5.1.2 Excretion as an example of Homeostatic Control Flashcards
What is excretion?
Process of removing metabolic wastes e.g. carbon dioxide & nitrogen-based byproducts to maintain metabolism. Enables organisms to maintain pH
balance & regulate osmotic pressure.
Describe the gross structure of the mammalian liver.
Liver lobules (cylinders of hepatocytes arranged in rows & connected at the centre) are connected to: Liver lobules (cylinders of hepatocytes arranged in rows & connected at the centre) are connected to: And bile duct: transports bile to gall bladder for storage.
Outline the functions of the mammalian liver.
● Site of gluconeogenesis, glycolysis, glycogenesis.
● Stores glycogen.
● Deaminates excess amino acids, forming ammonia & organic acids. Acids can be respired or converted into glycogen. Ammonia is detoxified by addition of CO2 in ornithine cycle.
● Detoxifies chemicals e.g. converts alcohol to ethanal
then acetic acid.
Describe the gross structure of a mammalian kidney.
Fibrous capsule: protects kidney.
Cortex: outer region consists of Bowman’s capsules, convoluted tubules, blood vessels.
Medulla: inner region consists of collecting ducts, loops of Henle, blood vessels.
Describe the blood vessels associated with a
nephron.
Wide afferent arteriole from renal artery enters renal capsule & forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole. Efferent arteriole branches to form capillary network that surrounds tubules.
Describe the sections of a nephron.
Bowman’s capsule at start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes.
Proximal convoluted tubule (PCT): series of loops surrounded by capillaries, walls made of epithelial cells with microvilli.
Loop of Henle: hairpin loop extends from cortex into medulla.
Distal convoluted tubule : similar to PCT but fewer capillaries.
Collecting duct: DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney.
Describe the process of ultrafiltration.
Occurs in Bowman’s capsule. Occurs in Bowman’s capsule. Basement membrane acts as filter. Blood cells & large molecules e.g. proteins remain in capillary.
How are cells of the Bowman’s capsule adapted for
ultrafiltration?
● Fenestrations between epithelial cells of capillaries.
● Fluid can pass between & under folded membrane of podocytes.
State what happens during selective reabsorption
and where it occurs.
Useful molecules from glomerular filtrate e.g. glucose are reabsorbed into the blood. Occurs in proximal convoluted tubule.
How does the kidney produce urine?
After selective reabsorption, filtrate passes through Loop of Henle, which acts as countercurrent multiplier & then through distal convoluted tubule, where water & mineral ions are reabsorbed. More water is reabsorbed in collecting duct. Remaining fluid (urine) contains only waste materials & water.
What happens in the loop of Henle?
- Active transport of Na+ & Cl- out of ascending limb.
- Water potential of interstitial fluid decreases.
- Osmosis of water out of descending limb (ascending limb is impermeable to water).
- Water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of ascending limb.
Explain the role of the distal convoluted tubule.
Reabsorption:
a. of water via osmosis
b. of ions via active transport permeability of walls is determined by
action of hormones
Define osmoregulation.
Control of plasma water potential via negative feedback homeostatic mechanisms.
Explain the role of the hypothalamus in
osmoregulation.
- Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink.
- This triggers hypothalamus to produce more antidiuretic hormone (ADH).
Explain the role of the posterior pituitary gland in
osmoregulation.
Stores and secretes the ADH produced
by the hypothalamus.
