1. D.5: Hormones & metabolism

2. Transported by the blood stream
The endocrine system
Produce and secrete hormones
What are hormones?
Hormones are chemical messengers, usually they have an effect away from the organs secreting them
Transported by the blood stream
Target cells are cells affected by a particular hormone.
Most hormones are controlled by negative feedback e.g. insulin (secreted by pancreas, lowers blood-glucose level)
Some hormones controlled by positive feedback e.g. ocytocin (secreted by pituitary gland, several functions during labour)
All hormones are transported by the blood

3. Endocrine glands
Endocrine glands secrete hormones directly into the blood stream.
Hormones travel to target cells, examples of hormones include: Steroids, proteins, glycoproteins, polypeptides, amines.
An example of an endocrine gland is the thyroid.

4. Categorised?
Type
Category
Example
Effect of example
Steroid
Lipid
Oestrogen
Thickens endometrium layer (uterus)
Peptide
Protein
Insulin
Removal of glucose from blood
Steroids synthesised from cholesterol – this is why they are classified as lipids (similar chemical/soluble properties, non polar – easily transfer across plasma membrane). Steroids affect the production of proteins, selectively binding to genes affecting the rate of transcription.
Peptide hormones do not enter the cell, they bind to receptor proteins on the membrane.
Page 695, read the paragraphs under subtitle ‘types of hormones and their mode of action’

5. Steroid hormones
These hormones bind to receptor proteins in the cytoplasm of the target cell to form receptor-hormone complex.
Peptide & lipid hormones differ in their solubility. This means they behave differently, but they both bind to receptors.
Estrogen is an example of a steroid hormone.
The receptor-hormone complex promotes the transcription of specific genes

6. Calciferol
Another steroid hormone, crosses the intestinal cell membrane and binds to a receptor within the nucleus of the cell.
The receptor-hormone complex effects the expression of the calcium transport protein, calbindin in the small intestines.
Calcium is then able to be absorbed in the intestine.

7. Mechanisms of peptide hormones
Peptide hormones bind to receptors in the plasma membrane of the target cells. Protein hormones are typically hydrophilic so they cannot pass through the membrane directly. Therefor they must bind to receptors and pass through the membrane using a series of reactions caused by secondary messengers.
Secondary messengers are small, water soluble molecules that quickly spread through the cytoplasm.
Calcium ions & cAMP (cyclic AMP) are the most common messengers.
Example of use: Epinephrine mediates fight/flight. Supply of blood glucose is essential in this instance. When epinephrine reaches the liver, it binds to a receptor called G-protein couple receptor. This activates the G-protein which uses GTP as an energy source to activate the enzyme adenylyl cyclase. The converts ATP to cAMP. The cAMP activates the protein kinase enzymes which activate the processes of glycogen breakdown and inhibit glycogen synthesis
Epinephrine mediates fight/flight. Supply of blood glucose is essential in this instance. When epinephrine reaches the liver, it binds to a receptor called G-protein couple receptor. This activates the G-protein which uses GTP as an energy source to activate the enzyme adenylyl cyclase. The converts ATP to cAMP. The cAMP activates the protein kinase enzymes which activate the processes of glycogen breakdown and inhibit glycogen synthesis.

8. Iodine deficiency
Thyroid hormones include two derivatives of tyrosine, triiodothyronine (3 iodine atoms) and tetraiodothyronine (4 iodine atoms). Therefore the thyroid requires iodine to function properly.
Consequences of deficiency
Goiter (swelling of the neck) as a result of the thyroid being continually stimulated by the hypothalamus & anterior pituitary gland.
During pregnancy, iodine deficiency can affect fetal nervous development  mental retardation in children.
There is currently a global effort to reduce iodine deficiency.

9. Cerebral hemispheres Hypothalamus Cerebellum Pituitary gland
You must be able to label and annotate a diagram of the human brain. Pg. 490
Pituitary gland
Medulla oblongata

10. Hypothalamus & Pituitary gland
Neurosecretory cells are long/thin cells fig.7, page 698
Hypothalamus secretes ‘releasing hormones’ e.g. GnRH
Pituitary gland is controlled by the action of the hypothalamus (fig. 19.2, pg. 603)
Pituitary gland has two nodes – anterior and posterior

11. Hypothalamus
Controls hormone secretion by the anterior and posterior lobes of the pituitary gland.
The hypothalamus is the region of the brain linking the nervous system to the endocrine system, using the pituitary gland.
The hypothalamus releases secreting factors which stimulate the pituitary to release hormones.
The hypothalamus is linked to multiple receptors to detect changes in the body to regulate negative feedback.

12. Pituitary hormones
Hormones secreted from the pituitary gland control growth, developmental changes, reproduction and homeostasis.
Anterior pituitary
Synthesis & secretion of FSH, LH (as well as other hormones responsible for growth, homeostasis & reproduction)
Posterior pituitary
Oxytocin and ADH (these hormones are not produced here)
Oxytocin and ADH produced by the hypothalamus within neurosecretory cells.

13. Posterior
Neurosecretory cells (dendrites & cell bodies in hypothalamus, axons inside p. pit. gland)
e.g. Oxytocin produced in the hypothalamus but secreted by p. pit. gland
Read page 697 for further explanation

14. Anterior
Capillary beds in hypothalamus absorb hormones secreted here. Portal vein transports hormones to cap. Beds around ant. pit. Gland. Hormones target ant. Gland, releasing specific hormones
e.g. FSH, LH, GH, prolactin, TSH all released by ant. pit. gland

15. Milk secretion Controlled by oxytocin and prolactin.
Prolactin: hormone. Produced by the anterior pituitary, stimulates growth of mammary glands and the production of milk. During pregnancy estrogen stimulates production of prolactin but also inhibits the production of milk.
Oxytocin: hormone. Stimulates the contraction of cells surrounding the milk storing structures, causing milk to be released. Oxytocin is produced in the hypothalamus and stored in the posterior pituitary gland.

16. Growth hormones & athletes
Growth hormone also produced in the anterior pituitary gland.
Liver cells are the target. The hormone binds to receptors and causes the release of an insulin-like growth factor.
Growth factor circulates in the blood, stimulates bone, cartilage growth and a gain in muscle mass. For this reason it has been used as a performance enhancing drug.

17. What is ADH?
Hormone, controlling reabsorption of water in collecting duct (kidney). Presence of ADH = water reabsorbed, No ADH = collecting duct impermeable to water.
Produced?
Dendrites of neurosectretory cells (NC)
Diffusion?
Down axon, stored in granules within synaptic end of NC
Secretion from granules?
Dependent on action potential from hypothalamus
Osmorecptors?
Monitor water content of blood
High water content?
No action potential = no ADH secretion
Low water content?
Action potential = ADH secretion
Fig. 19.4, page 604