Urinary system #1 Flashcards
Functions of the Urinary System - Kidneys -
The kidneys are the major organs of the urinary system so most off the functions of the urinary system are preformed by the kidneys : Functions of the kidneys : Homeostasis of the blood ions such as Calcium, Sodium ,Potassium, Chloride, Phosphate. Maintenance of blood osmolarity (concentration of solutes kept at or close to 290 mOsm/liter.) Regulation of body fluids, especially blood volume and interstitial fluid. Regulation of blood glucose by deamination of amino acids to make new glucose. Excretion of wastes and foreign substances including : ammonia from urea and amino acids, bilirubin, creatinine from creatine phosphate and uric acid from nucleic acid catabolism. Release of erythropoietin for RBC production. Regulation of blood pressure: via blood volume regulation, secreation of renin, and the adjustment of blood flow in the kidneys. Regulation of blood pH by excreation of H+ and conversion of HCO-3. Release of calcitriol which increases calcium absorption for calcium homeostasis.
Structure of the Kidneys -
Located between T12 and L3, retroperitoneal. They are 4-5 inches long and 2-3 inches wide. The right kidney is slightly lower due to the fact that most of the liver is on the right side.
3 Coverings of the kidney from outer to inner layer -
- renal fascia - anchors the kidneys to the back wall of the body (dense fibrous connective tissue) 2. perirenal fat capsule - fatty protective capsule (aka adipose capsule) 3. fibrous capsule - fibrous membrane, also known as the renal capsule.
Adrenal glands - one sits on top of each kidney.
Renal hilum - the indentation that allows for the exit and entry of renal arteries, renal veins, nerves and uterers. (aka renal hilus)
Renal pelvis - the funnel shaped structure that is continious with the uterer and contains major and minor calyces. Renal sinus - a cavity that the renal pelvis sits in.
Cortex- the outer layer of the kidney. Medulla - the inner layer of the kidney that contains the renal pyramids. Renal papilla - the apex of the renal pyramid that points toward the center. Renal column - the space in between the renal pyramids that contain the blood vessels. Parenchyma - the functional part of the kidney that includes the renal cortex and the renal pyramids (in the medulla), formed mostly by the nephrons. Nephron - the functional unit of the kidney, the number of nephrons is about 1 million per kidney, the numbers do not change after birth.
Typically, there are 8-18 minor calyces and 2-3 major calyces.
Blood supply and vasculatureof the kidneys -
The kidneys combined comprise 1% of the body mass but they get 20-25% of the resting cardiac output because they are functioning as a blood filter.
Renal arteries - branches from the abdominal artery (one per kidney). Segmental arteries - branches fron the renal arteries that supply particular sections of the kidneys. Interlobar arteries - btanch off of lobar arteries and extend between the pyramids. Arcuate arteries - next branch that turns and extends right between the medulla and cortex at the base of the pyramids. Cortical radiate arteries - branch off of the arcuate and extend into the cortex.
Afferent arterioles - smaller arteies, one enters each glomerulus where it branches into a capillary network.
Efferent arteries - the capillary network merges to exit the glomerulus at this arteriole. Peritubular capillaries surround the tubules of the nephron in the cortex for reabsorption of nutrients. Vasa recta - capillaries that surround the tubules of the juxtamedullary nephrons for the reabsorption of nutrients. Veins that complete the circuit include: cortical radiate vein , arcuate vein, interlobar vein and renal vein. (note there are no segmental veins). Renal plexus - the nerve supply to the kidneys from the sympathetic division of the ANS. It regulates the blood flow through the kidneys.
Nephron - Two main parts -
- Renal corpuscle - includes the glomerular capsule(aka Bowman’s capsule) and the glomerulus (capillary ball). 2. renal tubule - includes the proximal convoluted tubule, desending limb of the nephron loop, ascending limb of the nephron loop and distal convoluted tubule.
Functions : Glomerular filtration, tubular reabsorption, and tubular secretion. Glomerular filtration - hydrostatic blood pressure froces fluild and substsances into the capsule which flows into the tubule. Tubular filtration - nutrients that are needed by the body are reclaimed and returned to the blood via the peritubular capillaries and the vasa recta. Tubular secreation - final screen to fine tune the pH , and remove remaining wastes from the blood to the urine.
Types of Nephrons: Two kinds -
Cortical nephrons (80-85%) - The majority of the nephron is in the “renal cortex”, only a small part (if any) of the nephron loop is found in the medulla.
Juxtamedullary nephron (15-20%) - they start very close to the boundary between the cortex and the medulla. The nephron loop goes deep into the medulla.
Either type of nephron flows into collecting ducts that merge at the renal papillae and drain into the minor calyces.
Histology of the Nephron - In general : A single layer of epithelial cells lines the entire tube. Different features depending upon the function of the area: simple cuboidal versus simple squamous, microvilli and the presence of hormones.
Glomerular capsule - has a parietal layer of simple squamous epithelium and a visceral layer of modified SSE called podocytes that have finger like projections called foot processes.
PTC cells - proximal convoluted tubule cells - simple cuboidal epithelium with microvilli and lots of transport proteins for water and solutes to return to the blood.
Nephron loop - thin descending limb - aka thin segment, it is sometimrs also found in the ascending limb as well simple squamous epithelium with very few transport proteins, water can leave.
Nephron loop - thick ascending limb - simple cuboidal cells coated with a glycoprotein layer which prevents water and most solutes from leaving the tubule.
DCT - distal convoluted tubule simple cuboidal epithelium with very few microvilli, few transport proteins for reabsorption.
Collecting duct - structures that the DCT from each nephron feed into. Late portions of the DCT share some same charicteristics as the collecting ducts.
Collecting duct cells are also simple cuboidal epithelium with few microvilli. Special cells : principal cells are intercalcated cells are present. Principal cells have receptors fro the hormones ADH and aldosterone. Intercalated cells secrete H+ for pH homeostasis.
Juxtaglomerular Complex (JGC) -
JGC - made up of the granular cells of the afferent arteriole, the macular densa cells of the ascending limb of the nephron loop and extraglomerular mesangial cells.
Granular cells - modified smooth muscle cells in the afferent arteriole that detect changes in the blood pressure. These cells secrete renin when blood pressure is low.
Macula densa - located at the ascending limb of the nephron loop; monitors the concentration of water and ions.
Extraglomerular mesangial cells - located in between the affrent arteriole and the macular densa cells. They are thought to play a role in the communication of signals between the macula densa and the granular cells.
