Hormones as chemical messengers
Hormones are chemical messengers, produced in endocrine glands, travel through the blood and affect the target tissue.
Types of Hormones
Steroid --> Oestrogen
Peptide derivative --> Insulin
Tyrosine derivative --> Thyroxin
Action of Hormone
They pass straight through the plasma membrane and directly affect the expression of the genes.
Attachment to receptor protein on outer cell membrane (Glycoprotein)
The attachment triggers action of a secondary messenger
The secondary messenger in cytoplasm alters the action of the cell
Hypothalamus and the Pituitary Gland.
Anterior Pituitary Gland
Hormones are sent from the hypothalmus to the anterior pituitary via blood vessel called the portal vein.
The hypothalamus acts as the endocrine gland and produces releasing hormones.
Hormones travel through the blood through the portal vein to the cells in the anterior pituitary. Releasing hormone causes secretion of specific hormones
Posterior Pituitary Gland
Neurosecretory cells connect the hypothalamus and the posterior pituitary lobe
Hormones secreted from the posterior lobe are produced in the hypothalamus
Nerve impulses travel down the axon into the posterior pituitary. This causes the release of the vesicles of hormones into the blood stream at the posterior pituitary.
Control of ADH Secretion by Negative Feedback.
The homeostatic regulation of water is controlled by secretion of anti-diuretic hormone (ADH)
Osmoreceptor cells monitor the water content of the blood as it passes through the hypothalamus
Neurosecretory cells in the hypothalamus synthesise ADH and transport this along the axon of their nerves for storage in their synaptic end.
Osmoreceptor cells send action potential through the neurosecretory cells to the posterior pituitary if water content is low, secreting ADH and reabsorbing water into the bloodstream.
ADH is secreted and targets the collecting duct making it more permeable to water.
If the water content is too high no signal is sent for ADH secretion