Some is saved. This represents a leakage from the circular flow. In addition to the consumer spending, firms also carry out investment spending. This is an injection to the circular flow of income, as it does not originate from consumers' current income. In the real world the government and international trade sectors must also be included.
Economic systems are in reality three sector open economies.
Consequently there will be additional leakages and injections. Government spending will be injected into the circular flow and taxation will leak from it. Export flows will be injected and imports flows leaked. A full circular flow with leakages and injections is shown below. This model of the economy demonstrates that economic activity is a flow.