01: Intro & The Hypothalamus and Pituitary Flashcards
Define Endocrine System
integrates and controls organ function via secretion of hormones
Define Hormone
Chemicals released from cells tissues and glands, travel through blood to distal target organs (from hormone synthesis)
+exert their effects at low concentrations
+ action terminated via negative feedback loops
+ released in short bursts = 24hr clinical monitoring
Same hormone = different effects in different cells bc of downstream pathways
Define Neurohormone
NERVES release hormones entering BLOOD > TARGET
e.g. hypothalamic - posterior pituitary axis
Define Endocrinology
a
Compare and contrast the main features of nervous and endocrine modes of communication
Endocrine comm.: HORMONES, blood, detection via receptors in order to produce response @ target
Vs
Nervous: chemical release from NERVES crosses synapses. locally within cleft.
Describe the ‘life history’ of a typical hormone
INSULIN reaches:
SKEL MUSC/ADIPOSE = ⇧glucose uptake
LIVER = ⇧glycogenesis, ⇩gluconeo
Classify hormones according to their chemistry and mechanisms of action upon target cells
PEPTIDE/PROTEIN: A.A
-preprohormone triggered by stimulus = prohormone and stored
=> COSECRETION: active hormone fragment + inactive peptide fragment released into blood
* measuring inactive fragments: C-peptide inactive part of insulin
=> HYDROPHILLIC/LIPOPHOBIC thus bind to receptors.
- GPCR or Tyrosine kinase-linked receptors
- fast responses (seconds/minutes)
AMINE HORMONES: all derived from TYROSINE (tryptophan -melatonin only)
*melatonin - circadian rythm
1) CATECHOLAMINES (dopamine + norepinephrine - NT epinephrine - hormone)
* HYDROPHILLIC
2) THYROID HORMONES (thyroxine, triiodothyroxine)
* LIPOPHILLIC
STEROID HORMONE: derived from cholesterol
- synth as required bc cannot be stored bc LIPOPHILLIC
- transported BOUND such as ALBUMIN
- longer half-life
- slow onset of action, but longer effect of peptide or amine hormones
- produced by GONADS, PLACENTA, KIDNEY, ADRENAL CORTEX
- specific hormone prod. determined by enzymes cells possess
=> INTRACELLULAR RECEPTORS = genomic effect = protein synthesis altered d/t gene expr. altered
ENDOCRINE GLANDS
Ductless endocrine glands
Ducted Exocrine
Autocrine secretions = secretions bind to receptors on same cell (cytokines)
Paracrine secretions = diffuse in ECF to affect neighbouring cells (histamine)
C-Peptide
Indicative of endogenous insulin production from pancreas. Typically 5x higher than insulin bc insulin metabolised much faster.
Measuring C-peptide only rules out synthetic insulin being taken.
State in logical sequence the factors that determine the availability of a hormone or
neurohormone to its target cells.
Free hormone:protein bound hormone ratio favours bound.
- In health levels of free hormone remain constant
- The Law of Mass Action: as free hormone taken up by cells, more hormone is released from carriers
=> free hormone + complexed hormone = total plasma hormone
- [hormone]pl. determined by secretion/degradation
- negative feedback reflexes mostly control.
*neuroendocrine response to neural feedback loops (e.g. adrenaline)
List major categories of physiological function that are governed by endocrine pathways and mechanisms.
a
Describe the main routes and types of signal that determine the rates of hormone synthesis and secretion by a typical endocrine cell.
a
Describe diagrammatically the compartmentation and routes of communication within the hypothalamus-pituitary gland complex
HYPOTHALAMUS-POST. PITUITARY via INFUNDIBULUM; project hypothalamic axons and nerve terminals
- neuroendocrine nature
- neurohormones secr. originating from hypothal.
HYPOTHALAMUS-ANTERIOR PITUITARY via NEUROHORMONES travel via CAPILLARY PORTAL SYSTEM
- true endocrine
- blood supply from hypothalamus
*Pars intermedia releases melanocyte stimulating hormone
Define the terms: troph; trophic hormone; hypophysiotrophic hormone.
TROPIC: govern release of another hormone (released by both hypothal. and ant. pituitary.)
non-TROPIC: NEUROHORMONES > post. pit. via axons > blood
* synth @ magnocellular neurons = 2 peptide neurohormones
= 1) VASOPRESSIN/ / ADH: maintain water balance
= 2) OXYTOCIN: uterine contraction at parturition, and aids expression of milk in alctating breast
TROPH: largely has direct/indirect effect in growth
List the hormone families and major individual hormones secreted by the adenohypophysis (anterior pituitary lobe).
TROPIC NEUROHORMONES
RELEASING HORMONES (peptide):
i) (GHRH) promotes growth;
ii) CORTICOTROPIN (CRH) causes the adrenal cortex to secrete corticosteroid hormones => ACTH
iii) PROLACTIN (PRH) causes milk synthesis in the mammary glands
iv) THYROTROPIC HORMONE (TSH) stimulates the thyroid gland to secrete thyroxine
v) Gonadotropin releasing hormone (GnRH) => FSH & LH
INHIBITING HORMONES (peptide):
i) GHIH aka SOMATOSTATIN
ii) Dopamine aka Prolactin Inhib. Hormone (amine hormone)
- Prolactin only ant pit hormone NOT tropic
- (FSH) & luteinizing hormone (LH) interact to regulate the function of the gonads
- LIPOTROPIN (LPH) affects fat metabolism;
- MELANOPHORE-STIMULATING HORMONE (MSH) stimulates melanin synthesis in pigment cells;
- OPIODS (endorphins and enkephalins) reduce pain.
