Chapter 15The Urinary System

Functions of the Urinary SystemFunctions of the Urinary System1. Elimination of waste

Nitrogenous wastes

Toxins

Drugs

2. Regulates homeostasis

Water balance

Electrolytes

Acid-base balance in the blood

Blood pressure

RBC blood cell production

Activation of vit. D

Organs of the Urinary systemOrgans of the Urinary system

Kidneys

Ureters

Urinary bladder

Urethra

Location of the KidneysLocation of the Kidneys

Against dorsal wall

T12 to L3

Right lower than left

Attached to ureters, renal blood vessels, & nerves at renal hilus

Atop kidney is adrenal gland

Coverings of the KidneysCoverings of the Kidneys1. Renal capsule

Surrounds kidney

2. Adipose capsule Surrounds kidney

protection

keeps kidney in location

Regions of the KidneyRegions of the Kidney

Renal cortex – outer region

Renal medulla – inside the cortex

Renal pelvis – inner collecting tube

Kidney StructuresKidney Structures Medullary pyramids

– triangular regions of tissue in medulla

Renal columns – extensions of cortex-like material inward

Calyces – cup-shaped structures that funnel urine towards renal pelvis

Blood Flow in the KidneysBlood Flow in the Kidneys

NephronsNephrons Structural and

functional units of the kidneys

Forms urine

Main structures

a. Glomerulus

b. Renal tubule

GlomerulusGlomerulus

Capillaries covered with podocytes from the renal tubule

Glomerulus sits within a glomerular capsule (1st part of the renal tubule)

Specialized capillary bed

Arterioles on both sides (maintains high pressure)

- Large afferent arteriole

- Narrow efferent arteriole

Renal TubuleRenal Tubule Glomerular

(Bowman’s) capsule

Proximal convoluted tubule

Loop of Henle

Distal convoluted tubule

Types of NephronsTypes of Nephrons1. Cortical

entirely in cortex

most nephrons

2. Juxtamedullary at boundary of

cortex & medulla

Urine FormationUrine Formation Filtration

Reabsorption

Secretion

Peritubular CapillariesPeritubular Capillaries Arise from efferent arteriole

Normal, low pressure capillaries

Attached to venule

Cling to renal tubule

Reabsorb substances from collecting tubes

FiltrationFiltration Nonselective passive process

Water and solutes smaller than proteins are forced through capillary walls

Blood cells cannot pass out to the capillaries

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

ReabsorptionReabsorption Peritubular capillaries reabsorb

- Some water, Glucose, Amino acids, Ions

Some passive, most active

Most reabsorption occurs in proximal tubule

Nitrogenous waste products

- Urea

- Uric acid

- Creatinine

Excess water

Not ReabsorbedNot Reabsorbed

Secretion – Reabsorption in ReverseSecretion – Reabsorption in Reverse Materials move from peritubular capillaries into

renal tubules

- H+ & K+

- Creatinine

Materials left in renal tubule move to ureter

Formation of UrineFormation of Urine

Figure 15.5

Characteristics of UrineCharacteristics of Urine

Yellow due to pigment urochrome (from break-down of hemoglobin) & solutes

Sterile

Slightly aromatic

Normal pH of ~ 6

Specific gravity of 1.001 to 1.035

UretersUreters

Slender tubes from kidney to bladder

- Continuous with renal pelvis

- Enter the posterior aspect of the bladder

Runs behind the peritoneum

Peristalsis aids gravity in urine transport

Urinary BladderUrinary Bladder Smooth, collapsible,

muscular sac

Temporarily stores urine

Trigone – 3 openings

- Two from ureters

- One to urethrea

Urinary Bladder WallUrinary Bladder Wall

Detrusor muscle – pushes down

3 layers of smooth muscle

Walls - thick & folded in empty bladder

Transitional epithelium - expands without increasing internal pressure

UrethraUrethra Thin-walled tube

Carries urine from bladder by peristalsis

Release controlled by 2 sphincters

- Internal urethral sphincter (involuntary)

- External urethral sphincter (voluntary)

Urethra Gender DifferencesUrethra Gender Differences

Length

- Females – 3–4 cm (1 inch)

- Males – 20 cm (8 inches)

Location

- Females – along wall of the vagina

- Males – through the prostate and penis

Function

- Females – only urine

- Males –urine and sperm

Micturition (Voiding)Micturition (Voiding)

Both sphincters must open

- internal relaxes after bladder stretches

- Activation - impulse to spinal cord and back via pelvic splanchnic nerves

- external voluntarily relaxes

Maintaining Water BalanceMaintaining Water Balance

Normal amount of water in humans

- Adult females – 50%

- Adult males – 60%

- Babies – 75%

- Old age – 45%

Water is necessary for many functions and levels must be maintained

Water intake = water output

Sources for water intake

- foods and fluids

- metabolic processes

Sources for water output- Vaporization from lungs

- perspiration

- feces

- Urine

Distribution of Body FluidDistribution of Body Fluid

Intracellular fluid (inside cells)

Extracellular fluid (outside cells)

- Interstitial fluid

- Blood plasma

Figure 15.7

Link Between Water and SaltLink Between Water and Salt

Changes in electrolyte balance causes water to move from one compartment to another

- Alters blood volume & blood pressure

- Can impair the activity of cells

Regulation of ReabsorptionRegulation of Reabsorption

Hormones

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

- Aldosterone regulates sodium

- Triggered by the renin-angiotensin mechanism

Monitored by kidneys and hypothalamus

Maintaining Blood pHMaintaining Blood pH Normal Blood pH

- Alkalosis – pH above 7.45

- Acidosis – pH below 7.35

Most ions are metabolic byproducts

Most pH balance is maintained by kidneys

Other acid-base controlling systems

- Blood buffers

- Respiration

Blood BuffersBlood Buffers Molecules to prevent dramatic changes in [H+]

- Bind to H+ when pH drops

- Release H+ when pH rises

Three major chemical buffers

- Bicarbonates

- Phosphates

- Proteins

Buffering SystemsBuffering Systems

DevelopmentalDevelopmental Control of voluntary sphincter ~ 18 mos

Urinary infections - common problems

Bladder shrinks

Decline in function

Retention if prostate enlarges (males)

AgingAging

Fetal/NewbornFetal/Newborn Functional kidneys by 3rd month

Bladder is small in newborn

Urine cannot be concentrated