Urinary System Ch 25 Flashcards
The kidneys regulate the bodies internal environment by:
Regulating total water volume and solutes (Osmolality)
Regulating concentrations of ions in extra-cellular fluid
Ensuring long term acid-base balance.
Excreting metabolic wastes and toxins
Producing erythropoietin and renin
Converting vitamin D to it’s active form
Carrying out glyconeogenesis during fasting
3 layers of supportive tissue that surround the kidneys
Renal fascia: outermost layer of fibrous connective tissue that anchors the kidneys
Perirenal fat capsule: A fatty mass that surrounds and cushions the kidneys.
Fiberous capsule: transparent capsule that protects the kidney from infection.
3 region of the kidneys
Cortex: Light colored superficial surface
Medulla: deeper dark reddish cone shaped tissue masses called renal pyramids.
Pelvis: funnel shaped tube continuous with the ureter leaving the hilum. ( branching extensions form the major and minor calyces.
Renal corpuscle
A tuft of capillaries called a glomerulus and a cup shaped Bowmans capsule.
Glomerulus
capillaries with fenestration to allow large amounts of solute rich (protein free) fluid which becomes filtrate.
Glomerular Capsule
External parietal and visceral layer that clings to the glomerular capillaries.
Renal Tubule
Consists of: Proximal Convoluted tubule Nephron Loop Distal Convoluted Tubule and connects to the collecting duct
Proximal convoluted tubule (PCT)
Luminal (Apical) surface is covered with microvilli to increase surface area. Consists of cuboidal epithelial cells
The most active reabsorbers
Nephron Loop (Loop of Henle)
U shaped loop has descending and ascending limbs.
The proximal part of the descending limb is continuous with the PCT and its cells are similar. The descending “thin” limb consists of simple squamous epithelium. There are thick and thin segments of the ascending and descending limbs
The rule for water is that it leaves the descending limb but not the ascending limb. The opposite it true for solutes.
Distal convoluted tubule
made of cuboidal cells confined to the cortex and lack microvilli.
Fine tuning for the small amount of filtrate before it becomes urine.
Collecting duct
Each collecting duct receives filtrate from many nephrons. They contain two cell types:
Principal cells: more numerous and have sparse short microvilli for maintaining the bodies water Na+ balance
Intercalated cells: Cuboidal cells with abundant microvilli (types A&B) play a role in acid-base balance of the blood
Classes of nephrons
Cortical: 85% of all nephrons and are located in the cortex except for a small part of their loops that dip in the medulla.
Juxtamedullary: Originate close to the cortex and play a role in the kidney’s ability to produce concentrated urine. Long nephron loops that deeply invade the medulla.
Nephron Capillary Beds
Glomerulus: Produce filtrate
Peritubular and Vasa Recta: reclain that filtrate
Glomerulus capillaries
capillaries run in parallel, both fed and drained by arterioles (afferent and efferent)
Peritubular Capillaries
Cling close to the adjacent renal tubules
fed by the high resistant efferent arterioles so the only have low pressure so they readily reabsorb water and solutes from the tubule cells.
Vasa Recta
“straight vessels” Extend deep into the medulla paralleling the longest nephron loops.
Juxtaglomerular Complex (JGC)
JGC includes 3 populations of cells that help regulate the rate of filtrate formation and systemic blood pressure: macula densa, granular cells and exteragromerular mesangial cells
Macula densa
Chemoreceptors that monitor NaCl content of the filtrate entering the DCT
Granular cells
In the arteriolar walls
3 processes for urine formation
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Glomerular Filtration
Passive process in which hydrostatic pressure forces fluids and solutes through a membrane.
Filtration membrane
Fenestrated endothelium: allow blood components, not blood cells, to pass through.
Basement membrane: middle layer that blocks all but the smallest proteins and solutes from passing through.
Podocytes: visceral layer that has foot processes with filtration slits that bock any macro molecules that may have sneaked through.
Pressure that affect filtration
Hydrostatic pressure in glomerular capillaries the outward pressure from the BP.
The inward pressures that oppose it are:
Hydrostatic pressure in capsule itself and colloid osmotic pressure in glomerular capillaries.
Net filtration pressure
The forward pressure remaining when you take the outward pressure minus the inward pressure opposing it. This largely determines the GFR
Glomerular Filtration Rate (GFR)
The volume of filtration formed each minuet by the combined activities of all 2 million gomeruli in the kidneys
Factors affecting the GFR
Net filtration rate: the main controllable factor, controlled by dilation and constriction of the afferent and efferent arterioles.
Total surface area available for filtration.
Filtration membrane permeability
Intrinsic controls of renal regulation
Renal auto regulation: by adjusting its own resistance to blood flow the kidney can maintain almost constant GFR:
Myogenic mechanism and Tubuloglomerular feedback mechanism.
Myogentic Mechanism
Vascular smooth muscle property to relax when not stretched and contract when stretched. In this was the pressure going into the gloerulus is kept constant.
Tubular feedback mechnism
Directed by the macula densa cells of the JGC located in the walls of the ascending limb and respond to NaCl concentration. Release vasoconstriction chemicals in response to high NaCl and cause the afferent arterioles to constrict.
Extrinsic controls
Purpose to maintain BP:
- Sympathetic NS controls
- Renin-angiotensin-aldosterone mechanism.
Sympthetic NS controls
Serve the body as a whole, kidneys com second in the case of hypovolemic shock. The blood is shunted away from the kidneys to other more vital organs to raise BP.
Renin-Angiotension-Aldosterone Mechanism
Low BP causes the granular cells to release Renin by one of three pathways:
Direct stimulation on granular cells
Stimulation of granular cells by input of activated macula densa cells.
Reduced stretch of granular cells
Tubular Reabsorbtion
Selective transepithelial process that begins as soon as the filtrate enters the proximal tubules. This reclaims most of the filtrate and returns it to the blood.
Reabsorption of sodium
80% of active transport energy goes to reabsorbing sodium.
1. transport across the basolateral membrane: primary active transport by ATPase Na+ K+ pump then it is swept to the adjacent pretubular capillaries because of the high osmotic pressure in the capillaries.
Reabsorption of Nutrients water and ions
Na+ reabsorption provides the energy for almost every other substance.
