Urine pt2

Components of urinary system

kidneys (filter blood), ureters (transport urine), bladder (stores urine), urethra (excretes urine)

Effect of increased filtration on BP

Increased filtration decreases blood volume which lowers blood pressure

Salt and water regulation

Sodium reabsorption causes water to follow via osmosis, affecting blood volume and BP

Aldosterone function

Increases sodium reabsorption, water follows, increases blood volume and blood pressure

Kidney endocrine functions

Renin (BP), erythropoietin (RBC production), vitamin D activation, gluconeogenesis

Cortex vs medulla

Cortex is outer region with most nephrons, medulla is inner region with pyramids and collecting ducts

Urine flow through kidney

Minor calyx to major calyx to renal pelvis to ureter to bladder

Renal pelvis blockage effect

Urine backup increases pressure and decreases filtration leading to kidney damage

Kidney supportive layers

Renal capsule (protection), adipose capsule (cushion/insulation), renal fascia (anchors kidney)

Nephron

Functional unit of kidney, about 1 million per kidney

Filtrate flow through nephron

Glomerulus to Bowman’s capsule to PCT to descending loop to ascending loop to DCT to collecting duct

Juxtamedullary nephron advantage

Long loops allow more water reabsorption and more concentrated urine

Cortical vs juxtamedullary nephrons

Cortical (85%, short loops), juxtamedullary (15%, long loops for concentration)

Filtration membrane layers

Fenestrated endothelium, basement membrane, podocytes

Why proteins stay in blood

Basement membrane repels proteins based on size and charge

Podocyte function

Create filtration slits and restrict large molecules

Glomerular filtration

Passive, nonselective movement of plasma into tubules

Tubular reabsorption

Movement of substances from filtrate back into blood

Tubular secretion

Movement of substances from blood into filtrate

Why glucose not in urine

All glucose is reabsorbed in PCT unless pathology is present

Main filtration pressure

Glomerular hydrostatic pressure pushes fluid out of blood

Pressures opposing filtration

Capsular hydrostatic pressure and blood colloid osmotic pressure

Capsular pressure increase effect

Decreases filtration and urine output

Afferent arteriole constriction effect

Decreases blood flow and decreases GFR

Efferent arteriole constriction effect

Increases glomerular pressure and increases GFR

Why efferent constriction raises GFR

Blood backs up increasing pressure in glomerulus

Myogenic mechanism

Smooth muscle responds to stretch to regulate blood flow

Tubuloglomerular mechanism

Macula densa senses sodium and adjusts afferent arteriole

Low sodium filtrate response

Vasodilation of afferent arteriole increases GFR

Renin release trigger

Low blood pressure or low stretch in afferent arteriole

RAAS outcome

Increased aldosterone increases sodium and water reabsorption raising BP

RAAS in dehydration

Activated to conserve water and increase blood volume

Where most reabsorption occurs

Proximal convoluted tubule (~65%)

Descending loop function

Permeable to water, water leaves filtrate

Ascending loop function

Impermeable to water, salts leave filtrate

Loop of Henle importance

Creates osmotic gradient for urine concentration

ADH function

Opens aquaporins to increase water reabsorption

Alcohol effect on ADH

Inhibits ADH leading to increased urination

Countercurrent exchange

Opposite flow maximizes concentration gradient

Why countercurrent is efficient

Maintains gradient allowing more reabsorption

Urination trigger

Stretch receptors activate parasympathetic reflex

Internal vs external sphincter

Internal is involuntary smooth muscle, external is voluntary skeletal muscle

Intracellular vs extracellular fluid

Intracellular is 2/3 of fluid, extracellular is 1/3

Electrolytes importance

Dissociate into ions and create strong osmotic gradients

Normal blood pH

7.35 to 7.45

Effect of increased hydrogen ions

Lowers pH making blood more acidic

Thirst triggers

Increased osmolarity or decreased blood volume

Low ADH effect

Decreased water reabsorption and increased urine output

Severe dehydration response

Decreased blood volume triggers renin release, activating RAAS which increases aldosterone, sodium reabsorption, water reabsorption, and raises blood pressure

Hemorrhage effect on kidneys

Loss of blood decreases BP leading to sympathetic activation, vasoconstriction, decreased GFR, and activation of RAAS to conserve fluid

High blood pressure effect on GFR

Increased pressure stretches afferent arteriole causing myogenic constriction to prevent excessive GFR

Obstruction in ureter effect

Increases capsular hydrostatic pressure which opposes filtration and decreases GFR

Alcohol consumption and urine production

Alcohol inhibits ADH resulting in decreased water reabsorption and increased urine output

Low sodium diet response

Macula densa detects low sodium causing afferent arteriole dilation and increased GFR

High sodium filtrate response

Macula densa triggers vasoconstriction of afferent arteriole decreasing GFR

Efferent arteriole constriction scenario

Backs up blood in glomerulus increasing hydrostatic pressure and increasing GFR

Efferent arteriole dilation scenario

Allows blood to leave quickly decreasing glomerular pressure and decreasing GFR

Kidney stone effect on filtration

Increases capsular pressure reducing net filtration pressure and decreasing urine formation

Loop of Henle dysfunction effect

Reduced ability to create osmotic gradient leading to inability to concentrate urine

Damage to podocytes effect

Proteins leak into urine due to loss of filtration barrier selectivity

Reduced albumin in blood effect

Decreases blood colloid osmotic pressure leading to increased filtration and possible edema

Increased plasma proteins effect

Increases blood colloid osmotic pressure pulling water into capillaries and decreasing filtration

Sympathetic nervous system activation

Systemic vasoconstriction reduces renal blood flow and decreases GFR to preserve blood for vital organs

ADH overproduction effect

Increased water reabsorption leads to low urine volume and more concentrated urine

ADH suppression effect

Aquaporins remain closed resulting in high urine volume and dilute urine

Aldosterone overproduction effect

Excess sodium and water reabsorption increases blood volume and blood pressure

Failure of proximal convoluted tubule

Leads to loss of glucose, amino acids, and ions in urine due to lack of reabsorption

Descending loop impermeability change

If it becomes permeable to solutes gradient is disrupted and urine concentration decreases

Ascending loop permeability change

If water becomes permeable gradient is lost and urine cannot be concentrated

Hypernatremia response

Triggers thirst and ADH release to dilute plasma and restore balance

Hyponatremia response

Decreases ADH release leading to increased water excretion

Increased hydrostatic pressure in glomerulus

Increases filtration rate and urine formation

Decreased hydrostatic pressure

Reduces filtration and urine production

Macula densa damage effect

Loss of sodium sensing leads to poor regulation of GFR

Juxtaglomerular cell damage effect

Decreased renin production leads to impaired blood pressure regulation

Excessive sweating response

Loss of water increases osmolarity triggering ADH release and water conservation

Overhydration response

Decreases osmolarity suppressing ADH leading to increased urine output

Blocked collecting duct effect

Backflow increases pressure and decreases filtration upstream

Chronic hypertension kidney damage

Damages vessels leading to impaired autoregulation and decreased filtration over time

Loss of nephron function

Remaining nephrons compensate but overall GFR declines

Increased afferent arteriole diameter

Increases renal blood flow and increases GFR

Decreased afferent arteriole diameter

Reduces blood flow and decreases GFR

Renal artery stenosis effect

Decreased blood flow to kidney triggers RAAS increasing systemic blood pressure

Metabolic acidosis kidney response

Increases secretion of hydrogen ions and reabsorption of bicarbonate

Metabolic alkalosis kidney response

Increases bicarbonate excretion to lower pH