Leture 13 - Endocrine System Flashcards
Endocrine Cells
- cells that produce and release hormones
Endocrine Gland
Group of endocrine cells forming a secretory organ
Hormones
chemical signal released by endocrine cells that influences the activity of other cells at a distance
Long distance signaling
- travel through blood stream
- blind to receptors on or in distant target cells
- target cell must have the proper receptor to bind the hormone
Timing of endocrine system:
Coordination fo endocrine system:
- longer to turn on and off than more direct signaling (ie neurotransmitters)
- can coordinate many different responses
3 chemical groups of hormones
- Peptide or protein hormones
- steroid hormones
- Amine hormones
Peptide/protein hormones
- majority of hormones
- ex: insulin
- water soluble
- transported through blood without carriers
- receptors on the cell surface
steroid hormones
- ex: testosterone
- synthesized from cholesterol
- lipid soluble
- easily pass through cell membranes
- bound to carrier molecules in blood
- receptors are mostly intracellular (in cytoplasm or nucleus)
Amine hormones
- ex: thyroxine
- synthesized from the amino acid tyrosine
- can be water soluble OR lipid soluble
Cell’s response to a signal depends on:
which receptors it possesses
- for that particular signal
- different types of cells have different types of receptors that bind the ligand –> different responses
Receptors and intracellular pathways
- intracelllula rpathways activated by a particular receptor differ
- same receptor that binds ligand, but different responses
- due to cell’s predetermined state
*which “responders” are called to scene of activation
Same Hormone, different responses in different cells…
Epinephrine
Ex: epinephrine
- one hormone can bind to receptors in many different tissues
- initiates fight or flight response
- heart pumps faster and stronger
- blood vessels to skin and gut constrict, shunting blood to muscles
- liver breaks down glycogen to supply glucose to blood
- fat cells release fatty acids to blood
Receptor Specificity of Cells
- No receptor at all = no response
- different receptors might bind the same hormone = different pathways activated in those cells = different responses
Control of hormone release
- brain responds to environmental conditions
- provide a signal to the endocrine cells to release hormones
- hormones released into blood stream
- bind to receptors on target cell
- physiological response
Step 1: Brain communicated with endocrine system
- Hypothalamus: integrates infotmation from body and environment and communicates this to endocrine system
- sends it to the “control center”/pituitary gland of endocrine system
- pituitary then regulates other glands of body
Pituitary
“mouthpiee through which the brain speaks to the body”
2 lobes:
- anterior
- posterior
- Hypothalamus speaks to pituitary
- regulates each lobe differently
Posterior Pituitary
- NO secretory cells
- just capillaries
- hypothalamus releases neurohormones into capillaries in posterior pituitary
- hypothalamus axons extend down to posterior pituitary
- release hormones that go into blood stream
- from there, continue circulating through body
Two hormones released by hypothalamus
- oxytocin
(childbirth, lactation, promotes bonding) - ADH
( increases water conserved by kidneys, inresponse to blood volume and salt concentration)
Anterior pituitary
- an actual gland that synthesizes and releases itw own hormones
- neurones from the hypothalamus do not project all the way to pituitary
- release hormones onto blood vessels that run to anterior pituitary
- releasing hormones and releasing inhibiting hormones
- these hormones cause pituitary cells to secrete or stop secreting hormones into blood stream
Type of hormones released by anterior pituitary
Tropic hormones
- control activities of other endocrine glands
- tropic hormones act on thyroid, adrenal gland, testes and ovaries
- ex: corticotropin –> signal the adrenal gland to release cortisol
The Stress Response
- Hypothalamus:
- releases Corticotropin releasing hormone (CRH) - Ant Pituitary
- CRH causes pituitary to release corticotropin into blood stream - Adrenal Glan
- Corticotropin causes Adrenal gland to release cortisol - Cortisol
- mobilizes energy reserves
- supresses immune system
- effect neuron activity in short- and long-term
Negative feedback loop
- endocrine cells in pituitary are also under negative feedback control by hormones f the glands that they stimulate
- tropic hormones released from pituitary stimulates release of a hormone from another endocrine gland
- this second hormone inhibits release of more tropic hormone from the pituitary
Ex: stimulates adrenal gland to release cortisol. Cortisol inhibits further release of corticotropin and corticotropin release hormone
Thyroid gland
Hormones regulate its two main functions:
- cell metabolism (thyroxine)
- regulation of blood calcium levels (calcitonin, parathyroid hormone - PTH, calcitrol)
Thyroxine synthesis
- release stimulates by thyroid stimulating hormone (TSH) produced by anterior pituitary
- thyroxine is modified by iodine atoms
- initially four iodine atoms are added onto the hormone
- Thyroid releases mostly T4 into bloodstream
- but thyroxine is active when only 3 iodines are on it, T3
- T4 is converted to T3 by an enzyme in the target cells
- therefore each target cell can set its own sensitivity to thyroid hormones by controlling the conversion step
Role of Thyroxine
Regulates cell metabolism:
Elevates metabolic rates of most cells and tissues
- most cells int he body have thyroxine receptor
- promotes amino acid uptake and protein synthesis
- very important during development
hypothalamus regulates release in response to temperature, day length, etc
- ex: exposure to cold leads to increased level of thyroxine
Hyperthyroidism
- excess production of thyroxine
- high metabolic rates, jumpy/nervous, feel hot
Hypothyroidism
- deficiency of functional thyroxine
- low metabolism, intolerance of cold, physical and mental sluggishness
- ex: iodine deficiency
- can both lead to goiter
Thyroid gland and blood calcium concentrations
Regulates blood calcium concentrations:
- 99% of body calcium is stored in bones
- very important for the amount circulating in the blood to be tightly regulated
- body has multiple mechanisms for changing blood calcium levels:
1. deposition of absorption levels
2. excretion or retention of calcum (by kidneys)
3. absorbption of calcium from digestive tract
3 hormones that regulate blood calcium levels
- calcitonin
- parathyroid hormone (PTH)
- Calcitrol
Calcitonin
Blood calcium too high:
- reduces blood calcium
- its deposited into bone
- more important in young individuals that are actively growing
Parathyroid hormone
Blood calcium levels too low:
- increase in blood calcium
- breakdown of bones releases calcium
- most important hormone in regulation of blood calcium levels
- activates synthesis of calcitrol
calcitrol
Blood calcium levels too low:
- synthesized from vitamin D
- stimulates kidneys and git to reabsorb calcium back into the blood rather than excrete it
Pancreas
Produces insulin and glucagon
Insulin
- released in response to eating a meal (high blood glucose)
- stimulates insertion of glucose transporters into cell membrane
- glucose can enter cell and be used as fuel
- also promotes storage of glucose as glycogen in liver
- glucose as fuel
- storage of glucose as glycogen
Glucagon
- released in response to low blood glucose levels
- stimulates the lover to break down the stored glycogen and release glucose
Diabetes Mellitus
- lack on insulin (type i)
- lack of insulin responsiveness in target tissues (Type ii)
- glucose entry into cells is impaired
- high blood sugar
- cells suffer from a lack of metabolic fuel
Adrenal Gland
Medulla and cortex
Adrenal medulla
- inner core
- epinephrine
- norepinephrine
- acute release in response to stresful situations
- direct innervation from autonomic nervous system
- fight or flight response
Adrenal cortex
- surrounds medulla
- produces steroid hormones
- ex: cortisol
- release controlled by corticotropin from anterior pituitary
- slower to turn on, longer lasting stress response
- mobilizes energy reserves
- suppress immune system
Cortisol and chronic stress
- cortisol release normally turned off by negative feedback
- repeated activation of cortisol system has been shown to lead a decreased inability to terminate the stress response
- old rats also shown to be able to turn on stress response as well as young ones, but unable to turn it off as effectively
- digestive system problems, cardiovascur problems, strokes, impaired immune system
- mice given daily injections of cortisol show signs of neuron death
Gonads and their hormones
Male: testes
- produce androgens –> testosterone
female: ovaries
produce estrogen, progesterone
Pineal gland
- produces melatonin
- melatonin released int he dark
- marks length of the night
- exposure to light inhibits its production
- involved in biological rhythms
Photoperiodicity
- changes in day length cause physiological changes
Ex: siberian hamsters
- white in winter and do not reproduce
- brown in summer and breed
How does the body change blood calcium levels?
- deposition of absorption levels
- excretion or retention of calcum (by kidneys)
- absorption of calcium from digestive tract
Importance of sex hormones
Development:
- Y chromosome –> gonads produce androgens in 7th week of development
- androgens –> undifferentiated reproductive system into a male
Puberty:
- production of sex steroids increases dramatically at the beginning of uberty
- hypothalamus stimulates pituitary to release gonadotropins
- gonadotropins stimulate release of sex hormones from gonads
- initiate development of secondary sex characteristics
