Topic 7: the Kidneys

How genes can be switched on and off by DNA transcription factors

• they initiate and regulate the transcription of genes by switching them on and off

• they bind to specific sections of DNA called enhancer or promoter sequences and thus initiate transcription then protein synthesis

Ultrafiltration

occurs in the glomerulus

• driving force is the high blood pressure in the glomerular capillaries because the afferent arterioles has a wider diameter than the efferent arterioles

• high hydrostatic pressure forces small molecules out of the blood into the Bowman’s capsule, forming the glomerular filtrate

Selective Reabsorption

in the proximal tubule

• microvilli provide a large SA

• reabsorption of glucose amino acids & salts by active transport

in the loop of henle

• acts as a countercurrent multiplier to create a conc gradient for water to be reabsorbed

  • descending: water mores out by osmosis

  • ascending: ions actively transported out

Tubular Secretion

Occurs in the DCT & collecting duct

• h+ regulates pH, k+ ion balance & NNH4+ removes toxins

• ADH increases water reabsorption

• Aldosterone regulates Na⁺ & K⁺ for fluid balance

How is ADH involved in the controls of water potential of the blood?

water potential of blood is monitored by osmoreceptors in hypothalamus

ADH is released from the pituitary gland and acts on collecting duct

so it increases in permeability to water so more water is reabsorbed so water potential of blood can go back to normal range