Option D Human Physiology Notes
IB Biology
D.5 Hormones and Metabolism
Nature of Science: Cooperation and collaboration between groups of scientists: the International
Council for the Control of Iodine Deficiency Disorders includes a number of scientists who work to
eliminate the harm done by iodine deficiency. (pg 695)
UNDERSTANDING STATEMENTS
 Endocrine glands secrete hormones directly into the bloodstream.
o Endocrine glands are structures that secrete chemical messages, called hormones,
directly in the blood. (Examples of Endocrine glands )
o Hormones can be steroids, proteins, glycoproteins, polypeptides, amines or tyrosine
derivatives.
Illustrate here.

Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a
receptor-hormone complex.
o Steroid hormones can cross directly through the plasma membrane and the nuclear
membrane and bind to receptors in the cytoplasm. Why can steroid hormones do this?
The receptor-hormone complex then serves as a transcription factor, promoting or
inhibiting the transcription of a certain gene.
The receptor-hormone complex promotes the transcription of specific genes.
o Give an example…
o


Peptide hormones bind to receptors in the plasma membrane of the target cell.
o Why?

Binding of hormones to membrane receptors activates a cascade mediated by a second
messenger inside the cell.
o Second messengers –
 Examples of second messengers –
o Epinephrine 

Hormones secreted by the pituitary control growth, developmental changes, reproduction and
homeostasis.
o Examples 

The hypothalamus controls hormone secretion by the anterior and posterior lobes of the
pituitary gland.
o What is the role of the hypothalamus?
o
Give an example of negative feedback involved in the control of secretion pituitary
hormones.
APPLICATIONS
1.
2.