Hormones in Humans | Biology for GCSE/IGCSE - Year 11 PDF Download

Hormones & Their Associated Glands

What is a Hormone?

• Hormones are chemical substances synthesized by glands and transported through the bloodstream.
• These compounds modify the activity of particular target organs, essentially serving as messengers that convey information and induce changes in various parts of the organism.
• Collectively, the glands responsible for hormone production in animals are referred to as the endocrine system.

Transport around the body

• Endocrine glands are well-vascularized to ensure rapid release of hormones into the bloodstream. This allows hormones to swiftly reach their target organs and elicit a response.
• Hormones exert their effects by binding to specific receptors on target cells, which can be located either on the cell membrane or within the cell. Receptor-hormone binding occurs only if the receptor is complementary to the hormone.
• The liver plays a crucial role in regulating hormone levels in the blood by metabolizing or breaking down any excess hormones.

Important hormones in the human body:

Comparison of Nervous & Hormonal Control

Glucagon

• Blood glucose levels are regulated through a negative feedback loop orchestrated by two pancreatic hormones: insulin and glucagon.
• Insulin and glucagon, both originating in the pancreas, govern blood glucose concentrations.
• Insulin is secreted in response to elevated blood glucose levels, prompting liver and muscle cells to convert surplus glucose into glycogen for storage.
• Conversely, glucagon is released when blood glucose levels drop, signaling liver and muscle cells to break down stored glycogen into glucose for release into the bloodstream.

The Hormone Adrenaline

• Adrenaline, also called the 'fight or flight' hormone, is secreted in situations where the body perceives danger.
• In the context of this hormone, 'flight' refers to swiftly removing oneself from a perilous scenario, such as running away, while 'fight' indicates resorting to physical combat if fleeing is not an option to overcome the danger.
• Its primary function is to prepare the body for action, specifically geared towards movement, whether to fight or flee.
• Adrenaline triggers several physiological responses in the body to facilitate this readiness for action, including:
  • Heightening blood glucose levels to enhance respiration in muscle cells.
  • Accelerating both pulse and breathing rates, ensuring swift delivery of glucose and oxygen to muscle cells while efficiently removing carbon dioxide from them.
  • Redirecting blood flow towards muscles and away from non-essential body parts like the alimentary canal, ensuring that respiratory substrates are readily available.
  • Dilating pupils to maximize light intake, aiding in sending more information to the brain.

More on Adrenaline

Additional effects of adrenaline include:

• Elevating blood glucose concentration serves to supply muscles with ample glucose for energy production during heightened activity.
• Accelerating heart rate achieves a similar objective, ensuring optimal readiness of all muscles for heightened activity during a fight-or-flight response.