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Unit 2

Urinary System

Functions of the Urinary System
1
...
Elimination of waste products
• nitrogenous waste
• toxins
• drugs
2
...
Kidneys-preform functions listed previously
2
...
Urinary Bladder
4
...
1a

Kidneys
Characteristics of the Kidneys: renal=kidney
▪ against the dorsal body wall
▪ at the level of T12 to L3
▪ right kidney is slightly lower than the left
because of the liver
▪ attached to ureters, real blood vessels, and
nerves at the renal hilum (kidney indent)
▪ atop each kidney is an adrenal gland
(endocrine)

Organs of the Urinary system
adrenal gland
renal blood
vessels
(vein and artery)

Kidney
Ureter

Kidney
renal hilum

Ureter
Urinary
bladder
Urethra
Figure 15
...
Renal fascia
▪ outermost
▪ helps hold them in correct location
2
...
Fibrous capsule
▪

innermost, encloses each kidney

Anatomy of the Kidney
There are three regions:
-renal cortex (outer)
-renal medulla (middle)
-renal pelvis (inner)

Anatomy of the Kidney
1
...
2

Anatomy of the Kidney
2
...
2

Anatomy of the Kidney
3
...
2

Anatomy of the Kidney
Renal cortex
Renal column

Renal medulla
(pyramids)

renal pelvis

calyces (calyx)

Figure 15
...
2

Blood Flow in the Kidneys
Very rich blood supply to kidneys
▪
▪
▪

1/4 of blood in body goes through per minute
continuously cleanses blood
adjusts composition of blood

Anatomy of the Kidney
Nephrons
▪

structural and functional units of kidneys

▪

responsible for forming urine

2 main structures of nephrons:
1
...
Renal tubule

Anatomy of the Kidney
Glomerulus

cortex

- specialized capillary bed

renal tuble
glomerulus

Renal Tubule
- tube that extends from
the glomerulus to
collecting duct

collecting duct

medulla
Figure 15
...
3

Glomerulus
▪ Attached to arterioles
on both sides
▪ afferent arteriole
(large) brings blood
to the glomerulus
▪ efferent arteriole
(narrow) brings
blood away from the
glomerulus

Figure 15
...
distal convoluted
tubule
(DCT)

collecting duct

2
...
glomerular
capsule

3
...
3

Capillaries of the Nephron
Two types:
1
...
Peritubular capillaries
▪

arise from efferent
arteriole

▪

around renal tubule

▪

low pressure capillaries

▪

attached to a venule

▪

exits capsule

peritubular capillaries

Organs of the Urinary system
1
...
Ureters
3
...
Urethra
▪

all three involved in storage and transport of urine

Ureters
▪ slender tubes attaching kidney to bladder
(25-30 cm long)
▪ continuous with renal pelvis
▪ enter the posterior aspect of bladder
▪ peristalsis and gravity help transport urine
▪ urine is prevented from flowing backwards by valves

Anatomy of the Kidney
Renal cortex
Renal column

Renal medulla
(pyramids)

Renal pelvis
Calyces
ureter

Figure 15
...
6

Urinary Bladder
▪ 3 layers of smooth muscle
▪ Mucosa made of transitional epithelium
▪ Walls are thick and folded when empty
▪ Expands significantly

Figure 15
...
Internal urethral sphincter (involuntary)
2
...
Afferent arteriole
(large)

4
...
Glomerular
capsule
2
...
Peritubular capillaries
Collecting duct

Loop of Henle
Figure 15
...
Micturition (urination)
2
...
Maintaining homeostasis
- water/electrolyte (salt) balance
- acid/base (pH) of blood

1
...
bladder fills to about 200 ml which stretches
bladder wall
2
...
strong contractions force urine past involuntary
internal urethral sphincter causing urge to void
(pee)
4
...
Urine Formation Processes
3 Processes Form Urine:
a) Glomerular Filtration
b) Tubular Reabsorption
c) Tubular Secretion

Urine Formation Processes
a) Glomerular Filtration
▪ nonselective(not being selective of what it filtrates)
passive process(no energy needed)
▪ water and solutes smaller than proteins are forced
through walls of glomerular capillaries into capsule
due to high pressure
▪ small stuff (water&solutes) go out of blood stream in
capsule, large stuff (proteins) stays in blood stream
▪ moves into the proximal convoluted tubule portion of
the renal tubule
▪ blood cells are too large to pass out of the capillaries

Urine Formation Processes
Glomerular Filtration

Afferent arteriole

(1)

Glomerular

capillaries
Efferent

arteriole

1

Glomerular

capsule
Rest of

renal tubule

containing

filtrate

2

3

Figure 15
...
4

Glomerular

capillaries

Peritubular

capillary

Urine Formation Processes
b) Tubular Reabsorption
▪ some materials remain in renal tubule during tubular
reabsorption:
▪ excess water (that the body no longer needs)
▪ nitrogenous waste products
▪ UREA (from protein breakdown)
▪ URIC ACID (from nucleic acid breakdown)
▪ CREATININE(waste from muscle metabolism)

Urine Formation Processes
c) Tubular Secretion
▪

“reabsorption in reverse”

▪

some materials move back from peritubular
capillaries into renal tubule

▪

this is to make sure the blood is exactly how it
should be (perfect) “last minute tuning”
▪
▪
▪

hydrogen ions
potassium ions
drugs

- materials left in renal tubule move to collecting duct
and then towards renal pelvis to bladder

Urine Formation Processes
Tubular Secretion

Afferent arteriole

(3)

Glomerular

capillaries
Efferent

arteriole

1

Glomerular

capsule
Rest of

renal tubule

containing

filtrate

2

3

Figure 15
...
Maintaining Water Balance
▪ Normal amount of water in the human
body

▪ Young adult females – 50%
▪ Young adult males – 60%
▪ Babies – 75%
▪ Old age – 45%

Distribution of Body Fluid
Water occupies two main locations:
1
...
Extracellular fluid (outside cells)
▪
▪
▪
▪
▪

Interstitial fluid
Blood plasma
Cerebrospinal fluid
Serous fluids
Humor(aqueous and vitreous) of the eye

The Link Between Water and Salt
Electrolytes
▪ changes in electrolyte balance causes water
to move from one location to another▪ water follows salt-Increase in
electrolytes=water follows
▪ creates high blood pressure and alters
blood volume
▪ can impair the activity of cells

Maintaining Water Balance
▪

water intake must equal water output=balance

▪

sources for water intake include:
▪ 1
...
Water produced from metabolic processes
(cellular respiration)
▪ sources for water output include:
▪ 1
...
Sweating - lost in perspiration
▪ 3
...
Crying
▪ 5
...
Antidiuretic hormone (ADH)
• causes kidney to reabsorb more water
• less urine/ concentrated produced
2
...
Blood Buffers
2
...
Kidneys

Blood Buffers
Acid- A substance that releases hydrogen ions
(H+) in a solution(blood plasma)
...

Base- A substance that pick up hydrogen ions
(H+) in a solution(blood plasma)
...


Blood Buffers
pH Scale
▪ measures how acidic or basic a solution is
▪ pH 7= Neutral

Basic

▪ pH 7+= Basic
▪ pH 0-7=acidic
Neutral

Acidic

Blood Buffers
pH
▪ determined by how many hydrogen ions (H+) are in
a solution
▪ Acidic solution- has lots of hydrogen ions
(H+)
▪ Basic solution- have very few hydrogen
ions (H+)

Blood Buffers
Acidic solutions have lots of
hydrogen ions (H+)

Blood

Basic solutions have few hydrogen
ions (H+)

Figure 2
...
35 and 7
...
45

Acidosis

▪ blood pH below 7
...
35
-7
...
Blood buffers
2
...
Kidneys

Maintaining Acid-Base Balance in Blood
Respiratory Control
▪ carbon dioxide transported in plasma
▪ too much carbon dioxide causes blood pH to
lower(too acidic)
▪ respiratory rate can increase to get rid of
more CO2 returning blood to normal pH

Maintaining Acid-Base Balance in Blood
Kidneys
▪ regulate what is in our blood and excrete what
we don’t want (in urine)
▪ If blood pH rises(too basic), bicarbonate ions are
excreted(in urine) because ions get ride of H+, but when ph
rises you need more H+

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