10.2 Hormones

What is a hormone? a hormone is a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver hormones like nervous system coordinates the activities of the body hormones are produced by endocrine glands such as the pancreas, pituitary gland, adrenal gland, testes, ovary etc. endocrine glands are ductless glands i.e. they don’t have ducts thus they release their secretions into the blood stream which carries the hormones to the target organs i.e. the organ where the hormone brings about its effects Examples: insulin, produced by the pancreas, alters the activity of the liver & skeletal muscles

Main endocrine glands pituitary gland, produces hormones such as Follicle stimulating hormone (FSH) & Luteinising Hormone (LH) adrenal gland, produces hormone adrenaline pancreas, produces hormones insulin & glucagon ovaries, produces hormones such as Progesterone & Oestrogen testes, produces hormone testosterone

Role of the hormone adrenaline hormone adrenaline is produced by adrenal glands located above the kidneys adrenaline prepares the body for flight & (or) fight – both of which are designed to cope with danger hormone adrenaline prepares the body for action by stimulating the following: liver converts glycogen into glucose, making more glucose available to muscles to produce more energy for rapid contractions needed for sudden action increase in heart rate so that more oxygen & glucose are supplied to muscles to produce more energy for fighting or flight dilation of air pathways so that more air reaches the alveoli for more gas exchange vasodilation of arterioles in the brain & muscles so more glucose & oxygen are delivered to these organs vasoconstriction of arterioles in the gut & other organs such as skin allowing more blood to be delivered to muscles

Situations in which adrenaline secretion increases

Comparison between nervous and hormonal control systems Nervous system Hormonal system made up of glands containing secretory cells information transmitted in form of chemicals called hormones hormones carried dissolved in blood plasma speed of information transmission is slow duration of effect of hormone is usually long lasting many responses such as conversion of glucose to glycogen, protein synthesis, rate of respiration made up of neurones information transmitted in form of electrical impulse impulse transmitted along nerve fibres speed of information transmission is fast duration of effect of nerve impulse is for a short time response by muscle contraction or secretion by glands

Use of hormones in food production hormones are at times used by famers to increase animal growth rate or to increase the yields of certain products such as milk one such hormone is Bovine somatotropin (BST) BST is a hormone naturally produced by cattle if dairy cows are given extra quantities of BST, their milk production increases by 20% use of BST increase milk yields – thus more profit & reduce the size of the herd thus cutting down costs arguments against use of BST: worries about drinking milk from cows treated with BST – they think it may cause health risks there are no risks to consumers because only small quantities of BST get into milk & these are digested in the gut into amino acids concerns that BST may harm the cows by causing infertility & mastitis i.e. inflammation of the udders surplus production of milk in certain parts of the world such as Europe – so why use BST? use of BST is banned in European union but still in use in USA

Revision Questions Define the following terms: endocrine system; hormone & target organ State the role of the hormone adrenaline in chemical control of metabolic activity Give three examples of situations in which adrenaline secretion increases State the effect of adrenalin on the following: heart rate; breathing rate; blood supply to the gut and blood supply to the brain & skeletal muscles State four ways in which coordination by nervous system differs from coordination by hormones Discuss the use of hormones in food production