.
The segmental branches of the renal undergo further divisions to supply the renal parenchyma:
- Each segmental artery divides to form interlobar arteries. They are situated either side every renal pyramid.
- These interlobar arteries undergo further division to form the arcuate arteries.
- At 90 degrees to the arcuate arteries, the interlobular arteries arise.
- The interlobular arteries pass through the cortex, dividing one last time to form afferent arterioles.
- The afferent arterioles form a capillary network, the glomerulus, where filtration takes place. The capillaries come together to form the efferent arterioles.
In the outer two-thirds of the renal cortex, the efferent arterioles form what is a known as a peritubular network, supplying the nephron tubules with oxygen and nutrients. The inner third of the cortex and the medulla are supplied by long, straight arteries called vasa recta.
Fig 4
Arterial and venous supply to the kidneys.
Bowman’s Capsule
The nephron is the filter of the kidney where your blood is cleaned. Waste material is expelled as urine. The Bowman’s capsule is part of the nephron.
Overview
Bowman’s capsule is part of the nephron, which is the filtering unit of your kidney.
What is Bowman’s capsule?
Bowman’s capsule is a part of the nephron which is a part of your kidney. The nephron is the filtering unit of your kidney. There are about 1 million nephrons in each kidney.
Every nephron has a glomerulus, which is a group of tiny blood vessels and the starting point for filtering waste products out of your blood. Bowman’s capsule is a two-walled pouch that covers the glomerulus. The space in between the walls of the capsule is called Bowman’s space.
Bowman’s capsule is known by other names, including the glomerular capsule, the Malpighian capsule and the renal corpuscular capsule. Bowman’s space also has other names, including glomerular capsule space, filtration space and urinary space.
Function
What does Bowman’s capsule do?
Bowman’s capsule and the glomerulus make up the renal corpuscle. They are all parts of the kidney. Your kidneys have many important jobs, including controlling the pH balance of your blood, regulating blood pressure and maintaining electrolyte balance. As part of the urinary system, the kidneys are also responsible for ridding your body of waste through urine (pee).
The capsule helps the glomerulus to filter blood. Small molecules from the blood pass freely into Bowman’s space, but as long as the kidney filter is working normally, cells and large proteins stay in the blood. The small molecules then pass through tubes in the kidney, and the kidney regulates which molecules get absorbed back into your blood and which leave your body in urine.
Anatomy
Where is Bowman’s capsule located?
Bowman’s capsule is located in the renal cortex, part of your kidney. The kidneys are located below your ribcage and behind your belly. Usually, there is one kidney on either side of your spine. The kidneys reside between your intestines and diaphragm. Each kidney is connected to your bladder by a tube called a ureter.
What does Bowman’s capsule look like?
You need a microscope to see Bowman’s capsule. It resembles a pouch or sac. It’s also described as being “cup-like.”
The capsule is made up of two layers. One is the outer layer, called the parietal layer. This layer is made of body tissue known as simple squamous epithelium. The inner layer of the capsule is the visceral layer, and it’s made up of cells called podocytes. These podocytes have pedicles that look like fingers. These pedicles link together like they’re holding hands (“interdigitation”). The way they are joined creates slits that let some things go through but stops other things. When you’re healthy, protein and cell content can’t get through.
This system is the way that blood is cleaned and returned to your body, while waste materials are sent out of your body as urine through tubules (tiny tubes). The blood pressure in the glomerulus (the glomerular blood hydrostatic pressure) helps to move the blood along. As the fluids are leaving, water and nutrients are reabsorbed.
Conditions and Disorders
What are the common conditions and disorders that affect Bowman’s capsule?
Diseases and conditions that affect your kidneys also affect Bowman’s capsule. Bowman’s capsule is especially vulnerable to diseases of the glomeruli (small blood vessels that Bowman’s capsule surrounds). There are different types of glomerular diseases. Causes range from environmental reasons to genetic ones. Glomerulonephritis refers to inflammation of the glomeruli. These conditions can be autoimmune, genetic, or infection-related diseases. Glomerulosclerosis is when the glomeruli become hard and scarred. Untreated, these diseases can result in kidney failure. Nothing causes more cases of glomerular disease and kidney failure than diabetes-related nephropathy.
What are common signs or symptoms of disorders that affect the Bowman’s capsule?
Signs and symptoms of glomerular diseases may include:
- High levels of protein in your urine (proteinuria). Your urine might be foamy.
- Blood in your urine (hematuria). Your urine might look pink or like cola.
- Low levels of protein in your blood (hypoproteinemia).
- Swelling of body parts, such as your hands or feet (edema) or puffiness in your eye area.
What are some common tests to check the health of the Bowman’s capsule?
Healthcare providers use several tests to measure kidney function and diagnose kidney problems. Your provider may recommend:
- Blood tests: These can show how well your glomeruli filter your blood.
- Urinalysis: This measures specific substances, such as protein or blood, in urine.
- Imaging tests like ultrasound. These let your providers examine the size and shape of your kidneys.
- Kidney function tests (also called renal function tests): These tests show how well the kidneys are working.
- Kidney biopsy: In this test, your provider removes a small amount of kidney tissue to examine under a microscope.
What kinds of treatments are available for conditions that affect Bowman’s capsule?
There’s no one-size-fits-all treatment for diseases that affect the kidneys. Your treatment will depend on what condition you have and how severe it is. Possible therapies for diseases that affect Bowman’s capsule may include:
- Diets low in sodium.
- Medications like antibiotics, blood pressure drugs, immunosuppressants and steroids.
- Dialysis.
- Kidney transplant.
Care
What kinds of things can I do to keep Bowman’s capsule healthy?
You can help to keep Bowman’s capsule healthy by working to keep your kidneys healthy. It’s important to have regular checkups and blood and urine tests to monitor kidney health. This is especially true if you have high blood pressure, obesity and/or diabetes. You can reduce your risk of developing a kidney problem by:
- Avoiding or quitting smoking.
- Cutting out excess salt.
- Increasing daily exercise, which can reduce high blood pressure.
- Limiting your use of non-steroidal anti-inflammatory drugs, substances that can cause kidney damage when overused.
- Maintaining a healthy weight.
- Monitoring your blood pressure levels.
- Watching your blood sugar levels if you have diabetes.
When should I contact my healthcare provider if I’m worried about the Bowman’s capsule or kidney disease?
If you think you might be having problems with your kidneys, you should contact your healthcare provider. You might experience signs and symptoms that include:
- Changes in your urine, including bloody urine, dark urine, cloudy or foamy urine.
- Changes in how often you pee.
- Fatigue (extreme tiredness).
- High blood pressure (hypertension).
- Muscle cramps.
- Poor appetite or metallic taste of food.
- Nausea and vomiting.
- Swelling, especially around your ankles or hands.
Your provider might suggest regular kidney function tests or blood tests if you have certain conditions, including:
- A family history of kidney disease.
- Diabetes.
- Heart disease.
- High blood pressure.
- Obesity.
- Regular use of certain medications, such as medicine to control your blood pressure.
Your kidneys perform many important jobs in your body. Staying healthy by keeping blood pressure and blood glucose levels in check is key. If you think you may be having some issue with your urinary tract, whether it’s an infection or a change in your urinary habits, talk to your healthcare provider. They’ll work with you to find a solution.
