Lecture 25: Urinary 1: Kidney Structure/ Function and Glomerular Function Flashcards
What are the functions for the kidney?
-Urinary system is the primary regulator of fluid volume and ion concentration
-Concentration and volume of the body fluids must remain constant (blood, extracellular fluid) by
-Stabilizing osmolality
-Secrete excess/retain when source is scarce
-Selective excretion: important products retained (glucose, AA, proteins) waste removed
-Excrete foreign substances
-Excrete body organic wastes: urea, bile
-Continue to the acid balance by removing H+ and bicarbonate (HCO3-)
-Produce glucose by glycogenesis
-Produce erythropoietin to stimulate the formation of erythrocytes
-Produce calcitriol= active form of Vit D
-Produce renin, an enzyme that regulates the formation of angiotensin2 (regulates blood pressure and aldosterone)
Where are the kidneys located?
-on the upper abdominal wall close to the start of rib cage
-Arteries, veins and uteters enter through the renal hilus
What is the structure of the kidneys?
-Composed of an outer cortex and an inner medulla
-Basic urine forming units= nephron (thousands) and tubular system
-Each nephron is connected to 1 glomerulus and 1 arteriole to have a close connection b/w the blood supply and the functional unit
What is the nephron structure and function?
-Glomerulus: filters blood
-Tubular system composed of several sections: reabsorption of filtered substances, and secretion of others
-Blood supply composed of 3 capillary beds: glomerular capillaries, peritubular capillaries, and vasa recta (capillaries of the medulla)
What is the glomerulus?
-Confined in the cortex
-Enclosed in the bowman’s capsule
-Protein free fluid is filtered and accumulate in the bowman’s space then enters the first part of the tubule= PROXIMAL TUBULUS
-Composed of many parallel capillaries
-Blood enters through afferent arteriole
-Capillaries DO NOT connect with venules
-Capillaries connect with efferent arteriole that will feed the peritubular capillaries
What is the tubular system?
-Walls made of a single layer of epithelial cells
-Structure function of the epithelial cells define the 4 major components of the tubular system
1. Proximal tubule: Bulk absorption of highly convoluted tubes in the cortex
2. Loop of henle: Hairpin structure in the medulla; composed of the descending thin limb, the ascending thin limb and the thick ascending limb (down from the cortex to medulla and makes pack up, critical to concentration so permeability very important)
3. Distal tubule: Highly convoluted in the cortex (last chance to reabsorb/secrete things, under hormonal regulation)
4. Collecting duct: receive distal tubules from multiple nephrons, small suits merge into large ducts and bring urine to the renal pelvis (move down towards medulla have dilution of urine, so we let water go or not, chance to dilute with ADH)
What is considered an important histological feature of the kidney?
-Initial part of distal tubule passes b/w the afferent and efferent arteriole of its own glomerulus using epithelial cells called macula densa
-Adjacent smooth muscle cell= juxtaglomerular and produce/secrete RENIN (where Bp and fluid will be detected by stretch on arteriole)
What are the 3 basic renal processes?
Glomerular filtration
-Filtration of plasma from glomerular capillaries into bowman’s space (glomerular filtrate)
Tubular reabsorption
-Movement of substance from tubular lumen to peritubular capillaries (back into blood compartment)
Tubular secretion
-Movement of substance from peritubular plasma to tubular lumen
What is glomerular filtration?
-Production of a protein-free filtrate of plasma (contains all the small solutes like glucose, sodium)
-Glomerulus has a complex network of capillaries and specialized structure designed to retain cells and medium and high molecular weight proteins
-GFR (glomerular filtration rate) is an important index of renal function
What does the glomerular membrane do and how many layers does it have?
3 layers (inner to outer)
1. Capillary endothelium: fenestrated (perforations) on about 10% of their surface –> blocks cells, not blood constituents
2.Basal lamina: mesh of protein fibers –> blocks most of the plasma proteins (negatively charged)
3. Inner epithelial layer of bowman’s capsule (visceral epithelium): composed of podocytes –> last level of filtration b/w the fingers
-Function collectively as a fine sieve
-Basal lamina is the best size selection unit against proteins
-Basal lamina also neg charged= repulses proteins
What is the glomerular filtration rate?
-Forces across glomerular capillary wall govern filtration pressure (same as in capillaries) differences in hydrostatic and oncotic pressures
-Filtration facilitated by: higher hydrostatic pressure of blood in capillaries (remains daily constant along capillary)
-Filtration reduced by: hydrostatic pressure in bowman’s space (normally low), plasma oncotic pressure within glomerular capillary
-Rate of filtration higher in the first part of the capillary where the somatic pressure is lower
-Rate decreases further along while the osmotic pressure increases due to the proteins stuck in the blood compartment
What is the GFR equation?
-permeability of the filtration barrier and the surface area available for filtration are other primary determinants of the GFR
GFR=Pf x Kf
Pf: net filtration pressure (average over the entire glomerulus) can change by playing w/ vasoconstriction
Kf: ultrafiltration coefficient= product of the filtration barrier permeability and surface area
How do you regulate the GFR?
-Kidneys maintain a tight control over GFR
-however, hydrostatic pressure in glomerular space and oncotic pressure can’t be regulated
-Thus only blood flow in the glomerular capillaries (hydrostatic pressure) is regulated. depends on 2 arterioles:
1. Afferent= enters the glomerulus
2. Efferent= exists the glomerulus
-Affecting the construction level os the arterioles will determine the hydrostatic pressure in the capillaries (locally)
How is the GFR regulated?
2 levels of control will affect the blood (capillaries) hydrostatic pressure:
-Renal modulation of SYSTEMIC blood pressure and blood volume (extrinsic as it affects the entire body) emergency situations, response to drastic changes in BP level entire body
-Renin-angiotesin-aldosterone system
-Intrinsic control of RENAL blood flow, glomerular capillary pressure, and ultra-filtration coefficient= auto regulatory mechanisms *under normality, locally small changes throughout day to makes sure have constant filtration)
What is the renin-angiotensin-aldosterone system?
-involved in long standing falls in BP or when decreased BP is accompanied by decreased extracellular fluid volume
-Release of renin from juxtaglomerular cells by:
-Reduced stretch of the renin cells in the renal afferent arterioles (baroreceptors)
-Sympathetic nerve impulses: arterial baroreceptors respond to fall in BP by “unbraking” sympathetic nerve active in kidney
-Angiotensin 2 is a potent vasoconstrictor
-acts to increase systemic BP and renal perfusion pressure
-Stimulates release of aldosterone (adrenal cortex) and vasopressin (pituitary)
Aldosterone- enhances Na/water reabsorption
vasopressin (AHD)-enhances urea and water reabsorption
-Augmented fluid uptake increases intravascular volume –> improves real prefusion –> turn off renin release
