excretion

• Excretion

  - removal of metabolic waste from the body

  - plants produce very little waste

  - plants lose water and oxygen through the stomata
• epidermis

  - the malpighia layer divide by mitosis to produce new epidermis cells - these new cells produce the water proof protein called Keratin ( nails , claws , scales )

  - other cells in the malpighian layer produce a brown pigment, melanin

  - gives the colour to the skin , hair and coloured part of the eye

  - freckles and moles are where melanin is very concentrated
• functions of melanin

  - protects the skin against the harmful effects of ultra violet radiation

  - production of melanin increases fallowing exposure to sunlight
• Dermis


  - consists of connective tissue containing a protein, collagen

  - consists of sweat glands , hair follicles
• Functions of the skin epidermis

  - protects body from damage and prevents the entry of pathogens
• Functions of the skin dermis

  - protects internal organs from damage
• Functions of the skin melanin

  - protects skin against uv rays
• Functions of the skin sebum

  - oil that keeps hair moist ,felixble and prevent skin from drying out
• Functions of the skin vitamin production

  - vitamin D is produced in the skin by exposure to sunlight
• functions of the skin food store

  - fat in the adipose tissue acts as a food store
• functions of the skin sense organ

  - skin contains nerve receptors which detect temperature and sensation
• functions of the skin excretion

  - sweat glands act as organs of excretion

  - sweat contains salts and waters
• functions of the skin cold conditions

  - skin can help retain heat
• functions of the skin temp regulations

  erector muscle contract ( goose bumps ) which cause hair to stand up ( pilo erection )

  - a layer of warm air is trapped close to the skin by the hairs which help to reduce heat loss

  - blood vessels in the skin contract ( vasoconstriction ) reduce heat loss

  - part of brain respond to cold conditions causing muscles to contract and relax causing shivering

  - produces heat
• functions of the skin warm conditions

  - Sweat is produced and released onto the skin ( water evaporates to lower body temp ) - blood vessels in the skin expand ( dilate ) especially in the face this increases heat loss through the skin and reduces body temperature
• role of excretory system in homeostasis

  - regulating body temp .

  - controlling concentration of body fluids .

  - controlling osmosis ( salt + water balance of body )

  - removing waste products of metabolism from the body
• lungs

  excrete water and carbon dioxide
• skin

  excretes water and salts sweat
• kidney

  excrete water , salts . and urea in the form of urine
• Urine

  - 96 % water

  - 2.5 % nitrogenous waste ( urea ) -liver - deamination

  - 1.5 % ( excess amino acids )
• bladder

  - store 800ml urine

  - control of urination , sphincter reflex
• function of the kidney - excretion

  - remove waste products from the blood and converts them to urine
• function of the kidney / osmoregulation

  - water content : controls water content in body ( varies water content in urine

  - salt concentration : controls salt concentration

  - ph control : controls ph of the blood fluid ( varies the acidity of the urine )
• Urine formation filtration

  • bowmans capsule

  - afferent arteriole contains waste products

  - filtration takes place in the glomerulus ( glucose , amino acids , vitamins , hormones , urea , salts , water ) forced into the bowmans capsule

  - called the glomerular filtrate
• adaptations of the glomerulus for filtration

  - pressure is greater than normal blood pressure ( efferent arteriele narrow than afferent arteriole ) ( ultra filtration due to high pressure )

  - surface area of capillaries in the glomerulus is large ( increase area of absorption )

  - walls are very porous, one cell thick

  - large substances do not enter ( rbc, wbc, platelets )
• urine formation - reabsorption ( proximal tubule )

  - most of water reabsorbed by omosis

  - glucose and amino acids reabsorbed by diffusion and active transport ( energy )
• adaptations of proximal convoluted tubule

  - thin walled

  - long

  - numorous infoldings

  - lot of mitochondria ( energy )
• reabsorption - loop of henle

  - descending loop , water is reabsorbed by osmosis

  - ascending loop , reabsorbes salts
• reabsorption - distal convoluted tublule

  - water salts are reabsorbed
• collecting duct-

  - permeable to water , reabsorbed by osmosis

  - liquid passing from collecting duct is called urine
• secretion

  - some substances pass from the blood into the nephron

  - eg H+ , K + maintain pH
• How does glomerular filtrate differ from urine

  - glomerular filtrate has more water than urine

  - contains useful substances ( glucose, amino acids )
• Role of ADH

  - antidiuretic Hormone

  - made by pituitary gland

  - adh travels to kidneys

  - makes wall of distal tubule and collecting duct more permeable to water

  - remove water from urine, water stays in body
• role of ADH - control urine volume

  - blood plasma too concentrated

  - if water lost by sweating, concentration of plasma rises

  - receptors in brain ( hypothalamus ) triggered causes pituatary gland to release ADH

  - ADH travels to kindney making walls of distal tubule and collecting dict more permeable to water

  - lower volume of concentrated urine is produced
• blood plasma concentration normal to dilute

  - if adh not produced meaning distal tubule and collecting duct become impermeable to water

  - water is not reabsorbed from distal tubule staying in the nephron