Urinary System (Pt 1)

Ch 24

Intro to the urinary system (pt 1)

• Components of the urinary system

  • Kidneys, filter blood

    • Remove waste products and convert filtrate into urine

  • Ureters, transport urine

    • From kidneys to urinary bladder

  • Bladder, expandable muscular sac

    • Stores as much as 1 L urine

  • Urethra, eliminates urine from body

Intro to the urinary system (pt 2)

• Processes that occur as filtrate is converted to urine:

  • Elimination of metabolic wastes

  • Regulation of ion levels

    • Ex. Na⁺, K⁺, Ca²⁺

  • Regulation of acid-base balance

    • Alters levels of H⁺ and HCO₃^-

  • Regulation of bp

  • Elimination of biologically active molecules

    • Hormones, drugs

Intro to the urinary system (pt 3)

• Other functions of kidney

• Formation of calcitriol

• Production and release of erythropoietin

  • Secretes erythropoietin (EPO) in response to low blood oxygen

    • Stimulates red bond marrow to increase erythrocyte production

• Potential to engage in gluconeogenesis

  • During prolonged fasting or starvation

  • Occurs in kidney cortex

  • Produces glucose from noncarbohydrate sources; maintain glucose levels

Gross anatomy of the kidneys (pt 1)

FEATURES

Kidneys are 2 symmetrical, bean-shaped organs

Size of hand to second knuckle

Concave medial border, hilum

• Where vessels, nerves, ureter connect to kidney

Lateral border convex

Adrenal gland rests on superior aspect of kidney

Gross anatomy of the kidneys (pt 2)

FEATURES

• Located in the retroperitoneal space (posterior to the peritoneum)

• Extend from T12 to L3

• Protected posteriorly by the floating ribs

• Anchored by various layers of CT

3 connective tissue layers encapsulate the kidneys

FEATURES

• Renal fascia:

  • Most superficial layer

  • Dense irregular CT

  • Surrounds both kidneys and adrenal glands

• Perinephric/perirenal fat capsule:

  • Layer of adipose tissue = cushioning effect

• Renal capsule:

  • Directly covers the outer surface of the kidney

  • Dense irregular CT, helps prevent trauma and pathogen penetration

Internal kidney anatomy

FEATURES

• Renal cortex: outer regions (granular, reddish-brown)

• Renal medulla: inner regions (composed of renal pyramids w/striped appearance)

• Renal pyramids: clusters of many nephrons and collecting ducts

• Major and minor calyces: collect urine from renal lobes (a pyramid and surrounding cortical tissue)

Cortex vs. medulla

FEATURES

• The cortex and medulla have diff functions in the kidney

• The kidney cortex is the outer portion of the kidney; where filtration of blood occurs

• The medulla houses most nephron tubule space, where urine forms and is concentrated

Kidney histology (pt 1)

Kidney histology (pt 2)

Place the connective tissue layers surrounding the kidney in the correct order, from outside to inside.

A: Renal fascia—>renal capsule—>perirenal fat capsule

B: Renal fascia—>perirenal fat capsule—>renal capsule

C: Renal capsule—>perirenal fat capsule—>renal fascia

D: Perirenal fat capsule—>renal capsule—>renal fascia

B: Renal fascia—>perirenal fat capsule—>renal capsule

What structures collect urine from renal pyramids?

A: Renal capsules

B: Renal cortex

C: Renal medulla

D: Minor and major calyxes

D: Minor and major calyces

Structures and function of the ureters

FEATURES

• Carry urine out of the kidneys to the bladder

• Capable of peristalsis

• Connect to the bladder at an angle that prevents backflow of urine

• Further bladder filling also compresses the distal end of the ureter, further preventing backflow

Microscopic anatomy of the ureters

FEATURES

• Deepest layer (mucosa):

  • Transitional epithelium

  • Readily stretches to accommodate distension from urine filling

• Middle layer (muscularis):

  • Senses distension w/urine filling and triggers reflexive peristalsis

• Superficial layer (adventitia):

  • Fibrous CT

  • Anchors the ureter in place

Common features of the bladder in both men and women

• Inner mucosa of bladder: transitional epithelium

• Middle layer (detrusor): contains muscle that contracts to drive urination

• Thick muscle near the urethra forms the internal urethral sphincter

• Epithelium transitions to stratified squamous epithelium near the urethra’s opening to the outside

• Passes through a ring of skeletal muscle on its way out (external urethral sphincter)

Structure of the urinary system in females

• Urethra is only 3-5 cm in length; functions only in transport of urine

Structure of the urinary system in males

• Urethra is longer (20 cm); functions in transport of both urine and semen

Overall structure of kidney vasculature

FEATURES

• Renal artery enters at the hilum

• Branches into several segmental arteries, which branch into interlobar arteries

• Interlobar arteries travel through the renal columns and branch into arcuate arteries in the cortex

• These branch into cortical radiate arteries (interlobular), then microscopic afferent arterioles

Overall structure of kidney nephrons

Nephron: structural and functional unit of urine formation in the kidney

• Afferent arterioles drain into the glomerulus

• Filtration occurs when fluid and solutes are forced from the blood in the glomerulus into the space in the surrounding Bowman’s capsule

• Blood is drained from the glomerulus by efferent arterioles

Flow of fluid through the nephron’s tubules

Nephrons (pt 1)

• 2 types of nephrons: cortical & juxtamedullary

• Classified based on 2 factors

  • Relative position of renal corpuscle in the cortex

  • Length of nephron loop

1. Cortical nephrons

• Oriented w/renal corpuscles near peripheral cortex

• Short nephron loop barely penetrates medulla

• 85% of nephrons

• Main function is for solute reabsorption and excretion

Nephrons (pt 2)

• 2 types of nephrons (continued)

2. Juxtamedullary nephrons

• 15% of nephrons

• Long nephron loops extend deep into medulla

• Main function is to concentrate urine

2 types of nephrons

Collecting tubules and collecting ducts

• Nephrons drain into a collecting tubule

• Multiple collecting tubules empty into larger collecting ducts

• Numerous collecting ducts empty into papillary duct w/in renal papilla

• Specialized epithelial cells (in CT, CD)

• Principal cells

  • Responsive to hormones aldosterone and antidiuretic hormone (ADH)

• Intercalated cells

• Specialized epithelial cells

  • Help regulate urine pH and blood pH

Flow of fluid after filtration through the nephron

Anatomy of the juxtaglomerular apparatus (JGA)

FEATURES

• Occurs when a portion of the DCT comes into contact w/the afferent arteriole

• Macula densa cells in DCT: monitor concentrations of Cl^- and Na⁺ in filtrate

• Granular (aka juxtaglomerular) cells: respond to changes in bp in the afferent arteriole

Juxtaglomerular apparatus (pt 1)

• Juxtaglomerular (JG) apparatus

• Helps regulate blood filtrate formation, systemic bp

• JG apparatus components:

• Granular cells

  • Modified smooth muscle cells of afferent arteriole

  • Located near entrance to renal corpuscle

  • Contract when stimulated by stretch or sympathetic stimulation

  • Synthesize, store, and release renin

Juxtaglomerular apparatus (pt 2)

• JG apparatus components (continued)

• Macula densa

  • Modified epithelial cells in wall of DCT

  • Located on tubule side next to afferent arteriole

  • Detect changes in NaCl concentration of fluid in lumen of DCT

  • Signal granular cells to release renin through paracrine stimulation

Juxtaglomerular apparatus (pt 3)

Human fluid pools

FEATURES

• Human body composed of 3 interconnected pools:

  • Intracellular fluid

    • Inside cells

  • Intravascular fluid

    • In blood vessels

  • Interstitial fluid

    • Btwn cells

• Extracellular

  • Interstitial + Intervascular

Fluid pool solute profiles are not identical

Intracellular fluid (ICF)

• Water, electrolytes, small molecules, non-electrolytes, proteins

• 20-30% protein, pH 7.00

• K⁺ most common

Extracellular fluid (ECF)

• Far less protein, electrolytes

• pH 7.40

• Na⁺ most common

Thirst

Thirst is a sensation generated by:

• Exercise, eating salty food, dry mouth

• A 1-2% increase in osmolarity

  • Osmolarity — solutes/L, expressed as Osmoles/liter

  • 0.290 to 0.295 Osm/L

• Blood loss

• Release of antidiuretic hormone (ADH)

Thirst is quenched as soon as water contacts osmolarity receptors in our cheeks — this happens to prevent over-consumption of water

Water loss occurs in various ways

• Kidneys (60%)

• Sweat (8% or more) - depends on external temp, humidity, and activity lvl

• Lungs (28%) - breathing

• Feces (4%)

Several clinical disorders can arise from too much or too little water (pt 1)

Dehydration

• Excessive water loss via sweating, diarrhea, vomiting, little water ingestion

• Clinical symptoms include:

  • Sticky oral mucosa

  • Dry, flushed skin

  • Reduced urine formation

  • Thirst

  • Weight loss

  • Fever, CNS abnormalities and death

Several clinical disorders can arise from too much or too little water (pt 2)

Hypotonic hydration (rare)

• Ingestion of too much water

• Decrease in fluid pool osmolarity

• CNS dysfunction

Hypovolemia

• Loss of plasma volume

• Loss of water and solutes

• Diabetes, burns, wounds, diarrhea, vomiting

Hypervolemia

• Too much plasma volume

• Renal or liver failure

Which nephron’s major function is to concentrate urine?

A: cortical nephrons

B: juxtamedullary nephrons

C: Renal medulla

D: Minor and major calyces

B: juxtamedullary nephrons

Principal and intercalated cells can be found where?

A: Renal corpuscles

B: Proximal convoluted tubules

C: Distal convoluted tubules

D: Collecting tubules and collecting ducts

D: Collecting tubules and collecting ducts