Endocrine system Flashcards
What are the main endocrine glands?
- •Kidneys & Liver: Erythropoietin
- •Heart:Atrial natriuretic peptide
- •Adipose tissue: is endocrinologically active!
- •Paracrines: chemical messengers with locally acting effects (within the same tissue)
How are hormones classified?
- Amino acids
- Steroids
What are the characteristic of aminoacid based hormones?
- Are water-soluble and can not cross the cell membrane of target cells*
- *Exception: thyroid hormones (T4, T3)
What are the characteristics of steroids?
Are lipid-soluble and can diffuse across the cell membrane of target cells
Name some amino acid based hormones
Peptide chains & Proteins
- •ACTH, TSH, ADH
- •Insulin, Glucagon
- •Growth Hormone
Amino acid derivatives
- •Adrenaline, noradrenaline
- •Thyroid hormones (T4, T3)
Name the five Steroid hormones
Adrenal cortex
- •Referred to as Corticosteroids
- •Cortisol, Aldosterone
Synthesised from cholesterol
- •Gonadalhormones:
- •Progesterone, Androgens, Oestrogens
What are the actions of the hormones?
Target cells: influences the activity of only those tissue cells that have receptors for it
** note: some have more than one target cell - EG. noradrenaline at SA node
- •Alteration of cell membrane permeability or excitability
- •Stimulation of synthetic activity or secretion e.g. enzymes, proteins
- •Activation/deactivation of enzymes
- •Stimulation of mitosis
How do hormone communicate at target cells?
- second messenger systems
- •direct gene activation
What is the target cell communication mechanism for second messenger system?
- Are water-soluble and can not cross the cell membrane of target cells
- Act upon receptors embedded in the cell membrane of target cells
- Rely on intracellular signaling molecules (second messengers) to mediate their effects
What is the target cell communication mechanism for direct gene activation?
Steroids
- Are lipid-soluble and can diffuse across the cell membrane of target cells
- Are therefore capable of direct gene activation
- Bind to receptors within the cytosol of target cells
Thyroid hormones
- Are transported intotarget cells by membrane-bound transporter proteins
- Are also capable of direct gene activation
- Bind to receptors fixed to the DNAof target cells
What are the hormones that use second messenger system?
Amino acid based hormones
Example
•Cyclic AMP
- •E.g. ACTH, FSH, LH, Glucagon, PTH, Calcitonin
•Tyrosine Kinase
- •E.g.insulin
•PIP2& Calcium
- •E.g. oxytocin, ADH
What type of hormones use direct gene activation
lipid (Thyroid) and steroid-based hormone use direct activation
What type of hormones use second messenger activation ?
Amino acid hormones
What are the 3 mechanisms of regulation of hormone release?
Humoral stimulus
Neural stimulus
Hormonal stimulus
What is the neural stimulus as a mechanism for regulation of hormone release?
Hormone release can be caused by neural input
Example: short term response to stress
- •Sympathetic nervous stimulation of the adrenal medulla
- •Adrenal medulla releases adrenaline & noradrenaline
What is humoral stimulus as a mechanism for the regulation of hormone release?
•Hormone release can be caused by altered blood levels of certain ions or nutrients
example: •blood concentration of calcium (Ca2+)
What is hormonal stimulus as a mechanism for the regulation of hormone release?
Hormone release may be caused by another hormone (trophic) hormone
Example: endocrine glands controlled by the hypothalamic-pituitary axis
How is hormonal release turned off?
negative feedback control loop
- •When hormone levels rise sufficiently to cause target organ effects
- •Target organ effects “feed back” to the reduce the initial stimulus for hormone release
- •Results in the inhibition of further hormone release
What is neurophysis hormone and what is its function?
The posterior lobe, along with the infundibulum
- Composed largely of neural tissue
- •Hasneural connectionsto the hypothalamus – the hypothalamic-hypophyseal tract
FUNCTION
- •Not a true endocrine gland that manufactures hormones
- •Stores and releases releases “ready made” hormones received from the hypothalamus
What are the 2 posterior pituitary hormones?
Oxytoxcin
ADH
What is oxytocin and its function?
•Produced by paraventricularneurons
Stimulus for release from posterior pituitary:
- •Impulses from hypothalamus in response to cervical/uterine stretching; suckling of infant at breast
Function:
- •Uterine contractions (labour); milk ejection
- •Psychoactive effects: promotes nurturing, bonding and trust
What is the ADH hormone and its function?
•Produced by supraventricular neurons
Stimulus for release from posterior pituitary:
- •Impulses from hypothalamus in response to increased blood osmolarity or decreased blood volume
- Angiotensin II also stimulates the release of ADH
Function:
- •Increases the reabsorption of water by acting on the cells of the kidney tubules (DCT & CD)
What are the anterior pituitary hormones?
- Growth hormone
- Prolactin
- ADRENOCORTICOTROPHIC HORMONE (ACTH)
- THYROID STIMULATING HORMONE (TSH)
- FOLLICLE STIMULATING HORMONE (FSH)
- LUTEINISING HORMONE (LH)?
What is the location and function of the anterior pituitary gland?
- •The anterior lobe is referred to as the adenohypophysis
- •Composed largely of glandular tissue
- •Hasvascular connections to the hypothalamus – the hypophyseal portal system(a network of capillary plexuses connected by veins)
- •Hypothalamic hormones released into the portal system control the release of anterior pituitary hormones
FUNCTION
- Synthesises and releases six major hormones
- TSH, ACTH, FSH & LH are trophic hormones
- i.e. they regulate the secretions of other endocrine glands
What is the stimulus release and function for Growth hormone?
Stimulus for release:
- •GH Releasing Hormone (hypothalamic hormone) – released in response to low levels of GH
- •Secondary triggers: low levels of blood sugar and fatty acids, high levels of blood amino acids
Functions:
- •Anabolic hormone that stimulates somatic growth
- •Mobilises fats for use as an energy source, in preference over glucose
What is the stimulus release and function for Prolactin?
Stimulus for release:
- •Unlike other anterior pituitary hormones, PRL release is controlled by dopamine(also referred to as PRL inhibiting hormone)
- •Low levels of dopamine result in PRL release – this is enhanced by factors such as breast-feeding and oestrogens (e.g. use of OCP)
Functions:
- •Promotes mammary gland development and milk production
- • Promotion of sexual gratification after orgasm
What is the stimulus release and function for ADRENOCORTICOTROPHIC HORMONE (ACTH)?
Stimulus for release
- •Corticotrophin-releasing hormone (hypothalamic hormone) – in response to stressors e.g. fever, hypoglycaemia
Functions
- •Promotes release of hormones from the adrenalcortex
- •Glucocorticoids, androgens, mineralocorticoids
- •Thecleavage product of ACTH is alpha-Melanocyte Stimulating Hormone (a-MSH)
- •aMSHstimulates the production of melanin (relevant in certain endocrine pathologies)
What is the stimulus release and function for THYROID STIMULATING HORMONE (TSH)?
Stimulus for release
- •Thyrotrophin-releasing hormone (hypothalamic hormone)
Functions
- •Stimulates thyroid gland to release thyroid hormones: thyroxine/tetraiodothyronine (T4) and triiodothyronine (T3)
What is the stimulus release and function for FOLLICLE STIMULATING HORMONE (FSH)?
Stimulus for release:
- Gonadotrophin Releasing Hormone (GnRH) from the hypothalamus
Functions:
- •F: Stimulates maturation of ovarian follicle and production of oetrogens
- M:Stimulates production of androgen-binding protein by sustentacular cells (supports sperm production
What is the stimulus release and function for LUTEINISING HORMONE (LH)?
Stimulus for release:
- Gonadotrophin Releasing Hormone (GnRH) from the hypothalamus
Functions:
- •F: Triggers ovulation and converts the ruptured follicle into the corpus luteum (the corpus luteum secretes progesterone and some oestrogen)
- •M: Stimulates production of testosterone by interstitial (Leydig) cells
Image of the hypothalamus + hormones
Introduce the adrenal glands
LOCATION: Paired glands atop the kidneys
STRUCTURE:
- •Right adrenal gland– pyramidal in shape
- •Left adrenal gland – semilunarin appearance
- •Enclosed in a fibrous capsule and a cushion of fat
- •Each gland possesses a cortexand a medulla – both regions play an endocrine role
FUNCTION: production fo hormones
What is the vascular supply to the adrenal glands?
ARTERIAL SUPPLY: Superior, middle, inferior adrenal arteries (50-60 branches)
VENOUS DRAINAGE
- •Right adrenal vein àIVC
- •Left adrenal vein àrenal vein àIVC
LYMPHATIC DRAINAGE
- •Rich lymphatic drainage via the adrenal lymphatic vessels
- •Drainage to the lumbar nodes
What is the neurovascular supply to the adrenal glands?
Sympathetic supply:
- •Abdominopelvic splanchnic nerves: T10-L2
Parasympathetic supply:
- Hypothesised to be branches of Vagus nerve CNX
WHat are the 3 zones of the adrenal cortex?
- outer cortex: Zona glomerulosa
- Middle Cortex: Zona fasciculata
- InnerCortex: Zona reticularis
What are the functions of the zona glomerulosa?
- produce mineral corticodes: aldosterone
•Acts on thedistal aspectsof thenephron:
- •Na+ reabsorption
- •K+ secretion
•Primarily under control of RAAS
Otherstimuli for release:
- •High plasma levels of K+
- •Stress response – mediated by CRH & ACTH
- •Atrial natriuretic peptide inhibits aldosterone release
What are the functions of the zona fasciculata?
Produce glucocorticoids
- Promotes gluconeogenesis (Mobilization fatty acid, increase breakdown protein, maintain blood levels of glucose)
- Enhances the effect of SNS on vascular smooth muscle (BP regulation)
- Regulation of the immune response
What are the consequences of excess cortisol?
- •Hyperglycaemia
- •Negative effects on bone density
- •Muscle mass, cartilage formation
- •Hypertension
- •Immunosuppression
What are the functions of the Zona reticularis?
- Produces androgens to supplement those produced by the gonads
- DHEA and androstenedione
- Increase levels during the lead up to puberty
- Source of oestrogen after menopause
by which mechanism do steroid hormones act upon their target cells?
Direct regulation mechanism.
Important facts
****All hormones produced by the adrenal cortex are a steroid hormone
****Another name for this group of hormones: “corticosteroids”
What are the functions of the adrenal medulla?
- •Features spherical chromaffin cells clustered around blood-filled capillaries and sinusoids
- •Chromaffin cells synthesise catecholamines:
- •Adrenaline(80%) & Noradrenaline (20%)
- •Catecholamines augment the activity of the SNS:
- •áHR & cardiac contractility
- •Peripheral vessel constriction, áBP
- •ábloodglucose, BMR
How is the adrenal medulla regulated?
- •Preganglionic sympathetic fibres leave the cord at T10-L1
- •Unlike other abdominopelvic splanchnic nerves, these nerves pass through the prevertebral ganglia without synapsing
- •Instead, these preganglionic nerves terminate at the adrenal medulla, where they synapse directly with chromaffin cells
- •Chromaffin cells are considered to be modified postganglionic sympathetic neurons
What is hypercortisolism?
a range of conditions characterised by an excess of circulating cortisol
What is cushins disease vs. cushing’s syndrome?
- Cushing’s Disease: hypercortisolism due to increased ACTH secretion from the anterior pituitary - caused by pituitary microadenoma
- Cushing syndrome: hypercortisolism has occurred somewhere else - caused by iatrogenic
WHat are the clinical features of cushing’s syndrome
Increased glucocorticoid activity
hyperandrogenism
What is the management of cushings syndrome?
Surgery: remove the tumour
modification of glucocorticoid therapy
What are the two types of adrenocortical hypofunction?
PRIMARY ADRENOCORTICAL INSUFFICIENCY Addison’sDisease
decrease cortisol
SECONDARY ADRENOCORTICAL INSUFFICIENCY
What are the causes of Addison’s disease?
Autoimune
infection
metastatic disease
bilateral adrenalectomy
What are the clinical features for Addison disease?
Skin changes
+ ACTH = promote melanin production = + melanocyte stimulating hormone
What is Phaeochromocytoma?
- A tumour arising from the chromaffin cells of the adrenal medulla
- Most common cause of excess catecholamine production
What are the clinical features for Phaeochromocytoma?
Hypertension
Intermittent catecholamine secretion (systemic)
What is the pharamachological management for addison?
Hormone supplement of
- cortisol
- flurocortisone
