H1.1 Hormones as chemical messengers

Hormones are:

• Chemical messengers

• Produced in endocrine glands

• Travel through blood

• Affect the target tissues

 

 

H1.2 Types of Hormone

 

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H1.3 Action of hormone

• Steroid hormone:
  (a) Pass straight through the plasma membrane
        Directly affect the expression of genes.

• Peptide hormone

(b) Attachment to plasma membrane receptor ( Glycoprotein)
(c) Receptor-Hormone complex
(d) Stimulation of secondary messenger in cytoplasm which alters the action of the cell.

 

 

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H1.4 Hypothalamus and the pituitary

The diagram shows the posterior division of the forebrain; where the hypothalamus connects the cerebral hemispheres with the middle portion of the brain.

The hypothalamus has many receptors for changes of internal conditions and serves as a link between the nervous system and the endocrine system (pituitary).

Below the hypothalamus is a double lobed structure called the pituitary that produces the endocrine secretions when stimulated by the hypothalamus.

 

The hypothalamus controls each lobe of the pituitary slightly differently.

Control of Anterior Lobe

• Hormones are sent from the hypothalamus to the anterior pituitary via a blood vessel called the portal vein.

• The hypothalamus acts as the endocrine gland (a)

• Hormone travel in blood through the blood vessel (portal vein)(b).

• The target tissue is the anterior lobe of the pituitary(c). e.g. LH, TSH and FSH

Control of Posterior Lobe of the pituitary

(d) Neuro-hormones are synthesised in the hypothalamus neuron. They are transported and stored in vesicles in the axon ending located in the posterior pituitary.

(e) 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. e.g. Oxytocin, ADH

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H1.5 ADH and negative feedback control

This is an example of control of the posterior pituitary as outlines in steps (d) and (e) above.

This is an example of the how the hypothalamus and the posterior pituitary integrate to control the release of another hormone.

• The homeostatic regulation of water (osmoregulation) is brought about by the action of the hormone Anti-diuretic hormone.

• The hypothalamus is sensitive to changes in plasma concentrations.

• Neurosecretory cells in the hypothalamus synthesis ADH and transport this along the axon of their nerves for storage in their synaptic knob endings in the posterior lobe of the hypothalamus.

• Osmoregulatory sensitive cells in the hypothalamus which are sensitive to plasma concentrations stimulate the neurosecretory cells to transmit impulses to their storage regions in the posterior lobe of the hypothalamus.

• ADH is secreted and has its target tissue of the Distal Convoluted and Collecting tubules of the kidney.

• The ADH causes the opening of the Aquaporin (pores) which increases water reabsorption from kidney filtrate.

 

 

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Click4Biology: Option H, Hormonal Control

 

Hormonal Control