The Urinary System

Tubular Reabsorption• when water and nutrients leave tubules by diffusion and are reabsorbed

by surrounding tissue– Some nutrients enter the blood supply then return to circulation

• Any excess waste and urea are kept within the tubules to be excreted with urine

• Compounds reabsorbed– Amino acids– Glucose– Frutose– Na– K– Ca– HCO3

– Cl

The Kidneys

Location and External Anatomy

• Shape/size• Behind peritoneum on posterior abdominal• T12-L3• Protection=rib cage• Renal capsule• Renal fascia• Hilum• Renal sinus

Internal Anatomy

• Organized into two regions– Inner Medulla– Outer cortex

• Hilus

Blood Supply

• Renal artery takes blood to the kidneys– Subdivided into nephrons• Basic units of kidneys

Function of the kidneys

• Excretion of unwanted substances• Maintenance of water balance• Regulation of acid-base balance of body fluids• Regulation of blood pressure• Regulates production of RBC’s

Disease

• Polycystic Kidney Disease– Leading cause of renal failure– Inherit condition as an autosomal dominant trait– Enlarged and contain large, fluid filled cysts– Detected using ultra sound– Diagnosed between 30-50 years old

Ureter

• Tube extending from the kidneys to bladder– Extends inferiorly and medially from renal pelvis to renal hilum

of each kidney to urinary bladder• Function = carry urine• Transitional epithelium lines both ureters and urinary

bladder• Circular smooth muscle in walls of ureters undergo

peristaltic contractions which force urine through ureters– Occur every few seconds to once every 2-3 minutes

• Pressure inside of urinary bladder compresses that part of ureter to prevent backflow of urine

Urethra:

• Tube extending from bladder to outside of body– Males = conveys sex cells, drains bladder, about 8 inches long– Females = about 1.5 inches long, only drains bladder

• Function = urination/expelling urine from the bladder– Voluntary (External) and Involuntary (Internal) by aid of sphincters

• Sphincter = valve that controls flow of urine through urethra

• Lined with stratified (or pseudostratified) columnar epithelium

• Where urethra exists bladder elastic connective tissue and smooth muscle keep urine from flowing out of bladder until pressure in bladder is great enough to force urine out

Both:

• Triangular area wall between 2 ureters posteriorly and urethra anteriorly is called the trigone

• Irritation or bacterial infection of urethra can cause urge to urinate even if urinary bladder is empty

Tubular Secretion

Definition

• The third major process in urine formation.• It occurs when the nephron cells transport

solutes from the blood into the filtrate.• It’s the movement of nonfiltered substances,

toxic by-products of metabolism and drugs or molecules not normally produced by the body, from the blood into the filtrate.

• Tubular secretion is the transfer of materials from peritubular capillaries to renal tubular lumen and occurs mainly by active transport

• This removes excessive quantities of certain dissolved substances from body also maintains the blood at a normal healthy pH level.

• The substances that are secreted into the tubular fluid for removal from the body include: K+, H+, and NH4+, creatinine, urea, some hormones, and some drugs.

Urine Concentration

Ben Clark and Diana Kiori

Concentration of Urine

• 95% water • 5% dissolved solids/gases• pH= 6.0 • Concentration can range from a minimum of

65 to a max of 1200 mOsm/Kg. This can be done while maintaining the extracellular concentration close to 300 mOsm/Kg– mOsm= concentration of interstitial fluid

Urine concentration

• Concentration can depend on high amounts of solutes• Regulation of urine concentration can vary due to

hormonal changes and within the nervous system• If homeostasis calls for elimination of large volumes of

urine, then diluted filtrate will pass the urine into ureters.

• Countercurrent mechanism= method for concentrating urine based on movement of ions out of nephrons

• Water follows salt, so urine becomes more concentrated and volume will decrease.

Urinary Disorders

• Glomerulonephritis• Acute Glomerulonephritis• Chronic Glomerulonephritis • Pyelonephritis• Renal Failure• Acute Renal Failure • Chronic Renal Failure

The Hilus

Location

-a small indentation on the concave medial side of the kidney

-where the renal artery and ureter enter and the renal vein and ureter exit (connect to the inside of the kidney)

Structure-A cord-like structure with multiple

endings that lead to different areas of the kidney.

-Opens into the renal sinus

-Filled with adipose and connective tissue

-All structures that enter and leave kidney pass through this.

-Renal Artery: brings things into kidney

-Renal Vein: takes things out of kidney

-Hilus is central station of this

Function

-the renal artery brings the blood with waste in it into the kidney to be filtered

-the renal vein takes the filtered blood out to the rest of the body

-the ureter is where the waste from the blood goes and where urine begins to form

Possible Problems -Problems with being hit in the kidney:

-Hilus (renal artery, vein, and ureter) may become detached in an area

-Result: internal bleeding -Bleeding may involve blood with toxins/waste in it -Bleeding may involve blood that has already been

filtered

-Internal Bleeding may lead to blood poisoning

Possible Problems -Renal failure

-Could result in the shutting down of renal artery and vein -May not allow anything to pass in or out of the kidney if these aren’t working

-Kidney Stones -May pass through hilus in order to get to the ureter

-Could possibly result in blocking the hilus -Bacteria may infect the entire area

-Accumulation of waste in blood that does not get filtered properly may result in Acute Renal Failure -Result → Catheter (may have to pass through artery/vein in order to reach kidney)

Urinary Bladder

The ‘p’ brothers (pun intended)

General information

• Hollow, muscular container that lies in the pelvic cavity just posterior to the symphysis pubis.

• This container works as a temporary reservoir for urine• In males, it is just anterior to the rectum• In females, it is anterior to the vagina & inferior and

anterior to the uterus

The “ins and outs”• The ureters bring the urine from •the kidneys to the urinary bladder• From the bladder, the urethra •carries the urine outside of the body• The urinary bladder is lined with transitional •epithelium, which is surrounded by a connective •tissue layer and smooth muscles

Complications• Cystitis: inflammation of the urinary bladder• Tumors• Cancer• Automatic bladder: no control over the disposal of urine• A scenario that can/does happen: there is damage to the

sacral region of the spinal cord (nerves) can make the bladder unable to contract on demand

Glomerular Filtration • Process by which blood is filtered inside renal corpuscle to create urine• Glomerulus

– Permeable • Fenestrae – window-like openings of glomerular capillaries• Filtration slits – gaps between podocytes that allow fluid to enter capsule membrane

– Filtration membrane• Begins formation of urine• Fluid in capillaries filtered across membrane into lumen

• Arterioles– Afferent – supplies blood to glomerulus – Efferent – takes blood away– Juxtaglomerular cells

• Ring of muscle around arterioles at entrance into renal corpuscle

– Distal convoluted tube lies between two arterioles • Juxtaglomerular apparatus

– Macula densa (tube cells in this area) paired with afferent arteriole – Secretes enzyme called renin – Renin regulates filtrate formation and blood pressure

Renal Corpuscle