Kidneys

Parts and functions of Kidneys

Kidney

• Bean-shaped organ

• Master filtration system, purifying blood by removing metabolic waste and excess fluid to produce urine

• Regulates BP, electrolyte balance, and RBC production for homeostasis

Zone 1: Protective Layer

1) RENAL CAPSULE

• Translucent, high-collagen concentration fiber sheet of connective tissue

• Acts as inextensible skin

• Protects from dangerous expansion and protects from infections

2) PERIRENAL FAT PAD (ADIPOSE CAPSULE)

• Thick adipose(fat) tissue layer

• Acts as shock absorber to protect from force trauma

3) RENAL FASCIA

• Thin, strong, dense layer of connective tissue

• Anchors kidney and surrounding fat pad to Posterior abdominal wall and diaphragm.

Zone 2: Renal Parenchyma

RENAL CORTEX:

1) Glomerulus & Bowman’s Capsule

• Known as Renal Corpuscle

• High-pressure blood enters Glomerulus

• Forces water/electrolytes/metabolic waster across podocyte filter into Bowman’s Capsule

2) Proximal Convoluted Tubule (PCT)

• Twisted tube lined with cuboidal cells featuring “brush border” of microvilli

• Reabsorbs roughly 65% of all water and salt

• Reabsorbs 100% of filtered glucose and amino acids pumping them back into bloodstream

3) Distal Convoluted Tubule (DCT)

• Site for tight electrolyte fine-tuning

• Where body uses parathyroid hormone to selectively pull calcium back into blood

• Where thiazide diuretics block sodium reabsorption

RENAL MEDULLA
1) Medullary Pyramids:

• Contains millions of microscopic parallel tubes running down the center of kidney

• The tubes are Loops of Henle and Collecting Ducts

2) Loop of Henle (Juxtamedullary)

• plunges straight down out of cortex into the pyramid, loops, and climbs back up

• Descending limb: Permeable only to water, as fluid moves to salty medulla, water rushes out of the tube and is saved by body.

• Ascending limb: Impermeable to water, packed with salt pumps. Pumps sodium and chloride into medullary tissue. Creates osmotic gradient that pulls water out of descending limb.

3) Collecting Ducts

• Where aldosterone and antidiuretic hormone (ADH) make final stand

• If ADH is present, it opens aquaporins, allowing hyper-salty pyramid to pull water out of urine back into body

4) Renal Columns

• Cortical tissue that dips between the pyramids

• Serve as secure structural pathway for major blood vessels traveling to and from outer cortex

Zone 3: Collecting & Drainage System

1) Renal Papilla

• Smooth, perforated nipple-like apex at tip of medullary pyramid

• Collecting ducts empty here

• Urine drips out of papilla constantly

2) Minor Calyces

• Small, cup-like funnels, encloses each renal papilla

• Catch dripping urine and channel it forward

3) Major Calyces

• Wide junctions formed by several minor calyces joining together

• Merges fluid from different sectors of kidney

4) Renal Pelvis

• Large, central, smooth walled basin

• Temporary reservoir, catches urine from major calyces

• Channels urine into final exit structure

5) Renal Hilum

• Physical gateway

• Renal artery enters

• Renal vein exits

• Ureter emerges to descend down to bladder