What is excretion
The process by which organisms remove waste products of metabolism
What is metabolism
Reactions that take place in cells
What are the three main roles of the kidney
- Removal of urea from blood
- Adjustment of iron (salt) levels
- Adjustment of water content in blood
What are the organs in the excretory system and what do they excrete
- Kidney: urea and water (urine)
- Lungs: carbon dioxide (exhalation)
- Skin: water salt minerals and urea (sweating)
What is the function of the renal artery
Supplies blood to each kidney
What is the function of renal vein
Takes clean blood to vena cava
What is the function of Kidneys
Excretory and homeostatic organ
What is the function of the ureter
Tubes which carry urine from kidney to bladder
What is the function of the bladder
A muscular bag which stores urine
What is the function of the urethra
Tube from bladder to exterior of body
What is the function of the sphincter muscles
They are 2 ring like muscles, they contract to close urethra and prevent flow of urine
Lower is voluntary and upper is involuntary
Describe the structure of the kidney from outside to inside
Cortex
Medulla
Nephron (spread across the medulla)
Pyramids
pelvis
Ureter
Give a brief summary of how urine is produced
Blood is filtered by the kidney removing urea, sat an water to form urine. This passes to the bladder via the ureter and then excreted via the urethra
Describe the process of ultrafiltration
- Blood from the renal artery flows into the the glomerulus which is sat inside the Bowman’s capsule
- The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood
- small molecules are forced out of bloods plasma into Bowman’s capsule, where they form what is known as the glomerular filtrate
- The substances forced out of the capillaries are: glucose, water, urea, salts
- Big molecules like proteins stay in the blood
Describe the process of selective reabsorption
In the proximal convoluted tube all glucose is reabsorbed (as it is needed for respiration) by ACTIVE TRANSPORT so there are many mitochondria in the proximal convoluted tube for energy.
Describe what happens in the loop of Henle
Salts are reabsorbed into blood by diffusion and active transport
Water follows by osmosis (loop of henle high water potential into the medulla which has a low water potential)
What happens in the collecting duct
Water is reabsorbed from collecting duct depending on how much water the body needs. The walls of collecting duct are permeable to water and permeability depends on ADH
What are the collecting duct, loop of henle, proximal convoluted tube and bowmans capsule all features of
A nephron
What is osmoregulation
The process of controlling water (and salt) levels in the body
What are the effects of being dehydrated
- The cytoplasm of all cells is largely composed of water, as is the blood plasma
- So if there is less water reactions in the cytoplasm can no longer take place
- Plasma will become more viscous and heart will have to work harder and this could result in heart disease
- Cells could lose water due to osmosis and end up with shriveled cells that will eventually die
What are the effects of having too much water in the body
Too much water in the blood results in cells swelling as water moves into them via osmosis, this has a diluting effect and can lead to cell lysis (bursting)
How is permeability of the collecting duct controlled
By anti-diuretic hormone (ADH)
What are the effects of more and less ADH
More ADH:
More permeable walls, more water is reabsorbed
Less ADH:
Less permeable walls, less water reabsorbed
What would happen if the body was dehydrated
- Hypothalamus (part of brain) detects water loss
- Sens a signal to pituitary gland to release more ADH
- Walls of collecting duct become more permeable
- More water is reabsorbed
- As a result, the kidneys produce a small volume of concentrated urine
