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BIOLOGY SUMMARY

COMMUNICATION, HOMEOSTASIS AND ENERGY

MODULE 5

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MODULE 5Communication, Homeostasis & Energy

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TOPIC 1Communication & Homeostasis • Need for communication

○ Organisms must maintain certain conditions ○ Optimal conditions for cells and enzymes

• Cell signalling ○ Communication between cells ○ Neuronal system ○ Hormonal system

• Homeostasis = regulation of internal environment ○ Despite external changes ○ Temperature ○ pH ○ Water content ○ Blood pressure

• Negative feedback ○ Reversal of change back to optimal level ○ Change detected by sensors ○ Effectors act to oppose change ○ Optimal condition restored

• Positive feedback ○ Change exaggerated

• Stimulus = change in environment that initiates a response ○ Can be external or internal environment

• Response = reaction to stimulus●Endotherms

○ Maintain constant body temperature ○ Internal sources of heat ○ Activity possible in cool temperatures ○ Higher caloric requirements ○ Adaptations:

– Sweat glands on skin – Capillaries near skin surface – Hairs on skin

• Ectotherms ○ External environment controls body temp ○ Less food required ○ More energy available for growth ○ Warm up by lying on hot surfaces ○ When active, muscles generate some heat ○ Rely heavily on behaviour to help maintain body temp

TOPIC 2Excretion as an Example of Homeostatic Control • Excretion = removal of metabolic waste from body • Metabolic waste = unneeded byproducts of normal

metabolism • Carbon Dioxide

○ Harmful in excess (disturb pH balance) ○ Carried in blood buffer system ○ Removed by lungs

• Nitrogenous waste ○ Excess amino acids deaminated in liver ○ Converted into ammonia then urea ○ Urea excreted in urine by kidney

• Mammalian liver ○ Blood flow

– Oxygenated blood in hepatic artery – Deoxygenated blood in hepatic portal vein (also

carries products of digestion) – Blood exits via hepatic vein – Oxygenated and deoxygenated blood mixes in

sinusoids ○ Liver cells (“hepatocytes”)

– Cuboidal with microvilli – Multifunctional

○ Kupffer cells – Specialised macrophages in sinusoids – Break down old RBCs into bilirubin

○ Deamination – Amino acids keto acids + ammonia

○ Ornithine cycle – Ammonia + CO2 urea – Urea excreted by kidney

• Kidney ○ Nephron = functional unit

– Filter waste from blood ○ Structure and function

– Bowman’s capsule: ultrafiltration – PCT: selective reabsorption including glucose

reabsorption – Loop of Henle: water reabsorption – DCT: osmoregulation

○ Blood vessels: – Glomerulus – Afferent arteriole – Efferent arteriole – Peritubular capillaries – Vasa recta – Vanule

○ In PCT: – Reabsorption of salts, glucose and H2O – 85% of water reabsorbed here

○ In descending limb: – Salts added; water removed – Water potential decreases

○ In ascending limb: – Salts removed (active) – Water potential increases

○ In collecting duct: – Water removed; water potential decreases

• Ultrafiltration ○ Blood enters glomerulus via afferent arteriole ○ Afferent diameter > efferent diameter ○ Therefore blood is under high pressure ○ Small solutes enter bowman’s capsule ○ 3 layers to pass through:

– Capillary endothelium – Basement membrane – Epithelial cells of bowman’s capsule

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