IB Biology SL

Hormones: substances that stimulate target cells via the blood

→ released directly into the blood plasma from endocrine glands 

• produces slow, long-lasting & widespread responses 

The endocrine system contains several different glands = each gland secretes different chemicals called hormones directly into the bloodstream. 

Hormones travel in the blood to a specific/target organ or receptor & bring about a response. The response becomes a long-term change. 

The pituitary gland 

• in the brain
• secretes several hormones (reproductive hormones) => Follicle-stimulating hormone (FSH) & Luteinising hormone (LH). 

The thyroid gland

• located in the front of the neck below the larynx
• releases a hormone called thyroxin => helps to regulate the basal metabolic rate. 

The pancreas

• islets of Langerhans: groups of hormone-secreting cells: a cells => glucagon   b cells => insulin

The adrenal glands

• located…