Endocrine Physiology - Part 1 Flashcards
What are the two major control systems for body functions? What do they control?
- nervous system = rapid, precise responses
- endocrine system = slow and sustained functions, even at low concentrations
What are endocrine glands?
- ductless glands
- secrete chemical messengers (hormones) into the blood to communicate with target cells throughout the body
What are some characteristics of hormones?
- made in glands/cells
- transported by blood
- bind with target tissue receptors
- activates physiological response
How do hormones travel?
in blood, either dissolved in plasma or protein bound
What is a tropic hormone?
regulates hormone secretion by another endocrine cell
What happens at the target site when a hormone reaches it?
- action of hormone is amplified at target cell
- binds with receptors
- rapidly degraded by target cells or removed from the blood by kidneys or liver and excreted
What are the three classifications of hormones?
- Peptide and protein hormones
- Steroid hormones
- Amine hormones
What are the characteristics of Peptide and Protein hormones?
- most are this type
- hydrophilic
- stored in secretory granules
- have receptors on the surface of cell
- cause their effect most often by formation of second messengers inside the target cell (cAMP - most common)
What are the characteristics of Steroid hormones?
- primarily produced by adrenal cortex and the gonads/ placenta
- made from cholesterol
- not stored in the cell
- travel in bound form with proteins (99% bound, 1% free)
- receptors inside the target cell
- causes activation of specific genes
- can be given orally and absorbed by GIT
What are the characteristics of Amine hormones?
- derived from AA tyrosine
- two types: Thyroid hormones and Catecholamines
- stored until secreted
- Catecholamines have cell membrane receptors and 50% travel in bound form in blood
- Thyroid hormones behave more like steroid hormones with intracellular receptors that activate genes
Describe the secretion rate of hormones
- not secreted at a constant rate
- rate varies depending on control
- most are secreted in short bursts with little or no release in between.
- may maniifest diurnal circadian rhythm or 24hr cyclical variation, influenced by factors such as sleep, light,etc.
What is a negative feedback loop?
a reaction that causes a decrease in a function
What is a prominent feature of hormonal control systems and why is it important?
- negative feedback loops
- allows continuous changes and adjustments to be made to maintain an optimal concentration of a hormone.
What is an example of a positive feedback loop in hormone regulation?
surge in luteinising hormone (LH) that occurs as a result of the stimulatory effect of oestrogen before ovulation in humans
What are three characteristics of hormones?
- permissiveness: action of one hormone caused by another
- Synergism: action of one hormone complements another
- Competition: structurally similar substances compete for receptors (agonists vs. antagonists)
What do endocrine disorders commonly result from?
- hypo-secretion
- hyper-secretion
- abnormally low target cell responsiveness to the hormone (receptor defect, intracellular cell signalling pathway defect)
What are the major endocrine glands in/ around the brain?
- pineal gland
- hypothalamus
- pituitary gland
What are the major endocrine glands in the throat region?
- thyroid and parathyroid glands
What are the major endocrine glands in the abdomen
- Adrenal gland and kidney
- Pancreas
Where is the hypothalamus located?
below the thalamus
What is the function of the hypothalamus?
- processes sensory info from internal and external environment and mediates responses via ANS and endocrine system
- secretes hormones from the pituitary gland that majorly effect the secretion of other hormones
What are the three lobes of the pituitary gland?
- posterior lobe (Neurohypophysis, pars-nervosa)
- anterior lobe (Adenophysis, pars-distalis)
- intermediate lobe (pars-intermedia)
How are the pituitary gland and the hypothalamus connected?
by a stalk called the hypophysial stalk
How is the posterior lobe of the pituitary gland connected to the hypothalamus?
via a neural link through the hypohysial stalk
How are the anterior and intermediate lobes of the pituitary connected to the hypothalamus?
via a vascular like through the hypophysial stalk. This is called the hypothalamo-hypophysial portal system
how is the posterior pituitary controlled with neurons?
hypothalmic neurons secrete hormones which are stored in and released from the posterior lobe
What hormones are released from the posterior pituitary?
- ADH/ vasopressin
- Oxytocin
What 7 hormones are released from the anterior pituitary?
- Thyrotroponin-releasing H (TRH)
- Corticotroponin-releasing H (CRH)
- Gonadotroponin-releasing H (GnRH)
- GHRH
- GHIH or somatostatin
- Dopamine
- evidence of GnIH in most vertebrates
What stimulates the release of ADH/ vasopressin?
- increase in plasma osolarity
- reduction in extracellular fluid volume
What is the target of ADH/ vasopressin? What is its effect on these targets?
- Renal tubules (increases water reabsorption)
- blood vessels (vasoconstrictive effect if released in large amount)
What disorder is caused by excessive secretion of ADH?
syndrome of inappropriate ADH secretion (SIADH)
What disorder is caused by insufficient secretion of ADH?
diabetes insipidus
What are some causes of diabetes insipidus?
(iodiopathic or congenital or head trauma or neoplasia)
- Pituitary gland does not secrete enough ADH (central diabetes insipidus)
- ADH is secreted but kidneys do no respond (nephrogenic diabetes insipidus)
How is diabetes insipidus characterised?
polyuria, polydipsia, nocturia and incontinence
What stimulates the release of oxytocin?
- cervical and uterine stretch
- suckling
What is the target of oxytocin?
uterus and lactation tissue
What is the effect of oxytocin on target tissue?
- contraction of smooth muscle in uterus during parturition
- triggers the ‘let down’ reflex (milk ejection)
- influences social bonding (hormone of love)
What is the prominent cell in the intermediate lobe of the pituitary gland?
Melanotrophs
What hormone is released by the intermediate lobe of the pituitary gland? What is its effect?
Melanocyte stimulating hormone (MSH). melanin pigment synthesis, controlling skin colour (camouflage in some species)
What clinical relevance does the intermediate lobe of the pituitary gland have for older horses?
common site of hyperplasia and neoplasia in older horses
How are anterior pituitary hormones regulated?
regulated by hypothalamic hormones and feedback from target hormones.
What hormone regulates growth in vertebrates?
growth hormone.
Where is Growth Hormone secreted from?
somatotrophs of anterior pituitary
What does Growth Hormone do?
- promotes protein deposition in tissue
- enhances fat use for energy instead of carbs by cells and raises blood glucose levels
- increases growth of skeletal frame until growth plate closes, increases thickness of bone
- growth effects via production of somatomedins
How is growth hormone regulated?
by hypothalamus and IGF - I
What stimulates the release of Growth Hormone?
decreased glucose and free fatty acids
increased exercise, stress, etc.
What is caused by too little growth hormone?
pituitary dwarfism
what is caused by too much growth hormone?
acromegaly. pituitary tumours
Where is the pineal gland in lower invertebrates?
close to the skin and doesnt need the eye to register day/ night cycles
What is the function of the pineal gland in mammals?
- translator of photoperiods
- produces melatonin in response to darkness
What is the function of melatonin?
- allows seasonally reproductive animals to perceive day length changes
- induces sleep in diurnal animals and promotes activity in nocturnal animals
- plays a major role in sexual development, hibernation, metabolism and seasonal breeding.
- can be used to increase production in domestic animals by manipulating light
