27. Excretion Flashcards
Excretion def.
Excretion is the removal of waste products of cellular metabolism from an organism.
Nitrogenous wastes
Urea and Uric acid
Types of organs and their waste products
Lungs: Carbon Dioxide and water vapour.
Skin: Sweat- salts and water
Kidneys: Urine-urea, water and salts
How uric acid is formed
Nucleic acid broken down by liver (DNA and RNA)
How urea formed
Excess amino acids are broken down by the liver
Where are kidneys located
Abdominal Cavity
Urinary system labels
Vena cava Aorta Kidneys Renal vein and artery Ureter Urinary bladder Urethra
Functions
Renal Artery
Kidney
Renal vein
RA: carries blood with wastes to kidneys
K: Filters blood to remove these wastes and form urine.
RV: carries blood free of wastes away from kidneys
Functions
Ureters
Bladder
Urethra
Ureters: Transport urine to bladder
Bladders: Stores urine
Urethra: Releases urine
Label kidney
Renal Artery Nephron Cortex Medulla Pelvis Ureter Renal Vein
Functions of kidneys
- Excretion-
forming urine (excretes urea, salts, water) - Osmoregulation
- Control pH of body (urine more or less acidic)
pH of Body
7.4
How kidney forms urine
In nephron
- Filtration: Filters blood entering from the renal artery. Force wastes into kidneys
- Reabsorption: Useful substances are passed back into the blood and into the renal vein and transported by the body.
- Secretion: Substances pass from the blood into the kidneys to be excreted out.
- Filtration process
- Blood enters kidneys via renal artery with wastes and food particles.
- Renal artery divides into afferent arterioles and then into a capillary network: glomerulus at top of each nephron.
- Bowmans capsule surrounds each glomerulus
- Smaller molecules forced out of the blood in the glomerulus and into the bowmans capsule (salt, water, glucose, amino acids, vits, minerals)
- Large proteins and blood cells remain in the blood, they don’t pass into the bowmans capsule.
What type of pressure are molecules under in filtration
Ultra Filtration
How is filtration aided
Glomerulus: has thin walls, porous. Large supply of capillaries. Under high pressure as efferent arteriole is narrower than the afferent arteriole
Nephron structure
Renal Artery, Afferent arteriole, glomerulus, bowmans capsule, proximal convoluted tubule, descending loop of Henle, ascending LoH, Distal Convoluted tubule, Collecting duct, Pelvis to ureter to bladder and urethra.
Efferent arteriole, renal vein
Where does filtration occur
Glomerulus and bowmans capsule of nephron found in cortex of kidney
Reabsorption process
- Glomelular filtrate passes from the bowmans capsule into proximal convoluted tubule. (glucose, amino acids, vitamins, minerals, some salts and water reabsorbed back into blood.
- Glomelular filtrate then passes into descending loop of henle. Most water reabsorbed by osmosis. Into Ascending loop of Henle, salt reabsorbed by diffusion and active transport.
- GF passes to distal convoluted tubule, water and salts reabsorbed.
- GF into collecting duct, water reabsorbed.
- Urine then passes to the renal pelvis to the ureters and to the bladder.
How is reabsorption aided
Proximal and distal convoluted tubules have:
Thin walls
Large surface area/long
Many mitochondria (energy)
Beds of microvilli increased absorption due to an increased surface area.
What is Secretion
Where it happens
Secretion is where substances pass from the blood into the kidney.
Occurs in distal convoluted tubule and ascending loop of henle
Secretion process
Salt, water, potassium and hydrogen ions pass from the blood into the kidneys to be excreted in the urine.
why is secretion important for homeostasis
So blood isn’t diluted with with water (osmoregulation)
So pH remains 7.4
Osmoregulation definition
Is the maintenance of a constant water balance in an internal environment in an organism.
ie. Keeps bodily fluids and blood being too diluted or concentrated.
Hormone that controls Osmoregulation in the kidneys
Where produced and full name
Hormone called ADH. Secreted by pituitary
Antidiuretic hormone
What happens when body dehydrated
Blood concentration is high/low in water. Pituitary picks this up and secretes ADH. This stimulates distal convoluted tubule and collecting duct to reabsorb water into blood.
Results: Small amount of concentrated urine.
Causes of dehydration
Sweating, diarrhoea, exercise, high salty diet
What happens when high levels of water in body
Water conc. high. Pituitary picks this up and no ADH is secreted. DCT and collecting duct not permeable to water. No water reabsorbed into blood.
Result: Large amounts of dilute urine produced
Why would urine be high in Urea
High protein diets
What is the functional part of kidney
The nephron
Where in kidney does filtration take place?
Large diagram and in nephron
Cortex and glomerulus
Where in kidney does reabsorption take place?
Large diagram and in nephron
Medulla and tubules
