Urinary System

•     Organs

–   Kidneys

 

–   Ureters

•   Transport urine from the kidneys to the bladder

 

–   Urinary bladder

•   Provides a temporary storage reservoir for urine

 

–   Urethra

•   Transports urine from the bladder out of the body

 

 

 

 

Urinary System

•     Regulating plasma concentrations, blood volume & pressure

–    Maintain the proper balance between water and salts, and acids and bases

–    Regulate volume and chemical makeup of the blood

–    Osmolarity

–    Regulate blood pH

 

•     Produce hormones

–    Production of renin to help regulate blood pressure and erythropoietin to stimulate RBC production

 

•     Regulate glucose levels

 

•     Excrete wastes

–    Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine

 

 

 

 

 

KIDNEY

•     Retroperitoneal

•     Protective coverings

–   Renal capsule

–   Adipose capsule

•   Fatty mass that cushions the kidney and helps attach it to the body wall

–   Renal fascia

•   Outer layer of dense fibrous connective tissue that anchors the kidney

 

 

 

 

 

 

 

 

KIDNEY

•     Renal hilus

–    Leads to the renal sinus

–    Ureters, renal blood vessels, and nerves enter and exit at the hilus

 

•     Renal cortex

 

•     Medulla

–    Cone-shaped pyramids separated by renal columns

 

 

•     Renal sinus

 

 

 

 

 

KIDNEY

•     Nephron are the structural and functional units that form urine

–    Papillary duct

–    Renal papilla

–    Minor calyx

–    Major calyx

•   Large branches of the renal pelvis

–   Collect urine draining from papillae
–   Empty urine into the pelvis

–    Renal pelvis

•   Flat funnel shaped tube

•   Urine flows through the pelvis and ureters to the bladder

–    Ureter

 

 

 

 

KIDNEY

•      Renal blood supply

–    Approximately one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute

–    Arterial flow into and venous flow out of the kidneys follow similar paths

 

–    Renal artery

 

–    Segmental arteries

 

–    Interlobar arteries

 

–    Arcuate arteries

 

–    Interlobular arteries

•    Cortical radiate

 

–    Afferent arterioles

 

 

 

 

NEPHRONS

•    Renal blood supply

–  Glomerulus

–  Efferent arteriole

–  Peritubular capillaries

–  Renal vein

 

 

 

NEPHRONS

•     Renal corpuscle - the glomerulus and its Bowman’s capsule

–    Glomerulus

•   A tuft of capillaries associated with a renal tubule

–    Glomerular (Bowman’s) capsule

•   Blind, cup-shaped end of a renal tubule that completely surrounds the glomerulus

 

 

 

NEPHRONS

•    Renal tubule

–  Proximal convoluted tubule (PCT)

•  Reabsorbs water and solutes from filtrate and secretes substances into it

 

–  Loop of Henle

 

–  Distal convoluted tubule (DCT)

•  Function more in secretion than reabsorption

 

–  Collecting duct

 

–  Papillary ducts

 

 

 

 

Renal Tubule

 

 

 

 

Nephrons

•     Cortical nephrons

–   85% of nephrons; located in the cortex

 

•     Juxtamedullary nephrons:

–   Are located at the cortex-medulla junction

–   Have loops of Henle that deeply invade the medulla

–   Are involved in the production of concentrated urine

Nephron Anatomy

 

 

 

 

Juxtaglomerular Apparatus (JGA)

•     Where the distal tubule lies against the afferent (sometimes efferent) arteriole

•     Arteriole walls have juxtaglomerular (JG) cells

–   Enlarged, smooth muscle cells

–   Have secretory granules containing renin

–   Act as mechanoreceptors

•     Macula densa

–   Tall, closely packed distal tubule cells

–   Lie adjacent to JG cells

–   Function as chemoreceptors or osmoreceptors

 

 

 

 

Juxtaglomerular Apparatus (JGA)

 

 

 

 

Urine Formation

•     The kidneys filter the body’s entire plasma volume 60 times each day

•     The filtrate:

–    Contains all plasma components except protein

–    Loses water, nutrients, and essential ions to become urine

•     The urine contains metabolic wastes and unneeded substances

 

•     Remove waste products

–    Urea

–    Creatinine

–    Uric acid

 

•     Urine concentration 4x blood levels

 

•     Kidneys have to reabsorb useful materials

 

 

 

Urine Formation

•    Urine formation and adjustment of blood composition involves three major processes

–  Glomerular filtration

–  Tubular reabsorption

–  Secretion

 

 

 

FILTRATION

•     Glomerular filtrate

–   Filtration fraction

•     Filtration membrane is a filter that lies between the blood and the interior of the glomerular capsule

–   Glomerular endothelium

•   Fenestrated epithelium that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular capsule

–   Basal lamina

–   Filtration slits

•   Openings that allow filtrate to pass into the capsular space

 

 

 

 

Filtration Membrane

 

 

 

Filtration Membrane

 

 

 

Filtration Pressures

•     Glomerular hydrostatic pressure (GBHP)

 

•     Capsular hydrostatic pressure (CHP)

 

•     BCOP

 

•     Net filtration pressure (NFP)

–    The pressure responsible for filtrate formation

 

•     Glomerular filtration rate (GFR)

–    The total amount of filtrate formed per minute by the kidneys

 

 

 

 

GFR Regulation

•     If the GFR is too high:

–    Needed substances cannot be reabsorbed quickly enough and are lost in the urine

 

•     If the GFR is too low:

–    Everything is reabsorbed, including wastes that are normally disposed of

 

•     GFR is directly proportional to the NFP

 

•     Changes in GFR normally result from changes in glomerular blood pressure

–    Autoregulation

 

•     Neural regulation

 

•     Hormonal regulation

–    RAA System

–    ANP

 

 

 

 

Renin Release

 

 

 

 

Reabsorption and Secretion

•     Reabsorption routes

–    Paracellular

–    Transcellular

•     Transport mechanisms

–    Active

•   Primary

•   Secondary

–   Transport maximum (Tm)
»   Reflects the number of carriers in the renal tubules available
–   Exists for nearly every substance that is actively reabsorbed
–   When the carriers are saturated, excess of that substance is excreted

–    Passive

•   Diffusion

•   Osmosis

–   Obligatory
–   Facultative

 

 

 

 

 

 

Proximal Convoluted Tubule

•    Na+ transport

–  Symporters

–  Antiporters

 

•    Passive processes

–  Diffusion

•  Cations and fat-soluble substances

–  Osmosis

•  Aided by water-filled pores called aquaporins

 

 

 

 

 

 

 

Reabsorption by PCT Cells

 

 

 

 

 

Nonreabsorbed Substances

•    Substances are not reabsorbed if they:

–  Lack carriers

–  Are not lipid soluble

–  Are too large to pass through membrane pores

•    Urea, creatinine, and uric acid are the most important nonreabsorbed substances

 

 

 

 

Absorptive Capabilities of Renal Tubules and Collecting Ducts

•     Substances reabsorbed in PCT include:

–   Sodium, all nutrients, cations, anions, and water

–   Urea and lipid-soluble solutes

–   Small proteins

 

•     Loop of Henle reabsorbs:

–   H2O, Na+, Cl-, K+ in the descending limb

–   Ca2+, Mg2+, and Na+ in the ascending limb

 

 

 

DCT

•    DCT

–  Absorbs:

•  Ca2+, Na+, H+, K+, and water

•  HCO3- and Cl-

–  Na+-Cl- symporters

 

 

 

 

 

Collecting Duct

•    Na+ leakage channels

 

•    Principal cells

–  Help maintain the body’s water and salt balance

•    Intercalated cells

–  Function in maintaining the acid-base balance of the body

 

 

 

Hormonal Regulation

•         RAA system

 

•         ADH

–        99% of the water in filtrate is reabsorbed

–        Is the signal to produce concentrated urine

–       Aquaporin-2

 

•         ANP

 

 

 

 

Urine Transportation and Elimination

•     Ureters

–   Slender tubes that convey urine from the kidneys to the bladder

•     Urinary Bladder

–   Muscular sac that stores urine

•     Micturition

–   The act of emptying the bladder

–   Incontinence

•     Urethra

–   Muscular tube that:

•  Drains urine from the bladder

•  Conveys it out of the body

 

 

 

Renal Failure

•    Hemodialysis

 

•    Peritoneal dialysis

–  CAPD