Describe the four classes of chemical messengers
Autocrine: released by cells and have a local effect on same cell type from which chemical signals released eg, prostaglandin
Paracrine: released by cells and affect other cell types locally without being transported in blood, eg, somatostatin
Neurotransmitters: produced by neutrons, travels short distances eg, acetylcholine
Endocrine: type of intercellular signal. Produced by cells of endocrine glands, enter circulatory system, eg. Estrogen
Describe the characteristics of endocrine system
- glands that secrete chemical messengers (hormones) into circulatory system
- regulate activities of body structures
Hormone characteristics:
- produced by small quantities
- secreted into intercellular space
- transporter some distance in circulatory system
- acts on target tissues elsewhere in body.
What are the three characteristics of hormones?
- stability —> half life: length of time it takes for half a substance to be eliminated from circulatory system
- Communication
- Distribution
Describe the three patterns of hormone secretion
- CHRONIC - hormone regulation. Eg, thyroid hormone
- ACUTE - hormone regulation, epinephrine in response to stress
- EPISODIC (cyclic) - hormone regulation. Female reproductive hormones
Describe the control of hormone secretion
- most hormones are controlled by negative feedback
- secreted at a constant rate, but regulated by three different methods:
- Action of substance other than a hormone on endocrine gland
- Neural control of gland
- Control of secretory activity of one endocrine gland by hormone or neurohormone secreted by another gland
List 10 regulatory functions of of the endocrine system
- Metabolism
- Control of food intake and digestion
- Tissue maturation
- Ion regulation
- Water balance
- Heart rate and blood pressure regulation
- Control of blood glucose and other nutrients
- Control of reproductive milk release
- Uterine contractions and milk release
- Immune system regulation
Describe down regulation
Down regulation;
High hormones levels can cause down regulation of their own receptors
Decreases sensitivity of the target tissue to the hormone (even though hormone levels may still be high) — causes insensitivity to the hormone
Eg, type 2 diabetes seems to involve both alterations to the number of insulin receptors and significant changes to cell signalling
Eg, initial stages of puberty lots of hormones are present, then target cells get use to them so they become insensitive to the hormones
Describe up regulation
More receptors available on the site of action
Eg, ovaries, when LH hormone is present, receptor synthesis takes place (makes more receptors)
List two hormones of the posterior pituitary
- antidiuretic hormone (ADH)
- oxytocin
List hormones of the anterior pituitary gland
Growth hormone (GH) or somatotropin
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
What are the actions of GH (growth hormone)?
- stimulates uptake of amino acids
- stimulates breakdown of fats to be used as an energy source and decreases glycogen synthesis
- promotes bone and cartilage growth
- regulated blood levels of nutrients after a meal and during fasting
