Excretion Flashcards
Example waste products of metabolisms
- CO2
- Excess water
- Salts
- Nitrogenous wastes (e.g. Urea, uric acid, creatinine)
- Bile pigments
Metabolism
All chemical reactions taking place in a cell
Excretion definition
Removal of metabolic wastes from the body
Egestion definition
Removal of undigested substances from the alimentary system
Secretion
Release of useful substances produced by cells for important functions
Where do waste products first go when they leave cells?
- Diffuse from cells into tissue fluid
- From here they are moved to the blood stream
Excretory organs
- Lungs
- Kidneys and bladder
- Liver and intestines
- Skin
Origin of CO2 as a waste
- Product of cellular respiration
- All cells in the body
Origin of excess water as a waste
- Product of cellular respiration
- Also from intake of fluid and food
Origin of urea as a waste
- Formed largely in the liver
- from deanimation of excess amino acids
Origin of uric acid as a waste
- End product of metabolism of nucleic acids
- e.g. DNA and RNA
Origin of creatinine as a waste
Formed from creatinine phosphate in the cells
Origin of bile pigments as a waste
- Formed in liver with haemoglobin breakdown.
- Haemoglobin from red blood cells
Main parts of the urinary system
- Two kidneys
- Two ureters
- The bladder
- The urethra
Blood vessels associated with the kidneys
- Renal artery carrying oxygenated blood and rich in wastes
- Renal vein carrying deoxygenated blood and purified of wastes
What is the urinary bladder
- Thin walled muscular sac
- Urine is temporarily stored here
- Urine enters trough the two ureters
- Exits through the urethra
Function of the ureters
Transport urine from the kidneys to the bladder
Function of the urethra
Transport urine from the bladder to outside the body
Function of the sphincter muscle
- Found at the base of the bladder
- it controls the flow of urine to the urethra
External structure of kidney
- Dark bean shaped organ
- Kidneys enclosed in fat for insulation and protection
- Hilum - renal artery, vein and ureter enter/leave
- Renal capsule - membrane surrounding kidney
Internal (macro) structure of kidney - what you see when you dissect a kidney
- Renal capsule (outer membrane)
- Cortex (directly under capsule, dark red brown colour)
- Medulla (inner region, lighter in colour)
- Collecting tubes form pyramid (broad bases face cortex)
- Renal papilla (inner tips of pyramids)
- Renal calyx (renal papilla open into renal calyces)
- Renal pelvis (calyces open into this widened region of ureter)
Nephron
Structural and functional unit of kidney
Two main parts of a nephron
- Malpighian body
- Renal tubule
Two main parts of the Malpighian body
- Bowmans capsule
- Glomerulus
Parts of the renal tubule
- Bowman’s capsule
- proximal convoluted tubule
- loop of Henle
- distal convoluted tubule
- collecting duct
Parts of the glomerulus
- Wide afferent arteriole
- Capillary network
- Narrow efferent arteriole
Parts of the loop of Henle
- Descending limb
- Ascending limb
Parts of the nephron in the cortex
- Malpighian body
- Proximal convoluted tubule
- Distal convoluted tubule
Parts of the nephron in the medulla
- Loop of Henle
- Collecting duct
Structure of the Bowman’s capsule
- Inner lining of cells are specialised (called podocytes)
- Tiny slit pores between podocytes
- pores open into hollow capsular space
Structure of the renal tubule
- Long and twisted to increase surface area
- Lined by cuboidal epithelial cells
- Cells have many mitochondria for active reabsorption
- Cells have microvilli to increase surface area
Composition of blood plasma
- Water
- Dissolved gases
- Dissolved useful substances (glucoce, salts, amino acids etc.)
- Dissolved waste substances (urea, uric acid and creatinine)
- Large plasma proteins
Where does the efferent arteriole lead to?
- A network of capillaries running closely alongside the renal tubules
- This is called the peritubular capillary network.
- these link up with other capillaries to join a branch of the renal vein.
The three main processes taking place in the nephron
- Glomerular filtration / ultrafiltration
- Tubular re-absorption
- Tubular excretion
Glomerular filtration
- Blood in glomerulus under great pressure (narrower efferent arteriole)
- small substances forced out through pores into capsular space
- i.e. Water, glucose, amino acids, glycerol, fatty acids, salts as well as waste products urea, uric acid and creatinine
- blood cells and plasma proteins stay behind in blood vessels
- this filtrate called glomerular filtrate
- process is not selective, contains waste and useful substances.
Tubular re-absorption
- As glomerular filtrate passes proximal convoluted tubule
- water reabsorbed by osmosis into peritubular capillaries
- other useful substances re-absorbed actively
- cuboidal cells of the tubule have mitochondria for active transport and microvilli to increase surface area.
- filtrate with useful substances removed is now called dilute urine
Tubular excretion
- Wastes actively transported from the blood into the renal tubule
- e.g. Creatinine, drugs, ammonia, potassium, hydrogen and bicarbonate ions
How water is conserved (tubular reabsorption process)
- Sodium and chlorine ions pumped out of loop of Henle
- dilute urine leaving the loop of Henlee has a very high water potential
- because of a steep concentration gradient, water leaves the distal convoluted tubule by osmosis
- depending on the water levels of the body, urine is either more dilute or concentrated
Hormone that regulates how much water is reabsorbed
Anti-diuretic hormone (ADH)
The action of ADH on the distal convoluted tubules and collecting ducts
- It’s presence reduces the permeability of the distal convoluted tubules and collecting ducts
- this reduces water reabsorption
- urine is more diluted
Kidney tubule response if blood becomes too alkaline
- Hydrogen ions concentration in blood is too low (high pH)
- cells of tubules remove more bicarbonate ions
- Various ions act as buffer in filtrate (resists pH change)
- pH in blood returns to normal
Homeostasis
- a process that keeps the amounts of substances and conditions of the body within narrow limits.
- maintained by constantly adjusting these to prevent any large changes.
Homeostasis of water
Osmoregulation
Osmoregulation process (shortage of water in body)
- osmoreceptors in hypothalamus stimulated
- pituitary stimulated to produce more ADH
- ADH via blood increases permeability of distal convoluted tubules
- more water passes from tubules into blood by osmosis
- less water remains in tubules
- concentrated urine is excreted
Osmoregulation process (excess of water in body)
- osmoreceptors in hypothalamus stimulated
- pituitary stimulated to produce less ADH
- less ADH decreases permeability of distal convoluted tubules
- less water passes from tubules into blood by osmosis
- more water remains in tubules
- dilute urine is excreted
What is aldosterone
- A hormone
- regulates the salt concentration of the blood and tissue fluid
- secreted from the cortex of adrenal glands
Homeostasis of salt balance (e.g. when sodium in the body is too low)
- Sodium levels on the blood drop
- More aldosterone secreted from the adrenal glands
- The renal tubules are stimulated to increase active reabsorption of sodium ions from the filtrate into the blood
- Sodium levels in the blood increase
Causes of kidney failure
- Overuse of painkillers
- Chronic high blood pressure
- Type 2 diabetes
- Injury
- Infection e.g. Bilharzia
Kidney dialysis
- A short term treatment for those with kidney failure
- Entire blood volume is passed through a series of filters
- cleaned blood is returned to the body
- Done mainly in hospital with a dialysis machine
- several times per week
- expensive
Long term solution for kidney failure
- Kidney transplant
- Dysfunctional kidney removed
- Replaced by a healthy donated kidney
Process of dialysis
- Blood is removed from an artery
- A substance is added to prevent the blood from clotting
- It is pumped into semi-permeable tubes in the dialysis machine
- On the other side of these tubes is dialysis fluid
- This contains water, glucose and salts of same concentration as the blood
- Waste molecules move through the membrane into the dialysis fluid by diffusion
- useful molecules don’t move through (no concentration gradient)
- cleaned blood returned to a vein of the person
Issues with kidney transplants
- Risk of rejection (immune system attacks foreign cells)
- Finding a donor hard - often a close relative required
- shortage of donors
- Immuno-suppressants required for life
- Expensive
- public health system in SA will not treat those over 50 years old due to its cost
Kidney stone
- A solid formed from minerals in the diet
- E.g. Calcium, uric acid
Increased risk for getting kidney stones
- Dehydration
- Excess animal protein
- Sodium (salt)
- Sucrose
- Fructose
- High fructose corn syrup (e.g. In Coke)
Getting rid of kidney stones
- Small ones pass with urination
- Larger ones need treatment as they can cause blockages
- ultrasound to shatter them
- surgery
Effect and symptoms of kidney stones
- Blockage of different parts of the renal system
- Renal colic - intense pain
- Sometimes nausea and vomiting
Kidney failure caused by medicines
- Analgesic nephropathy
- Irreversible damage
- Damage builds up through time
- Leads to kidney failure
Common medicines causing kidney damage
- Paracetamol (e.g. Panado)
- Ibuprofen (e.g. Neurofen)
Risk of damage to kidneys by medicines increases…
- With dehydration
- With large amounts of exercise (e.g. long distance runners) mainly due to dehydration
An example parasite that affects the urinary system
Schistosomiasis / bilharzia
Symptoms of bilharzia
- Painful urination
- Blood in urine
Portal of entry for Bilharzia
- Schistosomiasis flatworms
- Burrow into skin from infected waters
- Female lays eggs in blood vessels lining the bladder
Place of exit by bilharzia from humans
- Eggs have spike that cuts blood vessel
- They enter bladder
- Exit body with next urination
Secondary host of bilharzia
A snail
Complications from bilharzia infection
- Eggs or larvae can obstruct different part of the system
- If not treated, can lead to chronic kidney failure
Ureters
Urinary bladder
Urethra
Renal pelvis
Adrenal glands
Renal capsule
Renal cortex
Renal pyramids
Renal calyces
Renal pelvis
Renal artery
Renal vein
Renal medulla
A: Collecting duct
B: Malpighian body
- A nephron
- Structural and functional unit of the kidney
A: Afferent arteriole
B: Bowmans capsule
C: Glomerulus (capillaries)
D: Distal convoluted tubule
E: Collecting duct
F: Loop of Henle
G: Proximal convoluted tubule
