Module 6 Endocrine Flashcards
The neck BORDERS
Major conduit for structures passing between head, trunk and limbs
Location of many clinically important structures including pharynx, larynx and trachea, oesophagus, thyroid and parathyroid glands
Boundaries
Anteriorly = inferior border of mandible manubrium of sternum (suprasternal notch)
Posterior = superior nuchal line of occipital bone to the intervertebral disc between the C7 and T1 vertebrae
Major muscles of the neck region
Sternocleidomastoid (CN XI)
Trapezius (CN XI)
Platysma (CN VII)
Infrahyoid and suprahyoid groups
Suprahyoid muscles and action
Digastric
Anterior belly (mandibular division of trigeminal nerve CNV3)
Posterior belly (facial nerve CNVII)
Mylohyoid (CNV3)
Geniohyoid (anterior ramus of C1 spinal nerve)
Stylohyoid (CNVII)
All act to elevate the hyoid bone
Mylohyoid helps to support and elevate floor of the mouth
Anterior belly of digastric and geniohyoid can help open the mouth by lowering (depressing) the mandible when the hyoid bone is fixed by other muscles
Infrahyoid muscles and action
Sternohyoid
Omohyoid – superior and inferior bellies
Thyrohyoid
Sternothyroid
Innervation = anterior rami of C1 to C3 spinal nerves through the ansa cervicalis
Thyrohyoid is just anterior ramus of C1
All act to depress the hyoid bone and larynx
Thyrohyoid can raise larynx when hyoid bone is fixed in position by other muscles
Cervical fascia
Superficial fascia: contains adipose, cutaneous nerves, superficial lymph nodes, superficial veins e.g. external jugular, platysma muscle
Deep cervical fascia
Investing layer: surrounds all structures and encloses the trapezius & SCM
Prevertebral layer: surrounds vertebral column and deep muscles of the back including scalene muscles. Forms axillary sheath to enclose brachial plexus and subclavian artery in axilla
Pretracheal layer: encloses neck viscera i.e. trachea, oesophagus and thyroid gland. Posterior part referred to as buccopharyngeal fascia, which separates pharynx from prevertebral layer
Two carotid sheaths: formed by the other fascial layers and surround the two major neurovascular bundles of the neck (common carotid artery, internal carotid, internal jugular vein and vagus nerve). Extend from base of skull to superior mediastinum
Layers arranged into four compartments: area surrounded by investing layer; vertebral compartment; visceral compartment; vascular compartment
Fascial spaces
Retropharyngeal space
Largest and most important fascial space in the neck
Between the pretracheal/buccopharyngeal fascia on the posterior surface of the pharynx and oesophagus and the prevertebral fascia on the anterior surface of the bodies and transverse processes of the cervical vertebrae
Extends from the base of the skull to the upper part of the posterior mediastinum
Pretracheal space
Between investing layer of cervical fascia covering the posterior surface of the infrahyoid muscles and the pretracheal fascia covering anterior surface of thyroid gland and trachea
Passes between neck and anterior part of superior mediastinum
Fascial space within the prevertebral layer covering the anterior surface of the cervical vertebral bodies and transverse processes. Base of skull posterior mediastinum
Main Triangles of the neck and their boundaries + subdivisions
Anterior triangle
Apex = suprasternal notch
Anterior border = midline of the neck
Superior border = inferior edge of mandible
Posterior border = anterior edge of sternocleidomastoid (SCM)
Carotid triangle
Muscular triangle
Submandibular triangle
Submental triangle
Posterior triangle
Apex = occipital bone posterior to mastoid process, between attachments for SCM and trapezius
Anterior border = posterior edge of SCM
Inferior border = superior edge of clavicle
Posterior border = anterior edge of trapezius
Occipital triangle
Subclavian (supraclavicular or omoclavicular) triangle
Carotid triangle
Borders
Anterior border = superior belly of omohyoid
Superior border = posterior belly of digastric
Posterior border = anterior edge of sternocleidomastoid (SCM)
Major contents
Common carotid artery, external carotid, internal carotid
Internal jugular vein
Vagus nerve, hypoglossal nerve, ansa cervicalis
Carotid sheath: encloses common carotid, internal carotid, internal jugular and vagus nerve
Muscular triangle (neck)
Borders
Anterior border = midline of neck
Superior/posterior border = superior belly of omohyoid
Posterior border = anterior edge of sternocleidomastoid (SCM)
Major contents
Infrahyoids (sternohyoid, omohyoid, thyrohyoid, sternothyroid)
Thyroid gland, parathyroid glands
Pharynx, larynx and trachea
Submandibular triangle
Borders
Anterior border = anterior belly of digastric
Superior border = inferior edge of mandible
Posterior border = posterior belly of digastric
Major contents
Submandibular gland
Submandibular lymph nodes
Hypoglossal nerve
Parts of facial artery and vein
Submental triangle
Borders
Anterior border = chin and midline of neck
Inferior border = body of hyoid bone
Posterior border = anterior belly of digastric
Major contents
Submental lymph nodes
Tributaries forming anterior jugular vein
Occipital triangle
Inferior belly of omohyoid subdivides posterior triangle into: Occipital triangle and Subclavian
Occipital triangle: Contains part of external jugular vein, posterior branches of cervical plexus of nerves, accessory nerve (CN XI), cervicodorsal trunk; cervical lymph nodes
Subclavian triangle
Inferior belly of omohyoid subdivides posterior triangle into: Occipital triangle and Subclavian
Subclavian triangle: Contains subclavian artery (third part, trunks of brachial plexus, part of subclavian vein (sometimes), suprascapular artery, supraclavicular lymph nodes
Carotid arteries and branches
Common carotid
Internal carotid: Does not branch in neck, Carotid sinus
External carotid: Superior thyroid, Lingual, Facial, Maxillary, Superficial temporal, Occipital, Posterior auricular
Carotid bifurcation
Located at superior border of thyroid cartilage (C3/4 level)
Carotid sinus detects pressure changes in arterial blood via baroreceptors
If hypersensitive then external pressure may lead to syncope
Carotid body chemoreceptors detect changes in composition of arterial blood e.g. pH, partial pressure of arterial O2 or CO2
Palpable facial and neck arteries
Superficial temporal artery can be palpated anterior to ear/posterosuperior to TMJ. Anterior branch can be palpated in anterolateral scalp
Facial artery palpated as it crosses the inferior border of mandible, anterior to masseter muscle
Common carotid pulse posterolateral to larynx
External carotid pulse halfway between superior margin of thyroid cartilage and greater horn of hyoid
Jugular veins
External jugular veins
Arises near angle of mandible
Formed by posterior branch of retromandibular vein and posterior auricular vein
Passes inferiorly through superficial fascia and crosses SCM before piercing the investing layer of cervical fascia
Travels deep to clavicle and drains into subclavian vein
Injury may result in a venous air embolus
Anterior jugular veins
Arise near hyoid bone from small veins
Descend on either side of midline of neck
Pierces investing layer of cervical fascia to enter subclavian vein
May drain into external jugular instead - variation
Internal jugular veins
Formed by continuation of sigmoid (dural venous) sinus at the jugular foramen of the skull
Contained within carotid sheath and runs deep to SCM
Receives blood from facial vein
Unites with subclavian vein to form brachocephalic vein at T1 vertebral level, superior to sternoclavicular joint and suprasternal (jugular) notch)
Large valve near end of the vein helps to prevent reflux
Lymphatic drainage of the head and neck
Superficial lymph nodes of the head
Occipital: occipital area of scalp
Mastoid (posterior auricular): posterior neck, upper part of external ear, lateral scalp, posterior wall of external acoustic meatus
Pre-auricular: superficial areas of face and temporal region
Parotid: nasal cavity, external acoustic meatus, tympanic cavity, lateral borders of orbit, scalp in temporal region, eyes, cheeks
Submandibular: medial canthus, cheeks, lateral aspect of nose, upper and lower lips, gums, anterior teeth
Submental: chin, central lower lip, floor of mouth, apex of tongue
Superficial cervical lymph nodes
Located along external jugular vein and superficial aspect of SCM and receive lymph from posterior and lateral regions of scalp via occipital and mastoid nodes
Drain to deep cervical nodes
Deep cervical nodes
Located along internal jugular vein and receive all lymph from head and neck. Divided into superior and inferior groups
Most superior node is jugulodigastric node – receives lymph from tonsils as well as face, mouth, pharynx
Commonly enlarged in tonsillitis
Jugulo-omohyoid node of inferior group is at tendon of omohyoid and receives lymph from tongue
If enlarged may be a sign of tongue carcinoma
Drain into right and left jugular trunks, then right lymphatic duct/trunk and thoracic duct respectively
Superficial nerves in the neck
Cutaneous nerves arise from cervical plexus (anterior rami of C1 – C4)
Transverse cervical (C2 & C3, anterior neck skin)
Great auricular (C2 & C3, skin of ear, mastoid region, parotid region)
Lesser occipital (C2, skin of neck and scalp posterior to ear)
Supraclavicular nerves (C3 & C4, skin over clavicle and shoulder)
Accessory nerve = cranial nerve 11 (CN XI), motor to SCM and trapezius. Crosses posterior triangle
Where would anaesthesia be injected to numb the ear and surrounding neck?
Erb’s point or nerve point of the neck: injection site to obtain anaesthesia of the skin around the ear and anterolateral neck
Mid posterior SCM
Deep nerves in the neck
Vagus nerve and branches
Glossopharyngeal nerve (CN IX)
Hypoglossal nerve (CNXII)
Phrenic nerve (anterior rami of C3, C4, C5)
Ansa cervicalis (anterior rami of C1, C2, C3)
Thyroid gland location and anatomy
Found in visceral compartment of neck and surrounded by pretracheal fascia
Lies lateral and inferior to the thyroid cartilage
Extends between C5 – T1 vertebra
The thyroid gland consists of:
Two lobes which cover anterolateral surfaces of the trachea, the cricoid cartilage, and lower part of the thyroid cartilage. Pair of parathyroid glands on posterior aspect of each lobe
An isthmus in the midline that connects the two lobes and usually covers the anterior surfaces of the second and third tracheal cartilages
Pyramidal lobe of thyroid
Present in around ~50% of thyroid glands
Extends superiorly from isthmus although in some cases isthmus may be absent
Remnant of thyroglossal duct from development of thyroid
Thyroglossal duct may sometimes form cysts in anterior neck
Blood supply to the thyroid
Superior thyroid artery (from external carotid)
Inferior thyroid artery (from subclavian artery via thyrocervical trunk)
Both arteries can be ligated during thyroidectomy to reduce intraoperative haemorrhaging
Superior laryngeal nerve is at risk of injury when superior thyroid artery ligated
Recurrent laryngeal nerve runs near inferior thyroid artery
Venous drainage is to the superior, middle and inferior thyroid veins
Superior and middle IJV
Inferior brachiocephalic vein
Hormones and cells in glucose homeostasis
Alpha cells: Glucagon (glucose agonist): hyperglycaemic effect, stimulates glucose production from the liver (glycogenolysis and gluconeogenesis; other functions on energy homeostasis and appetite.
Beta cells: Insulin released with high blood glucose, stimulates glycogen production via hypoglycaemia (increased glucose uptake); inhibits glucagon production.
Delta cells: ~5% of the cells; secrete Somatostatin, a paracrine inhibitor of glucagon and insulin release. Somatostatin release also regulated by β-cells providing a feedback mechanism.
PP cells: F-cells or pancreatic polypeptide (PP) cells, located in the periphery of islets, secrete PP – released post-prandially and has effects on metabolism, GI motility, and appetite.
What causes type I - Insulin deficiency diabetes?
Autoimmune disease in which pancreatic beta cells are destroyed and thus not enough insulin is produced
Incidence ~ 3 in 1000
Often develops before age 15 and seldom after 40
May be triggered by viruses and/or toxins
Tendency toward ketosis (developing keto-acidosis) – Why?
Patient requires insulin supplement (exercise and diet are key)
What causes type II - Insulin resistant diabetes?
Impaired b-cell function and/or resistance of tissues to Insulin
~ 3% of population (many undiagnosed), roughly 90% of cases
Onset usually > 40 years
Associated with lack of physical activity and/or obesity
Complications of diabetes
kidney damage, defined by proteinuria (microalbuminuria) and reduced GFR.
Peripheral nerve dysfunction, sensory, focal/multifocal, autonomic neuropathies.
Macrovascular complications of diabetes
microvascular complications; diabetic retinopathy
Pathogenesis of arterial damage
Damage to vessels and cells reflects the glucose concentration and duration of exposure.
Glucose can be converted to sorbitol which is an osmotic stresser.
Production of advanced glycation endproducts (AGEs). Glycation is a non-enzymatic adduction of targets by glucose. Not the same as glycosylation.
Diabetes symptoms
Thirst
Polyuria/nocturia/ incontinence in the elderly
Tiredness
Blurred vision (lens changes shape and size)
Recurrent thrush
Recurrent infections
Feeling of unwell/poor concentration
Weight loss – yes in Type 1, not always Type 2
Mood changes
Micro or macro-vascular problems
Diagnosis of Diabetes State
FPG 7 mmol
No food or drink for at least 8 hours
2 hour glucose 11.1mmol during an glucose tolerance test
A1C 48mmol/mol (6.5%)
Using an accepted and standardized laboratory test
If classic symptoms of high glucose = any glucose 11.1 mmol
Symptoms : Type 1 vs Type 2
More acute onset in Type 1
Type 2 progressive disease and symptoms more gradual
Symptoms might be not realised and put down to other things
Type 2 diabetes takes on average 10 years to present
IF IN DOUBT – TREAT AS TYPE 1 !
- Peptide hormone Biosynthesis
Peptide hormones are translated on the RER as a pre-prohormone.
This initial translational product is then cleaved to a prohormone which then undergoes further post-translational processing to produce the hormone which is then stored in secretory vesicles of the endocrine gland.
- Phenylalanine/tyrosine derived hormones
Hormone or neurotransmitter
Preganglionic fibres stimulate a mixture of epinephrine and norepinephrine into bloodstream.
(80% epinephrine and 20% norepinephrine).
- Fatty acid or Arachidonic acid derived hormone biosynthesis
Arachidonic acid derived hormones are involved in a number of processes involved in the regulation and control of inflammatory responses.
- Hormones derived from Cholesterol
The precursor for all steroid hormones is CHOLESTEROL
Cholesterol can be synthesised de novo but usually comes from diet (LDL) and is stored as cholesterol ester.
There are 4 families of lipid soluble steroid hormones
Corticoids
Progestins
Androgens
Estrogens-
Secreted by:
Adrenal cortex- cortisol & aldosterone
Ovaries- oestrogen & progesterone
Testes- Testosterone
Storage of Steroid hormones
Unlike peptide hormones, most steroid secreting cells do not store hormone but synthesize them as required
Slower time for steroid hormone to act
Water vs fat soluble hormone Signalling methods
Water soluble hormones
e.g. peptide hormones and those derived from phenylalanine and arachidonic acid
Signal via cell membrane receptors and activation of enzymes and other molecules via G protein coupled receptors or Tyrosine kinase coupled receptors
Lipid soluble hormones
e.g. Steroid or thyroid hormones readily cross cell membranes
Signal via intracellular cytoplasmic or nuclear receptors and modulation of gene expression
Short loop negative feedback
inhibition of hypothalamic tropic hormones by the anterior pituitary tropic hormone.
Long loop negative feedback
the hormone whose secretion is stimulated by the tropic hormone generally feeds back to the hypothalamus (and often the anterior pituitary as well) to inhibit secretion of the tropic hormone.
General adaptation syndrome stages
Initial fight or flight
A slower resistance response
Exhaustion
Action of Glucocorticoids – Cortisol (the stress hormone)
Increase in bone resorption and decreases collagen formation
EPO is increased, which stimulated RBC, it decreases NO, and increases constriction, decreases permeability It also increases effectiveness of catecholamines and so increases BP
Immunosuppressive and anti-inflammatory actions
Decreases calcium absorption from kidney
Cortisol stimulates the release of amino acids from muscle. Liver utilises these to make glucose. The increase in glucose stimulates insulin release. Cortisol inhibits the insulin-stimulated uptake of glucose in muscle via GLUT4 transporter.
Many effects on fetus. Required for lung development at correct stage
Adrenal axis disorders
Cushing’s Disease: Increased ACTH due to pituitary defect/pituitary tumour
Cushing’s Syndrome: Increased glucocorticoid due to ectopic sources of ACTH (small cell lung cancer) or Adenoma of adrenal gland
Ectopic ACTH syndrome
Addison’s Disease (primary adrenal insufficiency): Adrenals cannot produce sufficient steroids - poor BP control ,Increased ACTH- hyper pigmentation, refer to actions of cortisol
Dexamethasone suppression tests:Low and High dose tests
Low Dose test (1mg)
Injection (or take orally) low dose of Dexamethasone.
The normal situation would result in suppression of cortisol levels
In patient with excess production (e.g. Cushing’s disease) cortisol suppression is limited with this test
If cortisol remains high after low-dose DEX test, is raised in the urine 24 hr test and shows loss of diurnal variation – Diagnose Cushing’s
High dose test (2mg):
2mg Dex 6 hourly for 48 h; 0900h plasma cortisol measurements taken.
In Cushing’s disease, the cortisol level will decrease to <50% of pre-test value
(in CD, tumour doesn’t produce as much ACTH as ectopic ones and so some of the feedback is retained in response to this dose of dex)
If suppression is less than 50% then ACTH source is outside of pituitary
e.g. Adrenal tumour or ectopic ACTH secretion (as these tumours usually result in greater levels of ACTH than pit tumours)
Suspected pituitary hypofunction
Start with measurement of pituitary and target organ hormone in blood taken at 0900h.
In HPA axis
Normal plasma ACTH at 0900h is <50ng/L
Normal cortisol at 0900h is 140-690 nmol/L
If abnormal need to do dynamic testing using stimulation test
ACTH Stimulation Test for Adrenal Insufficiency (synacthen test):
The ACTH stimulation test is very specific for HPA axis.
Blood cortisol and/or urine cortisol are measured before and after an injection with synthetic form of ACTH.
After an injection of ACTH blood and urine cortisol levels rise.
Patients with adrenal insufficiency respond poorly or not all.
CRH Stimulation Test - adrenal insufficiency
To perform when the synacthen test is abnormal in order to establish possible cause of adrenal insufficiency (secondary/pituitary or tertiary/hypothalamic).
Blood cortisol levels are measured before and after (30, 60, 90, and 120 minutes after) synthetic CRH injection (i.v.).
Patients with Primary Adrenal insufficiency (Addison’s) : high ACTH, but not cortisol production.
Patients with Secondary adrenal insufficiency deficient cortisol responses and absent or delayed ACTH responses- (Absent ACTH response points to the pituitary; a delayed ACTH response points to the hypothalamus)
Hypothalamus: function
The main function of the hypothalamus is to maintain homeostasis by:
Autonomic Function Control
Endocrine Function Control
Motor Function Control
Food and Water Intake Regulation
Sleep-Wake Cycle Regulation
Circadian rhythm
Temperature regulation
Emotional and behavioural responses
Different hypothalamic regions or nuclei are involved
Neurohypophysis: The posterior pituitary gland
An extension of the hypothalamus, containing neural tissue consisting of the axon terminals of neurons originating in the hypothalamus which extend downwards as a large bundle behind the anterior pituitary.
Composed of:
The pars nervosa(neural lobe)
Infundibular stalk
Median eminence
