2. Homeostasis and excretion 

Excretion

The removal of waste products of metabolism from an organism

Wase products

  • Carbon dioxide
  • Urine
  • Water
  • Salt
  • Sweat
  • Bile

Organs of excretion

  • Lungs
  • Skin
  • Kidneys

Homeostasis

  • Maintenance of a constant internal internal enviorment
  • Humans must maintain a constant
    • Temperature (normal body temp is 37* C
    • Fluid
    • balance and chemical composition

Tempreture regulation

  • Temperature must be kept constant for their enzymes and metaboic activity’s to work
  • Heat is formed from metabolisms and respiration
  • They produce enough heat from their own metabolism to keep their bodies warm
  • Ectotherms: body temperature varies with enviorment

Fluid balance

Chemical composition

  • Aninal cells are bathed in tissue fluid
  • This provides constant internal enviorment
  • Variables (carbon dioxide levels, glucose concentration) must be kept constant

Function of homeostasis

Homeostasis allows for organisms to…

  • Function effectively
  • Indapendantly of the enviorment
  • Make slight changes when necessary to their internal enviorment

Plants and excretion

Daytime

  • Lose water and oxygen through the stomata and lenticels

Night time

  • Lose carbon dioxide also through stomata and lenticles

Response to hot conditions

  • Blood vessels: expand/ dialate (vasodilation) incresing blood flow to the skin surface
  • Sweat glands glands releces sweat a weak salt soilution onto the surface of the skin - evaporation of water removes heat ftom the body
  • Hair lies flat no layers of air traped close to skin to act as insulation

This loss of water and salts as sweat, must ne replacesd that is why it is important to drink water before during and after exersise to maintain the balance of water and salts in the body

Response to cold conditions

  • Blood vessels: contact (vasoconstriction) reduce blood flow to the skin surface. Reduces heat loss
  • Sweat glands: stop secreting
  • Hairs rise and goose bumps form: a layer of air traped close to the skin to act as insulation (piloreaction)
  • Shivering: caused by muscle action. Generates heat

Functions of the skin

  1. Protection:

    1. Epidermis prevents water loss and entry of pathogens
    2. Dermis: protects internal organs
    3. Melanin: protects from uv radiation
    4. Sebum: prevents skin drying out

  2. Vitamin d production : made on exposure to uv light. Helps to absorb calcium in the intestines

  3. Food store: adipose tissue

  4. Sence organ: contains receptors

  5. Excretion: contains sweat glands

Role of excretory syestem

  1. Regulate tempreture
  2. Control osmoregulation
  3. Control body fluid concentration
  4. Removal of waste products of metabolism

Excretory organs

OrganFunction and productsLocation
LungsExcretion ofCarbon dioxide (derived from glucose ) WaterIn the thorax (chest)
Skin.Excretion ofWater Some salts
KidneysExcretion ofWaterSaltsUrea (made from deamination of protiensIn the abdomen below the diaphragm

Overview of ruins formation

  1. Filtration takes place in the cortex
    • Waste products (salts urea water) are removed from blood
    • Useful products (glucose ami ie acids ) also removed but later retried to the blood
  2. Reobsorbtion . Takes place in the cortex and medulla
    • Useful substances are reobsorved in the blood
    • Waste products made into uurine sent to pelvis of kidney nd then to uretrs bladder and urethra
  3. Secretion . Occurs in the cortex

Proper ph 7.4 of the blood mania Ed of the blood is to acidic/ basic, chemicals are secreted from the blood into the kidneys

Urine

  • Made up of
    • Water
    • Urea produced in lover from deamination of protiens
    • Salts

Revision of movement  

  • Diffusion: movement of substances with a concentratrion gradient.  
  • Osmosis: movement of water through a semipermiable membraine from an area of high water concentration to an area of low water concentration  
  • Active transport:  movement of moliclue against concentration gradient. Requires energy  
  •  

 

 Urine formation occurs in the nephrons  

 

  1. Reabsorption 
    • Water and salts are reaobsrorbed by osmosis, diffusion and active transport 
    • The remainder is urine and passes into the pelvis of the kidney  

Adaptations of the proximal tubule for absorbsion  

  1.  thin walled  
  2. Long  
  3. Numerous infoldings  
  4. A lot of mitochondia (energy for active transport) 

 

Colleccting duct  

  • Permiable to water which is reabsorbed due to osmosis 
    • Note: the liquid passing from collecting duct is called urine 

Loop of henle: for reabsorbtion of water  

main proceses  

  1. Secretion: potassium and hydrogen ions are secreted into the distal tubule and excreted which maintains the blood ph  

Some substances pass from the blood into the nephron  

  • Proximal distal tubule = h ions respond to blood ph  
  • Distal tubule = potassium and h ions  

 

How dose glomerular filtrate differ from urine  

  • Glomerular filtrate has more water than urine  
  • Containds useful substances (glucose and amino acids) 
  •  

Control of urine  

  1. Blood plasma too concentrated 
    • An athleet produces very little urine after excerise because they are sweating 
    • The concentration of the blood incereses  
    • This is dectected bt receptors  
    • Brain in alerted  
    • The hormine ADH (anti-diuretic hormone) in secreted for the for the petuitary gland 
    • It travels in the blood to the distal tubule 
    • This stimulates reobsorbstion of water mmt making the walls of the distal tubule more permeable  

 

Control of urine volume  

  1. Blood plasma is normal or too dilute  
  • Blood plasma is diluted  
  • Adh not produced 
  • Distal tubes are relitivley impermeable to water 
  • Water is not reobsorved  
  • Dilute urine is produced  

 

If the kidneys malfunction dialysis is needed