Urinary System Flashcards
Kidney Functions
Production of hormones
Regulation of blood pressure
Regulation of water and acid/base balance
Excretion of wates
Unlobar vs Multilobar
Dog - Unilobar
Cow - Multilobar
Unilobar Kidney
Found in dog, cat, horses, and small ruminants
A single lobe formed by fusion of several lobes during development
Pyramid is no longer obvious
Broad papilla forms renal crest
Collecting ducts feed in to renal pelvis
Multilobar Kidney
Found in cow, pig, and primate
Has multiple lobes
The apex of each lobe is directed towards sinus and forms a papilla
Major and minor calices
Pig and primates have a smooth surface, cow has fissures
Renal Lobe
Each lobe consists of:
Outer Cortex
Inner Medulla
Renal Lobe: Outer Cortex
Outer Cortex: is made up of:
- Pars convoluta or cortical labyrinth
- Pars radiata or Medullary Rays
Renal Lobe: Inner Medulla
Inner Medulla: is made up of:
- Loops of Henle
- Collecting ducts
Collecting ducts open through tiny openings in papilla called Area Cribosa
Urine then drains into minor calyx, which feeds into Major Calyx (multilobar) or directly into renal pelvis (unilobar)
Pars Convoluta
Part of the renal cortex that contains renal corpuscles and convoluted tubules
Pars radiata
Part of the renal cortex alternating with pars convoluta consisting of collecting tubules and straight portions of nephrons
Area Cribosa
Collecting ducts open through tiny opening in papilla called Area Cribosa
Renal lobule
Medullary Ray + 1/2 of Pars convoluta on either side
Interlobular Arteries
Form the borders of the renal lobules
Uriniferous Tubules
The functional unit of each kidney is microscopic uriniferous tubule.
Includes:
Nephron - produces urin
Renal corpuscle
Renal Tubules
Collecting duct - collecting, concentrates, and transports urine
A medium-sized dog may contain 800,000 nephrons.
Nephron
A. Renal Corpuscle
Glomerulus
Glomerular Capsule
B. Renal Tubule
- Convoluted tubule
- Proximal ct
- Distal ct - Loop of Henle
- Proximal straight tubule
- Thin descending limb
- Thin ascending limb
- Thick ascending limb - Connecting Tubule
Renal Corpuscle
Includes tuft of capillaries called glomerulus housed in a bulbous capsule called glomerular (Bowman’s) capsule
The glomerulus connects the afferent arteriole to the efferent arteriole
The glomerular capsule consists of an internal (visceral) and external (parietal) part lined by epithelial cells
Parietal layer is lined by simple squamous cells
Visceral layer is lined by epithelial cells called podocytes
Vascular pole
Afferent and efferent arterioles enter/leave
Urinary pole
where proximal tubule originates
Podocytes
Epithelial cells lining the visceral layer of Bowman’s capsule
Have cytoplasmic processes called foot processes or pedicels
Pedicals interdigitate to form filtration slits
Podocytes cover the entire surface of the capillary except at the filtration slits
Mesangial Cells
Phagocytic cell found between capillaries of glomerulus
Cytoplasmic processes extend between endothelial cells
Function is to clean the GBM of the particulate matter
Filtration Barrier
Formed by:
- Fenestrated capillary epithelium
- Glomerular Basement Membrane (GBM)
- Filtration slit between the podocytes
Glomerular Basement Membrance (GBM)
Formed by fused basal lamina of endothelial cells and podocytes
Thicker than other basement membrances
Has three layers:
- Lamina rara interna - made up of heparan sulfate
- Lamina densa - made up of type IV collagen
- Lamina rara externa - made of heparan sulfate
Glomerular Basement Membrane Filter Substance by:
Size due to type IV collagen
Charge due to negatively charged heparan sulfate
Renal Function
Filtration, by which water and solutes in the blood leave vascular space and enter the lumen of the nephron
Tubular reabsorption, by which substances move from the tubular lumen across the epithelium into the interstitum and surrounding capillaries
Tubular secretion, buy which substances move from epithelial cells of the tubules into the lumens, usually after uptake form the surrounding interstitum and capillaries
Glomerular Filtration
Blood entering the glomerulus is subject to glomerular filtration
Renal blood flow ~ 20% - 25% of cardiac output
Of the total daily renal blood flow, ~60,000ml of fluid becomes the glomerular filtrate (capsular urine) in a 30lb dog.
Only 1% or ~600 ml of urine is excreted daily.
Glomerular Filtration Rate (GFR) - the volume of fluid filtered from the renal glomerular capillaries into the Bowman’s capsule per unit time.
Tubular Reabsorption
Substances are reabsorbed selectively in different parts of the uriniferous tubules
Active Transport:
Glucose
Amino acids
Na+
Passive Diffusion:
Water
Urea
Hormones like parathormone, aldosterone, antidiuretic hormone (ADH) also influence the reabsorption process
Tubular Reabsorption: Glucose
Passes freely through the filtration barrier
100% of filtered glucose is reabsorbed in proximal convoluted tubules
Glucosuria (glucose in urine) occurs when glucose threshold is exceeded (i.e. blood glucose levels reach twice the normal)
Tubular Reabsorption: Na+
98% reabsorbed in PCT and loop of Henle
Remainder absorbed in DCT and collecting duct
Tubular Reabsorption: Urea
Passes freely across the filtration barrier by diffusion
Passively absorbed in PCT
The extent of water reabsorption influence the amount of urea in the urine
BUN - Blood Urea Nitrogen
Tubular Secretion
The substances secreted include:
- Endogenous compounds
- Creatinine
- Histamine
- Metabolic products of hormones - Exogenous compounds
- Antibiotics
- Aspirin
- Other Drugs - Water, cations (H+, K+, Na+), and anions (Cl-, HCO3-, HPO4-2) pass into tubular lumen by passive or active mechanisms.
General Features of Tubular Epithelium
Channels, transporters, pumps, etc. within the apical and basolateral membranes differ in type and quantity
Function of epithelium is determined by:
1. The asymmetric distribution of channels and transporters in the apical and basolateral membranes (
