Kidney Anatomy and Circulation

• Kidneys main task is to purify, filter, and reabsorb substances, and are 10-12 cm long
• The renal artery, a branch of the abdominal aorta, provides the kidneys with blood

Renal Circulation

• Renal artery carries unpurified blood to the kidneys
• Renal vein carries purified blood away from kidneys, back into the circulatory system

Interlobar Artery

• Segmental artery branches out and goes between the pyramids towards the corticomedullary junction
• It passes through the renal columns, which separate the renal lobes

Arcuate Artery

• It is situated where the renal cortex meets the renal medulla and forms arches from the interlobar artery
• Runs parallel to the kidney's margin, perpendicular to the interlobar and interlobular arteries

Interlobular Artery

• Arises from the arcuate arteries, reaching towards the renal cortex and capsule
• Identifying it indicates being in the cortex

Afferent Arteriole

• Supplies blood to the glomerulus or glomerular capillaries

Glomerular Capillaries

• The primary site of filtering within the renal corpuscle's Bowman's capsule
• Filtrate drains into Bowman’s space towards the proximal convoluted tubule, then the Loop of Henle, then distal convoluted tubule, and finally the collecting duct

Efferent Arteriole

• Receives filtered blood from glomerulus and branches into either peritubular capillaries or vasa recta

Peritubular Capillaries

• Found around the convoluted tubules only in the cortex
• Drains into the renal vein
• Reabsorbs substances from the proximal convoluted tubule (PCT) and distal convoluted tubule (DCT)

Vasa Recta

• Exists around the Loop of Henle in the medulla
• Drains into the renal vein
• Indicates being in the medulla

Interlobular Vein

• Parallels the arteries of the same name and complements the venous system

Renal Vasculature Roles

• The renal artery, a branch of the abdominal aorta, enters the renal sinus and splits into segmental arteries
• The right renal artery is longer as it passes through the inferior vena cava
• Segmental arteries branch off the renal arteries inside the hilum

Nephron and Collecting Tubule

• Nephron is the main functional unit
• Cortical nephrons are located solely in the renal cortex
• Juxtamedullary nephrons are found spanning the renal cortex and renal medulla

Proximal Convoluted Tubules (PCT)

• Reabsorbs 60-65% of filtrate
• Site of secretion for urea and certain drugs
• Many of these cells have mitochondria
• Characterized by a prominent brush border for reabsorption

Loop of Henle

• The thick descending limb has epithelium comparable to the cuboidal cells of its section
• Thin descending limb is simple squamous epithelium and permeable to water
• Thick ascending limb is similar the DCT, and uses Na+-K+ ATPase to re-energize the hyperosmolar medullary interstitium

Distal Convoluted Tubule (DCT)

• Possesses a clearer lumen and more basophilic cuboidal cells compared to the PCT
• Absorption and secretion processes are less pronounced

Renal Corpuscle

• Contains Bowman's capsule and glomerulus
• Consists of Bowman's space between the capsule and glomerulus

Glomerulus Filtration

• It is key for filtering blood, featuring three layers that create the filtration barrier
• Innermost layer composed of fenestrated endothelial cells allowing water, ions, and small molecules through
• The Glomerular Basement Membrane (GBM) acts as a selective barrier that prevents larger proteins from crossing
• The podocyte layer is the outermost layer formed by podocytes, which have foot processes that interdigitate to create filtration slits covered by the slit diaphragm

Renal Corpuscle Poles

• The vascular pole allows entry and exit of blood vessels and serves as the meeting point for the DCT and renal corpuscle
• The urinary pole is where filtrate enters the PCT, draining urine from Bowman’s space

Glomerulus Structure

• Includes Glomerular capillaries, and Glomerular mesangial cells
• Supporting cells with phagocytic abilities

Fenestrated Glomerular Capillaries

• They have holes, only allowing certain plasma components through
• Does not allow big molecules like proteins and RBCs

Efferent Arteriole Structure

• Maintains filtration pressure as it has a smaller caliber than the afferent arteriole

Podocytes Structure

• Cells with pedicel processes encapsulating glomerular capillaries
• Their primary and secondary processes (pedicels) feature filtration slits and have electrical and molecular properties

Bowman’s Capsule

• Outer layer of renal corpuscle
• Contains ultrafiltrate, the precursor to urine

Macula Densa

• Consists of cuboidal cells located where the vascular pole intersects the distal tubule from the ascending loop of Henle
• Functions as osmoreceptors, able to detect filtrate osmolarity

Juxtaglomerular Apparatus (JGA)

• A structure that regulates the blood pressure and glomerular filtration rate (GFR) consisting of the macula densa and juxtaglomerular granular (JG) cells

Macula Densa

• Osmoreceptors that can detect osmolarity within the filtrate & recognizes hypo-osmolarity

Juxtaglomerular Granular (JG) Cells

• Act as baroreceptors detecting low blood pressure or low osmolarity
• Releases renin, which triggers the RAAS, to regulate blood pressure and sodium balance

Glomerular Filtration

• High blood pressure drives filtration through the afferent arteriole to glomerular capillaries
• Small substances smaller than 70 nM are permitted, but not large molecules
• GBM, composed of secondary processes of podocytes, permits substances smaller than 14 nM

Thick Descending Loop of Henle Appearance

• Resembles proximal convoluted tubule

Thick Ascending Loop of Henle Apperance

• Resembles the distal convoluted tubule

Damaged Renal Corpuscle

• Damage to the renal corpuscle can result in blood or proteins passing through GBN with blood in urine and frothy urine

Renin-Angiotensin-Aldosterone System

• Decreased blood volume and sodium levels stimulates the release of renin
• Angiotensin II increases blood pressure and stimulates aldosterone release.

Cortico-Medullary Junction in the Loop of Henle

• Arcuate artery is found in the cortico-medullary junction in the loop of Henle (the junction between cortex and medulla) in renal corpuscles

Kidney Stones

• Kidney stone formation can occur due to highly concentrated urine, resulting from retained urine along the excretion pathway

Inner Epithelial (Urothelium) Lining

• Ranges from the minor calyx to the proximal urethra
• Uroplakins provide extra protection in this inner epithelial (urothelium) lining
• Overlapping plaques keeps the bad urine out, into the deeper urothelium cells

Medulla Structures

• Do not include renal corpuscles but contain simple squamous epithelium for the thin limb of the loop of Henle, the collecting duct consisting of principal and intercalated cells, and the vasa recta

Descending and Ascending Limb

• Passive reabsorption of water occurs in the descending limb
• Active transport of ions occurs in the ascending limb

Erythropoietin Production

• Occurs in the interstitium of the cortex which surrounds proximal convoluted tubules and the peritubular capillaries

Urine Excretion

• After urine is made, then urine is drained from minor calyces, to major calyces, to the renal pelvis, to the ureter, to the urinary bladder

Urothelium

• Consists of a single layer of small basal cells and a stratified squamous epithelium known as umbrella cells when undestined

This lesson explores the anatomy and circulatory system of the kidneys. It details the path of blood flow through the renal artery, interlobar artery, arcuate artery, and interlobular artery. It also describes where these arteries are located within the kidney.