Anatomy & Physiology H Chapter 15 Urinary System Anatomy & Physiology H Chapter 15

15.1 Kidneys The urinary system consists of the kidneys, ureters, urethra and the urinary bladder The kidneys alone perform the functions of the urinary system; Maintain the purity and concentration of internal fluids Excrete nitrogenous waste Regulate blood volume and chemical makeup Secrete the enzyme renin to regulate blood pressure Secrete the hormone erythropoietin to stimulate RBC production Convert vitamin D to its active form

15.1 Kidneys The kidneys are located on the dorsal side of the body under the 12th rib They are small dark red organs, shaped like kidney beans The right is kidney is slightly lower than the left, due to crowding from the liver Adult kidneys are about 5 inches long, 2.5 inches wide and about 1 inch thick

15.1 Kidneys Each kidney has an indentation called the renal hilus where the ureters and blood vessels enter Atop each kidney is an adrenal gland The renal capsule is a fibrous, transparent enclosure of each kidney The adipose capsule of fat helps hold the kidneys in place

On page 503 in your book and expect it on the test

15.1 Kidneys When a kidney is cut lengthwise, three distinct regions are shown The outer region, which is lightly colored is called the renal cortex The middle region, called the renal medulla, is dark reddish-brown and contains triangle shapes called medullary pyramids Near the hilus is the renal pelvis which is a basin like cavity

On page 504 in your book

15.1 Kidneys Kidney blood supply; About 1/4th of the total blood supply passes through the kidneys each minute The arterial supply of each kidney is the renal artery which is a branch off of the aorta As the renal artery approaches the hilus it branches into segmental arteries, which further branch (see next slide)

15.1 Kidneys Nephrons Each kidney contains over a million functional units called a nephron Each nephron consists of two main parts; a glomerulus (knot of capillaries) and a renal tube The closed end of the renal tube is cup shaped and surrounds the glomerulus; its called the Bowman’s capsule or glomerular

15.1 Kidneys The renal tube extends about 1.25 inches PCT: proximal convoluted tubule is a twisted section of the renal tube just after the Bowman's capsule Loop of Henle: after the PCT, a long loop of the tube surrounded by capillaries DCT: distal convoluted tubule is a twisted section after the loop Collecting duct: receives urine from the nephron

15.1 Kidneys On page 506 in your book and expect it on your test

15.1 Kidneys Urine Formation Filtration: nonselective, passive process that occurs at the glomerulus due to pressure in the blood Tubular reabsorption: most occurs in the PCT, but some also occurs in the DCT and collecting duct Most of the reabsorption is passive but some is active Tubular secretion: reabsorption in reverse, primarily removing substances not already filtered

On page 508 in your book

15.1 Kidneys Urine makeup and characteristics: Urine contains urea (formed in the liver as an end product of protein breakdown) uric acid (released when nucleic acids are metabolized) and creatinine (metabolism in muscle tissue) In 24 hours the kidneys filter from 150-180 L of blood plasma and 1.0-1.8 L of urine are produced It is clear and pale to deep yellow (the more dilute the paler it is) The color is due to urochrome, a pigment that results from the breakdown of hemoglobin Eating certain foods can temporarily color our urine

15.2 Ureters, Bladder & Urethra The ureters are slender tubes about 10-12 inches long A ureter runs from the hilus of each kidney along the back of the body and along the back of the bladder, entering the bladder on the posterior side at a slight angle The ureters are passageways that carry urine from the kidney to the bladder

15.2 Ureters, Bladder & Urethra The bladder is smooth, collapsible, muscular sac that temporarily stores urine The bladder is in the pelvic region The trigone is the slightly triangular region just above the urethral opening in the bladder

On page 512 in your book

15.2 Ureters, Bladder & Urethra The urethra is a thin walled tube that carries urine, by peristalsis, from the bladder to the outside of the body At the bladder-urethral junction is a thickening of smooth muscle call the internal urethral sphincter Its control is involuntary and keeps the urethra closed when urine is not being passed (called micturition or voiding) The need to void usually happens when the bladder contains about 200 ml, which causes it to stretch and impulses are sent to the spinal nerves to cause contractions that push urine past the internal urethral sphincter and tell you its time to go to the bathroom

15.2 Ureters, Bladder & Urethra The external urethral sphincter is made of skeletal muscle and is voluntary The control of this is what is learned in potty training

15.3 Fluid, electrolyte and Acid/Base Balance Electrolyte changes cause water to move, severe changes can cause problems with blood volume and pressure We need to make sure we take in more water than we lose and water isn't just lost through the formation of urine; we lose about 8% in sweat, 28% in through our skin and lungs ( we aren't aware of this) and about 4% in the production of feces

15.3 Fluid, electrolyte and Acid/Base Balance Reabsorption of water and electrolytes is regulated by the kidneys through hormones ADH: antidiuretic hormone prevents the excess loss of water in urine Aldosterone: regulates the sodium and other electrolyte levels Renin: causes an increase in blood pressure and blood volume

15.3 Fluid, electrolyte and Acid/Base Balance Acid/Base balance is maintained by blood buffers A buffer is a substance that can balance an acid or base Most of fluids in in the body have a neutral pH (7) For example if you have a stomach ache it is usually because it is over acidic so you take Pepto (which is basic) to counteract it