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MindMap Gallery Hypothalamus-Pituitary Axis

Hypothalamus-Pituitary Axis

Welcome to a mind map that will unravel the intricate workings of the Hypothalamus-Pituitary Axis, a fundamental system in our bodies that governs various physiological processes. The Hypothalamus and the Pituitary Gland, located in the brain, work in harmony to regulate hormone production and maintain homeostasis. In this mind map, we will explore the structure and functions of the Hypothalamus-Pituitary Axis. By mapping out the Hypothalamus-Pituitary Axis, we can gain a deeper understanding of how this complex system influences our overall well-being.

Edited at 2023-03-15 20:05:07

Arvindbagati@gmail.com

Recent works View more works>>

Hypothalamus-Pituitary Axis
Welcome to a mind map that will unravel the intricate workings of the Hypothalamus-Pituitary Axis, a fundamental system in our bodies that governs various physiological processes. The Hypothalamus and the Pituitary Gland, located in the brain, work in harmony to regulate hormone production and maintain homeostasis. In this mind map, we will explore the structure and functions of the Hypothalamus-Pituitary Axis. By mapping out the Hypothalamus-Pituitary Axis, we can gain a deeper understanding of how this complex system influences our overall well-being.

Hypothalamus-Pituitary Axis

Arvindbagati@gmail.com

Recent works View more works>>

Hypothalamus-Pituitary Axis
Welcome to a mind map that will unravel the intricate workings of the Hypothalamus-Pituitary Axis, a fundamental system in our bodies that governs various physiological processes. The Hypothalamus and the Pituitary Gland, located in the brain, work in harmony to regulate hormone production and maintain homeostasis. In this mind map, we will explore the structure and functions of the Hypothalamus-Pituitary Axis. By mapping out the Hypothalamus-Pituitary Axis, we can gain a deeper understanding of how this complex system influences our overall well-being.

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Thyroid Gland

Thyroid Cancer

Causes

4 types

Papillary

most common (70–80%), 3x women

derived from thyroid follicular cells

spread lymphatic, multicfocal

Follicular

derived from thyroid follicular cells

10-15%, 2x women

agressive and spreads to lungs & bones

Anaplastic

Uncommon 10%, 1.5x men

Undifferentiated carcinoma

Very agressive & spreads via lymph nodes & blood

Medullary

Uncommon 5-10%, 1.5x men

Causes

Exposure to radiation, nuclear fall-out and neck irradiation

Presentation

lump (solitary or multinodular) in the neck, in a clinically euthyroid patient with no other symptoms.

Lumps generally benign

Can present symptoms due to bony metastasis

Tests

TSH & Free T4

Fine needle aspiration

Radionuclide scanning

Serum calcitonin and carcino-embryonic antigen (CEA)

Chest X-ray

U/S

CT or MRI

Treatment

Surgical

Thyroidectomy

Medical

Radioactive iodine (131I)

External beam radiotherapy

Hyperthyroidism

Causes

Excessive thyroid hormones

History

More in women in 3rd to 4th decade

Pathology

Fig 6.12

Presentation

Severity

Clinical

Overt

Manifestation

Table 6.13

Investigations

TSH and T4

T3 levels

Thyroid autoantibodies

U/S

Radioactive iodine uptake

Chest x-ray & CT

Treatment

Initial

b-Blockers

Identify and address the underlying cause

Medical

Antithyroid drugs

Propylthiouracil

Methimazole

Radioactive iodine

Surgical

Thyroidectomy

Hypothyroidism

Causes

Deficiency of thyroid hormone (Table 6.10)

Presentation

Severity

Clinical

Overt

Manifestation

Table 6.11

Myxoedema

Treatment

Thyroxine

IV liothyronine + hydrocortisone

Diseases

Hypothyroidism

Hyperthyroidism

Thyroid cancer

Tests

Total & Serum Free thyroxine

Hyperthyroidism

Hypothyroidism

Basal TSH

Hyperthyroidism

Hypothyroidism

Free T3

For toxicosis

Thyroid auto-antibodies

Physiology

2 thyroid glands connected by isthimus

Thyroid follicles with follicular cells

Thyroid hormones ( T3 & T4 )

Calcitonin ( Parafollicular cells)

Hypothalamus-Pituitary Axis

Hypothalamus

Location : Near the thalamus

Hormones secreted

Excitatory

Inhibitory

Pituitary

Size : 1-1.5 cm in diameter, pea shaped, in the hypophyseal fossa of the sella turcica of the sphenoid bone

Regions

Anterior lobe (Adenohypophysis) ; 75% , made of epithelial tissue

Regions

pars distalis is the larger portion

pars tuberalis forms a sheath around the infundibulum

Blood supply (Hypophyseal Portal System)

Internal carotid arteries → superior hypophyseal arteries → hypothalamus → primary plexus of the hypophyseal portal system → hypophyseal portal veins → infundibulum → anterior pituitary → secondary plexus.

Neutosecretory neuron cells → hypothalamic releasing and inhibiting hormones in cell bodies → hormones in vesicles → reach axon terminals → Exocytosis by nerve impulses → primary plexus of the hypophyseal portal system → act on anterior pituitary cells → secondary plexus capillaries → hormones secreted by anterior pituitary cells → anterior hypophyseal veins → general circulation → target tissues/endorcine flands (tropic hormones)

Cell types

Somatotrophs

human growth hormone → insulinlike growth factors

Thyrotrophs

thyroid-stimulating hormone → control thyroid gland

Gonadotrophs

gonadotropins: follicle-stimulating hormone → Act on gonads

luteinizing hormone → Act on gonads

Lactotrophs

prolactin → increases milk production in mammalary cells

Corticotrophs

adrenocorticotropic hormone → adrenal cortex → gluco-corticoids

melanocyte-stimulating hormone

Regulation of hormone secretion

Neurosecretory cells in hypothalamus

Releasing hormones

GHRH

TRH

GnRh

PRH

CRH

Inhibiting hormones

GHIH

PIH

Dopamine

Negative feedback loop

Thyrotrophs

Gonadotrophs

Corticotrophs

Posterior lobe (Neurohypophysis) composed of neural tissue

Regions

pars nervosa the larger bulbar portion

infundibulum attaches pituitary gland to the hypothalamus

pars intermedia atrophies during human fetal development and ceases to exist

Blood supply (Hypophyseal Portal System)

Internal carotid arteries → inferior hypophyseal arteries → posterior pituitary → capillary plexus of the infundibular process → posterior hypophyseal veins

Neuronal cell bodies of the neurosecretory cells (paraventricular and supraoptic nuclei of the hypothalamus) → hormone in vesicles → axons form the hypothalamohypophyseal tract → Axon terminals in posterior pituitary → Stored → Nerve impulse trigges exocytosis and hormone release → capillary plexus of the infundibular process → posterior hypophyseal veins → target cells

Hormones

Oxytocin

Impacts mothers utreus & breast

ADH

Impacts urine production

Pituitary

GH

Acromegaly

Pathology

Insidious disorder caused by pituitay adenoma secreting GH → bony & soft tissue overgrowth

Causes Acromegaly → caused by hypothalamic or ectopic GHRH

Scope of disease

Acromegaly can manifest singly/ combination of GH excess , local tumor effects or hypopituitarism

Multisystem disease. Increased GH leads to bone growth

GH excess leads to enlargement of heart, thyroid, liver or kidney

Hypertension 40%, IR 40%, MEN 5%

Clinical features

Diagnosis delayed by 9 years

Sweating, headache, tiredness, paraesthesia of hand, feet or arthralgia

Course features, macroglossia, prognathism, interdental separation, spade like hands, carpal tunnel syndrome, proximal muscle weakness

See Table 6.9

Investigations

Initial

(Growth hormone) glucose suppression test

Further

Anterior pituitary function tests

Goldmann perimetry

MRI of head

Management

Initial

Normalization of GH level, reversal of effect of pituitary tumor, treatment of hypopituitarism

Medical

Somatostatin analogues

Dopamine agonists

Radiotherapy

Surgical

Transsphenoidal surgery

Deficiency

Pathology

Children

Idiopathic growth hormone deficiency

Adult

Hypothalamic/Pituitary damage or growth hormone deficiency

Scope of disease

Children

Reduced growth rate

Reduced muscle mass

Bone remodelling

Adults

Asymptomatic

Poor sense of well-being, CV risk, muscle mass , bone density reduction

Clinical Features

Children

Failure to thrive

Adults

Fatigue, lack of energy, reduced muscle mass, insulin resistance GH def. suspected if clinical eval. uncovers hypothalamic/pituitary damage

Investigations

Pharma stimulation test

Insulin Tolerance Test

MRI of head

Management

Initial

No need for GH, treat other def. first

Medical

GH replacement

In children before epiphyses fused

In adults improves QOL without impact on survival

ADH Secretion Syndrome

Cause

Syndrome of inappropriate ADH secretion (SIADH) is the most common cause of hyponatraemia.

Pathology

See Fig

Peripheral oedema absent since extra & intracellular spaces impacted

Brain can be impacted but adapts well

Clinical features

Can be asymtomatic

Severe hyponatremia can cause CNS complications & oedema

Abnormalities in renal, liver, adrenal and thyroid fuction has to be excl.

Investigations

Paired serum and urine osmolality

Serum osmolalities

serum hypo-osmolality (<270 mOsm/kg).

Urine osmolalities

inappropriately concentrated urine (>100 mOsm/kg)

Urinary sodium excretion > 20 mmol/L

Management

Identify and address underlying cause

Fluid restriction

Demeclocycline

Diabetes insipidus

Cause

Large vol. of dilute/insipid urine passed due to

failure of vasopressin release (central)

failure of the kidneys (nephrogenic) to respond to vasopressin

Pathology

Table 6.6

Clinical Feature

persistent polyuria, nocturia, thirst and polydipsia

onset of central diabetes insipidus is usually more abrupt than nephrogenic diabetes insipidus

Dehydration can lead to loss of consciousness & coma

Nocturia is uncommon with primary polydipsia

Investigation

Initial

24-hour urine collection

Urea and electrolytes

Futher

Water deprivation test

CT/MRI of the brain

Management

Initial

Increase fluid intake

Identify and address any underlying cause

Medical management

Desmopressin

Pituitary Adenomas

Epidemiology

5-20% Autopsies

Less common with female prepoderance b/w 30-50 yrs

Causes

Types

Mostly benign

< 0.5% are carcinomas

Defined by size

Microadenomas ( < 10 mm)

Macroadenomas ( >10 mm)

Classified as per prominent cell type

Lactotrophs (PRL) -50%

Somatotrophs (GH) - 30%

Corticotrophs (ACTH) 20%

Gonadotrophs (LH, FSH)

Thyrotrophs (TSH)

Non-functioning adenomas (NFA) - contain secretory granules (25%)

Scope of Disease

Mass effects

Visual disturbances

Headaches

Cranial nerve palsies

Increased appetite, thrist, coma due to invasion into hypothalamus

Apoplexy

Hypopituitarism

Acute compression of optic chasm

Endocrine manifestations

Hypopituitarism

Prolactin excess

Acromegaly due to GH hypersecretion

Cushing disease due to ACTH excess

Macro-orchidism due to FSH excess

Thyrotoxicosis due to TSH excess

Tests

Basal anterior pituitary hormone profile

Dynamic function test

Perimetry

MRI

Treatment

Medical

Hormone replacement

Hormone antagonism

Surgical

Transsphenoidal surgery

Radiotherapy

Hyperprolactinaemia

Causes

Most common disorder of anterior pituitary

Pathology

Fig 6.5

Presentation

Manifestation

Reduced fertility impacts men and women

Spontaneous or expressible galactorrhoea

80% women

20% men

Oligo/amenorrhoea & symptoms of oestrogen def. in women of childbearing age

Men less frequently seek treatment for libido loss, gynaecomastia stc.

Symptoms of hypo-pituitarism

Pituitary adenoms give rise to headaches & visual disturbance

Investigations

Prolactin level

Thyroid function test

Pregnancy test

Basal anterior pituitary hormone profile

MRI of head

Treatment

Initial

Identify and address the underlying cause

Medical

Aim

Restoration of gonadal function

Reversal of galactorrhoea

In macroprolactinomas

Tumor size reduction

Avoidance of mass effects

Dopamine antagonists

Surgical

Transsphenoidal surgery

Radiation therapy

Hypopituitarism

Causes

Deficiency of one or more pituitary hormone (Table 6.3)

Develop in sequence GH - HT - TSH - ACTH - Prolactin - PPH

Presentation

Manifestation

Endocrine axes affected (Table 6.4)

Severity

Clinical

Overt

Rate of onset of hormone deficiency

Investigation

Aim

Confirm presence of hormone deficiency

Exclude disease of target organ

Test pituitary hormone levels on max stimulation

Tests done

Screening profile

Cortisol

TSH

Free T4

LH, FSH, Oestradiol (women)

Testosterone (men)

Prolactin , IGF

Combined pituitary stimulation test

Treatment

Hormone replacement

Hydrocortisone for glucocorticoid replacement

L-thyroxine replacement therapy

Sex steroid replacement therapy

GH replacement therapy

Diseases

Hypopituitarism

Hyperprolactinaemia and prolactinoma

Pituitary adenomas

Diabetes Insipidus

ADH secretion syndrome

GH Deficiency

Acromegaly

Tests

Basal anterior pituitary hormone profile

Assessment of

TSH + Thyroxine

ACTH + Cortisol

FSH/LH + Oestrogen/Testosterone

PRL

IGF-1

Dynamic pituitary function tests

Stimulation test for suspected hormone deficiency

Supression test in hormone excess

ITT

Glucagon test

Arginine test

Physiology

See Hypothalamus-Pituitary Axis