ch 20, 22, 23 MAIN

MAIN

Renal Hilum

The indented medial area of the kidney that serves as the point of entrance and exit for the renal artery, renal vein, ureter, nerves, and lymphatic vessels.

Renal Cortex

The outer superficial layer of kidney tissue situated directly beneath the renal capsule.

Renal Medulla

The inner region of the kidney located deep to the cortex, consisting of striated renal pyramids separated by renal columns.

Renal Pyramid

A triangular or cone-shaped tissue mass within the renal medulla whose base faces the cortex and whose apex terminates at a renal papilla.

Renal Papilla

The apex of a renal pyramid that projects into a minor calyx to discharge processed urine.

Minor Calyx

A cup-like structure that collects urine emerging directly from the papillary ducts of a renal papilla.

Major Calyx

A large urine-collecting channel formed by the convergence of several minor calyces that directs fluid into the renal pelvis.

Renal Pelvis

A broad, funnel-shaped basin that receives urine from all major calyces and channels it directly into the ureter.

Nephron

The microscopic structural and functional unit of the kidney responsible for filtering blood and processing filtrate into urine.

Afferent Arteriole

The larger-diameter blood vessel that delivers systemic arterial blood into the glomerular capillaries of the renal corpuscle.

Efferent Arteriole

The narrower blood vessel that drains blood out of the glomerulus, creating high hydrostatic pressure upstream within the glomerular capillaries.

Glomerulus

A specialized ball of fenestrated capillaries located inside the renal corpuscle where blood plasma is filtered.

Glomerular (Bowman's) Capsule

The double-walled epithelial cup that surrounds the glomerulus and collects fluid pushed through the filtration membrane into its capsular space.

Podocyte

A specialized octopus-like epithelial cell forming the visceral layer of the glomerular capsule that wraps around glomerular capillaries with foot processes.

Filtration Slits

Narrow clefts located between the interdigitating pedicels of podocytes that allow filtrate to pass into the capsular space while preventing the exit of proteins.

Glomerular Filtration Rate (GFR)

The total volume of filtrate formed each minute by all nephrons in both kidneys combined, averaging approximately $125\,mL/min$.

Hydrostatic Pressure

The mechanical pushing force that a fluid exerts against the walls of the vessel containing it, directing fluids from areas of higher pressure to lower pressure.

Colloid Osmotic Pressure (COP)

The inward osmotic pull generated by large, non-diffusible plasma proteins and cells that retains and reabsorbs water back into the capillary lumen.

Renal Autoregulation

The intrinsic dominant mechanism through which the kidney stabilizes GFR by altering the diameter of afferent and efferent arterioles despite fluctuations in systemic blood pressure.

Proximal Convoluted Tubule (PCT)

The coiled section of the renal tubule extending from the glomerular capsule where the vast majority of filtered solutes, nutrients, and water are reabsorbed into peritubular capillaries.

Nephron Loop (Loop of Henle)

A hairpin-shaped tubular segment consisting of descending and ascending limbs that establishes a counter-current exchange mechanism to concentrate urine.

Descending Limb of the Nephron Loop

The segment of the nephron loop that is permeable to water, allowing water to exit the tubule and be reabsorbed into the bloodstream via osmosis.

Ascending Limb of the Nephron Loop

The segment of the nephron loop that forms an impermeable barrier to water while permitting the transport of solutes, helping sustain medullary hypertonicity.

Distal Convoluted Tubule (DCT)

The twisted tubule segment following the ascending limb that is primary for tubular secretion and can be stimulated by aldosterone to reabsorb water and sodium.

Collecting Duct

A terminal tube that gathers fluid from multiple collecting tubules, responsive to ADH for final water recovery, before emptying into a renal papilla.

Renin

An enzyme released by the kidneys when urine osmolality becomes elevated or blood pressure drops, which initiates the production of angiotensin II.

Angiotensin II

A systemic hormone activated by renin that triggers the thirst center in the brain and stimulates the adrenal cortex to secrete aldosterone.

Aldosterone

An adrenal cortical hormone that stimulates the reabsorption of $Na^+$ in the renal tubules, thereby driving osmotic reabsorption of water to increase blood volume and pressure.

Atrial Natriuretic Peptide (ANP)

A cardiac hormone released by the heart when blood pressure rises that acts as an antagonist to aldosterone, promoting the urinary excretion of $Na^+$ and water.

Antidiuretic Hormone (ADH)

A hormone released from the posterior pituitary that promotes water reabsorption independently of salts by inducing the insertion of aquaporins into collecting tubules and ducts.

Aquaporins

Transmembrane water channel proteins inserted into the apical membranes of collecting tubule and duct cells in response to ADH to increase water permeability.

Micturition

The physiological discharge of urine from the urinary bladder, initiated by bladder stretch receptors triggering a spinal reflex.

Detrusor Muscle

The smooth muscle wall of the urinary bladder that contracts during micturition to push urine into the urethra.

Trigone

The smooth, triangular region located at the floor of the urinary bladder outlined by the two ureteral openings and the internal urethral orifice.

Internal Urethral Sphincter

The involuntary smooth muscle sphincter located closest to the urinary bladder that controls the entrance to the urethra.

External Urethral Sphincter

The voluntary skeletal muscle sphincter located within the deep muscles of the perineum that controls urine release from the body.

Body Fluid Compartments

The major functional divisions of total body water, consisting of intracellular fluid ($2/3$ of total fluid) and extracellular fluid ($1/3$ of total fluid, split into $2/3$ interstitial fluid and $1/3$ blood plasma).

Electrolytes

Mineral salts that dissociate into charged ions in solution, functioning to control osmosis, maintain acid-base balance, carry electrical currents, and serve as enzyme cofactors.

Physiological Buffers

Organ systems (specifically the kidneys and lungs) that regulate systemic acid-base balance by excreting ions or exhaling carbon dioxide, acting slower than chemical buffers but providing long-lasting effects.

Chemical Buffers

Fast-acting molecular solutions (bicarbonate, protein, and phosphate systems) that bind or release $H^+$ within seconds to temporarily stabilize pH until waste reaches the lungs or kidneys.

Protein Buffer System

The most abundant chemical buffer mechanism in intracellular fluid and blood plasma, using amino acids and hemoglobin to bond with free $H^+$ ions.

Respiratory Acidosis

An acid-base disturbance characterized by increased arterial $P_{CO_2}$ above $45\,mmHg$ and decreased blood pH below $7.35$, commonly caused by hypoventilation.

Respiratory Alkalosis

An acid-base disturbance characterized by decreased arterial $P_{CO_2}$ below $35\,mmHg$ and increased blood pH above $7.45$, commonly caused by hyperventilation.

Metabolic Acidosis

An acid-base disturbance characterized by decreased bicarbonate ($HCO_3^-$) below $22\,mEq/L$ and blood pH below $7.35$, commonly caused by diarrhea, ketosis, or renal dysfunction.

Metabolic Alkalosis

An acid-base disturbance characterized by increased bicarbonate ($HCO_3^-$) above $26\,mEq/L$ and blood pH above $7.45$, commonly caused by excessive loss of gastric acid through vomiting or ingestion of alkaline drugs.

what are the organs of the urinary system?

2 kidneys, 2 ureters, a urinaey bladder, and urethra

describe the path of blood flow in and out of the kidneys

renal artery→ segmental artery→ interlobar artery→ arcuate artery→ interlobular artery→ Afferent arteriole→ glomerular capillaries→efferent arteriole→peritubular capillaries→interlobular v→ arcuate v.→interlobular v→renal v

Which one is wider the afferent arteriole or the efferent arteriole?

The afferent arteriole is wider.

Think about a garden hose, when you put your thumb over the nozzle, the water sprays out with more force. where would pressure be the greatest, in the Glomerular capillaries or in the Efferent arteriole? Why?

Pressure is greatest in the glomerular capillaries because the narrower efferent arteriole restricts blood flow out of the glomerulus, maintaining high pressure for filtration.

write a definition of hydrostatic pressure

the pressure exerted by a fluid against the walls of its container.

Which substances cannot pass through the capillary clefts?

leukocytes, erythrocytes, and plasma proteins

Name at least one molecule in the human body with which you are familiar that would be a protein floating around in the plasma.

albumin

Which type of molecules can pass through the capillary clefts?

small solutes and ions

Name at least 4 molecules in the human body with which you are familiar that would be floating around in the plasma.

sodium (na) CHloride (cl) potassium (k) and glucose

what is the rule of osmosis?

water will always move where there are more solutes and colloid. water follows salt

If the concentration of large molecules, such as plasma proteins, increases in the capillary, how would this affect the magnitude of the colloid osmotic pressure? Why?

Colloid osmotic pressure increases because more plasma proteins attract and retain water inside the capillary.

Some conditions, such as seasonal allergies and inflammation, can make glomerular capillaries permeable to large molecules like proteins. How would this affect the magnitude of the colloid osmotic pressure? Why?

Colloid osmotic pressure inside the capillary decreases because proteins escape into the surrounding fluid, reducing the osmotic force retaining water in the blood.

what is the glmerular filtration rate>

is the volume of filtrate produced every minute by all the nephrons in both kidneys and is equal to about 125 mL/min.

what are the two ways to change blood pressure in the glomerulus?

1) vasodilation of the afferent arterioles- increases glomerular capillary pressure

2) vasoconstriction of efferent arteriole- increases glomerular capillary pressure

why is the effernt arteriole narrower than the efferent arteriole?

so that more blood comes into the glomerulus than what leaves it

what happens if GFR rises of falls too far from normal level?

nephron function is impaired

what is autoregulation?

the dominant mechanism that is used to decrease or increase GFR as needed

what two structures make up autoregulation?

Juxtaglomular cells, Macula Densa Cells

what are Juxtaglomerular Cells?

a group of modified smooth muscle cells around the afferent arteriole. They secrete the enzyme Renin (remember we discussed Renin in our Water Balance chapter)

what are Macula Densa Cells?

a group of modified epithelial cells within the wall of the distal convoluted tubule adjacent to the afferent arteriole. They act as chemoreceptors that sense changes in solute concentration of the filtrate.

If the volume of blood increases in the Afferent arteriole, stretch receptors will stimulate the Juxtaglomerular Cells to constrict. Will this increase or decrease blood flow into the glomerulus?

Blood flow into the glomerulus decreases.

If the volume of blood increases in the Afferent arteriole, stretch receptors will stimulate the Juxtaglomerular Cells to constrict, what effect will this have on the pressure of blood inside the glomerular capillaries?

Glomerular blood pressure decreases

If Blood Pressure decreases, the GFR also decreases. This results in a decrease in filtrate flow in the renal tubules and a decrease of solutes (Na+ and Cl-) in the filtrate. The Macula densa cells can detect an increase of solutes in the filtrate and respond by causing constriction of the afferent arteriole.

Will this increase or decrease blood flow into the glomerulus?

Blood flow into the glomerulus decreases

If Blood Pressure decreases, the GFR also decreases. This results in a decrease in filtrate flow in the renal tubules and a decrease of solutes (Na+ and Cl-) in the filtrate. The Macula densa cells can detect an increase of solutes in the filtrate and respond by causing constriction of the afferent arteriole.

What effect will this have on the GFR?

GFR decreases

If we want the filtrate to move into the nephron tubular system, will the Hydrostatic Pressure in the Glomerular Capillaries be higher, lower, or equal to that of the Colloid Osmotic Pressure? Explain.

Hydrostatic pressure must be higher than colloid osmotic pressure to push fluid out of the glomerular capillaries and into the capsular space.

Recall our Tissues chapter. How many layers of cells make up the wall of a capillary?

One layer of endothelial cells.

Defend the following statement: “If the Hydrostatic Pressure in the Glomerular Capillaries gets too high, the capillaries may rupture and burst open.”

Glomerular capillaries have thin walls made of a single layer of endothelial cells. Excessively high pressure can damage or rupture these delicate walls.

What is the name of the large, octopus-like cell that is wrapped around the glomerular capillary?

Podocyte

What do you predict is the purpose of podocytes is?

Podocytes support the glomerular capillaries and help form the filtration barrier, allowing small substances to pass while restricting larger molecules.

Do the Podocytes wrap around the capillary completely, or do they leave space for the filtrate to move out of the capillary? Explain your answer in complete sentences

No. Podocytes have foot processes called pedicels that leave narrow

filtration slits between them, allowing filtrate to pass into the capsular space.

The nephron is made up of two basic parts, what are they?

Renal corpuscle and renal tubule

The renal corpuscle is composed of a cup-shaped outer membrane that contains a ball of capillaries with a capsular space between the two. Locate these two structures and identify them below.

1) Cup-shaped outer membrane = Glomerular capsule (Bowman's capsule)

2) Ball of capillaries = Glomerulus

in which part of the nephron does filtration occur?

In the renal corpuscle, where fluid passes from the glomerular capillaries into the capsular space.

When filtrate leaves the Renal Corpuscle, it enters the Renal Tubule. Put the following parts of the Renal Tubule in the correct order of fluid flow:

Proximal convoluted tubule → Descending limb of nephron loop → Ascending limb of nephron loop → Distal convoluted tubule → Collecting tubule.

What is Reabsorption?

Reabsorption is the movement of substances from the tubular fluid back into the blood.

In which part of the nephron does Reabsorption mostly occur?

Proximal convoluted tubule (PCT).

What is Secretion?

Secretion is the movement of substances from the blood into the nephron's tubular fluid.

In which part of the nephron does Secretion mostly occur?

The proximal convoluted tubule (PCT) is a major site of secretion. Secretion also occurs in the distal convoluted tubule and collecting duct.

Why is secretion needed?

Secretion removes additional waste products and helps regulate blood pH and electrolyte balance.

which limb of the nephron loop allows water to be reabsorbed into the bloodstream?

the descending limb

which limb of the nephron loop DOES NOT allow water to be reabsorbed, only permeable solutes?

Ascedning limb forms barrier against water but allows permeable solutes

Describe osmosis and why this mechanism is going to cause water to leave the tubule.

Water moves by osmosis from an area of lower solute concentration to an area of higher solute concentration. The ascending limb transports solutes into the surrounding medulla but does not allow water to pass. This creates an osmotic gradient that causes water to leave the descending limb and enter the surrounding tissue and blood.

describe glomerular filtration?

the movement of substances from the blood within the glomerulus into the capillary space

describe tubular reabsorption

the movement of substances from the tubular fluid back into the blood

describe tubular secretion

the movement of substances from the blood into the tubular fluid

Where does ADH effect the nephron?

primarily the collecting duct

What does ADH do?

ADH increases water reabsorption by stimulating the insertion of aquaporin-2 water channels into the collecting duct cells. This decreases urine volume.

Where does Aldosterone effect the nephron?

The late distal convoluted tubule and collecting duct

What does Aldosterone do?

Aldosterone increases sodium reabsorption and potassium secretion. Water follows sodium, increasing blood volume and blood pressure.

Diuretics are commonly used in states of hypertension & edema (ex: Heart Failure, liver cirrhosis, nephrotic syndrome, pulmonary edema). What is the general effect of a Diuretic drug?

Diuretics increase urine production by reducing sodium and/or water reabsorption, helping the body eliminate excess fluid and lower blood pressure.

Lasix is a common Loop Diuretic (named because it lasts six hours.) Lasix inhibits the symport system (Na+/K+/2Cl−) of the thick ascending limb of loop of Henle. This impairs the ability of the nephron loop to concentrate urine. This helps the body lose water through the urine. Look at the Diuretics Diagram to answer the following questions:

Use the (Na+/K+/2Cl−) symport system to describe what a symport system is.

A symport system transports two or more substances across a membrane in the same direction. The Na⁺/K⁺/2Cl⁻ symporter moves sodium, potassium, and chloride together.

Lasix is a common Loop Diuretic (named because it lasts six hours.) Lasix inhibits the symport system (Na+/K+/2Cl−) of the thick ascending limb of loop of Henle. This impairs the ability of the nephron loop to concentrate urine. This helps the body lose water through the urine. Look at the Diuretics Diagram to answer the following questions:

Compare your answer to (a) to the (Na+/K+/H+) antiport system on the collecting tubule. Describe what an antiport system is.

An antiport system transports substances across a membrane in opposite directions. For example, one ion moves into a cell while another moves out

Unfortunately, Lasix often leads to increased potassium wasting. Potassium is needed for magnesium and calcium reabsorption. If all the K+ is in the filtrate, this will lead to the wasting of both magnesium and calcium.

What is the side effect of being low in Potassium? (What body systems will not function correctly without it?)

Low potassium can cause muscle weakness, cramps, and abnormal heart rhythms because potassium is essential for muscle contraction and nerve signaling.

What is the side effect of being low in Calcium? (What body functions will not function correctly without it?)

Low calcium can cause muscle spasms, tingling, impaired muscle contraction, and abnormal heart function because calcium is necessary for nerve signaling, muscle contraction, and blood clotting.

Observe the Diuretic Diagram, is there another class of drug that would NOT result in Potassium wasting? (hint: it blocks Aldosterone)

Potassium-sparing diuretics, such as spironolactone, which blocks aldosterone.