The Urinary System The Urinary System General Renal (kidney) - - PowerPoint PPT Presentation

The Urinary System

The Urinary System

• General Renal (kidney) Functions

– Urine formation and concentration – Maintain the volume and composition of the ECF! – Eliminate toxins, metabolic wastes, and excess water

• ut of the body
• Main waste products produced are:

– Urea – Uric acid – Creatinine

– Hormone Production:

• Calcitriol – derivative of Vit D3 that increases Ca2+

absorption by intestinal mucosa

• Renin – regulation of blood pressure
• EPO (erythropoeitin) – increases erythrocyte production

produced by peritubular capillary endothelium

The Urinary System

• Function of other urinary system

components:

– Ureters

• Conduct urine from renal hilus to urinary bladder

– Urinary Bladder

• Store urine & involved in micturition

– Urethra

• Female: conduct urine from bladder to external

environment

• Male: conduct urine & semen to external

environment

Organs of the Urinary System

• Kidneys
• Ureters
• Urinary bladder
• Urethra

Figure 23.1a

Location and External Anatomy

• f Kidneys
• Located in the retroperitoneal position
• Lateral to T12–L3 vertebrae
• Average kidney – 12 cm tall, 6 cm wide, 3 cm

thick

• Hilus

– on concave surface

• Kidney surrounded by:

– Renal capsule (dense irregular c.t.) – Adipose capsule – Renal fascia (continuous with the renal capsule)

Internal Anatomy of the Kidneys

Microscopic Anatomy of the Kidneys

• Functional unit of the kidney = Nephron

– Microscopic – approx 1.25 million/kidney equating to about 85 miles of tubules! – Nephron Components:

• Vascular – renal corpuscle
• Tubular – PCT, Loop of Henle (Nephron Loop), DCT
• Tubovascular – Juxtaglomerular apparatus

– Collecting Components:

• Collecting Duct
• Papillary Duct

– Nephron + Collecting Components = Uriniferous Tubule (means tubule which conducts urine)

Mechanisms of Urine Production

• Glomerular Filtration

– filtrate of blood leaves kidney capillaries

• Tubular Reabsorption

– most nutrients, water, and essential ions reclaimed

• Tubular Secretion –

active process of removing undesirable molecules

Uriniferous Tubule Location

Figure 23.4a

The Nephron

• Renal corpuscle – glomerulus and

glomerular capsule

– Glomerulus – tuft of capillaries

• Capillaries are fenestrated
• Glomerular (Bowman’s) capsule

– Parietal layer – simple squamous epithelium – Visceral layer – consists of podocytes

Renal Corpuscle and the Filtration Membrane

Renal Corpuscle and the Filtration Membrane

• Large molecules are

prevented from passing through the filtration membrane, due to fenestrations & filtration slits Negatively charged molecules are repelled by large anions in basement membrane

Tubular Section of Nephron

• Filtrate proceeds to renal tubules

from glomerulus

– Proximal convoluted tubule – Loop of Henle (nephron loop)

• Descending limb
• Thin segment
• Thick segment

– Distal convoluted tubule

Tubular Section of Nephron

Figure 23.4b

Classes of Nephron

• Cortical nephrons – 85% of nephrons

– Most of nephron is in the cortex of kidney

• Juxtamedullary nephrons – 15% of

nephrons

– Extend deep into the renal pyramid & have long Loop of Henle – Responsible for urine concentration & dilution

Classes of Nephron

Figure 23.9a

Collecting Tubules (Collecting ducts)

• Collecting tubules – receive urine from

distal convoluted tubules

Figure 23.4a

Microscopic Blood Vessels

• Nephrons are associated with several

types of capillary beds:

– Glomerulus – fed and drained by afferent & efferent arterioles – Peritubular capillaries – arise from efferent arterioles

• Low-pressure, porous capillaries
• Absorb solutes

– Vasa recta – thin-walled looping vessels

• Part of the kidney’s urine-concentrating mechanism

Summary of Blood Vessels Supplying the Kidney

abdominal aorta renal artery segmental arteries Interlobar arteries arcuate arteries Interlobular arteries afferent arterioles glomerular capillaries efferent arterioles peritubular capillaries & vasa recta interlobular vein arcuate vein Interlobar vein renal vein inferior vena cava

1 ~ 1,000,000 1

Summary of Blood Vessels of the Kidney

The Tubovascular Component

• Juxtaglomerular apparatus

– Functions in the regulation of blood pressure

• Vascular – afferent arteriole
• Tubular - DCT
• Juxtaglomerular cells of afferent arteriole

– Act as mechanoreceptors – JGA cells secrete renin

• Macula densa cells of distal convoluted tubule

– Tall, closely packed epithelial cells – Act as chemoreceptors control vasodilation/vasoconstriction of afferent arteriole

Juxtaglomerular Apparatus

Figure 23.11

Ureters

• Carry urine from the kidneys to the

urinary bladder

• Oblique entry into bladder prevents

backflow of urine

• Histology of ureter

– Mucosa – transitional epithelium – Muscularis – two layers

• Inner longitudinal layer
• Outer circular layer

– Adventitia – typical connective tissue

Urinary Bladder

• A collapsible

muscular sac

• Stores and expels

urine

– Full bladder – spherical

• Expands into the

abdominal cavity

– Empty bladder

• Lies entirely within

the pelvis

Figure 23.14

Figure 23.15

Urinary Bladder

• Urachus – closed

remnant of the allantois

• Prostate gland –

in males

– Lies directly inferior to the bladder – Surrounds the urethra

Structure of the Urinary Bladder and Urethra

Figure 23.17a

Structure of the Urinary Bladder and Urethra

Figure 23.17b

Urethra

• Epithelium

– Transitional epithelium – near the bladder – Stratified and pseudostratified columnar – mid urethra – Stratified squamous epithelium – near the distal end

• Internal urethral sphincter – involuntary

smooth muscle

• External urethral sphincter – voluntarily

inhibits urination

Urethra

• In females – length of 3–4 cm
• In males – 20 cm in length – three named

regions

– Prostatic urethra – passes through the prostate gland – Membranous urethra – through the urogenital diaphragm – Spongy (penile) urethra – passes through the length of the penis

Micturition

Slides

• Renal cortex
• Cross section & long section through

pyramids

• Ureter
• Urinary bladder
• urethra

Renal cortex

Renal Pyramid (cs)

Renal Papillae

ureter cross section

Urinary Bladder

Urethra (male)

Urethra (female)