Excretion In Humans and osmoregulation - The kidneys Flashcards
What are the three main roles of the kidneys and how do they do this?
1) removal of urea from the blood
2) adjustment of salt levels in the blood
3) adjustment of water content of the blood
They do this by filtering stuff out of the blood under high pressure, and then reabsorbing the useful things. The end product is urine.
What is the first step of blood passing through the nephron?
Ultrafiltration:
1) blood from the renal artery flows through the glomerulus.
2) a high pressure is built up which squeezes water, urea, salts and glucose out of the blood and into the Bowman’s capsule.
3) the membranes between the blood vessels in the glomerulus and the Bowman’s capsule act like filters, so big molecules like proteins and blood cells are not squeezed out. They stay in the blood. The filtered liquid in the Bowman’s capsule is known as the glomerular filtrate.
What is the glomerulus?
A bundle of capillaries at the start of the nephron
What is the second step of blood passing through the nephron?
Reabsorption:
As the filtrate flows along the nephron, useful substances are selectively reabsorbed back into the blood:
1) all the glucose is reabsorbed from the proximal convoluted tubule. This involves the process of active transport across the concentration gradient.
2) sufficient salt is reabsorbed. Excess salt isn’t.
3) sufficient water is reabsorbed from the collecting duct into the bloodstream.
What is the third step of blood passing through the nephron?
Release of wastes:
The remaining substances (including water, salt and urea) form urine. This continues out of the nephron, through the ureter and down to the bladder, where it is stored before being realised via the urethra.
How is water lost from the body?
Sweating, breathing and weeing
How is water taken into the body?
Food and drink
What is osmoregulation?
The body has to constantly balance the water coming in against the water going out
What is ADH?
Anti-diuretic hormone which controls the amount of water reabsorbed in the kidney nephrons
What does ADH do?
ADH makes the nephrons more permeable so more water is reabsorbed back into the blood
What is negative feedback?
If the water content gets too high or too low a mechanism will be triggered that brings it back to normal
Low blood water content means…
Increased ADH production and more water reabsorbed into the kidneys
High blood water content means…
Decreased ADH production and less water reabsorbed
Where is urea produced?
In the liver
Is blood entering the glomerulus under high pressure or low pressure?
High pressure
Where is urine stored before being released from the body?
The bladder
What is the bladder?
Where urine is held in the body before it is released into the environment.
What is the Bowman’s capsule?
The cup shaped structure at the start of a nephron where ultrafiltration occurs.
What is a collecting duct?
The tube at the end of a nephron, where additional water is reabsorbed from urine.
What are convoluted tubules?
The two sections of a nephron closely associated with a capillary; selective reabsorption of glucose takes place in the proximal convoluted tubule.
What is the glomerular filtrate?
The liquid in the Bowman’s capsule produced by ultrafiltration.
What is the glomerulus?
A small knot of capillaries associated with a Bowman’s capsule.
What is the hypothalamus?
The part of the brain that monitors water content of the blood.
What is the loop of henlé?
A large loop of the nephron which dips into the medulla of the kidney.
What is a nephron?
A tiny kidney tubule where ultrafiltration and reabsorption take place to produce urine.
What is osmoregulation?
The regulation of the concentration of water in the blood.
What does the urinary system include?
Kidneys, ureters, bladder and urethra
What is selective reabsorption?
The reabsorption of more of some substances than others.
What is ultrafiltration?
Filtration on a molecular scale, as happens between the glomerulus and Bowman’s capsule.
What are the ureters?
Tubes that connect the kidneys to the bladder. The urethra is a tube that connects the bladder to the outside of the body.
What is urine?
A liquid waste produced by kidneys, containing water, urea and salts.
