Download The Urinary System - leavingcertbiology.net

Chapter 37: The human
urinary system
Leaving Certificate Biology
Higher Level
The Urinary System
• The urinary system consists of:
– Kidneys – filters/purifies the blood
– Ureters – carries the urine from kidney to
bladder
– Bladder – stores urine until pressure builds up
and urine is released
– Urethra – passes the urine from the bladder to
the outside of the body
Macrostructure
of the Urinary
System
Structure
and
Position of
Nephrons
Structure of Bowman’s Capsule
Glomerulus
Afferent arteriole
Bowman’s capsule
Efferent arteriole
Structure of Nephron
The Urinary System
• The urinary system is an excretory system
that consists of the critical excretory
organs, the kidneys
• The kidneys are excretory organs
because they get rid of the waste products
of metabolism from the blood
– REMEMBER!
• Metabolism is the sum of all the chemical
reactions occurring in the body
• Homeostasis is the process of maintaining a
constant internal environment
The Urinary System
• In addition to filtering the blood the kidneys
also have other functions:
– Osmoregulation (water balance)
– Chemical regulation (salt and other chemical
balance)
– pH balance
Urine Formation
•
Urine formation occurs in two main
steps:
1. Filtration
2. Selective reabsorption
Urine Formation
1. Filtration:
– Occurs in the glomerulus – blood passes
into glomerulus via afferent arteriole and
passes out deficient in many substances via
the efferent arteriole
– The afferent arteriole is wider than the
efferent arteriole so as to cause an increase
in blood pressure within the glomerulus so
that filtration occurs more efficiently
– Glomerular filtrate is produced which passes
into the Bowman’s capsule – it does not
contain plasma proteins as they are to big to
pass through
Urine Formation
2. Selective reabsorption:
– The glomerular filtrate contains many useful
substances that the body needs such as water,
glucose, salts, and amino acids – these must be
reabsorbed prior to excretion
– Reabsorption of these substances occurs mostly in
the proximal convoluted tubule (which is in the
cortex)
– The parts of the nephron present in the medulla of
the kidney (loop of Henle and collecting ducts) are
also involved in reabsorption of water
– Reabsorption of these substances occurs by
diffusion, osmosis (water) and active transport
(all glucose and amino acids are absorbed actively)
The Urinary System
• Osmoregulation (water balance)
– The amount of water in the blood is monitored by the
osmoreceptors in the hypothalamus of the brain:
– Not enough water in the blood → hypothalamus sends
signal to pituitary to secrete anti-diuretic hormone (ADH),
which travels in blood to distal convoluted tubules &
collecting ducts of nephrons → causes tubules to become
more permeable to water → water is reabsorbed
– Too much water in blood → hypothalamus sends signal
to pituitary to stop/reduce ADH secreted → causes distal
convoluted tubules and collecting ducts to become
impermeable to water → water is excreted