THE EXCRETORY SYSTEM(AKA THE URINARY SYSTEM)

FUNCTIONS OF THE URINARY SYSTEM

• Elimination of waste products

• Nitrogenous wastes = uric acid

• Toxins

• Drugs

• Regulation of homeostasis by maintaining balanced levels of:

• Water

• Electrolytes

• Acid-base in the blood

• Blood pressure

• Red blood cell production

• Activation of vitamin D

ORGANS OF THE URINARY SYSTEM

• KIDNEYS

• URETERS

• URINARY BLADDER

• URETHRA

KIDNEY

• Two bean shaped structures

• Extract waste from the blood

• Form urine

STRUCTURES OF THE KIDNEYS

• Nephrons = the filtering units of the kidneys

• Responsible for forming urine

• Main structures of the nephrons:

oGlomerulus

oRenal tubule

GLOMERULUS

• A specialized bundle ofcapillaries

• Attached to arterioles on both sides to maintain an even pressure

• Filtration system

RENAL TUBULE• Carries fluids to the glomerulus

• Made up of the:

o Glomerular (Bowman’s) capsule

o Proximal convoluted tubule

o Loop of Henle

o Distal convoluted tubule

TYPES OF NEPHRONS

• CORTICAL NEPHRONS

o Located entirely in the cortex

(outer portion of the kidney)

• JUXTAMEDULLARY NEPHRONS

o Found at the boundary of the

cortex and medulla (inner portion

of the kidney)

URINE FORMATION PROCESSES

URETERS

• Slender tubes attaching the

kidney to the bladder

• Peristalsis (rhythmic

contractions) aids gravity in

urine transport

URINARY BLADDER

• Smooth, collapsible, muscular sac

• Temporarily stores urine

• Trigone = three openings

• Two from the ureters

• One to the urethra

• Walls consist of:

o Three layers of smooth muscle

o Mucosa made of transitional

epithelium

• Can expand significantly without

increasing internal pressure

URETHRA

• Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis

• Females – only carries urine

• Males – carries urine and is a passageway for sperm cells

• Release of urine is controlled by two sphincters

• Internal urethral sphincter (involuntary)

• External urethral sphincter (voluntary)

FUN FACT!

A sphincter is a ring of muscle that opens and closes a tube.

Believe it or not you have over 50 sphincters in your body.

Learn more about them in this video:

https://www.youtube.com/watch?v=gtLO9rpXV0g

MICTURITION (VOIDING)

• Both sphincter muscles must open to allow voiding

• The internal urethral sphincter is automatically relaxed after

stretching of the bladder

• The external urethral sphincter must be voluntarily relaxed

MAINTAINING WATER BALANCE• Water intake must equal water output

• Sources for water intake

• Ingested foods and fluids

• Water produced from metabolic processes

• Sources for water output

• Vaporization out of the lungs

• Lost in perspiration (sweat)

• Production of saliva and tears

• Leaves the body in the feces

• Urine production

• Regulation is primarily by hormones

• Antidiuretic hormone (ADH) prevents excessive water loss in urine

• Aldosterone regulates sodium ion content of extracellular fluid

• Cells in the kidneys and hypothalamus are active monitors of water and electrolyte balance

MAINTAINING ACID-BASE BALANCE IN BLOOD• Blood pH must remain between 7.35 and 7.45 to maintain homeostasis

• Alkalosis – pH above 7.45

• Acidosis – pH below 7.35

• Most ions originate as byproducts of cellular metabolism

• Most acid-base balance is maintained by the kidneys

• Other acid-base controlling systems

• Blood buffers

• Respiration