©2016 by UVa Health System. Division of Endocrinology.

FACTS ABOUT THE KIDNEY

AND

HYPERTENSION

 What are the effects of Hypertension?

Your heart works to pump blood around your body, so your arteries need to be both strong and elastic to accommodate for blood flow. High blood pressure not only places stress on your heart to work harder, it also deteriorates artery walls causing fat buildup in the arteries, called atherosclerosis. This build up makes it harder for blood to move through arteries and can prevent blood from moving around the body, leading to ischemia or when an organ cannot get the oxygen blood is supposed to deliver.

Basic Overview:

Causes of Hypertension

Humans have two kidneys. The main function of the kidney is to expel wastes from our body by filtering blood that passes through it. The basic functional unit of the kidney is known as the nephron and it is responsible for reabsorbing any essential nutrients, electrolytes, and ions that were filtered from the blood alongside wastes. Blood vessels that pass through the kidney's can be damaged due to chronic hypertension resulting in kidney damage or even renal failure.

Hypertension can develop from a number of factors such as smoking, lack of physical activity, and excessive salt intake. However, genetics can also play a factor. Our genes can provide an understanding of how easily our bodies may or may not be affected by salt intake. This is known as salt sensitivity of blood pressure.

What is the function of the kidney?

The nephron is the functional unit of the kidney, and there are many nephrons in each kidney. A group of blood vessels called the glomerulus are packed into a cup like structure at the beginning of the nephron. Glomeruli act much like Brita filters. They retain large and essential molecules in the blood and accumulates small molecules in a liquid solution called the ultrafiltrate which is ultimately expelled from the body as urine. Blood vessels also surround the kidney, providing it with the oxygen and nutrients it needs to function. They wrap around the nephrons to reabsorb any essential nutrients or ions from the ultrafiltrate as it passes through the nephron.

Effects on the Heart:

Fat build up in the arteries that supply blood to the heart can result in coronary artery disease. Because fat build up makes the lumen of the arteries more narrow, the heart works harder to pump blood through your body. As a result, the heart muscle grows larger and stiffens. Because the heart grows to accommodate harder work, it becomes more difficult to get enough oxygen to this muscle. This leads to ischemic damage, or when the heart doesn't get enough oxygen to sustain the muscle, potentially leading to heart failure.

Effects on the Brain:

Small arteries deliver blood to your brain; when atherosclerosis occurs in those arteries or when they become too stressed, your brain does not get enough oxygen and nutrients. When blood cannot get to certain parts of the brain at all, this is an ischemic stroke. When blood pressure in the brain is so high that the small vessels burst, this is a hemorrhagic stroke. On a smaller scale than stroke, if certain parts of the brain are not getting the nutrients they need, then they can become damaged, leading to vascular dementia.

 

Effects on the Kidney:

The clusters of tiny vessels that filter your blood in your kidneys  the glomeruli  can be damaged by high blood pressure. This damage is called glomerulosclerosis. High blood pressure can also damage the arteries that deliver blood to your kidneys, resulting in kidney disease or even kidney failure. This damage renders your kidney less efficient in filtering wastes out of your body resulting in dangerous levels of toxic waste buildup within the body.

The consequences of hypertension can be severe, which is why being able to manage blood pressure is so important. We are still learning important information about blood pressure management with our study focusing on diet and the salt sensitivity of hypertension. In particular, we are looking at how study participants’ with certain genes GRK4 and SLC4A5 respond to changes in dietary salt intake. We believe that certain people with a genetic predisposition for salt sensitivity are susceptible to adverse cardiovascular events. In salt sensitive individuals, the normal blood pressure drop at night that allows our systems to heal is missing*. However, this also leaves us information about who will benefit from diet changes. Ultimately, it is our aim to use the findings from this study to develop a drug to mitigate the effects of hypertension due to high salt intake by inhibiting the aforementioned proteins.

Basic Overview:

Anatomy of the Kidney

What is salt sensitivity?

The general public has the misconception that "high salt intake will result in high blood pressure." This, however, is not always true. Salt sensitivity is defined as your body's response to sodium by either increasing or decreasing your blood pressure. Each individual is unique in the way their body responds to different levels of sodium.

Some individuals may be salt sensitive. Others may be salt resistant. Still others may have inverse salt sensitivity. The definition of these terms are provided below:

Basic Overview:

Blood Pressure Measurements

Kidney functions requires a lot of blood vessels in order to obtain enough oxygen and nutrients to function well. Hypertension results in damaged blood vessels, which in turn, hinders the performance of the kidney due to a lack of adequate resources. Damaged kidneys do not filter blood well and fail to regulate blood pressure, eventually resulting in kidney disease then potentially renal failure.

Our study focuses on the proteins that act to move sodium out of the blood and into the urine. One of these proteins is GRK4, encoded by the GRK4 gene.  This protein can act in the proximal convoluted tubule to block the message that the body should excrete sodium when there is too much sodium in the blood. The second protein is SLC4A5, encoded by the SLC4A5 gene. This protein is a cotransporter that moves sodium and bicarbonate back into the blood from the ultrafiltrate so they do not get excreted from the body.

 

 

 

Taking Blood Pressure

Our study looks at changes in blood pressure; measuring blood pressure is an integral part of our research. Specifically, we use mean arterial blood pressure to measure how your body responds to changes in sodium intake. Based on your change in blood pressure over the course of the two-week diet, we can tell if you are salt sensitive, salt resistant, or inverse salt sensitive.

Basic Overview:

Blood Pressure Measurements

Salt sensitivity is defined as a major increase in blood pressure in response to high salt intake.

Salt resistance is defined as a minimal or no increase in blood pressure in response to high salt intake.

Inverse salt sensitivity is defined as a paradoxical decrease in blood pressure in response to high salt intake.