chapter 15 part a

Chapter 15: Urinary System

Part A: Kidneys & Urine

1.     Functions of the urinary system

a.    Elimination of waste products:

                                          i.    Nitrogenous wastes: urea, uric acid, ammonia

                                        ii.    Toxins-harmful or fatal in small doses

                                       iii.    Drugs- have specific and significant effects on cells

b.    Regulate aspects of homeostasis

                                          i.    Water balance-osmosis

                                        ii.    Electrolytes: ions such as Na, Ca, Mg, Cl, H

                                       iii.    Acid-base balance in the blood

                                       iv.    BP = blood pressure

                                         v.    RBC = red blood cell production

                                       vi.    Activation of vitamin D

2.    Organs of the system

a.    Kidneys- where blood is actively processed

                                          i.    Renal=kidney

b.    Ureters –tubes draining kidneys

c.    Urinary bladder-urine storage

d.    Urethra-from bladder to exterior of body

3.    Kidneys

a.    Location

                                          i.    Retroperitoneal = against the dorsal body wall

                                        ii.    Level of the T12 to L3 vertebrae

                                       iii.    Right kidney is slightly lower than the left( due to position of the liver)

b.    Features

                                          i.    Shape-kidney bean

                                        ii.    Renal hilum-a medical indentation where several structures enter or exit the kidney( ureters, renal blood vessels, and nerves)

                                       iii.    Adrenal gland sits atop each kidney

c.    Coverings

                                          i.    Fibrous capsule-surround each kidney= connective tissue

                                        ii.    Perirenal fat capsule-surrounds the kidney and cushions against blows

                                       iii.    Renal fascia-outermost capsule that helps hold the kidney in place against the muscles of the trunk wall

d.    Anatomical regions – renal:

                                          i.    Cortex-outer region

                                        ii.    Medulla-inside the cortex

                                       iii.    Pelvis-inner collecting tube, like a funnel

e.    Internal structures

                                          i.    Renal or medullary pyramids- triangular regions of tissue in the medulla

                                        ii.    Renal columns-extensions of cortex-like material inward that separate the pyramids

                                       iii.    Renal calyces (calyx)-cup-shaped  structures that funnel urine towards the renal pelvis

f.    Blood supply

                                          i.    25% of the total blood supply of the body passes through the kidneys each time

                                        ii.    Renal artery

                                       iii.    Arterioles and capillary beds – details below

4.    Nephrons

a.    Structural and functional units of the kidneys

b.    Over a million in each kidney

c.    Responsible for forming urine

d.    Main structures of the nephrons:

                                          i.    Glomerulus- ball of capillaries

                                        ii.    Renal tubule- kidney filtering tubes

e.    Anatomy-glomerulus:

                                          i.    Knot of capillaries

                                        ii.    Podocytes cover capillaries from the renal tubule

                                       iii.    Bowman’s capsule is where glomerulus sits within a glomerular

                                       iv.    Renal tubule extends from glomerular capsule and ends at the collecting duct

1.     Bowman’s capsule-first part of renal tubule

2.    Proximal convoluted tubule (PCT)

3.    Loop of Henle-deep into medulla

4.    Distal convoluted tubule (DCT)

f.    Types

                                          i.    Cortical nephrons- located entirely in the cortex, towards the outside, includes most nephrons

                                        ii.    Juxtamedullary nephrons- found at boundary of the cortex and medulla, extend deeper in the kidneys.

g.    Collecting ducts

                                          i.    Receives urine from many nephrons

                                        ii.    Runs through the medullary pyramids

                                       iii.    Delivers urine into the calyces and renal pelvis

h.    Capillary beds

                                          i.    Glomerulus

1.     Arterioles leading in and out

a.    Afferent arteriole- arises from corticle radiate artery and feeds the glomerulus…going in

b.    Efferent arteriole- receives blood that has passed through the glomerulus..going out

2.    Specialized in filtration

3.    High pressure forces fluid and solutes out of blood and into the glomerular capsule

                                        ii.    Peritubular

1.     Arise from efferent arteriole of the glomerulus

2.    Pressure=normal, low pressure capillaries

3.    Adapted for absorption instead of filtration

4.    Cling close

5.    Urine formation

a.    Glomerular filtration

                                          i.    Nonselective  passive process

                                        ii.    Water and solutes smaller than proteins are forced through capillary walls

                                       iii.    Proteins and blood cells are normally too large to pass through the filtration membrane

                                       iv.    Filtrate  is collected in the glomerular capsule and leaves via the renal tubule

b.    Tubular reabsorption

                                          i.    Peritubular capillaries reabsorb useful substances: water, glucose, amino acids, ions

                                        ii.    Some passive, but most reabsorption is active

                                       iii.    Most occurs in the proximal convoluted tubule

                                       iv.    Materials not reabsorbed

1.     Nitrogenous

a.    Urea-protein breakdown

b.    Uric acid-nucleic acid breakdown

c.    Creatinine-associated with creatine metabolism in muscles

c.    Tubular secretion =

                                          i.    Movement from the peritubular capillaries into the renal tubules

                                        ii.    Examples-hydrogen and potassium ions

                                       iii.    Materials left in the renal tubule move toward the ureter

d.    Urine

                                          i.    Characteristics

1.     Yellow color due to the pigment urochrome )from the destruction of hemoglobin) and solutes

a.    Concentration

2.    Odor-slightly aromatic

3.    Sterile-kills many bacteria because

4.    pH = around 6

5.    Specific gravity=density

6.    Normal production in 24 hours is about 1.0 to 1.9 liters of urine are produced…varies on how much you drink and sweat

7.    Urine vs. filtrate are different:

a.    Filtrate = contains everything that blood plasma does (except proteins)

b.    Urine = is what remains after the filtrate has lost most of its water, nutrients, and necessary ions

                                        ii.    Contains substances less valuable or harmful to the body:

                                       iii.    Does not contain things that are valuable or are too large to diffuse through membranes: