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Birgit Woelker, PhD
Chapter 16
Urinary System and Excretion
Animals must dispose of nitrogenous wastes
• Nitrogenous wastes are toxic breakdown products of protein Proteins Nucleic acids
Amino acids Nitrogenous bases
— NH2 Amino groups
Most aquatic animals, including most fishes
Mammals, amphibians, sharks, some bony
fishes
Birds and many other reptiles, insects, land
snails
NH3 O C NH2
NH2
O
C C
C O
O C
C
N H N
H
HN
H N
Uric acid Urea Ammonia
The liver per forms many functions, including the production of urea
Liver
Intestines
Kidneys
Hepatic Portal vein
The liver produces urea, breaks down toxins, produces bile, plasma proteins, and lipoproteins and it adjusts the nutrient content of the blood
Organs of the Urinary System
Functions of the urinary System
1. Kidneys
2. Ureters
3. Urinary Bladder
4. Urethra
1. Excretion of Metabolic Wastes
2. Maintenance of Water-Salt Balance
3. Maintenance of Acid-Base Balance
4. Secretion of Hormones
1. Kidneys produce urine.
2. Ureters transport urine.
3. Urinary bladder stores urine.
4. Urethra passes urine to outside.
renal artery
renal vein
aorta
inferior vena cava
• Urine leaves the kidneys via ureters
– Is stored in the urinary bladder, and is expelled through the urethra
Renal cortex
Renal medulla
Renal pelvis
Ureter
B The kidney
• Nephrons, the functional units of the kidneys extract a filtrate from the blood and refine it to urine
Bowman’s capsule
C Orientation of a nephron within the kidney
Renal artery
Renal vein
Nephron tubule
Collecting duct
To renal pelvis
Renal cortex
Renal medulla
Capillaries
glomerulus
collecting duct
Renal Cortex
glomerular capsule (Bowman's capsule)
proximal convoluted
tubule
distal convoluted
tubule
venule
peritubular capillary network
descending limb Loop of the nephron (loop of Henle)
ascending limb
renalvein renal artery
afferent arteriole
efferent arteriole
Renal Medulla a. A nephron and its blood supply
16.2 Anatomy of the Kidney and Excretion
Filterable Blood Components
Nonfilterable Blood Components
Water Formed elements (Blood cells and platelets)
Nitrogenous wastes Plasma proteins Nutrients Salts (ions)
Becomes part of filtrate Remains in blood
Urine Formation
– Nephrons filter about 180 liters of primary filtrate water per day
– Most of the water, nutrients and salt are reabsorbed
– Nitrogenous waste and toxins get excreted
• Reabsorption and secretion in a nephron
Blood
Bowman’s capsule
Proximal tubule Distal tubule
NaCI – HCO3
Nutrients H2O
Some drugs and poisons
+ H
Cortex
NaCI – HCO3
H2O
+ H + K
Collecting duct
Loop of Henle NaCI
NaCI
NaCI
Urea
H2O
H2O
Urine (to renal pelvis)
Medulla
Filtrate composition H2O NaCI HCO3
H Urea Glucose Amino acids Some drugs
+ –
Reabsorption
Secretion
Antidiuretic hormone (ADH) regulates the amount of water the kidneys excrete
Aldosterone regulates Na+ reabsorption
Major processes of the excretory system
• Filtration: blood pressure forces water and many small solutes into the nephron
• Reabsorption: valuable solutes are reclaimed from the filtrate
H2O, other small molecules Urine
Excretion Secretion Reabsorption Filtration
Capillary Interstitial fluid
Nephron tubule
• Secretion: excess H+ and toxins are added to the filtrate
• Excretion: The finished product, urine is excreted
Regulatory Functions of the Kidneys Acid-Base Balance
• Normal pH for most body fluids is 7.4
• Alkalosis: pH is greater than 7.4
• Acidosis: pH is less than 7.4
• Several Mechanisms Maintain a pH of ~ 7.4
– Acid-Base buffer system
– Respiratory Center
– The Kidneys
Regulatory Functions of the Kidneys Acid-Base Balance
• Acid-Base Buffer Systems
– Buffer – chemical or combination of chemicals • Can take up excess H+ or OH�• Prevents large changes in pH
– When H+ added to blood the following occurs H+ + HCO3
� ! H2CO3
– When OH- added to blood the following occurs OH- + H2CO3 ! HCO3
� + H2O
Acid-Base Balance
HCO3-
NH4+
H+
capillary
kidney tubule
H+ + NH3+ HCO3
-
Disorders of the Urinary System Disorders of the Kidneys
• Many major illnesses can cause kidney disease
– Diabetes, hypertension, and certain autoimmune diseases, can also cause serious kidney disease
– Pyelonephritis: Infections of the kidneys
– Kidney Stones
– Retention of water and salt lead to edema • Can lead to heart failure
An Artificial Kidney Machine - Dialysis
pump
blood
semipermeable tubing dialysate flow
blood flow
dialysate
used dialysate (contains urea
and excess salts)
fresh dialysate
Do we need to drink eight glasses of water each day?
Recently researchers have had success in growing entire human bladders in the lab, and implanting them into a limited number of patients
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