Urinary System Summary

Overview of the Urinary System

• Kidneys are the primary organs; ureters, bladder, and urethra are accessory organs.

• Regulates blood plasma content to maintain the “dynamic constancy” or homeostasis of internal fluid environment.

Anatomy of the Urinary System

• Kidneys:

  • Oval shape,

  • Size ~11cm x 7cm x 3cm

  • Left kidney larger than right ; right kidney is lower

  • Located in Retroperitoneal position between T12 and L3.

  • Internal structures of kidney is Cortex and medulla with renal pyramids and columns composed of medullary tissue

  • Calyx is a cuplike structure at renal papilla collects urine, forming renal pelvis, which narrows to become the ureter.

• Blood Vessels:

  • Renal artery - (large branch of abdominal aorta) ; brings blood into each kidney

  • Interlobular arteries - between the pyramids of the. medulla and renal artery branches

  • Blood flow: abdominal aorta → renal artery → segmental arteries → lobar arteries → interlobar arteries → arcuate arteries → interlobular artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries (vasa recta) → interlobular veins → arcuate veins → interlobar veins → lobar veins → segmental veins → renal vein → inferior vena cava.

  • Glomerulus: where filtration happens

• Juxtaglomerular Apparatus:

  • Located where afferent arteriole brushes past distal tubule; secretes renin to maintain blood flow homeostasis when blood pressure in afferent arteriole drops.

• Renin: enzyme regulates the body’s water balance & pressure level

• Ureter:

  • Tube from kidney to bladder;

  • Three layers: mucous lining, muscular middle layer, fibrous outer layer.

• Urinary Bladder:

  • Collapsible bag behind pubic symphysis, smooth muscle tissue, rugae lining.

  • Functions: Stores urine and expels urine through the urethra.

  • Voiding: voluntary relaxation of external sphincter, reflexive detrusor muscle contraction. Urine is flushed out of bladder and through urethra

• Urethra:

  • Small Mucous membrane-lined tube from bladder (trigone) to body exterior.

  • Female: ~3 cm long, posterior to pubic symphysis and anterior to vagina.

  • Male: ~20 cm long, passes through prostate gland (joined by ejaculatory ducts), extends through penis; part of both urinary and reproductive systems.

Microscopic Structure of the Nephron

• Nephrons are functional units, make up bulk of kidney ; each nephron is made of various structures

• Renal Corpuscle:

  • Bowman’s capsule cup shaped mouth nephron

• Nephrons Proximal Tubule:

  • First part of renal tubule nearest to Bowman’s capsule, follows a winding, convoluted course; also known as proximal convoluted tubule.

• Loop of Henle:

  • Thin descending limb, a sharp turning, and a thick ascending limb

• Distal Tubule:

  • Convoluted tubule beyond loop of Henle, also known as distal convoluted tubule.

• Collecting Duct:

  • Straight tubule joined by distal tubules; merges into larger ducts opening at renal papilla into a calyx.

Physiology of the Urinary System

• Kidney Function Overview:

  • Processes blood and forms urine via nephrons

  • Nephrons is basic functional unit of kidneys

  • Three processes: filtration, tubular reabsorption, tubular secretion.

• Filtration:

  • First step in blood processing that occurs in the renal corpuscles

  • About 180 liters of water and solutes filtered into Bowman’s capsule daily ; takes place through glomerular-capsule membrane

• Antidiuretic hormone (ADH): chemical produced in the brain causing kidney to release less water, decreasing amount of urine produced

• High ADH = less urine

• Low ADH = high urine

• ADH - secreted by posterior pituitary & target cells of distal tubules & collecting ducts

• Reabsorption:

  • Second step in urine formation; occurs as result of passive and active transport mechanisms from all part of renal tubules major portion of reabsorption occurs in proximal tubules

  • Reabsorption in proximal tubule - mostly water and solutes are recovered by blood, leaving only a small volume of tubule fluid to move on to the loop of Henle

• Urine Composition:

  • ~95% water with dissolved substances.

  • Nitrogenous wastes: result of protein metabolism. EX: urea, uric acid, ammonia, creatinine.

  • Electrolytes: mainly followed by ions. Ex: sodium, potassium, ammonium, chloride, bicarbonate, phosphate, sulfate.

  • Toxins: during disease, bacterial poisons leave body in urine

  • Pigments: urochromes.

  • Hormones: high hormone levels may spill into filtrate.

  • Abnormal constituents: such as blood, glucose, albumin, casts, calculi.

Urinary System and Homeostasis

• Maintains water and electrolyte balance with proper function of kidneys

• Nephrons adjust blood content to maintain constant internal environment.

• Urinary systems are Interdependent with cardiovascular system.

• Requires proper endocrine and nervous system function for proper kidney function.

Summarize the functions of the urinary system

- The urinary system regulates the volume and composition of body fluids.
- It excretes unwanted materials.

Other systems involved in excretion

- The urinary system is not the only system that excretes unneeded substances.
- Other systems also contribute to waste removal, but the urinary system finely adjusts water and electrolyte balance.

Primary function of the urinary system

- The urinary system is described as a "blood plasma balancer."
- It adjusts water content and ion levels (sodium, potassium) in the blood.

Kidney structure and function

- Kidneys are encased in perirenal fat and anchored by renal fasciae.
- The hilum is the notch where blood vessels enter/leave the kidney.
- The kidney consists of the renal cortex (outer region) and renal medulla (inner region).

Renal pyramids and urine collection

- Renal pyramids make up the medullary tissue.
- Renal papilla release urine into calyces, which begin the urinary system's plumbing.

Blood flow through kidneys

- Approximately 1200 ml of blood flows through the kidneys every minute.

Ureters function

- Ureters convey urine from the kidneys to the bladder.
- Each ureter is retroperitoneal and attaches to the bottom of the bladder.

Homeostatic balance

- Kidneys maintain fluid, electrolyte, and acid-base balance.
- Kidney failure leads to homeostatic failure and death.

Additional kidney functions

- Kidneys influence the secretion of ADH and aldosterone.
- They synthesize active vitamin D, erythropoietin, and certain prostaglandins.

Filtration and reabsorption

- Kidneys filter much of the plasma and then reabsorb what should not be excreted before the filtrate becomes urine.
- Urination (voiding or micturition) begins with involuntary contractions of the detrusor muscle.