WEEK TEN - ENDOCRINE SYSTEM, HYPOTHALAMUS AND PITUITARY GLAND, ENDOCRINE GLANDS AND DISORDERS Flashcards
Define hormone and endocrine system
hormone - chemical messages that alter activity of target cell - target cells contain specific receptor proteins for specific hormones
endocrine system - controlling system that influences metabolic activities of cells using hormones
every organ in endocrine system secretes hormones via endocrine gland
Discuss differences between endocrine and exocrine glands
endocrine - absence of ducts
- chemical messengers are secreted into bloodstream onto epithelial surface
exocrine - presence of ducts
List similarities and differences between the endocrine and nervous systems
similarities
- several chemicals act as BOTH neurotransmitters and hormones eg norepinephrine and dopamine
- hormones + neurotransmitters produce overlapping effects on same organ
- both act via receptors
differences
- NS communicates via electrical [AP] and chemical [neurotransmitter] - endocrine is just chemical via hormones
- endocrine = more widespread effects on body, NS = local, specific effects
- endocrine = slower reaction to stimuli and continue to respond after signal stops, NS= quicker response and stops when stimulation ceases
List the main classes of hormones, give examples of each & state how they are synthesised
- steroid hormones
- derived from cholesterol but different functional groups attached to four-ringed steroid backbone - protein/polypeptide hormones
- derived from amino acid chains [3-200 long]
- synthesised in inactive form [preprohormone], trimmed to become prohormone then packaged by golgi apparatus as hormone
- eg oxytocin, insulin, growth hormone - monoamine
- modified amino acids synthesised from tyrosine [except melanin synthesised from typtophan]
- eg neurotransmitters eg dopamine, norepinephrine, epinephrine
Describe how hormones are transported to their site of action
peptides + monoamine = hydrophilic
= mix w blood plasma
steroid + thyroid hormone = hydrophobic
= must bind to transport proteins in bloodstream eg globulin
= bound hormones = longer circulating time [1/2] in the bloodstream as the transport protein protects hormone from being broken down by enzymes
= must then unbind in order to leave a capillary
- free hormones circulate for minutes, bound hormones circulate for hours - weeks
Describe how hormones stimulate their target cells & state any differences between the 3 main groups of hormones
hormones action only occurs at target cells that have receptors for that specific hormone
receptors located on
- nucleus [steroid hormones]
cell membrane [protein, peptide and amine hormones
steroid hormone - lipid soluble = must attach to plas mem for transport [inactive until they enter cell and attach to receptor in nucleus]
peptide + monoamine hormone = CANNOT pass through plas mem
- bind to receptor proteins on outer surface of plas mem = activates second messengers eg AMP-cyclic adenosine monophosphate
- second messenger adds phosphate groups to proteins that change its 3D shape and activate it
Describe how target cells can adjust their sensitivity to a hormone
adjusted by changing number of receptors
up-regulation = cell receptors increased
down-regulation = reduces cell receptors = cell less sensitive to hormone [occurs with long-term exposure to high hormone concentration]
Describe the anatomy of the hypothalamus & pituitary gland & their relationship to each other
hypothalamus - superior to pituitary gland
pituitary gland - situated at base of brain, inferior to hypothalamus - connected to hypothalamus by stalk [infundibulum - contains blood vessel linkage between ANT pituitary and hypothalamus]
- two regions
anterior pituitary gland
posterior pituitary gland
List hormones produced by the hypothalamus, list target organ/s or tissue & state principal effects (6)
Thyrotropin releasing hormone [ TRH]
secretion of thyroid stimulating hormone [TSH] + prolacting [PRL]
corticotropin releasing hormone [CRH]
secretion of adrenocorticotropic hormone [ACTH]
gonadotropin-releasing hormone [GnRH]
promotes secretion of follicle-stimulating hormone [FHS] and luteinizing hormone [LH]
growth hormone releasing hormone [GHRH]
stimulating on growth hormone [GH]
prolactin inhibiting hormone [PIH/dopamine]
inhibits secretion of PRL
somatostatin
inhibits secretion of growth hormone [GH] and thyroid stimulating hormone [TSH]
List hormones produced by the anterior pituitary gland, list target organ/s or tissue & state principal effects
Follicle-stimulating hormone [FSH]
- ovaries/testes
- growth of ovarian follicles+secretion of oestrogen
- sperm production
Luteinizing hormone [LH]
- ovaries/ testes
- ovulation
- testosterone secretion
Thyroid-stimulating hormone [TSH]
- thyroid gland
- growth of thyroid, secretion of thyroid hormone
Adrenocorticotropic Hormone [ACTH]
- adrenal cortex
- growth of cortex
- secretion of glucocorticoids
Prolactin [PRL]
- mammary glands, testes
- milk synthesis
- increased LH sensitivity
Growth hormone [GH]
- liver, bone, cartilage, muscle, fat
- widespread tissue growth, protein synthesis
List hormones stored by the posterior pituitary gland, list target organ/s or tissue & state principal effects
Antidiuretic hormone [ADH]
- kidneys
- water retention
Oxytocin [OT]
- uterus, mammary glands
- labour contractions, milk release, sperm transport, sexual affection
Explain how pituitary secretion is controlled by the hypothalamus and target organs and exemplify using multiple examples
hypothalamus sends signals in the form of releasing hormones that instruct pituitary to secretes hormones
eg suckling infant –> stimulates nerve endings in nipples –> hypothalamus –> posterior pituitary lobe secretes oxytocin = milk ejection
eg hypothalamus secretes TRH
–> stimulates ant pit. to secrete TSH
–> stimulates thyroid gland to secrete TH
–> TH stimulates metabolism of most cells + inhibits release of TSH by ant pit. and TRH by hypothalamus
Describe the effects of growth hormone
secreted by ant pit.
Widespread effects on body tissue - cartilage, bone, muscle, fat
- Bone growth, thickening and remodelling bone especially during childhood and adolescence
- induces liver to produce growth stimulants called insulin like growth factors
- Protein synthesis increases - boosts transcription of DNA
- Lipid metabolism increased = provides energy for growing tissue
Pineal gland; state its location, list the hormone/s it produces and their effects
- near centre of brain between hemispheres in roof of third ventricle
- produces melatonin [contribute to biological clock
- regulates reproduction and seasonal breeding in animals but reproduction function unclear in humans
Thyroid gland; state its location, describe its structure, list hormones produced & their effects & describe its disorders
- located in neck inferior to larynx and wrapped around trachea
- secretes calcitonin and Thyroxine[T3] and Tri-iodothyronine [T4]
- T3+T4 function = increase basal metabolic rate eg respiration rate, oxygen consumption, breakdown of fat, protein and carbs for energy
- calcitonin function = increase osteoblast activity = calcium deposition and bone formation
disorders
1. hypothyroidism = stunted bone growth [dwarfism]
- severe mental retardation, thickened facial features
- decreased metabolic rate –> weight gain, low body temp
- soft/fragile/deformed bones
- treated with oral thyroid hormone
- hyperthyroidism [deficiency of blood calcium]
- depolarises neurons/ muscle fibres = AP causes spontaneous involuntary muscle contractions [tetany] - goitre [enlargement of thyroid gland from excessive stimulation of gland]
- high levels of TRH/TSH = stimulate growth of gland
