iGCSE Biology - Chemical Coordination

• A gland is an organ that secretes a substance.
• Exocrine glands secrete their product through a duct.
• Endocrine glands secrete their product directly into a bloodstream.
• Differences between nervous and endocrine control:

Nervous System	Endocrine System
Works by nerve impulses transmitted through nerve cells (although chemicals are used at synapses)	Works by hormones transmitted in the bloodstream
Nerve impulses travel fast and usually have an instantaneous effect	Hormones travel more slowly and take longer to act
Response is usually short-lived	Response is usually longer-lasting
Impulses act on individual cells such as muscle fibres, so have a very localised effect.	Hormones can have widespread effects on different organs

 

• Main endocrine glands:

Gland	Hormone	Some functions
Pituitary	Follicle stimulating hormone (FSH)	Stimulates egg development and oestrogen secretion in females and sperm production in males
	Luteinising hormone (LH)	Stimulates egg release in females testosterone production in males
	Anti-diuretic hormone (ADH)	Controls the water content of the blood
	Growth hormone (GH)	Speeds up the rate f growth and development in children.
Thyroid	Thyroxin	Controls the body’s metabolic rate
Pancreas	Insulin	Lowers blood glucose
	Glucagon	Raises blood glucose
Adrenals	Adrenaline	Prepares body for physical activity
Testes	Testosterone	Controls development of male secondary sexual characteristics
Ovaries	Oestrogen	Controls development of female secondary sexual characteristics; regulates menstrual cycle
	Progesterone	Controls menstrual cycle

 

• Adrenaline produces a number of changes in the body:

                     Breathing rate increases and breaths become deeper.

                     The heart beats faster.

                     Blood is diverted from intestine to muscles.

                     Glycogen is turned into glucose and released into the blood in     the liver.

                     The pupils dilate.

                     Body hair stands on end.

                     Mental awareness is increased.

• Insulin causes glucose to be converted into glycogen in the liver.
• Glucagon causes glycogen to be converted into glucose in the liver.
• Diabetes is where a person cannot produce enough insulin.