renal columns - extensions of the cortex that project inward toward sinus
renal pyramids - 6-10 with broad base facing cortex and renal papilla facing sinus

Minor Calyx: cup that nestles the papilla of each pyramid; collects its urine

Major Calyces: formed by convergence of two or three major calyces

Rena Calyces: formed by convergence of two or three major calyces

Ureter: a tubular continuations of the pelvis that drains the urine down to the bladder

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Renal artery divides into segmental arteries in the kidney

In the cortes, peritubular capallaries branch off of the efferent arterioles supplying the tissue near the glomerulus, the proximal and distal convoluted tubules

The Nephron

each kidney has about 1.2 million nephrons
each composed of two principle parts
-Renal corpuscle filters the blood plasma
- Renal tubule: long coiled tube that converts the filtrate into urine
Renal corpuscle consists of the glomerulus and a two layered glomerular (Bowman) capsule that encloses glomerulus

-parietal (outer) layer of Bowman capsule

-viscera; (inner) layer of Bowman capsule

capsular space separates the two layers of Bowman capsule

The Renal Tubules

Renal tubule - a duct that leads away form the glomerular capsule and ends at the tip of the medullary pyramid
- Divided into 4 regions
- Proximal convoluted tubule, nephron loop, distal convoluted tubule: parts of one nephron
- Collecting duct receives fluid from many nephrons
Proximal convoluted tubule (PCT) arises from glomerular capsule
Nephron loop - long U shaped portion of renal tubule
- descending limb and ascending limb
Distal convoluted tubules (DCT) - begins shortly after the ascending limb reenters the cortex
-shorter and less coiled than PCT
-DCT is the end of the nephron
Collecting duct - receives fluid from the DCTs of several nephrons as it passes back into the medu;;a
-numerous collecting ducts converge toward the tip of the medullary pyramid
-Papillary duct: formed by merger of several collecting ducts
- 30 papillary ducts end in the tip of each papila
- collecting and papillary ducts lined with simple cuboidal epithelium

Cortical Nephrons

85% of all nephrons
Short nephron loops

Juxtamedullary nephrons

15% of all nephrons
Very long nephron loops, maintain salinity gradient in the medulla and helps conserve water

Urine Formation 1: Glomerular filtration

learning outcomes:

-describe the process by which the kidney filters the blood plasma, including the relevant cellular structure of the glomerulus

-Explain the forces the promote oppose filtration, and calculate the filtration pressure if given the magnitude of these forces

-describe how the nervous system, hormones, and the nephron itself regulate filtration

glomerular filtration creates a plasma like filtrate of the blood
Tubular reabsorption removes useful solutes from the filtrate, returns them to the blood
Tubular secretion removes additional wastes from the blood, adds them to the filtrate
water conservation removes water from the urine and returns it to blood; concentrates wastes

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-kidneys convert blood plasma to urine in three stages

glomerular filtration - a special case of the capillary fluid exchange process in which water and soome solutes in the blood plasma pass from the capillaries of the glomerulus into the capsular space of the nephron
tubular reabsorption and secretion
water conservation

Glomerular filtrate: the fluid in the capsular space - similar to blood plasma except that it has almost no protein

Tubular fluid: fluid from the proximal convoluted tubule though the distal convoluted tubule - substances have been removed or added by tubular cells

Urine: fluid that enters the collecting duct - undergoes little alteration beyond this point except for changes in water content

The filtration Membrane

filtration membrane - three barriers through which fluid passes

Fenestrated endothelium of glomerular capillaries
- highly permeable
Basement membrane
- blood plasma is 7% protein, the filtrate is only 0.03%
Filtration slits
- Podocyte cell extensions wrap around the capillaries to form a barrier layer with 30 nm filtration slits
- negatively charged which is an obstacle for large anions

-almost any molecule smaller than 3 nm can pass freely through the filtration membrane

ex. water, electrolytes, glucose, fatty acids, amino acids

-some substances of low molecular weight are bound to the plasma proteins and cannot get through the membrane

-most calcium, iron, and thyroid hormone

unbound fraction passes freelin into the filtrate

-Proteinurie (albuminurie); presence of protein in urine

-Hematuria: presence of blood in the urine

Filtration pressure

blood hydrostatic pressure
much higher in glomerular capillaries
because afferent arteriole is large than efferent arteriole
larger inlet and smaller outlet

Hydrostatic pressure in capsular space

glomerulur filtration rate
-total amountn of filtrate produced equals 50 to 60 times the amount of blood in the body
- 99% of filtrate is reabsorbed since only 1 to 2 L urine expected per day

Urine Formation 2: Tubular reabsorption and Secretion

PCT reabsorbs about 65% of glomerular filtrate, removes some substances from the blood, and secretes them into the tubular fluid for disposal in urine

Tubular reabsorption - process of reclaiming water and solutes from the tubular fluid and returning them to the blood

-sodium reabsorption is the key to everything else

creates an osmotic and electrical gradient that drives the reabsorption of water and other solutes
most abundant cation in filtrate
creates sleep concentration gradient that favors its diffusion into the epithelial cells

Two types of transport proteins in the apical cell surface are responsible for sodium uptake

-sodium is prevented from accumulating in the epithelial cells by NA-K pumps in the basal surface of the epithelium

-secondary active transport: NA transporting symports in apical cell membrane do not consume ATP, are considered an example of secondary active transport for their dependance on the NA-K pumps

negative chloride ions follow the positive sodium ions by electrical attraction

The proximal convoluted tubule

Two routes of reabsorption

transcellular route- substances pass through the cytoplasm of the PCT epithelial cells and out their base
Paracellular route- substances pass between PCT cells, junctions between cells all significant amounts of water to pass, solvent drag - water carries with it a variety of dissolved solutes

Potassium, magnesium, and phosphate ions diffuse through the paracellular route with water
Phosphate is also cotransported into the epithelial cells with NA
some calcium is reabsorbed through the paracellular route in the PCT
Glucose is cotransported with NA+ by sodium-glucose transport (SGLT) proteins
Urea diffuses through the tubule epithelium with water reabsorbs 40% to 60% in tubular fluid
- kidneys remove about half of the urea from the blood; creatinine is not reabsorbed at all

The Transport Maximum

there is a limit to the amount of solute that the renal tubules can reabsorb
limited by the number of transport proteins in the plasma membrane
if all transporters are occupied as solute molecules pass
- excess solutes appear in urine
Transport maximum is reached when transporters are saturated
each solute has its own transport maximum

Tubule secretion

tubular secretion - process in which renal tubule extracts chemicals from capillary blood and secretes them into tubular fluid
two purposes in proximal convoluted tubule and nephron loop
-waste removal
-acid-base balance / homeostasis

The Nephron Loop

-Primary function of nephron loop is to generate salinity gradient that enables collecting duct to concentrate the urine and conserve water

The Distal Convoluted Tubule and Collecting Duct

-fluid arriving in the DCT still contains about 20% of the water and 7% of the salts from glomerular filtrate

-Two kinds of cells

Principal cells
- most numerous
- have receptors for hormones
- involved int salt and water balance
Intercalated cells
- involved in acid-base balance by secreting H+ into tubule lumen and reabsorbing K+

-Aldosterone - the “salt retaining hormone”

steroid secreted by the adrenal cortex
created when sodium concentration falls or when potassium concentration rises or if there is a drop in blood pressure

-functions of aldosterone

acts on thick segment of nephron loop, DCT, and cortical portion of collecting duct
stimulates the reabsorption of more sodium and secretion of potassium
water and CL follow the sodium
Net effect is that the body retains NaCl water
-helps maintain blood volume and pressure
urine volume is reduced
urine has an elevated potassium concentration

Composition and Properties of Urine

urinalysis - the examination of the physical and chemical properties of urine
Appearance - clear, almost colorless to deep amber-yellow color due to urochrome pigment from breakdown oh hemoglobin
- cloudiness or blood could suggest urinary tract infection, trauma, or stones
- Pyuria: puss in the urine
- Hematuria: blood in urine due to UTI, trauma, or kidney stones
Odor - bacteria degrade urea to ammonia, some foods impart aroma
Specific gravity - compare to distilled water
PH range: 4.5 to 8.2; usually 6.0
Chemical composition 95% water 5% solutes
- normal to find: urea, NaCl, KCl, creatinine, uric acid, phosphates, sulfates, traces of calcium, magnesium, and sometimes bicarbonate, urochrome, and a trace of bilirubin
- abnormal to find: glucose, free hemoglobin, albumin, ketones, bile pigments

Urine Volume

normal volume for average adult - 1 to 2L a day
Polyuria - output in excess of 2L/day
Oliguria - output of less tan 500mL/day
Anuria - 0 to 100 mL/day

-low output form kidney disease, dehydration, circulatory shock, prostate enlargement

-low urine output of less that 400mL.day, the body cannot maintain a safe, low concentration of waste in the plasma

diabetes - any metablolic disorder resulting in polyuria
at least four forms of diabetes
- diabetes mellitus type 1, type 2, and gestational diabetes ( from pregnancy)
- high concentration of glucose in renal tubule
- glucose opposes the osmotic reabsorption of water
- More water passes in the urine
- Glycosuria - glucose in the urine
Diabetes insipidus
-ADH hypersecretion causes not enough water to be reabsorbed in the collecting duct
-more water passes in the urine
Diuretics - any chemical that increases urine volume
-some increase GFR
-reduce tubular reabsorption of water
commonly used to treat hypertension and congestive heart failure by reducing the body’s fluid volume and blood pressure

Urine Storage and Elimination

urine is produced continually
Does not drain continually from the body
Urination is episodic - occuring when we allow it
Made possible by storage apparatus and neural controls of this timely release

The Ureters

ureters - retroperitoneal, muscular tube that extends the kidney to the urinary bladder
- about 25 cm long
- passes posterior to bladder and enters it from below
- flap of mucosa acts as a valve into bladder
- keeps urine from backing up in the ureter when bladder contracts

-Three layers of ureter

Adventitia - connective tissue layer that connects ureter to surrounding structures

Muscularis - two layers of smooth muscle with third layer in lower ureter

      -urine enters, it stretches and contracts in peristaltic wave

Mucosa - transitional epithelium
- begins at minor calyces and extends through the bladder
-lumen very narrow, easily obstructed kidney stones

The Urinary Bladder

urinary bladder - muscular sac located on floor of pelvic cavity

-three layers

parietal peritoneum, superiorly, fibrous adventitia other areas
Muscularis: detrusor muscle: three layers of smooth muscle
Mucosa: transitional epithelium
- rugae - conspicuous wrinkles in relaxed bladder
Trigone - smooth-surfaced triangular area marked with opening of ureters and urethra
capacity - moderate fullness is 500mL, maximum fullness is 700 to 800 mL
- highly distensible
-As it fills, it expands a lot
-rugae flatten

Kidney stones

renal calculus (kidney stone) - hard granule of calcium phosphate, calcium oxalate, uric acid or a magnesium salt called struvite
Form in the renal pelvis
usually small enough to pass unnoticed in the urine flow

-large stones might block renal pelvis or ureter and can cause pressure buildup in kidney which destroys nephrons

passage of large jagged stones is excruciatingly painful and may damage ureter causing hematuria

-causes include hypercalcemia, dehydration, pH imbalances, frequent UTIs, or enlarged prostate gland causing urine retention

-treatment includes stone-dissolving drugs, ofen surgery, or lithotripsy (nonsurgical technique that pulverizes stones with ultrasound)

The Urethra

female urethra: 3 to 4 cm long
bound to anterior wall of vagina
internal urethral sphincter
- detrusor muscle thickening
- smooth muscle under involuntary control
External urethral sphincter
- where the urethra passes through the pelvic floor
- skeletal muscle under voluntary control

Urinary Tract Infection (UTI)

Cystitis - infection of the urinary bladder
-especially common in females due to short urethra
-frequently triggered by sexual intercourse
-can spread up the ureter causing pyelitis
Pyelitis - infection of the renal pelvis
Pyelonephritis - infection that reaches the cortex and the nephrons

Voiding Urine

-between acts of urination, the bladder is filling

detrusor muscle relaxes

urethral sphincters are tightly closed

accomplished by sympathetic pathway from upper lumbar spinal cord
postganglionic fibers travel through the hypogastric nerve to the detrusor muscle (relax) and internal urethral sphincter (excite)

Micturition - the act of urinating

Renal Insufficiency and hemodialysis

renal insufficiency - a state which the kidneys cannot maintain homeostasis du to extensive destruction of their nephrons
causes of nephron destruction

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Note