Endocrine System Chapter 45 Hormones a hormone is

Endocrine System Chapter 45

Hormones • a hormone is a chemical signal that is released in one part of the body & travels to another part of the body (through the circulatory system) where it elicits a particular response in the target cells • 3 major classes of hormones: water-soluble; tend to bind to – proteins & peptides receptor proteins on cell surface – amines of target cells – steroids: lipid-soluble; tend to bind to cytoplasmic receptors inside target cells

Simple Endocrine Pathway • a signal molecule (stimulus) binds to a receptor protein on an endocrine cell which triggers the release of hormones • hormones travel through blood stream to effector cells, eliciting a response

Simple Neurohormonal Pathway • endocrine gland receives a stimulus from a sensory neuron which triggers the release of hormones • hormones travel through blood stream to effector cells, eliciting a response

Simple Neuroendocrine Pathway • endocrine gland receives a stimulus from a sensory neuron which triggers the release of hormones • hormones travel through blood stream & bind to receptor proteins on endocrine cells of another endocrine gland which triggers the release of a second hormone • this hormone travels through the blood stream to effector cells, eliciting a response

Feedback Loops • Negative Feedback Loops – effector response reduces the initial stimulus thereby preventing overreaction • Positive Feedback Loops – effector response reinforces the initial stimulus thereby leading to an even greater response

Events of Hormonal Signaling • reception – the binding of a signal molecule to a receptor protein on/in a target cell • signal transduction – the series of events in the cell triggered by the binding a signal molecule to a receptor protein • response – the change in cell behavior as a result of the signal transduction pathway – gene transcription, enzyme activation, change in uptake/secretion of specific molecules, rearrangement of the cytoskeleton *Review Chapter 11

Human Endocrine Glands • hypothalamus • pineal gland • anterior & posterior pituitary glands • thyroid gland • parathyroid glands • adrenal glands (cortex & medulla) • pancreas • gonads (ovaries, testes)

Hypothalamus • bridge between the endocrine & nervous systems – acts as part of the nervous system when it sends electrical signals to the adrenal gland to release adrenaline during times of stress – acts like a nerve when it secretes gonadotropicreleasing hormone which stimulates the anterior pituitary to release FSH & LH – acts as an endocrine gland when it produces oxytocin & ADH that it stores in the posterior pituitary • contains the body’s thermostat • contains centers for regulating hunger & thirst

hypothalamus posterior pituitary anterior pituitary

Pituitary Gland • anterior pituitary – synthesizes & secretes several hormones – FSH & LH: stimulate activities ovaries & testes – TSH: promotes normal thyroid development – ACTH: stimulates adrenal cortex to produce & secrete steroid hormones – GH: stimulates bone growth • posterior pituitary – stores & secretes 2 hormones made in hypothalamus – oxytocin: stimulates uterine contractions & mammary glands – ADH: promotes water-retention by kidneys

Pineal Gland • located near the center of the brain • releases melatonin which is involved in biological rhythms regulated by light & dark cycles

Thyroid Gland • located on trachea • produces… – thyroxine: controls metabolic rate – calcitonin: lowers blood calcium levels

Parathyroid Glands • located on the surface of the thyroid gland • releases parathyroid hormone (PTH) – raises blood calcium levels – counteracts effect of calcitonin

Adrenal Glands • located above the kidneys • adrenal medulla releases epinephrine (adrenaline) & norepinephrine (noradrenaline) – involved in the fight-or-flight response (short-term stress response) – raises blood sugar level by increasing rate of glycogen breakdown by the liver • adrenal cortex releases glucocorticoids – involved in long-term stress response – raises blood sugar level

Pancreas • releases… – insulin: lowers blood glucose levels – glucagon: raises blood glucose levels

Gonads • ovaries (females) – estrogens: maintenance of the female reproductive system & development of secondary sex characteristics; stimulate uterine lining growth – progesterone: promote uterine lining growth • testes (males) – androgens (ex: testosterone): maintenance of the male reproductive system & development of secondary sex characteristics; aid in sperm formation