The Urinary System

Parts of the urinary system

2 kidneys, 2 ureters, 1 urinary bladder, 1 urethra

What is the urinary system composed of?

A pair of kidneys and urinary tract (comp)

What do the kidneys do?

Filter blood to remove metabolic waste products; modify the resulting fluid for the following purposes:

Fluid and electrolyte homeostasis
Acid-base and blood pressure homeostasis regulate blood volume and pH.

What is the urinary tract composed of?

pair of ureters, urinary bladder, and a single urethra

Where does the urine exit the kidneys?

ureters found on the posterior body wall

Where do the uterers empty into?

The urinary bladder on floor of the pelvic cavity, where urine is stored

Where does the urine in the urinary bladder go?

The urethra allows urine to exit the body

What are the functions of the kidneys?

▪ Filter blood to remove metabolic wastes → urine

▪ Regulate fluid and electrolyte balance
▪ Regulate blood pH
▪ Influence blood pressure
▪ Releasing hormone erythropoietin (EPO)
▪ Detoxifying substances in the blood
▪ Vitamin D (calcitriol - absorption Ca)

What do the kidneys look like?

beans in both shape and color

Where are the kidneys located?

Outside and posterior to the peritoneal membrane

Are the kidneys retroperitoneal or intraperitoneal?

retroperitoneal

Where is the right kidney located?

Slightly inferior position due to the liver

Where is the left kidney located? (one)

between level of T12 and L3 vertebrae

What do the 11th and 12th ribs provide to the kidney?

Protection

What is the adrenal gland?

component of the endocrine system; found on the superior pole of each kidney

What are the 3 external layers of CT of the kidney (deep to superficial)

Renal Capsule

Adipose capsule
Renal fascia

What is the renal capsule?

thin layer of dense irregular connective tissue; covers the exterior of each kidney

What is the adipose capsule?

mass of fatty tissue that protects the kidney from trauma and holds it in place

What is the renal fascia?

dense irregular CT; anchors each kidney to the peritoneum and musculature of the posterior abdominal wall

What is the hilum of the kidney?

An opening on the medial surface of the kidney where the renal artery, vein, nerves, and ureters enter and exit

What does the renal cortex and renal medulla make up?

Urine-forming portion of the kidney

What is the renal cortex?

90-95% of all the kidney's blood vessels are found in the renal cortex

What are renal columns?

extensions of the renal cortex; pass through the renal medulla toward the renal pelvis

What is a nephron?

functional unit of the kidney

Where is the nephron located?

renal cortex and medulla of each kidney

Where is the renal corpuscle located?

renal cortex

Where is the renal tubule located?

mostly in the cortex with sometubules dipping into the medulla

Where are the renal pyramids located within the kidney?

within the renal medulla, separated by renal columns on either side

What does the renal pyramid taper into?

A slender papilla→ minor calyx→ major calyx→ renal pelvis→ ureter

Where is smooth muscle located within the kidneys?

within the walls of the calyces and renal pelvis

What do the smooth muscles in the kidneys do?

Propel urine towards the ureter

Left and right renal arteries are branches of the abdominal aorta

renal artery → segmental artery → interlobar artery → arcuate artery → interlobular (cortical radiate artery) → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries

What does the kidney contain?

unusual capillary bed system where arterioles both feed and drain capillaries; normally function of a venule

How does venous blood exit the kidney?

parallel to the arterial pathway

interlobular veins → arcuate veins → interlobar vein → renal vein

Where do the renal veins exit?

The kidney from the hilum to drain into the inferior vena cava

What are the two main divisions of the nephron?

renal corpuscle and renal tubule

What does the renal corpuscle do?

filters blood

What is the glomerulus?

group of loop fenestrated capillaries

What is the glomerular capsule (Bowman's capsule)?

consists of an outer parietal and an inner visceral layer

What is the capsular space?

hollow region between the parietal and visceral layers

Where does the filtrate go after leaving the Bowman's capsule?

Renal tubule

What are the parts of the renal tubule?

proximal convoluted tubule, nephron loop (descending and ascending limbs, distal convoluted tubule

Proximal Convoluted Tubule (PCT)

The first segment of the renal tubule is for reabsorption.

What epithelium types are a part of the proximal tubule?

Simple cuboidal epithelium with lots microvilli

nephron loop (loop of Henle)

dips into the medulla; consists of a descending and an ascending limb (reabsorption)

What epithelium types are a part of the nephron loop?

simple squamous epithelium

Distal Convoluted Tubule (DCT)

The last part of the renal tubule, reabsorption and secretion

What epithelium types are a part of the distal tubule?

Simple cuboidal epithelium with very few microvilli (distal)

Juxtaglomerular Apparatus (JGA)

composed of both macula densa and juxtaglomerular (JG) cells

Macula Densa

a group of cells in contact with modified smooth muscle cells (juxtaglomerular(JG) cells)

What does the juxtaglomerular apparatus do?

Regulates blood pressure (BP) and glomerular filtration rate (GFR)

When BP is too low, JG cells → renin
RAAS activated → increased BP

collecting system

Both the medullary collecting duct (cd) and the papillary duct further modify the filtrate before it exits the kidney (last chance to add/remove anything)

▪ cortical cd → medullary cd → papillary duct

What epithelium types are a part of the collecting system?

Simple cuboidal epithelium with very few microvilli (s)

What happens to the filtrate when it enters the papillary duct?

It turns into urine

What epithelium types are a part of the papillary collecting duct?

Low columnar epithelium with very few microvilli (duct)

Where does urine go after leaving the papillary duct?

Minor calyx

Cortical nephrons make up about…

80% of the nephrons in the kidneys

Where are the cortical nephrons found?

Found in the outer renal cortex; have short nephron loops that barely enter the renal medulla

juxtamedullary nephrons

much less common than cortical nephrons (10-20%)

Where are juxtamedullary nephrons found?

found at the boundary of the cortex and medulla; have long nephron loops that travel deep within the renal medulla

nephrolithiasis

Formation of renal calculi (kidney stones)

Supersaturated

Form when concentrations (high levels) of ions (also sodium ions, hydrogen ions, and uric acid) are present in the filtrate in higher-than-normal amounts

What is glomerular filtration?

Selectively based on size, so cells and large proteins are not filtered and remain in the circulating blood

What do smaller substances do within the glomerular filtration?

Exit blood to enter capsular space as filtrate

glomerular filtration

Glomerulus → Bowman's capsule

What is tubular reabsorption?

Reclaiming or reabsorbing substances such as water, glucose, amino acids, and electrolytes from tubular fluid to return them into the circulating blood (basic)

Reabsorption

Tubules → Blood

What is tubular secretion?

Substances are added into the filtrate from the peritubular capillaries

What does tubular secretion help maintain?

electrolyte and acid-base homeostasis; removes toxins from the blood that did not enter the tubular fluid by filtration

Secretion

Blood → Tubules

What type of capillaries make up the glomerulus?

fenestrated capillaries

What type of pores does fenestration have?

Large pores

Why are glomerular capillaries fenestrated?

For water and small dissolved solutes to pass through more easily

Nitrogenous wastes

group of small substances that are readily filtered; includes: Urea, ammonium ions (NH4+), Creatinine, Uric acid

What are urea and ammonium ions (NH4+) used for?

Protein metabolism

Creatinine

waste product of muscle metabolism

Uric acid

product of nucleic acid metabolism

Glomerular Filtration Rate (GFR)

The amount of filtrate formed per minute by the two kidneys combined is 125 ml/min (180 liters/day)

What is the net filtration pressure at the glomerulus determined by?

Glomerular hydrostatic pressure (GHP), Glomerular colloid osmotic pressure (GCOP), Capsular hydrostatic pressure (CHP)

Glomerular hydrostatic pressure (GHP)

blood pressure; higher than average capillary bed hydrostatic pressure (Pushing out)

Glomerular colloid osmotic pressure (GCOP)

created mostly by albumin

opposes filtration by pulling water back into the glomerular capillaries (pulls in)

Capsular hydrostatic pressure (CHP)

The generated ascapsular space rapidly fills with new filtrate (10 mm Hg) as fluid can only move so quickly into the renal tubule, which opposes filtration (pulls in)

Net Filtration Pressure (NFP)

NFP = GHP - (GCOP + CHP)

NFP favors filtration as GHP is greater than the sum of forces that oppose filtration (GCOP + CHP)

Glomerulonephritis

inflammation of the glomeruli of the kidney

What does glomerulonephritis increase?

blood flow and capillary permeability; increases GHP

What does glomerulonephritis cause?

filtration membrane to become excessively leaky, leading to loss of blood cells and proteins in the urine

Autoregulation

internal kidney mechanisms that work to maintain GFR

Myogenic mechanism

Constriction of smooth muscle in blood vessel walls in response to increases in BP (efferent and afferent constrict and dilate to affect BP)

tubuloglomerular feedback

uses the macula densa of the distal renal tubule to control pressure in the glomerulus in response to NaCl (sodium) concentration of filtrate

Hormonal Regulation of GFR

Involves the regulation of systemic BP, Angiotensin II, and atrial natriuretic peptide (ANP)

Renin-Angiotensin-Aldosterone System (RAAS)

A hormone system that regulates blood pressure (increases BP and GFR)

Atrial natriuretic peptide (ANP)

hormone released by heart cells in atria in response to increasing fluid volume (lowers BV and BP)

What does ANP increase?

increases glomerular hydrostatic pressure and increases GFR by dilating afferent arterioles (BP increases) and constricting efferent arterioles (BP decreases)

Neural Regulation of GFR

The sympathetic division of the ANS stimulates smooth muscle of the afferent arterioles

Afferent arteriole vasoconstriction

Decreases GFR and Hydrostatic pressure of the glomerular capillary

Efferent arteriole vasoconstriction

increases glomerular filtration rate and hydrostatic pressure

Afferent arteriole vasodilation

Increases GFR and Hydrostatic pressure of the glomerular capillary

Efferent Arteriole Vasodilation

decrease GHP and GFR

renal failure

loss of kidney function resulting in its inability to remove waste products from the body and maintain electrolyte balance

acute renal failure

Short-term condition, resolved with treatment