Endocrine System

What is the endocrine system concerned with?

maintaining homeostasis

What are the types of endocrine glands?

• exocrine glands

• endocrine glands

What does the exocrine gland do?

secrete hormones into a duct that carries the secretion to the body surface or to one of the body cavities (e.g. sweat glands, mucous glands, salivary glands, glands of the alimentary canal)

What does the endocrine gland do?

secrete hormones into the extracellular fluid that surrounds the cells that make up the gland, secretion usually passes into the capillaries to be transported by the blood

What are hormones?

chemicals secreted by the endocrine glands

How are hormones transported around the body?

transported in the blood

What is the purpose of the endocrine system?

change cell functioning (cell type, activities or quantitites of proteins produced)

What may hormones do?

• activiate certain genes in the nucleus of a cell so a particular enzyme/structural protein is produced

• change shape/structure of an enzyme (turn ‘off’ or ‘on’)

• change rate of transcription or translation during protein production (change rate of production of enzyme/structural protein)

Hormones affect different cells depenending on the hormone, they may affect:

• all cells

• target cells (particular groups)

• target organs (particular organs)

What can hormones also be?

• steroids

• proteins

• amines

Do steroid hormones dissolve in water?

• lipid soluble (do not dissolve in water)

What are some examples of steroid hormones?

• oestrogen

• progestrone

• cortisol

• aldosterone

How do steroid hormones travel in the blood?

bind to transport proteins

How do steroid hormones get to traget cells?

at target cell, the sertoid hormone seperates from the transport protein and diffuses across the cell membrane

How do steriod hormones work inside the cell?

Combine with a receptor protein in the cytoplasm or nucleus

• hormone receptor complex activates genes controlling formation of particular proteins

  • binds to promoter section of a certain gene, stimulating or inhibiting transcription (and protein synthesis)

How effective are steriod hormones?

Slow to cause effect, but long lasting.

Are protein and amine hormones water soluble?

Yes.

Cannot diffuse across cell membrane (not lipid soluble).

How do protein and amine hormones work if they cannot diffuse across the cell membrane?

• attach to the receptor proteins in target cell membrane

  • causes secondary messenger substances to diffuse through cell and activate particular enzymes

What does insulin do in cells? How?

• insulin binds to receptor protein and leads to increase in glucose absorption by the cell

Outline hormone receptors

• specific (only bind with 1 specific molecule)

• ‘lock and key model’ - receptor protein (lock) only works with correct molecule (key)

• limited number in membrane of each cell

  • when all bound to a molecule, there can be no futher increase in a cell’s activity

    • e.g. if insulin binds to each insulin receptor in a cell, cells uptake of glucose cannot increase anymore (irrespective of if insulin increases) (saturation)

• different cells have different types and numbers of receptors (variation in sensitivities between cells)

Outline enzyme amplification

• 1 hormone molcule activates thousands of molecules

  • hormone triggers cascading effect in which the number of reacting molecules involved is increased 100’s/1000’s of times for each step along the meabolic pathway

• small stimular → very large effect

Outline hormone clearance

• once hormone completed required effect it must be turned off

• some hormones broken down in the target cells, most in the liver and kidneys

• degraded hormones excreted in either bile or urine

How does the body control hormone secretions?

• amount of hormone produced must be regulated (homeostasis)

  • oversecretion/undersecretion causes body to function abnormally

• secretion regulated by negative feedback systems

  • responding hormone produced by the secretion of a hormone is the opposite of the stimulus that caused the initial secretion