1. HOMEOSTASIS

2. Importance of homeostasis
To maintain internal environment of organisms especially
higher vertebrates in a steady and balanced state.
To establish optimum condition of organisms

3. Benefits
a. Life of organism become less dependent on the external
environment
b. The organism can live in a wider range of habitats and the
species can live in areas with variable conditions
c. The organism can increase and decrease its metabolic rate
according to its requirements
d. A controlled internal environment enables more efficient
and economical metabolic reactions
e. Enzyme can function at the optimum level ensuring
metabolic balance.

4.  Homeostasis refers to the physiological processes by which organisms
maintain constant and balanced physical and chemical factors in their
internal environment.
Internal environment – environment surrounding
cell (tissue fluid)
Physical factor – temperature, blood pressure and
osmotic pressure
Chemical factor – pH value, concentration of sugar
and salt in blood and tissue fluid.
 Any variation from normal conditions will initiate homeostatic reaction
 A series of correction mechanisms will act to restore the physical and
chemical composition of the tissue fluids to normal conditions.

5. Homeostatic control processes include:
- negative feedback
- positive feedback
Any changes in the physical or chemical factors of the internal
environment will be detected by receptors.
Part of nervous system
Send information about the changes to the central control system
(brain)

6. Parts of homeostatic control system:
a. Receptors – able to detect any change
b. A control centre – define changes
c. A mechanism that triggers appropriate corrective actions
d. Effectors – execute the corrective actions

7. Homeostatic Control System

8. Negative Feedback
From the control centre, action signals are transmitted
through the nerve impulses or hormones to the target organ.
This will trigger correction mechanism to return the physical
and chemical factors to their normal conditions.
Conversely, a reduction in the value of the physical or
chemical factor will trigger a mechanism to increase the
amount of that factor.

9. Positive Feedback
Occurs when a change in a factor causes the value of the
factor to rise or fall even further.
Might be harmful or useful.

10. Example of negative
feedback
1. Control of blood glucose level
2. Body temperature control in Mammals

11. Control of blood glucose level

12. 1. Control of blood glucose level
Normal concentration of sugar/glucose in human blood is
about 90mg per 100cm3 blood.
Excess sugar in blood will result in the loss of water from
tissues through osmosis
Low blood sugar level in blood will cause low blood
pressure, fatigue or coma (extreme cases)

13. Pancreas and liver regulates
blood glucose level
Glusose (simple sugar) is carried
from the intestine to the liver
through the hepatic portal
vein
In the liver, glucose maybe:
- converted to CO2 and water
through cell respiration
- converted into glycogen for
storage
- converted into fat to be stored
as diapose tissue
- released into the bloodstream

14. When the blood sugar level
arises:
- glucose to glycogen
When the blood sugar level
falls:
- glycogen to glucose

15. Changes in blood glucose
level is detected by
pancreas
Functions as endocrine gland
to secrete the hormones
insulin and glucagon
Both hormones are secreted
by the islets of
Langerhans

16. Islets of Langerhans comprise of 2 types of cells:
a. alpha cells (glucagon)
b. beta cells (insulin)

17. When the blood sugar level arises, hormone insulin is secreted
into the blood and taken to the liver
Insulin in liver causes :
a. the speed up the oxidation of glucose to CO2 and water through
cell respiration (aerobic respiration)
C6H12O6 6CO2 + 6H2O + energy

18. b. speed up the conversion of glucose to glycogen and fat for
storage
insulin
nC6H12O6 + 6O2 (C6H10O5)n + nH2O
c. to prevent the formation of glucose from glycogen and non-
carbohydrate sources
 The overall effect is that the blood sugar level is lowered to
normal

19. When the blood sugar level drops, the hormone glucagon is
secreted into the blood and transported to the liver.
Glucagon in liver causes:
- Slow down the oxidation of glucose and prevent the conversion
of glucose to glycogen
- Promote the conversion of stored glycogen into glucose.
The overall effect is that the blood sugar level is raised to
normal.

20. 2. Body temperature control in
mammals
To enable metabolic cell activities at normal rates
Birds and mammals are homoiotherms (endoterms)
Body temperature constant, for mammals is at 370C while birds
it is between 40-430C
Animal obtain heat from within the body through physiological
metabolic processes.
They are called endothermic animals.

21. When the external temperature rises, the metabolic rate
falls and physiological processes such as blood circulation
increase to get rid of excess heat from the body
Thus the body temperature does not rise.
When the external temperature drops, the reverse happens
to prevent the loss of the heat from the body

23. Heat is loss from the bodies of humans and these animals through
i. conduction, convection and radiation from the skin
ii. Evaporation of sweat produced by the skin
iii.Urination and defecation
iv. Exhalation

24.  Conversely, they obtain heat through
i. Heat absorption from the environment
ii. Heat production through cell respiration

25. There are receptors in the skin that are sensitive to
temperature changes in the external environment
These receptors are called thermoreceptors.
Thermoreceptors comprise of 2 primary types:
i. The bulb of Krause (cold stimuli)
ii. The organ of Ruffini (heat stimuli)

26. Stimuli received by these thermoreceptors are sent in the
form of impulses through afferent nerves to the
hypothalamus of the brain (act as the heat regulatory
centre)
The hypothalamus also senses temperature changes in the
body.
After interpretation, message are sent to effector organs
such as skin arterioles, hair/fur erector muscles, sweat
glands, skeletal muscles and specific endocrine glands
through efferent nerves
These effector organs then respond to regulate the body
temperature.

27. Homeostatic
Organs
Kidney
Liver

28. Liver

29. Liver
Liver Structure
- Food is processed and stored in liver before distributed to
other parts of the body
- Metabolic centre of the body
- Received blood supply through 2 main blood vessels:
a) hepatic artery – bring oxygenated blood from the dorsal
aorta
b) hepatic portal vein – bring nutrient-rich blood from the
small interstine

31. Liver is made up of many
cylindrical lobules (each
1mm diameter)
Each lobule made up of
rows of liver cells , branch
radially from the centre to
the periphery
Liver cell (hepatocyte) is
undifferentiated cell, have
identical structure.

32. • interlobular blood vessels – branches of the hepatic artery and
hepatic portal veins
• intralobular vein – centre of each lobule, branches of hepatic
vein merged

33. Blood from interlobular blood vessels passes through
sinusoids in the liver tissue to the intralobular vein.
The bile duct branches into a network of fine vessels called
canaculli which pass between the cells of the lobule.

34. Oxygenated blood from hepatic artery and nutrient-rich blood
from hepatic portal vein pass from the interlobular blood
vessels through the sinusoids into the intralobular vein.
The liver cells extract the required substances from the
following blood and release their processed products into the
blood.
Bile also produced by liver cells, passes directly into the
canaliculi to be taken to the bile duct.
Kupffer cells – specialised phagocytic cells
- found on the wall of sinusoids
- function in destroying old red blood corpuscle

35. Structure of Liver Lobules

36. Homeostatic Functions of
Liver
a) Regulation of blood glucose level in the metabolism of
carbohydrate
b) Regulation of the amino acids and proteins (the
urea/ornithine cycle)
c) The formation of urea
d) Regulation of fatty acids
e) Detoxification

37. a) Regulation of blood glucose level in the metabolism of
carbohydrate
- excess glucose in the blood is converted into glycogen by
insulin for storage in the liver
- this process is called glycogenesis

38. - when the level of blood glucose falls below a certain crucial
level, glycogen is broken down into glucose in the liver
through a process called glycogenolysis.
- requires activation of the enzyme by glucagon

39. b) Regulation of the amino acids
and proteins (the urea/ornithine
cycle)
- excess amino acids and proteins
cannot be stored in the body
- must be returned to the liver
and broken down into non-
nitrogenous (keto acid) and
nitrogenous parts (amino group,
-NH2)
- through the process of
deamination

40. In the liver, non-nitrogenous keto acids are either:
- converted into glycogen
- broken down in cellular respiration to release heat
The nitrogenous part, the amino group (-NH2) undergoes:
- used to synthesise organic bases (guanine, cytosine, thymine,
uracil) – component of nucleotides
- combined with a keto acid to synthesise another amino acid
through process transamination
- converted and excreted as urea – less toxic than ammonia
through process detoxification

42. c) The formation of urea
- urea is less soluble than ammonia
- much less toxic than ammonia
- less water is needed for safe elimination of urea from the body
compared to ammonia
- urea is synthesised from ammonia and carbon dioxide by utilising
amino acid, ornithine
- Arginine, an intermediate amino acid formed during the cycle is split
by enzyme action into urea and ornithine
- this process is called ornithine cycle

43. d) Regulation of fatty acids
- liver processes fatty acid and glycerol to produce lipid
- transport them to fat storage area to form adipose tissues
- liver cell extract cholesterol and phospholipids from blood
to be added to bile – used for digestion lipid
- liver cells also involved in making chemical changes to
lipids and mobilisation of lipids as energy substrates

44. e) Detoxification
- drugs, toxins and poisons taken in with diet/ produced by
bacteria in the body are transported in the bloodstream to
the liver
- harmful if accumulated in the body
- the harmful substances are biochemical broken down in the
liver before delivered elsewhere in the body

45. Kidney
- Primary organ for maintaining homeostatic balance in
mammals
- Play importance role in osmoregulation and excretion
- Osmoregulation
- - control the vol of water, ion concentration, osmotic
pressure and pH of blood
- Excretory Organ
- - excrete toxic substances, urea

46.  Kidney and nephron structure
- pair of kidney, one on each side of the vetebral column below
the liver and behind the lining of the abdominal activity

47. - bean shaped, 10cm long, 6cm
wide, 3cm thick, weigh 150g
- each kidney supplied by renal
artery and drained by renal vein
- form afferent and efferent
arterioles and network of capillaries
- each kidney has two section :
cortex and medula
- internal structure is made up of
nephrons
- nephrons is 3cm length and
divided into 6 section with specific
functions

48. - glomerulus consists of a network
of capillaries between the afferent
arterioles and efferent arterioles
- enclosed by cup-like capsule
called Bowman’s capsule
- the bowman’s capsule surrounds
the glomerulus form the first
region of the nephrons called
Malphigian corpuscle (body)
- Malphigian corpuscle leads to
proximal convulated tubule,
loop of Henle, followed by
distal convulated tubule and
collecting duct.

49. Nephrons

50. - afferent arterioles supplies blood to glomerulus
- from glomerulus, blood is carried by the efferent arterioles
forms networks of capillaries to serve the proximal convulated
tubules, distal convulated tubule
- one single straight capillary network called vasa recta served
the limbs of the loop of Henle

52. Urine Formation
a) Ultrafiltration
b) Selective reabsorption
c) Secretion of toxic substances
d) Differential permeability

53. a) Ultrafiltration
- in glomerulus, high hydrostatic pressure because of
diameters of the efferent arterioles and capillaries are
narrower than the diameter of afferent arterioles
- filtration pressure – hydrostatic pressure
- forces almost all contents of the blood through the pores of
capillaries and seive-like inner epethelial wall of Bowman’s
capsule into the lumen of capsule
- glomerulus filtrate – same as blood plasma (but no plasma
protein and blood cells)
- they cannot pass through the pores in the capillaries and
inner wall of Bowman’s capsule (big size)

55. b) Selective reabsorption
- reabsorption of almost all the glucose and free amino acids
from the glomerulus filtrate occurs in the proximal convulated
tubule through active transport
- against concentration gradient – requires ATP
- tubule wall is one cell thick, brush like-border of microvili
and lots of mitochondria in epithelial cells lining the wall.
- pinocytotic process – to remove any blood protein left in
the filtrate
- result: reduced vol. of filtrate, isotonic to body fluid passes
into decending loop oh Henle (urine concentration)

58. c) Secretion of toxic substance
- poisonous by-product of metabolism
- added into the filtrate by active transport from the cell in the
proximal convulated tubule
d) Differential permeability
- certain substance such as water, inorganic ions and urea
cannot be diffused or transported back into the blood
- Antidiuretic hormone (ADH) control impermeability of
collecting duct and distal convoluted tubule wall

59. Water balance and urine
concentration
- Water is loss during excretion through formation of urine
- Mammals and humans are capable of producing urine that is
more concentrated (hypertonic) than blood plasma
- Loop of Henle plays important role in the conservation of
water and structurally modified for the production of
hypertonic urine

60. - Each loop of Henle consists of 2 parallel limbs:
a) descending limb
b) ascending limb

61. - The parallel descending and
ascending limbs of the loop of
Henle are very close together
- They have different
permeability to water and
solutes
- Descending limb (thin
segment) permeable to water,
impermeable to solutes/ions
- High osmotic concentration
- Ascending limb (thick
segment) impermeable to both
water and ions

62. - In thick segment of ascending limb, sodium and chloride ions actively
transported/pumped out from the filtrate into the peritubular fluid
(tissue fluid surrounding nephrons)
- Osmotic gradient occurs between the filtrate and peritubular fluid
- In the thin segment of the ascending limb, some sodium and chloride
ions diffuse into the peritubular fluid - contribute to osmotic gradient

63. Countercurrent multiplier
mechanism
- Countercurrent: fluid in each limb
moving in opposite direction
- Multiplier: effect increases as fluid
movement continues
- Highest osmotic concentration is at
the hairpin bend of loop
- Osmotic concentration is reduced as
the filrate reach the end of ascending
limb
- Result: hypotonic filtrate

64. - Urine is further concentrated in the distal convulated tubule and
collecting duct
- Wall of collecting duct is permeable to water but not to salt
- More water is drawn out by osmosis as the fluid flows through the
osmotic gradient
- Osmotic gradient provide forces but ADH determine the rate of urine
concentration
 High ADH
- collecting duct becomes more permeable to water
- increase in water removal
- Result: Less but more concentrated urine excreted
 Low ADH
- decrease water removal
- result: larger vol of more dilute urine exreted

65. Role of hormones in water regulation and
osmoregulation of mineral ions
 Antidiuretic hormones (ADH)
- secreted by posterior lobe of pituitary gland
- influence water absorption in kidney tubules
- increase in osmotic pressure of blood will stimulate specialised sensory
receptors called osmoreceptors in the hypothalamus in the brain
- osmoreceptors send impulses through nerves to the posterior lobe of
the pituitary gland
- ADH is secreted into the blood and carried to the kidney
- influences the reabsorption of water from the glomerular filtrate
- diabetes insipidus : excessive and frequent production of urine

66. Osmoregulation

67. Regulation of sodium absorption and potassium
secretion by aldosterone
- regulated by hormone aldosterone secreted by adrenal cortex
- occur when the vol of body fluid drops because of dehydration
- total sodium ion content also drop
- adrenal gland is stimulated to secrete aldosterone
- reabsorption of sodium ions and water
- reduce production of urine
- maintain the water balance of body fluids
- deficiency of aldosterone reduces the reabsorption of sodium
- sodium loss through urine

68. Aldosterone
-stimulated the secretion of potassium in the distal convulated
tubule
- also has the ability to stimulate sodium potassium ATPase
activity in the cell of the distal tubule
- also has the ability to alter the apical (urinary) membrane
conductance of potassium in these cells
i) in the absence of aldosterone, potassium ion content in the
body and plasma are increased due to a decrease in the renal
excretion of potassium
ii) in the presence of excess aldosterone, potassium ion content in
both body and plasma are decreased
iii) an increased potassium content in plasma stimulates
aldosterone secretion and a decreased content suppresses it