MCAT Biology Chapter 10: Homeostasis, Renal Physiology & Skin Thermoregulation

What is the primary role of the excretory system?

To maintain internal balance in the body.

How does the excretory system regulate blood pressure?

By controlling how much water and sodium are retained or excreted.

What does the excretory system regulate in terms of blood composition?

Blood osmolarity, or the concentration of solutes in the blood.

What is the significance of acid-base balance in the excretory system?

It keeps the blood pH within a narrow, life-compatible range.

What type of wastes does the excretory system remove?

Nitrogenous wastes, which are toxic byproducts of protein and nucleic acid metabolism.

What organ is primarily responsible for the functions of the excretory system?

The kidneys.

What is the functional unit of the kidney?

The nephron.

What are the main components of the excretory system?

Kidneys, ureters, urinary bladder, and urethra.

What is the role of the renal artery in the excretory system?

It brings blood into the kidney for filtration.

What happens to blood after it is filtered by the kidneys?

It exits through the renal vein into the vena cava.

What is the function of the ureters?

To transport urine from the kidneys to the urinary bladder.

What is the role of the urinary bladder?

To store urine temporarily until elimination.

What is the pathway of urine from the kidneys to the outside of the body?

Kidneys → renal pelvis → ureters → urinary bladder → urethra.

What is the outermost layer of the kidney called?

The fibrous capsule.

What is the cortex of the kidney responsible for?

It contains the glomeruli and initial filtration structures of the nephron.

What is the medulla's role in the kidney?

It plays a key role in urine concentration.

What is the renal hilum?

The entry and exit point for blood and urine in the kidney.

What is unique about the kidney's blood flow system?

It has a portal system with two capillary beds arranged in series.

What is the function of the glomerulus?

To filter blood and form filtrate.

What is the role of the efferent arteriole in the nephron?

It carries blood away from the glomerulus after filtration.

What is the function of the vasa recta?

To support reabsorption and secretion in the nephron.

What happens to fluid and small solutes in the glomerulus?

They are pushed out of the bloodstream and into the nephron to form filtrate.

What is the main function of the nephron?

To perform filtration, reabsorption, and secretion.

What is the renal pelvis's function?

To act as a collecting area that funnels urine out of the kidney.

How does the kidney maintain specific pressure conditions?

By having blood enter through an arteriole, pass through capillaries, and leave through another arteriole.

What is the primary job of the nephron?

To stabilize the internal environment through its combined activities.

What is the primary function of capillary beds in the kidney?

They provide fine control over what ends up in the urine versus what is kept in the body.

What is Bowman's capsule?

A structure that collects filtrate produced when fluid leaves the glomerular capillaries.

What is the role of the proximal convoluted tubule (PCT)?

It is the major site of reabsorption, reclaiming water, ions, glucose, and amino acids.

What does the loop of Henle establish in the kidney?

An osmotic gradient critical for controlled water reabsorption.

What is the function of the distal convoluted tubule (DCT)?

It fine-tunes the composition of urine based on hormonal signals.

What is the collecting duct's role in urine formation?

It determines the final urine concentration and adjusts water reabsorption.

What is the detrusor muscle?

A specialized smooth muscle layer in the bladder that contracts during urination.

What controls the internal urethral sphincter?

It is made of smooth muscle and is under involuntary control.

What is the external urethral sphincter composed of?

Skeletal muscle, allowing voluntary control over urination.

What does osmoregulation refer to?

The kidney's ability to regulate blood volume and osmolarity by adjusting urine composition.

How do kidneys respond when the body is dehydrated?

They conserve water and produce a low volume of concentrated urine.

What happens when blood volume is high and blood osmolarity is low?

The kidneys excrete excess water, producing a high volume of dilute urine.

What are the three main kidney processes?

Filtration, secretion, and reabsorption.

What drives the filtration process at the glomerulus?

A balance of physical forces known as Starling forces.

What is glomerular hydrostatic pressure?

The pressure of blood inside the glomerular capillaries that pushes fluid into Bowman's space.

What opposes filtration in the kidneys?

Blood oncotic pressure and hydrostatic pressure within Bowman's space.

What is the net effect of filtration in the kidneys?

Fluid is pushed out of the blood and into the nephron due to higher glomerular hydrostatic pressure.

What is the fluid that enters Bowman's space called?

Filtrate.

What is the primary job of the urinary bladder?

To temporarily store urine before it is eliminated from the body.

What happens to the detrusor muscle during urination?

It contracts to facilitate the release of urine.

What is the significance of the osmotic gradient established by the loop of Henle?

It creates conditions necessary for controlled water reabsorption.

How does the DCT adjust solute levels in the body?

It responds to hormonal signals to make targeted decisions about solutes.

What is the relationship between urine concentration and blood osmolarity?

High blood osmolarity leads to concentrated urine, while low osmolarity leads to dilute urine.

What is the role of hormonal signals in the collecting duct?

They regulate the permeability of the duct, affecting urine concentration.

Why is the nephron's organization important for kidney function?

It allows for constant exchange between the tubule and bloodstream, facilitating regulation.

What happens to urine after it is formed in the nephron?

It drains toward the renal pelvis for elimination from the body.

What does filtrate resemble in composition?

Blood plasma, but does not contain proteins or blood cells.

What is the filtration barrier's role?

It allows water and small solutes to pass while retaining larger molecules and cellular components.

How much fluid do the kidneys filter per day?

About 180 liters.

What is the purpose of secretion in the kidneys?

To remove substances present in excess or not efficiently filtered at the glomerulus.

What distinguishes secretion from filtration?

Secretion is an active, targeted process, while filtration is driven by pressure and is relatively nonselective.

What are common substances that are secreted by the kidneys?

Hydrogen ions, potassium ions, ammonia, various drugs, and metabolic waste products.

How does secretion contribute to acid-base balance?

By secreting hydrogen ions into the nephron, it helps lower blood acidity.

What is reabsorption in the context of kidney function?

The movement of water and useful solutes from the filtrate back into the bloodstream.

What substances are typically reabsorbed during reabsorption?

Glucose, amino acids, vitamins, and most of the filtered water.

Which hormone increases water reabsorption in the kidneys?

Antidiuretic hormone (ADH).

What is the role of aldosterone in kidney function?

It increases sodium reabsorption, promoting water retention and regulating blood volume and pressure.

What happens to the filtrate after all three kidney processes?

What remains in the tubule becomes urine.

What is the proximal convoluted tubule (PCT) known for?

It is the site of bulk reabsorption and also an important site of secretion.

What substances are reabsorbed in the PCT?

Glucose, amino acids, soluble vitamins, sodium, chloride, bicarbonate, and a large fraction of water.

What is the defining feature of the descending limb of the loop of Henle?

It allows water to move but does not allow salt to move.

What happens to the filtrate as it moves down the descending limb?

Water leaves the filtrate by osmosis, concentrating the fluid inside the tubule.

What is the countercurrent multiplier system?

It is created by the opposing flow of blood in the vasa recta and filtrate, allowing efficient water removal.

What is the role of the ascending limb of the loop of Henle?

It is permeable to salt but impermeable to water, diluting the filtrate as sodium and chloride ions leave.

What is the distal convoluted tubule (DCT) responsible for?

Fine control of reabsorption, responding to hormonal signals like aldosterone.

How does sodium reabsorption in the DCT affect blood volume?

As sodium is reabsorbed, water follows, influencing blood volume and blood pressure.

What is the overall purpose of filtration, secretion, and reabsorption in the kidneys?

To precisely control blood composition while efficiently removing waste.

What is the significance of the nephron's structure in kidney function?

Each segment is specialized to handle different regulatory tasks for blood volume, osmolarity, electrolytes, and pH.

What is the end product of the kidney's filtration processes?

Urine.

What is the primary function of the kidneys?

To maintain homeostasis by regulating the composition of blood and excreting waste.

What does the term 'osmoregulation' refer to?

The process of maintaining the balance of water and solutes in the body.

What is the importance of the filtration barrier in the kidneys?

It selectively allows substances to pass based on size and charge, protecting the bloodstream from large molecules.

What happens to substances that are not reabsorbed during kidney function?

They remain in the filtrate and are eventually excreted as urine.

What is the role of the distal convoluted tubule (DCT) in the kidneys?

The DCT secretes hydrogen and potassium ions, playing a key role in electrolyte balance and acid-base regulation.

What is the function of the collecting duct in the nephron?

The collecting duct is the last major decision point before urine leaves the nephron, responsive to aldosterone and ADH, with variable permeability to water.

How does ADH affect the permeability of the collecting duct?

When ADH levels are high, the collecting duct becomes more permeable to water, leading to increased water reabsorption and concentrated urine.

What happens when ADH levels are low in the collecting duct?

The collecting duct remains relatively impermeable to water, resulting in the excretion of dilute urine.

What is the renin-angiotensin-aldosterone system (RAAS)?

RAAS is a hormonal system activated by low blood pressure or volume, starting with renin release from the kidneys.

What does renin do in the RAAS pathway?

Renin converts angiotensinogen, released by the liver, into angiotensin I.

What is the role of angiotensin-converting enzyme (ACE) in the RAAS?

ACE converts angiotensin I into angiotensin II as it circulates through the lungs.

What effect does angiotensin II have on the adrenal cortex?

Angiotensin II stimulates the adrenal cortex to release aldosterone.

What is the primary effect of aldosterone on the kidneys?

Aldosterone increases sodium reabsorption in the distal convoluted tubule and collecting duct, which raises blood volume and blood pressure.

How does aldosterone affect potassium and hydrogen ions?

Aldosterone promotes the excretion of potassium and hydrogen ions, helping to regulate electrolyte balance and pH.

What is the relationship between aldosterone and blood osmolarity?

Aldosterone increases blood volume and pressure without significantly changing blood osmolarity, as sodium and water are reabsorbed together.

What triggers the release of antidiuretic hormone (ADH)?

ADH release is triggered by low blood volume and high blood osmolarity.

What is the primary action of ADH in the kidneys?

ADH increases the permeability of the collecting duct to water, promoting water reabsorption.

What happens to blood volume and osmolarity when ADH levels are high?

High ADH levels increase blood volume and blood pressure while decreasing blood osmolarity.

How do the kidneys regulate blood pH?

The kidneys adjust blood pH by selectively reabsorbing or secreting bicarbonate and hydrogen ions.

What is the primary function of the skin in homeostasis?

The skin serves as a protective barrier, preventing water loss, pathogen entry, and physical damage.

How does the skin contribute to immune defense?

Cells within the skin detect and respond to invading microorganisms, preventing deeper spread.

What role does the skin play in temperature regulation?

The skin regulates temperature through sweating and changes in blood flow near the surface.

What sensory functions does the skin provide?

The skin contains specialized nerve endings that detect temperature, pain, pressure, and touch.

What is the significance of keratin in the epidermis?

Keratin is a tough, fibrous protein that gives the skin strength and resistance to wear.

What is the primary function of the epidermis?

The primary function of the epidermis is protection, forming a barrier against pathogens and preventing water loss.