Renal System 1 Flashcards
Basic Renal Function
• WATER AND ION BALANCE *** • EXCRETION – Metabolites – Foreign chemicals • REGUL ATION OF BLOOD PRESSURE *** – Sodium balance – Renin-angiotensin system • REGUL ATION OF RED BLOOD CELL PRODUC TION – Erythropoietin (EPO) • REGULATION OF VITAMIN D ACTIVITY
Renal Corpuscle
The site of blood filtration Glomerulus -knot of capillaries Glomerular Capsule -is connected to the initial segment of the renal tubule -forms outer wall of renal corpuscle -encapsulates glomerular capillaries Filtration slits -narrow gaps between adjacent pedicles -materials passing out of blood at glomerulus (must be small enough to pass between slits)
Filtration at renal corpuscle
Filtration at renal corpuscle
- is passive
- blood pressure: forces water and small solutes across membrane into capsular space
- solutes enter capsular space: metabolic wastes and excess ions; glucose, free fatty acids, amino acids and vitamins
- larger solutes, such as plasma proteins, are excluded
Proximal Convoluted Tubules
The site of tubular reabsorption
- is the first segment of renal tubule
- reabsorption of water, ions, and all organic nutrients
- keep the “good stuff” before filtrate leaves kidneys
- epithelial cuboidal cells
- has microvilli on apical surfaces
The Nephron Loop
- renal tubule turns toward renal medulla
- descending limb: fluid flows toward renal pelvis
- ascending limb: fluid flows toward renal cortex
- each limb contains:
- thick segment
- thin segment
Limbs of the Nephron Loop
The Thick Descending Limb
-has functions similar to PCT
-pumps sodium and chloride ions out of tubular fluid
Ascending Limbs
-of juxtamedullary nephrons in medulla
-create high solute concentration in peritubular fluid
The Thin Segments
-are freely permeable to water
-water movement helps concentrate tubular fluid
Distal convoluted tubule
- the third segment of the renal tubule
- has a smaller diameter than PCT
- epithelial cells lack microvilli
- initial portion passes between afferent and efferent arterioles
Three processes at the DCT
- Active secretion of ions, acids, drugs and toxins
- Selective reabsorption of sodium and calcium ions from tubular fluid
- Selective reabsorption of water: concentrates tubular fluid
Collecting Ducts
- variable reabsorption of water: concentrates the tubular fluid
- variable reabsorption or secretion of sodium, potassium, hydrogen and bicarbonate ions from tubular fluid
- delivery of urine
Juxtaglomerular Complex
Formed by:
Macula Densa: a collective of specialised DCT cells
Juxtaglomerular Cells
-sense changes in filtrate concentration and flow rate in the DCT
-secretes renin
-secretes erythropoiten (EPO)
Basic processes of urine formation
- filtration
- reabsorption
- secretion
How much urine do the kidneys usually produce?
usually produce concentrated urine
-1200-1400 mOsm/L (four times plasma concentration)
Kidneys functions
- concentrates filtrate by altering tubular secretion and tubular reabsorption of water and ions
- even partial failure to reabsorb water could lead to fatal dehydration
- absorbs and retains valuable materials for use by other tissues
- sugars and amino acids
Reabsorption and Secretion at the kidneys involves
- diffusion
- osmosis
- channel-mediated diffusion
- carrier-mediated diffusion
Transport maximum (Tm) and the Renal Threshold
- if the nutrient concentrations rise in tubular fluid reabsorption rates increase until carrier proteins are saturated
- concentration higher than transport maximum
- exceeds reabsorptive abilities of nephron
- some material will remain in the tubular fluid and appear in the urine - determines the renal threshold
Renal Threshold
- is the plasma concentration at which a specific compound or ion begins to appear in urine
- varies with the substance involved
