Urinary system Flashcards
What does the urinary system consist of?
Paired kidneys, ureters, unpaired bladder and urethra
Transitional epithelium
Urethra: strat cuboidal to columnar
What are the functions of the kidney?
Produce urine
Removal of waste products
Regulate electrolyte level
Maintaining acid base and electrolyte homeostasis
Regulate blood pressure and erythropoiesis
How is the kidney divided?
Morphologically divided into outer cortex and inner medulla
How are kidnyes in domestic animals classified?
Uni-pyramidal, multi-pyramidal and multi-lobar
Uni-pyramidal
One pyramid
Cortical and medullary tissues fused into one lobe
In cats, dogs, horses and small ruminants
Multi-pyramidal in pigs and man
Cortical tissue fused but medullary tissue is separate as pyramids within a lobe
Multi-pyramidal in adult cattle
Cortical tissue is partially separate and medullary tissue is separate as pyramids within a lobe
Multi-lobar
Each lobe has a separate cortex and medulla
In seals
Pelvis
Space (center) where urine collects
Lamina propria contains mucous glands in horses (frothy appearance of urine)
Cortex
Outer region where most of the glomeruli found
Contains renal corpuscle, proximal convoluted tubule, distal convoluted tubule, and initial portions of the collecting tubules
Medulla inner region
Collecting ducts empty into pelvis with thin segments of desc and asc. limbs, collecting tubules and papillary ducts
Medulla outer region
Contains thick and thin segments of descending limb, thick segments of the ascending limb and collecting tubules
What does the parenchyma of the kidney consist of?
Nephrons
Collecting ducts
What are the 4 parts of the nephron?
Renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
What does each renal corpuscle have?
Glomerulus (branches of afferent arteriole)
Bowman’s capsule (sites for blood filtration)
What does the Loop of Henle have?
Descending limb (thick and thin segments)
Ascending limb (think and thick segments)
What are the 2 types of nephrons?
Cortical and juxtamedullary
Cortical nephrons
Renal corpuscles are in the periphery of the cortex
Have shorter loop of henle and extend to outer medulla
Juxtamedullary nephrons
RC located near the cortico-medullary junction
Longer LH, extend to tip of medulla
Nephron
Urine forming parts
Filters blood and modify renal ultrafiltrate
Collecting duct
Straight tubules that begin in cortex, descend into medulla and open at tip of papilla
Collecting duct function
Collect, modify and transport urine to the ureter
Significance of a longer LH?
The longer the LH, the greater the urine concentration
Fish: short
Camel: longest amoung domestic animals
Birds: longer than camels
Renal corpuscle characteristics
150-200 microns
2 poles: vascular, urinary
F: blood filtration and renal ultrafiltrate formation
Vascular pole of the RC
Where afferent arteriole enters and efferent arteriole leaves
Urinary pole of the RC
Where renal ultrafiltrate leaves the capsular space and enters the PCT
What does the capsular space of the RC do?
Collects renal ultrafiltrate that enters the PCT
Podocytes
Modified squamous cells of visceral layer
Feet-like primary processes (podocytes)
Secondary processes (pedicles)
Bowman’s capsule characteristics
Visceral layer (inner)
Parietal layer (outer)
Layers enclose capsular space
Visceral layer of the Bowman’s capsule
Inner layer
Surround capillaries’ endothelial cells
Made of podocytes
Parietal layer of the Bowman’s capsule
Outer layer
Simple squamous cells that change into cuboidal cells of the proximal tubule
What forms the blood-urine barrier?
Podocytes and endothelial cells of capillaries
Macula Densa
Modified cells of the distal tubule next to modified smooth cells of afferent arteriole (juxtaglomerular cells)
F: Monitor changes in the osmolality and vol of fluid entering the DCT
Blood-urine barrier
Endothelium (fenestrated)
Thick basal lamina of endothelial cells and podocytes
Pedicles separated by filtration slits
Basal lamina of the blood-urine barrier
Charge and size barrier
Molecules smaller than 65 K can enter
Negatively charged heparin sulphate particles and glycoprotein
Why is the glomerular filtrate formed?
Because glomerular capillaries are interposed between 2 arterioles (afferent and efferent) and have a higher hydrostatic pressure
GF of a beagle
10 kg beagle will produce 37 ml of Gf perminute, 14 gallons a day
1% of filtrate will be excreted in urine and rest reabsorbed
Proximal convoluted tubule absorption
100%reabsorption of glucose, amino acids and small proteins
80% reabsorption of NaCl and water
PCT
Lined with simple high cuboidal epithelial cells
Brush border, pinocytic vesicles, lysosomes
Mitochondria in PCT
Extensive infoldings that supply energy for active transport of Na+, K+ pump @ basolateral plasma membrane
PCT secretion
Secrete into renal filtrate certain organic acids (creatinine) and foreign substances (drugs and toxic chemicals)
Distal Convoluted Tubule
Lined by simple low cuboidal epithelial cells
Well developed infoldings that transport cells across basal cell membrane
DCT cells
Na+ ions are removed from filtrate (5-10%) and are replaced by K+, H+ and ammonia ions, then K and H are secreted into the lumen
What are the DCT cell processes stimulated by?
Aldosterone
Function of DCT
Maintaining acid-base, electrolyte and K+ balance
Hows does DCT compare to PCT?
DCT has larger lumen (no brush border and lower cell height), greater number of cells per cross section
Thick descending and ascending segments of Loop of Henle
DS is structurally and functionally like PCT
AS is structurally and functionally like DCT
Simple low to high cuboidal epithelium, diluting segments
Thin descending and ascending segments of Loop of Henle
20-25 mm
Lined by simple squamous epithelium
Function: Water retention and only animals with thin can concentrate urine
Only the _____ descending limb is freely permeable to water
Thin
T/F: The entire ascending limb is impermeable to water
True
What are apart of the countercurrent mechanism for urine concentration?
Descending and ascending limbs, arterial and venous vasa recta in the medulla
Collecting duct system
Arched and straight collecting tubules
Papillary ducts (high columnar)
2 cells: principal with light cytoplasm and intercalated with dark cytoplasm
Simple Cuboidal (cortex)
When does an animal suffer from polyuria and polydipsia?
In the absence of ADH, urine is hypnotic
What stimulates ADH release?
Dehydration and factors that lower blood pressure
What decreases ADH secretion?
Alcohol
Principal cells in the cortex
Absorb sodium and water under the effect of aldosterone and K secretion
Secrete hydrogen ions
Principal cells in the medulla
Impermeable to water, and become permeable under the effect of ADH
Intercalated cells
Dark cytoplasm due to many mitochondria, polyribosomes and membrane-bound vesicles
Secrete hydrogen ions and reabsorb bicarbonate ions- acid-base homeostasis
Thick descending and ascending segments of Loop of Henle are sites of _________
diuretic action
What does furosemide (loop diuretic) do?
Block Na+, K+ 2Cl cotransporter,
What does thiazides (tubule diuretic) do?
Block Na+, Cl- cotransporter at the apical cell membrane resulting in retention of Na+ and water in the lumen
What are the 3 components of the Juxtaglomerular apparatus?
JG cells, macula densa and extra-mesangial cells
JG cells
Modified smooth muscle cells of afferent arteriole
Endocrine and secrete renin
Extra- mesangial cells
Lie between afferent and efferent arterioles
Intra- mesangial cells
Lie within the RC
F: maintain the normal thickness of the basal lamina by phagocytosing foreign particles
What is the function of the JG apparatus?
Maintain blood pressure
How does JG maintain blood pressure?
Renin- angiotensin- aldosterone pathway
1.Decrease in fluid volume detected by macula densa cells
2. JG stimulated and secretes renin
3. Renin acts on angiotensin 1
4. angiotensin converted into angiotensin 2
5. angiotensin 2 to aldosterone
6. absorption of Na+ and water
7. Increased BP and homeostasis of water and ions
What does angiotensin 2 do?
Leads to increased blood pressure (most potent vasoconstrictor)
Blood supply to the kidney
- Renal artery branches to form interlobar arteries
- IA branch and turn into arcuate arteries
- AA branch and turn into interlobular arteries
- interlobular arteries branch to form afferent arterioles
- afferents break up into glomersular capillaries
- Blood filtered then leaves via efferent arterioles
- EA break into cortical peritubular capillaries that surround PCT, DCT and collecting tubules
- Fluid absorbed and enters back into circulation
How often does the body blood pass through both kidnyes?
Every 4-5 minutes
Ureter
Mucous glands in horses
T. muscularis (2-3 layers)
Inner longitudinal and outer circular
T. adventitia (outer long.)
