Question

After 3 days in the hospital,Mr. Brown’s cardiovascular and respiratory conditions were still deteriorating, but Nurse Nan discovered something new. Mr. Brown’s urine output was almost nonexistent. Nurse Nan informed Dr. Collins, who was gravely concerned. Dr. Collins met with Mrs. Brown to tell her that her husband could not survive kidney failure. Mrs. Brown looked shocked. She then became very upset and angry. “What did you do, Dr. Collins? My husband had a heart attack, but his kidneys were fine; he’s never had a kidney problem! How could you let this happen?” Nurse Nan put her arm around Mrs. Brown’s shoulders and Dr.Collins handed her a tissue.

4. The cardiovascular system most directly controls/ affects which of the three functions of the nephron - glomerular filtration;tubular secretion;or tubular reabsorption? Type answer as one of the 3 choices given

5. Explain in your own words how Mr. Brown’s left heart failure relates to the function of the kidney answered for question 4.

6. Explain in your own words why Mr. Brown’s urine output was almost nonexistent.

Answer 1

When you have heart disease, your heart may not pump blood in the right way. Your heart may become too full of blood. This causes pressure to build in the main vein connected to your kidneys, which may lead to a blockage and a reduced supply of oxygen rich blood to the kidneys. This can lead to kidney disease.

4)

Glomerular filtration rate :
Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood.

Tubular Reabsorption and Secretion :
Tubular reabsorption occurs in the PCT part of the renal tubule. Almost all nutrients are reabsorbed, and this occurs either by passive or active transport. Reabsorption of water and some key electrolytes are regulated and can be influenced by hormones. Sodium (Na+) is the most abundant ion and most of it is reabsorbed by active transport and then transported to the peritubular capillaries. Because Na+ is actively transported out of the tubule, water follows it to even out the osmotic pressure. Water is also independently reabsorbed into the peritubular capillaries due to the presence of aquaporins, or water channels, in the PCT. This occurs due to the low blood pressure and high osmotic pressure in the peritubular capillaries. However, every solute has a transport maximum and the excess is not reabsorbed.

In the loop of Henle, the permeability of the membrane changes. The descending limb is permeable to water, not solutes; the opposite is true for the ascending limb. Additionally, the loop of Henle invades the renal medulla, which is naturally high in salt concentration and tends to absorb water from the renal tubule and concentrate the filtrate. The osmotic gradient increases as it moves deeper into the medulla. Because two sides of the loop of Henle perform opposing functions, it acts as a countercurrent multiplier. The vasa recta around it acts as the countercurrent exchanger.

Loop diuretics are drugs sometimes used to treat hypertension. These drugs inhibit the reabsorption of Na+ and Cl– ions by the ascending limb of the loop of Henle. A side effect is that they increase urination.

By the time the filtrate reaches the DCT, most of the urine and solutes have been reabsorbed. If the body requires additional water, all of it can be reabsorbed at this point. Further reabsorption is controlled by hormones, which will be discussed in a later section. Excretion of wastes occurs due to lack of reabsorption combined with tubular secretion. Undesirable products like metabolic wastes, urea, uric acid, and certain drugs, are excreted by tubular secretion. Most of the tubular secretion happens in the DCT, but some occurs in the early part of the collecting duct. Kidneys also maintain an acid-base balance by secreting excess H+ ions.

Although parts of the renal tubules are named proximal and distal, in a cross-section of the kidney, the tubules are placed close together and in contact with each other and the glomerulus. This allows for exchange of chemical messengers between the different cell types. For example, the DCT ascending limb of the loop of Henle has masses of cells called macula densa, which are in contact with cells of the afferent arterioles called juxtaglomerular cells. Together, the macula densa and juxtaglomerular cells form the juxtaglomerular complex (JGC). The JGC is an endocrine structure that secretes the enzyme renin and the hormone erythropoietin. When hormones trigger the macula densa cells in the DCT due to variations in blood volume, blood pressure, or electrolyte balance, these cells can immediately communicate the problem to the capillaries in the afferent and efferent arterioles, which can constrict or relax to change the glomerular filtration rate of the kidneys.

Urine is a waste byproduct formed from excess water and metabolic waste molecules during the process of renal system filtration. The primary function of the renal system is to regulate blood volume and plasma osmolarity, and waste removal via urine is essentially a convenient way that the body performs many functions using one process.
Urine formation occurs during three processes:

1. Filtration
2. Reabsorption
3. Secretion

Filtration :
During filtration, blood enters the afferent arteriole and flows into the glomerulus where filterable blood components, such as water and nitrogenous waste, will move towards the inside of the glomerulus, and nonfilterable components, such as cells and serum albumins, will exit via the efferent arteriole. These filterable components accumulate in the glomerulus to form the glomerular filtrate.

Normally, about 20% of the total blood pumped by the heart each minute will enter the kidneys to undergo filtration; this is called the filtration fraction. The remaining 80% of the blood flows through the rest of the body to facilitate tissue perfusion and gas exchange.

Reabsorption :
The next step is reabsorption, during which molecules and ions will be reabsorbed into the circulatory system. The fluid passes through the components of the nephron (the proximal/distal convoluted tubules, loop of Henle, the collecting duct) as water and ions are removed as the fluid osmolarity (ion concentration) changes. In the collecting duct, secretion will occur before the fluid leaves the ureter in the form of urine.

Secretion :
During secretion some substances±such as hydrogen ions, creatinine, and drugs—will be removed from the blood through the peritubular capillary network into the collecting duct. The end product of all these processes is urine, which is essentially a collection of substances that has not been reabsorbed during glomerular filtration or tubular reabsorbtion.

Urine is mainly composed of water that has not been reabsorbed, which is the way in which the body lowers blood volume, by increasing the amount of water that becomes urine instead of becoming reabsorbed. The other main component of urine is urea, a highly soluble molecule composed of ammonia and carbon dioxide, and provides a way for nitrogen (found in ammonia) to be removed from the body. Urine also contains many salts and other waste components. Red blood cells and sugar are not normally found in urine but may indicate glomerulus injury and diabetes mellitus respectively.

Heart plays a major role in maintaining the homeostasis of the body. As it pumps the blood to every part of the body to continue its function by providing nutrients to the tissues. Failure of heart may lead every organ function improperly. Even kidneys are affected with the diseased heart. Glomerular filtration may be effected with a diseased heart.

5)

As the left heart pumps the oxygenated blood directly to other parts. It pumps the blood to kidneys even. Due to less flow of blood to the kidneys, the filtration rate would become low. As a result waste materials would be high in blood and ions not be reabsorbed into the blood again. Thus leading the urine composition to abnormal state. This in return effects the function of kidney and reduces it's efficiency to filter. Therefore, it may be to kidney disease.

6)

Due to the malfunction of kidney as mentioned above the output in the urine may be abnormal. The ionic concentration would be effected and the body's ion exchange would be affected.

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