Human Biology - Hormones

UNIT 3 Chapter 2 - Hormones Help Control The Body

Endocrine system - list at least 5 of the endocrine glands

System: made up of endocrine glands that secrete hormones

Endocrine glands: Pineal gland, Hypothalamus, Pituitary gland, Thyroid gland, Parathyroid glands (usually 4), Thymus, Adrenal glands (2), Kidneys (2), Pancreas, Ovaries (2), Uterus, Testes.

Exocrine glands vs Endocrine glands

Exo - secrete into a duct carries secretion to the body surface or one of the body cavities. e.g. sweat glands, mucous glands, salivary glands, alimentary canal glands, etc.

Endo - secrete hormones into extracellular fluid surrounding the cells that make the gland - then passes into the capillaries then transported by blood.

Hormones

Chemicals secreted by endocrine glands transported through the body in the blood.

They change the functioning of cells by changing the type, activities, or quantities of proteins produced.

They are not enzymes but exert their influence by changing activity of enzymes or their concentration

They may:

• Activate certain genes in the nucleus to make a certain enzyme or protein produced

• Change the shape or structure so its ‘on’ or ‘off’

• Change the rate of production of an enzyme by changing rate of transcription or translation

They can affect all cells or only particular cells or organs

Steroid hormones

e.g. oestrogen, progesterone, cortisol, aldosterone.

They are lipid-soluble - don’t dissolve in water

Once released into the blood, hormones bind to transport proteins enabling them to travel in the bloodstream

Once they reach the target cell they seperate from transport proteins and diffuse across the cell membrane

They combine with a receptor protein in the cytoplasm or nucleus. The hormone-receptor complex activates genes controlling formation of particular proteins

Binds to promoter section stimulating/inhibiting transcription therefore protein synthesis.

They are slow to have an effect but long lasting

Protein and amine hormones

They are water-soluble - they are unable to diffuse across the cell membrane

They attach to a receptor protein in the membrane of the target cell

This combination causes a secondary messenger substance to diffuse through the cell

e.g. insulin binds to receptor → increase in glucose absorption by the cell

Quick to cause response, but short lasting

Hormone receptors

Each receptor binds with a specific molecule.

“Lock and Key” analogy

There is a limited number of receptor cells so once at capacity no further increase in rate of cells activity can occur

e.g. once each insulin receptor is bound to insulin, the cells rate of glucose uptake cannot increase any further, even if insulin increases. Meaning saturation can occur.

Enzyme Amplification

One hormone molecule does not cause the manufacture or activation of just one molecule of an enzyme - it activates thousands of molecules.

Process - enzyme amplification.

The hormone triggers a cascading effect in the number of reacting molecules is increased by hundreds or thousands of times for each step of the metabolic pathway.

Thus very small stimulus can produce large effects

Hormone clearance

Once the hormone produces the desired effect, it is turned off.

Done by breaking down the hormone molecules. Some are broken down in the target cells, but most are in the liver and kidneys. They are then excreted in bile or urine