This blog is the beginning of a series of blogs about the risk factors for kidney disease. In this first blog, let’s start with talking about the functional kidney mass at birth and itsconnection of future kidney health. The development of the human kidney is generally completed by the 36th week of pregnancy in the unborn baby. Most of the filtering functional units (nephrons) of the kidneys are completed before the full term birth. These filtering units are called the nephrons.
Defining the Nephron: The basic filtering unit of the kidney
Each kidney contains several tiny filtering units called the nephrons. Each nephron includes two sections: a filter, called the glomerulus (pleural: glomeruli), and the tubules. Blood gets filtered in the nephron in two stages. First, the blood enters the glomerulus which is a cluster of miniature blood vessels with thin walls that serve as a sieve allowing large amounts of water, waste products and some nutrients to pass through while keeping larger molecules such as protein and blood cells in. In the second stage, filtered water, waste and nutrients enter tiny tubes (called tubules). These tubules help the body retrieve large portions of water and nutrients that were lost in the first stage while the waste gets excreted in the urine. This process is crucial for the body’s ability to regulate water, salt, minerals and acidity.
Nephron Endowment: The functional kidney mass at birth
Each kidney has about one million nephrons and filters about 150 liters of blood every day. Babies born at term have their complete number of nephrons. Adults cannot generate any new nephrons. However, as the body grows, the nephrons and the kidneys grow by enlargement of the glomeruli, tubules, and supporting structures. The number of nephrons a person is born with is called nephron endowment.
Many variables can lower that number including poor maternal health, diet or smoking during pregnancy. The use of steroids or alcohol, iron, vitamin A or vitamin D deficiencies during pregnancy were also linked to smaller child kidneys with a smaller number of nephrons at birth. It has been shown that a decrease in the nephron endowment is associated with a declinein kidney function and high blood pressure in adults. So, in summary, the number of nephrons at birth is a risk factor for kidney disease and high blood pressure.
Birth Weight and the Functional Kidney Mass
In most studies, reduced nephron endowment was associated with reduced birth weight. People who were born with a weight of <2.5 kg (<5.5 lbs) were found to be at higher risk for ending up with kidney failure requiring dialysis. In addition, preterm babies were also noted to be at an increased risk for decreased kidney function in adulthood. What happens is that with low nephron numbers at birth, the remaining nephrons enlarge and work harder leading to their accelerated aging and loss. This is worsened with any “catch up” after-birth growth and even obesity. Simply put, low birth weight is associated with a low number of nephrons at birth which increases the risk for kidney disease and high blood pressure.
The Role of Genetics and Epigenetics
The development of the human kidney is influenced by genetic and epigenetic factors. The deletion or alteration of a few genes has been associated with small kidneys and a decreased number of nephrons. The expression of some of these genes can be influenced by the nutritional health of the pregnant mother. What is more interesting is that the poor health of a pregnant mother not only affects the development of the kidneys of her children but also affects her grandchildren and further generations even if the new generations were born to well-nourished mothers. Throughout the world, small maternal stature is the most common risk factor associated with low birth weights. This is presumed to be caused by generations of nutritional deprivation and its effect on gene expression.[bctt tweet=”The poor health of a pregnant mother not only affects the development of the kidneys of her children but also affects her grandchildren and further generations even if the new generations were born to well-nourished mothers” username=””]
Bottom Line
If you are born with low birth weight or preterm you are at a higher risk for kidney disease and high blood pressure. Nutritional, genetic and epigenetic factors play an important role. Modifying gene expression with nutrients in these circumstances might be helpful and is being researched.
References:
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