Excretion Flashcards
Excretion in plants
Plants also excrete waste products of metabolism
In light, leaves produce oxygen from photosynthesis
In dark, plant excrete CO2 from respiration
Plant exchange these gases through pores in the leaf called stomata
Excretion in humans
Unlike plants, humans have organs which are specialised for the removal of certain excretory products
Excretory organs in humans include lungs, kidney, skin
Lungs, what it excretes, and explanation
Excretes Carbon dioxide during exhalation
Kidneys, what it excretes, and explanation
Excretes excess water, excess salts and urea by producing urine
Skin, what it excretes, and explanation
Excretes water, salts and urea through sweat glands in the skin. Not excreted as excess but rather to lower body temperature
What are 2 main functions of the kidney and explain
Excretion- process by which waste products of metabolism are removed from the body
Osmoregulation- Control of water content in the blood plasma
What is Homeostasis?
Keeping the conditions in the internal environment relatively constant, particularly blood together with another liquid called tissue fluid
Eg: Blood glucose level, blood water and salt, blood ph, body temperature, CO2 levels in blood
Homeostasis is important to cells, as cells will only function properly if they are bathed in tissue fluid, which contains optimum conditions. Otherwise, cells might not function efficiently and cause permanent damage
Tissue fluid
Watery solution of glucose, salts, and other solutes surrounds the cells of the body forming a pathway for the transfer of nutrients between blood and the cells
Tissue fluid is formed by leakage from blood capillaries, it is similar to blood plasma but it lacks plasma proteins
Urea
Formation takes place in Liver
It is the main excretory product of the human kidneys
Excess amino acids are broken down in the liver by a process called deamination into urea and passes to the blood
Amino acids cannot be stored in the body as it would be toxic to cells if built in blood
Urea rich blood is filtered out by kidney tubules/nephrons to form urine
Composition of urine
Mainly urea
Water
Salt/Ions
Structure of the kidney- 3 parts
Cortex-darker outer region. Contains many blood vessels, microscopic filtering units; kidney tubules or nephrons
Medulla- middle layer has bulges called pyramids; tubules run down through this region.
Pelvis- funnel like structure that urine emptying and it connects with the ureter carrying the urine to the bladder
Nephron or kidney tubule
In kidney to to act as the filtering units of blood to form urine
Nephrons are very small structures that have their own blood supply branching off the renal artery and are responsible for filtering a small amount of blood
Nephron has a cup shaped structure, 2 coiled tubules separated by a U- shaped loop and it is joined to a collecting duct
Function of Bowman’s capsule
Filters the different sized molecules in the glomerulus under pressure in to the capsule in a process known as ultrafiltration
Function of Glomerulus
High pressure in the glomerulus forces fluid to filter through the capillary and capsule walls
Function of first coiled tube
Reabsorb all glucose from filtrate back into blood by active transport in a process known as Selective reabsorption
Function of Loop of Henle
Reabsorb water and salts from the filtrate back into the blood
Function of collecting duct
Reabsorbs most of the water in the blood depending on the ADH levels in blood in a process called osmoregulation
2 main stages in the process of urine formation
Ultrafiltration in Bowman’s capsule
Selective reabsorption
Ultrafiltration in the Bowman’s capsule
Blood vessel that carries blood away from the glomerulus has a smaller diameter than the blood vessel carrying blood in the glomerulus, so pressure in blood in the glomerulus is high
This pressure forces fluid from the blood into the Bowman’s capsule through the capsule wall
This filtrate is called glomerular filtrate
Only small items such as water, ions, glucose and urea can filter through.
Blood cells and plasma proteins are too big to filter through
Selective reabsorption
First coiled tube and second coiled tube are separated by a U-shaped loop that runs down into the medulla of the kidney called the Loop of Henle
99% of glomerular filtrate is reabsorbed by the blood and 100% of glucose is reabsorbed
Sodium ions and glucose are reabsorbed by active transport
Loop of Henle
U-shaped tube that involves with concentrating the fluid by reabsorbing more water back to the blood
Some salts and ions are reabsorbed back to the blood
Size of Loop of Henle in animals
Long LH- can make more concentrated urine so that desert mammals can conserve water
Short LH- animals who have easy access to water
Mixture of long and short- human
Osmoregulation and ADH
Control of body’s water content
Changes to volume of urine are controlled by hormone ADH produced by the pituitary gland
ADH travels through the blood to the kidney and acts on the kidney tubules
Action of ADH follows the principle of Negative Feedback
Action of ADH
ADH causes the collecting ducts to be more permeable to water so that more water is reabsorbed back into the blood
This makes urine more concentrated, so body loses less water and blood becomes more dilute
