A&P II Chapter 25

What are the three supportive tissue layers surrounding the kidneys

Renal fascia (outer layer),Perirenal fat capsule (middle layer), Fibrous capsule (inner layer) 

Renal fascia

Dense fibrous connective tissue that anchors kidneys and adrenals to surrounding structures.

Perirenal fat capsule

Fatty cushion (adipose tissue) that protects kidneys from trauma.

Fibrous capsule

Transparent capsule directly covering the kidneys that prevents infection in surrounding tissue from spreading into kidneys.

What are the modifications seen on the cells of the proximal convoluted tubule (PCT)

Dense Microvilli, cuboidal epithelial, and large mitochondria

Microvilli

Forms brush border, which increases surface area for more reabsorption in the proximal convoluted tubule (PCT).

Cuboidal Epithelial Cells

Enhances the capability for reabsorption of water and solutes from filtrate

Large Mitochondria

Provides more energy for active transport in the proximal convoluted tubule (PCT).

What are the three processes in the kidneys that work together to form the filtrate/urine?

Glomerular filtration, Tubular reabsorption, and Tubular secretion

What is Glomerular filtration

Produces cell- and protein-free filtrate; a passive process.

What is Tubular reabsorption

Selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts.

How does maintaining osmolality regulate urine concentration, and why is it important?

prevent cells, especially in the brain, from shrinking or swelling due to osmotic movement of water. 

Tubular secretion

Selectively moves substances from blood to filtrate in renal tubules and collecting ducts.

What is Hydrostatic pressure in glomerular capillaries

Outward pressure that impacts filtration through the filtration membrane.

What is Hydrostatic pressure in capsular space

Inward pressure that impacts filtration through the filtration membrane.

What is Colloid osmotic pressure in capillaries

Inward pressure that impacts filtration through the filtration membrane.

What Molecules normally pass through the filtration membrane

Small molecules such as water, glucose, amino acids, and nitrogenous waste.

What is Glomerular filtration rate (GFR)

Volume of filtrate formed per minute by both kidneys (normal = 120-125 ml/min).

What properties within the kidney impact GFR

Net filtration pressure (NFP),Total surface area available for filtration, Filtration membrane permeability  

What is Net filtration pressure (NFP)

It is the sum of forces, and main pressure is glomerular hydrostatic pressure.

What is the Total surface area available for filtration

Controlled by glomerular mesangial cells contracting.

What is Filtration membrane permeability

Much more permeable than other capillaries.

Intrinsic controls (renal autoregulation)

To maintain GFR in the kidney by adjusting its own pressure.

Extrinsic controls

To maintain systemic blood pressure through hormonal/neural regulation.

Local changes when GFR is too high

Constriction of the afferent arteriole, which lowers hydrostatic pressure. (uses tubuloglomerular feedback mechanism)

Local changes when GFR is too low

Dilation of afferent arterioles, which raises hydrostatic pressure.(Uses Myogenic mechanism)

Renin

An enzyme produced by the kidney that is crucial for regulating blood pressure and fluid balance. It also plays a role in maintaining systematic blood pressure

Source of energy for tubular reabsorption

Active transport of sodium ions (Na+).

Where does the Hormonal regulation in nephron occurs

the distal convoluted tubule and collecting duct.

what does Atrial natriuretic peptide (ANP) regulate

reabsorption by reducing blood Na+, which decreases blood volume and blood pressure.

What does parathyroid hormone (PTH) regulate?

reabsorption by increasing Ca reabsorption in the DCT.

What does antidiuretic hormone (ADH) regulate?

reabsorption by increasing water reabsorption.

What does aldosterone regulate?

reabsorption by increasing blood pressure and decreasing K+ levels.

What part of the nephron does ANP act on?

Collecting duct by the cardiac atrial cells if blood volume  or pressure elevated

What part of the nephron does ADH act on?

Principal cells of the colleting duct

What part of the nephron does PTH act on?

distal convoluted tubule

What part of the nephron does aldosterone act on?

the principal cells of the collecting ducts and distal convoluted tubule

Tubular secretion importance

• Disposing of substances, such as drugs or metabolites, that are bound to plasma proteins 

• Eliminating undesirable substances that were passively reabsorbed (example: urea and uric acid) 

• Ridding body of excess K+ (aldosterone effect) 

•  Controlling blood pH by altering amounts of H+ or HCO3– in urine 

Part of nephron for tubular secretion

Almost all in the proximal convoluted tubules but some in the distal convoluted tubules.

Main solutes that are secreted

K+ (potassium), H+ (hydrogen), NH4+ (ammonium ions), creatinine, organic acids and bases, HCO3– (bicarbonate ions), urea, and uric acid.

Ureters purpose

Transport urine from the kidneys to the urinary bladder. Its Starts in the L2

Ureters Innervation

Sympathetic and parasympathetic fibers and plays an insignificant role in peristaltic contraction

Movement of the urine through the ureters

Starts at renal pelvis and descends behind the peritoneum to the bladder 

Where does the movement of urine through the ureters facilitate?

peristaltic contractions of the muscularis layer 

Mechanism that prevents backflow of urine from bladder back up ureters 

• The oblique angle of ureter entry to the bladder 

• Bladder pressure compresses distal ends of the ureters 

• Peristaltic contractions are a one-way flow 

Pathway of urine

Renal cortex (formation begins) → Renal pyramid (in renal medulla) → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra

What are the mechanisms that regulate urine concentration and volume

Countercurrent mechanism : countercurrent multiplier and countercurrent exchanger. ADH and Maintaining Osmolality 

Countercurrent mechanisms

Fluid flows in opposite directions in two adjacent segments of same tube with hairpin turn, allows exchange of substance between the two segments

Why is the countercurrent multiplier important?

• It allows water to leave descending limbs and NaCl to leave the ascending limb 

• It also allows the kidneys to produce urine with varying concentrations 

Why is countercurrent exchanger important?

It maintains medullary osmotic gradient by preventing rapid removal of salt from interstitial space and removing reabsorbed water 

Countercurrent multiplier

Interaction of filtrate flow in ascending/descending limbs of nephron loops of juxtamedullary nephrons

Countercurrent exchanger

Blood flow in the ascending/descending limbs of vasa recta

How does ADH regulate urine concentration, and why is it important?

It produces concentrated (high levels) or diluted (low levels) of urine 

Less urine = more concentrated, leading to dehydration

More urine = less concentrated, leading to overhydration 

 

Step 1 of the event for micturition

Contraction of detrusor muscle by ANS

Step 2 of the event for micturition

Opening of internal urethral sphincter by ANS

Step 3 of the event for micturition

Opening of external urethral sphincter by somatic nervous system

Renal cortex function/definition

Site of blood filtration in the kidneys. Directly in contact with the transparent fibrous capsule.

Renal cortex location

granular-appearing superficial region

Renal corpuscle function/definition

The spherical portion of a nephron consisting of a glomerulus and its associated glomerular capsule

Renal corpuscle location

renal cortex.

Glomerulus function/definition

Tuft of capillaries composed of fenestrated endothelium

Glomerulus location

renal corpuscle

Afferent arteriole function/definition

Arteriole that supplies blood to the glomerulus of a nephron.

Afferent arteriole location

renal cortex, nephron capillary beds within the glomerulus

Renal medulla (renal pyramid)  function/definition

The darker, reddish-brown region of the kidney

Renal medulla (renal pyramid) location

deep to the renal cortex

Renal pelvis function/definition

A funnel-shaped tube in the inner region of a kidney that receives urine from the major calyces

Renal pelvis location

continuous with the ureter leaving the renal hilum.

Proximal convoluted tubule (PCT) function/definition

site of most reabsorption like : nutrient, water, and ions (Na+) also secretion

Proximal convoluted tubule (PCT) location

It confined to the renal cortex, The first segment of the renal tubule

Nephron loop - Descending limb function/definition

H₂O can leave; solutes cannot (water reabsorption)

Nephron loop - Descending limb location

extends from the proximal convoluted tubule to the bend of the nephron loop.

Nephron loop - Ascending limb function/definition

H₂O cannot leave; solutes can (Na⁺, Cl⁻, K⁺ reabsorption)

Nephron loop - Ascending limb location

extends from the bend of the nephron loop to the distal convoluted tubule.

Distal convoluted tubule function/definition

Regulate reabsorption of Na+ (aldosterone) and Ca2+ (parathyroid), and regulate secretion of K+ (aldosterone) (more secretion than absorption)

Distal convoluted tubule location

The renal cortex after the nephron loop, farthest from the renal corpuscle.  

Collecting ducts location

the renal cortex and runs through the medullary pyramids (renal medulla)

Collecting ducts function/definition

Receive urine/filtrate from the distal convoluted tubule. either principal cells or intercalated cells