Ch 17/18 Flashcards
What are the classes of chemical messengers?
Autocrine chemical messengers: released by cells and have a local effect on same cell type from which chemical signals released
Paracrine chemical messengers:
Released by cells and affect other cell types locally without being transported in blood
Neurotransmitter: produced by neurons and secreted into extracellular spaces by pre synaptic nerve terminals
Endocrine chemical messengers: type of intercellular signal. Produced by cells of endocrine glands, enter circulatory system
Characteristics of the endocrine system:
- glands that secrete chemical messengers ( hormones) into circulatory system
- hormone characteristics
- produced in small quantities
- secreted into intercellular space
- transported some distance in circulatory system
- acts on target tissue elsewhere in body
- regulates activities of body structure
- ligands: more general term for chemical signals
Comparison of nervous & endocrine system:
- Both systems associated with the brain
- hypothalamus
- epithalamus
- May use same chemical messengers as neurotransmitters and hormone
* epinephrine - Two systems are cooperative
- nervous system secretes neuroendocrine peptides, or neurohormones, into circulatory system
General characteristics of hormones
- Stability
- half life: the length of time it takes for half a dose of substance to be eliminated from circulatory system
- long life: regulates activities that remain at a constant rate through time
- short half life: have a rapid onset and short duration
- Communication :
- interaction with target cell
- Distribution :
- hormones dissolve in blood plasma
- hormones are distributed quickly because they circulate in blood
Patterns of hormone secretion
- Chronic hormone regulation: maintenance of relatively constant concentration of hormone. Thyroid hormone.
- Acute hormone regulation: epinephrine in response to stress
- Episodic hormone regulation : female reproductive hormones
Control of hormone secretion:
- most hormones controlled by negative feedback systems
- most hormones are not secreted at a constant rate
Negative feedback:
- Anterior pituitary secretes tropic hormone, travels in blood to target endocrine cell
- Hormone from target endocrine cell travels to its target
- Hormone from target endocrine cell has a negative feedback effect on anterior pituitary & hypothalamus and decreases secretion of tropic hormone
Positive feedback:
- Anterior pituitary secreted tropic hormone, travels in the blood to target endocrine cell
- Hormone from the target endocrine cell travels to target
- Hormone from target endocrine cell also has a positive feedback effect on the anterior pituitary and increases secretion of tropic hormone
Overview of the endocrine system
- Metabolism
- Control of food intake and digestion
- tissue maturation
- Ion regulation
- H20 balance
- Heart rate and blood pressure regulation
- Control of blood glucose and other nutrients
- Control of reproductive functions
- Uterine contractions and milk release
- Immune system regulation
Pituitary gland and hypothalamus
- where nervous and endocrine systems interact
- hypothalamus regulates secretions of anterior pituitary
- posterior pituitary is an extension of the hypothalamus
- anterior pituitary produce nine major hormones that :
- regulate body functions
- regulate the secretion of other endocrine glands
Hormones of posterior pituitary ADH
- osmoreceptors : specialized neurons of hypothalamus monitor changes in intercellular osmolality. If the concentration of electrolytes increases or if the concentration of H20 decreases, then ADH secretion is stimulated
- Baroreceptors: specialized neurons found in walls of atria of heart, large veins, carotid arteries. If BP decreases then ADH secretion is stimulated
Anterior pituitary hormones
- growth hormones (GH)
- thyroid - stimulating hormone ( TSH)
- adrenocorticotropic hormone (ACTH)
- melanocyte- stimulating hormone (MSH)
- beta endorphins
- lipotropins
- luteinizing hormone (LH)
- follicle stimulating hormone (FSH)
- prolactin
Growth hormone
- stimulates uptake of amino acids; protein synthesis
- stimulates breakdown of fats to be used as an energy source but stimulates synthesis of glycogen
- promotes bone and cartilage growth
- regulates blood levels after meals
Growth hormone stimulation
- functions in regulation growth, tissue maintenance and metabolism
Growth hormone inhibition
- hypothalamus produces growth hormone inhibiting hormone
- inhibits production of GH by anterior pituitary
- GHRH secretion in response to low blood glucose , stress
- GHIH secretions in response to high blood glucose
