Excretion in humans Flashcards
Catabolic reactions
- chemical reactions in which complex substances are broken down into simpler ones
- e.g. glucose (complex substance) oxidised/ broken down into carbon dioxide and water (simpler substances) with release of energy during cellular respiration
- e.g. proteins and amino acids are deaminated in the liver to form urea
Anabolic reactions
- chemical reactions in which simple substances are built up into complex ones
- e.g formation of new proteins from amino acids
- e.g. conversion of glucose into glycogen in liver and muscles
- e.g. photosynthesis
Metabolism
- catabolism + anabolism , the sum of all chemical reactions in body
- metabolic reactions produce waste products, can be harmful, toxic if accumulated
- removed thru excretion
Excretion
- the process by which metabolic waste products and toxic substances are removed from the body of an organism
- excretory products refer to metabolic waste products and toxic substances
- unicellular organisms: excrete waste products via diffusion into surrounding environment
- multicellular organisms: esp animals with impermeable skin need excretory organs
Excretory products of lungs
- carbon dioxide
- excreted as gas in expired air - excess water
- water vapour in expired air
Excretory products of kidneys
- excess mineral salts, nitrogenous waste products
- e.g. mainly urea (indirectly from deamination of protein), uric acid (from breakdown of nucleic acids), creatinine (from breakdown of muscle proteins)
- excreted as a constituent of urine - excess water
- excreted as main constituent of urine
Excretory products of skin
- excess mineral salts and nitrogenous waste products
- mainly urea (indirectly from deamination of protein)
- uric acid (from breakdown of nucleic acids)
- creatinine (from breakdown of muscle proteins)
- excreted as constituents of sweat, but only in small quantities for nitrogenous waste products - excess water
- excreted as a main constituent of sweat
Excretory products of liver
- bile pigments (from breakdown of haemoglobin)
- excreted as constituent of faeces via intestines
Human Urinary System: Hilus
- the depression at the centre of the concave surface
- renal vein, renal artery and nerves are connected to the kidney at the hilus
Human Urinary System: Ureter
-narrow tube that connects the kidney to urinary bladder that urine passes thru
Human Urinary System: Urinary bladder
- an elastic muscular bag located in front of the rectum
- stores urine
Human Urinary System: Urethra
-the duct thru which urine passes from the bladder to outside of the body
Human Urinary System: Sphincter muscle
- located at bottom of bladder
- used to control urination
- when bladder is full, sensory neurones send nerve impulses to the brain
- to urinate, brain sends nerve impulses to sphincter muscle to relax, urine can flow into urethra and out of body
Structure of kidney: Cortex
- outer dark red region
- covered and protected by fibrous capsule
Structure of kidney: Medulla
- inner pale region
- contains renal pyramids
Structure of kidney: Renal pyramids
- conical structures located in the medulla, human kidney contains 12-16 renal pyramids
- radial stripes indicate numerous kidney tubules (nephrons)
- urine is formed in these nephrons
Structure of kidney: Renal Pelvis
-enlarged portion of the ureter inside the kidney
Structure of nephron: Bowman’s capsule
- cup-like structure
- contains glomerulus
Structure of nephron: Proximal (first) convoluted tubule
-short, coiled tubule, straightens out as it passes into the medulla
Structure of nephron: Loop of Henle
- in medulla, tubule extends into renal pyramid, makes u-turn back into cortex
- u-shaped portion is known as loop of Henle
Structure of nephron: Distal convoluted tubule
-when tubule enters cortex again, becomes convoluted
Structure of nephron: Collecting duct
- tubule then opens into a collecting duct
- runs straight thru the medulla
- eventually opens into the renal pelvis
Flow of blood in nephrons (kidney tubules)
- blood enters kidney via renal artery, branches out into arterioles
- arterioles further branches into a mass of blood capillaries (glomerulus) in Bowman’s capsule
- Bowman’s capsule + glomerulus = renal corpuscle
- blood leaving the glomerulus enters blood capillaries surrounding nephron
- blood capillaries unite to form venules,
- venules join to form a branch of the renal vein
Urine formation: Ultrafiltration
- blood flow from renal artery to glomeruli in renal corpuscles
1. caused by hydrostatic blood pressure - diameter diff between afferent and efferent arteriole
- creates high blood pressure, main force required for filtration process
2. Basement membrane - partially permeable membrane, wraps arnd glomerular blood capillaries like a fine filter
- small pores, only allow water, glucose, amino acids, mineral salts and nitrogenous waste products to flow thru), called filtrate
- retains rbc and plasma proteins
Urine formation: Selective reabsorption
- normal adult, 120cm3 of filtrate formed in kidney every min
- if this amt of filtrate were allowed to pass out as urine, body lose too much water and other useful substances, become dehydrated
- thus as filtrate passes thru tubule, useful substances reabsorbed into bloodstream
Selective reabsorption: Proximal convoluted tubule
- most mineral salts (sodium ions), all glucose and amino acids absorbed thru walls of tubule into surrounding blood capillaries
- these solutes reabsorbed via diffusion and active transport
- reabsorption highly selective, readily absorb substances required by body
- most water reabsorbed via osmosis here
Selective reabsorption: Loop of Henle
-some water reabsorbed
Selective reabsorption: Distal convoluted tubule
-some water and mineral salts reabosrbed
Selective reabsorption: Collecting duct
- some water reabsorbed
- excess water, salts and metabolic wastes such as urea, uric acid and creatinine pass out of collecting duct into renal pelvis as a mixture called urine
Composition of urine
Water: 96.0g Mineral salts (mainly sodium chloride): 1.8g Urea: 2.0g Other nitrogenous substances: 0.2g Total: 100.0g
Protein rich diet (composition of urine)
- more urea present in urine
- urea is formed when excess amino acids are deaminated in liver
Consuming more water-rich food/more liquids (composition of urine)
- increases water potential of blood
- vol of urine excreted is larger
- also happens in cold weather (sweat secretion is reduced)
High intake of salty foods (composition of urine)
-excess salts excreted in urine
Diabetes mellitus
- excrete large amt of glucose in urine
- diabetic unable to store up excess glucose as glycogen, high glucose conc in blood
- glucose filtered out of glomerulus to form part of glomerular filtrate
- nephrons unable to absorb glucose fast enough
Osmoregulation
-the control of water and solute concentrations (levels) in blood to maintain a constant water potential in body
Why water potential of blood in body needs to be kept relatively constant?
- drastic changes can result in serious problems
- blood plasma too diluted, more water enter blood cells via osmosis, swell, might burst
- blood plasma too concentrated, more water leaves blood cells via osmosis, dehydrated, shrink, unable to carry out metabolic functions properly, may be fatal
Water potential of blood
-depends on amt of water and mineral salts in blood plasma
Antidiuretic hormone (ADH)
- controls amt of water in blood plasma
- ADH produced by region of brain called hypothalamus
- released by pituitary gland, increases water reabsorption at nephrons
How kidneys help to regulate wp in blood
-kidneys are called osmoregulators, help to regualte water and solute conc in blood
Loss of water/Large in intake of water (osmoregulation in kidneys)
- e.g. sweating / drinking
1. wp of blood decreases/increases, stimulates hypothalamus in brain
2. pituitary gland releases more/less ADH into bloodstream
3. cells in walls of collecting ducts become more/less permeable to water, more/less water reabsorbed from collecting ducts into blood capillaries
4. smaller/larger vol of urine produced
5. urine produced is more/less concentrated
6. water potential of blood returns to normal
How is water potential of blood related to blood pressure?
- amt of water reabsorbed affects blood vol
- blood vol rise, blood pressure rise
- large increase in blood pressure can cause blood vessels in brain to burst, lead to stroke
- drug called diruretics reduce production ADH, less water reabsorbed, large vol of dilute urine, wp in blood decreases, bp decreases
Why are kidneys impt?
- excretory organs
- excrete metabolic waste products e.g. urea, excess water, mineral salts (in form of urine) - osmoregulators
- regualte water and solutle conc in blood so wp is constant in blood
Causes of kidney failure
- high bp
- diabetes
- alcohol abuse (constant heavy drinking)
- severe accidents that physically damage kidneys
- complications from undergoing major surgery
Dialysis
- if no kidney donors
- dialysis machine mimics functions of kidney
- helps to clean patient’s blood from metabolic waste products and toxins
- patient need to undergo dialysis treatment 2-3 times a week, 3-5 hrs per session
How does a dialysis machine work?
- Blood is drawn from the vein in the patient’s arm, allowed to be pumped thru the tubing in the dialysis machine
- tubing is bathed in a specially controlled dialysis fluid, its walls are partially permeable
- small molecules such as urea and other metabolic waste products diffuse out of tubing and into dialysis fluid (blood cells and platelets are retained)
- filtered blood is then returned to a vein in the patient’s arm
Features of a dialysis machine
- Dialysis fluid contains same conc of essential substances as healthy blood
- Dialysis fluid does not contain metabolic waste products
- Tubing in machine is narrow, long and coiled
- Direction of blood flow is opposite to the flow of dialysis fluid
Feature 1: Dialysis fluid contains same conc of essential substances as healthy blood
- ensures essential substances (e.g. glucose, amino acids, mineral salts) dont diffuse out of blood and into the dialysis fluid
- if patient’s blood lacks these essential substances, these substances will diffuse from the dialysis fluid and into the blood
Feature 2: Dialysis fluid does not contain metabolic waste products
- sets up conc gradient that allow waste products such as urea, uric acid, creatinine and excess water and mineral salts to diffuse out of tubing and into dialysis fluid
- waste products removed frm blood
- maintains correct solute composition and wp of blood
Feature 3: Tubing in machine is narrow, long and coiled
- increases sa:v ratio
- helps to speed up rate of exchange of substances between patient’s blood and dialysis fluid
Feature 4: Direction of blood flow is opposite to the flow of dialysis fluid
-maintains conc gradient for removal of waste products
