Chapter 37: The human Chapter 37: The human urinary systemurinary system

Leaving Certificate BiologyLeaving Certificate Biology

Higher LevelHigher Level

The Urinary SystemThe 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 Macrostructure of the Urinary of the Urinary

SystemSystem

Structure Structure and and

Position of Position of NephronsNephrons

Afferent arteriole

Efferent arteriole

Bowman’s capsule

Glomerulus

Structure of Bowman’s CapsuleStructure of Bowman’s Capsule

Structure of NephronStructure of Nephron

The Urinary SystemThe 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 SystemThe 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 FormationUrine Formation• Urine formation occurs in two main

steps:1. Filtration

2. Selective reabsorption

Urine FormationUrine Formation1. 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 FormationUrine Formation2. 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 SystemThe 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