Urinary system Flashcards
Components of The Urinary System
- Excretory system that filters blood and removes excess fluids, metabolic wastes, and ions
Macroscopic components: - Kidneys (2)
- Ureters (2)
- Urinary bladder (1)
- Urethra (1)
Location of Kidneys
- The kidneys are retroperitoneal
- Located behind the parietal peritoneum
- The lower ribs offer some protection of the kidneys
Functions of the Kidney
- Filter blood, removing metabolic wastes, toxins, and ions
- Regulate volume and chemical makeup of blood
- Balance water, salts, acids, and bases
Macroscopic Anatomy of the Kidney
- Kidney is surrounded by a tough, fibrous capsule (dense irregular CT)
- Around this capsule is the perirenal fat capsule
What is Internal Anatomy of Kidney?
- The tip of a pyramid is called a papilla
- Urine that is produced in the pyramids drains into a minor calyx
(calyx = cup) - Multiple minor calices drain into a major calyx
- The major calices drain into the renal pelvis which drains into the ureter
What is the main structural and functional unit of the kidney?
- The main structural and functional unit of the kidney is the nephron
- There are more than a million nephrons in each kidney
What is the Nephron Structure?
- Each nephron is composed of a renal corpuscle and a renal tubule
- Renal corpuscle = glomerular capsule + glomerulus (a tuft of capillaries)
- The renal tubule is subdivided into
- Proximal convoluted tubule
- Nephron loop (loop of Henle)
- Distal tubule
- Distal tubule drains into the
collecting duct - Many nephrons drain into one collecting duct
- Help concentrate the urine
What are Cortical Nephrons
Cortical nephrons
* Make up 85% of all nephrons
* Are located almost entirely within the cortex
* Nephron loops dip into medulla only a short distance
What are Juxtamedullary nephrons?
Juxtamedullary nephrons
* Make up 15% of nephrons
* Are called juxtamedullary because the renal corpuscle is near the cortex-medullary border
* Nephron loops dip deeply into medulla
* Long loops help produce concentrated urine
What are Peritubular Capillaries?
- Surround renal tubules
- Branch from efferent arteriole
- Designed for absorption and secretion
- Very porous
- Cortical nephrons have only peritubular capillaries
What is Vasa Recta?
- Surround only tubules of juxtamedullary
nephrons - Branch from efferent arteriole of these nephrons
- Descend deep into the medulla of kidney
- Involved with concentrating urine
What are the Steps of Urine Formation?
Steps of urine formation
1. Filtration
* Blood is filtered, filtrate is formed
2. Resorption
* Substances to keep in the body are
returned to blood
3. Secretion
* Substances to be removed from the
body enter into filtrate
Nephron Activities during urine production?
Processes that occur within a nephron that are involved in producing urine:
* Filtration
- Movement of fluids/wastes from blood capillaries (glomeruli) into nephron
- Any particles small enough to move through –> non-specific
* Resorption
- Nutrients, water, ions recovered by body; they move from nephron back into peritubular capillaries
- ~99% of original filtrate may be resorbed
* Secretion
- Additional molecules actively and selectively moved from peritubular capillaries into the nephron (to be excreted)
What is the purpose of the Renal Corpuscle?
- Site of all filtration
- Made of glomerulus surrounded by glomerular capsule
What is the Structure of Renal Corpuscle?
- Glomerulus
- Glomerular capsule
What is the Glomerulus?
Glomerulus
* Ball of fenestrated capillaries
* Afferent arteriole leads into glomerulus
* Efferent arteriole leads out of glomerulus
What is the Glomerular capsule?
Glomerular capsule
* Two layers
- Parietal layer forms outer layer of capsule
- Visceral layer surrounds capillaries
What is the Structure of Renal Corpuscle?
- The visceral layer is made of unusual, branching epithelial cells called podocytes (= foot cells)
- Branches of octopus-like podocytes end in foot processes which interdigitate with each other
- Filtrate passes into capsule space through filtration slits
What is the Filtration Membrane?
The filtration membrane consists of
1. Fenestrated epithelium of fenestrated capillary
* Only allows small substances through (no cells)
2. Filtration slits (between foot processes of podocytes)
* Slits are covered with a thin slit diaphragm
3. Basement membrane (fused basal laminae of epithelium and podocyte epithelium)
* Pressure within arterial system pushes small molecules through filtration membrane
* Only the very smallest proteins and small molecules (water, ions, urea, glucose, amino acids) are able to pass through the filtration membrane
- Is called filtrate
What is the Proximal Convoluted Tubule?
- Confined to renal cortex
- Made of simple cuboidal epithelium with microvilli
- Lots of microvilli that increase resorption of water, ions, solutes from filtrate
- Resorption & Secretion
What is Thin Segment Descending Nephron Loop?
- Resorption and secretion
- Water can leave filtrate by osmosis
- Walls made of simple squamous epithelium
What is the Ascending Nephron Loop?
- Resorption and secretion
- Walls made of simple cuboidal epithelium
What is the Distal Convoluted Tubule?
- Resorption and secretion (less so than the proximal convoluted tubule)
- Walls made of simple cuboidal epithelium
What is the Collecting Duct?
- Several nephrons empty into one collecting duct
- Urine can be concentrated here
- Walls made of simple cuboidal epithelium
What are Kidney Stones?
- Can precipitate out of urine —> most commonly from calcium
- If they block ureter, urine can collect w/in renal pelvis
- Drugs & ultrasound (lithotripsy) most common treatments
- HYDRATE —>difficult to form if urine is rich in water
What is the Ureter?
- Drains urine from renal pelvis
- Lined with transitional epithelium
- Able to stretch and recoil (as urine moves through) with help of smooth muscle
What is the Urinary Bladder?
- Muscular sac that collects and stores urine
What are the components of the Urinary Bladder?
- Detrusor muscle
- Under parasympathetic control –> signals contraction when bladder is stretched
- Internal urethral sphincter
- Smooth muscle
- Under sympathetic control –> signal contraction when bladder is filling
- External urethral sphincter
- Skeletal muscle
- Under voluntary control (somatic motor NS)
Urethra of the Female
- The urethra drains the urinary bladder
- Is made of transitional epithelium close to bladder and changes to stratified squamous as it nears opening to body
- 3-4 cm in length (females)
- Internal urethral sphincter
- Smooth muscle
- Keeps urethra closed when urine not passing through
- External urethral sphincter
- Skeletal muscle; voluntary control
Urethra of the Male
- The male urethra is approx. 20 cm in length
- Carries both urine and semen
- Has different regions
- Prostatic urethra
– Length of prostate - Intermediate part of urethra (also called membranous urethra)
– Between spongy and prostatic sections - Spongy urethra
– Length of the penis
*Internal urethral sphincter - Smooth muscle, involuntary control
- External urethral sphincter
- Skeletal muscle, voluntary control
- Urinary retention is common in men as the prostate (and potential hypertrophy) press on the urethra
