Virginia Tech BMSP 2136 RAT #16

tubular reabsorption

If 180 L of fluid is filtered out each day, does that mean that we urinate out 180L a day? Of course not! We would rapidly dehydrate! That fluid needs to be absorbed back into the blood stream. That process is called __________ ____________________, and your kidneys are very efficient at it.

lipids

Bile serves two critical functions:

(1) It is required for the digestion and absorption of __________

(2) it is the mechanism by which the liver excretes wastes and other substances that the kidneys cannot excrete

peritubular capillary → peritubular capillary endothelial cells → interstitial fluid → tubule cells → tubule lumen

If a waste molecule is in the peritubular capillary lumen, which structures must it pass through in order to move into the tubule lumen?

paracellular

On the __________________ route, substances pass between adjacent tubule cells. The tight junctions between the tubule cells are just leaky enough to allow some substances such as small ions and water to move passively between them, particularly in the proximal tubule

transcellular

On the ___________________ route, substances such as glucose and amino acids must move through the tubule cells. A reabsorbed substance first crosses the apical membrane of the tubule cell, then travels through the cytosol, and finally exits the cell through the basolateral membrane (the side of the membrane facing the interstitial fluid).

apical membrane

the membrane facing the tubule lumen

basolateral membrane

the side of the membrane facing the interstitial fluid

facilitated diffusion

a carrier protein passively transports a solute with its concentration gradient, without using energy from ATP

primary active transport

a carrier protein "pump" directly uses ATP to move a solute against its concentration gradient

secondary active transport

a concentration gradient set up by a primary active transport pump is used to drive the transport of a second solute against its concentration gradient via another carrier protein

antiport pumps (antiporters)

move two or more solutes in opposite directions

Symport pumps (symporters)

move two or more solutes in the same direction

Transport maximum

when all the sites of transporters become filled, the carrier proteins are said to be saturated, as they have reached their ____________ _____________

microvilli

the cells of the proximal tubule have prominent _____________ that provide these cells with a large surface area. This facilitates the remarkably rapid reabsorption that occurs in this very active segment of the renal tubule.

proximal tubule

where is the most metabolically active part of the nephron?

proximal tubule

where is most filtrate reabsorbed?

secretion

In addition to all of this reabsorption, a great deal of ______________ takes place in the proximal tubule as well

glucose

Absorbed Substances in the Proximal Tubule

- electrolytes (sodium, chloride, potassium, sulfate, phosphate ions)

- nearly 100% of nutrients such as _____________, amino acids, and other organic solutes (e.g., lactic acid, water-soluble vitamins)

- many of the bicarbonate ions

- about 65% of the water

sodium is key to reabsorbing many other substances in the proximal tubule

Why is sodium ion reabsorption so important?

by the transcellular route through sodium ion leak channels on the apical surface of the proximal tubule cell

Sodium Ion Reabsorption

how does the majority of the sodium ion reabsorption occur?

facilitated diffusion

Sodium Ion Reabsorption

3 other transcellular sodium ion reabsorption methods involve carrier proteins located in the apical membranes of proximal tubule cells

(1) carrier proteins specific for sodium ions that enable _____________ ____________ of sodium ions from the filtrate into the tubule cells

glucose

Sodium Ion Reabsorption

3 other transcellular sodium ion reabsorption methods involve carrier proteins located in the apical membranes of proximal tubule cells

(2) Na+ symporters that bring sodium ions from the filtrate into the cells with other solutes (such as ___________)

filtrate

Sodium Ion Reabsorption

3 other transcellular sodium ion reabsorption methods involve carrier proteins located in the apical membranes of proximal tubule cells

(3) Na+/H+ antiporters that bring sodium ions into the cells while secreting hydrogen ions into the __________.

Na+/K+ pumps

Sodium Ion Reabsorption

Both the leak channels and the carrier proteins rely on a concentration gradient created by ________ ___________ in the basolateral membrane. These pumps continually drive sodium ions out of the tubule cells and into the interstitial fluid. This creates a relatively low sodium ion concentration in the cytosol of the proximal tubule cells

symporters

Reabsorption of Organic Solutes

Other ______________ in the apical membrane of the proximal tubule cells function in a similar fashion, allowing the secondary active transport of sodium ions and another solute, such as an ion (e.g., SO42− or HPO42−) or an organic solute (e.g., amino acids or lactic acid) from the filtrate into the tubule cell.

tubular secretion

Some waste substances are not filtered out. These substances can be moved into the tubule in order to remove them from the body in urine. That process is called ___________ ________________.

interstitial fluid

Reabsorption of Chloride Ions

As sodium ions are passively transported out of the tubule lumen, the lumen accumulates a net negative charge. This creates an electrical gradient that pushes the negatively charged chloride ions across the epithelium through the paracellular route. These chloride ions similarly follow sodium ions into the ______________ ___________ and into the plasma, as well

carbonic anhydrase

what is the name of the enzyme that catalyzes the bicarbonate reaction?

carbonic acid

Bicarbonate Ion Reabsorption

(1) Hydrogen ions secreted into the filtrate combine with bicarbonate ions to form ___________ __________.

carbon dioxide and water

Bicarbonate Ion Reabsorption

(2) Carbonic acid is converted, via carbonic anhydrase, to what?

bicarbonate and hydrogen ions

Bicarbonate Ion Reabsorption

(3) Carbon dioxide diffuses into the tubule cell cytosol and combines with water to become what?

into the interstitial fluid and then move into the blood

Bicarbonate Ion Reabsorption

(4) Bicarbonate ions are transported where?

filtrate

Bicarbonate Ion Reabsorption

(5) The process repeats as hydrogen ions are again secreted into the _________.

osmotic pressure

By the time the filtrate has reached the second half of the proximal tubule, many of the sodium ions as well as glucose and other organic compounds have been reabsorbed. The accumulation of solutes in the cytosol and interstitial fluid draws water out of the filtrate by osmosis along both paracellular and transcellular routes.

therefore, what creates the gradient that drives the passive reabsorption of water?

obligatory water reabsorption

Water reabsorption in the kidneys that occurs without the regulation of hormones and irrespective of the medullary concentration gradient

aquaporin

A kind of water channel in the plasma membrane called an _______________ greatly enhances rapid water reabsorption. These channels, which are located in both the apical and basolateral membranes of proximal tubule cells, allow water to move through these cells via the transcellular route.

sodium

Reabsorption of Chloride Ions

The reabsorption of __________ ions also leads to the reabsorption of anions such as chloride ions in another way, too.

ammonium

Secretion in the Proximal Tubule

Additionally, ________________ ions (NH4+), creatinine, and small amounts of urea are also secreted. Drugs such as penicillin and morphine have significant renal secretion.

water

Reabsorption in the Nephron Loop

The thin descending limb of the nephron loop is freely permeable to _________, but much less permeable to solutes such as sodium and chloride ions.

increase

Reabsorption in the Nephron Loop

because the descending limb is so permeable to water but not solutes, water can move out of the thin descending limb cells by osmosis, but few solutes follow. This causes the osmolarity of the filtrate to (increase/decrease) as it passes down the descending limb and rounds the bend of the loop.

NaCl

Reabsorption in the Nephron Loop

The cells of the thick ascending limb are impermeable to water, but they transport ________ into the tubule cells with the use of Na+/K+/2Cl− symporters

ascending

Reabsorption in the Nephron Loop

As filtrate passes through the (ascending/descending) limb, it loses solutes and gradually becomes less concentrated as ions are pumped into the interstitial fluid

85, 90

By the time the filtrate enters the first part of the distal tubule, about ___% of the water and ____% of the sodium ions have been reabsorbed

uric acid

Secretion in the Proximal Tubule

In addition to the hydrogen ion secretion, other substances are secreted into the filtrate by the proximal tubule cells, including many nitrogenous waste products and drugs. In the first half of the proximal tubule, most of the _____ ______ in the filtrate is reabsorbed, but nearly all of it is secreted back into the filtrate in the second half of the tubule

distal tubule

Reabsorption of the remaining water and sodium ions in the _________ _________ is still critical. If we excreted the remaining water and sodium ions in the urine, we would lose about 29 liters of water and a significant portion of our sodium ions every day. This situation would be incompatible with life.

facultative water reabsorption

Water reabsorption that is controlled by hormones to maintain a constant extracellular fluid osmolarity; water is reabsorbed in accordance with the body's needs, controlled via hormones

late distal tubule and cortical collecting duct

where does facultative water reabsorption occur?

aldosterone, ADH, ANP

what 3 hormones are involved in facultative water reabsorption?

water and chloride ions

Hormones Involved in Facultative Water Reabsorption

ALDOSTERONE

- steroid hormone released by the adrenal cortex

- interacts with the DNA of cells to increase their permeability to sodium ions and the number of their Na+/K+ pumps → increase the reabsorption of sodium ions from the filtrate and the secretion of potassium ions into the filtrate

- the above effects also indirectly cause reabsorption of what 2 things?

hydrogen

Hormones Involved in Facultative Water Reabsorption

ALDOSTERONE

- Aldosterone also stimulates secretion of _____________ ions into the filtrate by another type of cell found in the late distal tubule and cortical collecting duct, called intercalated cells.

diuresis

refers to losing body water to the urine

aquaporins

Hormones Involved in Facultative Water Reabsorption

ADH

- produced by the hypothalamus

- released from the posterior pituitary gland

- causes water retention and reduces urine output by causing ___________ to be inserted into the apical membranes of principal cells, permitting rapid water reabsorption

natriuresis

Hormones Involved in Facultative Water Reabsorption

ANP

- triggers ______________ = urinary excretion of sodium ions

- also inhibits release of ADH and aldosterone, causing fewer sodium ions (and also less water) to be reabsorbed, and so more sodium ions and water to appear in the urine.

water

the major modifications to filtrate that occur in the collecting ducts and papillary ducts:

(1) in the presence of ADH, they reabsorb large volumes of ____________

(2) urea moves into the interstitial fluid

(3) continue to reabsorb ions such as sodium, chloride, and bicarbonate from the filtrate

external body surface

the lining of the alimentary canal is actually considered an ___________ ___________ __________ because it is open to the outside on both ends.

Think of it like a paper towel roll—its outer surface is akin to the body's skin, and its inner surface is akin to the alimentary canal. Both its surfaces are in contact with the outside environment and thus are considered "external."

insulin, glucagon

the pancreas's endocrine secretions, the hormones _________ and ___________, are released from pancreatic islets into the blood and affect most cells in the body.

acinar cells

the pancreas's exocrine secretions are enzymes secreted primarily by clusters of _________ _______. These enzymes are released into ducts of the pancreas that empty into the alimentary canal, where they help with digestion.

retroperitoneal

The pancreas is mostly located in the left upper quadrant of the abdomen, where it extends from the duodenum to the spleen; most of it is (intraperitoneal/retroperitoneal).

(1) a wide head that contacts the duodenum,

(2) a middle body

(3) a thinner tail that tapers off toward the spleen

what are the regions of the pancreas?

acini

Acinar cells are modified simple cuboidal epithelial cells. They are found in clusters known as _______ (singular: acinus), each of which surrounds a small duct into which its cells secrete their products.

water, bicarbonate ions, and enzymes produced by pancreatic acinar cells

What is found in pancreatic juice?

main pancreatic duct, accessory pancreatic duct

What are the two ducts that deliver pancreatic juice to the duodenum?

Cholecystokinin (CCK), secretin

Name two hormones that stimulate pancreatic secretion.

liver

large pyramid-shaped organ in the right upper quadrant of the abdominopelvic cavity; functions include diverse metabolic activities, filtering blood from most abdominal organs, and bile production

gallbladder

smalls sac hollow organ on the liver's posterior side that stores and releases bile

right lobe, left lobe, caudate lobe, quadrate lobe

name the 4 lobes of the liver

falciform ligament

The right and left lobes of the liver are separated by a fold of visceral peritoneum called the __________ _____________, which also anchors the liver to the anterior abdominal wall.

hepatic artery

Numerous blood vessels enter and exit the liver at the porta hepatis, including the _________ __________, which brings oxygen-rich blood to the liver

hepatic portal vein

which blood vessel brings nutrient-rich, deoxygenated blood to the liver from multiple abdominal organs?

inferior vena cava

Hepatic veins, which drain blood from the sinusoids, empty into the __________ _______ __________ on the liver's superior surface.

liver lobule

What is the basic unit of the liver?

hepatocytes

what cell composes the liver lobule?

small central vein

what is found in the center of a liver lobule?

portal triad

At each of the six corners of the lobule, we find three structures collectively referred to as a __________ _______

(1) a branch of the hepatic artery called a hepatic arteriole

(2) a branch of the portal vein called a portal venule

(3) a small bile duct that carries bile.

what 3 structures compose a portal triad?

to produce bile

What is the main digestive function of the liver?

microvilli

the cells of the distal tubule lack significant _____________. most of the water reabsorption has already taken place, so the cells do not require extensive _____________ to reabsorb much of the remaining water and solutes

same answer

glycogen

Other Functions of the Liver

Nutrient metabolism

- the liver processes nutrients obtained from the diet.

- carbohydrates and proteins absorbed from the alimentary canal are delivered to the liver by the hepatic portal vein, and lipids by the hepatic arteries.

- within the liver, some of these nutrients are stored for later use, modified into another form, or used to synthesize other compounds.

- for example, some of the glucose taken in by the liver is stored in the form of _____________, and many of the dietary amino acids are used to synthesize plasma proteins such as albumin and clotting proteins.

alcohol

Other Functions of the Liver

Detoxification

- the liver detoxifies substances produced by the body, such as the previously mentioned bilirubin.

- In addition, the liver processes substances that we eat or drink, some of which are toxins harmful to the body (such as _____________).

- These substances are generally delivered to the liver first via the hepatic portal vein, where the liver converts them into less harmful materials that can be excreted in bile or in urine.

- The liver also metabolizes many drugs, such as antibiotics.

- Individuals with impaired liver function metabolize drugs more slowly than those with normal liver function, and the drugs remain in their systems much longer.

kidneys

Other Functions of the Liver

Excretion.

- recall that the liver directly excretes bilirubin in bile.

- Several other substances the liver processes are excreted in bile, particularly drugs such as certain antibiotics.

- The liver also modifies substances so that they can be excreted by the _____________

stores bile, concentrates it (removing water), and releases it when stimulated

What is the primary function of the gallbladder?

CCK (cholecystokinin)

What hormone triggers the release of bile?

produced by duodenal DNES cells

What is the source of CCK?

cystic duct

Which duct is connected to the gallbladder?

hepatopancreatic sphincter

The common bile duct joins the main pancreatic duct near the duodenum to form the hepatopancreatic ampulla. The ampulla is surrounded by a ring of smooth muscle called the _____________________ ________________, which controls the emptying of bile and pancreatic fluids into the duodenum.

detox

we don't have to ________, and we have our livers to thank for it. The liver is a magnificent organ that works tirelessly to convert harmful chemicals, or toxins, into nonharmful substances that can be excreted in bile or urine. There is simply no herbal supplement, foot pad, or magic bracelet that can even come close to doing the job our livers do every day. And what's more, the liver doesn't charge us for its services.

presence of lipids and partially digested proteins in the duodenum

What is its stimulus for release for CCK?

bile salts

the most potent stimulus for bile production and release is bile itself, specifically ______ _______

positive

bile salts are reabsorbed in the last section of the ileum and transported back to the liver through the hepatic portal vein. As bile salts re-enter the liver, bile secretion rises dramatically in a ____________ feedback loop. Bile secretion continues into the duodenum until the duodenum empties, at which point CCK and secretin levels decline.