(A Level) Homeostasis and the kidney

Learning objectives

Explain why mammals keep conditions such as blood glucose and water potential within narrow limits, and describe a homeostatic control loop in terms of stimulus, receptor, nervous or endocrine coordination, effector (muscle or gland) and negative feedback.

State that the liver deaminates surplus amino acids, producing urea, and describe the gross structure of the kidney — fibrous capsule, cortex, medulla, renal pelvis, ureter, and the renal artery and vein with their branches.

Recognise each region of the nephron (glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct) and its blood supply on diagrams, photomicrographs and electron micrographs.

Explain how ultrafiltration in the Bowman's capsule forms glomerular filtrate, relating high hydrostatic pressure, the capillary endothelium, the basement membrane and podocytes to which substances are filtered and which stay in the blood.

Explain selective reabsorption of glucose, amino acids, ions and water in the proximal convoluted tubule, relating microvilli, many mitochondria, sodium–potassium pumps and cotransporter proteins to their roles.

Describe osmoregulation as negative feedback: osmoreceptors in the hypothalamus, ADH released from the posterior pituitary gland, and aquaporins inserted into collecting duct cells so that more water is reabsorbed.