Fluid and Electrolyte Balance in the Human Excretory System

What is the primary function of the excretory system?

To regulate water content of the body and ion concentration in body fluids.

What is osmoregulation?

The maintenance of osmolarity of body fluids by the kidneys.

What happens if blood volume decreases significantly?

Blood pressure can fall dangerously low, preventing the heart from pumping effectively.

What is the main nitrogenous waste product generated from protein metabolism?

Ammonia (NH3).

What is urea?

A nitrogenous waste product that humans have a relatively high concentration of in the blood.

How does the body primarily excrete nitrogenous waste?

Humans primarily use urea for excretion.

What is the most toxic nitrogenous waste product?

Ammonia (NH3).

What type of nephrons reside in the renal cortex?

Cortical nephrons.

What are the two types of nephrons?

Cortical nephron and juxtamedullary nephron.

What are the components of the nephron?

Glomerulus and tubule.

What is the function of the glomerulus in the nephron?

It is a ball of capillaries where filtration occurs.

What is filtrate?

A fluid consisting of water, ions, and small organic molecules filtered from blood.

What does the term 'reabsorption' mean in the context of nephron function?

The movement of substances from the tubule back into the blood.

What does the term 'secretion' mean in the context of nephron function?

The movement of substances from the blood into the tubule.

What is the role of the Loop of Henle?

To facilitate the reabsorption of water and ions.

How does the distal tubule differ from the proximal tubule?

The distal tubule's processes are more regulated compared to the proximal tubule.

What is the function of antidiuretic hormone (ADH)?

To increase water reabsorption in the kidneys by making collecting ducts more permeable to water.

What is the function of renin in the kidney?

To activate the renin-angiotensin-aldosterone system (RAA) which regulates blood pressure.

What does angiotensin II do?

It stimulates the release of aldosterone and causes vasoconstriction of arterioles.

What is the result of aldosterone secretion?

Increased sodium and water reabsorption, raising blood volume and pressure.

What triggers the release of Atrial Natriuretic Hormone (ANH)?

Overfilling of the heart's atria due to increased blood volume.

What is the role of urodilatin?

To lower blood pressure by having effects similar to ANH on the collecting duct.

What is the structure that collects urine from the nephron?

Renal pelvis.

How much blood flow through the kidneys compared to other organs?

25 times more blood flow through the kidney than the average of other organs.

What type of cells compose the inner layer of the bowman's capsule?

Podocytes.

What determines the net filtration pressure in the bowman's capsule?

Capillary blood pressure minus osmotic pressure and hydrostatic pressure in the lumen.

How does the kidney handle fluid exchange across capillaries?

It has high pressure driving fluid out and osmotic pressure drawing fluid back in.

What occurs at the end of the nephron?

Urine is excreted and is not modified after leaving the tubule.

What happens in the collecting duct when dehydrated?

Water and urea are reabsorbed to conserve water.

What happens in the collecting duct when a person is overhydrated?

It becomes impermeable to water, allowing excess water to be excreted.

What creates the osmotic gradient necessary for water reabsorption in the nephron?

The reabsorption of solutes creates a gradient that drives water movement.

What are the structural adaptations of nephron epithelial cells?

They are polarized, with different functions on the apical and basal sides.

What process is used to transport sodium ions in the proximal tubule?

Active transport via the sodium-potassium pump.

What is the primary energy source for the sodium-potassium pump?

ATP.

How does alcohol affect kidney function?

It blocks the secretion of ADH leading to increased urine output.

What feature of collecting ducts allows for regulation of water retention?

Adjustable permeability controlled by hormones.

What is back pressure in the context of the nephron?

Fluid movement in the nephron caused by the displacement of interstitial fluid.

What does countercurrent exchange refer to?

The exchange between two fluids flowing in opposite directions in the kidney.

How does the body regulate kidney function during periods of high plasma osmolarity?

ADH is released to promote water reabsorption.

Why is reabsorption of solutes important in the nephron?

It helps maintain homeostasis and fluid balance in the body.

What role do tight junctions play in nephron cell function?

They limit diffusion of materials between cells, helping control movement across the epithelium.

How are materials transported into the peritubular capillaries from the nephron?

By diffusion down a concentration gradient.

What is the main effect of the renin-angiotensin-aldosterone system?

To increase blood volume and pressure.

What types of nephrons are involved in producing concentrated urine?

Juxtamedullary nephrons with long loops of Henle.

What occurs when there is high sodium and low water reabsorption?

Blood pressure decreases.

What factors lead to the secretion of renin from the juxtaglomerular apparatus?

Low blood pressure or decreased sodium chloride flow in the distal tubule.

What change occurs in the collecting duct when ADH is present?

Aquaporins are inserted into the apical membrane, increasing water reabsorption.

What effect does aldosterone have on potassium ions?

Stimulates their secretion from blood into the tubule for excretion.

What is the effect of ANH on the kidney?

It inhibits sodium and water reabsorption, decreasing blood pressure and volume.

What hormone influences thirst in response to plasma osmolarity?

ADH.

What does ADH do to arterioles throughout the body?

Stimulates vasoconstriction, raising blood pressure.

What happens to glucose levels in the urine during untreated diabetes mellitus?

Glucose levels are elevated due to inability to reabsorb glucose effectively.

What is the primary purpose of the countercurrent multiplier system in the kidney?

To create a concentration gradient to promote water reabsorption.

What occurs in the Loop of Henle's descending limb?

Facilitates passive water reabsorption.

What does the vasa recta do in the nephron?

It participates in the countercurrent exchange and helps maintain osmotic balance.

What happens when the body is dehydrated in terms of urine production?

Less urine is produced and it becomes more concentrated.

What is the function of the proximal tubule?

To reabsorb nutrients, ions, and water from the filtrate.

What do podocytes do in the nephron?

Form filtration slits that help control what is filtered from the blood.

What is an important characteristic of the glomerular capillaries?

They are highly permeable and under high pressure.

What can inhibit the secretion of renin?

Increased blood pressure or blood volume.

What effect does the release of ADH have during water deprivation?

It increases water reabsorption to conserve water.

What promotes water reabsorption during states of dehydration?

The presence of ADH increases permeability of collecting ducts to water.

What is the hormonal response to increased blood pressure and volume?

Secretion of Atrial Natriuretic Hormone (ANH).

What structure is responsible for filtering blood in the nephron?

Glomerulus.

What distinguishes the loop of Henle of juxtamedullary nephrons from cortical nephrons?

Juxtamedullary nephrons have a longer loop of Henle.

What do the ascending limb and descending limb of the Loop of Henle respectively transport?

Descending limb only water; ascending limb only ions.

How does fluid move through the nephron?

Driven by differences in pressure throughout the nephron.

What is the primary role of the renal pelvis?

To collect urine from the nephrons and channel it to the ureter.

What is required for the reabsorption of water in the proximal tubule?

A concentration gradient created by solute reabsorption.

What happens to secretion and reabsorption as fluid progresses through the nephron?

Active transport mechanisms adjust solute concentrations and volumes.

What effects can occur due to excessive angiotensin II?

Increased blood volume, blood pressure and stimulation of aldosterone secretion.

What physical structure do nephrons create during embryonic development?

A double-walled cup known as the Bowman’s capsule.

Why is kidney function critically important for overall health?

It helps regulate homeostasis, including fluid and electrolyte balance.

What occurs in nephron cells in response to changes in osmolarity?

They adjust reabsorption and secretion processes to maintain balance.