Renal Physiology Overview

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How do the kidneys maintain blood pH balance?

By excreting the acidic and alkaline waste products, or by stopping their reabsorption.

Which hormone directs the kidneys to keep the balance between electrolytes?

Aldosterone

Aside from acid-base balance, what three things do the kidneys do that affect the blood?

Kidneys can adjust blood volume, composition, and pressure

How do the kidneys adjust the blood volume?

By adjusting how much water is lost in the urine

What two hormones tells the kidneys how much water to excrete?

Aldosterone and ADH

What effect does aldosterone have on the kidneys themselves?

They cause the kidneys to increase sodium reabsorption. Since water follows the sodium, water is reabsorbed as well.

How do the kidneys affect blood composition?

By increasing RBC production

How do the kidneys increase RBC production?

By releasing erythropoietin, a hormone that signals the bone marrow to make more RBCs

How do the kidneys affect blood pressure?

By secreting renin

Release of renin does what to blood pressure?

Increases blood pressure

In what three ways does the sympathetic nervous system affect the kidneys?

Changes the rate of blood flow to the glomerulus

Stimulates the release of renin

Changes water and sodium reabsorption

How does the sympathetic nervous system affect the rate of blood flow to the glomerulus?

Changes the rate of blood flow (and therefore, the pressure) to the glomerulus by telling the precapillary sphincters when to contract or relax

What does it mean when the plasma is too concentrated (high osmotic pressure)?

There are many electrolytes and not enough water inside the blood vessels

If a person's plasma is too concentrated, is their osmotic pressure high or low?

High

What condition can cause osmotic pressure to be too high?

Dehydration

If water is drawn out of cells what will it cause them to do?

Shrink

What does it mean when plasma is too dilute?

There is too much water and too few electrolytes inside the blood vessels

What condition can cause low osmotic pressure?

Over-hydration

When plasma osmotic pressure is too low, what will it do to the nearby cells?

Make them swell

What affect does Aldosterone have on the kidneys, and how does this affect blood pressure?

It causes them to reabsorb more sodium. This will cause water to also be reabsorbed. Blood pressure will then go up.

When osmotic pressure is too high, what other endocrine gland secretes a hormone, and what is the name of the hormone?

Adrenal cortex, releases aldosterone

How does blood pressure affect the GFR?

The higher the blood pressure, the higher the GFR

What can also control how much blood pressure is in the glomerulus?

The pre-capillary sphincters

Name the 3 different mechanisms that can change the diameter of the afferent and efferent arterioles to alter the GFR

Hormones

Autonomic Nervous System

Autoregulation or local (smooth muscle sphincters around arterioles or capillaries near the glomerulus)

What is Tubular Reabsorption?

The removal of water and solute molecules from filtrate after it enters the renal tubules. These are then transferred back into the bloodstream.

What substances are reabsorbed?

Water and solutes

Describe the pathway that fluid takes in the nephron.

Fluid goes from the glomerulus to the proximal convoluted tubule (PCT), down the loop of Henle and back up, then into the distal convoluted tubule (DCT), and into the collecting duct.

Where are nutrients reabsorbed in the nephron?

Where do the excess nutrients (such as glucose) go if they are not absorbed?

In the Proximal Convoluted Tubule


Into the Urine

When the nutrients in the PCT (proximal convoluted tubule) are reabsorbed, what will happen to the water in the tubule?

Where does this occur in the nephron?

It moves from its high concentration (in the PCT) to its low concentration, so it will leave the tubule and enter the bloodstream.

Water is reabsorbed in the DCT.

What types of solutes are left by the time the fluid gets to the collecting tubule?

Ammonia, urea, bilirubin (all waste products)

Name the capillaries that follow the tubules longitudinally.

Name the capillaries that wrap around the tubules.

Vasa recta


Peritubular capillaries

What is the name of the space between the peritubular capillaries and the tubules?.

Peritubular space

How is water reabsorbed in the PCT?

Osmosis

What primarily causes water osmosis in the PCT?

It occurs after reabsorption of sodium

What condition can cause low sodium levels?

Excessive sweating (physical activity). Sweat is salty, so salt (sodium and chloride) is lost.

What is the difference between ADH and Aldosterone, and in what conditions does the body need one or the other?

-ADH will only raise the water levels in the bloodstream (needed during dehydration from not drinking enough water).
-Aldosterone will raise the water and salt levels in the bloodstream (needed if there is excessive sweating, which causes loss of water and salt)
-Both may be released if blood pressure or blood volume is too low, but if you do not need the salt, there will be more ADH than aldosterone.

What are two examples of substances which are unable to filter through the glomerulus, but are not wanted by the body?

How do we get rid of these substances?

pollutants like pesticides and many drugs.


These substances are removed as they pass through the peritublar capillaries directly into the PCT & DCT

When waste products are dumped from the peritubular capillaries into the tubules, what is this process called?

Tubular secretion

What is the juxtaglomerular apparatus (JGA)?

A group of cells next to the glomerulus. They fill in the space between the glomerulus and the distal convoluted tubule.

What are the two main cell types in the JGA?

Macula densa cells and juxtaglomerular cells

What does the Juxtaglomerular apparatus do?

Alters BP and GFR

When blood pressure is too low, what hormone do the macula densa cells release?

-What effect does that hormone have on the nephron?
-What effect does that hormone have on the GFR?
-What effect does that have on blood pressure?

adenosine

-Adenosine causes vasoconstriction of the afferent arterioles (blood entering the nephron).
-This will slow the GFR, so less water is lost
-BP increases

If the BP is still too low after adenosine has caused vasoconstriction what enzyme is released by the juxtaglomerular cells?

What effect does this enzyme have on blood volume and blood pressure?

Juxtaglomerular cells secrete renin.

Renin causes more sodium to be reabsorbed, and water flows into the bloodstream, so blood volume increases, so BP increases.

How does renin work (directly)?

It makes the lungs secrete angiotensin-converting enzyme (ACE).

What effect does ACE have?

It cuts angiotensin-1 (A1) into angiotensin-2 (A2).

What two effects does A2 have?

It causes blood vessel constriction in the afferent arterioles of the nephron. It also stimulates the hypothalamus to secrete aldosterone releasing hormone, which causes the adrenal cortex to release aldosterone, which also increases blood pressure.

Where is aldosterone produced?

What is the effect of aldosterone?

Adrenal cortex


Sodium ions are pumped out of the kidney tubules and into the bloodstream.

Where is ADH produced?

What is the effect of ADH?
Is sodium included in this process?

Posterior pituitary gland

Causes retention of additional water from the DCT and collecting ducts.

Sodium is not included in this process.

By what three mechanisms can the kidney adjust blood volume, composition, and pressure?

1) Adjusting the volume of water lost in urine by responding to ADH or aldosterone
2) Releasing erythropoietin
3) Releasing renin and/or adenosine

If O2 levels are low, what hormone is released by the kidney, and what part of the kidney releases it? What is the effect of that hormone?

Erythropoietin is released from the JGA. It stimulates the bone marrow to produce more red blood cells

What part of the autonomic nervous system is activated during a fight or flight situation?

What effect does this part of the nervous system have on the kidneys?

Why do we need this effect during a fight or flight situation?

Sympathetic nervous system


Decreases renal blood flow (GFR)


The blood can be used for skeletal muscles

Sympathetic activation of the nerve fibers innervating the kidney causes what three effects?

-Changes in glomerular blood flow and pressure
-The stimulation of renin release from the juxtaglomerular apparatus
-Changes in water and Sodium reabsorption by the nephron

What ions are normally found in urine?

What other substances are normal in the urine?

sodium, chlorine, and potassium

suspended solids (sediments) such as cells, mineral crystals, mucus threads, and sometimes bacteria.

What three main things can change the pH of urine?

Food and drink that we ingest
Acids produced through metabolism
Changes in breathing rate

What can increase the concentration of urine?

Losing fluids, such as during sweating and diarrhea

What is a urinalysis used for?

To identify abnormal process occurring in the body

What six substances are never normal when found in the urine?

Glucose
Blood
Protein
Pus
Bilirubin
Ketones

What can cause glucose in the urine?

Diabetes mellitus

What can cause blood in the urine?

Urinary tract infection, trauma, kidney stones

What can cause proteins in the urine?

Kidney disease, hypertension, excessive exercise, pregnancy

What can cause pus in the urine?

Bacterial infection in the urinary tract

What can cause bilirubin in the urine?

Liver malfunction

What can cause ketones in the urine?

Ketones are the waste product of breaking down lipids (lipid metabolism). We break down lipids for energy when there is not enough glucose. Therefore, ketones are in the urine because of starvation or diabetes

What is urination technically known as?

What part of the autonomic nervous system is activated to allow urination?

What is the difference between the internal urethral sphincter and the external urethral sphincter?

Micturition

parasympatheitc nervous system

internal sphincter is smooth muscle (involuntary)
external sphincter is skeletal muscle (voluntary)

What are two clinical conditions where a diuretic is needed?

Hypertension and congestive heart failure

What is the overall effect of a diuretic?

Decreases plasma volume

What effect does a diuretic have on the renal tubules?

inhibit the reabsorption of sodium and potassium from the renal tubule, causing more water to pass out as urine

Compared to sodium, is the homeostatic range of potassium broad or narrow?

What does that mean?

Narrow.


If potassium levels are just a little too high or too low, the body will be out of homeostasis and needs to compensate or it might be fatal. Sodium levels can fluctuate a little more before it causes problems.

What type of diuretic inhibits reabsorption of potassium more than other diuretics?

Thiazide drugs such as Lasix (furosemide)

When a person is on Lasix, how do they need to be careful with their diet?

They need potassium supplements or they need to eat fruits and vegetables that have a lot of potassium, such as cantaloupe. Bananas do not have much potassium (you have to eat one bunch per day; lot of calories!)

What are low blood levels of potassium called?

Hypokalemia

What are high blood levels of potassium called? Is that dangerous also?

Hyperkalemia. Yes, it also can be fatal.

List four diuretic drugs:

Furosemide (Lasix)
Mannitol
Spironolactone
Amiloride

How does mannitol work as a diuretic?

Causes dieresis by reducing net water reabsorption from the PCT.

What is a potassium sparing diuretic?

One that allows for water dieresis without potassium excretion

What are two examples of potassium sparing diuretics?

Spironolactone and amiloride

Which diuretic causes the greatest degree of hypokalemia (loss of potassium)?

Furosemide (Lasix)

If plasma is too concentrated with particles, what happens to nearby cells?

shrink & lose their function

If plasma is too dilute, what happens to nearby cells?

water can enter the nearby cells and cause them to expand, also decreasing their function

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