A PowerPoint Presentation on homeostasis

1. A2 Bio: Chapter 14

2. Homeostasis
 Homeostasis
 Maintenance of constant internal environment
 Physiological factors controlled:
 Body temp
 Metabolic wastes (CO2, urea)
 Blood pH
 Blood glucose concentration
 Water potential of blood
 Concentrations of CO2 and O2

3. Internal Environment
 Influence of tissue fluid
 Temperature
○ Low temp- slows metabolic rates
○ High temp – denatures enzymes
 Water potential
○ Decrease will cause osmosis to occur
○ Metabolic reactions – stops/slows
 Cells swell-bursts
 Concentration of glucose
○ Causes respiration to slow down

4. Homeostatic control
 Negative feedback
 Around set point
 Aided by
 Nervous system
 Endocrine system
 Control of body temperature
 Thermoregulation
 Involves both coordination systems
 Vasoconstriction/ vasodilation
 Shivering/ sweating
 Raising / Lowering body hairs
 Decreasing/Increasing production of sweat
 Increasing/Decreasing secretion of adrenaline
 Increasing/Decreasing the secretion of Thyroxine

6. EXCRETION
 Removal of metabolic wastes
 Carbon dioxide
 Aerobically by respiring cells
 Diffuses from blood into alveoli
 Urea
 Liver
 From excess amino acids
 Transported from liver to the kidney
 Kidney remove urea from blood, excreted as
urine

7. Deamination
 Removal of excess amino acid
 Avoids wastage
 In liver
 Amino acid removed with H atom
 Form ammonia
 Keto acid
 Enter Krebs cycle for respiration
 Converted to glucose
 Stored as glycogen or fat

8. Deamination
 Ammonia
 Soluble, toxic
 Prevents damage by converting into
 Urea – less soluble & toxic
○ Main nitrogenous excretory product
○ Removed in urine from kidney
 Other nitrogenous product
 Creatinine
○ Made in liver from aa
 Used in muscles as Creatine phosphate
○ Excreted as creatinine
 Uric acid
○ Breakdown of purines (nucleotides)

9. Structure of kidney
 Cortex
 Medulla
 Pelvis

11. Your name:
 A ___________
 B ___________
 C ___________
 D ___________
 E ___________
 F ___________
 G ___________
 H ___________
 I ____________
 J ____________
Labeling

12. ULTRAFILTRATION
 Filters small molecules out of blood into
Bowman’s capsule
 Blood separated by 2 cell layers
 Endothelium
○ Cell has holes
○ Basement membrane
 collagen & glycoproteins
 Epithelial cells
○ Inner lining of Bowman’s capsule
○ Has finger-like projections - podocytes

13. ULTRAFILTRATION
 Holes in endothelium, gaps between
podocytes
 Substances pass through
 Some substance cannot pass
 Protein with mass 69,000 +
 RBCs, WBCs
 Basement membrane acts as a filter
 Glomerular filtrate identical to blood plasma
 No plasma proteins

14. Factors affecting glomerular
filtration rate
 Rate at which fluid filters from the blood
 In a human, the rate is about 125 cm3 min−1
 Determined by
1. Differences in water potential between capillaries &
Bowman’s capsule
2. Difference in solute concentration
“the effect of differences in pressure outweighs the
effect of the differences in solute concentration”

15. Reabsorption in the PCT
 Cuboidal epithelial cells adapted by
 Microvilli
 Increase SA
 Tight junction
 Do not allow fluid to pass between cells
 Many mitochondria
 Energy for Na+-K+ pump proteins
- Outer membrane
 Co-transporter protein
 Sodium ions, glucose, amino acid
- Membrane facing lumen

21. Loop of Henle
 Counter current multiplier
 2 limbs – fluid flowing down
in one & up the other
 Enables maximum conc of
solutes both inside & outside
 Cells of AL & collecting
duct– permeable to urea

22. Reabsorption in DCT & CD
 Na+ pumped out
into tissue fluid
into blood
 K+ pumped into
tubule
 Rate of exchange
(Na+ & K+)
regulate conc of
these ions in blood

23. Control of water content
 Osmoregulation – control of water
potential of body fluids
 Involves the hypothalamus
(Osmoreceptors), posterior pituitary gland &
kidneys and Anti-diuretic Hormone(ADH)
 Water potential in blood monitored by
osmoreceptors

24. OSMORECEPTORS
 Sensory receptor primarily found in the
hypothalamus
 Detects decrease in water
 Sense change in osmotic pressure
 Nerve impulses sent along the neurons
 Stimulates the release of ADH

25. Summary of osmoregulation
 Dehydration
○ Decrease in blood water
○ Pituitary gland secrete ADH
○ Makes kidney reabsorb water
○ = concentrated urine
 Water-logged
○ Too much water in blood
○ Less ADH (or none) secreted by Posterior Pituitary
Gland(PPG)
○ Less water reabsorbed by kidney
○ = Dilute urine

27. ADH
 A peptide hormone
 Made of 9 amino acids
 ADH enter capillaries and carried
around body
 Key effect:
 Reduce loss of water in the urine
 By reabsorption
 Diuresis – production of diluted urine

29. ADH
 Target cells – collecting duct cells
 ADH acts on the cell surface membrane
of CDC
 Makes them more permeable to water
 By increasing no. of water-permeable
channels – aquaporins
 Bind to receptor proteins
 Activates enzymes in cells with vesicles
 Activated vesicles move to CSM & fuse
 Secretion of ADH increases
reabsorption of water into blood

32. ADH
 Enough water in body
 Increase in water potential
 Osmoreceptors no longer stimulated
 Neurons stop secreting ADH
 Makes aquaporins move out of CSM of collecting
ducts to cytoplasm
 Makes CD less permeable to water
 Dilute urine
 Takes 15-20 min for ADH to be broken down
 Once ADH stops arriving at the CD cells,
takes 10-15 for aquaporins to be removed

33. Control of glucose
 Every 100 cm3 of blood: 80-120 mg of
glucose
 Conc. below this = not enough for
respiration
 Especially for brain cells
 Very high conc = upsets normal cell
function
 Homeostatic control by 2 hormones by
endocrine tissue in pancreas
 α cells – glucagon
 ß cells - insulin

36. Control of high blood glucose conc
 α and β cells detect the increase
○ α cells stop secretion of glucagon
○ β cells secrete insulin
 How?
 Signaling molecule, cannot pass through
○ Binds to a receptor on cell surface membrane
 Affects through intracellular messengers
 Vesicles with GLUT proteins move to surface
○ Muscle cells = GLUT4
○ Brain cells = GLUT1
○ Liver cells = GLUT 2
 Also stimulates activation of glucokinase,
phosphofructokinase and glycogen synthase

38. Decrease in blood glucose conc
 α and β cells detect the decrease
 α secrete glucagon , β stop insulin production
 Glucagon binds to different receptor on liver
cells
 This activates a G protein
 This activates enzyme that catalyzes conversion
of ATP to AMP
 AMP+ Kinase enzyme = amplifies signal from
glucagon
 Glycogen phosphorylase – end of cascade
 Breakdown of glycogen  glucose

40. Decrease in blood glucose
conc
 Two sources of glucose:
 Enzyme cascade
1. Gluconeogenesis
○ From amino acids & lipids
 Glucagon in liver – increases glucose
 Muscle – no receptors for glucagon
2. Adrenaline
○ increases conc of glucose
○ breakdown of glycogen stores in muscle

42. Diabetes mellitus
 Type I diabetes
 due to a deficiency in the gene that codes for the
production of insulin
 Type II diabetes
 Liver & and muscle cells do not respond to insulin
 Symptoms
 the kidney cannot reabsorb all the glucose
 some passes out in the urine
 extra water and salts accompany this glucose
 feels extremely hungry and thirsty

43. Urine analysis
 Presence of glucose & ketones - diabetes
 Presence of proteins – problem with kidney
 Most proteins – too large
 Some filtered through
 Reabsorbed by endocytosis in PCT
 Broken down, amino acids absorbed into blood
 Dipsticks & biosensors
 Dipsticks has glucose oxidase & peroxidase
 Biosensors measure conc of glucose

47. Homeostasis in plants
 Stomata – the hole between the guard cells
 Opening during the day
 Diffusion of gases
 diffusion of water vapor in transpiration
 Closure of stomata at night
 abscisic acid (ABA)
 Stomata respond to
 increasing light intensity
 low carbon dioxide concentrations in the air spaces
within the leaf.

49. Opening & Closing of stoma
 Guard cells lose/gain water by osmosis
 Decrease in water potential by
 ATP-powered proton pumps transport H+
 Decrease of H+ in cells causes K+ to move
in
 Electrochemical gradient
 Extra K+ lower WP inside
 Osmosis occur
 Increases turgor of cells, stoma opens
 Bundles of microfibrils arranged lengthwise

50. Opening & Closing of stoma
 Stomata close when
 H+ pump proteins stop
 K+ leave guard cells
 enter other cells
 Effects
 Reduces uptake of CO2
 Reduces rate of transpiration
 Abscisic acid – stimulate closure