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 adrenalinehormone 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 adrenalinesecretion increases

Comparison between nervous and hormonal control systemsNervous system Hormonal system

made up of neuronesinformation transmitted in

form of electrical impulseimpulse transmitted along

nerve fibres speed of information

transmission is fastduration of effect of nerve

impulse is for a short timeresponse by muscle

contraction or secretion by glands

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

Use of hormones in food productionhormones 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 QuestionsDefine 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