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Homeostasis
- 1. Homeostasis Biology 2: Form and Function MOHD ASIF KANTH M.SC ZOOLOGY ,B.ED 9070262786 aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 2. Overview • Homeostasis = maintenance of constant internal environment • Physiological controls – Negative feedback loops – Positive feedback loops • Behavioral controls aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 11. Osmoregulation • Water is vital to the chemistry of life • Therefore, must attain a water balance within the body • Water balance systems are based on three processes: – Diffusion – Osmosis – Active transport • Osmoregulation processes often tied to excretion aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 12. • Diffusion – The spread of molecules along a concentration gradient by brownian motion, towards a state of entropy • Osmosis (the diffusion of water) – Water moves from a low solute concentration (hypotonic) to a high solute concentration (hypertonic) • Active transport – The movement of molecules across a membrane, usually against a gradient, involving the expenditure of energy aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 14. Osmoregulation in invertebrates • Since most invertebrate phyla evolved in water, no shortage • However, differences in concentration between the cell and the solution surrounding it may cause problems – e.g., Amoeba in freshwater: hypertonic cell in hypotonic solution – Result: movement of water into cell – Defense: Contractile vacuole pumps out water aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 15. • Multicellular organisms use transport epithelia to control water loss and excretion – Platyhelminthes • Protonephridia (flame cells) collect excess water in addition to nitrogenous wastes, empty into nephridiopore, excretes NH3 – Annelida • Metanephridia organized on a per segment basis collect waste from coelom via the nephrostome, counters water uptake by epidermis, excretes NH3 – Insecta • Malpigian tubules collect nitrogenous wastes from haemocoel, excretes Uric Acidaasifibrahim786@gmail.com/asifkant h89@gmail.com
- 20. Osmoregulation in fish • Depends on environment – Freshwater • Cells are hypertonic to environment, must defend against water uptake – Excretion of dilute urine – Mucous covering of epidermis – Marine • Cells are hypotonic to environment, must defend against water loss – Water gain through food uptake and drinking – Concentration of urine aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 29. Filtration • Occurs in Bowmans capule – Afferent arteriole from renal artery enters glomerulus, exits via efferent arteriole – Blood filtered by capsule: all non-cellular products pushed into nephron (proximal tubule) – Filtrate includes products that must be retained: blood sugars, salts and vitamins aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 32. Secretion • Occurs in proximal and distal tubule • Secretion is initially active, although certain molecular transport occurs passively as a result • e.g., NaCl actively pumped out, H2O follows aasifibrahim786@gmail.com/asifkant h89@gmail.com
- 34. Reabsorption • Materials that must be retained are brought back by active transport or passive diffusion • Result of absorption/secretion in Loop of Henle is highly concentrated urine • Nephron tubule is lined by transport epithelia • Amount of water retained is controlled by hormones that control activity of transport epitheliaaasifibrahim786@gmail.com/asifkant h89@gmail.com
- 35. The Loop of Henle • Descending limb is permeable to water but not NaCl • H2O moves by osmosis to high salt concentration in interstitial fluid • Thin segment of ascending limb is permeable to NaCl which moves passively by diffusion to equalize gradient • Thick segment of ascending limb actively transports NaClaasifibrahim786@gmail.com/asifkant h89@gmail.com