Hypothalamo-hypophysial axis Flashcards
Functions of the endocrine system?
- growth and development
- sex differentiation
- metabolism
- adaption to an ever changing environment: regulation of digestion, use and storage of nutrients, electrolyte and water metabolism, and reproductive functions
Where does magnocellular neurosecretory neurons have their effect?
- posterior lobe of the pituitary gland (on oxytocin and ADH)
Where does the parvocellular neurosecretory neurons have their effect?
- on anterior lobe of the pituitary gland
Autonomic nerves have effects on what target organs?
- pancreas (has both pre and post ganglionic autonomic neuron) and adrenal gland (just preganglionic autonomic neuron)
What do hormones function as?
- move through the blood/lymph to distant target sites of action (these are endocrine and neuroendocrine cells)
- can also act more locally as paracrine or autocrine (have effect on themselves (like a T cell) messengers that incite more local effects
- most are present in body fluids at all time in greater or lesser amounts as needed
- signal amplification
Characteristics of hormones?
- a single hormone can exert various (pleiotropic) effects in different tissues
- a single function can be regulated by several hormones (ex: HR)
How do water soluble hormones effect cells?
- needs a receptor on cell membrane -> first messenger binds to receptor and this activates G protein , effector cell and second messenger and target cell response in the cell
How do fat soluble hormones effect cells?
These can pass right through cell membrane and bind to receptor, now it is able to go into nucleus and have impact on cell
What are the factors that affect the response of a target cell to a hormone?
- blood level of the hormone
- relative number of receptors: up-regulation, down regulation
- affinity of these receptors for hormones: affected by number of conditions, ex: pH of body fluids plays an important role in the affinity of insulin receptors
Describe up and down regulation of the receptors?
up regulation: number of receptors on the cell wall are increased so this means that there are more areas for the hormones to attach so more hormones are secreted resulting in a greater response
down regulation- ex: sympathetic system stimulates heart for prolonged periods -> leads to tachycardia and to reduce tachycardia, the receptor sites on teh cell are reduced, and there are less receptors for hormones to attach to. Beta blockers decrease the number of sites available on the cell surface, being selective and increasing output
Humoral response of parathyroid glands to low concentration of Ca2+
- capillary blood contains low concentration of Ca this stimulate secretion of parathyroid hormone (PTH) by parathyroid glands
Neural effect on medulla of adrenal gland?
- preganglionic SNS finber stimulates adrenal medulla cells to secrete catecholamines
Hormonal effect on hypothalamus and target organs?
- the hypothalamus secretes hormones that stimulate the anterior pituitary gland to secrete hormones that stimulate other endocrine glands to secrete hormones (thyroid, adrenal cortex and gonads)
How are hormone levels controlled?
- affected by fluctuations that vary with the sleep-wake cycle: GH and ACTH
- secreted in a complicated cyclic manner: femal sex hormones
- regulated by feedback mechanisms that monitor substances such as glucose (insulin) and water (ADH) in the body
- regulated by feedback mechanisms that involve the hypothalamic pituitary target cell system
When do glucocorticoid levels peak?
after you wake up in the morning, between 8 and 9 am (maybe why MIs occur more in the morning)
What has an effect on estrogen levels?
- LH and FSH, when they peak -> estrogen levels rise