1. Excretion in Plants and Animals

2. Contents Homeostasis Excretion Excretion in Plants
Control of gaseous exchange in plants
Secretion
Homeostasis and Excretion in Humans
The Lungs
Control of gaseous exchange in humans
The Skin
The Urinary System
The kidneys
Urinary System Parts & Functions
Nephrons
Formation of Urine
Pathway of Urine
Skin disorders
Urinary disorders

3. Homeostasis
Definition: the maintaining of a constant internal environment of a cell or organism or the processes involved with this.
It involves controlling temperature, pH, concentrations of water, salts, glucose, carbon dioxide, turgidity, the removal of waste products of cell metabolism, etc.

4. Necessity for homeostasis
Organisms may live in external environments with fluctuating conditions.
These fluctuating conditions may not be tolerable to the organisms cells.
Animal cells are bathed in tissue fluid.
This produces an internal environment.

5. Excretion
Definition: is the elimination of the waste products of metabolism.
Takes place in all organisms.
Some waste products are poisonous e.g. urea and carbon dioxide.
Others (e.g. water) if allowed to accumulate will have damaging effects on the cells.

6. Excretion in Plants Major waste products are gases: -
O2 from photosynthesis, and
CO2 and water from respiration.
Leaf is the major organ of excretion in plants – lenticels also contribute.
The O2 from photosynthesis diffuses from the cells into the air spaces of the spongy mesophyll.

7. Diffusion of oxygen in a leaf

8. The structure of a lenticel

9. What happens to the oxygen?
Some of it may be taken in by cells and used in respiration (produces CO2).
The rest will diffuse out through the stomata and into the atmosphere.
The shedding of leaves by deciduous trees will also remove some waste products from plants.

10. Control of gaseous exchange in plants (1/4)
Takes place through the stomata.
More found on under surface than upper surface of leaf.
Each stoma is enclosed by two guard cells.
Their cell walls where they touch are much thicker than the outer cell walls.

11. Guard cells around stoma

12. Control of gaseous exchange in plants (2/4)
As water enters the guard cells they expand unevenly and the inner walls bend away from each other forming the opening called a stoma.
K+ ions in guard cells control the amount of water entering the cells.
Guard cells take in K+ ions when light is present and CO2 levels are low and water then enters by osmosis.

13. Control of gaseous exchange in plants (3/4)
CO2 levels affect the uptake of K+ ions – may be related to photosynthesis.
This uptake requires energy (ATP).
Provided by the chloroplasts in guard cells.
In darkness – no photosynthesis - CO2 levels rise - K+ ions exit along with water – stomata close.

14. The effect of K+ ions on guard cells

15. Control of gaseous exchange in plants (4/4)
If water loss during the day becomes too great, water will leave the guard cells and the stomata will close.

16. Secretion
secretion: is the release of something ‘useful’ from a cell or gland e.g. hormones, enzymes.
Excretion is an animal function
the loss from plants is more appropriately called secretion

17. Homeostasis and Excretion in Humans
The Lungs,
Skin and
Kidney have a role in both homeostasis and excretion.

18. The Lungs
Remove waste CO2 – helps maintain the correct pH in the blood.
Remove water and heat (secondary function of lungs) – no real control over quantities of these lost – depends on the temp. and humidity of the air we breathe in.

19. Control of gaseous exchange in humans
Controlled by the brain.
Sensors (chemoreceptors) in the brain and in the walls of the aorta and arteries going to the head, are sensitive to pH and CO2 levels.
When the level of CO2 rises (pH falls) sensors pick up the change and the brain will increase the rate of breathing.
O2 levels in the blood have little effect on the rate of breathing.

20. The Skin Removes water and urea when we sweat.
Body temperature must be kept within certain limits. Why?
If the temperature goes above or below the limits permanent damage can be done to the organism.
A constant temperature will allow faster metabolism and greater energy release.
Sweating helps maintain a constant body temperature.

21. Ectotherms & Endotherms
Animals that cannot regulate their internal temperature are called ectotherms e.g. lizard – moves into and out of sunshine.
Animals that can regulate their internal temperature are called endotherms.
They use waste heat from cell activity to warm up and can also reduce their temp. if they get too hot.

22. Skin & temp. regulation (1/2)
The skin uses Blood vessels, Sweat glands and Hairs to control body temperature e.g. if the body is too hot - when exercising.
Blood capillaries at the skin surface dilate (expand) and allow more blood to flow through them carrying more heat to the skin surface thus allowing more heat to be lost by radiation.

23. Skin & temp. regulation (2/2)
Sweat glands releases sweat onto the surface of the body. It picks up heat from the body and evaporates with it - leaving the body cooler. Sweating is a cooling process.
Hairs lie flat against the body allowing free movement of air over the body surface thus cooling the body. In cold weather hairs stand erect (by contraction of the erector muscles = piloerection) and trap a layer of air, which acts as an insulator.

24. A diagram of the skin showing some of the structures used in temperature regulation.

25. Diagram of skin structure

26. Sweating May cause a lack of water if the body overheats.
Various salts also lost.
Water should be drunk during and after exercise, to replace lost water.
‘Sports’ drinks have various salts added to them to help replace the ones lost.

27. Sweat sweat: perspiration, or liquid produced by sweat glands;
contains water (95%),
salts (2%),
carbon dioxide (3%),
urea (%) and
lactic acid (%).

28. Skin & heat retention Adipose tissue – good insulator.
Blood capillaries constrict (= vasoconstriction) – what effect will this have?
Erector muscles contract – hairs stand up - what effect will this have?
Brain initiates an increased metabolic rate - what effect will this have?

29. The Urinary System
The kidneys are the main excretory organs of the body.
They excrete nitrogen-containing waste products e.g. urea.
They are brown bean-shaped organs found in the lower addomen, one each side of the back bone.

30. The human excretory system

31. Human urinary system

32. Note the following
Thee tubes attached to each kidney – name, direction of flow & contents of each.
Bladder – muscular bag that stores urine.
Urethra carries urine to the exterior through the penis in males and exits above the opening of the vagina in females.
Sphincter muscle at base of bladder.

33. The kidneys Three main areas: Cortex – outer edge.
Medulla – lying inside cortex made of pyramids – striped appearance
Pelvis – hollow area connected to ureter.

34. L.S. through a kidney 1

35. L.S. through a kidney 2

36. Urinary System Parts & Functions
Kidney
Excretion = remove waste products from the blood.
Osmoregulation = control the amount of water and salt in the blood.
Ureter
Carries urine from kidney to the bladder.
Bladder
Stores urine (approx 500ml).
Urethra
Carries urine from bladder to the exterior

37. The structure of a nephron

38. The structure of a nephron

39. Nephrons Between one and two million nephrons in each kidney.
The functional units of the kidney.

40. Formation of Urine
Water and dissolved substances (e.g. urea, uric acid, glucose, amino acids, vitamins, salts) pass from the blood in the glomerulus to the space in the Bowman's Capsule.
This process called PRESSURE-FILTRATION is aided by

41. Pressure-filtration aided by:
(a)   The efferent arteriole being narrower than the afferent causes a build up of pressure in the glomerulus.
(b)    Blood in the afferent arteriole is under pressure from the heart.
Blood cells and plasma proteins are too big to pass through the wall of the capillaries and do not enter the Bowman’s capsule.

42. In Proximal Convoluted Tubule
Cells here have micro-villi and numerous mitochondria.
All the high threshold substances are reabsorbed here by a combination of diffusion, osmosis and active transport.

43. In the Loop of Henle DESCENDING LIMB - water is drawn out by osmosis.
ASCENDING LIMB - salt diffuses out into the cells of the medulla. Salt concentration of the medulla is increased.

44. In Distal Convoluted Tubule
Some water reabsorbed here by osmosis and
salts secreted from the blood by active transport.

45. In Collecting Duct (1/3)
The urine passes down the collecting duct (through the medulla) into the ureter.
Due to high salt concentration in the medulla water is drawn from the collecting ducts by osmosis thus concentrating the urine and conserving water in the body.
The reabsorption of water here is controlled by the hormone ADH (Anti Diuretic Hormone).

46. In Collecting Duct (2/3)
Its action depends on the water content of the blood.
If the blood contains not enough water (or too much salt) the pituitary gland releases ADH - this increases the permeability of the collecting ducts and results in more water being reabsorbed and the production of a concentrated urine.

47. In Collecting Duct (3/3)
If the blood contains too much water (or too little salt) then the production of ADH is reduced, thus reducing the permeability of the collecting ducts resulting in the production of copious amounts of watery urine = DIURESIS.
Note: Alcohol inhibits ADH production –
no ADH leads to diabetes insipidus.

48. Pathway of Urine Urine passes into pelvis of kidney,
flows down the ureters
into the bladder for storage.
When the bladder is approx. 60% full we get the urge to empty it.
Sphincter muscle relaxes and urine released through urethra.

49. Summary of urine formation

50. Not examinable for information only
Skin disorders
Not examinable
for information only

51. Acne vulgaris

52. Boils

53. Epidermal cyst

54. Warts

55. Moles

56. Skin cancer

57. Not examinable for information only
Urinary disorders
Not examinable
for information only

58. Incontinence

59. Kidney stones

60. END