ENDOCRINE SYSTEM Flashcards
ENDOCRINE SYSTEM
- works alongside the nervous system to regulate & coordinate activities of the body’s tissues & organs
- glands produce blood-borne chemical signals = hormones
- glands located in different parts of the body (the main one called the pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, ovaries & testes)
- maintain balance (homeostasis) in the body
- help to keep blood glucose within normal range
ENDOCRINE GLANDS:
pituitary glands & hypotalamus
pienal gland
Thyroid gland
parathyroid gland
Adrenal gland
pancreatic gland
organs with endocrine functions
Local hormones
- Homeostasis is internal environment maintained by the autonomic nervous system
AUTOMONIC NERVOUS SYSTEM: deals with rapid changes, endocrine is slower and precise adjustments
- The heart secretes atrial natriuretic peptide (ANP), = acts on the kidneys
- The hypothalamus is part of the brain endocrine gland that controls pituarity gland & influence on others
ENDOCRINE SYSTEM
- Hormones influence metabolic activity
- hormones = chemcial mesengers
hormones control & regulate:
> reproduction
> growth & development
> Electrolyte & water & nutrient balance of the blood
> regulating cellular metabolism & energy balance
> molising body defence
HORMONES EFFECT ON THE BODY
- hormones = chemicals = instruct cells to perform/carry functions
- hormones may manufacture & release chemical substances into circulation
- hormone cells increase/decrease absorption of chemcials substances across the cell membrane
NON-STEROID ACTIONS (WATER-SOLUBLE)
- water soluble hormone, e.g. amino acid/peptide & can not pass through the lipid cell membrane (communicate with cells from outside)
- hormone attaches to receptors in the cell membrane = activating production of chemicals (enzyme in the cell to be activated) then released into the cell
STEROID ACTION (LIPID SOLUBLE)
- steroid action used by soluble hormone = pass through lipid cell membrane
- receptors for hormones inside the cells in the cytoplasm
- hormones bind to receptors, moves to the nucleus = insturctions to cell produce a response = production of another chemcial protein
NERVOUS VS ENDOCRINE SYSTEM
NERVOUS SYSTEM:
- responses rapid
- sort-duration response
- acts via action potential & neurotransmitter
- acts on specific locations determined by axon pathways
- The neurotransmitter acts over a short distance
ENDOCRINE SYSTEM:
- response slowly
- long-duration response
- acts via a hormone released into the blood
- acts diffuse locations - targets anywhere blood reaches
- Hormone acts over long distance
DEFINITIONS:
EXOCRINE GLANDS: ducts carry secretions to the membrane surface
ENDOCRINE GLANDS: ductless, release hormones into tissue fluids
HORMONES: long distance chemical signals that travel in lymph/blood
ENDORCIRNE ORGANS STIMUALTED TO PRODUCE HORMONES
HUMORAL STIMULUS: hormone released = altered level of ion or nutrient (e.g. low level of calcium in the blood) ( detected by parathyroid gland releases parathyroid hormone telling bone cells to release calcium, kidneys to reabsorb more calcium from the urine)
NERVOUS STIMULUS: The nervous system stimulates organs to release hormones (fight/flight response)(adrenaline)
HORMONAL STIMULUS: a hormone released by another hormone (hypothalmus release hormone instructing pituarity gland to release more hormones
ENDOCRINE GLAND
HYPOTHALUMUS
PITUARITY GLAND
- Pituitary gland lies in the hypophyseal fossa of the sphenoid bone (blow the hypothalmus attached by stalk)
PITUARITY GLAND & HYPOTHALMUS
Regulates the activities of the endocrine glands
pituarity gland =
- size of a pea
- consists of anterior & posterior pituitary
- anterior pituitary secretes growth hormones (somatotropin) = promotes the growth of bone, muscles and most major internal organs
Hypothalamus controls the release hormones from both the anterior and posterior pituarity glands
HYPOTHALAMUS AND ANTERIOR PITUITARY (AP) GLAND
- linked to the pituarity portal system (PPS)
PPS transport blood to AP, entering tiny sinusoid in close contact with secretory cells = easy passage of hormone into the bloodstream - transports O2 & nutrients
HORMONE OF HYPOTHALAMUS
secretion of anterior pituitary hormones follows sitmaulation of glands releasing specific hormones produced by the hypothalmus carried through the glands through PPS
NEGATIVE FEEDBACK SYSTEM:
- The level of hormones in the blood supplying the hypothalamus is low
- produces hormones = stimulating the release of trophic hormone by the anterior pituitary
- Simulating target gland to produce & release hormone
- blood levels that hormone rises & inhibits secretion its releasing factors by the hypothalmus
- T3 = triiodothryonine
- T4 = thyroxine
POSTERIOR PITUARITY
- formed in nervous tissue (in glial cells
- Synthesised in nerve cells, transported along the axon & stored in the axon terminals
- oxytocin, antidiuretic hormone (ADH) released in axon terminals
- stimulates uterine smooth muscle & muscle of the lactating breast
ADH: - reduces urine output
- acting on distal convoluted tubules & collecting ducts of the kidney, increasing permeability to water
- Reabsorption of water from the glomerular filtrate = reduction in urine
- ADH is determined by the osmotis pressure circulating in the blood to osmoreceptors which lies in hypothalamus
- prevents dehydration.
PINEAL GLAND
- The roof of the third ventricle is connected by a short stalk containing nerves
- Melatonin = hormone secreted by the pineal gland
- secreation = suppressed by daylight: & increased during darkness
- The gland tends to atrophy after puberty and become calcified in later life
- melatonin: coordination of the circadian diurnal rhythms of tissues influencing the hypothalamus
- mood (melatonin) implicated in SAD (usually during winter months due to lack of daylight hours)
- inhabition of gorwth and development of sex organs before puberty = preventing synthesis/release of gonadotrophins
THYROID GLAND
- neck in the anterior of the larynx and trachea
- butterfly-shaped (2 lobes, one on either side of the thyroid cartilage & the upper cartilaginous ring of the trachea
- lobes joined by a narrow isthmus (anterior to the trachea)
- produces T3 & T4 (essential for growth and development)
- other organs & systems influenced by thyroid: hormone, skin, digestive, reproductive system
- arterial blood supply gland through the superior & inferior thyroid arteries
- Venous return by thyroid veins drains into the internal jugular veins
- Recurrent laryngeal nerves pass upwards lobes of artery of gland lies near the inferior thryroid artery
THYROID GLANDS
- spherical follicles formed from cuboidal epithelium = secrete and store collid
- collides precures molucles of thyroid hormones (T4 & T3)
parafollicular cells (c-cells) secreate - calcitonin
TRI-IODOTHYRONINE T3 & THYROXINE T4
- T3 & T4 related to exposure to cold, exercise, stress, malnutrition, low plasma glucose and sleep
- helps the body when experiencing physiological challenges
T3 & T4
> increases metabolic rate & heat production
> regulates metabolism (fats, carbs & proteins)
- release of T3 & T4 in blood stimulated by the hypothalamus
- T3 & T4 control carcadian rhythms
- iodine is essential for the formation of thyroid hormones T3 & T4, the thyroid takes iodine from the blood
- The release into blood is stimulated by the thyroid-stimulating hormone (TSH) anterior pituitary
- secretion of TSH stimulated by thyrotropin-releasing hormone (TRH) from the hypothalamus
- TRH secretion depends on plasma levels of T3 & T4 because hormones controlled senstitivity of pituarity gland to TRH
- Negative feedback mechansims increase levels of T3 & T4 TSH secretion
- thyroid hormone enhances the effect of hormones e.g. adrenaline
T3 and T4 affect most cells of the body by:
- Increasing the metabolic rate and heat production
- Regulating metabolism of carbohydrates, proteins and fats.
Essential for normal growth and development especially the skeleton and the nervous system.
- Most other organs and systems are also influences by thyroid hormones
Physiological effects of T3 and T4 on the heart, skeletal muscles, skin and digestive and reproductive systems are more evident when there is under-activity or over-activity of the thyroid gland.
HORMONE PRODUCED BY THE THYROID GLAND
Calcitonin- hormone secreted by the parafollicular or C-cells in the thyroid glands.
Calcitonin lowers the blood calcium (Ca2+) levels.
Acts on the bone cells promoting storage of calcium – Calcium can move from the blood to be stored in the bones (MSK)
Kidney tubules inhibiting the reabsorption of calcium – so more calcium passes out in urine.
PARATHROID GLANDS
4 parathyroid glands: embedded in the posterior surfaces of the thyroid glands
- secreated parathyroid hormone (PTH-parathormone) increases blood calcium levels
- Surrounded by the fine connective tissue capsules, which contain spherical cells, with sinusoids containing blood in between them.
PARATHYROID HORMONE (PTH)
- increases blood calcium hormone level by:
> releasing calcium stored in the bone into the bloodstream
> increasing calcium reabsorb back into blood during the formation of urine
PTH & calcitriol (from the thyroid) work together to keep blood calcium levels within the normal range
Calcium is essential for:
> Muscle contraction
> Transmission of nerve impulses
> Blood clotting
> The normal action of many enzymes
PANCREASE & PANCREATIC ISLETS
- pink and creamy gland
- situated in the epigastric and left hypochondriac region of the abdominal cavity
- head lies at the curve of the duodenum, body behind the stomach, and tail in front of the kidney
- The pancreas is both an exocrine (secreting substances through ducts) and an endocrine gland (release hormones directly into the bloodstream)
- The abdominal aorta and the IVC(inferior Vena Cava) lie behind the gland.
ENDOCRINE PANCREASE
- specialised cell of the pancreas islet of Langerhans distributed throughout the gland close to the capillary network
- islet = no duct (diffuse directly into the bloodstream
different type of islet cells secreate different hormones
> alpha cells secreate glucagon
> beta cells secreate insulin
both control blood glucose levels - normal blood glucose level is between 3.5 and 8 mmol/L
ENDOCRINE ACTION OF INSLUON AND GLUCAGON
INLSUIN: reduces blood glucouse
Increases conversion of glucose to glycogen in the liver and skeletal muscle (Glycogenesis)
Glucagon: (increases blood glucose levels)
Increases conversion of glycogen to glucose in the liver and skeletal muscle (Glycogenolysis)
In severe circumstances encourages the breakdown of fats and proteins to form new sugar (Gluconeogenesis
