Chapter 13: Homeostasis and the Human Urinary System
Form 4 Biology Bab 13: Homeostasis and the Human Urinary System
13.1 Homeostasis
Homeostasis regulates physical and chemical factors of the internal environment within normal ranges for cells to function optimally. (p.246)
Physical factors: temperature, osmotic pressure, blood pressure. Chemical factors: pH, mineral concentration, blood sugar. (p.246)
Negative feedback returns a deviation to the normal range. (p.246)
Body temperature is detected by thermoreceptors in the skin and hypothalamus. (p.247)
High temperature: vasodilation, sweating, erector muscles relax, reduced adrenaline and thyroxine, no shivering. (p.247)
Low temperature: vasoconstriction, no sweating, erector muscles contract, shivering, more adrenaline and thyroxine. (p.248)
Normal blood sugar is 75–110 mg/100 ml; insulin from beta cells lowers it, glucagon from alpha cells raises it. (p.249)
Insulin drives cell respiration and converts excess glucose to glycogen; glucagon converts glycogen to glucose. (p.249)
Breathing is regulated by the respiratory control centre in the medulla oblongata; chemoreceptors detect pH and CO2 changes. (p.250)
Blood pressure: baroreceptors send impulses to the cardiovascular control centre; high pressure causes vasodilation and weaker contractions, low pressure causes vasoconstriction and stronger contractions. (p.251)
13.2 The Urinary System
The urinary system consists of kidneys, ureters, bladder and urethra; it excretes nitrogenous wastes and regulates body fluid volume, osmotic pressure and pH. (p.252)
Kidney functions: excretion and osmoregulation. (p.252)
Renal artery brings blood to the kidney; renal vein carries it away; urine flows via the ureter to the bladder. (p.253)
Nephron: Bowman's capsule, glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule, then collecting duct. (p.254)
Ultrafiltration: high hydrostatic pressure because the afferent arteriole is wider than the efferent; filtrate lacks red blood cells, platelets and plasma proteins. (p.255)
Reabsorption: proximal tubule reabsorbs all glucose and amino acids by active transport, Na+ actively and Cl- passively, water by osmosis. (p.255)
Loop of Henle and distal tubule reabsorb more water and salts. (p.255)
Secretion: H+, K+, NH4+, urea, creatinine, toxins; most active at the distal convoluted tubule. (p.255)
Urine contains water, urea, NaCl, uric acid and creatinine. (p.255)
Osmoregulation via ADH: high osmotic pressure stimulates hypothalamus, more ADH, more water reabsorbed, small volume of concentrated urine. (p.256)
Low osmotic pressure: less ADH, less water reabsorbed, large volume of dilute urine. (p.256)
Experiment: drinking 250–1000 ml of water and measuring urine volume over 60 minutes. (p.257)
13.3 Health Issues Related to the Urinary System
Diabetes mellitus and high blood pressure damage the glomerulus and cause kidney failure. (p.259)
Kidney stones are hard masses of uric acid, calcium oxalate or calcium phosphate; drinking plenty of water reduces the risk. (p.259)