Chapter 37: The human urinary system Leaving Certificate Biology Higher Level

The Urinary System The urinary system consists of: Kidneys – filters/purifies the blood Ureters – carries the urine from kidney to bladder Bladder – stores urine until pressure builds up and urine is released Urethra – passes the urine from the bladder to the outside of the body

Macrostructure of the Urinary System

Structure and Position of Nephrons

Structure of Bowman’s Capsule Glomerulus Afferent arteriole Bowman’s capsule Efferent arteriole

Structure of Nephron

The Urinary System The urinary system is an excretory system that consists of the critical excretory organs, the kidneys The kidneys are excretory organs because they get rid of the waste products of metabolism from the blood REMEMBER! Metabolism is the sum of all the chemical reactions occurring in the body Homeostasis is the process of maintaining a constant internal environment

The Urinary System In addition to filtering the blood the kidneys also have other functions: Osmoregulation (water balance) Chemical regulation (salt and other chemical balance) pH balance

Urine Formation Urine formation occurs in two main steps: Filtration Selective reabsorption

Urine Formation Filtration: Occurs in the glomerulus – blood passes into glomerulus via afferent arteriole and passes out deficient in many substances via the efferent arteriole The afferent arteriole is wider than the efferent arteriole so as to cause an increase in blood pressure within the glomerulus so that filtration occurs more efficiently Glomerular filtrate is produced which passes into the Bowman’s capsule – it does not contain plasma proteins as they are to big to pass through

Urine Formation Selective reabsorption: The glomerular filtrate contains many useful substances that the body needs such as water, glucose, salts, and amino acids – these must be reabsorbed prior to excretion Reabsorption of these substances occurs mostly in the proximal convoluted tubule (which is in the cortex) The parts of the nephron present in the medulla of the kidney (loop of Henle and collecting ducts) are also involved in reabsorption of water Reabsorption of these substances occurs by diffusion, osmosis (water) and active transport (all glucose and amino acids are absorbed actively)

The Urinary System Osmoregulation (water balance) The amount of water in the blood is monitored by the osmoreceptors in the hypothalamus of the brain: Not enough water in the blood → hypothalamus sends signal to pituitary to secrete anti-diuretic hormone (ADH), which travels in blood to distal convoluted tubules & collecting ducts of nephrons → causes tubules to become more permeable to water → water is reabsorbed Too much water in blood → hypothalamus sends signal to pituitary to stop/reduce ADH secreted → causes distal convoluted tubules and collecting ducts to become impermeable to water → water is excreted